DE69713677T2 - Paper-making process - Google Patents

Description

The present invention is in the technical field of papermaking and more particularly in the technical field of wet end additives to papermaking raw materials.

In the manufacture of paper, an aqueous cellulose suspension or slurry is formed into a paper sheet. The cellulose slurry is generally diluted to a consistency (percent dry weight of solids in the slurry) of less than 1% and often less than 0.5% prior to the paper machine, while the finished sheet must have less than 6% water by weight. Therefore, the dewatering aspects of papermaking are extremely important to the efficiency and cost of manufacturing.

The lowest cost dewatering method in the process is draining, and thereafter more expensive methods are used, such as vacuum, pressing, evaporation and the like, and in practice a combination of such methods is used to dewater or dry the sheet to the desired water content. Since draining is both the first dewatering method used and the least expensive, improving the efficiency of draining reduces the amount of water that must be removed by other methods and thus improves the overall efficiency of dewatering and reduces its cost.

Another aspect of papermaking that is extremely important for the efficiency and cost of production is the retention of raw material components on and within the fiber mat formed during papermaking. Papermaking raw materials generally contain particles in a size range from about 2 to 3 mm in size for cellulose fibers to fillers of a few micrometers and to colloids. Within this range are cellulose fine particles, Mineral fillers (used to increase opacity, gloss and other paper properties) and other small particles which, without the inclusion of one or more retention aids, would generally pass to a significant extent through the spaces (pores) between the cellulosic fibres in the fibre mat formed during paper manufacture.

One method of improving the retention of cellulose fines, mineral fillers and other furnish components on the fiber mat is to use a coagulant/flocculant system added prior to the paper machine. In such a system, a coagulant, such as a low molecular weight cationic synthetic polymer or a cationic starch, is first added to the furnish, the coagulant generally reducing the negative surface charges present on the particles in the furnish, particularly the cellulose fines and mineral fillers, and thereby effecting a degree of agglomeration of such particles, followed by the addition of a flocculant. Such a flocculant is generally a high molecular weight anionic synthetic polymer which bridges the particles and/or agglomerates from one surface to another, thereby binding the particles into large agglomerates. The presence of such large agglomerates in the paper furnishes increases retention when the fiber mat of the paper sheet is formed. The agglomerates are filtered from the water onto the fiber felt where non-agglomerated particles would to a large extent pass through such a paper mat.

Although a flocculated agglomerate does not generally interfere with the drainage of the mat to the extent that would occur if the papermaking furnishes were gelled or contained a quantity of gelatinous material, when such flocs are filtered through the mat, its pores are reduced to some extent, reducing the efficiency of drainage therefrom. Therefore, retention is increased with some degree of detrimental effect on drainage.

Another system used to provide an improved combination of retention and drainage is described in U.S. Patent No. 4,753,710 and U.S. Patent No. 4,913,775, inventors Langley et al., issued June 28, 1988 and April 3, 1990, respectively. Briefly, such a process first adds a high molecular weight linear cationic polymer to the aqueous cellulosic papermaking suspension prior to shearing the suspension, followed by the addition of bentonite after shearing. Shearing is generally provided by one or more of the cleaning, mixing and pumping stages of the papermaking process, and shearing breaks up the large flocs formed by the high molecular weight polymer into microflakes, and further agglomeration then follows with the addition of the bentonite clay particles.

Another system uses the combination of cationic starch followed by colloidal silica to increase the amount of material retained on the web by the process of charge neutralization and adsorption of smaller agglomerates. This system is described in U.S. Patent No. 4,388,150, inventors Sunden et al., issued June 14, 1983.

It is believed that dewatering in general, and dewatering by draining in particular, is improved when the pores of the paper web are less clogged, and retention by adsorption is believed to reduce such pore clogging compared to retention by filtration.

