PROCESSING OF PULP
This is a continuation-in-part of application Ser. No.
08/075,177 entitled Treatment of Cellulosic Pulp filed July 9,
1993, which is a continuation-in-part of application Ser. No. 07/981,354 entitled Treatment of Cellulosic Pulp filed November 25,
1992.
This invention relates to treating cellulosic pulp to improve its whiteness and to enhance the retention of fines in paper made from the treated pulp. More particularly, it relates to methods of treating virgin pulp and/or recycled paper and the like to reclaim the pulp and mask or remove contaminants which discolor the pulp and to methods of improving the properties and quality of paper made from pulp.
Recycling of paper products to reclaim the pulp has become a widespread effort, mainly to curb use of exhaustible raw materials. However, recycled pulp must produce paper products with acceptable characteristics such as strength and cosmetic appearance. The reclamation process should preferably avoid producing polluting effluent and, to be commercially viable, must produce reclaimed pulp at a cost less than virgin pulp.
The most difficult problems associated with recycled waste paper pulp stem from its contamination with inks, toners, adhesives and the like. Currently, waste paper pulp is subjected to de- inking methods or treatments such as bleaching and/or whiteners. Typical current processes for treating recycled pulp as well as virgin pulp are disclosed by Rydhol , "Pulping Processes," Interscience Publishers, 1965, and the TAPPI Monograph No. 27, "The Bleaching of Pulp," Rapson Editor, The Technical Association of Pulp and Paper Industry, 1963. However, the abundance and variety of inks, toners and other contaminants found in recycled waste paper products presents a variable complexity not readily treated by conventional bleaching and/or whitening methods. Accordingly, the pulp is usually exposed to extended treatments which degrade and/or destroy fiber and reduce fiber quality. Such processes also generally produce effluents which require post treatment and reduce pulp yields. Furthermore, many inks and the like remain dispersed in the pulp and are only partially masked by whiteners. In accordance with the present invention, pulp slurry (either virgin pulp or recycled pulp) is treated with a treatment agent which comprises compounds or mixtures formed when water soluble trivalent metal salts and water soluble monovalent, divalent and/or tetravalent metal salts are precipitated by adding a source of alkalinity to the acid salt solution which may, of necessity, contain hydrochloric acid in order to dissolve the tetravalent mineral salts. The treatment agent masks contaminants in the pulp to obtain paper products with improved brightness, strength and
other properties. As best understood, the treatment agent comprises a compound or mixture of compounds of the representative formula: wherein M is a monovalent metal ion; is a number from 0 to 0.4; T is a trivalent metal ion; y is a number from 0 to 1; z is a number greater than 0 and equal to or less than 3; A is an anion other than hydroxyl; and a = — 3 * m - 2Y -z— and is equal to or greater than 0 and
(valence of A) less than 3. The composition defined in formula (1) above is believed to represent the basic composition of the treatment agent of the invention disclosed herein. However, as will be described hereinbelow, variations of the basic composition which include other elements may be used to accentuate certain preferred characteristics.
In the preferred practice of the invention, T is aluminum and A is chlorine. However, it will be readily recognized that other trivalent metals such as iron, gallium or chromium may be used. Aluminum is most preferred when improved whiteness is desired in the pulp. Likewise, other monovalent or polyvalent anions such as other halides, sulfates, nitrates, chlorates, lactates and acetates can be used. For purposes of the following disclosure, T will be discussed and described herein as aluminum and A will be described as chloride. Furthermore, whenever aluminum chloride is referred to herein, it is assumed to be in the hexahydrate form.
