Use of a binder in a paper-making process

Abstract: An improved binder for use in paper-making contains three ingredients, a cationic starch having a degree of substitution of at least 0.01, a high molecular weight anionic polymer having a molecular weight of at least 500,000 and a degree of anionic substitution of at least 0.01, and a dispersed silica having a particle size ranging from between 1 - 50 nanometers.

Description: The present invention relates to a binder for use in paper-making processes and for products made thereby and, more particularly, to the use of a specific binder to achieve better binding between cellulosic fibers in paper-making processes using cellulosic fiber slurries, particularly when those slurries also contain various inorganic fillers and/or pigment materials having an electrically charged surface character. The binders used according to this invention allows the papermaker to operate at a higher speed because the paper sheet formed is more easily dewatered. In addition, improved retention of added mineral materials used in paper-making processes, such as various clays, TiO 2 and other pigments, is achieved by the binders used according to the invention. Because improved retention and improved dewatering are observed using the improved binders of this invention, it is also possible to improve clarification of the white water resulting from the paper-making processes using the improved binders of this invention. It is an object of this invention to provide to the papermaker an improved binder which can be used to achieve both improved dewatering and improved retention of mineral fillers and pigments used in the paper-making process, and to achieve a paper having improved strength characteristics. Prior Practices U.S. - A- 3,253,978, Bodendorf et al, teaches a method of forming a water-laid sheet containing colloidal silica and a cationic starch. The method combines colloidal silica and a cationic agent, preferably a cationic starch in the head box of a paper-making machine which is manufacturing a strictly inorganic fibrous sheet. The type of sheet being manufactured is, therefor, referred to as an inorganic sheet and utilizes inorganic fibers, such as glass fibers, quartz fibers, ceramic fibers, mineral wool, glass flakes, quartz flakes, mica flakes and combinations thereof. In column 4, lines 53 et seq., Bodendorf et al. disclose that organic fibers may also be incorporated in the sheet but that the presence of substantial percentages of these organic materials in these kinds of sheet products are considered deleterious for intended applications of these inorganic sheets. U.S. -A- 4,385,961, Svendling et al., teaches a paper-making process in which a cellulosic pulp is formed, and in which a binder is used, which binder comprises a colloidal silicic acid and a cationic starch. The manner of addition is taught to involve the initial addition of a portion of a colloidal silicic acid to the paper-making stock followed subsequently by the addition of cationic starch, which then is followed, finally. by the addition of the remainder of the colloidal silicic acid prior to the formation of the paper sheet. U.S. -A- 4,388,150, Sunden et al, continues to teach the use of a binder comprising colloidal silicic acid and cationic starch for improving paper and the retention of various paper stock components. EP-A-41 056 discloses a method of modifying the cellulosic pulp prior to sheet formation by adding a bicomponent binder comprising colloidal silicic acid and a cationic starch which has a degree of substitution of not less than 0.01 wherein the weight ratio of cationic starch/silicic acid is between 1:1 and 25:1. Addition of an anionic polymer and especially of an acrylamide copolymer is neither anticipated nor suggested. In the paper manufacturing process of WO-A-82 01 020 a get coated filler/fiber structure is processed as a paper making furnish wherein the coating was prepared as an amphoteric mucus-like composition by reacting a cationic starch having a low degree of substitution of 0.02 to 0.10 with a minor amount of an anionic polymer having a high degree of substitution of 0.5 to 1.0 such as high charge density carboxymethyl cellulose. This mucus coat is transformed to a less hydrated and a mechanically resistant get coating by adding a colloidal solution of polymer microparticles consisting of polysilicic acid or polyaluminumoxi compound. Fillers and fibers are not uniformly distributed within the get and same applies to the