Papermaking method for improving yield and drainage properties

Abstract

To provide a papermaking method for a papermaking raw material using a yield improving system in a papermaking process, wherein the papermaking method can achieve improved yield of the papermaking raw material without causing decrease in freeness and water squeezing property while elevating the addition rate.SOLUTION: By applying a papermaking method where a cationic or an amphoteric water-soluble polymer having a specific composition is added to a papermaking raw material before paper-making, followed by adding an anionic water-soluble polymer having a specific composition and an intrinsic viscosity of 7dl / g or under as measured in a 1 normal saline solution at 25°C, improvement of its yield can be achieved without decreasing freeness. Preferably, the intrinsic viscosity of the cationic or amphoteric water-soluble polymer, measured in the 1 normal saline solution at 25°C, is 15-30 dl / g.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a papermaking method using a yield improver in the papermaking process. More specifically, it relates to a papermaking method for improving the yield and drainage property of papermaking raw materials on a wire by a yield improvement system using a yield improver in the papermaking process.

Background Art

[0002] In the papermaking process of coated base paper, PPC paper, fine paper, board paper, newsprint, etc., a yield improver or a drainage property improver (or yield-drainage property improver) that emphasizes the function of improving drainage while improving the yield is used to improve the yield rate of raw pulp, fine fibers, fillers, papermaking chemicals, etc. on the wire. Generally, polyacrylamide-based (PAM-based) polymers are widely used as yield improvers. However, due to the diversification of papermaking conditions in recent years, effective yield improvers and yield improvement systems are different from each other. As a yield improvement system using two or more liquids, various systems considering the ion balance centered on PAM-based polymers have been devised according to papermaking conditions and the properties of papermaking raw materials. For example, a formulation in which anionic PAM is added after adding cationic or amphoteric PAM (Patent Document 1), or a formulation in which a branched anionic water-soluble polymer having a intrinsic viscosity exceeding 3 dl / g and a tanδ at 0.005 Hz of 0.5 or more is added after adding a cationic synthetic polymer having a high intrinsic viscosity (Patent Document 2). However, although the yield rate of papermaking raw materials can be improved by these formulations, in many cases, excessive moisture is taken into the flocs formed by the anionic PAM added in the second liquid, resulting in a decrease in drainage and pressing properties and a decrease in productivity. Therefore, various yield-drainage property improvement formulations that do not reduce drainage and pressing properties have been proposed. For example, a formulation in which bentonite, an anionic inorganic substance, is added after adding a cationic polymer (Patent Document 3), a formulation in which an acrylamide-based polymer having a cationic group and colloidal silica are added (Patent Document 4), etc. can be mentioned. However, while these formulations show a tendency towards improved drainage and dewatering properties, they do not achieve the expected yield. Therefore, there is a need for a yield improvement system that can maintain the yield effect in the wire part of the papermaking raw material while improving the drainage effect, particularly in order to increase production efficiency.

[0003] [Patent Document 1] Japanese Patent Publication No. 2001-254290 [Patent Document 2] Special Publication No. 2002-509587 [Patent Document 3] Japanese Unexamined Patent Publication No. 62-191598 [Patent Document 4] Japanese Patent Publication No. 15391 / 1983 [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention relates to a papermaking method for papermaking raw materials using a yield improver in the papermaking process, and aims to provide a papermaking method that can improve the yield of papermaking raw materials on a wire without reducing the drainability or dewatering properties. [Means for solving the problem]

[0005] As a result of diligent research to solve the above problems, we have found that by adding a cationic or amphoteric water-soluble polymer with a specific composition to the papermaking raw material before papermaking, and then adding an anionic water-soluble polymer with a specific composition and physical properties, it is possible to improve the yield and drainage of the papermaking raw material. [Effects of the Invention]

[0006] By adding a cationic or amphoteric water-soluble polymer according to the present invention to the papermaking raw materials before papermaking, and then adding an anionic water-soluble polymer, the yield effect can be achieved without reducing drainability or dewatering properties, even when the addition rate is increased, thereby improving productivity and paper quality. [Modes for carrying out the invention]