The term "pulp" is used herein to mean either virgin pulp or recycled pulp. Virgin pulp is obtained by changing wood chips or other particulate matter to fibrous form. Recycled pulp is generally obtained from paper products using chemicals and various
process steps such as agitation, flotation and bleaching. Recycled pulp can be obtained from office papers, newspapers, magazines, etc., including paper with thermally cured print or adhesives and the like. Many different types of inks are commonly used in various paper applications, all of which require specific methods of ink removal in recycling pulp. Some inks, such as flexographic solvent inks, offset printing inks, laser toner inks and ultraviolet light cured inks, are difficult to remove from recycled pulp. There are also a number of methods of measuring pulp brightness. It usually is a measure of reflectivity expressed as a percentage of some scale. A standard method (known as "GE brightness") is expressed as a percentage of maximum GE brightness as determined by TAPPI Standard Method TPD-103. It is known that aluminum hydroxide and aluminum hydroxide salt gels, colloids and small particulate solids have unique properties and that their associated properties are sensitive to slight changes in pH. In accordance with the present invention, it is believed that an alumina hydrate in a colloidal state is the active agent. It is known that crystallized hydrates of alumina, α-alumina trihydrate, β-trihydrate and new β-trihydrate contain up to about 0.4% alkali metal atoms in their crystalline lattices. However, under special conditions hydrates containing no alkali metals can be precipitated. All these hydrates chemisorb various anions very effectively. Particle sizes range from about 0.3-50μ and are amphoteric. When prepared by adding alkali to an acid aluminum salt solution, a precipitate of aluminum hydroxide (usually containing some fraction of anions other than hydroxide) results which is primarily amorphous in form and which may exist as a colloidal sol or gel. In this colloidal state the positively charged particles remain in relatively even distribution. As in many gels, a slight change in pH can cause rapid precipitation. As a result, precipitated particles usually are only slightly larger
than colloidal particles, have a low crystalline order and are hydrophilic.
To produce the preferred embodiment of the treatment agent of the present invention, a solution of 8.5% aluminum chloride is mixed in equal volumes with a 5% solution of sodium hydroxide in a T-mixer. The resulting mass exhibits three physical states:
(1) a clear liquid with
(2) a crystalline mass which decomposes within hours of its formation and reverts to liquid form and (3) a colloid body.
If the entire preparation is washed and filtered, a white crystalline form is derived which is not conducive to treatment of pulp. However, the unwashed preparation exhibits dramatic activity in the treatment of pulp in concentrations as low as 0.1% to dry weight of fiber.
It is believed that in the colloidal state the positively charged particles are attracted to surfaces with a negative zeta potential and form attachments to certain surfaces which contain groups with which the aluminum hydroxide compounds can interact by ion exchange or complexation. In particular, aluminum ions are known to form complexes with ether groups (found in abundance in ethoxylate compounds) . Additionally, aluminum hydroxide compounds are known to ion exchange with various anions while ethoxylate groups are known to ion exchange with cations. Therefore, it is believed that attachment to surfaces treated with ethoxylated surfactants is possible through an ion exchange mechanism. Since aluminum hydroxide particles are relatively opaque, white and minute, deposition of many particles is believed to cause an increase in reflectance of the treated surface. The interaction of these particles with a cellulosic substrate results not only in changes in physical properties of the outer layers of the cellulose, but can bond two cellulosic surfaces together. In a wood pulp system, this can result in attachment of cellulosic fines
to larger cellulosic fibers and, in some cases, produce a greater measured average fiber length. Longer fibers and more fiber-to- fiber attachments change strength properties of paper subsequently made from the pulp. This may be the reason for observed improvements in pulp and paper products made from pulp treated with the aluminum hydroxide compounds described herein.
The following are exemplary methods for making the treatment agent described and were used to make various compositions for test purposes: PREPARATION 1
An aqueous solution of 8.5% aluminum chloride hexahydrate was staged to a one liter graduated cylinder. An aqueous solution of 5.0% sodium hydroxide was staged to a second one liter graduated cylinder and a feed tube leading to a peristaltic pump having a flow rate of 135 ml/hr and suction tubes inserted into each cylinder. The outflow from each tube was conducted via a T- connector to a product capture vessel. The product appeared to form at the T-connector with no perceptible exothermic reaction. As the product collected, it formed a stalagmite approximately two to four centimeters in height with a body of clear liquid forming around the solid body. After pumping all the solutions from the feed cylinders, the formed product was divided into two approximately equal portions. One portion was filtered through P8 filter paper laid on a frit and vacuum drawn. The unfiltered portion was designated "Preparation 1". The filtered product was of solid form with clay-like consistency and designated "Preparation la".