polymer microparticles which are only surface-bonded. Such a mucus coat structure does not anticipate a binder composition of the present invention. The Invention It was found that the above object of this invention can be achieved by using in a paper-making process, in which a paper-making stock containing at least 50 % of cellulosic pulp is formed into a sheet and then dried, of a specific binder comprising a ternary combination of a specific cationic starch, a specific anionic high molecular weight polymer and a specific dispersed silica wherein the weight ratios of anionic polymer to silica and of cationic starch to silica are within specific ranges and wherein the binder is formed in situ by a specific sequential addition of the components of the improved binder to the paper-making stock. Subject-matter of the present invention is the use in a paper-making process, in which a paper-making stock containing at least 50 % of cellulosic pulp is formed into a sheet and then dried, of a binder comprising a cationic starch having a degree of substitution of at least 0.01 and silica particles, and being characterized in that it comprises a ternary combination of a cationic starch having a degree of cationic substitution ranging between 0.01 and 0.20, an anionic high molecular weight polymer having a molecular weight of at least 1 000 000 and a degree of anionic substitution of at least 0.01, and a dispersed silica having a particle size ranging from 1 to 50 nm, wherein the weight ratio of anionic polymer to silica ranges between 20:1 and 1:10 and the cationic starch to silica weight ratio is between 100:1 and 1:1, and wherein the binder is formed in situ by a sequential addition to the paper-making stock of the cationic starch, then the anionic polymer and then the dispersed silica or by a sequential addition to the papermaking stock of the cationic starch, then followed by an admixture of the silica sol and the anionic polymer, each addition occuring after each prior addition has been thoroughly admixed. The binder used according to this invention can be added to the paper-making stock in an amount of 0.1 to 15 weight percent. The use of the binder described above is preferably accomplished by adding to the beater or mixer a cationic starch having a cationic substitution ranging between 0.01 and 0.15, which cationic starch is preferably derived from a modified potato starch, which potato starch normally contains some small amount of covalently bound phosphorous containing functional groups and is of a highly branched amylopecton type of starch. However, it must be pointed out that other cationically modified starches, for example, cationic starch derived from corn starch, cationic starches derived from waxy maize, and the like, may be used in the practice of the invention and in the formulation of the improved binder, as long as the degree of cationic substitution on the starch ranges from 0.01 to 0.20, preferably between 0.02 to 0.15, and most preferably between 0.025 to 0.10. To the cationic starch admixed with cellulosic fibers, preferably in the headbox of a paper-making machine, is added a quantity of the admixture of a high molecular weight anionic polymer and a dispersed silica, which admixture contains a ratio of anionic polymer to dispersed silica ranging between about 20:1 to about 1:10 on a weight-to-weight basis. This binder may be formed by initially admixing the cationic starch with the cellulosic fiber slurry used in the paper-making process. After the cationic starch has been fully admixed, an electroneutralizing amount of the admixture of anionic polymer and dispersed silica may be then added to the paper-making stock containing the cationic starch. An electroneutralizing amount of the anionic combination means that sufficient amounts of the combination of both the anionic polymer and the dispersed silica should be added to the paper-making stock containing the cationic starch in such a way as to approach within 75 to 125 percent of electroneutrality. Depending on the character of the cellulosic fiber, the type, amount and character of inorganic filler/pigment, as well as the character of the cationic starch, this electroneutralizing amount of combined anionic ingredients can be achieved by adding anywhere from about 75 to 125 percent of an electroneutralizing amount of the combination of anionic polymer and silica sol to the cationically modified starch/paper stock admixture. On a weight basis, this will vary considerably depending upon the