MXPA98006653A - Paper making process - Google Patents

Abstract

A paper making process comprises:(a) adding to an aqueous paper furnish containing pulp and optionally inorganic filler a water-soluble polyparticulate polysilicate microgel and a water-soluble cationic polymer, and (b) forming and drying the product of step (a), wherein the microgel has an average particle size in the range 20 to 250 nm and a surface area in excess of 1000 m2/g. The polysilicate microgel is preferably a polyaluminosilicate, especially one having a mole ratio of alumina:silica of between 1:10 and 1:1500. The use of such microgels leads to improved drainage and retention characteristics.

Description

PAPER MANUFACTURING PROCESS DESCRIPTION OF THE INVENTION This invention relates to processes for papermaking, and is especially related to processes such as the use of water-soluble polysilicate microgels, especially polyaluminosilicate microgels and non-aluminized polysilicate microgels, as retention and drainage aids.

BACKGROUND OF THE INVENTION The formation of water soluble polysilicate microgels and their use in papermaking is known. U.S. Patent No. 4,954,220 relates to polysilicate microgels and their use in papermaking. The Tappi Journal of December 1994 (vol 77, No. 12) on pages 133-138 contains a review of such products and their uses. U.S. Patent No. 5,176,891 describes a process for the production of polyaluminosilicate microgels, which involves the initial formation of a polysilicic acid microgel followed by the REF. 28103 k microgel reaction of polysilicic acid with an alumina, to form the polyaluminosilicate. The use of polyaluminosilicate microgels as improved retention and drainage agents in papermaking is also described. US Patent No. 5,127,994 describes a process for the production of paper by forming and drying a suspension of cellulosic fibers in the presence of three compounds: an aluminum salt, a cationic polymeric retention agent and polysilicic acid. The process of the polyaluminosilicate microgel described in US Pat. No. 5,176,891 comprises three steps, namely (1) the acidification of an aqueous solution of an alkali metal silicate to form the polysilicic acid microgel, (2) the addition of an alumina soluble in water to the polysilicic acid microgel to form the polyaluminosilicate, and (3) the dilution to stabilize the product against gelation. There is a necessary aging period involved following the acidification stage, during which the silicic acid formed first becomes polysylic to the linear polysilicic acid, and then to the microgel structure that is critical for the efficiency of the polyaluminosilicate products. The products are described having a surface area greater than 1000 square meters per gram, a surface acidity greater than about 0.6 milliequivalents per gram and an alumina / silica molar ratio greater than 1: 100, preferably between 1:25 and 1: 4. WO 95/25068 describes an improvement over the processes described in US Pat. No. 5,176,891 in which it combines the steps of acidification and alumina. An unexpected and important benefit that results is that the aging period required for the formation of the microgel to occur is significantly reduced. The poly-viniliculate polyaluminosilicate products produced by the process of that invention have good activity as retention and drainage agents in papermaking immediately after their formation (there is no aging period), and reach their optimum efficiency in a significantly shorter time than those prepared by the previous methods. Aging periods required for product formation are avoided or minimized when possible in papermaking, since they require additional equipment or oversized equipment, and are known to give rise to problems such as products of non-uniform quality .

