BACKGROUND OF INVENTION [0002] Composite board products used in construction applications such as particleboard, medium density fiberboard, oriented strand board and the like have been produced for many years and their method of manufacture is well known in the industry.

[0003] The primary component of these composite materials is a natural fibrous material. In forming the board product the fibrous material typically is combined with a minor amount of resin and a waxy composition, formed into sheets and subjected to pressure and heat.

[0004] In selecting wax compositions for use in construction board applications the focus has theretofore been placed on oil content and stream grade or viscosity range, i. e. , the SUS viscosity at 100°F. This viscosity typically is given as a"Neutral"member, e. g., 100N, 300N etc. In any event, previous studies, using both emulsions and neat applications of waxes have shown trends indicating improved board properties with lighter stream grade waxes, e. g. , below grade 30 (550N) and for waxes with lower oil content. For example"The Effect of Wax Type and Content on Waferboard Properties", Hsu, et al, International Particleboard/Composite Materials Symposium, April 3-5, 1990, pp. 85-93 discusses waferboard swelling in response to 0 to 45% wax content and 0 to 30 wt% oil content; and USP 6,183, 849 discloses preparing composite boards using waxes with oil content greater than 30 wt%.

[0005] Experience has shown that use of low wax stream grades, i. e. , grades below 30 (550N) in producing composite boards, board quality and performance typically is fine; however, when using high wax stream grade, i. e. , above about 30 (550N) problems with board quality often are encountered. This is particularly troublesome since it often is desirable to employ higher grade stream waxes for safety and environmental reasons. For example, in the production of oriented strand boards heavy steam grade waxes are desirable to minimize volatility in presses that typically operate at over 400°F (205°C).

[0006] Consequently, there is a need to be able to predict the suitability of a wax composition for composite board manufacture, and to be able to adjust the wax composition, if needed, to be suitable for such board manufacture. Also, there is a need to be able to adjust the volatility of wax compositions to be used in construction board applications to meet emission requirements. Additionally, the ability to blend numerous product streams into a suitable wax composition offers suppliers flexibility in meeting market needs. The present invention is directed to these and other needs.

SUMMARY OF INVENTION [0007] Very simply, the present invention is based on the discovery that the n-paraffin content of a wax composition is the key compositional parameter for waxes used in construction board and this n-paraffin content should be at least 21 wt% for the wax composition to be suitable. Thus the suitability of a wax for construction board applications can be determined based on its n-paraffin content, and blends of waxes and oils and oils can be composed to meet the required n-paraffin content.

[0008] These, and other features, will be described in greater detail hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS [0009] Figures 1 and 2 are graphs illustrating features of the invention.

DETAILED DESCRIPTION OF INVENTION [0010] Composite board products used in the construction industry such as particle board, medium density fiberboard, wafer board, oriented strand board and the like are typical manufactured from natural fibrous materials, resin and a wax composition.

[0011] The natural fibrous materials typically used include wood chips, wafers, saw dust, wood fibers, cotton and other plant fibers, straw, bamboo cellulose and the like. The fibrous material generally comprises about 90 to 98 wt% of the final board product.

[0012] Resins used in the production of manufactured board materials are well known to those skilled in the art of making construction board products and the choice will depend upon the particular compositional and economic needs of the manufacturer. Non-limiting examples of such resins are those thermosetting resins produced by the polycondensation of formaldehyde with other suitable compounds. Illustration of these are phenol formaldehyde, urea formaldehyde, and malamine formaldehyde resins.

[0013] The wax composition used in composite board manufacture comprises one or more natural, synthetic or petroleum waxes and a hydrocarbonaceous oil.

[0014] Synthetic waxes include waxes made by Fisher-Tropsch process from synthesis gas. Other synthetic waxes include polyethylene wax, ethylene copolymer wax, carbo waxes.

[0015] Petroleum waxes include waxes recovered by, e. g. , the solvent dewaxing of waxy hydrocarbon oil streams as part of the petroleum refinery process including slack waxes and also includes hydrocracked waxes. Other petroleum waxes include waxy petroleum stocks such as waxy distillates, raffinates, petrolatum, microcrystalline waxes, etc.

[0016] In the present invention wax compositions containing at least 21 wt% for example from 21 wt% to about 90 wt% and preferably between 21 wt% to 30 wt% based on the weight of the total wax composition.

[0017] Analyses of typical waxes used in construction board applications have shown a wide range of n-paraffin content that decreases the average molecular weight of the wax increases. Typical n-paraffin content ranges for various stream guides is given in Table 1.

TABLE 1 Grade (SUS) % n-paraffins 100-300 45-65 300-500 35-50 500-650 10-35 650-850 5-20 850+ 0-10 [0018] Bright stock slack wax and microcrystalline wax typically do not contain significant quantities of normal paraffins.

[0019] Thus, the suitability of wax compositions in grades higher than about grade 30 for construction board applications is determined by analysis of the n-paraffin content of the wax with those having a n-paraffin content of at least 21 wt% being deemed suitable.

[0020] Wax compositions that meet the suitability requirement may be blended with the same or different viscosity grade wax composition and still meet suitable board performance so long as the minimum 21 wt% n-paraffin content is met. Thus the volatility can be adjusted as necessary, and even the economics may be influenced. A scheme of blending parameters and their impact on the wax composition is given in Table 2.