[0007] The cationic or amphoteric water-soluble polymers in the present invention are produced by polymerizing an aqueous monomer mixture containing 5 to 100 mol% of a cationic monomer represented by the following general formula (1), 0 to 30 mol% of an anionic monomer represented by the following general formula (2), and 0 to 95 mol% of a nonionic monomer. The cationic monomer represented by general formula (1) is preferably 5 to 50 mol%, and more preferably 5 to 30 mol%. This is because high molecular weight polymers are more easily obtained when the cationic monomer is within this range. JPEG0007872909000001.jpg2460 General formula (1) R1 represents hydrogen or a methyl group, R2 and R3 represent alkyl or alkoxy groups with 1 to 3 carbon atoms, R4 represents alkyl or alkoxy groups with 1 to 3 carbon atoms, or alkyl or aryl groups with 7 to 20 carbon atoms, A represents oxygen or NH, B represents alkylene groups with 2 to 4 carbon atoms, X1 - These represent anions, respectively. JPEG0007872909000002.jpg2671 General formula (2) R5 is hydrogen, a methyl group, or a carboxymethyl group, and Q is SO3. - , C6H4SO3 - CONHC(CH3)2CH2SO3 - , C6H4COO - Or COO - R6 represents hydrogen or COOY2, and Y1 or Y2 represents hydrogen or a cation.

[0008] Examples of cationic monomers represented by general formula (1) include the following: quaternary compounds of dimethylaminoethyl (meth)acrylate and dimethylaminopropyl (meth)acrylamide, which are composed of methyl chloride or benzyl chloride. Examples include (meth)acryloyloxyethyltrimethylammonium chloride, (meth)acryloyloxy-2-hydroxypropyltrimethylammonium chloride, (meth)acryloylaminopropyltrimethylammonium chloride, (meth)acryloyloxyethyldimethylbenzylammonium chloride, (meth)acryloyloxy-2-hydroxypropyldimethylbenzylammonium chloride, and (meth)acryloylaminopropyldimethylbenzylammonium chloride. It is also possible to combine two or more of these.

[0009] Examples of anionic monomers represented by general formula (2) include vinyl sulfonic acid, vinylbenzene sulfonic acid or 2-acrylamido-2-methylpropanesulfonic acid, methacrylic acid, acrylic acid, itaconic acid, maleic acid, phthalic acid or p-carboxystyrene acid, or salts thereof. Two or more of these may be combined.

[0010] Examples of nonionic monomers used in the present invention include (meth)acrylamide, N,N'-dimethylacrylamide, acrylonitrile, (meth)acrylate-2-hydroxyethyl, diacetoneacrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, and acryloylmorpholine. Two or more of these can be combined.

[0011] The anionic monomer used in the production of the anionic water-soluble polymer in the present invention, i.e., the monomer represented by the general formula (2), is produced by polymerizing an aqueous monomer mixture containing 5 to 80 mol% and 20 to 95 mol% of a nonionic monomer. If the amount is less than 5 mol%, a significant aggregation effect by the anionic groups of the anionic water-soluble polymer cannot be obtained, and if it is more than 80 mol%, it becomes difficult to form proper fine flocs with the unreacted cationic groups in the polymer in the flocs formed by the cationic or amphoteric water-soluble polymer added earlier, and with the cationic substances in the papermaking raw material suspension. Preferably, the amount is in the range of 10 to 60 mol%, and more preferably, in the range of 10 to 50 mol%.

[0012] Examples of anionic monomers represented by general formula (2) include vinyl sulfonic acid, vinylbenzene sulfonic acid or 2-acrylamido-2-methylpropanesulfonic acid, methacrylic acid, acrylic acid, itaconic acid, maleic acid, phthalic acid or p-carboxystyrene acid, or salts thereof. Two or more of these may be combined.

[0013] Examples of nonionic monomers used in the production of anionic water-soluble polymers include (meth)acrylamide, N,N'-dimethylacrylamide, acrylonitrile, (meth)acrylate-2-hydroxyethyl, diacetoneacrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, and acryloylmorpholine. Two or more of these may be combined. The molar amount of nonionic monomer is 20 to 95 mol%, preferably 40 to 90 mol%, and more preferably 50 to 90 mol%.