PREPARATION 2 A 2% solution of sodium hydroxide was substituted for the 5.0% solution used in PREPARATION 1 above. A solid body product formed which liquified almost immediately. The product was filtered through P8 filter paper laid on a frit dampened with distilled water and vacuum drawn. A slight residue of solid, crystalline
matter was observed. The filtered solution was designated "Preparation 2". After four hours, a suspension of crystalline matter was observed in the filtered solution. This solution was designated "Preparation 2a". PREPARATION 3
A 15% solution of sodium hydroxide was substituted for the 5% solution of PREPARATION 1 above. The product formed was a clear liquid with no visible particulate matter. When the solution was filtered through vacuum drawn P8 filter paper, no solids were captured on the filter. The filtered solution was designated "Preparation 3". At the end of four hours, there were no visible solids in the filtered solution.
A series of pulp treatments was conducted using the above- described preparations. In each case pulp slurry of 5.0% consistency was formed by adding 100 grams dry weight waste paper to two liters of tap water in a Maelstrom disintegrator which was then activated for ten minutes and the slurry removed. One liter of tap water was then added to reduce the consistency of the pulp slurry. One hundred fifty milliliters of slurry prepared as described above was placed in each of six (6) 250 ml beakers to establish a 2.5 gram dry weight of fiber equivalent. At this time the slurry exhibited a GE brightness of 54 when made into a hand sheet. One beaker was designated as a control for reference purposes. To each of the five remaining beakers was added 0.00025 wt. fraction NEODOL 91-6. Hydrogen peroxide equivalent to 0.5% by weight dry fiber was introduced and the slurry heated and agitated until the temperature attained 115°F. Sodium carbonate equivalent to 0.5% by weight of dry fiber was added. The slurry in one of the beakers was treated with a portion of "Preparation 1" as described above equivalent to 1.0% of dry weight fiber. The slurry was agitated and maintained at temperature for two minutes, then washed for fifteen seconds on a 50 mesh sieve
(Tyler 48) with tap water. The GE brightness was determined to be 86.
The slurry in each of the remaining four beakers was treated in the same manner with "Preparation la", "Preparation 2", "Preparation 2a" and "Preparation 3", respectively. In each case, little or no improvement in GE brightness was observed.
It should be noted that raising the sodium hydroxide concentration somewhat above 5.0% for mixing in equal volumes with an 8.5% aluminum chloride hexahydrate solution results in a complex mixture which has less activity for pulp treatment. Furthermore, by varying concentrations of the aluminum chloride or the caustic solution (which are mixed in equal volumes) , the resulting complex mixture of aluminum hydroxide compounds may be a true solution, a colloid sol, a colloid gel or a crystalline solid. Filtration of colloidal suspensions to recover solid material produces various quantities of material which have only minor activity when exposed to pulp fiber. In the case of the crystalline solid, the mass is of chalk-like consistency and has little noticeable effect on pulp fiber. It has been found that in treating pulp slurry produced from hydropulping waste papers, pretreatment of the fiber may be necessary to establish a suitable condition for attachment of the aluminum hydroxide compounds to the pulp fiber. First, a slurry is made by determining the dry weight of fiber after which water is introduced to achieve a consistency of about 4-9% fiber-to-water. A surfactant with ethoxylated or carboxylate and ethoxylate groups is then introduced in concentrations from about one part surfactant to 100,000 parts pulp slurry by weight to about one part surfactant to 10,000 parts pulp slurry. Then, should a nonionic surfactant be the choice, hydrogen peroxide (about 0.5% to dry weight of fiber) is introduced. This solution is heated to a temperature of about 115°F and sodium carbonate added to equal 0.5% to dry weight of fiber. For best results, the treatment agent described in formula
(1) above should be added immediately. The reaction which then occurs imparts brightness to the pulp.