Greater retention of fines and fillers allows a reduction in the cellulosic fiber content of a given paper grade. When lower quality pulps are used to reduce papermaking costs, the retention aspect of papermaking becomes even more important since the fines content of such lower quality pulps is generally greater than that of higher quality pulps.

Greater retention of fines, fillers and other slurry components reduces the amount of such substances lost to the white water and thus reduces the amount of waste materials, the cost of waste disposal and the harmful environmental impacts thereof.

Another important property of a given papermaking process is the formation of the paper sheet produced. Formation is determined by the variation of light transmittance within a paper sheet, and a high variation indicates poor formation. As retention increases to a high level, such as a retention level of 80 to 90%, the formation parameter generally decreases abruptly from good formation to poor formation. It is believed, at least theoretically, that as the retention mechanism of a given papermaking process changes from filtration to adsorption, the deleterious effect on formation when high retention levels are achieved is reduced, and a good combination of high retention with good formation is attributed to the use of bentonite in U.S. Patent No. 4,913,775.

It is generally desirable to reduce the amount of material used in a papermaking process for a given purpose without compromising the desired result. Such additional reductions can realize both material cost savings and handling and processing advantages.

It is also desirable to use additives that can be fed to the paper machine without undue problems. An additive that is difficult to dissolve, slurry or otherwise disperse in the aqueous medium may require expensive equipment to feed it to the paper machine. If difficulties arise in feeding it to the paper machine, the additive is often maintained in the form of an aqueous slurry using high energy input equipment. In contrast, Additives that are easily dissolved or dispersed in water require less energy and expenditure, and their feed uniformity is more reliable.

Summary of the invention

The claimed invention comprises a papermaking process comprising: forming an aqueous cellulosic papermaking slurry, subjecting the slurry to one or more shear stages, adding a mineral filler to the slurry before at least one of the shear stages, adding to the slurry after the addition of the mineral filler and before at least one of the shear stages from 0.5 to 100 ppm by weight of dry pulp contained in the slurry of a cationic dispersion polymer obtainable by dispersion polymerization of a monomer mixture soluble in an aqueous solution of a polyvalent anionic salt, the polymer being selected from the group consisting of copolymers of acrylamide and quaternary dimethylaminoethylacrylate methyl chloride salt (DMAEA.MCQ), quaternary dimethylaminoethyl acrylate methyl chloride salt (DMAEM.MCQ), quaternary dimethylaminoethyl acrylate benzyl chloride salt (DMAEA.BCQ) and quaternary dimethylaminoethyl methacrylate benzyl chloride salt (DMAEM.BCQ), and wherein the polymer is insoluble in the aqueous solution, shearing the slurry, adding an amount of microparticles selected from the group consisting of copolymers of polyacrylic acid, bentonite and silica sol to the slurry, draining the slurry to form a sheet, and drying the sheet to form a paper sheet.

Description of the preferred embodiments

According to the invention, a water-soluble polymer is added to a cellulose slurry prior to the formation of a paper product. The water-soluble polymer should in any event be substantially dispersed in the slurry prior to the formation of the paper product. The microparticle of the invention is added to the slurry after shearing. Addition of the polymer to an aqueous medium, such as a water solution or dispersion, facilitates dispersing the polymer into the slurry. In a preferred embodiment, the polymer is added to the cellulosic slurry prior to the processing steps of draining and forming the paper sheet.

The present process is believed to be applicable to all grades and types of paper products and is further applicable for use with all types of pulps including, without limitation, whole pulps, including sulfate and sulfite pulps from both hard and soft woods and acid pulps, thermomechanical pulps, mechanical pulps, reclaimed pulps and ground wood pulps, although it is believed that the benefits of the process of the present invention are best achieved when the pulp used is of the whole pulp type, particularly whole alkaline pulp.

In a preferred embodiment, the filler used in the cellulose slurry is anionic or at least partially anionic. However, other mineral or inorganic fillers may be used, such as calcium carbonate, clay, titanium dioxide or talc, or a combination may be present.

