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Patent Searching and Data


Title:
HYDRAULICALLY SETTING SHEATH AND METHODS
Document Type and Number:
WIPO Patent Application WO/1995/021063
Kind Code:
A1
Abstract:
This invention is a marking implement (10) with a hydraulically setting sheath (12) and a marking core (14). The hydraulically setting sheath (12) has a hydraulically setting matrix formed from the reaction products of hydraulic cement and water. Additional components may be utilized in the hydraulically setting matrix such as aggregate materials, fibrous materials, and rheology modifying agents.

Inventors:
KHASHOGGI ESSAM
ANDERSEN PER J
HODSON SIMON K
Application Number:
PCT/US1995/001497
Publication Date:
August 10, 1995
Filing Date:
February 06, 1995
Export Citation:
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Assignee:
KHASHOGGI E IND (US)
International Classes:
B43K19/02; B43K3/00; B43K19/14; B43K19/16; B43K21/00; (IPC1-7): B43K19/14
Foreign References:
GB185502426A
US4115135A1978-09-19
US4452635A1984-06-05
US3979217A1976-09-07
US3993408A1976-11-23
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Claims:
1. An article of manufacture comprising: a marking implement having a marking core and a sheath for retaining therein the making core, the sheath having a hydraulically settable matrix formed from a hydraulically settable mixture comprising a hydraulically settable binder and water.
2. An article of manufacture as defined in claim 1 , wherein the marking core is removable.
3. An article of manufacture as defined in claim 1 , wherein the marking core is fixedly retained within the sheath.
4. An article of manufacture as defined in claim 3, wherein the sheath forms an adhesiveless bond with the marking core.
5. An article of manufacture as defined in claim 1 wherein a portion of the marking core extends beyond the sheath and the sheath encapsulates the remainder of the marking core.
6. An article of manufacture as defined in claim 1 wherein the marking core is a graphiteclay lead.
7. An article of manufacture as defined in claim 1 , wherein the marking core is a colored lead.
8. An article of manufacture as defined in claim 1 , wherein the marking core is a cartridge containing a marking fluid and having means for dispensing the marking fluid.
9. An article of manufacture as defined in claim 1 , wherein the marking core is an absorbent filament saturated with marking fluid.
10. An article of manufacture as defined in claim 9, wherein the absorbent filament is connected to a reservoir containing a marking fluid.
11. An article of manufacture as defined in claim 1 , wherein the marking core comprises a solid cosmetic product in contact with the sheath.
12. An article of manufacture as defined in claim 1 , wherein the marking core comprises a crayon.
13. An article of manufacture as defined in claim 1 , wherein the marking core comprises an oil pastel.
14. An article of manufacture as defined in claim 1 , wherein the marking core comprises a china marker.
15. An article of manufacture as defined in claim 1 , wherein the marking core comprises a predetermined amount of marking fluid retained within the sheath and dispensed therefrom by means for dispensing the marking fluid.
16. An article of manufacture as defined in claim 1, further comprising an eraser and means for attaching the eraser to an end of the sheath.
17. An article of manufacture as defined in claim 1 , further comprising a clip secured to the sheath for attaching the marking implement to a pocket.
18. An article of manufacture as defined in claim 1, further comprising a protective cap for enclosing an exposed end of the marking core.
19. An article of manufacture as defined in claim 1 , further comprising means for affixing the marking core in a secure manner within the sheath.
20. An article of manufacture as defined in claim 1 , further comprising means for moving the marking core within the sheath.
21. An article of manufacture as defined in claim 1 , wherein the hydraulically settable matrix has a tensile strength to bulk density ratio in the range from about 1 MPa cm3/g to about 300 MPacm3/g.
22. An article of manufacture as defined in claim 1 , wherein the hydraulically settable matrix has a strength to bulk density ratio in the range from about 2 MPacm3/g to about 50 MPacm3/g.
23. An article of manufacture as defined in claim 1 , wherein the hydraulically settable matrix has a strength to bulk density ratio in the range from about 3 MPacm3/g to about 20 MPacm3/g.
24. An article of manufacture as defined in claim 1 , the hydraulically settable matrix having a maximum thickness of about 10 mm.
25. An article of manufacture as defined in claim 1, the hydraulically settable matrix having a maximum thickness of about 5 mm.
26. An article of manufacture as defined in claim 1, the hydraulically settable matrix having a maximum thickness of about 2 mm.
27. An article of manufacture as defined in claim 1 , wherein the hydraulically settable matrix can achieve form stability in less than about 60 seconds.
28. An article of manufacture as defined in claim 1 , wherein the hydraulically settable matrix can achieve form stability in less than about 30 seconds.
29. An article of manufacture as defined in claim 1 , wherein the hydraulically settable matrix can achieve form stability in less than about 10 seconds.
30. An article of manufacture as defined in claim 1 , wherein the hydraulically settable matrix can achieve form stability in less than about 2 seconds.
31. An article of manufacture as defined in claim 1 , wherein the hydraulically settable binder comprises hydraulic cement.
32. An article of manufacture as defined in claim 1 , wherein the hydraulically settable binder comprises gypsum.
33. An article of manufacture as defined in claim 1 , wherein the hydraulically settable binder is included in an amount within the range from about 5% to about 90% by weight of the hydraulically settable mixture.
34. An article of manufacture as defined in claim 1, wherein hydraulically settable binder is included in an amount within the range from about 8% to about 60% by weight of the hydraulically settable mixture.
35. An article of manufacture as defined in claim 1, wherein hydraulically settable binder is included in an amount within the range from about 10% to about 45% by weight of the hydraulically settable mixture.
36. An article of manufacture as defined in claim 31 , wherein the hydraulic cement comprises a portland cement.
37. An article of manufacture as defined in claim 31 , wherein the hydraulic cement comprises a microfine cement.
38. An article of manufacture as defined in claim 31 , wherein the hydraulic cement is selected from the group consisting of slag cement, calcium aluminate cement, plaster, silicate cement, gypsum cement, phosphate cement, white cement, highalumina cement, magnesium oxychloride cement, aggregates coated with microfine cement particles, and mixtures of the foregoing.
39. An article of manufacture as defined in claim 1 , wherein the hydraulically settable binder is selected from the class consisting of MDF cement, DSP cement, Pyramenttype cement, and Densittype cement.
40. An article of manufacture as defined in claim 1, wherein the water is included in an amount up to about 10%> by weight of the hydraulically settable mixture.
41. An article of manufacture as defined in claim 1 , wherein the hydraulically settable mixture has a water to hydraulically settable binder ratio in the range of from about 0.01 to about 4.
42. An article of manufacture as defined in claim 1 , wherein the hydraulically settable mixture has a water to hydraulically settable binder ratio in the range of from about 0.1 to about 3.5.
43. An article of manufacture as defined in claim 1 , wherein the hydraulically settable mixture has a water to hydraulically settable binder ratio in the range of from about 0.15 to about 3.
44. An article of manufacture as defined in claim 1 , wherein the hydraulically settable mixture further comprises a fibrous material.
45. An article of manufacture as defined in claim 44, wherein the fibrous material increases the tensile strength of the hydraulically settable matrix.
46. An article of manufacture as defined in claim 44, wherein the fibrous material is selected from the group consisting of abaca fiber, glass fiber, cellulose, hemp, metal, carbon, ceramic, and silica.
47. An article of manufacture as defined in claim 44, wherein the fibrous material is a plastic.
48. An article of manufacture as defined in claim 47, wherein the plastic is a biodegradable plastic.
49. An article of manufacture as defined in claim 44, wherein the fibrous material comprises fibers having an aspect ratio of at least 10:1.
50. An article of manufacture as defined in claim 44, wherein the fibrous material comprises fibers having an aspect ratio of at least 900: 1.
51. An article of manufacture as defined in claim 44, wherein the fibrous material comprises fibers having an aspect ratio of at least 3000:1.
52. An article of manufacture as defined in claim 44, wherein the fibrous material comprises fibers having a length that is at least twice the effective diameter of individual hydraulically settable binder particles within the hydraulically settable mixture.
53. An article of manufacture as defined in claim 44, wherein the fibrous material comprises fibers having a length that is at least ten times the effective diameter of individual hydraulically settable binder particles within the hydraulically settable mixture.
54. An article of manufacture as defined in claim 44, wherein the fibrous material comprises fibers having a length that is at least 100 times the effective diameter of individual hydraulically settable binder particles within the hydraulically settable mixture.
55. An article of manufacture as defined in claim 44, wherein the fibrous material comprises fibers having a length that is at least 1000 times the effective diameter of individual hydraulically settable binder particles within the hydraulically settable mixture.
56. An article of manufacture as defined in claim 44, wherein the fibrous material is included in the range from about 0.2% to about 50% by volume with respect to the hydraulically settable mixture.
57. An article of manufacture as defined in claim 44, wherein the fibrous material is included in the range from about 0.5% to about 30% by volume of the hydraulically settable mixture.
58. An article of manufacture as defined in claim 44, wherein the fibrous material is included in the range from about 1% to about 15% by volume of the hydraulically settable mixture.
59. An article of manufacture as defined in claim 44, wherein the fibrous material comprises continuous fibers.
60. An article of manufacture as defined in claim 59, wherein the continuous fibers are selected from the group consisting of Kevlar, polyaramite, glass fibers, carbon fibers and cellulose fibers.
61. An article of manufacture as defined in claim 44, wherein the fibrous material comprises a mixtures of continuous fibers and noncontinuous fibers.
62. An article of manufacture as defined in claim 1 , wherein the hydraulically settable mixture further comprises a rheologymodifying agent which increases the plastic characteristics of the hydraulically settable mixture during a forming process and imparts form stability to the hydraulically settable matrix after forming.
63. An article of manufacture as defined in claim 62, wherein the rheology modifying agent comprises a polysaccharide based material, including polysaccharides and any derivative thereof.
64. An article of manufacture as defined in claim 63, wherein the polysaccharide based material comprises a cellulose based material, including cellulose and any derivative thereof.
65. An article of manufacture as defined in claim 64, wherein the cellulose based material comprises a material chosen from the class consisting of methylhydroxy¬ ethylcellulose, hydroxymethylethylcellulose, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, ethylcellulose, hydroxyethylpropylcellulose, and mixtures thereof.
66. An article of manufacture as defined in claim 64, wherein the cellulose based material comprises methylhydroxyethylcellulose.
67. An article of manufacture as defined in claim 66, wherein a 2% solution of the methylhydroxyethylcellulose in water has a viscosity within the range from between about 4,000 cps to about 15,000 cps measured at 20°C.
68. An article of manufacture as defined in claim 64, wherein the cellulose based material comprises hydroxyethylcellulose.
69. An article of manufacture as defined in claim 62, wherein the rheology modifying agent comprises wood flour.
70. An article of manufacture as defined in claim 63, wherein the polysaccharide based material comprises a starch based material, including starches and any derivative thereof.
71. An article of manufacture as defined in claim 70, wherein the starch based material comprises a material chosen from the class consisting of amylopectin, amylose, seagel, starch acetates, starch hydroxyethyl ethers, ionic starches, longchain alkyl starches, dextrins, amine starches, phosphate starches, dialdehyde starches, and mixtures thereof.
72. An article of manufacture as defined in claim 63, wherein the polysaccharide based material comprises a material chosen from the group consisting of alginic acid, phycocolloids, agar, gum arabic, guar gum, locust bean gum, gum karaya, gum tragacanth, and mixtures thereof.
73. An article of manufacture as defined in claim 62, wherein the rheology modifying agent comprises a protein based material, including proteins and any derivative thereof.
74. An article of manufacture as defined in claim 73, wherein the protein based material comprises a material chosen from the class consisting of prolamine, gelatin, glue, casein, and mixtures thereof.
75. An article of manufacture as defined in claim 62, wherein the rheology modifying agent comprises a synthetic material comprising a material chosen from the class consisting of polyvinyl alcohol, polyvinyl pyπolidone, polyvinylmethyl ether, polyacrylic acids, polyacrylic acid salts, polyvinylacrylic acids, polyvinylacrylic acid salts, polyacrylimides, ethylene oxide polymers, synthetic clay, latex, and mixtures thereof.
76. An article of manufacture as defined in claim 62, wherein the rheology modifying agent is included in an amount within the range from about 0.5% to about 50% by weight of the hydraulically settable mixture.
77. An article of manufacture as defined in claim 1 , wherein the hydraulically settable mixture further comprises an aggregate material.
78. An article of manufacture as defined in claim 77, wherein the aggregate material is chosen from the group consisting of perlite, mica, clay, kaolin, micro spheres, hollow glass spheres, porous ceramic spheres, and calcium carbonate.
79. An article of manufacture as defined in claim 78, wherein the aggregate material has a diameter within the range from about 0.01 microns to about 3 millimeters.
80. An article of manufacture as defined in claim 78, wherein the aggregate material has a diameter within the range from about 0.1 microns to about 0.5 millimeters.
81. An article of manufacture as defined in claim 78, wherein the aggregate material has a diameter within the range from about 0.2 microns to about 100 millimeters.
82. An article of manufacture as defined in claim 77, wherein the aggregate material is chosen from the group consisting of vermiculite, diatomaceous earth, exfoliated rock, sodium silicate macrospheres, exfoliated rock, lightweight concrete, tabular alumina, aerogel, lightweight expanded clay, expanded fly ash, expanded slag, pumice, and mixtures thereof.
83. An article of manufacture as defined in claim 77, wherein the aggregate material is selected from the group consisting of glass beads, metals, polymers, ceramic, alumina and cork.
84. An article of manufacture as defined in claim 77, wherein the aggregate material includes a material selected from the group consisting of sand, calcite, bauxite, dolomite, granite, quartz, gravel, rock, limestone, unreacted cement particles, sandstone, gypsum, silica, ground quartz, and mixtures thereof.
85. An article of manufacture as defined in claim 77, wherein the aggregate material includes a material selected from the group consisting of seeds, starches, gelatins, and agartype materials.
86. An article of manufacture as defined in claim 77, wherein the aggregate material is included in the range of from about .01%) to about 80%> by weight with respect to the hydraulically settable mixture.
87. An article of manufacture as defined in claim 77, wherein the aggregate material is included in an amount within the range from about 3%> to about 60% by weight of the hydraulically settable mixture.
88. An article of manufacture as defined in claim 77, wherein the aggregate material is included in an amount in the range from about 20% to about 50% by weight of the hydraulically settable mixture.
89. An article of manufacture as defined in claim 77, wherein the aggregate material comprises hollow glass spheres.
90. An article of manufacture as defined in claim 89, wherein the individual hollow glass spheres have effective diameter of less than about 1 millimeter.
91. An article of manufacture as defined in claim 89, wherein the individual hollow glass spheres have a plurality of effective diameters.
92. An article of manufacture as defined in claim 89, wherein the effective diameters of the individual hollow glass spheres are selected to maximize the efficient packing of the hollow glass spheres.
93. An article of manufacture as defined in claim 77, wherein the aggregate material comprises plastic particles.
94. An article of manufacture as defined in claim 93, wherein the hydraulically settable matrix is flexible.
95. An article of manufacture as defined in claim 93, wherein the plastic particles are included in an amount within the range from about 1% to about 10% by weight of the hydraulically settable mixture.
96. An article of manufacture as defined in claim 93, wherein the plastic particles are included in an amount within the range from about 3% to about 6% by weight of the hydraulically settable mixture.
97. An article of manufacture as defined in claim 93, wherein the plastic particles are included in an amount within the range from about 1% to about 10% by weight of the hydraulically settable mixture.
98. An article of manufacture as defined in claim 93, wherein the plastic particles are included in an amount within the range from about 2% to about 4%> by weight of the hydraulically settable mixture.
99. An article of manufacture as defined in claim 77, wherein the aggregate material comprises plastic particles, wherein the hydraulically settable matrix has a surface and a center, and wherein the plastic particles are more concentrated near the surface of the hydraulically settable matrix than near the center.
100. An article of manufacture as defined in claim 93 , wherein the surface of the hydraulically settable matrix is more flexible than the center.
101. An article of manufacture as defined in claim 77, wherein the hydraulically settable matrix has a thickness and wherein the individual particles forming the aggregate material have an effective diameter in the range form about 1/10 to about 3/4 of the thickness of the hydraulically settable matrix.
102. An article of manufacture as defined in claim 77, wherein the hydraulically settable matrix has a thickness and wherein the individual particles forming the aggregate material have an effective diameter in the range form about 1/10 to about 1/2 of the thickness of the hydraulically settable matrix.
103. An article of manufacture as defined in claim 77, wherein the hydraulically settable matrix has a thickness and wherein the individual particles forming the aggregate material have an effective diameter of less than approximately 1/4 of the thickness of the hydraulically settable matrix.
104. An article of manufacture as defined in claim 77, wherein the aggregate material imparts a predetermined color to the hydraulically settable matrix.
105. An article of manufacture as defined in claim 77, wherein the aggregate material imparts a predetermined texture to the hydraulically settable matrix.
106. An article of manufacture as defined in claim 1 , wherein the hydraulically settable mixture further comprises means for creating a discontinuous phase of finely dispersed, nonagglomerated voids within the hydraulically settable matrix.
107. An article of manufacture as defined in claim 1 , wherein the hydraulically settable matrix further comprises a discontinuous, nonagglomerated phase including finely dispersed voids.
108. An article of manufacture as defined in claim 106, wherein the means for creating a discontinuous phase of finely dispersed, nonagglomerated voids within the hydraulically settable matrix includes an air entraining agent.
109. An article of manufacture as defined in claim 108, wherein the air entraining agent is a surfactant.
110. An article of manufacture as defined in claim 108, wherein the air entraining agent is chosen from the class consisting of a polypeptide, an alkylene, a polyol, or a synthetic liquid anionic biodegradable solution.
111. An article of manufacture as defined in claim 108, further including a stabilizing agent for retaining the finely dispersed air voids within the hydraulically settable mixture as it cures into the hydraulically settable matrix.
112. An article of manufacture as defined in claim 111, wherein the stabilizing agent is vinsol resin.
113. An article of manufacture as defined in claim 111, wherein the stabilizing agent is a polysaccharide based rheologymodifying agent.
114. An article of manufacture as defined in claim 106, wherein the means for creating a discontinuous phase of finely dispersed, nonagglomerated voids within the hydraulically settable matrix includes a material which reacts with the components of the hydraulically settable mixture to produce a gas in order to incoφorate voids into the hydraulically settable matrix.
115. An article of manufacture as defined in claim 114, wherein the material which reacts with the components of the hydraulically settable mixture comprises a metal.
116. An article of manufacture as defined in claim 114, wherein the material which reacts with the components of the hydraulically settable mixture is aluminum.
117. An article of manufacture as defined in claim 114, further comprising a base which accelerates the production of the gas.
118. An article of manufacture as defined in claim 117, wherein the base is sodium hydroxide.
119. An article of manufacture as defined in claim 1 , wherein the hydraulically settable mixture further comprises a dispersant.
120. An article of manufacture as defined in claim 119, wherein the dispersant includes a sulfonated naphthaleneformaldehyde condensate.
121. An article of manufacture as defined in claim 119, wherein the dispersant is selected from the group consisting of sulfonated melamineformaldehyde condensate, lignosulfonate, and acrylic acid.
122. An article of manufacture as defined in claim 119, wherein the dispersant is included up to about 5% by weight of the hydraulically settable binder.
123. An article of manufacture as defined in claim 119, wherein the dispersant is included in the range from about 0.25% to about 4% by weight of the hydraulically settable binder.
124. An article of manufacture as defined in claim 119, wherein the dispersant is included in the range from about 0.5% to about 2% by weight of the hydraulically settable binder.
125. An article of manufacture as defined in claim 1, further comprising a coating on at least a portion of the surface of the hydraulically settable matrix.
126. An article of manufacture as defined in claim 125, wherein the coating on at least a portion of the surface of the hydraulically settable matrix prevents leaching of any material into or out of the hydraulically settable matrix.
127. An article of manufacture as defined in claim 125, wherein the coating on at least a portion of the surface of the hydraulically settable matrix increases the ability of the matrix to resist water penetration.
128. An article of manufacture as defined in claim 125, wherein the coating on at least a portion of the surface of the hydraulically settable matrix strengthens such portion.
129. An article of manufacture as defined in claim 125, wherein the coating comprises an FDAapproved material.
130. An article of manufacture as defined in claim 125, wherein the coating comprises a material selected from the group consisting of edible oils, melamine, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyacrylate, hydroxypropyl methylcellulose, polyethylene glycol, acrylics, polyurethane, polylactic acid, starch, soy bean protein, polyethylene, synthetic polymers, waxes, elastomers and mixtures thereof.
131. An article of manufacture as defined in claim 125, wherein the coating comprises a material selected from the the group consisting of sodium silicate, calcium carbonate, aluminum oxide, silicon oxide, clay, kaolin, ceramic and mixtures thereof.
132. An article of manufacture as defined in claim 125, wherein the coating is formed by the step of spraying carbon dioxide on the sheath.
133. An article of manufacture as defined in claim 1 , wherein the hydraulically settable matrix is disposable.
134. An article of manufacture as defined in claim 1 , wherein the hydraulically settable matrix is reusable.
135. An article of manufacture as defined in claim 1, wherein the sheath comprises a plurality of matrices of differing properties that are joined together.
136. An article of manufacture as defined in claim 1, further including metal fillings in the hydraulically settable mixture.
137. An article of manufacture as defined in claim 1, further including a dye in the hydraulically settable mixture.
138. An article of manufacture as defined in claim 1, further including a magnetized metal in the hydraulically settable mixture.
139. An article of manufacture as defined in claim 1, the hydraulically settable matrix having high green strength immediately after being formed.
140. An article of manufacture for marking, writing, drawing, coloring, painting, or applying cosmetics, comprising: a marking core; and a sheath for retaining therein the marking core, the sheath having a hydraulically settable matrix formed from a hydraulically settable mixture comprising: a hydraulically settable binder and water in an amount resulting in a hydraulically settable binder to water ratio within the range of from about 0.01 to about 4; a fibrous material having a concentration in the range of from about 0.2%) to about 50% by volume with respect to the hydraulically settable mixture, wherein the fibrous material has an aspect ratio of greater than 100:1; a rheologymodifying agent having a concentration in the range of from about 0.5% to about 50% by weight of the hydraulically settable mixture, wherein the rheologymodifying agent increases the plastic characteristics of the hydraulically settable mixture during the molding process and imparts form stability to the shaped hydraulically settable mixture as it cures into the hydraulically settable matrix; and an aggregate material having a concentration up to about 80% by weight with respect to the hydraulically settable mixture.
141. An article of manufacture as defined in claim 140, wherein the hydraulically settable binder comprises hydraulic cement.
142. An article of manufacture as defined in claim 141, wherein the hydraulic cement comprises a portland cement.
143. An article of manufacture as defined in claim 140, wherein the hydraulically settable binder comprises gypsum.
144. An article of manufacture as defined in claim 140, wherein the hydraulically settable mixture further comprises a fibrous material included in an amount within the range from about 0.5% to about 30% by volume of the hydraulically settable mixture.
145. An article of manufacture as defined in claim 140, wherein the rheology modifying agent comprises a polysaccharide material, including polysaccharides and any derivatives thereof.
146. An article of manufacture as defined in claim 145, wherein the rheology modifying agent comprises methylhydroxyethylcellulose.
147. An article of manufacture as defined in claim 140, wherein the aggregate material comprises hollow glass spheres.
148. An article of manufacture as defined in claim 140, wherein the hydraulically settable mixture further comprises means for creating a discontinuous phase of finely dispersed, nonagglomerated voids within the hydraulically settable matrix.
149. An article of manufacture as defined in claim 140, wherein the hydraulically settable mixture further comprises an air entraining agent for incoφorating finely dispersed, nonagglomerated air voids within the hydraulically settable mixture during a mixing process.
150. An article of manufacture as defined in claim 149, wherein the air entraining agent is a surfactant.
151. An article of manufacture as defined in claim 140, wherein the hydraulically settable mixture further comprises a metal which reacts with components of the hydraulically settable mixture to produce a gas, which is incoφorated into the hydraulically settable mixture as finely dispersed, nonagglomerated gas bubbles.
152. An article of manufacture as defined in claim 151, wherein the metal comprises aluminum.
153. An article of manufacture as defined in claim 151, wherein the hydraulically settable mixture further comprises a base which aids in the formation of the gas.
154. An article of manufacture as defined in claim 153, wherein the base comprises sodium hydroxide.
155. An article of manufacture as defined in claim 140, further comprising a coating on the sheath formed by the step of spraying carbon dioxide on the sheath.
156. An article of manufacture as defined in claim 140, wherein the hydraulically settable mixture further comprises a dispersant.
157. An article of manufacture as defined in claim 156, wherein the dispersant includes a sulfonated naphthaleneformaldehyde condensate.
158. An article of manufacture as defined in claim 156, wherein the dispersant is selected from the group consisting of sulfonated melamineformaldehyde condensate, lignosulfonate, and acrylic acid.
159. A method of manufacturing a marking implement the method comprising the steps of: mixing a hydraulically settable binder and water to form a hydraulically settable mixture; forming the hydraulically settable mixture into a sheath having a hydraulically settable matrix, the sheath being formed to retain a marking core; and hardening the hydraulically settable matrix of the sheath in a time period sufficiently short for the sheath to be mass producible.
160. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath imparts form stability to the hydraulically settable matrix.
161. A method of manufacturing as defined in claim 159, further comprising the step of positioning a marking core within the sheath.
162. A method of manufacturing as defined in claim 161, wherein the marking core is removable.
163. A method of manufacturing as defined in claim 161, wherein the marking core is fixedly retained within the sheath.
164. A method of manufacturing as defined in claim 163, wherein the step of positioning a marking core within the sheath creates an adhesiveless bond between the marking core and the sheath.
165. A method of manufacturing as defined in claim 162, wherein the step of forming the hydraulically settable mixture into a sheath and the step of positioning a marking core within the sheath occur simultaneously.
166. A method of manufacturing as defined in claim 162, wherein the step of forming the hydraulically settable mixture into a sheath and the step of positioning a marking core within the sheath occur sequentially.
167. A method of manufacturing as defined in claim 163, wherein the step of forming the hydraulically settable mixture into a sheath and the step of positioning a marking core within the sheath occur simultaneously.
168. A method of manufacturing as defined in claim 163, wherein the step of forming the hydraulically settable mixture into a sheath and the step of positioning a marking core within the sheath occur sequentially.
169. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath comprises the steps of: extruding the hydraulically settable mixture into parts of a sheath; and assembling the parts into a sheath.
170. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath comprises the steps of: extruding the hydraulically settable mixture into sections of a sheath; and assembling the sections into a sheath.
171. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath is performed by extruding the hydraulically settable mixture into a sheath.
172. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath is performed by coextruding the hydraulically settable mixture and a marking core, the sheath being formed from the hydraulically settable mixture around the marking core.
173. A method of manufacturing as defined in claim 172, wherein the marking core is removable.
174. A method of manufacturing as defined in claim 172, wherein the marking core is fixedly retained within the sheath.
175. A method of manufacturing as defined in claim 174, wherein an adhesiveless bond occurs between the marking core and the sheath.
176. A method of manufacturing as defined in claim 172, wherein coextruding the hydraulically settable mixture and the marking core is performed by peφendicular extrusion.
177. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath is accomplished by piston extrusion.
178. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath is accomplished by auger extrusion.
179. A method of manufacturing as defined in claim 159, further comprising the step of deairing the hydraulically settable mixture.
180. A method of manufacturing as defined in claim 179, wherein the deairing step is accomplished by vacuum extrusion of the hydraulically settable mixture.
181. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath is accomplished by molding the hydraulically settable mixture into a sheath.
182. A method of manufacturing as defined in claim 181, wherein the forming step further comprises the use of a mold releasing agent to aid in releasing the sheath formed by molding.
183. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath is accomplished by molding the hydraulically settable mixture into a portion of a sheath.
184. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath is accomplished by molding the hydraulically settable mixture into a section of a sheath.
185. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath comprises the steps of: fashioning a sheet from the hydraulically settable mixture; and convoluting the sheet around the marking core.
186. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath comprises the steps of: fashioning a sheet from the hydraulically settable mixture; and spiral winding the sheet around the marking core.
187. A method of manufacturing as defined in claim 159, wherein the step of forming the hydraulically settable mixture into a sheath is accomplished by powder compaction of the hydraulically settable mixture.
188. A method of manufacturing as defined in claim 159, wherein the hydraulically settable binder comprises hydraulic cement.
189. A method of manufacturing as defined in claim 188, wherein the hydraulic cement comprises portland cement.
190. A method of manufacturing as defined in claim 159, wherein the hydraulically settable binder comprises gypsum.
191. A method of manufacturing as defined in claim 159, wherein the water is included in an amount within the range of from 5% to about 10% by weight of the hydraulically settable mixture.
192. A method of manufacturing as defined in claim 159, wherein the hydraulically settable mixture has a water to hydraulically settable binder ratio in the range of from about 0.01 to about 4.
193. A method of manufacturing as defined in claim 159, further including the step of adding a fibrous material to the hydraulically settable mixture.
194. A method of manufacturing as defined in claim 193, wherein the fiber is chosen from the group consisting of Kevlar, polyaramite, glass fibers, carbon fibers and cellulose fibers, and mixtures thereof.
195. A method of manufacturing as defined in claim 193, wherein the fibrous material is included in an amount within the range from between about 0.2% to about 50% by volume of the hydraulically settable mixture.
196. A method of manufacturing as defined in claim 193, wherein the fibrous material is included in an amount within the range from between about 0.5% to about 30% by volume of the hydraulically settable mixture.
197. A method of manufacturing as defined in claim 193, wherein the fibrous material is included in an amount within the range from between about 1% to about 15% by volume of the hydraulically settable mixture.
198. A method of manufacturing as defined in claim 159, further including the step of adding a rheologymodifying agent to the hydraulically settable mixture in order to increase the plasticlike consistency of the hydraulically settable mixture.
199. A method of manufacturing as defined in claim 198, wherein the rheologymodifying agent is included in the range from about 0.5%) to about 50% by weight of the hydraulically settable mixture.
200. A method of manufacturing as defined in claim 198, wherein the rheologymodifying agent includes a polysaccharide material.
201. A method of manufacturing as defined in claim 198, wherein the rheologymodifying agent includes a protein material.
202. A method of manufacturing as defined in claim 198, wherein the rheologymodifying agent includes a synthetic organic material.
203. A method of manufacturing as defined in claim 198, wherein the rheologymodifying agent includes a latex material.
204. A method of manufacturing as defined in claim 159, further including the step of adding an aggregate material to the hydraulically settable mixture.
205. A method of manufacturing a as defined in claim 204, wherein the aggregate material is included in an amount up to about 80% by weight of the hydraulically settable mixture.
206. A method of manufacturing as defined in claim 204, wherein the aggregate material is included in an amount within the range from between about 3% to about 60%) by weight of the hydraulically settable mixture.
207. A method of manufacturing as defined in claim 204, wherein the aggregate material increases the strength of the sheath.
208. A method of manufacturing as defined in claim 204, wherein the aggregates are of a plurality of different sizes so as to increase the particle packing efficiency of the aggregates.
209. A method of manufacturing as defined in claim 159, further including the step of adding a dispersant to the hydraulically settable mixture.
210. A method of manufacturing as defined in claim 209, wherein the dispersant includes a sulfonated naphthaleneformaldehyde condensate.
211. A method of manufacturing as defined in claim 209, wherein the dispersant is selected from the group consisting of sulfonated melamineformaldehyde condensate, lignosulfonate, and acrylic acid.
212. A method of manufacturing as defined in claim 209, wherein the dispersant is included in an amount up to about 5% by weight of the hydraulically settable binder.
213. A method of manufacturing as defined in claim 209, wherein the dispersant is included in an amount within the range from about 0.25% to about 4.0%> by weight of the hydraulically settable binder.
214. A method of manufacturing as defined in claim 209, wherein the dispersant is included in an amount within the range from about 0.5% to about 2% by weight of the hydraulically settable binder.
215. A method of manufacturing as defined in claim 159, wherein the hydraulic cement and water are mixed in a high energy, high shear mixer.
216. A method of manufacturing as defined in claim 159, further including the step of introducing air voids into the hydraulically settable mixture, thereby forming air voids in the resultant hydraulically settable matrix.
217. A method of manufacturing as defined in claim 216, wherein the air voids are introduced by maintaining high pressure within an extruder to cause vaporization of the water within the hydraulically settable mixture as the hydraulically settable mixture exits the extruder.
218. A method of manufacturing as defined in claim 216, wherein the step of introducing air voids is accomplished by adding a metal to the hydraulically settable mixture, the metal being easily oxidized in the presence of aqueous basic conditions so as to produce a gas, thereby forming air voids in the resultant hydraulically settable matrix.
219. A method of manufacturing as defined in claim 218, wherein the metal is selected from the group consisting of magnesium, aluminum, zinc, and tin.
220. A method of manufacturing as defined in claim 218 further comprising the step of adding heat to the hydraulically settable mixture and the metal in order to increase the rate of reaction and gaseous formation.
221. A method of manufacturing as defined in claim 218, further comprising the step of adding a base to the hydraulically settable mixture in order to increase the rate of reaction and gaseous formation.
222. A method of manufacturing as defined in claim 216, further comprising the step of adding an air entraining agent to the hydraulically settable mixture in order to stabilize the air voids.
223. A method of manufacturing as defined in claim 159, further comprising the step of adding a magnetized metal to the hydraulically settable mixture.
224. A method of manufacturing as defined in claim 159, further comprising the step of adding metal fillings to the hydraulically settable mixture.
225. A method of manufacturing as defined in claim 159, further comprising the step of adding a dye to the hydraulically settable mixture.
226. A method of manufacturing as defined in claim 159, further including the step of passing the sheath through a drying tunnel in order to remove a significant amount of the water within the hydraulically settable mixture.
227. A method of manufacturing as defined in claim 226, wherein the removal of a significant amount of the water increases the form stability of the hydraulically settable matrix.
228. A method of manufacturing as defined in claim 226, wherein the removal of a significant amount of the water is accomplished through the use of waves having a wavelength within the range from about the wavelength of microwaves to about the wavelength of xrays.
229. A method of manufacturing as defined in claim 159, further including the step of coating at least a portion of the surface of the hydraulically settable matrix of the sheath.
230. A method of manufacturing as defined in claim 229, wherein the coating on at least a portion of the surface of the hydraulically settable matrix of the sheath is coated with a material selected from the group consisting of sodium silicate, orthosilicates, siloxanes, colloidal silica in organic polymer dispersions, colloidal silica in films, colloidal silica in fibers, biodegradable plastics, calcium carbonate, acrylics, polyacrylates, polyurethanes, melamines, polyethylene, synthetic polymers, hydroxy propylmethylcellulose, polyethyleneglycol, kaolin, clay, Zein®, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, ceramics, waxes and paint.
231. A method of manufacturing as defined in claim 229, wherein the coating on at least a portion of the surface of the hydraulically settable matrix of the sheath is coated with carbon dioxide.
232. A method of manufacturing as defined in claim 229, wherein the coating on at least a portion of surface of the hydraulically settable matrix of the sheath strengthens such portion.
233. A method of manufacturing as defined in claim 229, wherein the step of coating the sheath renders the sheath safe for human contact.
234. A method of manufacturing as defined in claim 159, further including the step of laminating the sheath.
235. A method of manufacturing as defined in claim 159, further including the step of printing indicia on the sheath.
Description:
HYDRAULICALLY SETTING SHEATH AND METHODS