ratio of anionic polymer to silica sols, as well as depending upon the type of anionic polymer chosen and the type of silica dispersion chosen. It will also vary according to the character, type, amount and the like of cationic starch used, as well as the types of fiber, fillers, and the like, used to form to paper stock. Sunden, et al, U.S. -A- 4,388,150, teaches the use of a weight ratio of cationic starch to silica ranging between 1:1 and 25:1. Svendling et al, U.S. -A- 4,385,961, teaches a weight ratio of cationic starch to silica ranging between 1:1 to 25:1 in a binder use which is improved by first adding colloidal silicic acid and then a cationic starch, forming an agglomerate, and then adding a remainder of colloidal silicic acid to the paper-making stock prior to the formation of the paper sheet. This complicated procedure normally requires that the first portion of colloidal silicic acid comprises between 20-90 percent of the total colloidal silicic acid added to the paper-making stock. A preferred binder used according to the present invention is a combination of cationic starch, preferably a cationically modified potato starch having a degree of cationic substitution ranging between 0.02 to 0.15, wherein said potato starch also contains naturally, not synthetically, bound phosphorous containing functionality, with an electroneutralizing amount of the combination of a high molecular weight anionic polymer and a dispersed silica wherein the dispersed silica has a particle size ranging between 1.0 to 50 nanometers. The combination of anionic polymers to dispersed silica, preferably a colloidal silicic acid or a colloidal silica sol ranges within a weight ratio of between 20:1 to 1:10, and, most preferably, ranges between a weight ratio of anionic polymer to silica of from 15:1 to 1:1. The Anionic Polymers The anionic polymers used are high molecular weight water soluble polymers having a molecular weight of at least 1,000,000 and most preferably having a molecular weight ranging between 5,000,000 - 25,000,000. These anionic polymers are preferably water-soluble vinylic polymers containing monomers from the group consisting of acrylamide, acrylic acid, AMPS and/or admixtures thereof, and may also be either hydrolyzed acrylamide polymers or copolymers of acrylamide or its homologues, such as methacrylamide, with acrylic acid or its homologues, such as methacrylic acid, or even with monomers, such a maleic acid, itaconic acid or monomers such as vinyl sulfonic acid, AMPS, and other sulfonate containing monomers. The anionic polymers may be homopolymers, copolymers, terpolymers or contain multible monomeric repeating units. The anionic polymers may also be sulfonate or phosphonate containing polymers which have been synthesized by modifying acrylamide polymers in such a way as to obtain sulfonate or phosphonate substitution, or admixtures thereof. The anionic polymers may be used in solid, powder form, after dissolution in water, or may be used as water-in-oil emulsions, wherein the polymer is dissolved in the dispersed water phase of these emulsions. The anionic polymers have a molecular weight of at least 1,000,000. The most preferred molecular weight is at least 5,000,000, with best results observed when the molecular weight is between 7.5-25 million. The anionic polymers have a degree of substitution of at least 0.01, preferably a degree of substitution of at least 0.05 and most preferably a degree of substitution of 0.10 to 0.50. Degree of substitution means that the polymers contain randomly repeating monomer units containing chemical functionality which when dissolved in water become anionically charged, such as carboxylate groups, sulfonate groups, phosphonate groups, and the like. As an example, a copolymer of acrylamide (AcAm) and acrylic acid (AA) wherein the AcAm:AA monomer mole ratio is 90:10, would have a degree of substitution of 0.10. Similarly, copolymers of AcAm:AA with monomer mole ratios of 50:50 would have a degree of anionic substitution of 0.5. The Dispersed Silica The anionic polymers are used in combination with a dispersed silica having a particle size ranging between 1-50 nanometers (nm), preferably having a particle size ranging between 2-25 nm, and most preferably having a particle size ranging between 2-15 nm. This dispersed silica may be in the form of colloidal silicic acid, silica sols, fumed silica, agglomerated silicic acid, silica gels, and precipitated silicas, as long as the particle size or ultimate particle size