The amount of alkaline inorganic filler such as one of the alkali carbonates generally used in a papermaking furnish is 10 to 30 parts by weight of the filler, as CaCO3, per 1100 parts by weight of dry pulp in the slurry, but the amount of such filler may occasionally be as low as 5 or even 2 parts by weight and as high as 40 or 50 parts by weight on the same basis.

The reduced specific viscosities of the polymers and copolymers reported herein were determined in 0.125 M sodium nitrate solution from published data. Similarly, all molecular weights of the polymers reported herein are The approximate weight average molecular weights of the polymers are given.

The dispersion polymerization process used to prepare the polymers of the invention offers numerous advantages that were previously unavailable. Since the polymers of the invention are synthesized entirely in water, no oil solvent is required. This is significant because:

1) the polymers of the invention do not pose a fire hazard;

2) no oil is added to the water to be treated (more environmentally friendly);

3) Dissolution of the polymers of the invention requires only the addition of water, no special activators are required;

4) the ability of the polymers of the invention to dissolve/transform is superior to that of the oil dispersion latexes, and

5) the polymers of the invention can be diluted to virtually any concentration using appropriately concentrated salt water.

Another major advantage is that the bulk viscosity of the polymer is low, unlike some oil dispersion latex polymers. This physical property allows any standard chemical pump to deliver the material to the pumping point.

A new class of water-soluble dispersion polymers has been discovered to be more effective at increasing drainage and retention than currently available chemical treatments. As discussed in more detail below, the polymer dispersion is prepared in an aqueous solution of a polyvalent anionic salt. The polymer dispersion achieves fine particle sizes and aqueous solubilities not available with other polymers used for this application. Furthermore, there is no problem with overdosing the polymer dispersion, which is a disadvantage with latex polymers.

According to the process, the dispersion polymer of the invention is added to a cellulose papermaking slurry. The polymer is added in an effective amount of 0.5 to 100 ppm. More preferably, the amount of polymer added is 2 to 40 ppm; and most preferably 4 to 25 ppm. It is believed that no maximum dosage occurs at which the polymers adversely affect the system. At some higher doses, the beneficial effect may reach a plateau, and on a cost basis, such higher doses, probably above about 100 ppm, are not cost effective. The polymers of the invention are preferably added to the system in neat form. However, in some applications, the polymers may be added as an aqueous solution.

The preferred polymers of the invention are manufactured by Hymo Corporation, Japan. Methods for preparing the polymer dispersion used in the invention are described in detail in U.S. Patent 5,006,590 and U.S. Patent No. 4,929,655, assigned to Kyoritsu Yuki Co., Ltd., Tokyo, Japan.

According to the invention, after the introduction of shear to the slurry, an organic or inorganic microparticle is added. Preferably, the organic microparticle is an anionic medium molecular weight polymer such as the copolymers of acrylic acid described in U.S. Patent No. 5,098,520 or anionic medium molecular weight sulfonated polymers such as those described in U.S. Patent No. 5,185,062. The inorganic microparticles may preferably be selected from bentonite and silica sol.

According to the invention, the dispersion polymer used to treat the cellulose papermaking slurry can be further prepared from a water-soluble monomer mixture containing at least 5 mol% of a cationic monomer represented by the general formula (I):

in which R₁ is H or CH₃; R₂ and R₃ are each an alkyl group having 1 to 2 carbon atoms; R₄ is benzyl or CH₃; A₁ is an oxygen atom or NH; B₁ is an alkyl group having 2 to 4 carbon atoms or a hydroxypropyl group and X is a counter anion.

The above water-soluble monomer mixture is soluble in an aqueous solution of the polyvalent anionic salt. However, the polymer produced from the monomer mixture is insoluble in the aqueous solution of a polyvalent anionic salt. The polymer of the monomer mixture can also be used as a seed polymer. The seed polymer is described in detail below.

