JP5288538B2 - Paper making method - Google Patents

Description

The present invention relates to a papermaking method capable of achieving improvement in yield, drainage, improvement in water squeezing, and improvement in paper quality without impairing the texture in paper and board making processes.

2. Description of the Related Art Conventionally, in a papermaking process such as coated base paper, PPC paper, high-quality paper, paperboard, and newsprint, various yielding systems have been used in order to improve the yield rate of fine fibers, fillers, and the like. For example, an addition formulation (Patent Document 1) in which a high molecular weight water-soluble cationic polymer is added before the shearing step and bentonite is added after the shearing step, and similarly, a water-soluble cationic polymer is added before the shearing step, As the second stage, a prescription in which anionic polymer microparticles are added is used (Patent Document 2). However, in these yield systems, in order to obtain a further yield effect, when the addition rate is increased, the texture is lowered, or excessive moisture is taken in, so that the drainage is reduced in the wire part, the dryer part. This will cause a decrease in water squeezing and drying efficiency. For this reason, the conventional yield system is in a state where it is impossible to maintain the texture and to improve the yield, drainage and squeezing. There is also a prescription (Patent Document 3) for adjusting the texture by adding a cationic coagulant as the first liquid and adding an anionic polymer as the second liquid. In this case, although the texture is maintained, by addition Significant improvement in yield and drainage cannot be expected. There is a prescription (Patent Document 4) in which a cationic coagulant is added as the first stage, a cationic polymer is added to the second stage, and anionic organic polymer fine particles are added to the third stage for the purpose of blocking anionic trash. Therefore, the management is complicated and the cost is uneconomical.
JP-A-5-239800 JP-A-11-286890 JP 2005-120494 A JP 2005-54311 A

It is an object of the present invention to provide a papermaking method for improving yield, drainage, squeezing, and productivity without impairing the texture in the paper and paperboard papermaking process.

As a result of intensive studies to solve the above problems, in the papermaking process, a yield improver composed of a cationic or amphoteric acrylamide copolymer is added as the first step in the papermaking raw material before papermaking, and the second step as described above. The present invention relates to a papermaking method characterized by adding a water-soluble polymer having a molecular weight lower than that of a yield improver. The water-soluble polymer having a molecular weight lower than that of the yield improver is preferably a cationic or amphoteric water-soluble polymer obtained by dispersion polymerization in the presence of a polyalkyleneimine and / or a modified polyalkyleneimine. In addition, when a cationic or amphoteric water-soluble polymer obtained by dispersion polymerization is added in the presence of the polyalkyleneimine and / or polyalkyleneimine-modified product, the yield is improved without sacrificing the texture, drainage, The present inventors have found that it is possible to improve aqueous properties and have reached the present invention.

In the papermaking process, in the papermaking process, as a first step, a yield improver comprising a cationic or amphoteric acrylamide copolymer is added to the papermaking raw material before papermaking, and in the second step, a water solution having a molecular weight lower than that of the yield improver is added. The functional polymer is added to the stock. The water-soluble polymer having a molecular weight lower than that of the yield improver is preferably a cationic or amphoteric water-soluble polymer obtained by dispersion polymerization, particularly in the presence of a polyalkyleneimine and / or a polyalkyleneimine modified product. .

The water-soluble polymer having a lower molecular weight than the yield improver used in the present invention is a cationic or amphoteric water-soluble polymer obtained by dispersion polymerization, particularly in the presence of a polyalkyleneimine and / or a polyalkyleneimine modified product. Preferably, by adding this water-soluble polymer after the addition of a yield improver, yield improvement, drainage and water squeezing effect can be obtained without impairing the texture, reduction of addition cost, productivity improvement, Improvement of paper quality can be achieved.

The yield improver comprising the cationic or amphoteric acrylamide copolymer of the present invention is not particularly limited in form and can be any of aqueous solution polymerization type, emulsion polymerization type and dispersion polymerization type, but the weight average molecular weight is 700. 10,000 or more, particularly 10 million or more are preferable.

The cationic or amphoteric water-soluble polymer obtained by dispersion polymerization in the presence of polyalkyleneimine and / or polyalkyleneimine-modified product preferably has a weight average molecular weight in the range of 2 million to 10 million, particularly Preferably it is 5 million to 10 million. If it exceeds 10 million, the texture is lowered, which is not preferable.