If the slurry is of optimal consistency, treatment optimization occurs within minutes. At this stage, the slurry may be transported to a sieve or screen and a cursory wash conducted. From pulp having initial brightness readings in the range of GE 52 to 54, the treatment has consistently produced brightness levels of above GE 87. Additionally, the resultant fiber mass is of even distribution, without the presence of entangled clumps. The role of each additive to the slurry is somewhat specific and is believed to interact in an integrated fashion. The ethoxylated surfactant is thought to be deposited onto the fiber and contaminant surfaces by a "salting out" mechanism which results from the addition of certain salts known to reduce the solubility of polyethylene glycol compounds. Heating the system to a higher temperature is known to reduce the solubility of polyethylene glycol compounds. Sodium carbonate, known to be one of the salting put agents, is chosen as an example because of its effectiveness and availability, and surfactant is deposited onto the fiber or contaminant surface by addition of sodium carbonate. Addition of hydrogen peroxide to the wood pulp slurry enhances the affinity of the cellulosic surface for the aluminum hydroxide compounds as well as contributes to the precipitation of ethoxylated surfactants. Prior addition of hydrogen peroxide produces additional receptor sites within the complex of the ethoxylate groups of the nonionic surfactant. Apparently the increased affinity of the surface for aluminum hydroxide compounds results from a complexation of hydrogen peroxide with the ethoxylated surface, giving a more negative zeta potential to the surface. It has been noted that little coating of the fibers occurs if the treatment agent is introduced to the pulp slurry before salting out of the ethoxylates occurs since apparently the treatment agent particles and the fibers are then coated with ethoxylate and the
two similarly-coated and similarly-charged surfaces do not attract each other. Bonding of the treatment agent particles and the surface of the surfactant-coated fiber apparently occurs through a hydrogen bonding or an ion exchange mechanism. Since ethylene oxide polymers are known to be weak cation exchangers and the multivalent inorganic hydroxide is an anion exchanger, an ion exchange mechanism between the two surfaces could account for the tenacious attachment which occurs. Furthermore, the ethoxylate ether groups are election-rich and could form hydrogen bonds with the h droxyl groups on the multivalent inorganic hydroxide particles. Simultaneously, an agglomeration of fines occurs through interaction of the small ethoxylate-coated fines and the small multivalent inorganic hydroxide particles. This agglomeration (plus occasional bonding of an agglomerate with a larger fiber) results in retention of most of the fines with the pulp in a papermaking process. The coating process thus defined causes an opaque white layer to form on the fibers which masks pigments or dyes and thereby produces a paper product having marked visual whiteness when the metal components of the hydroxide are non-coloring, for example, magnesium and aluminum.
The treatment agent of the invention may be formed in situ or may be formed as a treatment agent to be added to the pulp slurry during processing. When the treatment agent is prepared in advance, it is preferably added to a slurry of pulp from a hydropulping process (preferably after washing) after addition of an ethoxylated surfactant (preferably nonionic) and an oxidant such as hydrogen peroxide. The surfactant is then precipitated by adding a salting out agent and/or by application of thermal energy. Compounds known to induce salting out of ethoxylates include (but are not limited to) Na 3 P0 4 , K 2 S0 4 , Na 2 Si0 3 , Na 2 C0 3 , K 2 C0 3 , MgS0 4 and the like. When the pulp containing the ethoxylated surfactant and one of these salts is heated, the salting out phenomenon causes the ethoxylated surfactant to be deposited on the surface of the fiber
as well as any ink, toner or adhesive which is present in the pulp. Hydrogen peroxide (or some other oxidizing agent) may be added to the pulp slurry before or after precipitation of the ethoxylated surfactant in order to increase the tendency of the hydroxide treatment agent to deposit on the precipitated ethoxylate surface.