The above cationic monomer; represented by the general formula (I) is preferably a quaternary ammonium salt obtained by the reaction of methyl chloride or benzyl chloride and dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminohydroxypropyl acrylate, dimethylaminopropylacrylamide, dimethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, and dimethylaminopropyl methacrylamide.

The concentration of the above-mentioned monomers in the polymerization reaction mixture is suitably in the range of 1.0 to 30 wt.% for the quaternary ammonium chloride salt. Preferably, the concentration is 10 to 20 wt.%. For the quaternary benzylammonium chloride salts, the concentration in the polymerization reaction mixture is suitably in the range of 1.0 to 35 wt.%. Preferably, the concentration is 10 to 20 wt.%.

Monomers which are preferably copolymerized with the cationic monomer represented by the general formula (I) include acrylamide, methacrylamide and the cationic monomers represented by the general formula (II):

in which R₅ is H or CH₃; R₆ and R₅ are each an alkyl group having 1 to 2 carbon atoms; R₈ is H or an alkyl group having 1 to 2 carbon atoms; A₂ is an oxygen atom or NH; B₂ is an alkyl group having 2 to 4 carbon atoms or a hydroxypropyl group and X₂ is a counter anion.

Preferred monomers represented by the formula (II) include the ammonium salts of dimethylaminoethyl acrylate, diethylaminoethyl acrylate; dimethylaminopropylacrylamide, diethylaminopropylacrylamide and dimethylhydroxypropylacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminopropylmethacrylamide, diethylaminopropylmethacrylamide and dimethylhydroxypropylmethacrylate, as well as the methylated and ethylated quaternary salts. Among the more preferred cationic monomers represented by the general formula (II) are the salts and methylated quaternary salts of dialkylaminoethyl acrylate and dialkylaminoethyl methacrylate.

The polyvalent anionic salt to be incorporated into the aqueous solution is suitably a sulfate, a phosphate or a mixture thereof. Preferred salts include ammonium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, ammonium hydrogen phosphate, sodium hydrogen phosphate and potassium hydrogen phosphate. In the present invention, these salts can each be used as an aqueous solution thereof having a concentration of 15% or more.

A dispersant is present in the aqueous solution of anionic salt in which polymerization of the above monomers takes place. The dispersant is a water-soluble cationic polymer of high molecular weight. The dispersant is soluble in the above-mentioned aqueous salt solution. The dispersant is preferably used in an amount of 1 to 10% by weight based on the total weight of the monomers. The dispersant is composed of 20 mol% or more of cationic monomer units represented by the formula (II). Preferably, the remaining mol% is acrylamide or methacrylamide. The behavior of the dispersant is not greatly affected by the molecular weight. However, the molecular weight of the dispersant is preferably in the range of 10,000 to 1,000,000 g/mol (Dalton). A polyhydric alcohol, such as glycerin or polyethylene glycol, can be present in the polymerization system. The deposition of the fine particles is carried out uniformly in the presence of these alcohols.

For the polymerizations, a conventional water-soluble radical-forming agent can be used, but preferably water-soluble azo compounds such as 2,2'-azobis(2-amidinopropane) hydrochloride and 2,2'-azobis(N,N'-dimethyleneisobutylamine) hydrochloride are used.

A seed polymer may be added to the above monomers before starting the polymerization for the purpose of obtaining a fine dispersion. The seed polymer is a water-soluble cationic polymer which is insoluble in the aqueous solution of the polyvalent anionic salt. The seed polymer is preferably a polymer prepared from the above monomer mixture by the method described herein. Nevertheless, the monomer composition of the seed polymer need not always be the same as that of the water-soluble cationic polymer formed in the polymerization. However, like the water-soluble polymer formed in the polymerization, the seed polymer should contain at least 5 mol% of cationic monomer units represented by the general formula (I). The seed polymer used in a polymerization reaction may be the water-soluble polymer that was produced in a previous reaction using the same monomer mixture.