The above cationic or amphoteric water-soluble polymers are mainly coagulating, but there are many polymers with high molecular weights, so even if they are added as the second stage, yield is improved without breaking the texture. It is thought that it contributes to the effect. Moreover, since it has a high cation equivalent value (meq / g), it is thought that it is excellent in drainage and squeezability.

For the above reasons, when this two-component formulation is used, the yield, drainage and squeezability can be increased while maintaining the texture. It is considered that the texture is maintained in order to appropriately control the distribution state of the pulp fiber and the filler between the flocs formed by the high molecular weight polymer in the first stage by the action mainly of condensation.
In particular, excellent effects are exhibited with high-quality paper, PPC paper, coated base paper, fine coated paper, etc., which need to maintain the texture and increase the yield.

The yield improver comprising the cationic or amphoteric acrylamide copolymer of the present invention and the water-soluble polymer having a molecular weight lower than that of the yield improver are water-soluble polymers, and are represented by the following general formula (1) and / or ( 2) The polymer containing the cationic monomer represented by 2), and the yield improver comprising the first-stage cationic or amphoteric acrylamide copolymer is represented by the following general formula (1) and / or (2) It is assumed that the polymer contains 5 to 50 mol% of a cationic monomer represented by
General formula (1)
R ₁ is hydrogen or a methyl group, R ₂ and R ₃ are an alkyl group or alkoxyl group having 1 to 3 carbon atoms, R ₄ is hydrogen, an alkyl group having 1 to 3 carbon atoms, an alkoxyl group or a benzyl group, A may be different, A is oxygen or NH, B is an alkylene group or alkoxylene group having 2 to 4 carbon atoms, and X ₁ is an anion.
General formula (2)
R ₅ represents hydrogen or a methyl group, R ₆ and R ₇ each represent an alkyl group having 1 to 3 carbon atoms, an alkoxy group or a benzyl group, and X ₂ represents an anion.

The cationic water-soluble copolymer is a copolymer of a cationic monomer and a nonionic monomer exemplified below. That is, the cationic monomer is a cationic vinyl monomer such as a salt of an inorganic acid or an organic acid such as dimethylaminoethyl (meth) acrylate or dimethylaminopropyl (meth) acrylamide, or quaternary ammonium by methyl chloride or benzyl chloride. A copolymer of salt and acrylamide. For example, as a monomer, (meth) acryloyloxyethyl trimethylammonium chloride, (meth) acryloyloxy 2-hydroxypropyltrimethylammonium chloride, (meth) acryloylaminopropyltrimethylammonium chloride, (meth) acryloyloxyethyldimethylbenzyl Examples include ammonium chloride, (meth) acryloyloxy 2-hydroxypropyldimethylbenzylammonium chloride, (meth) acryloylaminopropyldimethylbenzylammonium chloride, and the like. Also, diallylammonium salts such as dimethyldiallylammonium chloride can be used.

The amphoteric water-soluble copolymer can be synthesized by copolymerization of an anionic vinyl monomer and the cationic monomer. Anionic vinyl monomers are acrylamide 2-methylpropane sulfonic acid, styrene sulfonic acid, (meth) allyl sulfonic acid, vinyl sulfonic acid, (meth) acrylic acid, maleic acid or itaconic acid. Use to copolymerize.

Examples of nonionic monomers include (meth) acrylamide, N, N-dimethylacrylamide, vinyl acetate, acrylonitrile, methyl acrylate, 2-hydroxyethyl (meth) acrylate, diacetone acrylamide, and N-vinyl pyrrolidone. N-vinylformamide, N-vinylacetamidoacryloylmorpholine, acryloylpiperazine and the like. Of these, acrylamide is most preferred.

The molar% of the cationic monomer and the nonionic monomer in these cationic water-soluble copolymers is 5 to 50 mol% of the cationic monomer and 50 to 95 mol% of the nonionic monomer. Yes, preferably 10 to 40 mol% of a cationic monomer and 60 to 90 mol% of a nonionic monomer.

Further, the mol% of the cationic monomer and the anionic monomer of the amphoteric water-soluble copolymer is 5 to 50 mol% of the cationic monomer and 5 to 50 mol% of the anionic monomer, Is 10 to 40 mol% of the cationic monomer and 5 to 50 mol% of the anionic monomer.