When heated to a temperature between about 80° and 212°F, the surfactant precipitates onto the fiber and other particles. The precipitated surfactant coats the fibers in the slurry and provides them with a stronger negative potential which attracts the positive multivalent inorganic hydroxide. At this point there is substantially no surfactant in the solution since all of the surfactant is deposited on the fiber by the salting out process prior to introduction of the treatment agent. Variations of the treatment agent or formula (1) above may include mixed metal hydroxides such as shown in United States
Letters Patent No. 4,790,954 to Burba, et al. These hydroxides characteristically from monodispersed layers and are known to be useful as gelling agents. To incorporate the mixed metal hydroxides, formula (1) above may be modified to:
M m D d T(0H) 2 A a (2) wherein D is a divalent metal ion and d is a number determined by appropriate stoichiometry.
For example, the advantages of the present invention can be achieved by treating an aqueous pulp slurry with an effective amount of a multivalent inorganic hydroxide of the formula:
M m D d T0 y (0H) 2 A a (3) wherein M is a monovalent metal ion; m is a number from 0 to 1; D is a divalent metal ion; d is a number from greater than 0 to 4; T is a trivalent metal ion; y is a number from 0 to 1;
z is a number from 0 to 11.4; A is an anion other than hydroxyl; and a is a number from greater than 0 to 1. The divalent metal D can be magnesium, calcium, iron, nickel, copper, manganese, barium, strontium or zinc. Most preferably, M is magnesium, calcium and/or barium when improved whiteness is desired. The trivalent metal T can be aluminum, iron, gallium or chromium. Most preferably, T is aluminum when improved whiteness is desired. The anion A can be monovalent or polyvalent and includes halides, sulfates, nitrates, chlorates, lactates, acetates and the like.
The multivalent inorganic hydroxides may be used in various states of hydration and may be composed of either pure multivalent inorganic hydroxide compounds or physical mixtures of multivalent inorganic hydroxide compounds with themselves or other hydrous oxides of the M and T metals such as hydrous alumina, hydrous magnesia, hydrous zinc oxide and the like. The multivalent inorganic hydroxides may comprise up to about five percent (5%) of the slurry without detrimentally affecting the paper product. Compounds which have been found particularly useful in practicing the invention are, for example, MgAl(OH) 47 Cl 03 , MgAl(0H) 4 Cl, BaAl(0H) 5 , MgAl(0H) 5 , CaAl(OH)4.7Cl 0-3 , CaAl(0H) 5 , CaFe(OH) 4 (S0 3 ) Q . r BaAl(OH) 47 Cl 3 and the like.
The following examples illustrate certain embodiments but the invention is not limited to the particular embodiments described.
EXAMPLE 1 To five hundred pounds of dry pulp prepared from waste paper was added a solution of 0.5% hydrogen peroxide prepared from 1875 gallons of water to form a slurry. One-half pound of NEODOL 91-6 (nonionic surfactant) was added to the slurry and the mixture heated to a temperature of about 115°-140°F. Twenty-five pounds of sodium carbonate was added with stirring. Then ten pounds of MgAl(0H) 47 C1 03 was added and the mixture hydropulped for about ten
minutes. The resulting mixture was filtered, washed with water and dried. The pulp had a GE brightness of 87 and could be processed into paper.
EXAMPLE 2 A series of runs were performed in which the initial pulp comprised old newsprint, mixed office wastes, old magazines and colored and printed ledgers. A dry charge of each of the above paper materials was prepared. The charge was sampled for moisture content and adjusted to an equivalent of 480 g. The charge was then introduced into a 12.5 1 Dynapulper which contained 12 1 of 0.5% hydrogen peroxide and 1.2 g of NEODOL 91-6 (nonionic surfactant) . The unit was activated and the dry charge was defibrillated for about five minutes. After the pulping action, 2.4 g of sodium carbonate was added and the mixture agitated. The mass was then heated to a temperature of 115°F. 4.8 g of MgAl(OH) 47 C1 03 was then added and the mixture allowed to react for two minutes. The resulting mixture was filtered and washed with water.