TABLE 2 Component Typical Impact On Composition Initial non-blended slack wax Sets initial n-paraffin content, oil content and volatility r S Foots oil or soft wax Increases oil content Fully refined wax Increases n-paraffin content, lowers oil content High n-paraffin wax'Increases in n-paraffin content, lowers oil content DWO2-lube basestock Lowers n-paraffin content, raises oil content s, loyer_vscosity/gxade, _. .... a. ... Tnereases, volatlt s,.". _..,... . _. _.

Foots oil or soft wax Increases oil content Fully refined wax Increases n-paraffin content, lowers oil content High n-paraffin wax Increases in n-paraffin content, lowers oil content DWO2-lube basestock Lowers n-paraffin content, raises oil content ; volatils Foots oil or soft wax Increases oil content Fully refined wax Increases n-paraffin content, lowers oil content High n-paraffin wax Increases in n-paraffin content, lowers oil content DWO2-lube basestock Lowers n-paraffin content, raises oil content (D E. g. , non-isomerized Fischer-Tropsch wax (D DWO = dewaxed oil [0021] To further illustrate the foregoing consider that a 600N slack wax with over 20 wt% oil may well have a n-paraffin content below 21 wt%. A fully refined 250-300N petroleum wax containing 60-80 wt% n-paraffins or a non- isomerized Fischer-Tropsch wax that typically contains greater than 90 wt% n- paraffins can be blended with the slack wax to bring the n-paraffin content of the wax composition to at least 21 wt% and preferably in the range of 21 wt% to 30 wt%.

[0022] Alternatively a dewaxed oil, such as a basestock in the 100-850N range are blended with sufficient petroleum wax or non-isomerized Fischer- Tropsch wax to provide a wax composition containing at least 21 wt% n- paraffins.

EXAMPLES [0023] A series of wax blends were prepared with varying n-paraffins and oil content. These blends were then evaluated for use in construction board manufacture by reference to the water absorption and internal bond strength.

The example wax compositions and the test results are given in Table 3. TABLE 3 ornai ; Blend 1T :, e. nal ° nô mina ax- T' hie kness :'. w Tric une sus _ ointe Watt ruz , rnal B S. A S 600 1 zend : a= B land. n= - : : W ; Oil.. oïl, air f D a fion 5, tell abus, ex w 1 F o tion a. bso tion oritl= ame s ;. es cri tio N rade : _ Cori : p Ga de : Co nten. t tem. t ho r us. ours. s 4 houT wax/DW O_ p_01-600. : :. 60 0 89 : x 10 9. 9 30. 2 25. 5 71. 3 0. 277 F='T wax/DWO XD=02 600. = 600 83-15. 8 24. 8 20. 3 58. 5 0. 324 F=T wax lDVO XD=Q3 600'60U v.'78, =20.'= 7. 6 21. 7 19. 4 52. 9 0. 332 F-T wa/DWQ XD-_04-=600 = 00 7 25--6. 7 17. 7 14. 9 39. 5 0. 326 F-T wax =/DVO. XD-OS'f : 600-=° 00. 674 30 : 6. 3 18 14. 4 39. 2 0. 3 Et wa t 1DWO : m 06 L 60 Q L ß. _ 5. 5 15. 7 11. 7 33. 2 0. 291 F-TwaxDWO XD-07 4. 8 14. 4 11. 2 31. 9 0. 313 600N slack waR. XD-Q8. 60p.. 9 57 2 = 6. 1 19. 2 14 44. 5 0. 256 250 300N sl ac k 0 1 300-t < < 16. 4 12. 1 38. 6 0. 293 wax/DWO >"ß z)-10 < 0 7 : 660 5. 7 17. 1 12. 2 41. 8 0. 285 waxlDWO 609N, slak waX +' : . 11 y600. 600 23< 21 v 6 17. 4 13. 1 42. 9 0. 282 wax/DWO. . /.'7 : f. : ;' '''- ' ; : x F-T wax% DWO ; 600Nynlly refiried. -12 °600 600 60 » 21 : 5. 3 16. 8 13 37. 7 0. 213 waxIDWO O 7. 2 19. 3 15. 5 43. 5 0. 275 -wax/DWO 3qON. sl'acl, c,'w'-a'x. 60ON slack wax 4. 9 15. 4 11. 7 33. 5 0. 308 600N slack waX XD=15 600 9 : 57. 21 :,. : 4. 9 15. 1 11. 7 33. 7 0. 349 CE) F-T wax = Fischer-Tropsch wax 2) DWO = dewaxed oil (D This slack wax was used neat rather than in an emulsion g) Target maximum swell for this study was 20%. Commercial results are likely to be different because of different conditions such as press strengths. (s) The trends for water absorption and internal bond strength values follow the thickness swell results.

[0024] The effect of n-paraffin content on thickness swell and water absorption is graphically illustrated in Figure 1 and the effect of oil content on thickness swell is shown graphically in Figure 2.

[0025] The graphs and data illustrate that a n-paraffin level of at least 21 wt% is needed for good board performance and that oil content has no effect unless it is high enough to reduce the n-paraffin content below 21 wt%.