A typical form of a yield improver comprising a cationic or amphoteric acrylamide copolymer is a dispersion polymerization type comprising a salt water dispersion. A cationic or amphoteric water-soluble polymer comprising a dispersion in brine can be produced by the following operation. That is, a water-soluble polymer comprising a polymer fine particle dispersion dispersed in an aqueous salt solution can be produced by Japanese Patent Application Laid-Open No. 62-15251. In this method, a cationic monomer or a cationic monomer and a nonionic monomer are stirred in a salt aqueous solution in the presence of a dispersant composed of an ionic polymer soluble in the salt aqueous solution. It is made of a dispersion of polymer fine particles having a particle diameter of 100 μm or less. As the dispersant made of an ionic polymer, a homopolymer of dimethyldiallylammonium chloride or (meth) acryloyloxyethyltrimethylammonium chloride or a copolymer with a nonionic monomer is used. The inorganic salts constituting the aqueous salt solution are more preferably polyvalent anion salts, and sulfates or phosphates are suitable. Specifically, ammonium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, ammonium hydrogen phosphate, hydrogen phosphate Examples thereof include sodium and potassium hydrogen phosphate, and these salts are preferably used as an aqueous solution having a concentration of 15% or more.

The yield improver comprising the cationic or amphoteric acrylamide copolymer of the present invention preferably has a weight average molecular weight of 7 million or more, particularly 10 million or more. If the weight average molecular weight is less than 7 million, the yield tends to decrease. To greatly improve the yield, it is 10 million or more, more preferably 15 million or more. The range of the weight average molecular weight is 700 It is preferable that it is 10,000 to 30 million.

As described in the background art, when the amount of the high molecular weight polymer is simply increased, an excessive floc is formed, and the paper quality, particularly the texture is deteriorated. Moreover, since an excessive floc takes in water excessively, the fall of the drainage in a wire part, the squeezing in a dryer part, and the fall of drying efficiency will be caused. There are prescriptions that use anionic inorganic substances and fine-particle polymers in the second stage, and cationic coagulants in the first stage, and anionic polymers in the second stage. It is not possible to expect a significant yield improvement due to an increase in the rate, and an improvement in drainage and water extraction.
Therefore, in the present invention, a high molecular weight polymer is used as the first stage, and a water-soluble polymer having a molecular weight lower than that of the yield improver as the second stage, in particular, a polyalkyleneimine having a weight average molecular weight of 2 million to 10 million and / or When a water-soluble polymer obtained by dispersion polymerization in the presence of a modified polyalkyleneimine is used, a remarkable effect is exhibited.

The addition rate of the yield improver comprising a cationic or amphoteric water-soluble acrylamide copolymer used in the present invention is 0.001 to 0.1% by weight with respect to the total stock dispersion, and is 0.005 to 0.005. 1% by weight is preferred. If the amount is 0.001% by weight or less, the effect may not be exhibited. In addition, the water-soluble polymer having a molecular weight lower than that of the yield improver, in particular, the addition rate of the water-soluble polymer obtained by dispersion polymerization in the presence of polyalkyleneimine and / or polyalkyleneimine-modified product is relative to the total stock dispersion. 0.001 to 0.5% by weight, preferably 0.005 to 0.1% by weight.

As a first step, when a yield improver comprising a cationic or amphoteric water-soluble acrylamide copolymer is added, a strong floc is formed with pulp fibers and fillers due to aggregation and cross-linking adsorption action due to having a high molecular weight.

After the addition of a yield improver comprising a first-stage cationic or amphoteric water-soluble acrylamide copolymer, a water-soluble polymer having a molecular weight lower than that of the yield improver, particularly a polyalkyleneimine, through at least one shearing step. Further, by adding a water-soluble polymer dispersion obtained by dispersion polymerization in the presence of a modified polyalkyleneimine, further improvement in yield, drainage / squeezing effect, and improvement in texture can be obtained. When a high molecular weight acrylamide copolymer is added to the second liquid, the yield can be improved, but the squeezing ability, particularly the texture, is greatly reduced.

The location where the yield improver comprising a cationic or amphoteric water-soluble acrylamide copolymer is added during the papermaking process is assumed to be before the fan pump, at the entrance of the screen, or the like. On the other hand, the water-soluble polymer having a molecular weight lower than that of the yield improver, in particular, the addition location in the papermaking process of the water-soluble polymer dispersion obtained by dispersion polymerization in the presence of polyalkyleneimine and / or polyalkyleneimine modified product is An entrance or exit of the screen is assumed.