Each of the resulting pulps was processed into paper which had a GE brightness of at least 87 with a dirt count (T21.3 om-89) of 3.4 mm 2 /m 2 .
EXAMPLE 3 Fifty grams dry weight of pulp from paper containing adhesive received from a hydropulping process was added to an agitated one liter solution of 0.5% hydrogen peroxide and 0.01 grams of NEODOL 91-6. The mixture was heated to 115°F and 0.25 grams of NaC0 3 added. One-half gram of MgAl(0H) 5 was added and allowed to react for two minutes.
The mixture was filtered and washed with tap water. The resulting pulp was processed into paper which had a GE brightness of 87.
In lieu of MgAl 47 Cl 07 an equal amount of CaAl(OH) 47 C1 03 or ZnAl(0H) 47 (SO 4 ) 015 may be used.
EXAMPLE A Five grams of recycled pulp was placed in each of two containers with 30 ml of water and stirred. A charge of 0.05 grams MgAl(OH) 47 Cl 0>3 was added to one of the containers. The pulp from each container was processed into paper. The paper formed from the pulp without MgAl(OH) 47 C1 03 had a GE brightness of about 78. Paper from the treated pulp had a GE brightness of about 80.
In one embodiment of the invention a pulp slurry is made with pulp and about 0.2 to 1% (preferably about 0.5%) of dry weight pulp hydrogen peroxide. An ethoxylated surfactant is added to provide a surfactant concentration in the slurry of about 0.0005% to about 0.01%. The slurry is then heated to a temperature between about 80° and 212°F, preferably about 115° to 140°F. About 0.1 to 1% (preferably about 0.5%) by weight of dry pulp of a salting out compound such as an alkali metal carbonate (preferably sodium or potassium carbonate) is added. Then about 0.1% to about 2.0% by weight of dry pulp of a multivalent inorganic hydroxide is added. An excess amount is not detrimental to the quality of the paper product. Since the reactions take place within a short period of time (normally less than two minutes) , the pulp can be further processed immediately. That is, the resultant pulp can be filtered, washed with water and further processed into paper. A brightened pulp is obtained when the multivalent inorganic hydroxide does not contain color-forming metal ions. The trivalent hydroxide salts described in formula (1) are easier to prepare and use than mixed metal hydroxide compounds. In most cases, processes using the simpler trivalent hydroxides are more efficient, more reliable and less expensive than processes employing mixed metal hydroxides and do not require formation of the monodispersed layers characteristic of mixed metal hydroxide compositions.
When the treatment agent is made prior to treatment of the pulp, the preferred process for improving whiteness and bonding of
fines to fibers of recycled pulp involves the sequence steps comprising:
A. treating a pulp slurry with an ethoxylated surfactant, especially a nonionic surfactant, in an amount of about 0.3% to about 0.5% by weight of pulp;
B. optionally treating the slurry with dilute hydrogen peroxide or other oxidant;
C. treating the resultant slurry with a precipitating agent such as an alkali metal carbonate in an amount to precipitate out all the surfactant;
D. adding a treatment agent as described hereinabove; and
E. heating the slurry to a temperature of about 80° to 212°F, preferably about 80° to 140°F. (The slurry can be heated initially or after the addition of the different components. ) Suitable nonionic surfactants include:
(a) aliphatic alcohol ethoxylates containing from eight to twenty-two carbon atoms in either straight chain or branched configuration with four to fifteen mols of ethylene oxide per mol of alcohol; (b) alkyl phenol ethylene oxide condensates wherein the alkyl group contains eight to twelve carbon atoms and the condensate contains about four to eighteen mols of ethylene oxide per mol of alkyl phenol represented by the formula (C n H 2rγt1 ) (C 6 H 6 ) (OCH 2 CH 2 ) χ OH where n equals at least 8 and (OCH 2 CH 2 ) equals fifty-eight to seventy-eight percent of the total weight of the compound;