*

5 BACKGROUND OF THE INVENTION

1. The Field of the Invention.

The present invention relates to novel hydraulically settable materials and their methods of manufacture and, more particularly, to marking implements with hydraulically

10 settable sheaths containing a marking core. The marking implements with a hydraulically settable sheath and a marking core, such as pencils, pens and the like, can be manufactured in a manner which is efficient, inexpensive, and environmentally neutral.

2. The Related Technology.

15 A. Traditional Marking Implements.

Sheaths used in traditional marking implements such as disposable and nondisposable pens, mechanical and non-mechanical pencils, ink markers, and cosmetic pencils, etc. typically consist primarily of either plastic or wood. Plastic and wood have been regarded as the preferable materials in manufacturing sheaths for marking 20 implements but their use creates problems related to cost, efficiency and environmental impact.

Plastic is the material used in the vast majority of marking implement sheaths such as plastic pencils, disposable and nondisposable pens, mechanical pencils, ink markers (sometimes referred to as "magic markers"), and cosmetic pencils. The widespread use 25 of plastic resulted from its apparent superiority as sheaths for such marking implements.

Plastic is generally inexpensive, lightweight, strong, and durable. The cost of producing marking implements with a plastic sheath is directly related to the cost of petroleum

products which provide the raw materials necessary for plastic production. Although , plastic is generally inexpensive, as petroleum resources become more scarce, the cost of items dependent on the availability of petroleum products will increase.

In addition, to the obvious chemical hazards of plastic production, plastics used in pens, and pencils are very slow to degrade. This is especially true when buried deep inside of landfills and away from the corrosive effects of light, air, and water.

The continued use of plastic, however, is due in part to economic forces such as resistance to change, habit, and the fact that large manufacturers set an industry standard and tend to resist the creation of a new standard, thereby risking losing their market share of the old industry.

While pencils are commonly manufactured with plastic sheaths, wood continues to be the dominant utilized material in disposable pencils. Manufacturing pencils with a wooden sheath has, however, become more expensive based upon the increasing cost of slats for the wooden sheath. Additionally, it is not possible to manufacture pencils with a wooden sheath by an inexpensive continuous process. Pencils with a wooden sheath are conventionally manufactured by a process involving considerable work, many special conditions, and individual operations.

In the standard method of making pencils with a wooden sheath, only wood that is first class and specially selected may be used. The number of suitable woods is limited, and it is only cedar wood that is normally used for high grade products. The wood has to be dried under suitable climatic conditions. The resin or essential oil content should neither exceed nor fall below certain limits. The prepared wood is cut with special saws into thin boards which are subjected to the following operations: staining, grooving, inserting the leads, gluing together, coarse sanding, cutting into crude pencils, and further sanding to give the familiar hexagonal or round forms. The polishing and varnishing process also involves considerable work and a number of individual operations. Finally, erasers are installed.

This technique for manufacturing pencils with a wooden sheath is costly and time consuming; additionally, a large quantity of wood is wasted. With the increasing shortage of wood acceptable for pencils, the waste factor becomes less tolerable.

* Additionally, the environmental impact of obtaining the wood used to produce pencils

5 contributes to global deforestation.

Substitutes for the wooden sheaths, as well as for the involved manufacturing process, have long been sought. Substitute materials for traditional wooden sheaths include plastics, recycled paper products, and wood flour mixed with a nonabsorbent cellulose material. Although pencils with sheaths made from materials other than wood

10 slats, these substitutes have been unable to replace traditional wooden pencils.

Manufacturing pencils with sheaths made from materials other than wooden slats alleviates some of the problems associated with using wooden slats, such as the costly multistep process and depending upon the increasingly expensive wood. The alternative materials, however, also produce their own problems. For instance, the pollutants created

15 from utilizing recycled paper, wood pulp, and plastic in the manufacturing process.

Metals are also used as sheaths for some marking implements. Manufacturing sheaths from metals is expensive and also results in environmental degradation.

B. Traditional Cementitious Materials.

20 The need for an inexpensive and environmentally benign material in the manufacture of marking implements has not lead to the use of hydraulically settable

- materials, such as cement or gypsum (hereinafter "hydraulically settable," "hydraulic,"

' or "cementitious" compositions, materials, or mixtures). Hydraulically settable materials, however, are inexpensive and comprise environmentally innocuous components like 25 rock, sand, clay and water. From an economic and ecological standpoint, hydraulically settable materials are ideally suited to replace wood, plastics and metals, as the materials of choice for such marking implements.

Hydraulically settable materials have not been utilized for manufacturing lightweight objects such as marking implements due to the recognized characteristics of hydraulically settable materials and problems associated with processing the materials. Some of the recognized characteristics and problems associated with such materials and the processing of such materials include: high fluidity, low tensile strength, low form stability after shaping the materials, lengthy curing times, adhesion to the forming apparatus and bleeding of water to the surface of the formed article. As a result of the recognized characteristics and processing problems of hydraulically settable materials, their usefulness has generally been limited to large, bulky structures that are durable, strong, and relatively inexpensive.

Structures containing a hydraulic cement are generally formed by mixing hydraulic cement with water and usually some type of aggregate to form a cementitious mixture, which hardens into concrete. Ideally, a freshly mixed cementitious mixture is fairly nonviscous, semi-fluid, and capable of being mixed and formed by hand. Because of its fluid nature, concrete is generally shaped by being poured into a mold, worked to eliminate large air pockets, and allowed to harden. Some concrete mixtures have also been extruded into substantially flat slabs of simple shape. In the latter case, the cementitious mixture must be viscous and cohesive enough to avoid slumping (that is, changing from the desired shape). If the surface of the concrete structure is to be exposed, such as on a concrete sidewalk, additional efforts are made to finish the surface to make it more functional and to give it the desired surface characteristics.

Due to the high level of fluidity required for typical cementitious mixtures to have adequate workability, the uses of concrete and other hydraulically settable mixtures have been limited mainly to simple shapes which are generally large, heavy, and bulky, and which require mechanical forces to retain their shape until sufficient hardening of the material has occurred. The uses of cementitious materials have also been limited by the strength properties of concrete, namely, the high ratio of compressive strength to tensile

strength with relative low tensile strength. The ratio of compressive strength to tensile strength is typically in the order of 10: 1.