Any reduction in the aging period is thus an improvement in the paper manufacturing process and in the quality of the product. An important aspect of the processes described in WO 95/25068 is the addition of a water soluble aluminum salt to an acid used for the acidification of an alkali metal silicate solution. In this way, hydrated aluminum hydroxide is produced at the same time as silicic acid and thus, during the polymerization of silicic acid to polysilicic acid and the formation of a polyparticulate microgel, aluminum hydroxide is incorporated directly into the polymer with the concomitant formation of polyaluminosilicate. This process can produce useful polyaluinosilicates (PAS) over a wide range of compositions having molar ratios of alumina / silica in the range from about 1: 1500 to 1:10 but generally about 1: 1000 or less preferably 1: 750 to 1. : 25, and more preferably 1: 1500 to 1:50. Because of the low alumina / silica ratio, the total surface acidity of the polyaluminosilicate does not differ significantly from that of the non-aluminized polysilicate microgels. At the same time, an anionic charge is maintained within lower pH ranges than is observed with non-alumina polysilicic acid. The process of WO 95/25068 can be carried out as a two-step process comprising: (a) acidifying an aqueous solution of an alkali metal silicate containing 0.1-6% by weight of SiO2 at a pH of 2. -10.5, using an aqueous acid solution containing an aluminum salt; and (b) diluting the product of step (a) with water before gelation to a contain of Si02 of = 2% by weight. Optionally, after the acidification step, an aging step can be employed to improve the efficiency of the product further. Such a period of aging is not required, and is somewhat contrary to the benefit gained by the process, a reduction in the time required for the polyaluminosilicate products to reach maximum activity. Any water-soluble silicate salt can be used in the process, with alkali metal silicates such as sodium silicate being preferred. As an example, sodium silicate, Na20: 3.2 SiO2 by weight can be used.

Any acid with a pKa of less than about 5 may be used. Inorganic mineral acids are preferred over organic acids; Sulfuric acid is the most preferred. Any aluminum salt that is soluble in the acid used can be used. The suitable selections are sulfate, chloride, nitrate and aluminum acetate. You can also use basic salts such as sodium alumina and chlorohydrol, Al (OH) 2Cl. If alkali metal aluminas are used, they can be converted first to an aluminum metal salt by reaction with the acid. To carry out the process of WO 95/25068, a dilute aqueous solution of an alkali metal silicate containing from about 0.1-6% by weight of SiO2, preferably about 1-5% by weight of SiO2 and more preferably 2% by weight. -4% by weight, is rapidly mixed with a dilute aqueous solution of an acid containing a dissolved aluminum salt, to produce a solution within a pH range of about 2-10.5. A more preferred pH range is from 7-10.5 and the most preferred range is a pH of 8-10. Suitable acid concentrations are in the range of 1-5% by weight, although both lower and higher concentrations can be used, provided that proper mixing is employed. A concentration of about 20% by weight of acid is generally preferred. The amount of aluminum salt dissolved in the acid solution can vary from about 0.1% by weight up to the solubility limit of the salt in the acid. The molar ratio of Al203 / Si02 in the polyaluminosilicate microgels produced by this process can vary widely, from about 1: 500 to 1:10 depending on the concentration of the acid used, the amount of aluminum salt dissolved in the acid, and the pH of the resulting partially neutralized silicate solution. Acidification at lower pH ranges requires the use of more acid, and may result in the production of polyaluminosilicates containing higher molar ratios of alumina / silica. The solubility data of an Al2 (S04) 3-H2SO4-H20 system (Linke, "Solubility of Inorganic Compounds", 4th edition 1958, Vol. 1) provide a basis for calculating the maximum Al203 / Si02 ratios available in polyaluminosilicates (when used in Na20: 3.2Si02 as silicate) using sulfuric acid solutions containing from 10-50% by weight of acid, saturated with aluminum sulfate, for the acidification of a silicate solution at pH 9. (A this pH, approximately 85% of the alkalinity of Na20: 3.2Si02 is neutralized).