[0014] The product forms of the cationic or amphoteric water-soluble polymers and anionic water-soluble polymers in the present invention are not particularly limited and can be manufactured by known methods. They can be manufactured by copolymerizing a monomer mixture containing a cationic monomer and / or anionic monomers and a nonionic monomer. Polymerization is carried out by preparing an aqueous solution of these monomers, and then polymerizing by, for example, aqueous solution polymerization, water-in-oil emulsion polymerization, water-in-oil dispersion polymerization, or brine dispersion polymerization, after which any product form can be used, such as an aqueous solution, water-in-oil emulsion, brine dispersion, or powder. For cationic or amphoteric water-soluble polymers, among these polymerization methods, water-in-oil emulsion polymerization or brine dispersion polymerization are preferred because they are easier to produce high molecular weight polymers with. Brine dispersion polymerization is more preferred due to its dispersibility in papermaking raw materials and its reactivity with the anionic water-soluble polymer added as the second liquid.

[0015] As a method for producing a water-in-oil emulsion, it can be appropriately manufactured in accordance with Japanese Patent Publication No. 55-137147, Japanese Patent Publication No. 59-130397, Japanese Patent Publication No. 10-140496, Japanese Patent Publication No. 2011-99076, etc. Specifically, a monomer mixture containing anionic monomers and nonionic monomers is mixed with water, an oily substance consisting of a hydrocarbon immiscible with water, and at least one surfactant having an effective amount and HLB for forming a water-in-oil emulsion, and then vigorously stirred to form a water-in-oil emulsion, after which polymerization is carried out.

[0016] When the cationic or amphoteric water-soluble polymers and anionic water-soluble polymers in the present invention are produced by dispersion polymerization in salt water, they can be manufactured appropriately in accordance with Japanese Patent Publication No. 62-20511, Japanese Patent Publication No. 10-212320, or Japanese Patent Publication No. 2004-231822, etc. That is, they are produced by dispersion polymerization of a mixture of cationic monomers and / or anionic monomers and nonionic monomers in a salt aqueous solution, with a polymer dispersant soluble in the salt aqueous solution present.

[0017] The cationic or amphoteric water-soluble polymer in the present invention may use a crosslinkable monomer such as N,N'-methylenebis(meth)acrylamide or triallylamine as a structure modifier during or after polymerization. This crosslinkable monomer is present in the range of 0.5 to 200 ppm by mass based on the total amount of monomers. Also, using a chain transfer agent such as sodium formate, isopropyl alcohol, sodium methallyl sulfonate, etc. in combination is also effective as a method for adjusting crosslinkability. The addition rate is 0.001 to 1.0% by mass based on the total amount of monomers. Regarding the anionic water-soluble polymer in the present invention, a crosslinkable monomer may be used, but a linear polymer is preferred. It is preferably produced in the absence of a crosslinkable monomer and substantially has no branched structure or crosslinked structure. This is because linear polymers tend to have higher reactivity with the cationic water-soluble polymer added in the first liquid, thus improving the performance of the yield improvement system in the present invention.

[0018] The cationic or amphoteric water-soluble polymer in the present invention requires a high molecular weight to obtain high cohesion. When expressed in terms of intrinsic viscosity, the intrinsic viscosity of the water-soluble polymer in a 1N aqueous sodium chloride solution measured at 25°C is 15 to 30 dl / g, preferably in the range of 18 to 30 dl / g. If the intrinsic viscosity is lower than 15 dl / g, the yield improvement effect is significantly reduced, and if it is higher than 30 dl / g, the quality of the paper, especially the formation, tends to deteriorate, which is not preferable. In terms of the weight average molecular weight by the limiting viscosity method, the range of 10 million to 30 million is preferred.

[0019] On the other hand, for the anionic water-soluble polymer in the present invention, the intrinsic viscosity of the water-soluble polymer in a 1N aqueous sodium chloride solution measured at 25°C is 7 dl / g or less. If the intrinsic viscosity is higher than 7 dl / g, the diffusibility in the papermaking raw material decreases, which is not preferable. Also, to exhibit a certain yield effect, it is preferably 0.3 dl / g or more, preferably 2 dl / g or more, and more preferably 3 dl / g or more. In terms of the weight average molecular weight by the limiting viscosity method, the range of 30,000 to 3 million is preferred.

[0020] In the present invention, after adding the cationic or amphoteric water-soluble polymer of the first liquid, the anionic water-soluble polymer is added as the second liquid.