Another limitation has been that traditional cementitious mixtures or slurries have little or no form stability and are molded into the final form by pouring the mixture into a space having externally supported boundaries or walls. It is precisely because of this lack of moldability, coupled with the low tensile strength per unit weight, that cementitious materials have traditionally been useful only for applications where size and weight are not limiting factors and where the forces or loads exerted on the concrete are generally limited to compressive forces or loads, as in, e.g., columns, foundations, roads, sidewalks, and walls.

The lack of tensile strength (about 1 -4 MPa) in concrete is ubiquitously illustrated by the fact that concrete readily cracks or fractures upon shrinkage or bending, unlike other materials such as metal, paper, plastic, or ceramic. Consequently, typical cementitious materials have not been suitable for making small, thin-walled, lightweight objects, such as sheaths, which must be made from materials with much higher tensile and flexural strengths per unit weight compared to typical cementitious materials and where a large cross-section is impractical. More recently, higher strength cementitious materials have been developed which might be capable of being formed into smaller, denser objects. One such material is known as "Macro-defect Free" or "MDF" concrete, such as is disclosed in U.S. Patent No. 4,410,366 to Birchall et al. See also, SJ. Weiss,

E.M. Gartner & S.W. Tresouthick, "High Tensile Cement Pastes as a Low Energy Substitute for Metals, Plastics, Ceramics, and Wood," U.S. Department of Energy CTL Project CR7851-4330 (Final Report, November 1984). However, such high strength cementitious materials have been prohibitively expensive and would be unsuitable for making inexpensive sheaths where much cheaper materials better suited for such uses

{e.g., wood and plastic) are readily available. Another drawback is that MDF concrete cannot be used to mass produce small lightweight objects due to the high amount of time

and effort involved in forming and hardening the material and the fact that it is highly water soluble. Additionally, such materials have high viscosity and high yield stress which impedes molding and achieving form stability after molding.

Another problem with traditional, and even more recently developed high strength concretes has been the lengthy curing times almost universally required for most concretes. Typical concrete products formed from a flowable mixture require a hardening period of 10-24 hours before the concrete is mechanically self-supporting, and upwards of a month before the concrete reaches a substantial amount of its maximum strength. Extreme care has had to be used to avoid moving the cementitious articles until they have obtained sufficient strength to be demolded. Movement or demolding prior to this time has usually resulted in cracks and flaws in the cementitious structural matrix. Once self-supporting, the object could be demolded, although it has not typically attained the majority of its ultimate strength until days or even weeks later.

Economically and commercially mass producing cementitious objects has been difficult since the molds used in forming cementitious objects are generally reused in the production of concrete products and a substantial period of time is required for even minimal curing of the concrete. The molding difficulties are magnified for small, lightweight articles. Although zero slump concrete has been used to "mass produce" large, bulky object such as molded slabs, large pipes, or bricks which are immediately self-supporting, such "mass production" is only useful in producing objects at a rate of thousands per day. Such compositions and methods cannot be used to mass produce small, lightweight, objects at a rate of thousands per hour. Additionally, zero slump concrete generally has high viscosity and high yield stress which impedes molding and achieving form stability after molding. Demolding the cementitious object can create further problems. As concrete cures, it tends to bond to the forms unless expensive releasing agents, such as release oil, are used. It is often necessary to wedge the forms loose to remove them. Such wedging,

if not done properly and carefully each time, often results in cracking or breakage around the edges of the structure. This problem further limits the ability to make small, lightweight, cementitious articles or shapes other than flat slabs, particularly in any type of a commercial mass production. If the bond between the outer wall of the molded cementitious article and the mold is greater than the internal cohesive or tensile strengths of the molded article, removal of the mold will likely break the relatively weak walls or other structural features of the molded article. Hence, traditional cementitious objects must be large in volume and thickness, as well as extraordinarily simple in shape, in order to avoid breakage during demolding unless expensive releasing agents and other precautions are used.

Typical processing techniques of concrete also require that it be properly consolidated after it is placed in order to ensure that no voids exist between the forms or in the structural matrix. This is usually accomplished through various methods of vibration or poking. The problem with consolidating, however, is that extensive overvibration of the concrete after it has been placed can result in segregation or bleeding of the concrete.

Bleeding is the migration of water to the top surface of freshly placed concrete caused by the settling of the heavier aggregate. Excessive bleeding increases the water to cement ratio near the top surface of the concrete slab, which correspondingly weakens and reduces the durability of the surface of the slab. The overworking of concrete during the finishing process not only brings an excess of water to the surface, but also fine material, resulting in subsequent surface defects.

Additionally, the nature of traditional cementitious materials presents another design limitation related to the porosity of the cementitious materials and costs. Utilization of traditional cementitious materials requires either undesirably high porosity to achieve a low cost product or lower porosity at a high cost.

For each of the foregoing reasons, as well as numerous others, cementitious materials have not had significant commercial application outside of the formation of large, slab-like objects, such as in buildings, foundations, walk- ways, highways, roofing materials or as mortar to adhere bricks or cured concrete blocks. It is completely counterintuitive, as well as contrary to human experience, to even imagine (let alone actually experience) the manufacture from cementitious materials of small, lightweight objects such as sheaths for marking implements, which are presently manufactured from lightweight, yet relatively high strength to mass, materials such as wood, plastic and paper. In short, what are needed are improved methods for manufacturing sheaths for marking implements at a cost that is competitive with or even superior to, the costs involved in manufacturing marking implements with sheaths made from wood, plastic, or metal materials.

Additionally, it would be a significant advancement to produce sheaths from materials which have a much lesser impact on the environment; decrease the need for wood, plastic and metal materials; comprise renewable materials; and do not result in the generation of wastes involved in the manufacture of sheaths from wood, plastic or metal materials.

It would also be a completely novel and an important advancement if such methods yielded sheaths and other objects having a chemical composition compatible with the earth into which they eventually might be discarded.

It would also be novel in the art of cement making to provide sheaths and methods for manufacturing sheaths which can be commercially formed from hydraulically settable materials, will rapidly obtain form stability and maintain their shape without external support for subsequent handling shortly after formation.

It would be still another advancement in the art to provide sheaths formed from hydraulically settable mixtures and methods for mass producing such sheaths which do

not adhere to the forming apparatus and can be removed from the forming apparatus directly after forming without degradation to the sheaths.

Finally, it is still another object of the present invention to provide sheaths and methods for removing sheaths from the forming apparatus directly after forming without degradation to the sheath. Such methods are disclosed and claimed herein.

BRIEF SUMMARY OF THE INVENTION

The present invention encompasses marking implements with a marking core and a sheath having a structural matrix formed from hydraulically settable materials, such as hydraulic cement, gypsum and other materials that set or harden with water, and methods for manufacturing such marking implements. Marking implements with a marking core and a sheath having a structural matrix formed from hydraulically settable materials within the scope of the present invention are particularly useful for marking, writing, drawing, coloring, painting, or applying cosmetics in the manner that pencils, pens, mechanical pencils, ink markers, and cosmetic pencils and the like are used.

The structural matrix of the sheaths (hereinafter "hydraulically settable sheath" or "sheath") formed from the hydraulically settable materials have properties that have not previously been achieved through the use of such materials. Utilization of these materials allows the economic mass production of sheaths without the processing problems typically associated with such materials. Additionally, additives can be optionally utilized with the binders which also results in a structural matrix having unique properties.

The manufacture of sheaths through the use of hydraulically settable materials without the undesirable characteristics and processing problems associated with traditional hydraulically settable materials was achieved through microstructural engineering. Microstructural engineering is the process of building into the microstructure of hydraulically settable compositions certain desired, predetermined

properties into the final product such as strength, flexibility, color and density. This microstructural engineering approach allows for the design of sheaths having a structural matrix with predetermined properties from a wide variety of commonly available materials. Utilizing this method, the desired properties are designed into the microstructure of the structural matrix, while optimizing the costs and other aspects of a mass production manufacturing system.

The result of the microstructural engineering approach is the ability to manufacture a wide variety of different products heretofore manufactured from wood, plastic, and metal. Moreover, the present invention can be manufactured at a cost that is usually competitive with, and in most cases even superior to, the costs involved in manufacturing marking implements with sheaths made from wood, plastic, or metal materials.

Because the hydraulically settable sheaths of the present invention comprise only environmentally neutral components, which also are far more renewable, the manufacture of such sheaths has a much lesser impact on the environment than the manufacture of marking implements with a sheath made from wood, plastic, or metal materials. Unlike the manufacture of wood sheaths, hydraulically settable sheaths require no cutting of trees to supply the raw materials for their manufacture.

The major components within the sheaths of the present invention include mainly inorganic materials, such as hydraulically settable binders (such as hydraulic cement and gypsum), aggregates (such as sand, calcite, bauxite, dolomite, granite, quartz, glass, silica, perlite, vermiculite, clay, and even waste concrete products), fibers (organic and inorganic fibers), rheology-modifying agents, dispersants, and accelerators along with water necessary to hydrate, or react with, the hydraulically settable binders. These materials form a hydraulically settable mixture.

The preferred structural matrix of the sheaths manufactured according to the present invention is formed from the reaction products of a cementitious or other

hydraulically settable mixture. The hydraulically settable mixture will at a minimum contain a hydraulic binder, such as hydraulic cement or gypsum hemihydrate, and water. The porosity of the hydraulically settable structural matrix resulting from these mixtures can be minimized by maintaining a low water to hydraulic binder ratio. In order to design the desired properties into the hydraulically settable mixture and/or the cured hydraulically settable structural matrix, a variety of other additives are included within the hydraulic mixture, such as one or more aggregate materials, fibers, rheology-modifying agents, dispersants, accelerators, air entraining agents, blowing agents or reactive metals. The identity and quantity of any additive will depend on the desired properties of both the hydraulically settable mixture, as well as the final hardened sheath made therefrom.

In some cases it may be preferable to include one or more aggregate materials within the mixture to create a smooth surface, to add bulk and decrease the cost of the mixture. Aggregates often impart significant strength properties and improved workability. Examples of such aggregates are ordinary sand, calcite, limestone, bauxite, dolomite, granite and quartz which are completely environmentally safe, extremely inexpensive, and essentially inexhaustible.

In other cases, lightweight aggregates can be added to yield a lighter, final cured product. Examples of lightweight aggregate are expanded perlite, vermiculite, hollow glass spheres, aerogel, xerogel, and other lightweight mineral materials. These aggregates are likewise environmentally safe and relatively inexpensive.

Fibers are added to the hydraulically settable mixture to increase the tensile strength, flexural strength, compressive strength, cohesive strength and impact resistance of the sheaths. Fibers should preferably have high tear strengths, burst strengths, and tensile strengths. Fibers with a high aspect ratio work best in imparting strength and toughness to the hydraulically settable material.

Due to the versatility of the hydraulically settable mixtures used in the manufacture of the sheaths, a wide range of fibers, both organic and inorganic, can be used. Examples of preferred fibers include biodegradable plastics, glass, silica, ceramic, metals, carbon, hemp, plant leaves and stems, wood fibers (such as southern pine), flax, bagasse (sugar cane fiber), cotton and hemp (high aspect ratio). Abaca is a preferred fiber which is extracted from a banana-like hemp plant found naturally in the Philippines. Additionally, continuous fibers can be utilized such as Kevlar, polyaramite, glass fibers, carbon fibers and cellulose fibers.

Rheology-modifying agents can be added to increase the cohesive strength, "plastic-like" behavior, and the ability of the mixture to retain its shape when molded or extruded. They act as thickeners and increase the viscosity of the mixture as well as the yield stress of the mixture, which is the amount of force necessary to deform the mixture. This creates higher "green strength" in the molded or extruded product. Suitable rheology-modifying agents include a variety of cellulose-, starch-, and protein-based materials which act by both bridging the individual cement particles together and by gelation of the water.

Dispersants, on the other hand, act to decrease the viscosity and yield stress of the mixture by dispersing the individual hydraulic binder particles. This allows for the use of less water while maintaining adequate levels of workability. Suitable dispersants include any material which can be adsorbed onto the surface of the hydraulic binder particles and which act to disperse the particles, usually by creating an electrical charged surface area on the particle or by placing electrical charges in the near colloid double layer.

In the case where both a rheology-modifying agent and dispersant are used, it will usually be advantageous to add the dispersant first and then the rheology-modifying agent second in order to obtain the beneficial effects of each. Otherwise, if the rheology- modifying is first adsorbed by the binder particles, it may create a protective colloid

layer, which will prevent the dispersant from being adsorbed by the particles and imparting its beneficial effect to the hydraulically settable mixture.

The hydraulically settable structural matrix is composed of mainly inorganic materials, although, certain embodiments may also include organic components, such as cellulose-based fibers and/or rheology-modifying agents. These organic components, however, represent only a small fraction of the overall mass of the hydraulically settable materials used to manufacture the sheaths. Additionally, some of the organic fibers utilized in this invention can be planted and harvested in an agribusiness setting, such as the abaca fibers. Additionally, the marking implements with hydraulically settable sheaths utilize no petroleum-based products or derivatives as starting materials unlike the manufacture of marking implements with plastic sheaths. Thus, although some amount of fossil fuel is necessary to generate the energy used in the manufacture of the marking implements with a hydraulically settable sheath, far less will be consumed. The general method of manufacturing the marking implements includes: (1) mechanically mixing a powdered hydraulic cement and water in order to form a cement paste in a high shear mixer and (2) forming a sheath from the mixture around a marking core or forming a sheath and later inserting a marking core into the sheath. In addition to mixing a powdered cement and water, it may be desirable to add other desired materials such as aggregates, fibers, rheology-modifying agents, dispersants, and accelerants to create a hydraulically settable mixture having the desired rheological as well as ultimate strength, weight, and low cost properties. The sheaths formed from the mixture can subsequently be dried or cured. The manner of mixing and curing can also effect the final properties of the hardened hydraulically settable structural matrix. Additionally, coatings and laminates can be utilized to achieve a desired finish.

The present invention can be rapidly processed into sheaths of a desired shape having sufficient strength to be self-supporting, form stable, and moveable shortly after

formation for subsequent curing. Furthermore, the marking implements with a hydraulically settable sheath and a marking core are easily removed from their forming device.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more fully understand the manner in which the above-recited and other advantages and objects of the invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope, the invention in its presently understood best mode for making and using the same will be described with additional specificity and detail through the use of the accompanying drawings in which:

Figure 1 is a perspective view of a marking implement in accordance with the present invention, the implement being in a sharpened condition.

Figure 2 is a perspective view of a marking implement in accordance with the present invention.

Figure 3 is a perspective view of another marking implement in accordance with the present invention. Figure 4 is a perspective view of still another marking implement in accordance with the present invention.

Figure 5 is a perspective view of another marking implement in accordance with the present invention.

Figure 6 is a perspective view of yet another marking implement in accordance with the present invention.

Figure 7 is a perspective view of still another marking implement in accordance with the present invention.

Figure 8 is a perspective view of yet another marking implement in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to marking implements with a hydraulically settable sheath and a marking core for use in marking, writing, drawing, coloring, painting, or applying cosmetics, as used by traditional marking implements with sheaths made from wood, plastic, or metal such as mechanical and non-mechanical pencils, pens, and ink markers. Using a microstructural engineering approach it is possible to design a hydraulically settable mixture that can be readily and economically mass produced into sheaths with significantly less environmental impact than conventional sheaths. More particularly, the present invention is directed to marking implements with a hydraulically settable sheath and a marking core in which the sheath is manufactured from hydraulically settable materials that are generally lightweight and yet have a high strength to bulk density ratio, can be cost effectively produced, and are more environmentally neutral than currently used marking implements. The marking implements within the purview of the present invention can be either a disposable or nondisposable marking implement.

I. General Discussion.

The sheaths result in a decreased cost in materials and production compared to conventional sheaths and a decreased environmental impact in obtaining the materials to manufacture the sheaths, processing the materials into sheaths, and disposing of used sheaths. These objectives are achieved through the utilization of sheaths formed from hydraulically settable materials while overcoming the undesirable characteristics and processing problems associated with traditional hydraulically settable materials.

The undesirable characteristics associated with traditional hydraulically settable materials has indicated until now that hydraulically settable materials could not be utilized to mass produce sheaths which are small, lightweight, and thin-walled. The characteristics and processing problems of traditional hydraulically settable materials which have precluded the mass production of these materials for sheaths includes: high porosity, low tensile strength, low form stability after shaping the materials, lengthy curing times, adhesion to the forming apparatus and bleeding of water to the surface of the formed article. These undesirable characteristics and processing problems are overcome by unique combinations of mixture designs and processing. To achieve the desired properties in the resultant sheaths without the undesirable characteristics and processing problems of traditional hydraulically settable materials, suitable hydraulically settable binders have been developed based on a microstructural engineering approach. A detailed description of the hydraulically settable binders used to manufacture food or beverage containers is set forth in detail in co-pending application Serial No. 08/095662 entitled "Hydraulically Settable Containers for Storing, Dispensing, and Packaging Food and Beverages and Methods for their Manufacture" filed July 21, 1993, in the names of Per Just Andersen, Ph.D., and Simon K. Hodson. In addition, a detailed description of the cementitious materials used to manufacture general packaging and storing containers for all kinds of goods is set forth in detail in co-pending application Serial No.08/019, 151 , entitled "Cementitious Materials For Use in Packaging

Containers and Their Methods of Manufacture," filed February 17, 1993, in the names of Per Just Andersen, Ph.D., and Simon K. Hodson. For purposes of disclosure, these applications are incorporated herein by specific reference. Once suitable hydraulically settable materials were produced, the specific methods of more rapidly and inexpensively manufacturing sheaths disclosed and claimed herein were developed.

In short, the undesirable properties and processing problems of traditional hydraulically settable materials are overcome by the present invention, in part, by

collaborative combinations of some of the following: the disclosed hydraulically settable mixture components, mixture component ratios, mixing components morphology and chemical properties, sequence of adding the mixture components, mixing methods, utilizing microstructural engineering to properly place the mixture components resulting in uniform properties throughout the sheath, methods of forming the sheaths from the mixture, the forming equipment, curing methods, application of coatings, and laminates, as well as the structural designs. This technology is disclosed in greater detail hereinafter.

The specific properties or qualities desired for any product can be engineered by proper selection of the components and manufacturing processes as taught herein.

Hence, the marking implements within the scope of the present invention can be made to have a variety of physical characteristics and properties based on varied types of materials and concentrations utilized to create the mixtures which are subjected to either molding, casting, or extrusion. The matrix of the present invention may be designed to have a tensile strength to bulk density ratio within the range from about 1 to about 300 MPa-cm 3 /g. The tensile strength to bulk density ratio of the matrix will be more preferably within the range from about 2 to about 50 MPa-cm 3 /g and most preferably within the range from about 3 to about 20 MPa-cm 3 /g.

A. Microstructural Engineering Design.

As mentioned above, the implements of the present invention have been developed from the perspective of microstructural engineering. Microstructural engineering involves configuring the microstructure and utilizing processing steps to achieve a uniform microstructure resulting in a final product with matrix uniformity.

Microstructural engineering permits designing into the microstructure of the hydraulically settable material certain desired, predetermined properties, while at the

same time remaining cognizant of costs and other manufacturing complications. The microstructural engineering approach, instead of the traditional trial-and-error mix and test approach, has resulted in the ability to design the hydraulically settable materials with those properties of strength, weight, cost, and environmental concerns that are necessary for appropriate marking implements.

The number of materials available to engineer a specific product is enormous estimates range between fifty thousand and eighty thousand. They can be drawn from such disparately broad classes as metals, polymers, elastomers, ceramics, glasses, composites, and cements. Within a given class, there is some commonality in properties, processing, and use-patterns. Ceramics, for instance, have high modula, while polymers have low modula; metals can be shaped by casting and forging, while composites require lay-up or special molding techniques; cements have high flexural strength, while elastomers have low flexural strength.

However, this compartmentalization has its dangers; it can lead to specialization (the metallurgist who knows nothing of ceramics) and to conservative thinking ("we use steel because that is what we have always used"). It is this specialization and conservative thinking that has limited the consideration of using hydraulically settable materials for a variety of products, such as in connection with marking implements. Nevertheless, once it is realized that hydraulically settable materials have such a wide utility and can be designed and microstructurally engineered, then their applicability to a variety of possible products becomes obvious.

The design of the compositions of the present invention have been developed and narrowed, first, by primary constraints dictated by the design, and then by seeking the subset of materials which maximize the performance of the components. At all times during the process, however, it is important to realize the necessity of designing products which can be manufactured by a cost-competitive process.

Primary constraints in materials selection are imposed by characteristics of the design of a component which is critical to a successful product. With respect to a marking implement with a hydraulically settable sheath, those primary constraints include minimal weight, strength, and toughness requirements while keeping the costs comparable to or less than wood, plastic or metal counterparts. In addition, other restraints include creating hydraulically settable materials which are comparable to sheaths of traditional marking implements in weight, strength, toughness and flexibility.

As discussed above, one of the problems in the past with hydraulically settable materials such as cement has been that typical cement mixtures are poured into a form, worked, and then allowed to set and cure over a long period of time, typically days or weeks. Experts generally agree that it takes at least one month for concrete products to reach a substantial degree of their optimum strength, but they also admit that most concrete products do not reach their maximum strength for several decades. Such time periods are certainly impractical for the economic mass production of marking implements, particularly disposable marking implements.