H2S0% A12 (S0) 3% The ratio by weight per molar mass of Al203 / Si02 in the polyaluminosilicate 10 19.6 1/22 20 13.3 1/32 30 8.1 1/61 40 4.3 1/138 50 2.5 1/283 It has been found that the PAS microgel preparation process can preferably be carried out using an acid solution containing about 20% by weight of sulfuric acid and 1-6% by weight of dissolved aluminum sulfate. Using such acid solutions over the preferred pH range of 8-10 (representing approximately 95-6056 by neutralization weight of Na20: 3.2Si02 microgels), polyaluminosilicate microgels with molar ratios of Al203 / SiO2 from about 1 can be obtained. : 35 to 1: 400. Within the preferred concentration and pH ranges, the solutions of polyaluminosilicates are clear and, after dilution to approximately 0.5% by weight of SiO2, retains its activity in flocculation processes for approximately 24 hours. While the process described in WO 95/25068 produces PAS microgels which are of particular advantage in papermaking, it has surprisingly been found now that even better results can be obtained with non-aluminized microgels or polyaluminosilicate having a size of average particle (microgel) or dimensions between 20 and 250 nanometers. Accordingly, the present invention provides a papermaking process comprising: (a) adding to an aqueous paper stock, containing pulp and optionally an inorganic filler, a water soluble polyparticulate polysilicate microgel, having an average particle size 20 - 250 nm, and a surface area greater than 1000 m2 / g, and a polymer, water-soluble cationic; and (b) forming and drying the product of step (a). The microgels used in this invention are preferably those having an average particle size in the range of 40-250 nm, more preferably 40-150 nm, and more preferably 50-100. They can be non-aluminized polysilicate microgels or PAS microgels. made, for example, by the two-step process described in WO 95/25068 wherein following the acidification stage the product is aged, for a time which depends on the process conditions (ie, pH, the concentration is silica) , the concentration of aluminum, the temperature) selected. Aging times in the range of 4 to 40 minutes, for example 5 to 30 minutes, can normally be used to produce the desired particle size. For example, an aging time of the order of 15 minutes can produce a microgel having an average particle size of about 100 nm. The surface area of the microgels is at least 1000 m2 per gram, preferably 1360 to 2720 2 per gram. The microgels are preferably polyaluminosilicate microgels, especially those having a molar ratio of alumina: silica of between 1:10 and 1: 1500. The activity of the polyaluminosilicate microgels can be further improved, and their activity can be maintained for longer periods of time by adjusting the pH of the microgel to about pH 1 to 4 before, after or concurrently with the dilution step. Another advantage of adjusting the pH of the microgel to approximately a pH of 1-4 is that the microgels can be stored at higher concentrations of silica. Thus, it may be possible to eliminate the dilution step completely, depending on the concentration of silica during the addition of the aqueous acid solution of the aluminum salt. The adjustment of the pH to between about 1-4 allows to store polyaluminosilicate microgels of up to 4-5% by weight. Any acid that decreases from the pH of the microgel to about pH 1-4 can be used. Inorganic mineral acids are preferred over organic acids; Sulfuric acid is the most preferred. Thus, according to a preferred embodiment of the invention, or process for the manufacture of paper comprises the steps of (a) adding to an aqueous raw material of paper, containing pulp and optionally an inorganic filler, up to 1%, preferably from 0.01-1% by weight, based on the dry weight of the raw material, of a water soluble polyparticulate polyaluminosilicate microgel, having a molar ratio of alumina: silica of between 1.10 and 1: 1500, prepared by a process comprising the steps of: (i) acidifying an aqueous solution of an alkali metal silicate containing 0.1-6% by weight of SiO2 at a pH of 2-10.5, by adding an aqueous acid solution containing sufficient aluminum salt to provide the molar relationships; and (ii) adjusting the pH of the product of step (i) to between 1-4 before, after or concurrently with a dilution step, but before gelation, to achieve an SiO2 content of = 5% by weight; and at least about 0.001% by weight, based on the dry weight of the raw material, of a water-soluble cationic polymer; wherein the microgel has an average particle size of 20-250 nm; and (b) forming and drying the product of step (a). The adjustment of the pH in step (a) (ii) above is preferably a reduction in pH, the acidification in step (a) (i) preferably produces a pH of 7 to 10.5, more preferably 8 to 10, and more preferably from 8 to 8.5. the alkali metal silicate solution preferably contains 2 to 3% SiO2 by weight. The polysilicates used in this invention can be used in a wide variety of flocculation processes, and act as retention and drainage agents in papermaking (used in the amount of up to 1%, preferably from 0. 01-1% by weight, based on the dry weight of the raw material of the paper). They can be used in combination with cationic polymers such as cationic starch, cationic polyacrylamide and cationic guar. These are described in US Patent Nos. 4,927,498 and No. 5,176,891. Such cationic polymer (water soluble) are present in a concentration of at least about 0.001% by weight based on the dry weight of the raw material. Thus, the invention also provides a process for making paper, comprising the steps of: (a) adding to an aqueous pulp-containing paper raw material and optionally an inorganic filler, a water soluble polypartice polyaluminosilicate microgel consisting essentially of (i) microgels having molar ratios of alumina: silica between 1:25 and 1: 1500 where aluminum ions are both intra- and inter-partice and where the particles in the microgel have diameters of 1-2 nm; Y (ii) water, such that the microgels are present in < 5% by weight, based on the content of Si02, and at a pH of 1-4; and at least about 0.001% by weight, based on the dry weight of the raw material of a water-soluble cationic polymer; wherein the microgel has an average particle size of 20-250 nm and (b) forming and drying the product of step (a). Anionic polymers such as anionic polyacrylamide, anionic starches, anionic guar, anionic polyvinyl acetate and carboxymethylcellulose and their derivatives can also be used in conjunction with the polysilicate and cationic polymer microgels with beneficial results.