Examples

The following examples are set forth to describe preferred embodiments and utilities of the invention and are not intended to limit the invention unless otherwise stated in the appended claims. In the following examples, terms used together throughout have the following meanings.

Microparticle A (colloidal silicon dioxide)

Dispersed silica in water with a particle size of 4 nm.

Microparticles B

Copolymer of acrylic acid

Microtelichen G (Bentonite)

Hydrated suspension of powdered bentonite in water.

Dispersion polymers

Polymer A 10 mol% DMAEA, BCQ RSV 19.6 dl/g

Polymer B 10 mol% DMAEA, MCQ RSV 21.4 dl/g

Polymer C 20 mol% DMAEA, MCQ RSV 27.6 dl/g

Latex polymer

Polymer D 10 mol% DMAEA, MCQ RSV 19.7 dl/g

The reduced specific viscosity (RSV) was measured as the concentration of 0.045% polymer in solution in a 0.125 M NaNO3 solution.

The Britt Jar test used in Examples 1 to 3 used a Britt CF Dynamic Drainage Jar developed by KW Britt of New York State University, which generally consists of an upper chamber with a capacity of about 1 liter and a lower drainage chamber, the chamber being separated by a support screen and a drainage screen. Below the drainage chamber is a downwardly extending flexible tube which is connected to a clamp for The upper chamber is equipped with a variable speed, high torque motor fitted with a 51 mm (2 inch) three-bladed propeller to create controlled shear conditions in the upper chamber. The test was carried out by placing the cellulosic pulp in the upper chamber and then subjecting the pulp to the following sequence:

Time Measure

0 seconds Start of shear stirring at 750 rpm (add starch if required)

10 seconds Add the cationic polymer, increase the speed to 2000 rpm

40 seconds Reduce shear stirring to 750 rpm

50 seconds addition of the microparticle

60 seconds Open the pipe clamp to start draining, and continue draining for 30 seconds

The material thus drained from the Britt jar (the "filtrate") is collected and diluted with water to 1 in 4 of its initial volume. The turbidity of the thus diluted filtrate, measured in formazin turbidity units or FTUs, is then determined. The turbidity of such a filtrate is inversely proportional to the papermaking retention property. The lower the turbidity value; the higher the retention of filler and/or fines. The turbidity values were determined using a Hach spectrophotometer, model DR2000.

The turbidity values (FTU) that were determined were converted into (percent improvement) values using the formula:

Percent improvement = 100 · (Turbidityu - Turbidityt)/Turbidityu

where Turbidityu is the turbidity reading for the blank sample to which no polymer or microparticles were added, and where Turbidity is the Turbidity reading result of the test using polymer or polymer and microparticles.

Filtration test

The filtration tests used in Examples 1 to 8 measured the rate of drainage (water removal) of the test pulp that had been subjected to various chemical treatments. A filtration cell mounted upright on a tripod was used. The capacity of this cell is approximately 220 ml. A 200 mesh drainage screen (76 µm screen with 8% openings) served as the filter medium. The pulp was filtered by gravity. The filtrate was collected in a beaker placed on a scale below the cell. This scale was connected to a computer so that the displayed weight was continuously recorded over time. The computer automatically recorded the change in weight over time.

The cellulose pulp was treated in the Britt Jar mentioned above. The treated pulp was transferred to the cell and filtered until complete. The rate of filtrate collection is an indication of drainage property; the higher the filtrate collection rate, the greater the improvement in drainage.

Test pulp Alkaline test pulp

The cellulosic pulp or slurry used in Examples 1-3 and 8 comprised 70% by weight fiber and 30% by weight filler diluted to a total consistency of 0.5% with formulation water. The fiber was a 60/40 weight blend of bleached hardwood kraft and bleached softwood kraft separately milled to a Canadian Freeness range of 320 to 360 CFS. The filler was a commercial calcium carbonate available in dry form. The formulation water contained 60 ppm calcium hardness (added as CaCl₂), 18 ppm magnesium hardness (added as MgSO₄) and 134 ppm bicarbonate basicity (added as NaHCO₃). The pH of the final thin pulp was pH 7.2.