The target paper is not particularly limited and can be applied to all kinds of paper. Especially in high-quality paper, PPC paper, coated base paper, fine coated paper, etc. that require improved yield without impairing the texture. The effect is more exhibited.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

(Synthesis example 1) The synthesis example of the yield improving agent (C-1) which consists of an acrylamide type copolymer added to the 1st step is shown. A 4-neck 500 ml separable flask equipped with a stirrer, reflux condenser, thermometer and nitrogen inlet tube was charged with 117.7 g of deionized water, 84.1 g of ammonium sulfate, and 80 wt% acryloyloxyethyltrimethylammonium chloride as a cationic monomer. Product (hereinafter DMQ) 17.7 g and 80% by weight acryloyloxyethyldimethylbenzylammonium chloride (hereinafter DMABC) 6.2 g, 50% by weight acrylamide (hereinafter AAM) 51.9 g, acryloyloxyethyltrimethylammonium chloride as a dispersing agent 22.5 g of a homopolymer (20% by weight liquid, viscosity 6450 mPa · s) was charged. Thereafter, nitrogen was introduced from the nitrogen introduction tube while stirring to remove dissolved oxygen. During this time, the internal temperature was adjusted to 35 ± 2 ° C. using a constant temperature water bath. 30 minutes after nitrogen introduction, 0.45 g of 1% by weight aqueous solution of 2,2′-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride as an initiator (as a monomer) 100 ppm) was added to initiate the polymerization. 0.45 g of the initiator was added after 6 hours from the start of polymerization while maintaining the internal temperature at 35 ± 2 ° C., and the reaction was further completed for 10 hours. This obtained dispersion is designated as prototype 1. The DMQ / DMABC / AAM molar ratio was 16/4/80, the dispersion viscosity was 540 mPa · s, and the weight average molecular weight was 15 million.

(Synthesis example 2) The synthesis example of the water-soluble polymer (C-2) added as a 2nd step is shown. In a reactor equipped with a stirrer and a temperature controller, 50 parts by weight of a 50% by weight polyethyleneimine aqueous solution (weight average molecular weight; 50,000) was dissolved in 21.5 parts of ion-exchanged water, and 28.5 parts of 75% by weight sulfuric acid was cooled. The mixture was added with stirring to adjust the pH to 4.8 to 5.5. A reactor equipped with a stirrer, a nitrogen aeration tube and a temperature controller was charged with 78.0 g of the aqueous solution of polyethylenimine neutralized by the above-mentioned operation, 48.8 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 63.2 g of ion-exchanged water. Were mixed. While substituting with nitrogen, 500 ppm by weight of a 2,2 azobis (N, N-dimethyleneisobutylamidine) dihydrochloride aqueous solution as a polymerization initiator was added by weight per monomer and polymerized at 36 ° C. for 18 hours with stirring. . As a result, a polymer dispersion of fine particles having a particle size of 10 to 100 μm was obtained. The resulting water-soluble polymer dispersion had a weight average molecular weight of 5 million. (Measured with a molecular weight measuring device by static light scattering, DLS-7000 manufactured by Otsuka Electronics Co., Ltd.).

(Synthesis example 3) The synthesis example of the water-soluble polymer (C-3) added as a 2nd step is shown. The monomer of acryloyloxyethyltrimethylammonium quaternary chloride is dissolved in ion-exchanged water so as to have a concentration of 20%, and the pH of the solution is adjusted to 3.5. The monomer aqueous solution is kept at 40 ° C., and nitrogen gas is allowed to flow for 30 minutes to remove oxygen in the solution. 0.1% by weight of 2,2 'azobisamidinopropane dihydrochloride (V50) is added per monomer, and polymerization is carried out by maintaining at 40 ° C. for 20 hours while flowing nitrogen gas. Thereafter, the solution was poured into acetone to precipitate a polymer, and then dried under reduced pressure to obtain a corresponding polymer. The produced water-soluble polymer had a weight average molecular weight of 4 million. (Measured with a molecular weight measuring device by static light scattering, DLS-7000 manufactured by Otsuka Electronics Co., Ltd.).