As a result, an important feature of the present invention is that when the hydraulically settable mixture is molded, it will maintain its shape (i.e., support its own weight subject to minor forces such as gravity and movement through the processing equipment) in the green state without external support. Further, from a manufacturing perspective, in order for economical production, it is important that the formed hydraulically settable sheath rapidly (in a matter of minutes if not seconds) achieve suffi¬ cient strength so that it can be handled for further processing, even though the hydra¬ ulically settable mixture may still be in a green state and not fully hardened.

Another advantage of the microstructural engineering approach of the present invention is that it is possible to develop a composition in which cross-sections of the structural matrix are more homogeneous than have been typically achieved in the prior art. Ideally, when any two given samples of about 0.5 n 3 (wherein "n" is the smallest

cross-section of the material) of the hydraulically settable structural matrix are taken, they will have substantially similar amounts of voids, aggregates, fibers, or any other additives and properties of the matrix. Achieving matrix uniformity is based on the proper placement of mixture components, which optimizes the properties of each mixture component and permits collaboration between the components to achieve the desired properties. The net effect of this uniformity is uniform performance throughout the product. Evidence of the collaboration between the components through this method is given by a tensile strength to compressive strength ratio which is substantially greater than that of traditional hydraulically settable materials. From the following discussion, it will be appreciated how each of the component materials within the hydraulically settable mixture contributes to the primary design constraints. Specific materials and compositions are set forth in the examples to demonstrate how the maximization of the performance of each component accomplishes the combination of desired properties.

B. Marking Implements with a Marking Core and a Sheath Having a Hydraulically Settable Structural Matrix.

The term "marking implement(s)" as used in this specification and the appended claims is intended to include a marking core and a sheath formed from hydraulically settable materials. Marking implements within the scope of this invention include any pencils, cosmetic pencils, ink markers, mechanical pencils, pens, china markers, crayons and oil pastels as used for marking, writing, drawing, coloring, painting, or applying cosmetics having a hydraulically settable sheath. The marking implement with a hydraulically settable sheath and a marking core should be capable of being utilized to make a mark, write, draw, color, paint, or apply cosmetics.

The term "hydraulically settable sheath(s)" as used in this specification and the appended claims is intended to include any sheath formed from hydraulically settable

materials which is shaped and used similarly to sheaths manufactured from conventional materials to form pencils, mechanical pencils, pens, cosmetic pencils, plastic ink markers, πv.al ink markers, china markers, crayons, and oil pastels.

The term "marking core(s)" as used in this specification and the appended claims is intended to include any means for making a mark on a surface, and includes but is not limited to any graphite-clay leads; colored leads; a cartridge containing a marking fluid and having means for dispensing the marking fluid, such as the ball point pen configuration; absorbent filaments saturated with a marking fluid as used in penmarkers; absorbent filaments connected to a reservoir containing a marking fluid; a marking fluid applied in any traditional manner by pens and ink markers; a predetermined amount of marking fluid retained within the sheath and dispensed therefrom by means for dispensing the marking fluid; and solid cosmetics traditionally applied with a pencil; china markers; crayons; oil pastels; etc. The term "marking fluid(s)" as used in this specification and the appended claims is intended to include any flowable solid or liquid which can be contained and dispensed to mark a surface, and includes but is not limited to liquid inks, paste inks, pigments, and dyes.

The term "marking core(s)" as used in this specification and the appended claims is also intended to include marking cores which are removable from the sheath and marking cores which are fixedly retained within the sheath. Additionally, marking implements with a marking core which is fixedly retained within the sheath can be designed to form an adhesiveless bond between the sheath and the marking core, although the use of adhesives is also within the scope of this invention.

Marking implements with a hydraulically settable sheath can be utilized with any structure utilized with conventional marking implements within the scope this invention, these structures can be formed from conventional materials such as metal, plastic, rubber and wood or from hydraulically settable materials. Marking implements within the scope of this invention also include such structures as clips secured to the marking implement

for pocket attachments and protective caps or covers to protect an exposed end of the marking core. Also, within the scope of this invention are means for containing erasers. An example of a means for containing erasers is the familiar crimped ring utilized with conventional pencils. Additionally, an end of the hydraulically settable sheath can be configured to receive an eraser and secure the eraser without the use of such a metal ring.

Another useful means for containing erasers is provided by configurations utilized with conventional mechanical pencils.

Other structures within the scope of this invention include means for affixing the marking core in a secure manner within the sheath and means for moving the marking core within the sheath. An example of a means for affixing the marking core in a secure manner is a conical portion similar to the conical portion utilized with inexpensive ink pens to support the ink cartridge and inserted into the plastic sheath. There are numerous means for moving the marking core within the sheath which are widely used. An example of a means for moving the marking core involves the use of a spring around one end of the marking core, the spring being secured within the sheath, and a mechanism at the other end of the marking core for engaging the marking core so that the marking core extends out of the sheath or is retracted within the sheath. Another familiar means for moving the marking core within the sheath is provided by a two piece sheath which moves the marking core when the sheath pieces are rotated in opposite directions. The means utilized with conventional mechanical pencils is also useful for moving the marking core within the sheath of marking implements within the scope of this invention.

II. Hydraulically Settable Mixture Components A. Hydraulically Settable Materials. The materials used in conjunction with the methods of the present invention develop strength through the chemical reaction of water and a hydraulic binder such as hydraulic cement, calcium sulfate (or gypsum) hemihydrate, and other substances which

harden after being exposed to water. The term "hydraulically settable materials" as used in this specification and the appended claims includes any material with a structural matrix and strength properties derived from the hardening or curing of a hydraulic binder. These include cementitious materials, plasters, and other hydraulically settable materials as defined herein. The hydraulically settable binders used in the present invention are to be distinguished from other cemer-ts or binders such as water insoluble polymerizable organic cements such as glues or aJhesives.

The terms "hydraulically settable materials", "hydraulic cement materials" or "cementitious materials," as used herein, are intended to broadly define compositions and materials that contain both a hydraulically settable binder and water, regardless of the extent of hydration or curing that has taken place. Hence, it is intended that the term "hydraulically settable materials" shall include hydraulic paste or hydraulically settable mixtures in a green (i.e., unhardened) state, as well as hardened hydraulically settable or concrete products.

1. Hydraulically Settable Binders.

The terms "hydraulically settable binder" or "hydraulic binder" as used in this specification and the appended claims are intended to include any inorganic binder such as hydraulic cement, gypsum hemihydrate, or calcium oxide which develop strength properties and hardness by chemically reacting with water and, in some cases, carbon dioxide within the air and water. The terms "hydraulic cement" or "cement" as used in this specification and the appended claims are intended to include clinker and crushed, ground, milled, and processed clinker in various stages of pulverization and in various particle sizes. Examples of typical hydraulic cements known in the art include: the broad family of portland cements (including ordinary portland cement without gypsum), calcium aluminate cements (including calcium aluminate cements without set regulators),

plasters, silicate cements (including β-dicalcium silicates, tricalcium silicates, and mixtures thereof), gypsum cements, phosphate cements, high alumina cements, microfine cements, slag cements, magnesium oxychloride cements, and aggregates coated with microfine cement particles. Other useful cements include: MDF cement, DSP cement, Pyrament-type cement, and Densit-type cement.

The term "hydraulic cement" is also intended to include other cements known in the art, such as α-dicalcium silicate, which can be made hydraulic under hydrating conditions within the scope of the present invention. The basic chemical components of the hydraulic cements within the scope of the present invention usually include CaO, SiO 2 , Al 2 O 3 , Fe 2 O 3 , MgO, SO 3 , in various combinations thereof. These react together in a series of complex reactions to form insoluble calcium silicate hydrates, carbonates (from CO 2 in the air and added water), sulfates, and other salts or products of calcium and magnesium, together with hydrates thereof. The aluminum and iron constituents are thought to be incorporated into elaborate complexes within the above mentioned insoluble salts. The cured cement product is a complex matrix of insoluble hydrates and salts which are complexed and linked together much like stone, and are similarly inert.

Hydraulically settable compositions are typically formed by mixing a hydraulic binder or combinations thereof (such as hydraulic cement) and water; the resulting mixture may be referred to as a "hydraulic paste" (or "cement paste"). The hydraulic binder and water are mixed either simultaneously or subsequently, with some sort of aggregate blended to form a "hydraulically settable mixture." Mortar and concrete are examples of hydraulically settable mixtures formed by mixing hydraulic cement, water, and some sort of aggregate, such as sand or rock.

Gypsum is also a hydraulically settable binder that can be hydrated to form a hardened binding agent. One hydratable form of gypsum is calcium sulfate hemihydrate, commonly known as "gypsum hemihydrate." The hydrated form of gypsum is calcium sulfate dihydrate, commonly known as "gypsum dihydrate." Calcium sulfate

hemihydrate can also be mixed with calcium sulfate anhydride, commonly known as "gypsum anhydrite" or simply "anhydrite."

Although gypsum binders or other hydraulic binders such as calcium oxide are generally not as strong as hydraulic cement, high strength may not be as important in some applications. In terms of cost, gypsum and calcium oxide have an advantage over hydraulic cement, because they are somewhat less expensive. Moreover, in the case where the hydraulically settable material contains a relatively high percentage of weak, lighter weight aggregates (such as perlite), the aggregates will often comprise a "weak link" within the structural matrix. At some point, adding a stronger binder may be inefficient because the binder no longer contributes its higher potential strength due to a high content of weaker aggregates.

In addition, gypsum hemihydrate is known to set up or harden in a must shorter time period than traditional cements. In fact, in use with the present invention, it will harden and attain most of its ultimate strength within about thirty minutes. Hence, gypsum hemihydrate can be used alone or in combination with other hydraulically settable materials within the scope of the present invention.

Terms such as "hydrated" or "cured" hydraulically settable mixture, material, or matrix refers to a level of substantial water-catalyzed reaction which is sufficient to produce a hydraulically settable product having a substantial amount of its potential or final maximum strength. Nevertheless, hydraulically settable materials may continue to hydrate long after they have attained significant hardness and a substantial amount of their final maximum strength.

In addition to a hydraulic binder and water, the hydraulically settable mixtures according to the present invention may include aggregates, fibers, rheology-modifying agents, dispersants, air entraining agents, and other additives in order to build into the structural matrix of both the cured and uncured mixture the desired strength and other performance properties.

Terms such as "green" or "green state" are used in conjunction with hydraulically settable mixtures which have not achieved a substantial amount of their final strength, regardless of whether such strength is derived from artificial drying, curing, or other means. Hydraulically settable mixtures are said to be "green" or in a "green state" just prior and subsequent to being molded into the desired shape. The moment when a hydraulically settable mixture is no longer "green" or in a "green state" is not altogether clear, since such mixtures generally attain a substantial amount of their total strength only gradually over time. Hydraulically settable mixtures can of course show an increase in "green strength" and yet still be "green." For this reason, the discussion herein often refers to the form stability of the hydraulically settable material in the green state.

As mentioned above, preferable hydraulic binders include white cement, portland cement, microfine cement, high alumina cement, slag cement, gypsum hemihydrate, and calcium oxide, mainly because of their low cost and suitability for the manufacturing processes of the present invention. This list of cements is by no means exhaustive, nor in any way is it intended to limit the types of binders which would be useful in making the hydraulically settable sheaths within the scope of the claims appended hereto.

The present invention may include other types of cementitious compositions such as those discussed in co-pending patent application Serial No. 07/981,615, filed November 25, 1992 in the names of Hamlin M. Jennings, Ph.D., Per Just Andersen, Ph.D. and Simon K. Hodson, and entitled "Methods of Manufacture and Use for

Hydraulically Bonded Cement," which is a continuation-in-part of patent application Serial No. 07/856,257, filed March 25, 1992 in the names of Hamlin M. Jennings, Ph.D. and Simon K. Hodson, and entitled "Hydraulically Bonded Cement Compositions and Their Methods of Manufacture and Use" (now abandoned), which was a file wrapper continuation of patent application Serial No. 07/526,231 filed May 18, 1990 in the names of Hamlin M. Jennings, Ph.D and Simon K. Hodson, and entitled "Hydraulically Bonded Cement Compositions and Their Methods of Manufacture and Use" (also abandoned).

In these applications, powdered hydraulic cement is placed in a near net final position and compacted prior to the addition of water for hydration.

Additional types of hydraulic cement compositions include those wherein carbon dioxide is mixed with hydraulic cement and water. Hydraulic cement compositions made by this method are known for their ability to more rapidly achieve green strength. This type of hydraulic cement composition is discussed in copending patent application Serial No. 07/418,027 filed October 10, 1989, in the names of Hamlin M. Jennings, Ph.D. and Simon K. Hodson, and entitled "Process for Producing Improved Building Material and Products Thereof," wherein water and hydraulic cement are mixed in the presence of a carbonate source selected from the group consisting of carbon dioxide, carbon monoxide, carbonate salts, and mixtures thereof.

An important advantage of using a hydraulically settable mixture is that the resulting structural matrix is generally water insoluble (at least over the period of time during which use of the product is intended), which allows it to encapsulate water soluble materials or other materials added to the hydraulically settable mixture. Hence, an otherwise water soluble component can be incorporated into the greatly insoluble hydraulically settable matrix and impart its advantageous properties and characteristics to the final product.

2. Hydraulic Paste.

In each embodiment of the present invention, the hydraulic paste or cement paste is the constituent which eventually gives the sheath the ability to set up and develop strength properties. The term "hydraulic paste" shall refer to a hydraulic binder which has been mixed with water. More specifically, the term "cement paste" shall refer to hydraulic cement which has been mixed with water. The terms "hydraulically settable,"

"hydraulic," or "cementitious" mixture shall refer to a hydraulic cement paste to which aggregates, fibers, rheology-modifying agents, dispersants, or other materials has been

added, whether in the green state or after it has hardened and/or cured. The other ingredients added to the hydraulic paste serve the purpose of altering the properties of the unhardened, as well as the final hardened product, including, but not limited to, strength, shrinkage, flexibility, bulk density, insulating ability, color, porosity, surface finish, and texture.

Although the hydraulic binder is understood as the component which allows the hydraulically settable mixture to set up, to harden, and to achieve much of the strength properties of the material, certain hydraulic binders also aid in the development of better early cohesion and green strength. For example, hydraulic cement particles are known to undergo early gelating reactions with water even before it becomes hard; this can contribute to the internal cohesion of the mixture.

It is believed that aluminates, such as those more prevalent in portland grey cement (in the form of tricalcium aluminates) are responsible for a colloidal interaction between the cement particles during the earlier stages of hydration. This in turn causes a level of flocculation/gelation to occur between the cement particles. The gelating, colloidal, and flocculating affects of such binders has been shown to increase the moldability (i.e., plasticity) of hydraulically settable mixtures made therefrom.

As set forth more fully below, additives such as fibers and rheology-modifying agents can make substantial contributions to the hydraulically settable materials in terms of tensile, flexural, and compressive strengths. Nevertheless, even where high concentrations of fibers and/or rheology-modifying agents are included and contribute substantially to the tensile and flexural strengths of the hardened material, it has been shown that the hydraulic binder nevertheless continues to add substantial amounts of compressive strength to the final hardened material. In the case of hydraulic cement, it also substantially reduces the solubility of the hardened material in water.

The percentage of hydraulic binder within the overall mixture varies depending on the properties that are to be microstructurally engineered into the hydraulically

settable sheaths, as well as the identities of the other ingredients. However, the hydraulic binder is preferably added in an amount ranging from between about 5% to about 90% as a percentage by weight of the wet hydraulically settable mixture, preferably from about 8% to about 60%, and most preferably from about 10% to about 45%. Despite the foregoing, it will be appreciated that all concentrations and amounts are critically dependent upon the qualities and characteristics that are desired in the final product. For example, in a very thin sheath where final cured strength is needed, it may be more economical to have a very high percentage of hydraulic binder with little or no added aggregate. In such a case, it also may be desirable to include a high amount of fiber to give flexibility or toughness.

The other important constituent of hydraulic paste is water. By definition, water is an essential component of the hydraulically settable materials within the scope of the present invention. The hydration reaction between hydraulic binder and water yields reaction products which give the hydraulically settable materials the ability to set up and develop strength properties.

In most applications of the present invention, it is important that the water to cement ratio be carefully controlled in order to obtain a hydraulically settable mixture which after forming is self-supporting in the green state. Nevertheless, the amount of water to be used is dependent upon a variety of factors, including the types and amounts of hydraulic binder, aggregates, fibrous materials, rheology-modifying agents, and other materials or additives within the hydraulically settable mixture, as well as the molding or forming process to be used, the specific product to be made, and its properties.

The preferred amount of added water within any given application is primarily dependent on two key variables: (1) the amount of water which is required to react with and hydrate the binder; and (2) the amount of water required to give the hydraulically settable mixture the necessary rheological properties and workability.

In order for the green hydraulically settable mixture to have adequate workability, water must generally be included in quantities sufficient to wet each of the particular components and also to at least partially fill the interstices or voids between the particles (including e.g., binder particles, aggregates, and fibrous materials). If water soluble addi- tives are included, enough water must be added to dissolve or otherwise react with the additive. In some cases, such as where a dispersant is added, workability can be increased while using less water.

The amount of water must be carefully balanced so that the hydraulically settable mixture is sufficiently workable, while at the same time recognizing that lowering the water content increases both the green strength and the final strength of the hardened product. Of course, if less water is initially included within the mixture, less water must be removed in order to allow the product to harden.

The appropriate rheology to meet these needs can be defined in terms of yield stress. The yield stress of the hydraulically settable mixture will usually be in the range from between about 5 kPa to about 5,000 kPa, with the more preferred mixtures having a yield stress within a range from about 100 kPa to about 1,000 kPa, and the most preferred mixtures having a yield stress in the range from about 200 kPa to about 700 kPa. The desired level of yield stress can be (and may necessarily have to be) adjusted depending on the particular forming process being used to form the sheaths. In each of the forming processes, it may be desirable to initially include a relatively high water to cement ratio in light of the fact that the excess water can be removed by heating the products during or shortly after the forming process. One of the important features of the present invention as compared to the manufacture of paper composites is that the amount of water in the initial mixture is much less; hence, the yield stress is greater for the hydraulically settable mixtures. The result is that the total amount of water that must be removed from the initial mixture to obtain a self-supporting

material (i.e., a form stable material) is much less in the case of the present invention when compared to the manufacture of paper composites.

Nevertheless, one skilled in the art will understand that when more aggregates or other water absorbing additives are included, a higher water to hydraulically settable binder ratio is necessary in order to provide the same level of workability and available water to hydrate the hydraulically settable binder. This is because a greater aggregate concentration provides a greater volume of inteφarticulate interstices or voids which must be filled by the water. Porous, lightweight aggregates can also internally absorb significant amounts of water due to their high void content. Nevertheless, one skilled in the art will understand that when more aggregates or other water absorbing additives are included, a higher water to hydraulically settable binder ratio is necessary in order to provide the same level of workability and water available to hydrate the hydraulically settable binder. This is because a greater aggregate concen¬ tration provides a greater volume of interparticulate interstices or voids which must be filled by the water. Porous, lightweight aggregates can lead to high permeability and can also internally absorb significant amounts of water due to their high void content.

Both of the competing goals of sufficient workability and sufficient green strength can be accommodated by initially adding a relatively large amount of water and then driving off much of the water as steam during the forming process and through the use of drying tunnels. Additionally, these competing goals can be accommodated by reducing the interstitial volume though high pressure during the forming process such that workability is sufficient and after formation the water level is low and sufficient green strength is achieved.

It is often preferable to mix the hydraulic binder, water, and other components together in a high shear mixer such as that disclosed and claimed in U.S. Patent No.

5,061,319 entitled "Process for Producing Cement Building Material", U.S. Patent No. 4,944,595 entitled "Apparatus for Producing Cement Building Material", U.S. Patent No.

4,552,463 entitled "Method and Apparatus for Producing a Colloidal Mixture" and U.S. Patent No. 4,225,247 entitled "Mixing and Agitating Device". For puφoses of understanding such high shear energy mixers and their methods of use, the disclosures of the aforesaid U.S. Patent Nos. 5,061,319; 4,944,595; 4,552,463; and 4,225,247 are incoφorated herein by specific reference. High energy mixers within the scope of these patents are available from E. Khashoggi Industries of Santa Barbara, California, the assignee of the present invention. The use of a high shear mixer results in a more homo¬ geneous hydraulically settable mixture, which results in a product with higher strength. Based on the foregoing qualifications, typical hydraulically settable compositions within the scope of the present invention will have a water to cement ratio within the range from about 0.2 to about 10, preferably from about 0.5 to about 5, and most preferably from about 0.75 to about 3. Additionally, the total amount of unreacted water will be less than 10% by weight with respect to the dry, hardened mixture. It should be understood that the hydraulic binder has an internal drying effect on the hydraulically settable mixture because binder particles chemically react with water and reduce the amount of free water within the inteφarticulate interstices. This internal drying effect can be enhanced by including faster reacting hydraulic binders such as gypsum hemihydrate along with slower reacting hydraulic cement.