(c) nonionics which are partial esters of fatty acids with sugar alcohols;
(d) those containing an average of one to three ester groups and up to fifty mols of ethylene oxide per molecule; (e) derivatives of ethylene oxide, propylene oxide, butylene oxide comprising block polymers having molecular weights within the range of about 1,000 to about 5,000;
(f) linear primary alcohol ethoxylates;
(g) ethoxylated fatty acids; (h) ethoxylated silicon-based surfactants; (i) ethoxylated sulfates of alcohols; and (j) mixtures thereof. Typical nonionic surfactants falling within these types which are commercially available include the following detergents:
NEODOL 91-6 (a C p -C^ linear primary alcohol ethoxylate with approximately six mols of ethylene oxide per mol of alcohol;
IGEPAL CO-630 (nonylphenol condensed with 9-10 mols of ethylene oxide) ;
IGEPAL CO-710 (nonylphenol condensed with 10-11 mols of ethylene oxide) ;
IGEPAL CO-730 (nonylphenol condensed with 15 mols of ethylene oxide) ; PLURONIC L62 (25 to 30 mols of polyoxypropylene condensed with 8.5 to 10.2 mols of ethylene oxide);
PLURONIC F68 (25 to 30 mols of polyoxypropylene condensed with 33 to 41 mols of ethylene oxide) ;
PLURONIC P85 (36 to 43 mols of polyoxypropylene condensed with 48 to 52 mols of ethylene oxide) ;
TWEEN 21 (polyoxyethylene (4) sorbitan onolaurate) ; TWEEN 40 (polyoxyethylene (20) sorbitan monopal itate) ; and TERGITOL XH (butoxy monoether of mixed (ethylene-propylene) polyalkylene glycol having a cloud point of 90°-100°C and an average molecular weight of 3,300).
Preferred nonionics are the water-soluble condensation products of aliphatic alcohols containing from eight to twenty-two carbon atoms (in either straight chain or branched configuration) with from four to fifteen mols of ethylene oxide per mol of alcohol. Particularly preferred are the condensation products of alcohols having an alkyl group containing from about nine to fifteen carbon atoms with from about five to twelve mols of ethylene oxide per mol of alcohol.
Suitable anionic surfactants include carboxylated alcohols sold by Alcolec, Inc. under the trademark AKYPO and sold by
Finetex, Inc. under the trademark GEMTEX; and alcohols sold by
Vista Chemical Co. under the trademark ALFONIC and by Ethyl Corp. under the trademark ETHONIC.
Suitable amphoteric surfactants include alkylether hydroxy sultaines. Other suitable surfactants are disclosed in McCutcheon's Emulsifiers & Detergents, North America, 1989, which is herein incorporated by reference. As noted above, crystallized hydrates of alumina contain up to about 0.4% alkali metal atoms in their crystalline lattices. Accordingly, the presence of a finite amount of alkali metal as set forth above conform to observed results and thus supports the theoretical discussions. However, they do not eliminate the possibility that the hydroxide which precipitates onto the pulp is in the form of ALOOH.
It will be recognized that although the invention is described hereinabove with particular reference to trivalent metal oxychlorides and mixed metal hydroxides of trivalent, divalent and monovalent metals, mixed hydroxides of tetravalent, trivalent, divalent and monovalent metals and mixed hydroxides of tetravalent and trivalent metals may be substituted for the specific compositions described in detail. The invention disclosed is therefore not limited to the monodispersed layered mixed metal hydroxides disclosed by Burba, et al. Furthermore, various other metal ions, such as tetravalent metal ions, may impart particularly unique properties to the final product. Because of its inherent properties of reflectivity and opacity in its fully oxidized state, titanium is the most likely tetravalent metal to be used in the compositions of the invention.