[0021] The cationic or amphoteric water-soluble polymer and the anionic water-soluble polymer in the present invention are added to the papermaking raw material before papermaking. Usually, in the papermaking process, the papermaking raw material that has been transferred from upstream with a pulp dry solid content concentration of 2.0% by mass or more is diluted with white water or fresh water to a papermaking raw material with a pulp dry solid content concentration lower than 2.0% by mass immediately before the paper machine. The diluted raw material is sprayed from a device called an inlet or a headbox onto the paper machine for papermaking. Generally, it is diluted to 0.5 - 1.5% by mass, and these are called inlet raw materials or headbox raw materials. A yield improver is added to these raw materials (hereinafter referred to as inlet raw materials) for papermaking. The yield improvement system in the present invention is also applied to the inlet raw materials.

[0022] The addition locations in the papermaking process of the cationic or amphoteric water-soluble polymer and the anionic water-soluble polymer in the present invention are applied before and after the fan pump or before and after the screen, which are shearing processes. As long as the anionic water-soluble polymer is added after the addition of the cationic or amphoteric water-soluble polymer in the present invention, it can be applied to any of these addition locations. In the present invention, since the reactivity between the cationic or amphoteric water-soluble polymer of the first liquid and the anionic water-soluble polymer of the second liquid is high, it can exert its effect without passing through the shearing process. That is, it is also possible to add the first liquid and the second liquid after the papermaking raw material passes through the fan pump and before the screen, or to add the first liquid and the second liquid after passing through the screen. The anionic water-soluble polymer of the second liquid is preferably added at the screen outlet after passing through the screen.

[0023] The cationic or amphoteric water-soluble polymer in this invention has a certain high molecular weight. The cationic groups in the cationic or amphoteric water-soluble polymer aggregate and form coarse flocs through neutralization and cross-linking adsorption with the anionically charged cellulose fibers and fillers in the papermaking raw material. Subsequently, the formed flocs are gradually broken down into smaller flocs during transport and shearing processes. After that, anionic water-soluble polymer is added as the second liquid, but if shearing and mixing are insufficient, the diffusion of the formed flocs is slow, and it takes time for floc formation to occur. As a result, coarse flocs are formed, fine fibers and fillers are lost, and moisture is brought into the flocs, resulting in a decrease in yield, filtration, and dewatering efficiency. This phenomenon is more pronounced the larger the molecular weight of the cationic or amphoteric water-soluble polymer in the first liquid. However, in the present invention, even under conditions where shearing and mixing are insufficient, the intrinsic viscosity of the anionic water-soluble polymer added as the second liquid is 7 dl / g or less. It is hypothesized that the reaction between the unreacted cationic groups in the polymer within the flocs and the cationic substances in the papermaking raw material suspension and the anionic water-soluble polymer forms fine flocs, and as a result of papermaking in the wire section, the yield can be improved without introducing too much moisture into the flocs. The papermaking method of the present invention is particularly effective when the shear force on the papermaking raw materials is weak or when the time from the point of addition of the anionic water-soluble polymer to the inlet is short. For example, in order for the yield improver and papermaking raw materials to be mixed and exert their maximum yield effect, it usually takes about 10 seconds from the time the yield improver is added until it reaches the inlet (headbox). However, the anionic water-soluble polymer of the present invention has high diffusivity to the papermaking raw materials and is effective even when the time to reach the inlet is less than 5 seconds.

[0024] The papermaking method described in this invention can be applied to various types of paper, including newsprint, fine printing paper, medium printing paper, gravure printing paper, PPC paper, coated paper, lightly coated paper, packaging paper, and cardboard such as liners and core paper. It is effective for papermaking raw materials with a relatively low anion content, i.e., cation demand. Specifically, the anionic water-soluble polymer in this invention is effective if the cation demand is 0.03 meq / L or less. It is also effective even if the papermaking raw material exhibits cationicity (= anion demand). It is particularly effective when applied to papermaking systems with a high addition rate of cationic or amphoteric starch, synthetic paper strength agents, or aluminum sulfate. The cation demand is expressed as the value (meq / L) measured using a commercially available particle charge meter (such as the PCD-05 model manufactured by BTG) for the filtrate of Whatman No. 41 filter paper.