A yield measurement test was performed using a dynamic jar tester. A 200-mesh wire was used, and the raw material used was a coated papermaking raw material having a solid content concentration of 0.94% by mass and containing 25.1% solid content concentration as Ash content such as light calcium carbonate. The physical properties of papermaking raw materials are pH 7.7, Whatman
No. 41 Cation requirement of filter paper filtrate 0.004 meq / L. SZP according to SZP-06 type manufactured by Mutek was -7.3 mV. As the cation demand, a PCD-03 type manufactured by Mutech was used. 50 ppm added to C-1 as a first liquid, and after stirring for 20 seconds at a rotation speed of 1200 rpm, C-2 was added as 50 ppm to a solid content of the second liquid, After stirring for 10 seconds, the filtrate was collected and ADVANTEC, no. After filtration with two filter papers, SS was measured, and the total yield was measured. Then, the filter paper was ashed at 525 ° C. for 2 hours, and the ash yield was measured. The results are shown in Table 1.

(Comparative example 1) The test similar to Example 1 was implemented using C-1, C-2, C-3, A-1, and A-2. A-1 is an anionic polymer microparticle of water-swellable polyacrylamide particles. That is, a monomer mixture consisting of 88% by mole of acrylamide, 12% by mole of acrylic acid, and 0.5% by weight of methylenebisacrylamide with respect to the monomer was formed into a water-in-oil emulsion using a sorbitan oleate-based hydrophobic surfactant, Water-insoluble particles obtained by polymerization (particle size after dispersion in water was about 700 nm) were used. For A-2, an anionic polyacrylamide salt water dispersion (acrylamide / sodium acrylate = 30 mol% / 70 mol% copolymer, molecular weight 15 million) was used.

The order of addition was C-2 for the first liquid, C-1 for the second liquid, C-1 for the first liquid, C-1 for the second liquid, and C-1 for both the first and second liquids. formulation, one-part first C-1, a two-liquid-th a-1 formulation, one-part first C-1, the formulation of two-component first a-2, one-part eyes against additive versus the stock solids 50ppm or 100 ppm, 50 ppm or 100 ppm of the second liquid was added. These results are shown in Table 1.

( Table 1 )

Example 1 using C-1 as the first stage of the present invention and C-2 as the second stage, compared to Comparative Examples 1-1, 1-5 , and 1-7, the total yield rate, the ash content yield It can be confirmed that the rate has improved.

Using the same paper material as in Example 1, a measurement test of drainage and sheet moisture content was performed using a dynamic drainage tester DDA (Dynamic Drainage Analyzer, manufactured by Matsubo). The papermaking material is put into a DDA stirring tank with a 315 mesh wire at the bottom. 50 ppm added to C-1 as a first liquid, and after stirring for 20 seconds at a rotation speed of 1200 rpm, C-2 was added as 50 ppm to a solid content of the second liquid, After stirring for 10 seconds, the stock was sucked under a reduced pressure of 300 mBar, and the water content of the formed sheet was measured at the time when the sheet was formed on the wire, and the results are shown in Table 1 .

(Comparative Example 2) Using the same paper material as in Example 1, under the same test conditions, a test for measuring the drainage and the moisture content of the formed sheet was performed using a dynamic drainage tester DDA. C-2 as the first liquid, C-1 as the second liquid, C-1 as the first liquid, C-1 as the second liquid, C-1 as the first and second liquid, In the formulation of eye C-1, second fluid A-1, first fluid C-1 and second fluid A-2, 50ppm or 100ppm in the first liquid relative to the solid content of the additive, two liquids The filtration time and the moisture content of the formed sheet were measured when 50 ppm or 100 ppm was added. The results are shown in Table 1 .

C-1 as a one-th present invention, Example 1 using the C-2 as a two-part first is Comparative Example 1 -1, compared to 1-5,1-7, and shortened drainage time It can be confirmed that the drainage is good. Further, the sheet moisture content is low and the water squeezing is improved.
Comparative Example 1-3 In the formulation in which C-1 is added in both the first and second liquids, the drainage time is shortened, but the moisture content is taken in excessively, so that the sheet moisture content is higher than in Example 1 , and the drying efficiency is increased. As a result, it resulted in a decline.

Using the same sample as in Example 1, C-1 is added as the first liquid, C-2 is added as the second liquid, and a handsheet is prepared so that the basis weight is 50 to 52 g / m ^2. And the ground index is M / K
System Inc. It measured by "3-D Sheet Analyzer" by a company. The higher this number, the better the texture. Further, the ISO whiteness of the sheet was measured. The results are shown in Table 3.