Where a tetravalent ion is included in the formula, it will more likely require an oxide form and the generic composition for such variations may be expressed by the representative formula:
M ra D d TS s O y (OH) 2 A a (4) wherein M is an alkali metal ion; is a number from 0 to 3; D is a divalent metal ion; d is a number from 0 to 4;
T is a trivalent metal ion; S is a tetravalent metal ion; s is a number from 0 to 4; y is a number from 0 to 9; z is a number from 0 to 28;
A is an anion other than hydroxyl; and a is a number from 0 to 1. This may be done in the following manner:
Titanium tetrachloride makes a stable aqueous solution if greater than about 17% HC1 is present. Once this solution is made, aluminum chloride and, if desired, other metal chlorides may also be dissolved into the solution in the proper relative amounts. This solution is then mixed using a T-mixer with a volume of alkali metal hydroxide necessary to give a pH of about 3.5 to 7, depending upon the mixture of metals. The resulting reagent mixture is used for the treatment of pulp.
A quaternary amine salt of an EO/PO block copolymer, the quaternary amine salt of an EO/PO block copolymer, the ethoxylated dialkyl quaternary amine or aliphatic quaternary amine salt can be mixed with a slurry of a finely divided white inorganic material such as (but not limited to) titanium dioxide, aluminum oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide, calcium carbonate, clay or talc and that slurry subsequently mixed with one of the salts known to salt out polyethylene glycol. When the solution is heated, the inorganic particles will become coated with a uniform layer of quaternary amine. Cellulosic pulp is then slurried in water and treated with ethylene glycol or a surfactant. The pulp is then mixed with a salt known to salt out polyethylene
glycol and the pulp mixture is heated. Dilute hydrogen peroxide is added to the pulp mixture to impart a more negative zeta potential to the surface to enhance the salting out effect. The two heated slurries are mixed. The cationic slurry is deposited as a uniform coating on the fiber surface with effect similar to that described above. Other cationic groups such as tertiary amine salts, amine oxides or betaines could be substituted for the quaternary amine salts mentioned.
In an alternative method of practicing the invention, the treatment agent may be formed in situ in the hydropulper or other pulp slurrying device. In execution of this alternative, the pulp fiber is pretreated as before. The slurry is made by determining the dry weight of fiber and then introducing water to achieve a consistency of about 4-9% fiber-to-water. A surfactant with ethoxylate or carboxyl and ethoxylate groups is added in concentrations from about one part surfactant to 100,000 parts pulp slurry by weight to about one part surfactant to 10,000 parts pulp slurry. Hydrogen peroxide (about 0.5% to dry weight of fiber) is then introduced and the slurry heated to about 115°F. An aqueous solution of sodium hydroxide is then added to the dispersed paper pulp in the running hydropulper until a concentration of about 0.31% to dry weight of fiber is achieved. An aqueous solution of aluminum chloride is then slowly added to the running hydropulper until a concentration of about 0.34% is achieved. At this time, sodium carbonate is added to the running hydropulper until a concentration of about 0.5% to dry weight of fiber is achieved. The aluminum chloride solution precipitates as an alumina hydrate on and in the pulp fiber and other constituents of the pulp, including ink and toner particles. Addition of sodium carbonate after adding aluminum chloride results in pulp which produces paper with a lower speck count than if the sodium carbonate is added prior to the aluminum chloride. Although the reason for this is not fully understood, it is believed that when aluminum chloride is
added, it immediately begins precipitation on and in the fiber but not on the pigment or toner. This precipitate is intimately associated with the cellulose in the fiber which contains many other groups with which the alumina hydrate molecules have affinity. At this point, the surfactant has not completely coated the pulp surfaces. When the sodium carbonate is added, however, the surfactant is forced to salt out. The surfaces then present are of two types: (1) fiber coated with alumina hydrate and (2) uncoated pigment or toner. The fiber coated with alumina hydrate is very polar. The pigment or toner is very nonpolar. The surface thus has a strong differential tendency to deposit on the toner or pigment. The resulting ethoxylated surface formed on the toner or pigment has more affinity for the remaining aluminum hydroxide in solution or dispersion than the fibers already coated with alumina hydrate. Thus the pigment or toner gets coated preferentially.
Although the present invention has been described with some particularity, it is to be understood that the present disclosure has been made by way of example and that various changes and modifications may be resorted to without departing from the spirit and scope of the invention as defined by the appended claims.