[0025] The cationic or amphoteric water-soluble polymers and anionic water-soluble polymers in this invention are used after being diluted and dissolved in water to a concentration of 0.01 to 1.0% by mass. The water used for dissolution can be distilled water, deionized water, tap water, industrial water, etc. A mixture of these is also acceptable. Further secondary and tertiary dilutions of the diluted solution are also permitted. The addition rate of cationic or amphoteric water-soluble polymers and anionic water-soluble polymers is in the range of 10 to 1000 ppm (polymer purity) relative to the paper pulp solids concentration.

[0026] The cationic or amphoteric water-soluble polymers and anionic water-soluble polymers in this invention can be used in combination with paper strength agents, sizing agents, and other papermaking chemicals. They may also be used in combination with other yield-improving agents, but applying only the yield-improving system of this invention is preferable as it exhibits greater advantages. [Examples]

[0027] The papermaking method using cationic or amphoteric water-soluble polymers and anionic water-soluble polymers according to the present invention will be described in detail below, but the present invention is not limited to the following examples.

[0028] (Cationic water-soluble polymer sample) Cationic water-soluble polymer samples A and B for the present invention were prepared by conventional methods, specifically by dispersion polymerization in brine and water-in-oil emulsion polymerization, respectively. Their compositions and properties are shown in Table 1.

[0029] (Table 1) TIFF0007872909000003.tif2171 monomer; DMQ: acryloyloxyethyltrimethylammonium chloride, AAM: acrylamide Product form; D: Dispersed polymerization solution in brine, E: Water-in-oil emulsion Intrinsic viscosity; the intrinsic viscosity of a water-soluble polymer in a 1 N saline solution, measured at 25°C.

[0030] (Anionic water-soluble polymer sample) Anionic water-soluble polymer samples 1-4 and anionic water-soluble polymer samples 5-7, which fall outside the scope of the present invention, were prepared by conventional methods: aqueous solution polymerization, water-in-oil emulsion polymerization, and dispersion polymerization in brine, respectively. Their compositions and properties are shown in Table 2.

[0031] (Table 2) TIFF0007872909000004.tif4591 Monomer composition; AAC: Acrylic acid, AAM: Acrylamide Product form; AQ: Aqueous solution polymer, E: Water-in-oil emulsion, D: Dispersed polymerization solution in brine Intrinsic viscosity; the intrinsic viscosity of a water-soluble polymer in a 1 N saline solution, measured at 25°C.

[0032] (Example 1) (Water filtration performance evaluation test) The filtration performance was evaluated using a Dynamic Drainage Analyzer (DDA, PulpEye). Cardboard was disintegrated, and a pulp was prepared to a degree of beating of 270 mL. This pulp was then diluted with clean water to a pulp solid content of 1% by mass, and the pH was adjusted before being used as the prepared inlet pulp for the test. The physical properties of the prepared inlet pulp were pH 7.1 and electrical conductivity 86.6 mS / m. The SZP of the prepared inlet pulp was 7.2 mV, the turbidity of the Whatman No. 41 filter paper filtrate was 38 NTU (using a HACH 2100P filter), and the cation demand was 0.023 meq / L (using a BTG PCD-05 filter). A predetermined amount of prepared inlet pulp was placed in a DDA stirring tank equipped with a wire at the bottom. After stirring at 600 rpm for 5 seconds, 0.5% by mass of commercially available cationized starch was added (relative to the pulp solids), and the mixture was stirred at 600 rpm for 40 seconds, then at 200 rpm for 5 seconds. As the first liquid, 240 ppm of a 0.1% by mass aqueous solution of sample A from Table 1 was added relative to the pulp solids (polymer purity), and after stirring at 200 rpm for 3 seconds (assuming addition at the screen inlet), 100 ppm of a 0.1% by mass aqueous solution of sample 1 from Table 2 was added as the second liquid (polymer purity), and after stirring at 200 rpm for 4 seconds (assuming addition at the screen outlet), the pulp was aspirated under reduced pressure of 300 mBar, and the filtration time and sheet moisture content were measured at the point when a sheet was formed on the wire. Similar tests were also conducted by changing the combination of the first liquid sample from Table 1 and the second liquid sample from Table 2. These results are shown in Table 3.

[0033] (Comparative Example 1) Using the same prepared inlet pulp as in Example 1, similar tests were conducted under similar conditions using the cationic water-soluble polymer samples in Table 1, the anionic water-soluble polymer samples 5-7 in Table 2, and commercially available colloidal silica (sample 8). The results are shown in Table 3.