B. Fibers.

As used in the specifications and appended claims, the terms "fibers" and "fibrous materials" include both inorganic fibers and organic fibers. Fibers may be added to the hydraulically settable mixture to increase the cohesion, toughness, fracture energy, and tensile, and, on occasion, even compressive strengths of the resulting hydraulically settable material. Fibrous materials reduce the likelihood that the hydraulically settable sheath will shatter when a strong cross-sectional force is applied.

Fibers which may be incoφorated into the structural matrix are include naturally occurring fibers, such as fibers made from glass, silica, ceramic, metal, carbon. Glass fibers are preferably pretreated to be alkali resistant. Other naturally occurring fibers include extracted from hemp, plant leaves and stems, and wood fibers. Other fibers which can be incoφorated include plastics, polyaramite, and Kevlar. Biodegradable plastics, such as polylactic acid and Biopol, are environmentally benign fibers which provide significant reinforcement to the matrix.

Preferred fibers of choice include glass fibers, abaca, bagasse, wood fibers (both hard wood or soft wood, such as southern pine), and cotton. Recycled paper fibers can be used, but they are somewhat less desirable because of the fiber disruption that occurs during the original paper manufacturing process. Any equivalent fiber, however, which imparts strength and flexibility is also within the scope of the present invention. Abaca fibers are available from Isarog Inc. in the Philippines. Glass fibers, such as Cemfill® are available from Pilkington Coφ. in England. These fibers are preferably used in the present invention due to their low cost, high strength, and ready availability. Nevertheless, any equivalent fiber which imparts compressive and tensile strength, as well as toughness and flexibility (if needed), is certainly within the scope of the present invention. The only limiting criteria is that the fibers impart the desired properties without adversely reacting with the other constituents of the hydraulic material and without contaminating substances stored in the sheaths containing such fibers.

The fibers should preferably have a high length to width ratio (or "aspect ratio") because longer, narrower fibrous materials can impart more strength to the matrix without adding more bulk and mass to the mixture. Fibrous materials should have an aspect ratio of at least about 10:1, preferably at least about 900:1, and most preferably at least about 3000:1.

Preferred fibers should also have a length that is many times the diameter of the hydraulic binder particles. Fibers having at least twice the average diameter of the hydraulic binder particles will work, at least 10 times being preferred, at least 100 times being more preferred, and at least 1000 times being most preferred. The amount of fibrous material added to the hydraulically settable matrix will vary depending upon the desired properties of the final product, with strength, toughness, flexibility and cost being the principal criteria for determining the amount of fiber to be added in any mix design. In most cases, fiber will be added in an amount within the range from about 0.2% and to about 50% by volume of the hydraulically settable mixture, more preferably within the range from about 0.5% to about 30%, and most preferably within the range from about 1% to about 15%.

It will be appreciated, however, that the strength of the fiber is a very important feature in determining the amount of the fiber to be used. The stronger the tensile strength of the fiber, the less the amount that must be used to obtain the same tensile strength in the resulting product. Of course, while some fibers have a high tensile strength, other types of fibers with a lower tensile strength may be more elastic. Hence, a combination of two or more fibers may be desirable in order to obtain a resulting product that maximized multiple characteristics, such as high tensile strength and high elasticity. It should also be understood that some fibers such as southern pine and abaca have high tear and burst strengths, while others such as cotton have lower strength but greater flexibility. In the case where both flexibility and high tear and burst strength is desired, a mixture of fibers having the various properties can be added to the mixture.

Additionally, some embodiments may utilize continuous fibers or filament winding with such fibers as Kevlar, polyaramite, glass fibers, carbon fibers and cellulose fibers in the mixture. Continuous fibers are also very useful in spiral winding, which provides significant reinforcement to the matrix. Spiral winding involves the use of

fibers as an overlay wrapped onto or into the sheath in a spiraling fashion. Additional overlays of spiral winding can be wrapped onto or into the sheath. A significant increase in strength results from criss-crossing the fibers by spiral winding in opposite directions. The continuous fibers can be co-extruded in the sheath, in a manner such that the fibers overlap each other in a crisscrossing fashion.

The continuous fibers can also be utilized with the other fibers. Utilizing continuous fibers and combination of the other fibers with the continuous fibers results in a reduction in the volume percent of the fibers in the mixtures.

C. Rheology-modifying Agents.

The inclusion of a rheology-modifying agent acts to increase the plastic or cohesive nature of the hydraulically settable mixture so that it behave more like clay. The rheology-modifying agent tends to thicken the hydraulically settable mixture by increasing the yield stress of the mixture without greatly increasing the viscosity of the mixture. Raising the yield stress in relation to the viscosity makes the material more plastic-like and formable, while greatly increasing the green strength.

A variety of natural and synthetic organic rheology-modifying agents may be used which have a wide range of properties, including viscosity and solubility in water. Inasmuch as the sheaths may be expected to experience prolonged exposure to human perspiration which is water-based, it may be preferable to use a rheology-modifying agent which is less soluble in water after hardening of the hydraulically settable mixture or to use a high content of the hydraulic binder with respect to the rheology-modifying agent. On the other hand, it may be preferable to use a rheology-modifying agent which is more water soluble when it is desirable for the sheath to more quickly breakdown into environ- mentally benign components.

The various rheology-modifying agents contemplated by the present invention can be roughly organized into the following categories: polysaccharides and derivatives

thereof, proteins and derivatives thereof, and synthetic organic materials. Polysaccharide rheology-modifying agents can be further subdivided into cellulose based materials and derivatives thereof, starch based materials and derivatives thereof, and other polysacchar- ides. Suitable cellulose based rheology-modifying agents include, for example, methyl- hydroxyethylcellulose, hydroxymethylethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxyethylpropylcellulose, wood flour, etc. The entire range of possible permutations is enormous and cannot be listed here, but other cellulose materials which have the same or similar properties as these would also work well.

Suitable starch based materials include, for example, amylopectin, amylose, seagel, starch acetates, starch hydroxyethyl ethers, ionic starches, long-chain alkylstarches, dextrins, amine starches, phosphate starches, and dialdehyde starches.

Other natural polysaccharide based rheology-modifying agents include, for example, alginic acid, phycocolloids, agar, gum arabic, guar gum, locust bean gum, gum karaya, and gum tragacanth.

Suitable protein based rheology-modifying agents include, for example, Zein® (a prolamine derived from corn), collagen (derivatives extracted from animal connective tissue such as gelatin and glue), and casein (the principal protein in cow's milk). Finally, suitable synthetic organic plasticizers include, for example, polyvinyl pyrrolidone, polyethylene glycol, polyvinyl alcohol, polyvinylmethyl ether, polyacrylic acids, polyacrylic acid salts, polyvinylacrylic acids, polyvinylacrylic acid salts, polyacrylimides, and ethylene oxide polymers, synthetic clay, and latex, which is a styrene-butadine copolymer. More than one of the rheology-modify agents listed above can be utilized in a particular mixture to achieve the desired properties of plasticity or rheology-modifying effect and to optimize yield stress. Additionally, combinations of the rheology-

modifying agents optimize the rheology-modifying effect versus form stability at a minimum differential of temperature and water content.

Another potentially valuable rheology-modifying agent which does not necessarily clearly fall within the various categories mentioned above is polylactic acid. The rheology of this polymer is significantly modified by heat and can be used alone or in combination with other of the foregoing rheology-modifying agents.

A preferred rheology-modifying agent is methylhydroxyethylcellulose, examples of which are Tylose® FL 15002 and Tylose® 4000, both of which are available from

Hoechst Aktiengesellschaft of Frankfurt, Germany. Lower molecular weight rheology- modifying agents such as Tylose® 4000 can act to plasticize the mixture rather than thicken it, which helps during forming procedures.

More particularly, lower molecular weight rheology-modifying agents improve the internal flow of the hydraulically settable mixture during molding processes by lubricating the particles. This reduces the friction between the particles as well as between the mixture and the adjacent mold surfaces. Although a methylhydroxyethyl¬ cellulose rheology-modifying agent is preferred, almost any non-toxic rheology- modifying agent (including any listed above) which imparts the desired properties would be appropriate.

Another preferred rheology-modifying agent that can be used instead of, or in conjunction with, Tylose® is polyethylene glycol having a molecular weight of between

20,000 and 35,000. Polyethylene glycol works more as a lubricant and adds a smoother consistency to the mixture. For this reason, polyethylene glycol might be referred more precisely as a "plasticizer." In addition, it gives the molded hydraulically settable material a smoother surface. Finally, polyethylene glycol can create a coating around soluble components of the mixture thereby rendering the hardened product less water soluble and reducing the permeability of the hardened product.

The rheology-modifying agent within the hydraulically settable materials of the present invention will generally be included in an amount of up to about 50% by weight of the mixture.

D. Dispersants.

The term "dispersant" is used hereinafter to refer to the class of materials which can be added to reduce the viscosity and yield stress of the hydraulically settable mixture. A more detailed description of the use of dispersants may be found in the Master's thesis of Andersen, P.J., "Effects of Organic Supeφlasticizing Admixtures and their Components on Zeta Potential and Related Properties of Cement Materials" (1987).

Dispersants generally work by being adsorbed onto the surface of the hydraulic binder particles and/or into the near colloid double layer of the binder particles. This creates a negative charge around or on the surfaces of particles, causing them to repel each other. This repulsion of the particles adds "lubrication" by reducing the friction or attractive forces that would otherwise cause the particles to have greater interaction.

Hence, less water can be added initially while maintaining the workability of the hydraulically settable mixture.

Greatly reducing the viscosity and yield stress may be desirable where clay-like properties, cohesiveness, and/or form stability are less important. Adding a dispersant aids in keeping the hydraulically settable mixture workable even when very little water is added, particularly where there is a "deficiency" of water. Hence, adding a dispersant allows for an even greater deficiency of water, although the molded sheath may have somewhat less form stability if too much dispersant is used. Nevertheless, including less water initially will theoretically yield a stronger final cured sheath according to the Feret Equation.

Whether or not there is a deficiency of water is both a function of the stoichiometric amount of water required to hydrate the binder and the amount of water

needed to occupy the interstices between the particles in the hydraulically settable mixture, including the hydraulically binder particles themselves and the particles within the aggregate material and/or fibrous material. As stated above, particle packing reduces the volume of the interstices between the hydraulic binder and aggregate particles and, hence, the amount of water necessary to fully hydrate the binder and maintain the workability of the hydraulically settable mixture by filling the interstitial space.

However, due to the nature of the coating mechanism of the dispersant, the order in which the dispersant is added to the mixture is often critical. If a flocculating/gelating agent such as Tylose® is added, the dispersant must be added first and the flocculating agents second. Otherwise, the dispersant will not be able to become adsorbed on the surface of the hydraulic binder particles as the flocculating agents will be irreversibly adsorbed onto forming a protective colloid, and the surface, preventing the dispersant from being absorbed.

A preferred dispersant is sulfonated naphthalene-formaldehyde condensate, an example of which is WRDA 19, which is available from the W.R. Grace Co. in

B -nore, Maryland. Other dispersants which would work well include sulfonated mela- muic-formaldehyde condensate, lignosulfonate, and polyacrylic acid.

The amount of added dispersant will generally range up to about 5% by weight of the hydraulic binder, more preferably within the range of between about 0.25% to about 4%, and most preferably within the range of between about 0.5% to about 2%.

However, it is important not to include too much dispersant as it tends to retard the hydration reactions between, e.g., hydraulic cement and water. Adding too much dispersant can, in fact, prevent hydration, thereby destroying the binding ability of the cement paste altogether. The dispersants contemplated within the present invention have sometimes been referred to in the concrete industry as "supeφlasticizers." In order to better distinguish

dispersants from rheology-modifying agents, which often act as plasticizers, the term supeφlasticizer will not be used in this application.

E. Aggregates. Aggregates common in the concrete industry may be used in the hydraulically settable mixtures of the present invention, except that they often must be more finely ground due to the size limitations imposed by the generally thin- walled structures of the present invention. Aggregates utilized within the hydraulically settable mixtures will typically have a diameter within the range from about 0.01 microns to about 3 mm. More preferably, aggregates with a diameter within the range from about 0.1 microns to about

0.5 mm and most preferably within the range from about 0.2 microns to about 100 microns.

Aggregates may be added to increase the strength, decrease the cost by acting as a filler, decrease the weight, and/or increase the insulation ability of the resultant hydraulically settable materials. Aggregates are also useful for creating a smoother surface finish, particularly platelike aggregates. Examples of useful aggregates include perlite, vermiculite, sand (any combination of quartz, calcined bauxite and dolomite), gravel, rock, limestone, sandstone, glass beads, aerogels, xerogels, seagel, mica, clay, synthetic clay, diatomaceous earth, alumina, silica, fly ash, silica fume, tabular alumina, kaolin, micro spheres, hollow glass spheres, porous ceramic spheres, gypsum dihydrate, calcium carbonate, calcium aluminate, cork, seeds, lightweight polymers, xonotlite (a crystalline calcium silicate gel), lightweight expanded clays, unreacted cement particles, pumice, exfoliated rock and other geologic materials.

Unreacted cement particles may also be considered to be "aggregates" in the broadest sense of the term. Even discarded hydraulically settable materials, such as discarded sheaths of the present invention can be employed as aggregate fillers and strengtheners.

Both clay and gypsum are particularly important aggregate materials because of their ready availability, extreme low cost, workability, ease of formation, and because they can also provide a degree of binding and strength if added in high enough amounts. Clay is a general term used to identify all earths that form a paste with water and harden when dried. The predominant clays include silica and alumina (used for making pottery, tiles, brick, and pipes) and kaolinite. The two kaolinitic clays are anauxite, which has the chemical formula Al 2 O 3 » 3SiO 2 » 2H O, and montmorillonite, which has the chemical formula Al 2 O 3 »4SiO 2 »H 2 O. However, clays may contain a wide variety of other substances such as iron oxide, titanium oxide, calcium oxide, zirconium oxide, and pyrite.

In addition, although clays have been used for millennia and can obtain hardness even without being fired, such unfired clays are vulnerable to water degradation and have not been used to form sheaths that will be exposed to moisture. Nevertheless, unfired clay and fired clay provide a good, extremely inexpensive aggregate within the cementi- tious structural matrix.

Similarly, gypsum hemihydrate is also hydratable and forms the dihydrate of calcium sulfate in the presence of water. Thus, gypsum may exhibit the characteristics of both an aggregate and a binder depending on whether (and the concentration of) the hemihydrate or dihydrate form is added to a hydraulically settable mixture. Examples of aggregates which can add a lightweight characteristic to the cementitious mixture include perlite, vermiculite, glass beads, hollow glass spheres, calcium carbonate, synthetic materials (e.g., porous ceramic spheres, tabular alumina, etc.), cork, lightweight expanded clays, sand, gravel, rock, limestone, sandstone, pumice, and other geological materials. In addition to conventional aggregates used in the cement industry, a wide variety of other aggregates, including fillers, strengtheners, including metals and metal alloys (such as stainless steel, calcium aluminate, iron, copper, silver, and gold), balls or hollow

spherical materials (such as glass, polymeric, and metals), filings, pellets, powders (such as microsilica), and fibers (such as graphite, silica, alumina, fiberglass, polymeric, organic fibers, and such other fibers typically used to prepare various types of composites), may be combined with the hydraulic cements within the scope of the present invention. Even materials such as seeds, starches, gelatins, and agar-type materials can be incoφorated as aggregates in the present invention.

From the foregoing, it will be understood that the amount of a particular aggregate within a mixture will vary depending upon the desired performance criteria of a particular sheath. The amount can vary greatly from no added aggregate up to about 90% by weight of the hydraulically settable mixture, more preferably within the range from between about 3% to about 60%, and most preferably from between about 20% to about 50%.

Further, it will be appreciated that for any given product, certain of these aggregates may be preferable while others may not be usable. For example, certain of the aggregates may contain harmful materials that, for some uses, could leach from the hydraulically settable mixture; nevertheless, most of the preferred materials are not only nontoxic but they are also more environmentally neutral than the components in existing disposable products.

Fibrous materials are used in the present invention primarily to modify the weight characteristics of the cementitious mixture, to add form stability to the mixture, and to add strength and flexibility to the resulting cementitious matrix, although certain fibers may also impart some level of insulation to the final product. Therefore, the term "aggregates" will refer to all other filler materials, which are nonfibrous, and whose function is mainly to impart strength, rheological, textural, and insulative properties to the materials.

It is often preferable according to the present invention to include a plurality of differently sized and graded aggregates capable of more completely filling the interstices

between the aggregate and hydraulic binder particles. Optimizing the particle packing density reduces the amount of water necessary to obtain adequate workability by eliminating spaces which would otherwise be filled with interstitial water, often referred to as "capillary water." In addition, using less water increases the strength of the final hardened product (according to the Feret Equation).

In order to optimize the packing density, differently sized aggregates particle sizes ranging from as small as about 0.5μm to as large as about 2 mm may be used. (Of course, the desired puφose and thickness of the resulting product will dictate the appropriate particle sizes of the various aggregates to be used.) It is within the skill of one in the art to know generally the identity and sizes of the aggregates to be used in order to achieve the desired characteristics in the final hydraulically settable sheath.

In certain preferred embodiments of the present invention, it may be desirable to maximize the amount of the aggregates within the hydraulically settable mixture in order to maximize the properties and characteristics of the aggregates (such as qualities of strength, low density, or high insulation). The use of particle packing techniques may be employed within the hydraulically settable material in order to maximize the amount of the aggregates.

A detailed discussion of particle packing can be found in the following article co- authored by one of the inventors of the present invention: Johansen, V. & Andersen, P.J., "Particle Packing and Concrete Properties," Materials Science of Concrete II at 111 - 147,

The American Ceramic Society (1991). Further information is available in the Doctoral Dissertation of Anderson, P.J., "Control and Monitoring of Concrete Production — A Study of Particle Packing and Rheology," The Danish Academy of Technical Sciences. The advantages of such packing of the aggregates can be further understood by reference to the examples which follow in which hollow glass spheres of varying sizes are mixed in order to maximize the amount of the glass balls in the hydraulically settable mixture.

The preferred lightweight aggregates, which are also insulating, include expanded or exfoliated vermiculite, perlite, calcined diatomaceous earth, and hollow glass spheres ~ all of which tend to contain large amounts of incoφorated interstitial space. However, this list is in no way intended to be exhaustive, these aggregates being chosen because of their low cost and ready availability.

Aggregates can also be added to the mixture to impart a predetermined color or texture. The color or design can also be altered by adding metal fillings or conventional dyes. Additionally, magnetized metal could be added to magnetize the marking implement.

F. Air Voids.

It is generally desirable to minimize air voids in order to maximize strength. Minimizing air voids is especially desirable in marking implements where the marking core bonds directly to the hydraulically settable sheath to increase the strength of the bond.

Air voids within the cement matrix will be minimized in the manufacture of most marking implements but air voids can be intentionally incoφorated into the structure of a sheath when a very light weight sheath is desired. The incoφoration of air voids into the hydraulically settable mixture can be carefully calculated to impart the requisite density to the sheath, without degrading its strength to the point of nonutility. Air voids can be utilized in addition to, or in place of, lightweight aggregates in order to decrease the density of the sheaths. Generally, however, if the density or insulation ability is not an important feature of a particular product, it is desirable to minimize any air voids i n order to maximize strength and impermeability while minimizing volume. A matrix having air voids can be utilized in conjunction with a coating or a laminate to increase the strength of the sheath. The coatings and laminates which can be utilized with a matrix having air voids are discussed in greater detail below.

In certain embodiments, nonagglomerated air voids may be introduced by high shear, high speed mixing of the hydraulically settable mixture, with a foaming or stabilizing agent added to the mixture to aid in the incoφoration of air voids. The high shear, high energy mixers discussed above are particularly useful in achieving this desired goal. Suitable foaming and stabilizing agents include commonly used surfac¬ tants. One currently preferred surfactant is a polypeptide alkylene polyol, such as Mearlcrete ® Foam Liquid.

In conjunction with the surfactant, it may be necessary to stabilize the entrained material using a stabilizing agent like Mearlcel 3532®, a synthetic liquid anionic biodegradable solution. Both Mearlcrete® and Mearlcel® are available from the Mearl

Coφoration in New Jersey. Another foaming and stabilizing agent is vinsol resin. In addition, the rheology-modifying agent can act to stabilize the entrained air.

During the entrainment of air the atmosphere above the high speed mixer can be saturated with a gas such as carbon dioxide, which has been found to cause an early false setting and create form and foam stability of the hydraulically settable mixture. The early false setting and foam stability is thought to result from the reaction of CO 2 and hydroxide ions within the hydraulically settable mixture to form soluble sodium and potassium carbonate ions, which in turn can interact with the aluminate phases in the cement and accelerate the setting of the mixture. Foam stability helps maintain the dispersion, and prevents the agglomeration, of the air voids within the uncured hydraulically settable mixture. Failure to prevent the coalescence of the air voids actually decreases the insulation effect, while greatly decreasing the strength, of the cured hydraulically settable mixture. Raising the pH, increasing the concentration of soluble alkali metals such as sodium or potassium, adding a stabilizing agent such as a polysaccharide rheology-modifying agent, and carefully adjusting the concentrations of surfactant and water within the hydraulically settable mixture all help to increase the foam stability of the mixture.