Acidic test pulp

The cellulosic pulp or slurry used in Examples 4-5 comprised 93% by weight fiber and 7% by weight filler, diluted to a total consistency of 0.54% with formulation water. The fiber was a 50/50 weight blend of bleached hardwood kraft and bleached softwood kraft, separately milled to a Canadian Freeness range of 320 to 360 C.F.S. The fillers were clay as predispersed kaolin and titanium dioxide, commercially supplied in dry form. The pH was adjusted to pH 4.00 using dilute sulfuric acid, after which alum (0.005% of the final slurry) and sizing resin (0.0025% by weight of the final slurry) were added. The formulation water contained 60 ppm calcium hardness (added as CaCl₂), 18 ppm magnesium hardness (added as MgSO₄), and 1134 ppm bicarbonate basicity (added as NaHCO₃).

Wavy coated test pulp

The pulp used in Examples 6 and 7 was obtained as a thick pulp (consistency of 4.11%) from a paper mill. It consisted of a mixture of OCC, newsprint and cardboard. It was diluted to a total consistency of 0.8% with formulation water containing 60 ppm calcium hardness (added as CaCl2), 18 ppm magnesium hardness (added as MgSO4) and 1134 ppm bicarbonate basicity (added as NaHCO3). The final pH of the thin pulp was pH 6.5. The percentage of ash of the thin pulp was 7.3 wt%.

example 1

Using the alkaline test pulp described above, the Britt Jar test, also described above, was used to determine the retention behavior of the Polymer A dispersion compared to the reverse Polymer D emulsion, with Microparticle A as the microparticle. In each test, cationic potato starch was added to the test pulp at a rate of 4.5 kg/1000 kg (10 lb/ton) dry weight of slurry solids. The various programs tested are shown in Table 1 below. The test results are reported in Table 1 below as turbidity values of the dilute filtrate (FTU) and (percent improvement) as defined above for each of the programs tested.

The drainage performance of these programs was measured for the same alkaline pulp using the filtration test described above. In each test, starch was added to the test pulp at a rate of 4.5 kg/1000 kg (10 lb/ton) dry weight of slurry solids. The results are shown in Fig. 1 as plots of filtrate weight collected versus time for each of the programs tested.

Example 2

Using the alkaline test pulp described above, the Britt Jar test, also described above, was used to determine the retention behavior of the Polymer B dispersion compared to the reverse Polymer D emulsion, with Microparticle A as the microparticle. In each test, cationic potato starch was added to the test pulp at a rate of 4.5 kg/1000 kg (10 lb/ton) dry weight of slurry solids. The various programs tested are shown in Table 2 below. The test results are reported in Table 2 below as turbidity values of the dilute filtrate (FTU) and (percent improvement) as defined above, for each of the programs tested.

The drainage performance of these programs was measured for the same alkaline pulp using the filtration test described above. In each test, starch was added to the test pulp at a rate of 4.5 kg/1000 kg (10 lb/ton) dry weight of slurry solids. The results are presented in Fig. 2 as plots of filtrate weight collected versus time for each of the programs tested.

Table I Britt Jar Retention Tests Alkaline pulp Table II Britt Jar Retention Tests Alkaline pulp Example 3

Using the alkaline test pulp described above, the Britt Jar test, also described above, was used to determine the retention behavior of the Polymer C dispersion compared to the reverse Polymer D emulsion, with microparticles A as the microparticles. In each test, cationic potato starch was added to the test pulp at a rate of 4.5 kg/1000 kg (10 lb/ton) dry weight of slurry solids. The various programs tested are shown in Table 3 below. The test results are reported in Table 3 below as dilute filtrate turbidity values (FTU) and (percent improvement) as defined above for each of the programs tested.