Depending on the papermaking conditions, various other chemical compounds can also be employed in conjunction with the polysilicate microgels and the high molec weight cationic polymers. In systems containing large amounts of anionic compounds, for example, cationic polymers with high charge density and low molec weight, such as polyethylenimine, polydiallyldimethylammonium chloride and condensation products of α-epichlorohydrin can be added to achieve a charge balance within the system more effectively and obtain improved results. Additional amounts of aluminum salts beyond those contained in the acid solution, such as alum and sodium alumina, can also be added to obtain improved results in certain circumstances. These may be added to the papermaking feedstock either by pre-mixing them with the polysilicate microgels of this invention, or by separate addition. The following examples are given for the purpose of illustrating, but not limiting, the invention.

EXAMPLE 1 A solution of polyaluminosilicate (PAS) was prepared by mixing 21 g of sodium silicate in a ratio of 3.22 which contained 28.5% SiO2 with 260 grams of deionized water. To the solution of Si02 to 2.1 by weight, 9.84 ml of 5N H2SO4 containing 0.052 g of Al2 (S04) 3 • 17H20 were added to give a pH of 8.6. Aliquots of the 2% PAS solution were diluted and stabilized by the resulting weight (Si02 base) at 0.125% by weight of PAS (Si02 base) at pH 2.5, diluting them with 0.0085N H2SO4 solution at various times. The average microgel sizes of the PAS samples at 0.125% by weight (base of Si02) were determined using a light scattering goniometer from Brookhaven Instrument, model BI-200SM. The measurements were conducted at room temperature, using an ion laser in an argon atmosphere with a wavelength of 488 n: a operating at an energy of 200 iaW. The measurements of the light scattering intensity were made at different angles, and the data were analyzed using a Zimm plot. The average particle sizes of the microgel were obtained from the particle size distribution. The efficiency of PAS solutions being 0.125% by weight as a retention and drainage aid in papermaking was determined by conducting Canadian standard refining tests, using a bleached kraft raw material of pH 8, and 0.3% by weight of consistency containing 35% hardwood, 35% softwood and 30% precipitated calcium carbonate. The efficiency of the product was tested by adding to the paper raw material 9.O8 Vq / 1 (2 Lttm) dry raw material phase) of cationic potato starch BMB-40 15 seconds before the addition of 0.908 lq / taa (2fct) ) of the PAS solutions (Si02 base). The mixing was conducted in a Britt vessel at 750 rpm, and the flocculated raw material was then transferred to a Canadian standard refining test machine, and drainage measurements were made. The refining results (in me) and the particle size of the average silica (microgel) (in nanometers) versus dilution time are shown in table 1 below. Retention was also determined using a Britt vessel at 750 rpm, adding to the paper stock 9.08 kg / ton (20 Lb / ton) of BB-40 (see above) 15 seconds before the addition of 0.908 hg / txn (2 Lb / cn) of the PAS solutions (base of Si02). After an additional agitation of 15 seconds, drainage was started. Five seconds later the white water began to be collected, and this continued until 100 ml of the white water was collected. This was filtered through a glass fiber * filter, the solids were dried and then calcined. The resulting ash was weighed, and the ash retention was calculated. The results are also given in Table 1. The results are also shown in graphical form in Figure 1, which shows the refined plotted against the size of the microgel; and in Figure 2, which is a graph of ash retention versus microgel size. The efficiency of the PAS solutions was also tested (using the Canadian standard refining test procedure above) in different papermaking formulations, i.e. (i) where 4.54 kg / ton (10 Lb / t) of starch of cationic potato BMB-40 were added to the paper stock 15 seconds before the addition of 0.1135 kg / ton (0.25 Lb / t) of cationic percol 182, followed 15 seconds later by the addition of 0.454 kg / ton ( 1 Lb / ton) of the PAS solutions; (ii) where 6.81 kg / ton (15 Lb / t) of cationic potato starch BMB-40 were added to the paper stock 15 seconds before the addition of 0.1135 kg / ton (0.25 Lb / t) of alum (b from A1203), followed 15 seconds later by the addition of 0.454 kg / ton (1 Lb / t) of the PAS solutions; (iii) where 9.08 kg / ton (20 Lb / t) of cationic potato starch BMB-40 were added to the paper stock 15 seconds before the addition of 0.1135 kg / ton (0.25 Lb / t) of Percol 90L anionic, followed 15 seconds later by 0.454 kg / ton (1 Lb / t) c5e? S PAS solutions.