Air voids may alternatively be introduced into the hydraulically settable mixture by adding an easily oxidized metal, such as aluminum, magnesium, zinc, or tin into a hydraulic mixture that is either naturally alkaline, such as a cementitious or calcium oxide containing mixture, or one that has been made alkaline, such as those containing gypsum or another lower alkaline hydraulic binder. This reaction results in the evolution of tiny hydrogen bubbles throughout the hydraulically settable mixture. Adding a base such as sodium hydroxide to, and/or heating, the hydraulically settable mixture increases the rate of hydrogen bubble generation.

During the process of forming and/or hardening the hydraulically settable mixture, it is often desirable to heat up the hydraulically settable mixture in order to increase the volume of the air void system. Heating also aids in rapidly removing significant amounts of the water from the hydraulically settable mixture, thereby increasing the green strength of the formed product.

If a gas has been incoφorated into the hydraulically settable mixture, heating the mixture to 250 C C, for example, will result (according to the ideal gas equation) in the gas increasing its volume by about 85%. When heating is appropriate, it has been found desirable for the heating to be within a range from about 100°C to about 250°C. More importantly, if properly controlled, heating will not result in the cracking of the structural matrix of the sheath or yield imperfections in the surface texture of the sheath. In other applications, where viscosity of the hydraulically settable mixture is high, such as is required in certain forming processes, it is much more difficult to obtain adequate numbers of air voids through high shear mixing. In this case, air voids may alternatively be introduced into the hydraulically settable mixture by adding an easily oxidized metal, such as aluminum, magnesium, zinc, or tin into a hydraulic mixture that is either naturally alkaline (such as a hydraulic cement or calcium oxide containing mixture) or one that has been made alkaline (such as those containing gypsum or another alkaline hydraulic binder).

This reaction results in the evolution of tiny hydrogen bubbles throughout the hydraulically settable mixture. Adding a base such as sodium hydroxide to, and/or heating (as described below), the hydraulically settable mixture increases the rate of hydrogen bubble generation. It may further be desirable to heat the mixture in order to initiate the chemical reaction and increase the rate of formation of hydrogen bubbles. It has been found that heating the formed product to temperatures in the range of from about 50 °C to about 100°C, and preferably about 75 °C to about 85 °C, effectively controls the reaction and also drives off a significant amount of the water. Again, this heating process does not result in the introduction of cracks into the matrix of the formed product. This second method of introducing air voids into the structural matrix can be used in conjunction with, or in place of, the introduction of air through high speed, high shear mixing in the case of low viscosity hydraulic mixtures used in some forming processes.

Finally, air voids may be introduced into the hydraulically settable mixture during the forming process by adding a blowing agent to the mixture, which will expand when heat is added to the mixture. Blowing agents typically consist of a low boiling point liquid and finely divided calcium carbonate (talc). The talc and blowing agent are uniformly mixed into the hydraulically settable mixture and kept under pressure while heated. The liquid blowing agent penetrates into the pores of the individual talc particles, which act as points from which the blowing agent can then be vaporized upon thermal expansion of the blowing agent as the pressure is suddenly reduced.

During the forming process, the mixture can be heated while at the same time it is compressed. While the heat would normally cause the blowing agent to vaporize, the increase in pressure prevents the agent from vaporizing, thereby temporarily creating an equilibrium. When the pressure is released after the forming or extrusion of the material, the blowing agent vaporizes, thereby expanding or "blowing" the hydraulically settable material. The hydraulically settable material eventually hardens with very finely

dispersed voids throughout the structural matrix. Water can also act as a blowing agent as long as the mixture is heated above the boiling point of water and kept under pressure of up to 50 bars.

Air voids increase the insulative properties of the hydraulically settable sheaths and also greatly decrease the bulk density and, hence, the weight of the final product.

This reduces the overall mass of the resultant product, which reduces the amount of material that is required for the manufacture of the sheaths and which reduces the amount of material that will ultimately be discarded in the case of disposable sheaths.

G. Set Accelerators.

In some cases it may be desirable to accelerate the initial set of the hydraulically settable mixture by adding to the mixture an appropriate set accelerator. These include Na 2 CO 3 , KCO 3 , KOH, NaOH, CaCl 2 , CO 2 , triethanolamine, aluminates, and the inorganic alkali salts of strong acids, such as HCl, HNO 3 , and H 2 SO 4 . In fact, any compound which increases the solubility of gypsum and Ca(OH) 2 will tend to accelerate the initial set of hydraulically settable mixtures, particularly cementitious mixtures.

The amount of set accelerator which may be added to a particular hydraulically settable mixture will depend upon the degree of set acceleration that is desired. This in turn will depend on a variety of factors, including the mix design, the time interval between the steps of mixing the components and forming or extruding the hydraulically settable mixture, the temperature of the mixture, and the identity of the set accelerator. One of ordinary skill in the art will be able to adjust the amount of added set accelerator according to the parameters of a particular manufacturing process in order to optimize the setting time of the hydraulically settable mixture. The amount of set accelerator will be included in an amount less than 2% of the hydraulically settable binder by weight.

III. Forming the Marking Implements with a Hydraulically Settable Sheath and a Marking Core.

There are many methods of forming the marking implements of the present invention from hydraulically settable mixtures. Most methods generally involve substantial mechanical mixing of the materials and water, and formation by either extrusion or by molding. Another method involves the compaction of hydraulically settable materials into a desired shape and then hydrating the mixture without substantial mechanical mixing of the materials. After the marking implements are formed through one of these methods the marking implements can be subjected to several other processing steps, such as, heating, applying a coating, and laminating the sheath.

The combination of hydraulic binders, aggregates, fibers, and (optionally) air voids results in a composition that can be formed into sheaths having roughly the same thickness as conventional sheaths made from wood or paper. In addition, the composition can be formed into suitable shapes for sheaths with both removable marking cores and marking cores which are fixedly retained within the sheath.

It is generally possible to increase the strength of the sheath while decreasing the density of the sheath by using lightweight aggregates which contain air voids. This allows for a stronger, more continuous hydraulically settable binder matrix holding the particles together. The amount of aggregates in the mixture partially determines the ability of the sheath to adhere to the marking core in a marking implement, such as a pencil, without the use of adhesives. Additionally, the amount of aggregates in the mixture partially determines the porosity of the marking implements. The porosity of pencils having a hydraulically settable sheath is designed to permit the use of traditional pencil shaφeners to shaφen the pencils with a hydraulically settable sheath. The aggregates utilized in such pencils must be small enough to avoid creating a large open pore by cutting off the surface of an aggregate in a pencil shaφener.

In order for the material to exhibit the best properties of high tensile strength and toughness, the fibers can be unidirectionally or bidirectionally aligned or stacked according to the present invention, instead of being randomly dispersed, throughout the structural matrix. It is often preferable for the fibers to be laid out in a plane that is longitudinally parallel to sheath.

Such alignment of fibers can be achieved by any number of techniques such as by jiggering, ram-pressing, pull-trusion, hot pressing, extrusion, or calendering the hydraulically settable mixture. Generally, the fibers are oriented in the direction of the flow of material during the molding or extrusion process. By controlling the flow patterns of the material during the molding or extrusion process, it is possible to build a sheath having the desired fiber orientation.

These processes also result in near zero porosity in terms of relatively large, continuous and unwanted air pockets which usually occur during normal concrete manufacture. This greatly increases the compressive and tensile strengths of the hydraulically settable material and reduces the tendency of the matrix to split or tear when the sheath is exposed to external mechanical forces. Such undesirable air voids will be minimized by evacuating the material before forming. Minimization of the undesirable air voids is particularly important when manufacturing marking implements, such as pencils, which require a secure bond between the marking core and the hydraulically settable sheath.

The undesirable discontinuities and voids in typical cementitious products should not be confused with the finely dispersed non-connected micro-pockets of air (or other gas) that may be intentionally introduced into the hydraulically settable structural matrix by the direct introduction of gas, the use of a high shear mixer, or the addition of reactive metals. Undesired voids or discontinuities are large and randomly dispersed, and offer little in terms of altering the properties, such as the bulk specific gravity of the sheath,

while at the same time greatly reducing the integrity of the structural matrix and reducing its strength characteristics.

In contrast, the intentionally introduced gas bubbles or voids are generally uniformly and finely dispersed throughout the hydraulically settable mixture. The use of voids enables the manufacture of lightweight sheaths without substantially reducing the strength of the underlying hydraulically settable structural matrix. In addition, the sheaths of the present invention can be designed to have cushioning characteristics. Sheaths with cushioning characteristics can conform to the grip of the individual utilizing the marking implement. In order for the hydraulically settable mixtures of the present invention to be effectively formed, it is important that the hydraulically settable composition be form stable in the green state; that is to say, the formed product must rapidly (preferably in three seconds or less) be able to support its own weight. Further, it must harden sufficiently that it can be quickly ejected from a mold. Otherwise, the cost of molding may make the process uneconomical. In addition, the surface of the formed article cannot be too sticky, as that would make it difficult to remove from the forming device, to handle and stack the formed articles.

By altering the quantities of cement, water, aggregates, fibers, and rheology- modifying plasticizing agents, it is possible to control the rheology, or flow property, of the hydraulic paste. For example, when ram-pressing, jiggering or injection molding is used, it may often be preferable to start with a relatively highly viscous hydraulically settable mixture which will be highly form stable in the green state; the resulting molded product will then maintain its shape after being formed, even before being dried or hardened. When extrusion, calendering, pull-trusion, or hot pressing is used, the hydraulically settable mixture is preferably less viscous and has a lower yield stress so that it will be more workable and flow easier. Because sheaths formed by these methods

will usually be heated in order to remove much of the water in order to achieve a drier, more form stable product, it will not be necessary for the hydraulically settable mixture to have as high a yield stress or initial form stability as in other molding processes.

Nevertheless, even these less viscous hydraulically settable mixtures are able to achieve rapid form stability when heated, making the manufacturing processes using them commercially acceptable and capable of mass producing the products. This is important because the longer the product remains in the mold, the higher the cost of manufacturing in most cases.

Whether a more or less viscous hydraulic paste is required, it is generally desirable to include as little water as is necessary to impart the requisite rheology for a particular molding process. One reason for minimizing the water is to control the capil¬ lary action of the water in the hydraulically settable mixture, as this may cause stickiness of the hydraulically settable mixture, which in turn can cause problems in demolding the mixture from the mold. Minimizing the amount of water eliminates the free water and reduces the chemical and mechanical adherence of the material to the mold. Hence, the capillary action and related surface tension of the water should be minimized if possible in order for there to be quick release of the hydraulically settable mixture during the molding process.

Furthermore, the resulting hydraulically settable products are stronger if less water is used. Of course, adding more water initially will require that more water be removed from the hydraulic mixture during the drying or hardening process, thereby increasing manufacturing costs.

In order to obtain a hydraulically settable mixture having the appropriate properties of workability and green strength, it is important to adjust the water content in combination with the use of a rheology-modifying agent and, optionally, a dispersant within the hydraulically settable mixture. As discussed above, there are a variety of suitable rheology-modifying agents.

The rheology-modifying agent increases the yield stress and makes the mixture more plastic so that it can be deformed and molded and then maintain its shape upon release of the molding pressure. This allows the molded product to withstand forces such as gravitational forces (that is, it can support its own weight without external support) as well as forces involved in demolding the product from the mold and subsequent handling of the sheath before it has become substantially hardened.

There are several modifications to conventional molding processes which are preferably employed in order to ease the manufacturing process. For example, it is frequently desirable to treat the mold with a releasing agent in order to prevent sticking. Suitable releasing agents include silicon oil, Teflon®, Deleron®, and UHW®.

Preferably, the mold itself will be made of stainless steel and/or coated with a material having a very slick finish, such as Teflon®, Deleron®, or chrome plating polished to about O.l RMS.

The same effect can be achieved from the use of frictional forces. By spinning the head of the molding apparatus against the interior and/or exterior surfaces of the cementitious material, any chemical and mechanical adherence (i.e., stickiness) to the mold can be overcome.

During the process of forming and/or curing the cementitious mixture, it is often desirable to heat up the cementitious mixture in order to control the air void system by allowing for proper control of the porosity and the volume in the sheath. However, this heating process also aids in making the cementitious mixture form stable in the green state (immediately after forming) by allowing the surface to gain strength quickly. Of course, this heating aids in rapidly removing significant amounts of the water from the hydraulically settable mixture. The result of these advantages is that the use of the heating process can ease the manufacturing of the sheaths.

If a gas has been incoφorated into the hydraulically settable mixture, heating that mixture to 250°C will result (according to the gas-volume equation) in the gas increasing

its volume by about 85%. When heating is appropriate, it has been found desirable for that heating to be in the range from about 100°C to about 250°C. More importantly, when properly controlled, heating will not result in the formation of cracks within the structural matrix of the sheath or imperfections in the surface texture of the sheath. In fact, the process of adding CO 2 gas to the hydraulically settable mixture during the molding process can help the molded product to quickly gain stability. From the foregoing disclosure, it will be apparent that this can be accomplished by the addition of a CO 2 gas or CO 2 generating material, such as an easily oxidized metal like zinc or aluminum, wherein the CO 2 generating process can be accelerated by the addition of a base and/or heat.

A. Mechanical Mixing of the Hydraulically Settable Materials.

The mixing system used to prepare the hydraulically settable material used for forming the sheaths of the present invention includes a mixer, a handler, and usually an extruder system. The materials are loaded into a hopper where they are metered by weight and fed into a mixer for the creation of a hydraulically settable mixture. As previously discussed, the hydraulically settable mixture is microstructurally engineered to have certain desired properties. Consequently, the metering of the bulk materials is regulated to ensure proper proportioning according to design specifications of the hydraulically settable mixture.

The mixing method is substantially the same for sheaths formed by molding and by extrusion. The composition of the mixtures will, however, vary. After the mixtures are properly blended the mixtures can be utilized to form the sheaths by any of the above methods. A method of preparing the desired mixture includes the steps of (a) mixing a powdered hydraulically settable material and water in order to form a paste or mixture and optionally utilizing a dispersant; (b) blending a fibrous material (such as cellulose

fiber or from other sources such as glass, plastic, or metal) into the paste under high shear energy mixing to form a mixture in which the fiber is well dispersed; (c) adding a rheo¬ logy-modifying agent (such as methylhydroxyethylcellulose) to the mixture such that the resultant mixture develops a more plastic-like rheology; and (d) combining one or more aggregates into the mixture under normal low shear energy mixing so as to impart the desired properties to the mixture. In alternative embodiments, other additives such as air entraining agents and reactive metals can be incoφorated into the mixture so as to obtain a mixture with desired properties. The amount of water included in the mixture has an effect on the time duration necessary for mixing the components under high shear mixing. Mixtures with low amounts of water typically require longer mixing periods than mixtures with high amounts of water.

High shear energy mixing is used for the addition of fibrous material to insure that the fibrous materials are well dispersed throughout the mixture. This results in a more uniformly blended mixture, which improves the consistency of the uncured mixture as well as increasing the strength of the final cured product.

The addition of fibrous materials by normal cement mixing techniques results in the conglomeration of the fibrous materials, leading to deformities in the resulting sheaths or articles. Standard mixers, such as drum mixers, combine the components of the desired mixture by applying low energy stirring or rotating to the components. In contrast, high shear energy mixers are comparable to heavy duty blenders and are capable of rapidly blending the mixture so as to apply high shearing forces on the particles of the hydraulically settable materials and the added fibrous materials without damaging the fiber. As a result, the fibrous materials are uniformly dispersed throughout the mixture, thereby permitting a homogenous structure for the subsequent sheaths. Fine particulate aggregates of relative high strength, such as sand, silica, or alumina, can also be blended using a high speed mixer. Plasticizers, surfactants, and stabilizers can also be added.

Nevertheless, in the case of lightweight aggregates such as perlite, pumice, or exfoliated rock, it is usually best to use a low speed mixer to avoid breaking the aggregate into a powder. In addition, the flocculation of the hydraulically settable mixture using Tylose® is usually performed under low shear mixing conditions. In one embodiment, the materials utilized in the mixture are automatically and continuously metered, mixed, de-aired and extruded by a twin auger extruder apparatus. A twin auger extruder apparatus has sections with specific puφoses such as low shear mixing, high shear mixing, vacuuming and pumping. A twin auger extruder apparatus has different flight pitches and orientations enabling the sections to accomplish their specific puφoses. It is also possible to premix some of the components in a vessel, as needed, and pump the premixed components into the twin auger extruder apparatus. The preferable twin auger extruder apparatus utilizes uniform rotational augers wherein the augers rotate in the same direction. Counter rotational twin auger extruders, wherein the auger rotate in opposite directions, accomplishes the same puφoses. A pugmil may be utilized as well for the same puφoses.

In another embodiment, a cement mixer capable of both high and low shear mixing, such as the RV-11 mixer, available from EIRICH of Germany, is used to meter and mix the materials in a batch mode. A simple mixer can typically supply mixed hydraulically settable mixtures for downstream production lines used to form the sheaths. The mixer can handle up to 13 cubic feet of material per batch and, assuming a six minute mix cycle, is capable of producing 4,000 pounds of hydraulically settable mixture per hour assuming 31 pounds per cubic foot.

In an alternative embodiment, high energy mixers described in U.S. Patent No. 5,061,319 entitled "Process for Producing Cement Building Material", U.S. Patent No. 4,944,595 entitled "Apparatus for Producing Cement Building Material", U.S. Patent No.

4,552,463 entitled "Method and Apparatus for Producing a Colloidal Mixture" and U.S. Patent No. 4,225,247 entitled "Mixing and Agitating Device" which were previously

incoφorated here in by specific reference, can be used for mixing the hydraulically settable mixture. High shear energy mixtures within the scope of these patents are available from E. KHASHOGGI INDUSTRIES in Santa Barbara, California.

The internal components of the mixer are generally carbide hard coated for extended life, thereby resisting the abrasion expected from the aggregates and cement. The mixtures, however, within the scope of the present invention result in less abrasion than many hydraulically settable mixtures due to the low pressure utilized in processing and also due in part to the excess water that provides a high degree of lubrication when any pressure is applied.

B. Methods for Manufacturing the Sheaths from Mechanically Mixed Hydraulically Settable Materials.

Several different methods of manufacturing the marking implement with sheaths formed from hydraulically settable mixtures are within the scope of the present invention.

The sheaths can be formed by utilizing various combinations of these different methods which enhances the ability to design a variety of marking implements. Manufacturing marking implements with sheaths formed from hydraulically settable materials through these methods enables the optimization of the rheology of the mixture through the forming process selected and permits handling of the formed sheath shortly after forming due to the level of form stability.

The methods of manufacturing most marking implements with hydraulically settable sheaths formed from mechanically mixed hydraulically settable materials can be categorized into two broad groups: formation by molding and formation by extrusion. An additional method involves the use of sheets formed from hydraulically settable materials which are wrapped around a marking core to form marking implements such as china markers.

Formation by molding usually requires de-airing of the mixture before the step of actually forming the mixture into a sheath. De-airing the mixture can be accomplished by extruding the mixture. Consequently, the mixture may be extruded before it is molded. Similarly, de-airing is usually a prestep to forming sheets from hydraulically settable mixtures.

1. Formation of Sheaths by Extrusion. De-airing by Extrusion and Formation of Marking Implements by Co-extruding a Marking Core and A Sheath. Extrusion of hydraulically settable mixtures has several different uses within the scope of the present invention. Extrusion provides a useful method for forming sheaths and for forming sectioned sheaths. Extrusion can also be utilized as a prestep to forming sheaths by de-airing a hydraulically settable sheath. Extrusion also permits the formation of a marking implement in single step by co-extruding a hydraulically settable sheath around a marking core.

To form a marking implement by extruding a hydraulically settable mixture into a sheath a marking core must be inserted into sheaths. Similarly, forming a marking implement from parts of a sheath or sections of a sheath requires that the parts or sections be joined around a marking core. An example of forming a marking implement with a sectioned sheath is provided by extruding slats shaped as a halved sheath with a half circle groove similar to the shape of conventional wood slats utilized to from pencils with a wood sheath. After the extruded slats are formed, the slats can be joined in pairs around a marking core. Additionally, such slats can be extruded as a set of adjacent slats and paired with another set of extruded adjacent slats to sandwich a marking core. Extrusion is particularly useful for forming marking implements with a hydraulically settable sheath and a marking core in essentially one step. To form a marking implement by extrusion in one step, the marking core and the sheath are co- extruded. Formation of marking implements by co-extrusion is conventionally utilized

in forming pencils and ink markers with plastic sheaths and lead or filament winding marking cores. The contact between the marking core and hydraulically settable sheath can result in an adhesiveless bond between the marking core and the sheath, this is particularly useful when it is desirable for the marking core to be fixedly retained within the sheath as in pencils.