is within the ranges mentioned above. The dispersed silica is present at a ratio of cationic starch to silica of from 100:1 to 1:1, and is preferably present at a ratio of from 75:1 to 30:1. This combined anionic admixture is used within a dry weight ratio of from 20:1 to 1:10 of anionic polymer to silica, preferably between 10:1 to 1:5, and most preferably between 8:1 to 1:1. The Anionic Combination With regard to the anionic combination (or anionic admixture) it is preferable to add the polymer and dispersed silica to the paper-making stock after the addition of the cationic starch has occurred, and sufficient time and mixing energy used to accomplish a thorough homogeneous admixture of cationic starch and the cellulosic slurries, mineral fillers, clays, pigments, and other inorganic components of the paper-making stock. The anionic admixture is then added so as to essentially accomplish an electroneutralization of the cationic charges contained in the paper stock. Since the cellulosic fibers, and most inorganic pigments and clays, such as TiO 2 pigment, normally carry a negatively charged surface, it is a relatively simple matter to calculate electroneutrality on the basis of the amount of cationic starch added, the degree of substitution of cationic functionality on the starch added, and the amount of any other additional species carrying a cationic charge which may be present in the paper stock, i.e., alumina sols, alum, and the like. Depending on the molecular weight, degree of anionic substitution, and type of polymer used, as well as on the amount and type of cationic starch used, the starch to polymer weight ratio preferably ranges from 50:1 to 5:1. Simultaneously, the polymer to silica ratio runs from 20:1 to 1:10, and preferably ranges from 10:1 to about 1:5 and most preferably ranges between 8:1 to 1:1. The most preferred results are obtained when the starch to silica ratios range from 75:1 to 30:1. The anionic combination or admixture of anionic polymer to silica can be made prior to admixture with the paper stock containing the cationic starch, and then added to the paper stock, or preferably is made in situ during the paper-making process by adding to the paper stock, in sequence, the cationic starch, then the anionic polymer, and finally the dispersed silica. It is believed that a complex of undetermined structure is formed, in the presence of the paper stock and which may include components of the paper stock, between the cationic starch and the anionic polymer, and that this pre-coacervate complex contains, therein, at least some positive charges, which positive charges can then attract and bind both the added dispersed silica which carries a negative surface charge, as well as the cellulosic fibers, inorganic pigments, and the like. It is presumed that the formation of the complex between starch, polymer and silica leads to the improved preformance observed with the system of the invention relative to the use of any other combination of ingredients known in the art, such as only starch plus silica. Although it would be difficult to demonstrate that this mechanism exactly accounts for the improved performance observed, and the invention should not be limited in any way to the attempted mechanistic explanation, it is a simple matter to demonstrate the improved performance of the three-component binder system. A preferred binder used according to the invention is characterized in that the degree of cationic substitution of cationic starch ranges between 0.015 and 0.075, preferably between 0.02 and 0.075, and the cationic starch is a cationically modified potato starch, and wherein the anionic polymer is selected from the group consisting of copolymers of acrylamide with monomers selected from the group consisting of acrylic acid, methacrylic acid, AMPS, vinyl sulfonate, sulfonated styrene and mixtures thereof, and modified acrylamide polymers containing at least the sulfonate functional group. Another preferred binder used according to the invention comprises a ternary combination of a cationically modified potato starch having a degree of cationic substitution ranging between 0.01 and 0.15, an anionic polymer having a molecular weight of at least 1,000,000 and a degree of anionic substitution ranging between 0.05 and 0.95 and wherein the cationic starch to silica weight ratio is between 100:1 and 30:1 and the weight ratio of anionic polymer/silica ranging between 20:1 and 1:1. Preferably the weight ratio of cationically modified potato starch