(Comparative Example 3) A handsheet was prepared using the same paper material as in Example 1 under the same test conditions, and the texture index and ISO whiteness were measured. C-2 as the first liquid, C-1 as the second liquid, C-1 as the first liquid, C-1 as the second liquid, C-1 as the first and second liquid, In the formulation of eye C-1, second fluid A-1, first fluid C-1 and second fluid A-2, the first liquid is 100 ppm, the second liquid is 100 ppm relative to the solid content of the paper. The texture index and ISO whiteness at the time of addition were measured. The results are shown in Table 2 .

(Table 2 )

In Example 3 , it turns out that a texture index is higher than Comparative Examples 3-1 to 3-5, and the influence on a texture is low. It was also found that the ash content in paper and the ISO whiteness were also increased.

On the other hand, in the prescription in which C-1 was added to both the first and second liquids of Comparative Example 3-3, both the formation index and the ISO whiteness value were greatly reduced. This is considered to be because an excessive floc is formed and the floc is unevenly distributed locally.

From the above, it was found that the papermaking chemical formulation of the present invention improves the yield, drainage and water squeezability, and also increases the ISO whiteness without impairing the texture of the conventional chemical formulation. This means that productivity can be greatly improved in the papermaking process and high-quality paper products can be produced.

Claims (9)

In the papermaking process, a yield improver comprising a cationic or amphoteric acrylamide copolymer is added in front of the fan pump or at the entrance of the screen as the first step, and a water solution having a lower molecular weight than the yield improver as the second step. sex polymer is a paper making method of adding the screen inlet or outlet, the retention aid low water solubility polymer molecular weight water-soluble polymer microparticles and polyalkyleneimine particle size 100μm or less with a cationic and more A papermaking method comprising a water-soluble polymer coexisting with a modified polyalkyleneimine . Water-soluble polymer having a cationic property, said polyalkyleneimine and / or under polyalkyleneimine modified product coexistence monomer 5-100 mol% represented by the following general formula (1), water-soluble non-ionic The papermaking method according to claim 1 , wherein the monomer (mixture) comprising 0 to 95 mol% of the monomer is produced by dispersion polymerization under stirring.
General formula (1)
R ₁ is hydrogen or a methyl group, R ₂ and R ₃ are an alkyl group or alkoxyl group having 1 to 3 carbon atoms, R ₄ is hydrogen, an alkyl group having 1 to 3 carbon atoms, an alkoxyl group or a benzyl group, A may be different, A is oxygen or NH, B is an alkylene group or alkoxylene group having 2 to 4 carbon atoms, and X ₁ is an anion. The papermaking method according to claim 1 or 2 , wherein the polyalkyleneimine-modified product has a structural unit represented by the following general formula (4) and / or (5).
General formula (4)
General formula (5)
However, Equation (4), (5) p in is an integer of 0 to _20, the R 10 _{to R 18} hydrogen, or an alkyl group having 1 to 3 carbon atoms, a hydroxyalkyl group or a benzyl _{group, X} 3 ~ X ₆ is an anion. The polyalkyleneimine modified products, polyalkyleneimine and the following general formula (6) and / or according to claim 1 or 2, characterized by comprising a reaction product of polycationic substance represented by (7) Paper making method.
General formula (6)
General formula (7)
However, equation (6), (7) P in the epoxy group or a halohydrin group, p is an integer of _{0~20, R 23 ~R 26, R} 27 represents hydrogen, an alkyl group having 1 to 3 carbon atoms, A hydroxyalkyl group or a benzyl group, and X _{7 to} X ₁₀ are anions. The papermaking method according to claim 1 or 2 , wherein the polyalkyleneimine-modified product is crosslinked with a polycationic substance represented by the general formula (6). The papermaking method according to any one of claims 1 to 5 , wherein the polyalkyleneimine is polyethyleneimine. The papermaking according to any one of claims 1 to 6 , wherein the polyalkyleneimine and / or the modified polyalkyleneimine coexist in an amount of 50 to 500% by weight with respect to the cationic water-soluble polymer. Method. The water-soluble polymer in which the water-soluble polymer fine particles having a particle size of 100 μm or less and a polyalkyleneimine and / or polyalkyleneimine-modified product coexist has a weight average molecular weight in the range of 2 million to 10 million. The papermaking method according to any one of claims 1 to 6 , wherein the papermaking method is characterized. The papermaking method according to claim 1, wherein the yield improver comprising the cationic or amphoteric acrylamide copolymer has a weight average molecular weight of 7 million or more.