(a) Extrusion Variables.

The sheaths of the marking implements shown in FIGS. 1, 2, 3, 4, 5, and 6 can be formed by extruding a hydraulically settable mixture. The marking implements shown generally at 10 in FIGS. 1, 2, 3, 4, 5, and 6 have a hydraulically settable sheath 12 and a marking core 14. The sheaths shown in FIGS. 1, 2, 3, 4, 6 can be integrally formed by extrusion. The sheaths shown in FIGS. 1, 2, 3, 4, 5, and 6 can be formed in sections or parts by extrusion. The marking core shown in FIG. 1 is a traditional pencil, in FIG.2 the marking core is a cosmetic pencil core, in FIG. 3 the marking core is a traditional pen marker filament, in FIGS. 4 and 5 the marking core is an ink cartridge, and in FIG. 6 the marking core is a pencil lead.

A conventional piston extruder can be utilized to extrude the hydraulically settable mixture through a die. The shape of articles extruded from the mixture is determined by the cross-sectional shape of the die. The mixture can be extruded into articles having a variety of shapes. The shape of the extruded article depends on whether the extrusion process is utilized as the forming step or a prestep to forming the sheath of a marking implement. When utilized to form the sheath of a marking implement, the shape of the extruded marking implement also depends on which embodiment of the marking implement is being produced. The shape of the die should be configured to minimize the specific surface area of the extruded mixture, thereby minimizing the entrapment of air. It is desirable to

minimize the entrapment of air to avoid creating a defective or non-homogenous structural matrix.

The amount of pressure applied in extruding the mixture depends on several factors. High pressure extruding can assist in the production of high strength sheaths. Typically, the lower the concentration of water, the greater the strength of the extruded article. However, as the concentration of water decreases, the workability of the mixture also decreases. In part, this is because there is no longer sufficient water to surround the particles and reduce their frictional forces. Accordingly, the mixture becomes more difficult to position and shape. When high pressures are applied to hydraulically settable mixtures with low concentration of water, the space between the particles is decreased. As these interstitial spaces decrease, the water existing within the mixture becomes more effective in encasing the particles and reducing their frictional forces. Accordingly, as pressure is applied to a mixture, the mixture becomes more fluid or workable and, thus, less water needs to be added. In turn, the decrease in the concentration of water, increases the strength of the resulting product. In application to the present invention, the higher the pressure exerted by the extruder, the lower the amount of water that needs to be added to the mixture to make it workable. Also, internal lubricants can be added to ease extrusion even when very dry, similar to the use of such lubricants in powder compaction.

Although high pressures are generally desirable, they also have a negative effect in the production of lower bulk density sheaths, lightweight sheaths. To produce a lightweight sheath, low density aggregates (such as perlite or hollow glass spheres) are typically added to the mixture. As the pressure exerted by the extruder is increased, these aggregates are crushed, thereby increasing the density of the aggregate and the density of the resulting sheath. Crushing the aggregate also decreases the insulating effect of the aggregates since they no longer contain air pockets.

In the preferred embodiment, a negative pressure is applied to the mixture before it is extruded into a sheath or an article as a prestep to forming the article into a sheath. This can be accomplished by either attaching a vacuum to the extruder or by a conventional vacuum auger which can be used to feed the mixture to the extruder. This negative pressure removes air trapped in the mixture. Failure to remove such air c .< result in the extruded article having a defective or non-homogenous structure matrix. However, in some embodiments, a uniform dispersion of small air voids in the mixture may be desirable; and, thus, the negative pressure is not needed.

Trapped air can, however, be an effective means of decreasing the density of the sheath, consequently certain mixtures may be designed to include entrained air at a certain percentage. Accordingly, a formed sheath or article having trapped air pockets positioned within its walls will be less dense and will also have a lower K-factor.

It will be understood that the extrusion of hydraulically settable binder through the die will tend to unidirectionally orient the fibrous materials of the hydraulically settable mixture so that they are substantially planer, or parallel to, the extrusion flow direction.

Continuous fibers or filament winding such as Kevlar, polyaramite, glass fibers, carbon fibers and cellulose fibers can also be coextruded with the sheath to strengthen the sheath and to decrease the amount of necessary fiber. Disks within the extruder rotating in opposite directions can be utilized for co-extruding the continuous fibers to achieve a crisscrossing pattern of fiber overlay. Controlling the rotational speed and the forward extrusion speed permits control of the angle of the fibers. Controlling the angle permits optimal elasticity and tensile strength to be achieved. Additionally, the space between the fibers can be altered to achieve varying strengths. By properly spacing the fibers and yet achieving a desired strength, the amount of fiber utilized can be limited.

(b) Perpendicular Extrusion.

Conventional peφendicular extrusion is the preferred method of producing marking implements with a hydraulically settable sheath and a marking core in a single step. This method of forming marking implements in a single step can be utilized to form the embodiment of the present invention as shown in FIGS. 1, 2, 3 and 4.

Peφendicular extrusion is accomplished by extruding the hydraulically settable mixture by either piston extrusion or auger extrusion. The marking core is introduced peφendicularly to the flow of the extruded mixture and the mixture is then extruded with the marking core centrally located within in it. The hydraulically settable mixture has been found to adhere less when a piston extruder process is used than when an auger extruder process is used.

The marking core is introduced peφendicularly to the flow of the mixture within a peφendicular extruder by a marking core feeder such as a hydraulically operated reciprocating piston or any other suitable means for receiving a marking core and for ejecting it axially. The marking core can be introduced continuously or sequentially into the extruder. Leads, cosmetic cores and filaments can be in the form of a continuous strand while ink cartridges are introduced sequentially.

The marking core is advanced out of the marking core feeder within the peφendicular extruder into a chamber containing the hydraulically settable mixture and finally through a die orifice. As the marking core exits the die orifice it is encased by the hydraulically settable mixture forming a sheath. The cross-sectional shape of the die orifice generally determines the shape of the sheath, however a sizing jig in an evacuated chamber may also be utilized to render the diameter of the sheath more uniform. When a continuous marking core is utilized it is necessary to cut the advancing continuous marking implement into desired lengths.

A bond results between the materials comprising the sheath and the marking core, which is ideal for creating pencils. Adhesives can also be utilized when necessary to

improve the strength of the bond. To manufacture marking implements with marking cores which do not adhere to the sheath, the marking core receives a coating which is insoluble in water and prevents adhesion or the marking core can be intruded after the sheath has hardened or partially hardened.

(c) Initial Hardening. Once formed, the hydraulically settable mixture is allowed to harden in the desired shape of the hydraulically settable sheath. To economically produce the inventive sheath, it must be rapidly hardened to a point where it has sufficient strength to be packaged and shipped without substantial deformation.

Hardening of the sheath may be accomplished by exposing the sheath to heated air, such as in a conventional tunnel oven. The application of the heated air drives off a portion of the water in the hydraulically settable mixture, thereby increasing the frictional forces between the particles and, thus, increasing the strength of the resulting sheath. Furthermore, the application of heated air to the sheaths increases the reaction rate of the cement, which provides early strength to the sheath through curing. Accordingly, hardening results from both an increase in the friction forces between the particles and curing of the hydraulically settable mixture.

In the preferred embodiment, the sheath is hardened only to the extent that it has sufficient strength for packaging and transport without deformation. Ideally, the hardened sheath retains a small amount of unreacted water that permits the sheath to continue to cure, and thus increase in strength, during the period of time it is transported and stored prior to use.

In yet another embodiment, the air is blown over the sheath to increase the rate at which the hydraulically settable mixture dries, thereby increasing the rate of hardening.

Also, the air can be applied through an autoclave capable of regulating the humidity, pressure, and temperature in the environment in which the sheath is cured. Increasing the humidity and temperature assists in producing more complete hydration of the hydraulically settable mixture, thereby producing a stronger sheath. In any event, the temperature in the tunnel oven should preferably not exceed

250-C in order to prevent cracking of the hydraulically settable matrix or the destruction of fibrous or plastic additives. Preferred temperatures might range between 20-C and 250-C, more preferably between 30-C and 200-C, and most preferably between 20-C and 250-C. The dwell time within the tunnel oven depends on the temperature in the tunnel, as well as the thickness of the sheath to be dried. In the case of a sheath 1 mm thick and a drying tunnel temperature of 200-C, the sheath will preferably remain within a tunnel oven for period of 45 seconds.

In summary, the following conclusions can be drawn with respect to the drying of the hydraulically settable product:

1) The higher the temperature, the shorter the drying time.

2) The higher the air speed, the shorter the drying time.

3) Once a majority of the water is removed from a sheath, exposing the sheath to temperatures above 250°C will burn the fibers in the mixture, thereby decreasing tensile strength of the fibers and sheaths.

4) The thinner the material wall of the sheath, the shorter the drying time.

5) The higher the temperature, the lower the tensile strength of the sheath.

6) Air speed and total time in the oven have less effect on the tensile strength of the sheath.

2. Formation of Marking Implements by Molding.

Molding can be utilized to form the embodiment of the present invention as shown in FIGS. 1, 2, 3, 4, 5 and 6. Manufacturing the sheaths depicted in FIGS. 1, 2, 3, 4, 5, and 6 can be accomplished by a variety of possible molding approaches within the scope of the present invention, such as: injection molding, direct molding, wet sheet molding, dry sheet molding and blow molding. The sheaths can be formed by conventional molding processes known in the art of molding, utilizing such devices as split molds, multiple parting, progressive dies and multi-cavity molds. Most molding systems, however, are utilized with thermoforming materials such as plastic while the hydraulically se- able materials of the present invention are thermosetting. Thermoforming entails shaping a heated material and allowing it to cool while thermosetting entails shaping a material and allowing it to cure. The processes and equipment utilized within the scope of this invention are modified on the basis of this distinction. Additionally, the molding processes and equipment are modified to allow chemical activation of the hydraulically settable simultaneously or following forming. Another modification is the use of less pressure in forming sheaths from hydraulically settable materials than is necessary in forming sheaths from convention materials. Less pressure is needed due to the free flowing nature of the hydraulically settable materials resulting from the high amount of water in the mixture.

Before molding, however, the hydraulically settable mixture must first be mixed and Theologically prepared into the desired consistency in preparation for the molding process. Extrusion of the hydraulically settable mixture is desirable because certain extruders can be utilized as a continuous metering, mixing and de-airing device that enhances the ability to alter many different properties of the mixture and the final product.

3. The Injection Molding and Direct Molding Processes, (a) Positioning.

After the hydraulically settable mixture has been prepared as discussed above, the next step in the injection molding and direct molding processes is positioning the hydraulically settable mixture between a set of dies for subsequent shaping of the hydra¬ ulically settable sheath. The dies comprise a male die having a desired shape and a female die having a shape substantially complementary to that of the male die. Accordingly, as the hydraulically settable mixture is pressed between the dies, the hydra¬ ulically settable mixture is formed into a sheath having the complementary shape of the dies.

Injection molding utilizes a vacuum auger to inject or feed the hydraulically settable mixture between the dies. The vacuum auger applies a pressure differential to the hydraulically settable mixture as the mixture is being transferred for positioning between the dies. This pressure differential removes air trapped in the hydraulically settable mixture. Failure to remove such air (unless the air is desired to create voids to impart lightweight characteristics) can result in the sheath having a defective or nonhomogeneous matrix.

Injection molding can also utilize an extruder positioned to move towards the molding apparatus in a piston action, extrude into the molding apparatus and then move away from the molding apparatus. This arrangement can be useful for extruding and molding at different temperatures to avoid plugging the extruder with a mixture that has hardened due to the heat of the molds. The piston action of this apparatus minimizes the heat transfer from the mold to the extruder and results in a safe manner of production.

After the mixture has been extruded, the processing of the mixture under injection molding and direct molding both involve positioning the hydraulically settable mixture between the male die and the female die. The male die is partially inserted into the female die such that a gap distance is created between the dies. The "gap distance" is

defined as the distance one die must travel with respect to the other die for mating of the dies. The dies are "mated" when they are inserted into one another so as to form a mold area between the dies. The "mold area" defines the desired shape of the sheath and is the area that the hydraulically settable mixture is pushed into when the dies are mated. When the dies are positioned so as to have a gap distance, a cavity remains between the dies. This cavity comprises the mold area between the dies, and a second area also between the dies which corresponds to the gap distance. Once the cavity is formed, the hydraulically settable mixture can be positioned into the cavity, and thus between the dies, by being injected through a hole in one of the dies or through the gap distance.

In the preferred embodiment, the female die is positioned vertically above the male die. The hydraulically settable mixture is then injected between the dies through an injection port extending through the female die. The arrangement of having the female die above the male die is preferred since once the hydraulically settable sheath is formed and the dies are separated, the force of gravity assists in insuring the hydraulically settable sheath remains on the male die. This is beneficial as it is easier to subsequently remove the sheath from the male die without deforming the sheath.

Before positioning the hydraulically settable mixture, it is preferable to minimize the gap distance between the dies so as to limit the movement of the hydraulically settable mixture during the final pressing or mating of the dies. Minimizing the movement of the mixture decreases the chance of irregularities in the final sheath as a result of differential flow in the hydraulically settable mixture. The gap distance between the male die and the female die is typically in a range of about 2 mm to about 5.0 cm, with 2 mm to about 3 cm being preferred and 2 mm to about 1 cm being most prefeπed. Another method of positioning the hydraulically settable mixture between the dies is performed while the dies are still fully separated. The method comprises forming a portion of the hydraulically settable material into a mass, the portion being sufficient to

create the sheath, then placing the mass between the dies, typically by resting the mass on the top of the male die. Subsequently, as the dies are mated, the mass is pressed between the dies.

In an alternative embodiment, a template is used to position the hydraulically settable mass. In this embodiment, the male die has a base with a circumference; and the template has a passage with a perimeter substantially complimentary to the circumference of the base of the male die.

The method comprises forming a portion of the hydraulically settable mixture into a mass having a diameter sufficiently large to span the passage of the template. The mass is then placed on the template so as to span the passage. Finally, the template is placed between the male die and the female die such that the passage is complementarity aligned with the dies. Thereby, as the dies are pressed together, the male die travels through the passage of the template in order to press the hydraulically settable mixture between the dies. The above method can further include the step of depositing the template onto the male die such that the template becomes positioned about the base of the male while the mass independently rests on the male die. Subsequently, as the dies are pressed together, the mass is again pressed between the dies. Additional benefits relating to the use of the template will be discussed hereinafter with respect to the step relating to removing the sheath from the dies.

(b) Forming and Molding.

The next step in the manufacturing process is pressing the hydraulically settable mixture between the male die and the female die in order to mold the hydraulically settable mixture into the desired shape of the hydraulically settable sheath.

The pressure exerted by the dies forms the hydraulically settable mixture into the desired configuration for the sheath. Accordingly, the pressure must be sufficient to

actually mold the hydraulically settable mixture between the dies. Furthermore, it is preferable that the pressure be sufficient to produce a sheath with a uniform and smooth finished surface.

The amount of pressure applied to the hydraulically settable mixture also affects the strength of the resulting sheath. Research has found that the strength of resultant product is increased for mixtures where the cement particles are close together. The greater the pressure used to press the cement mixture between the dies, the closer together the cement particles are pushed, thereby increasing the strength of the resulting sheath. That is to say, the less porosity that there is in the hydraulically settable mixture, the higher the strength of the resulting product.

As high pressures are applied to hydraulically settable mixtures with a low concentration of water, the space between the particles is decreased. Thus, the water existing within the mixture becomes more effective in encasing the particles and reducing their friction force. In essence, as pressure is applied to a hydraulically settable mixture, the mixture becomes more fluid or workable and, thus, less water needs to be added. In turn, the strength of the resulting product is increased. In application to the present invention, the higher the pressure exerted by the dies, the lower the amount of water that needs to be added to the mixture.

Although a high pressure is generally desirable, it also has a negative effect. To produce a lightweight hydraulically settable sheath, low density aggregates (such as perlite or hollow glass spheres) are typically added to the mixture. As the pressure exerted by the dies is increased, these aggregates may be crushed, thereby increasing the density of the aggregate and the density of the resulting sheath, while decreasing the insulative effect of the aggregates. Accordingly, the pressure applied by the dies should be optimized so as to maximize the strength, structural integrity, and low density of the hydraulically settable sheath. Within the present invention, the pressure exerted by the male die and the female

die on the hydraulically settable mixture is preferably within a range from about 50 psi to about 100,000 psi, more preferably from about 100 psi to about 20,000, and most preferably from about 150 psi to about 2000 psi. However, as discussed below, the amount of pressure will vary depending upon the temperature and time of the molding process. Additionally, sheaths with a deep draw generally require an increase in velocity to decrease the time necessary for pressing. The time must be decreased to maintain the necessary flow without drying the material prematurely.

The step of pressing further includes expelling the air from between the dies when the dies are pressed together. Failure to remove such air can result in air pockets or deformities in the structural matrix of the hydraulically settable sheath. Typically, air between the dies is expelled through the gap distance between the dies as the dies are pressed together.

In an alternative embodiment, the dies may have a plurality of vent holes extending through the dies so as to make them permeable. Accordingly, as the dies are pressed together, the air between the dies is expelled through the vent holes. The vent holes thus prevent air pockets from forming within the cavity which could deform the hydraulically settable sheath.

The vent holes also prevent the creation of a vacuum within the cavity as the dies are separated, by allowing air to return into the cavity. Such a vacuum could exert an undue force on the newly formed hydraulically settable sheath, thereby disrupting its structural integrity. Furthermore, vent holes permit the escape of excess steam created during the heating process which will be discussed later. The vent holes can exist in either or both of the dies.

(c) Heating and Form Stability.

The next step in the manufacturing process is heating the hydraulically settable mixture for a sufficient period of time to impart form stability to the hydraulically

settable sheath. The preferred method for heating the hydraulically settable mixture com¬ prises heating the male die and the female die each to a respective temperature before pressing the hydraulically settable mixture.

Increasing the temperature of the dies prior to the pressing step, serves several functions. For ease in molding the hydraulically settable mixture into a sheath without crushing the aggregate, an excess of water is added to the mixture. By applying heated dies to the mixture, a portion of the water in the hydraulically settable mixture evaporates in the form of steam, thereby decreasing the volume percent of water and, thus, increas¬ ing the ultimate strength of the sheath. Furthermore, as the water on the surface of the sheath evaporates, that portion of the hydraulically settable mixture rapidly becomes dry. The friction forces between the dry particles in the hydraulically settable mixture forms a strong thin "shell" around the sheath which provides the hydraulically settable sheath with form stability.

The application of heat to the hydraulically settable mixture also increases the rate of curing. As is discussed below, however, the dies remain pressed on the hydraulically settable mixture for such a short period of time that only a fraction of the hydraulically settable mixture reacts to become cured. A substantial amount of strength required for form stability is thus a result of the friction forces and adhesion between the dry particles, as well as internal capillary forces. As a result, the sheath is still in the green state even after achieving form stability.

The ability to rapidly impart form stability to the hydraulically settable sheath in the green state is important as it permits mass production of the sheaths. Form stability allows the sheaths to be quickly removed from the pressing apparatus so that new sheaths can be formed using the same pressing or molding equipment. Another puφose for increasing the temperature of the dies is to minimize adherence of the hydraulically settable mixture to the dies. As the steam is emitted from the hydraulically settable mixture, it creates a boundary layer between the dies and the

hydraulically settable mixture. This boundary layer provides a substantially uniform force that pushes the hydraulically settable mixture away from the die and, thus, prevents the hydraulically settable mixture from sticking to the dies.

Furthermore, experiments have determined that if the male die and female die have a variance in temperature, the hydraulically settable material will have a tendency to remain on the die with the lower temperature when the dies are separated.

Accordingly, one can select the die on which the hydraulically settable sheath is to remain on as the dies are separated, by having the desired die have a lower temperature.

The respective temperatures of the dies are important to maximizing the speed of the manufacturing process and are dependent, in part, upon the duration that the dies are in contact with hydraulically settable material. In general, it is desirable that the temperature be as high as possible — the higher the temperature, the faster the drying on the surface of the sheaths, the quicker the sheaths can be removed, and the more sheaths that can be made per unit time. The problem with higher temperatures, however, is that if the hydraulically settable mixture becomes too hot, the water throughout the hydraulically settable mixture, as opposed to just on the surface of the sheaths, turns to steam. The sudden release in pressure associated within demolding can result in the cracking, or even explosion, of the molded sheath once the dies are separated. (However, this cracking can often be solved by faster closing and opening speeds of the press.) Moreover, the faster the hydraulically settable material cures, the greater the likelihood of a deformity forming within the hydraulically settable sheath as a result of differential flow. That is, as the dies are pressed together, the hydraulically settable material flows into the desired shape. However, once the hydraulically settable mixture on the surface of a sheath starts to dry, the drier cement has different flow properties than the remaining wet hydraulically settable material. This differential in flow properties can result in deformities such as agglomerates, voids, cracks, and other irregularities in the structural matrix of the hydraulically settable sheath.