to the anionic combination of anionic polymer and dispersed silica is between 50:1 and 1:1 and the weight ratio of cationic starch to silica is between 75:1 and 30:1, and the silica particles have a particle size ranging from 1.0 to 10 nm, the anionic polymer has a molecular weight of at least 5,000,000 and a degree of anionic substitution ranging between 0.05 and 0.50 and wherein the potato starch contains a degree of cationic substitution ranging between 0.01 and 0.10. Another preferred binder used according to the invention comprises a cationic potato starch having a degree of cationic substitution ranging from 0.010 to 0.150 and an anionic polymer having a degree of anionic substitution ranging between 0.01 and 1.0, wherein the weight ratio of cationic starch to anionic polymer is between 1.25:1 and 9:1. The following examples are to illustrate the invention. Example 1 Paper stock was prepared at 0.7% consistency from a thick paper stock (3.8% cellulosic fibers) and clarified white water obtained from a paper mill. The stock had a pH of 7.0-7.5. Cationic potato starch having a degree of substitution of 0.025 was prepared at a 2.0 weight percent solution in water, and diluted further, immediately prior to application to a concentration of 0.875%. A high molecular weight (about 10-20 million) anionic polyacrylamide containing about 30 mole percent acrylic acid and 70 mole percent acrylamide monomer, in the form of a water-in-oil latex containing about 30 weight percent polymer was inverted and diluted into water following the teachings of Anderson, et al, U.S. -E- 28,474 and U.S. -E- 28,576. The polymer solution was made up at 2.0 weight percent active polymer and further diluted to 0.0875 weight percent immediately prior to use. A 15 weight percent silica sol (or colloidal silica) having a particle size of about 4 nm was diluted with water to 0.0875 weight percent. Two separate batches of paper stock were obtained from the same mill approximately two weeks apart. The paper stock was admixed with cationic starch and then the various amounts of anionic polymers and/or silica sol were added thereto. Laboratory tests were completed using an "Alchem R Tester", which is designed to measure both water drainage rates under controlled conditions and also turbidity (nephelometric turbidity units, NTU) which is related to retention by the formula: % Retention = Turbidity (Blank) - Turbidity (Sample) Turbidity (BLank) x 100 The data from these tests are presented in Tables I and II. Table I presents data from the first paper stock. Table II presents data from the second paper stock. Starch 0.454 kg/t Silica 0.454 kg/t PAM 0.454 kg/t Drainage (ml/5 sec) Turbidity (NTU) 0 0 0 112 1640 25 0 0.5 126 390 25 0 1 148 200 25 0 2 182 105 25 0 3 178 100 0 0 1 111 445 0 0 2 108 420 0 0 3 106 405 25 2 0 128 360 25 5 0 142 215 25 7 0 153 180 The two-component PAM and starch combination is already superior to both starch/silica and the PAM alone, for retention* and drainage. Starch 0.454 kg/t Silica 0.454 kg/t PAM 0.454 kg/t Drainage (ml/5 sec) Turbidity**(NTU) 0 0.00 0.0 90 1312.5 5 0.00 0.0 90 1280 15 0.00 0.0 90 1325 25 0.00 0.0 94 1375 35 0.00 0.0 86 1500 25 0.00 1.0 114 300 25 0.25 1.0 110 300 25 0.50 1.0 114 280 25 0.75 1.0 116 270 25 0.00 1.0 114 300 25 0.00 2.0 134 180 25 0.00 3.0 154 140 25 0.50 0.5 94 460 25 0.50 1.0 114 280 25 0.50 1.5 130 200 25 0.50 2.5 162 140 The three (3) component system: starch, anionic polymer and dispersed silica provides superior retention and drainage as compared with the two component starch/silica binder systems taught in the prior art. The starch/polymer system alone gives comparable results when compared to the starch/silica system of the prior art for some of the drainage tests. Overall, the three component binder is superior in both retention and drainage. These tests are further illustrated in Figures I and II. Example 2 The addition to the paper stock of a small amount of an alumina source, for example, papermaker's alum, sodium aluminate or polyhydroxyaluminum chloride, further enhances the activities observed for the three component binder system. These further improvements are observed in Figures III and IV. When an alumina source is used, it is preferred to be used at levels ranging from 4,54 g to 4,45 kg active Al 2 O 3 per ton of paper (dried) manufactured. Example 3 A trial was run at a paper mill in the upper Mideast while this mill was making 30,65 kg per ream alkaline fine paper. The stock consisted of hardwood Kraft and softwood Kraft fiber with 20% filler loading comprised of an admixture of calcium carbonate, kaolin, and titanium dioxide. Fillers were added to the pulper. Paper stock pH was 7.5. Polyhydroxyaluminum chloride was added to the save-all with the reclaimed fiber and clarified water returning to the stock system. Cationic potato starch having a degree of substitution of 0.025 was added to the recycled white water prior to final stock dilution. The same high molecular weight anionic polyacrylamide (PAM) as used before was added to the intake of the centri-screen. Colloidal silica in the form of a 15% sol having a particle size of from 4-5 nanometers was added immediately before the headbox. At the start of the trial period stock treatment (I) was 8.17 kg/t cationic potato starch and 0.91 kg/t PAM. After 1.25 hours 0.36 kg/t of colloidal silica was added to the system. Drainage on the fourdrinier wire increased. The "wet line" receded 0.61 to 0.91 m and couch vacuum dropped form 152 to 131 kPa. This facilitated an increase in dilution water stream flow from 5905 to 6158 1/minute. Jordan refining was increased from 20 to 31 Amps. First pass retention increased from 86 to 91.5%. Headbox consistency decreased from 1.05% to 0.69%. These changes resulted in a considerable improvement in sheet formation. Sheet moisture before the size press dropped from 6 to 1%. Approximately 193 kPa of steam was removed from the main drying section to hold sheet moisture at the size press to 5%. Two hours after the start of the trial, cationic starch dosage was increased to 11.35 kg/t, PAM dosage was increased to 1.36 kg per ton and colloidal silica dosage was reduced to 3.11 kg/t (Stock Treatment II). First pass retention held at 89.5%, drainage on the wire, sheet drying and sheet formation remained essentially unchanged. An increase in drainage and reduction in dryer steam usage can be utilized by increasing machine speed, hence, increased production rate, or by improved sheet formation with savings in steam costs. The latter option was adopted during the trial. No significant change in sheet strength with regards to tensile, Mullen or Scott Bond was evident, as shown below for these two treatments. Treatment I II Basis Weight (kg) 30.65 30.65 Tensile (N/cm 2 ) 17.5 16.8 Mullen 38.0 36.0 Scott Bond 170.0 197.0 Example 4 Comparison of results when silica sol was added prior to anionic polymer: During the same trial period at the paper mill operation reviewed above, the dispersed silica injection point was moved to the inlet of the centri-screen. Previously, this silica sol injection point was at the discharge end exiting the centri-screen. Originally, the injection of dispersed silica followed both the injection of the cationic starch and the injection of the anionic polymer into the paper stock. With the silica sol injected at the inlet of the centriscreen, the sol was being injected into the paper stock prior to the injection of the anionic polymer. Within 30 minutes of this change being made, the following negative observations were made: 1. Drainage on the fourdrinier was drastically reduced as evidenced by the thruput in the headbox. Typical flows prior to the above change ranged between about 6435 - 6813 1 per minute. With the silica being added prior to the anionic copolymer, the thruput fell drastically to about 3407 1 per minute. 2. Paper formation was poor. This was evidenced by the inability of the furnish to drain accompanied by the inability to put more refining on the furnish. 3. Poor drainage and increased energy consumption indicated a poor result. The paper sheet became welter and the steam usage in the main dryer section increased by at least 104-138 kPa. 4. First pass retention worsened as evidenced by increased solids in both the tray waters and the flotation save-all. 5. Machine speed was necessarily reduced by about 8-10%. It would then appear that the anionic combination of the anionic polymer and dispersed silica most preferably occurs by sequentially adding to the paper stock from 4.54 to 22.7 kg per ton of dried paper of the cationically modified starch, then adding the anionic polymer; followed thereafter by the dispersed silicas. Prior addition of dispersed silica to paper stock containing polymer does not apparently allow formation of the coacervate complex, and the results of binder use are destroyed. All of the calculations indicating the addition of any ingredient in terms of kgit above refers to the kg of active ingredients used per ton of dried paper.

Claims: Use in a paper-making process in which a paper-making stock containing at least 50 % of cellulosic pulp is formed into a sheet and then dried of a binder comprising a cationic starch having a degree of substitution of at least 0.01 and silica particles characterized in that it comprises a ternary combination of 0.20, a cationic starch having a degree of cationic substitution ranging between 0.01 and an anionic high molecular weight polymer having a molecular weight of at least 1 000 000 and a degree of anionic substitution of at least 0.01, and a dispersed silica having a particle size ranging from 1 to 50 nm, wherein the weight ratio of anionic polymer to silica ranges between 20:1 and 1:10 and the cationic starch to silica weight ratio is between 100:1 and 1:1, and wherein the binder is formed in situ by a sequential addition to the paper-making stock of the cationic starch, then the anionic polymer and then the dispersed silica or by a sequential addition to the papermaking stock of the cationic starch, then followed by an admixture of the silica sol and the anionic polymer, each addition occuring after each prior addition has been thoroughly admixed. Use of claim 1 in which the weight ratio of cationic starch to anionic polymer ranges between 50:1 and 5:1 and the weight ratio of anionic polymer to silica sol ranges between 10:1 and 1:1, and wherein the degree of anionic substitution of the anionic polymer is at least 0.10, and the molecular weight of the anionic polymer is at least 1,000,000; the degree of cationic substitution on the cationic starch is from 0.02 to 0.10 and the particle size of the dispersed silica ranges from 2 to 25 nm. Use of claim 1 wherein the degree of cationic substitution of cationic starch ranges between 0.015 and 0.075, preferably between 0.02 and 0.075, and the cationic starch is a cationically modified potato starch, and wherein the anionic polymer is selected from the group consisting of copolymers of acrylamide with monomers selected from the group consisting of acrylic acid. methacrylic acid, AMPS, vinyl sulfonate, sulfonated styrene and mixtures thereof, and modified acrylamide polymers containing at least the sulfonate functional group. Use of claim 1 which comprises a terniary combination of a cationically modified potato starch having a degree of cationic substitution ranging between 0.01 and 0.15, an anionic polymer having a molecular weight of at least 1,000,000 and a degree of anionic substitution ranging between 0.05 and 0.95 and wherein the cationic starch to silica weight ratio is between 100:1 and 30:1 and the weight ratio of anionic polymer/silica ranging between 20:1 and 1:1. Use of claim 4 wherein the weight ratio of cationically modified potato starch to the anionic combination of anionic polymer and dispersed silica is between 50:1 and 1:1 and the weight ratio of cationic starch to silica is between 75:1 and 30:1. Use of claim 5 wherein the silica particles have a particle size ranging from 1.0 to 10 nm, the anionic polymer has a molecular weight of at least 5,000,000 and a degree of anionic substitution ranging between 0.05 and 0.50 and wherein the potato starch contains a degree of cationic substitution ranging between 0.01 and 0.10. Use of claim 1 which comprises a cationic potato starch having a degree of cationic substitution ranging from 0.010 to 0.150 and an anionic polymer having a degree of anionic substitution ranging between 0.01 and 1.0, wherein the weight ratio of cationic starch to anionic polymer is between 1.25:1 and 9:1. Use of claim 5 wherein the weight ratio of cationic starch to silica ranges between 50:1 and 30:1. Use of claim 7 which additionally contains from 0.01 to 2.0 weight percent of active alumina. Use of any of claims 1 to 9 in addition to from 0.0045 to 4.5 kg of active alumina (Al 2 O 3 ) per ton of dried paper. Use of claim 10 wherein the active alumina is selected from the group consisting of papermaker's alum, sodium aluminate and polyhydroxyaluminum chloride. Use of claims 10 or 11 in which paper-making stock having preferably a pk of 4 to 9 and containing at least 50% of cellulosic pulp and optionally a mineral filler/pigment material having at least partial anionic surface characteristics prior to sheet formation is added with the binder in an amount of from 0.1 to 15, preferably 0.05 to 10 %, based on the weight of said papermaking stock.

Inventors: JOHNSON KERRIE A, JOHNSON, KERRIE A.
Applicants: NALCO CHEMICAL CO, NALCO CHEMICAL COMPANY
Application year: 1987
Main classification: D21H23
IPC codes: D21H17, D21H23