[0034] (Table 3) TIFF0007872909000005.tif8891

[0035] In the example in which an anionic water-soluble polymer sample was added after the cationic water-soluble polymer sample in the present invention, the filtration time was shortened and the sheet moisture content was lower compared to the comparative example. In comparative examples of addition methods outside the scope of the present invention, the results showing both a shortened filtration time and a decrease in sheet moisture content simultaneously were not obtained. It was confirmed that the papermaking method in the present invention has superior filtration and dewatering performance.

[0036] (Example 2) (Yield rate measurement test) Yield rate measurement tests were conducted using a Dynamic Drainage Analyzer (DDA, PulpEye). A predetermined amount of the same prepared inlet pulp as in Example 1 was placed in a DDA stirring tank with a wire at the bottom. After stirring at 600 rpm for 5 seconds, 0.5% by mass of cationized starch was added (relative to the pulp solids), and the mixture was stirred at 600 rpm for 40 seconds, then at 200 rpm for 5 seconds. As the first liquid, 240 ppm of a 0.1% by mass aqueous solution of Sample A from Table 1 was added relative to the pulp solids (polymer purity), and after stirring at 200 rpm for 3 seconds (assuming addition at the screen inlet), 100 ppm of a 0.1% by mass aqueous solution of Sample 1 from Table 2 was added relative to the pulp solids (polymer purity), and after stirring at 200 rpm for 4 seconds (assuming addition at the screen outlet), the pulp was aspirated under reduced pressure of 300 mBar, and the filtrate was collected when a sheet formed on the wire. After filtration with ADVANTEC No.2 filter paper, the SS was measured and the total yield was determined. Furthermore, the same tests were conducted by changing the combination of the first liquid sample in Table 1 and the second liquid sample in Table 2. The results are shown in Table 4.

[0037] (Comparative Example 2) Using the same prepared inlet pulp as in Example 1, the same tests were conducted under the same conditions as in Example 2, using the cationic water-soluble polymer sample from Table 1, the anionic water-soluble polymer sample 6 from Table 2, and commercially available colloidal silica (sample 8). The results are shown in Table 4.

[0038] (Table 4) TIFF0007872909000006.tif4491

[0039] The papermaking method of the present invention was found to be able to maintain or improve yield and improve drainability and dewatering compared to the comparative example.

Claims

1. A papermaking method characterized by adding a cationic or amphoteric water-soluble polymer, comprising 5 to 100 mol% of a cationic monomer represented by the following general formula (1), 0 to 30 mol% of an anionic monomer represented by the following general formula (2), and 0 to 95 mol% of a nonionic monomer, to the papermaking raw materials before papermaking in the papermaking process, and then adding an anionic water-soluble polymer, comprising 5 to 80 mol% of the monomer represented by the following general formula (2) and 20 to 95 mol% of a nonionic monomer, wherein the anionic water-soluble polymer has an intrinsic viscosity of 7 dl / g or less in a 1 N saline solution measured at 25°C. General formula (1) R １ R is a hydrogen or methyl group. ２ , R ３ R is an alkyl or alkoxy group having 1 to 3 carbon atoms. ４ is an alkyl or alkoxy group having 1 to 3 carbon atoms, or an alkyl or aryl group having 7 to 20 carbon atoms, A is oxygen or NH, B is an alkylene group having 2 to 4 carbon atoms, X １ － These represent anions, respectively. General formula (2) R ５ is hydrogen, a methyl group or a carboxymethyl group, Q is SO ３ － , C ６ H ４ SO ３ － , CONHC(CH ３ ) ２ CH ２ SO ３ － , C ６ H ４ COO － or COO － , R ６ is hydrogen or COOY ２ , Y １ or Y ２ each represents hydrogen or a cation.

2. The papermaking method according to claim 1, characterized in that the intrinsic viscosity of the cationic or amphoteric water-soluble polymer in a 1 N saline solution measured at 25°C is 15 to 30 dl / g.

3. The papermaking method according to claim 1, characterized in that the location of addition of the anionic water-soluble polymer in the papermaking process is the screen exit.

4. The papermaking method according to claim 1 or 2, characterized in that the cationic or amphoteric water-soluble polymer is in the form of a dispersion in saline solution.

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