The results of these three tests are shown graphically in Figures 3 to 5, which show the refined plot against microgel size for tests (i) to (iii) respectively.

TABLE 1 EXAMPLE 2 A PAS solution was prepared by mixing 21 g of sodium silicate of a ratio of 3.22 containing 28.5% SiO2 with 260 grams of deionized water. To the solution of Si02 at 2.1% by resulting weight were added 8.75 ml of 5N H2SO4 solution containing 0.80 g of Al2 (S04) 3.17H20 to give a pH of 8.5. Aliquots of the 2% PAS solution were diluted and stabilized by weight (base of Si02) in PAS at 0.125% by weight (base of Si02) at pH 2.0 by diluting them with 0.0085N H2SO4 solution at various times. The average microgel sizes of the PAS samples at 0.125% by weight (base of SiO2) were determined as above, and the refining tests were conducted as described in Example 1. The results are given in Table 2.

TABLE 2 EXAMPLE 3 A non-aluminized polysilicate (PS) solution was prepared by mixing 21 g of sodium silicate of a ratio of 3.22, which contained 28.5% by weight of SiO2 with 260 g of deionized water. To the solution of Si02 at 2.1% by weight, 10 ml of 5N H2SO4 solution were added. Aliquots of the PS solution at 2% by weight (base of Si02) were diluted and stabilized in PS at 0.125% by weight (base of Si02) at pH 2.5, diluting them with 0.0085N H2SO4 solution at various times. The average sizes of the microgel were determined and the refining measurements were made as in Example 1. The results are given in Table 3.

TABLE 3 As can be seen from the data, the size of the microgel in the range of this invention provides the best papermaking efficiency (measured by both parameters, refining and ash retention).

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers. Having described the invention as above, property is claimed as contained in the following:

Claims (21)

1. A process for papermaking characterized in that it comprises (a) adding to an aqueous paper raw material, which contains pulp and optionally an inorganic filler, a water soluble polyparticulate polysilicate microgel, having an average particle size of 20 to 250 nm, and a larger surface area of 1000 m2 / g, and a cationic polymer soluble in water; and (b) forming and drying the product of step (a).

2. A process as claimed in claim 1, characterized in that the polysilicate microgel is a polyaluminosilicate microgel.

3. A process as claimed in claim 2, characterized in that the polyaluminosilicate microgel has a molar ratio of alumina: silica between 1:10 and 1: 1500.

4. A process as claimed in claim 2 or 3, characterized in that the polyaluminosilicate poly-galactosilicate microgel is made by a process comprising: (a) acidifying an aqueous solution of an alkali metal silicate containing 0.1-6% by weight of Si02 at a pH of 2-10.5, using an aqueous acid solution containing an aluminum salt; Y (b) diluting the product of step (a) with water before gelation to a SiO2 content of = 5% by weight.

5. A process as claimed in claim 4, characterized in that it comprises the aging of the product of step (a) from 4 to 40 minutes.

6. A process as claimed in claim 5, characterized in that it comprises the aging of the product of step (a) from 5 to 30 minutes.

7. A papermaking process characterized in that it comprises the steps of: (a) adding to an aqueous paper raw material, which contains pulp and optionally an inorganic filler, up to 1% by weight, based on the dry weight of the raw material , of a water soluble polyparticulated polyaluminosilicate microgel, having a molar ratio of alumina: silica of between 1110 and 1: 1500, prepared by a process comprising the steps of: (i) acidifying an aqueous solution of a metal silicate alkaline containing 0.1-6% by weight of Si02 at a pH of 2-10.5, adding an aqueous acid solution containing sufficient aluminum salt to provide the molar ratios; and (ii) adjusting the pH of the product of step (i) to between 1-4 before, after or concurrently with a dilution step, but before gelation, to achieve a SiO2 content of = 5% by weight; and at least about 0.001% by weight, based on the dry weight of the raw material, of a water-soluble cationic polymer; wherein the microgel has an average particle size of 20-250 nm and a surface area greater than 1000 m2 / g; and (b) forming and drying the product of step (a).

8. A process as claimed in claim 7, characterized in that the acidification in step (a) (i) produces a pH of 7 to 10.5.

9. A process as claimed in claim 7, characterized in that the acidification in step (a) (i) produces a pH of 8 to 10.

10. A process as claimed in claim 7, characterized in that the acidification in step (a) (i) produces a pH of 8 to 8.5.

11. A process as claimed in any of claims 7 to 10, characterized in that the alkali metal silicate solution contains 2 to 3% SiO2 by weight.

12. A papermaking process characterized in that it comprises: (a) adding to an aqueous paper raw material, which contains pulp and optionally an inorganic filler, a water soluble polyparticulated polyaluminosilicate microgel, consisting essentially of: (i) microgels having molar ratios of alumina: silica between 1:25 and 1: 1500 where aluminum ions are present both intra- and inter-particle and where the particles in the microgel have diameters of 1-2 nm; and (ii) water, such that the microgels are present at = 5% by weight, based on the SiO2 content, and at a pH of 1-4; and at least about 0.001% by weight, based on the dry weight of the raw material of a water-soluble cationic polymer, wherein the microgel has an average particle size of 20-250 nm; And (b) forming and drying the product of step (a).

13. The process according to any of claims 1 to 12, characterized in that to this is added an amount of the aluminum compound added to the raw material of the paper.

14. The process according to any of claims 1 to 13, characterized in that it is an anionic polymer added to the raw material of the paper.

15. A process according to any of claims 1 to 14, characterized in that the microgel has an average particle size in the range of 40 to 250 nm.

16. A process in accordance with the claim 15, characterized in that the microgel has an average particle size in the range of 40 to 150 nm.

17. A process in accordance with the claim 16, characterized in that the microgel has an average particle size in the range of 50 to 150 nm.

18. A process according to claim 17, characterized in that the microgel has an average particle size in the range of 50 to 100 nm.

19. A process according to any of claims 1 to 18, characterized in that the microgel has a surface area of 1360 to 2720 m2 per gram.

20. A water soluble polyparticulate polyaluminosilicate microgel characterized in that it consists essentially of: (a) microgels having molar ratios of alumina: silica of between 1:10 and 1: 1500 wherein aluminum ions are present both intra- and inter-particle; wherein the particles in the microgel have diameters of 1-2 nm; and wherein the microgels have an average particle size of 20-250 nm and a surface area greater than 1000 m2 / g; and (b) water, such that the microgels are present at = 5% by weight, based on the SiO2 content,

21. A microgel in water as claimed in claim 20, characterized in that the microgel has an average particle size in the range established in any of claims 15 to 18.