Table III Britt Jar Retention Tests Alkaline pulp Example 4

Using the acidic test pulp described above, the filtration test described above was used to determine the drainage behavior of the Polymer A dispersion compared to the reverse Polymer D emulsion, with Microparticle A as the microparticles. The results are shown as graphical Plots of collected filtrate weight versus time for each of the programs tested are shown in Fig. 3.

Example 5

Using the acidic test pulp described above, the filtration test also described above was used to determine the drainage behavior of the Polymer A dispersion compared to the reverse Polymer D emulsion, with Microparticle B as the microparticles. The results are shown in Figure 4 as plots of collected filtrate weight versus time for each of the programs tested.

Example 6

Using the corrugated coated test pulp described above, the filtration test also described above was used to determine the drainage behavior of the Polymer A dispersion, with Microparticle A as the microparticle. The results are shown in Figure 5 as plots of collected filtrate weight versus time for each of the programs tested.

Example 7

Using the corrugated coated test pulp described above, the filtration test also described above was used to determine the drainage behavior of the Polymer A dispersion, with Microparticle B as the microparticle. The results are shown in Figure 6 as plots of collected filtrate weight versus time for each of the programs tested.

Example 8

Using the alkaline test pulp described above, the filtration test also described above was conducted to determine the drainage behavior of the Polymer A dispersion compared to the reverse Polymer D emulsion, with microparticles C as the microparticles. In each test, cationic potato starch was added to the test pulp at a rate of 4.5 kg/1000 kg (10 lb/ton) dry weight of slurry solids. The results are shown in Figure 7 as plots of filtrate weight collected versus time for each of the programs tested.

Legend of Fig. 1 to 7:

blank (no treatment): blank sample (no treatment)

microparticle: microparticles

Claims (7)

1. A papermaking process comprising: forming an aqueous cellulose papermaking slurry, subjecting the slurry to one or more shear stages, adding a mineral filler to the slurry before at least one of the shear stages, adding to the slurry after adding the mineral filler and before at least one of the shear stages from 0.5 to 100 ppm by weight of dry fiber contained in the slurry of a cationic dispersion polymer obtainable by dispersion polymerization of a monomer mixture soluble in an aqueous solution of a polyvalent anionic salt, wherein the polymer is selected from the group consisting of copolymers of acrylamide and quaternary dimethylaminoethyl acrylate methyl chloride salt, quaternary dimethylaminoethyl methacrylate methyl chloride salt, quaternary dimethylaminoethyl acrylate benzyl chloride salt and quaternary dimethylaminoethyl methacrylate benzyl chloride salt, and wherein the polymer is insoluble in the aqueous solution; shearing the slurry; adding to the slurry an amount of microparticles selected from the group consisting of a copolymer of acrylic acid, bentonite and silica sol; draining the slurry to form a sheet; and Drying the leaf to form a sheet of paper. 2. A process according to claim 1, wherein the slurry is drained on a papermaking screen and pumped to the location of the papermaking screen prior to draining. 3. The method of claim 1, wherein the slurry is selected from the group consisting of an acidic pulp slurry, an alkaline chemical pulp slurry, a thermo-mechanical pulp slurry, a mechanical pulp slurry, a recycled pulp slurry, and a ground wood pulp slurry. 4. The method of claim 1, wherein the mineral filler is selected from the group consisting of titanium dioxide, clay and alkaline talc calcium carbonate. 5. A process according to claim 1, wherein the mineral filler is added to the slurry in an amount of 2 to 50 parts per hundred parts by weight of dry fiber contained in the slurry. 6. A process according to claim 1, wherein the dispersion polymer is added to the slurry in an amount of 2 to 40 ppm based on the weight of dry pulp contained in the slurry. 7. A process according to claim 6, wherein the dispersion polymer is added to the slurry in an amount of 4 to 25 ppm based on the weight of dry pulp contained in the slurry.