Accordingly, the interrelationship between time and temperature is that the temperature of the dies can be increased as the time that the dies are in contact with the hydraulically settable mixture is decreased. Furthermore, the temperature can be increased as the gap distance between the dies is decreased. However, there are limits to how high the temperature can go before the hydraulic mixtures become damaged.

To achieve the above desired objectives, it is preferable to heat the female and male die to a temperature within the range from between about 50 °C to about 200 °C, more preferably to between about 75 °C to about 160°C, and most preferably to between about 120°C to about 140°C. For reasons previously discussed, it is desirable to have the hydraulically settable sheath remain on the male die after separation of the dies. Accord¬ ingly, the male die preferably has a lower temperature than the female die. The temperature variance between the female die and male die should preferably be in the range from about 10°C to about 30°C.

The duration in which the heated male die and the heated female die are both in contact with the hydraulically settable material (i.e., the time that the dies are mated) is preferably within the range from about 0.05 seconds to about 30 seconds, more preferably between about 0.7 seconds to about 10 seconds, and most preferably between about 0.8 seconds to about 5 seconds.

In an alternative embodiment, the step of heating the hydraulically settable sheath further includes exposing the hydraulically settable sheath to heated air after the dies are separated, but before the sheath is removed from the die, that is, while the hydraulically settable sheath is supported on the male die. Exposure to heated air insures that the sheath is form stable before it is removed from the die.

In another alternative embodiment, the step of heating the hydraulically settable mixture can be accomplished by exposing the hydraulically settable mixture to microwaves, x-ray waves and infrared waves.

(d) Removing.

After the molded article has achieved some form stability, the newly formed hydraulically settable sheath is removed from the dies. In the preferred embodiment, when the dies are separated, the newly formed hydraulically settable sheath remains on the male die. In one embodiment, the male die and the female die are rotated as they are separated so as to prevent the hydraulically settable sheath from adhering to the dies.

Once the dies are separated, heated air can be blown over the sheath for a few seconds (as previously discussed) to further increase form stability. The hydraulically settable sheath can then be removed from the male die without deformation. In the preferred embodiment, a standard process known as airveying is used to remove the hydraulically settable sheath from the male die. Airveying is a process in which a negative pressure is applied to the sheath for sucking the sheath from off the die. The sheath then travels through a "U" shaped tube that deposits the sheath.

The airveying process is preferable due to its gentle handling of the form stable sheaths and its low operating and capital costs. Heating air which is present to dry sheaths may be used to provide the bulk air transport carrying the sheaths through the length of the tubes. The air ducts are simply ports in the male die through which air can be injected to provide a uniform force to push the sheath off the male die. Such air ducts have substantially the same size, shape, and position as the vent holes previously discussed.

In one embodiment, the air ducts and vent holes may be one and the same. The air inserted in the air ducts must be low enough not to damage the sheaths. It is envisioned in the preferred embodiment that air ducts are located on the male die to help eject the sheaths from the male die and into the tubes. In an alternative embodiment, the hydraulically settable sheath can be mechanically removed from the male die by simply picking up the sheath. Such a process, however, requires exceptional care so as not to deform the sheath. The preferred

method for mechanically removing the hydraulically settable sheath incoφorates using a template.

The template is circumferentially located at the base of the male die and is removable. The hydraulically settable sheath is loaded onto the template via the lip of the hydraulically settable sheath by either lifting the template or lowering the male die.

When the sheath is removed from the dies, the sheath is form stable due to its dried surface. However, the sheath will still have green cement betweer "+ •-. walls and, thus, it will not have reached its maximum strength. In such a condition, the hydraulically settable sheath is strongest in compression along its vertical axis. Accordingly, the benefit of using the template is that the force applied for removing the sheath is applied along the strongest axis of the sheath, thereby minimizing possible deformation to the sheath.

(e) Initial Hardening. Once initial form stability has been achieved, the hydraulically settable product can be dried and hardened by the same various techniques described above with respect to the extrusion forming process.

C. Formation of the Sheaths by Powder Compaction of the Hydraulically Settable Materials.

The matrix of the sheath can be designed to be very dense utilizing powder compaction techniques as set forth in detail in co-pending application Serial No.

07/981,615, entitled "Methods of Manufacture and Use For Hydraulically Bonded

Cement" filed November 25, 1992, in the names of Hamlin M. Jennings, Ph.D., Per Just Andersen, Ph.D., and Simon K. Hodson which is a continuation-in-part of patent application Serial No. 07/856,257, filed March 25, 1992 in the names of Hamlin M.

Jennings, Ph.D. and Simon K. Hodson, and entitled "Hydraulically Bonded Cement

Compositions and Their Methods of Manufacture and Use" (now abandoned), which was a file wrapper continuation of patent application Serial No. 07/526,231 filed May 18, 1990 in the names of Hamlin M. Jennings, Ph.D and Simon K. Hodson, and entitled "Hydraulically Bonded Cement Compositions and Their Methods of Manufacture and Use" (also abandoned). For pmposes of understanding such compaction techniques and their methods of use, the disclosure of the aforesaid applications are incoφorated by specific reference.

Powder compaction employs the manipulation and positioning of hydraulically settable binders into a desired configuration before hydrating the hydraulically settable binders with water. The hydraulically settable binder compositions are hydrated without substantial mechanical mixing of the hydraulically settable binder and water. These methods can be utilized to form the embodiment of the present invention as shown in FIGS. 1, 2, 3, 4, 5 and 6.

The benefit of positioning the powdered hydraulically settable binder into a desired configuration prior to hydration is that aggregates may be placed within the matrix of the sheath without subjecting the aggregates to hostile and damaging mixing forces usually associated with forming a hydraulically settable paste.

After the powdered hydraulic cement has been deliberately positioned into a predetermined configuration, the hydraulically settable binder is hydrated. Hydration is accomplished by diffusion of water (both gaseous and/or liquid) into the preconfigured sheath. Utilizing high pressures, the water is able to successfully penetrate the preconfigured sheath and chemically react with the hydraulically settable binder. The hydration may be in an autoclave which is a useful vessel for altering pressure and temperature to conveniently control the hydration condition. Additionally, carrier gases may be utilized which aid the process.

There are a number of different processing techniques capable of deliberately positioning the powdered hydraulically settable binder particles prior to hydration in the

shape of a sheath. The cement processing techniques suitable for such use include modified and adapted solids processing techniques, such as pressure compaction processes, slip casting, plastic forming processes, vibratory packing processes, warm pressing and pneumatic-mechanical impaction. Dry pressing is a pressure compaction process consisting of compacting powders between die faces in an enclosed cavity. Slip casting processes are particularly useful for manufacturing thin- walled sheaths. These processes involve shaping the sheath by casting a liquid suspension of the powdered hydraulically settable binder in a porous mold. Water is utilized in the suspension which is poured into a porous mold. The mold draws the liquid from the slurry and builds up a deposit of particles on the mold wall.

Drying the slurry allows the article to shrink for easier release with an appropriate water content. The remaining slurry is poured out of the mold resulting in an article having an outer configuration which reproduces the inner configuration of the mold.

Additionally, continuous isostatic pressing can be utilized to form sheaths from the hydraulically settable materials. Continuous isostatic pressing involves the compression of a mixture within a chamber toward a die and compression in a direction normal to the flow towards the die. Continuous isostatic presses can be obtained from Handle of Germany.

In a powder compaction process internal lubricants may be added to impart a plasticizing effect. After the mixture has been plasticized, it may be manipulated by conventional plastic forming processes such as extrusion, jiggering, wet pressing, and injection molding. Vibratory packing and pressing processes utilize vibrations with a suitable amplitude and can result in 100%) of theoretical packing density which is the highest conceivable packing density achievable with a given powder size distribution. Aggregates commonly utilized in the cement industry are utilized with the powdered hydraulically settable binder prior to hydration. It is preferable to include a plurality of differently sized aggregates capable of filling interstices between the

aggregates and the powdered hydraulically settable binder so that greater density can be achieved. The other mixture components may also be mixed with the powdered hydraulically settable binder prior to hydration.

The density of the resulting sheath can be decreased by utilizing lightweight aggregates with the powdered hydraulically settable binder. Additionally, the density of the resulting sheath can be decreased by compressing powdered hydraulically settable binder with a solid material, such as ice, dry ice, frozen aqueous solutions, or certain salts which will later melt, volatilize, evaporate, or dissolve leaving voids in the final sheath.

The result of these compaction techniques is the manufacture of sheaths which have high tensile strength and have a low porosity. The sheaths formed by this process may be subjected to heating, the use of coatings, and laminates, printing and assembly.

It is within the scope of this invention to utilize powder compaction in conjunction with the other methods disclosed for forming the sheaths. For example, it may be desirable to form a portion of a sheath by a powder compaction techniques and form another portion of a sheath by a molding technique. Additionally, it is within the scope of this invention to utilize powder compaction techniques to form laminates with multiple layers formed from hydraulically settable materials and with other materials.

D. Formation of the Sheaths bv Wrapping a Sheet formed from Hydraulically Settable Materials around a Marking Core.

Sheets formed from hydraulically settable materials can be utilized to from a sheath around a marking core. The sheets can be wrapped by convoluting the sheet or by spiral winding the sheet. Such sheets are utilized in forming marking implements as shown in FIGS. 7 and 8. The sheath in FIG. 7 is a series of convoluted sheets which can be removed through the use of a string and the marking core can be a variety of materials. This configuration is particularly useful with marking cores which cannot be shaφened

in a conventional pencil shaφener, such as china marker cores which are very useful for writing on substances such as glass. The sheath in FIG. 8 is a single convoluted sheet with overlapping ends and the marking core can be substances such as crayons and oil pastels. The sheets are formed utilizing techniques as set forth in detail in co-pending application Serial No. 08/101,500 entitled "Methods and Apparatus for Manufacturing Moldable Hydraulically Settable Sheets Used in Making Containers, Printed Materials, and Other Objects" filed August 3, 1993, in the names of Per Just Andersen, Ph. D., and Simon K. Hodson and in co-pending application Serial No.08/101,630 entitled "Sheets Made from Moldable Hydraulically Settable Materials and Methods for Manufacturing such Sheets" filed August 3, 1993, in the names of Per Just Andersen, Ph. D., and Simon K. Hodson. For puφoses of disclosure, these applications are incoφorated herein by specific reference.

E. Final Processing of the Sheath.

The hydraulically settable sheaths may also be subjected to several processing steps before the marking implement is finally completed. The processing steps may include coating the sheaths, applying printing or other indicia, and assembling the marking implements.

1. Coatings and Laminates.

The surface characteristics of the sheaths can be altered in a number of ways, such as coating the sheaths and creating laminates. Utilization of these techniques may increase the tensile strength of the sheath, wateφroof the sheath, and provide a smoother, glossier surface or scuff-resistant surface and help prevent fiber "fly away" . Additionally, they may also provide protection against nonneutral materials, such as saliva which can be slightly alkaline.

Some coatings can be applied to the surface of the product during the forming process, in which case the process is an "on-machine" process. In an on-machine process, the coating may be applied as a liquid, gel, or even a thin film sheet. It may be preferable to apply the coating after the hydraulic product has been formed and dried to at least a limited extent, in which case the process is an "off-machine" process.

The object of the coating process is usually to achieve a uniform film with minimum defects on the surface of the product. The selection of a particular coating process depends on a number of substrate variables, as well as coating formulation variables. The substrate variables include the strength, wettability, porosity, density, smoothness, and uniformity of the matrix of the product. The coating formulation variables include total solids content, solvent base (including water solubility and volatility), surface tension, and rheology.

The coatings may be applied to the sheaths using any coating means known in the art including blade coating, puddle coating, air-knife coating, Dahlgren coating, gravure coating, powder coating, sputtering, chemical plasma deposition, a high energy electron beam evaporation process and printing. The amount of coating can be controlled by the volume of the spray or the dwell time of the sheaths under the spray or both. Coatings may also be applied by spraying the sheath with any of the coating materials listed below or by dipping the sheath into a vat containing an appropriate coating material. Finally, coatings may be coextruded along with the sheath components in order to integrate the coating process with the extrusion process.

Appropriate organic coatings include edible oils, melamine, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyacrylates, polyamides, hydroxypropylmethyl- cellulose, polyethylene glycol, acrylics, polyurethane, polyethylene, polylactic acid, Biopol® (a polyhydroxybutyrate-hydroxyvalerate copolymer), starches, soybean protein, polyethylene, and synthetic polymers including biodegradable polymers, waxes (such as beeswax or petroleum based wax), elastomers and mixtures thereof. Biopol® is

manufactured by ICI in the United Kingdom. Appropriate inorganic coatings include sodium silicate, calcium carbonate, aluminum oxide, silicon oxide, kaolin, clay, ceramic and mixtures thereof. The inorganic coatings may also be mixed with one or more of the organic coatings set forth above. An FDA approved paint can also be utilized as a coating. Many FDA approved coating materials are also useful depending on the application involved. In some cases, it may be preferable for the coating to be elastomeric or deformable. In such cases, a pliable, possibly elastomeric, coating may be preferred.

An example of a particularly useful coating is sodium silicate which is FDA- approved and acid resistant. Many silicate based coatings provide acid resistant barriers which are also impermeable. Orthosilicates and siloxanes are particularly useful for sheath coatings due to their tendency to fill the pores of the hardened hydraulically settable matrix. Additionally, useful coatings are obtained from colloidal silica in organic polymer dispersions, films and fibers. These coating compositions provide water impermeable barriers and an increase in hardness and durability. It is generally unnecessary to protect the sheath from basic substances, but increased resistance to basic substances can be provided by an appropriate polymer or wax coating.

Biodegradable plastics provide particularly useful coatings. Biodegradable plastics, such as polylactic acid and Biopol, are insoluble in water and acidic solutions. Another useful coating material is calcium carbonate, which is acid resistant and also allows the printing of indicia on the surface of the sheaths.

It may also be desirable to spray the marking implement with CO 2 to impart added strength and to improve the surface appearance and form stability. This type of process is known for imparting strength and for improving surface appearance and form stability. The process is described in U.S. Patent No. 5,232,496 entitled "Process for

Producing Improved Building Material and Product Thereof and issued August 3, 1993, in the names of Hamlin M. Jennings, Ph.D.. and Simon K. Hodson.

A useful method of forming an aluminum oxide or silicon oxide coating within the scope of this invention involves the treating of the hydraulically settable sheath with an aqueous solution having an appropriate pH level to cause the formation of aluminum oxide or silicon oxide on the sheath due to the composition of the sheath. Laminates include multiple layers of sheets and/or coatings with at least one layer formed from hydraulically settable materials. Laminates enable the production of sheaths having an interior with a layer or coating with different properties from the layer or coating on the exterior of the sheath.

2. Printing.

Another optional step in the manufacturing process is applying print or designs to the sheath through the use of a conventional printer, such as an offset, Van Dam, laser, direct transfer contact, and thermographic printers. Additionally, methods include utilizing a relief printing, intaglio printing, stencil printing and hot stamping. Essentially any hand or mechanical means can be used. Of coarse, hydraulically settable products such as those disclosed herein are particularly well suited for such a use. In addition, decals, labels or other indicia can be attached or adhered to the sheaths using known methods in the art. Furthermore, as mentioned above, it is within the scope of the present invention to coat the sheaths with a government approved coating, most of which are currently used and well adapted for placing indicia thereon. In order to speed up the drying process, the sheaths can be passed through a second drying tunnel in order to increase the rate of drying of the ink.

3. Assembly of Marking Implements. The assembly involved in manufacturing the marking implements within the scope of the present invention varies based on the particular marking implement being

manufactured. The amount of assembly involved also varies with the method of formation and whether the sheath was integrally formed or formed in sections or portions. Sheaths formed by extrusion, molding and other forming processes can be manufactured as an integrally formed sheath or as sections or portions of a sheath. Sheaths which are integrally formed and sheaths assembled from portions or sections of sheaths can receive a marking core by insertion or intrusion to form a marking implement. Marking implements can also be formed by joining sheath sections or portions around a marking core.

Some marking implements within the scope of this invention which are manufactured with a hydraulically settable sheath may have structures formed from conventional materials. Such structures include clips for pocket attachments, protective caps and covers, means for affixing the marking core in a secure manner within the sheath, means for moving the marking core within the sheath, erasers and means for containing erasers. These structures can be formed from conventional materials such as metal, plastic, rubber and wood or from hydraulically settable materials. For example, an eraser can be attached to the hydraulically settable sheath by crimping a metal ring as utilized with conventional pencils or the sheath can be configured to receive the eraser without a metal ring by inserting an eraser into an end of the sheath and crimping the sheath around the eraser.

IV. Examples of the Preferred Embodiments.

To date, numerous tests have been performed comparing the properties of sheaths of varying composition. Below are specific examples of hydraulically settable compositions which have been created according to the present invention.

Example 1

A marking implement was formed by extruding a hydraulically settable mixture around a marking core, the mixture contained the following components:

Portland White Cement 1.00 kg

Water 1.60 kg

Glass balls 0.9052 kg

Tylose ® 4000 0.20 kg

Fiber 0.04 kg

The resulting marking implement formed from this mixture had a density of .23 g/cm 3 .

Example 2

A marking implement was formed by extruding a hydraulically settable mixture around a marking core, the mixture contained the following components:

Portland White Cement 2.00 kg Water 1.60 kg

Glass balls 0.9052 kg

Tylose ® 4000 0.20 kg

Fiber 0.08 kg

The resulting marking implement formed from this mixture had a density of .62 g/cm 3 .

Example 3

A marking implement was formed by extruding a hydraulically settable mixture around a marking core, the mixture contained the following components:

Portland White Cement 3.00 kg Water 1.60 kg

Glass balls 0.9052 kg

Tylose ® 4000 0.20 kg

Fiber 0.12 kg

The resulting marking implement formed from this mixture had a density of .85 g/cm 3 .

Example 4

A marking implement was formed by extruding a hydraulically settable mixture around a marking core, the mixture contained the following components:

Portland White Cement 4.00 kg Water 1.60 kg

Glass balls 0.9052 kg

Tylose ® 4000 0.20 kg

Fiber 0.16 kg

The resulting marking implement formed from this mixture had a density of .95 g/cm 3 , which is approximately the same density as conventional wood pencils.

Example 5 A marking implement was formed by extruding a hydraulically settable mixture around a marking core, the mixture contained the following components: Portland White Cement 1.00 kg

Water 1.60 kg

Perlite 1.98 kg

Tylose ® 4000 0.20 kg

Fiber 0.04 kg

Example 6

A marking implement was formed by extruding a hydraulically settable mixture around a marking core, the mixture contained the following components:

Portland White Cement 2.00 kg Water 1.60 kg

Perlite 1.98 kg

Tylose ® 4000 0.20 kg

Fiber 0.08 kg

Example 7

A marking implement was formed by extruding a hydraulically settable mixture around a marking core, the mixture contained the following components:

Portland White Cement 3.00 kg Water 1.60 kg

Perlite 1.98 kg

Tylose ® 4000 0.20 kg

Fiber 0.08 kg

Example 8

A marking implement was formed by extruding a hydraulically settable mixture around a marking core, the mixture contained the following components:

Portland White Cement 4.00 kg

Water 1.60 kg Perlite 1.98 kg

Tylose ® 4000 0.20 kg

Fiber 0.08 kg

V. Summary. From the foregoing, it will be appreciated that the present invention provides novel compositions and methods of manufacturing marking implements with a hydraulically settable sheath and a marking core for marking, writing, drawing, coloring, painting, or applying cosmetics in the manner that pencils, pens, mechanical pencils, ink markers, and cosmetic pencils and the like are used. The hydraulically settable sheaths formed thereby can take the place of almost any marking implement now produced from plastic, wood, paper or metal.

The present invention provides novel compositions and methods of manufacturing marking implements with a marking core and hydraulically settable sheaths produced at

relatively low cost which are tough, durable, flexible, and can be either disposable or reusable.

The present invention further provides novel compositions and processes which are much more environmentally sound in their manufacture than other sheaths, made from plastic, wood, paper or metal. The raw materials utilized as starting material in the manufacture of hydraulically settable sheaths may be obtained from the earth, decreasing the use of wood and petroleum products. Additionally, sheaths can be manufactured from recycled hydraulically settable materials, without the by products associated with other recycled materials. Further, the present invention provides novel compositions and processes for marking implements with a hydraulically settable sheath which are essentially comprised of the same compounds as the earth, and are similar to dirt and rock, and therefore pose little or no risk to the environment when discarded. Additionally, disposal of hydraulically settable sheaths does not create unsightly garbage which does not degrade, or which only very slowly degrade over time in landfills.

The present invention further provides novel hydraulically settable marking implements with a marking core and hydraulically settable sheaths which do not adhere to the forming apparatus and maintain their shape without external support during the green state and rapidly achieve sufficient strength so that the molded marking implements can be handled using ordinary methods.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects as illustrative only, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

What is claimed and desired to be secured by United States Letters Patent is: