JP7634831B2 - Papermaking method using a retention improvement system - Google Patents

Description

The present invention relates to a papermaking method that uses a retention aid in the papermaking process to improve the retention and drainage of papermaking raw materials. More specifically, the present invention relates to a papermaking method that uses a retention aid in the papermaking process to improve the retention and drainage of papermaking raw materials on the wire by using a retention improvement system.

In the papermaking process for coating base paper, PPC paper, fine paper, paperboard, newsprint, etc., retention aids are used to improve the retention rate on the wire of raw pulp, fine fibers, fillers, papermaking chemicals, etc., or drainage aids (or yield and drainage aids) that emphasize the function of improving drainage as well as retention are used. Generally, polyacrylamide (PAM) polymers are widely used as retention aids, but due to the diversification of papermaking conditions in recent years, effective retention aids and retention systems vary.
As a retention system using two or more liquids, various systems have been devised that take into consideration the ion balance, mainly using PAM-based polymers, in accordance with the papermaking conditions and the properties of the papermaking raw materials. Generally, a system is used in which a cationic polymer is first added to the papermaking raw materials before papermaking. For example, a method of adding a cationic or amphoteric PAM and then an anionic PAM (Reference 1), a method of adding a cationic polymer and then an anionic inorganic substance, bentonite (Reference 2), a method of adding a cationic or amphoteric PAM retention aid and then a water-soluble polymer with a lower molecular weight than the retention aid (Reference 3), etc., are in practical use.
In addition to the general recipe of adding a cationic polymer first, a recipe of adding an amphoteric or anionic polymer first and then adding a cationic polymer has also been proposed. For example, a recipe of adding a water-soluble branched anionic polymer and then adding a cationic or amphoteric polymer (Patent Document 4) and a recipe of adding an anionic polymer and then further adding an anionic polymer (Patent Document 5) have been disclosed. However, in these recipes, if the addition rate is increased to improve the retention rate of the papermaking raw material on the wire, excessive water is taken into the formed flocs, which may result in reduced freeness and water squeezing, or the paper quality may deteriorate, resulting in reduced productivity. Therefore, there is a demand for a retention improvement system that can improve the freeness improvement effect as well as the retention improvement effect on the wire part of the papermaking raw material in order to increase production efficiency.

JP 2001-254290 A JP 62-191598 Publication JP 2009-280925 A Special Publication No. 2010-518268 JP 2010-77546 A

The present invention relates to a method for making paper using a retention aid in the papermaking process, and aims to provide a papermaking method that can improve the retention of paper on the wire without reducing freeness or texture even when the addition rate is increased.

As a result of intensive research into solving the above problems, it was discovered that by adding an anionic water-soluble polymer with specific composition and physical properties to the raw paper material before papermaking, and then adding a cationic coagulant, it is possible to improve the yield and drainage of the raw paper material.

By adding the anionic water-soluble polymer of the present invention to the papermaking raw material before papermaking, and then adding a cationic coagulant, the retention effect can be achieved without reducing drainage or water squeezing, even when the addition rate is increased, thereby improving productivity and paper quality.

一般式（１）
Ｒ_１は水素、メチル基又はカルボキシメチル基、ＱはＳＯ_３ ^―、Ｃ_６Ｈ_４ＳＯ_３ ^―、ＣＯＮＨＣ（ＣＨ_３）_２ＣＨ_２ＳＯ_３ ^― 、あるいはＣＯＯ^―、Ｒ_２は水素又はＣＯＯＹ_２、Ｙ_１あるいはＹ_２は水素又は陽イオンをそれぞれ表わす。
The anionic water-soluble polymer in the present invention is produced by polymerizing an aqueous monomer mixture solution containing 5 to 80 mol % of a monomer represented by the following general formula (1) and 20 to 95 mol % of a nonionic monomer:

General formula (1)
R ₁ represents hydrogen, a methyl group or a carboxymethyl group, Q represents SO ₃ ^-- , C ₆ H ₄ SO ₃ ^-- , CONHC(CH ₃ ) ₂ CH ₂ SO ₃ ^-- or COO ^-- , R ₂ represents hydrogen or COOY ₂ , and Y ₁ and Y ₂ each represent hydrogen or a cation.

The anionic monomer used in producing the anionic water-soluble polymer of the present invention, i.e., the monomer represented by the general formula (1), is in the range of 5 to 80 mol %. If it is less than 5 mol %, the anionic group of the anionic water-soluble polymer will not exert a significant coagulation effect, and if it is more than 80 mol %, it will be difficult to obtain a high molecular weight polymer. The range is preferably 10 to 60 mol %.

Examples of the anionic monomer represented by the general formula (1) include vinylsulfonic acid, vinylbenzenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, methacrylic acid, acrylic acid, itaconic acid, maleic acid , and salts thereof. Two or more of these may be used in combination.

The nonionic monomers used in the present invention include (meth)acrylamide, N,N'-dimethylacrylamide, acrylonitrile, 2-hydroxyethyl (meth)acrylate, diacetone acrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, acryloylmorpholine, etc. Two or more of these may be combined. The molar amount of the nonionic monomer is 20 to 95 mol%, preferably 40 to 90 mol%.

When producing the anionic water-soluble polymer of the present invention, a cationic monomer can be used within a range that does not impair the effect. The amount of cationic monomer used is in the range of 0 to less than 10 mol %, and if it is 10 mol % or more, the function as an anionic water-soluble polymer will decrease. It is preferably less than 5 mol %.

When using cationic monomers in the present invention, the following are available. That is, quaternized products of methyl chloride or benzyl chloride such as dimethylaminoethyl (meth)acrylate and dimethylaminopropyl (meth)acrylamide. Examples include (meth)acryloyloxyethyl trimethylammonium chloride, (meth)acryloyloxy-2-hydroxypropyl trimethylammonium chloride, (meth)acryloylaminopropyl trimethylammonium chloride, (meth)acryloyloxyethyl dimethylbenzylammonium chloride, (meth)acryloyloxy-2-hydroxypropyl dimethylbenzylammonium chloride, and (meth)acryloylaminopropyl dimethylbenzylammonium chloride. Two or more of these can also be combined.

The product form of the anionic water-soluble polymer of the present invention is not particularly limited, and can be produced by a known method. The anionic water-soluble polymer of the present invention can be produced by copolymerizing a monomer mixture containing an anionic monomer and a nonionic monomer. After preparing an aqueous solution of these monomers, the polymerization is carried out by, for example, aqueous solution polymerization, water-in-oil emulsion polymerization, water-in-oil dispersion polymerization, dispersion polymerization in salt water, etc., and then any product form such as an aqueous solution, water-in-oil emulsion, dispersion in salt water, or powder can be used. Among these polymerization methods, water-in-oil emulsion polymerization or dispersion polymerization in salt water is preferred, as it is easy to produce a polymer with a high molecular weight.

The water-in-oil emulsion can be produced as appropriate according to JP-A-55-137147, JP-A-59-130397, JP-A-10-140496, JP-A-2011-99076, etc. That is, a monomer mixture containing an anionic monomer and a nonionic monomer is mixed with water, an oily substance consisting of a water-immiscible hydrocarbon, and at least one surfactant having an effective amount and HLB for forming a water-in-oil emulsion, and the mixture is stirred vigorously to form a water-in-oil emulsion, which is then polymerized.

When the anionic water-soluble polymer of the present invention is produced by dispersion polymerization in salt water, it can be produced appropriately in accordance with JP-A-62-20511, JP-A-10-212320, JP-A-2004-231822, etc. That is, the polymer dispersant that is soluble in the salt water solution is coexisted in the salt water solution, and a mixture of anionic monomers and nonionic monomers is dispersion polymerized to produce the polymer.

In the anionic water-soluble polymer of the present invention, a crosslinkable monomer such as N,N'-methylenebis(meth)acrylamide or triallylamine may be used as a structure modifier during or after polymerization. When a crosslinkable monomer is used, the amount of the crosslinkable monomer is preferably 10 ppm or less based on the total amount of monomers.
The anionic water-soluble polymer in the present invention is preferably a straight-chain polymer. It is preferable that it is produced in the absence of a crosslinkable monomer and has substantially no branched or crosslinked structure. This is because the straight-chain polymer tends to have a higher reactivity with the cationic coagulant added to the second liquid, improving the performance of the retention improvement system in the present invention.

The anionic water-soluble polymer in the present invention needs a high molecular weight to obtain a high cohesive force. The molecular weight is expressed in terms of intrinsic viscosity, and the intrinsic viscosity in a 4% by mass saline solution at 0.5% by mass of the water-soluble polymer measured at 25°C is 10 to 30 dl/g, preferably 15 to 30 dl/g, and more preferably 18 to 30 dl/g. If the intrinsic viscosity is lower than 10 dl/g, the effect of improving the retention rate is significantly reduced, and if it is higher than 30 dl/g, the quality of the paper, especially the texture, tends to deteriorate, which is not preferable. In terms of the weight average molecular weight measured by the intrinsic viscosity method, a range of 10 to 30 million is preferable.

In the present invention, after the anionic water-soluble polymer is added as the first liquid, a cationic coagulant is added as the second liquid. As the cationic coagulant, one or more selected from organic coagulants and inorganic coagulants are used. Examples of organic coagulants include dialkylaminoalkyl (meth)acrylate polymers, vinylamine polymers, ethyleneimine polymers, condensed amine polymers, amidine polymers, diallylamine polymers, and dicyandiamide polymers. Among these, vinylamine polymers and ethyleneimine polymers are preferred. Examples of inorganic coagulants include polyaluminum chloride, aluminum sulfate, aluminum chloride, ferric chloride, ferric sulfate, and polyferric sulfate. Among these, polyaluminum chloride (PAC) or aluminum sulfate (aluminum sulfate) is preferred. In addition, organic coagulants and inorganic coagulants may be used in combination.

Tertiary amino group-containing cationic monomers that serve as structural units of the dialkylaminoalkyl (meth)acrylate polymer of the organic coagulant include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide, diethylaminopropyl (meth)acrylamide, and salts thereof. In addition, quaternary ammonium base-containing cationic monomers formed by monohalogenation of the tertiary amino group-containing cationic monomers include (meth)acryloyloxyethyl trimethyl ammonium chloride, (meth)acryloyloxyethyl dimethyl benzyl ammonium chloride, (meth)acryloylaminopropyl trimethyl ammonium chloride, (meth)acryloylaminopropyl dimethyl benzyl ammonium chloride, (meth)acryloyloxy 2-hydroxypropyl trimethyl ammonium chloride, and the like. Polymers of these cationic monomers alone, polymers of two or more cationic monomers, and copolymers of cationic monomers and nonionic monomers may also be used. Examples of nonionic monomers include (meth)acrylamide, N,N'-dimethylacrylamide, vinyl acetate, acrylonitrile, methyl acrylate, 2-hydroxyethyl (meth)acrylate, diacetone acrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, acryloylmorpholine, etc., and copolymers of one or more of these with cationic monomers can be used. The weight average molecular weight of the dialkylaminoalkyl (meth)acrylate polymer is preferably in the range of 10,000 to 3,000,000.

Examples of vinylamine polymers include polyvinylamines made of acid or alkali modified polymers containing N-vinyl carboxylic acid amide, N-vinyl formamide, N-vinyl acetamide, etc. as essential monomers, and copolymers of vinylamine units with one or more selected from cationic monomers and nonionic monomers used in producing the dialkylaminoalkyl (meth)acrylate polymers. The weight average molecular weight is preferably in the range of 10,000 to 3,000,000.

Examples of ethyleneimine-based polymers include polyethyleneimine and polyethyleneimine derivatives. The weight-average molecular weight is preferably in the range of 10,000 to 3,000,000.

Condensation amine polymers include condensates of epichlorohydrin with monomethylamine, dimethylamine, monoethylamine, diethylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, etc., or condensates of the above aliphatic amine/epichlorohydrin condensates with ethylenediamine, diethylenetriamine, triethylenetetramine, or hexamethylenediamine. The weight average molecular weight is preferably in the range of 1,000 to 100,000.

The amidine polymer can be synthesized by hydrolysis of a copolymer of N-vinyl carboxylic acid amide and (meth)acrylonitrile with an acid. Examples of N-vinyl carboxylic acid monomers include N-vinyl formamide and N-vinyl acetamide. The acid used is preferably an inorganic or organic strong acid, such as hydrochloric acid, nitric acid, or p-toluenesulfonic acid. Acrylonitrile is the most common vinyl nitrile to be copolymerized. The mol % of amidine groups in the molecule after hydrolysis is 5 to 100 mol %, preferably 10 to 100 mol %, and most preferably 20 to 100 mol %. The nonionic structural unit is an unhydrolyzed carboxylic acid amide group and an unreacted nitrile group, and the mol % is 0 to 95 mol %, preferably 0 to 90 mol %, and most preferably 0 to 80 mol %. The weight average molecular weight is preferably in the range of 10,000 to 4,000,000.

Monomers used as the diallylamine polymer include allylamine, diallylmethylamine and their salts, diallyldimethylammonium chloride, etc. These may be polymerized alone or copolymerized with one or more selected from cationic monomers and nonionic monomers used in producing dialkylaminoalkyl(meth)acrylate polymers. The weight average molecular weight is preferably in the range of 10,000 to 4,000,000.

Dicyandiamide-based polymers include water-soluble dicyandiamide-formaldehyde condensates and dicyandiamide-formaldehyde-ammonium chloride condensates. Basically, they are products of condensation of dicyandiamide with formaldehyde in the presence of an acid or its ammonium salt. The weight-average molecular weight is preferably in the range of 10,000 to 500,000.

The cationic equivalent value of these organic coagulants at pH 7 is preferably 3.0 meq/g or more. A preferred range is 3.0 to 22.0 meq/g. When the organic coagulant is completely dissolved so that the polymer concentration is 0.5% by mass, the viscosity of a 4% by mass saline solution (SLV) measured with a rotational viscometer at 25°C is preferably in the range of 1 to 10 mPa·s. A B-type viscometer such as Tokyo Keiki's B8M is used, and the value is measured with a No. 1 rotor at 60 rpm.

The anionic water-soluble polymer and cationic coagulant of the present invention are added to the papermaking raw material before papermaking. Normally, in the papermaking process, the papermaking raw material transported from upstream with a pulp dry solids concentration of 2.0% by mass or more is diluted with white water or clean water just before the papermaking machine to a papermaking raw material with a pulp dry solids concentration of less than 2.0% by mass. Generally, it is diluted to 0.5 to 1.5% by mass, and these are called inlet raw materials or headbox raw materials. A retention aid is added to these raw materials (hereinafter referred to as inlet raw materials) and paper is made. The retention improvement system of the present invention is also applied to inlet raw materials.

The anionic water-soluble polymer and cationic coagulant of the present invention can be added in the papermaking process before or after the fan pump or before or after the screen, which is the shearing process. As long as the order of addition is such that the cationic coagulant is added after the anionic water-soluble polymer of the present invention, the present invention can be applied to any of these addition locations.

The anionic water-soluble polymer in the present invention has a certain high molecular weight, and forms relatively large flocs by coagulation with cationic groups of papermaking chemicals such as cationic starch and paper strength agents. The formed flocs are then gradually broken down into smaller flocs during transportation and shearing processes. Fine flocs are formed by the coagulation action of the unreacted anionic groups in the anionic water-soluble polymer in the flocs and the anionic substances in the papermaking raw material suspension and the cationic coagulant, and paper is made in the wire part. This is thought to be the mechanism by which the yield can be improved without introducing much moisture into the flocs.

The types of paper for which the anionic water-soluble polymer and cationic coagulant of the present invention are used include newsprint, fine printing paper, medium printing paper, gravure printing paper, PPC paper, coated base paper, lightly coated paper, packaging paper, liner and core base paper board, etc. It is effective for papermaking raw materials with a relatively low anion content, i.e., cation demand. Specifically, the anionic water-soluble polymer of the present invention is effective when the cation demand is 0.03 meq/L or less. It is preferably 0.02 meq/L or less. It is also effective even if the papermaking raw material shows cationicity (=anion demand). It is effective when applied to papermaking systems with a high addition rate of cationic or amphoteric starch, synthetic strength agents, and other paper strength agents, or aluminum sulfate. The cation demand is expressed as a value (meq/L) measured using a commercially available particle charge meter (such as PCD-05 model by Mutec Co., Ltd.) for the filtrate from Whatman No. 41 filter paper.

The anionic water-soluble polymer and cationic coagulant in the present invention are used by diluting and dissolving in water to a concentration of 0.01 to 1.0% by mass. The water used for dissolution may be distilled water, ion-exchanged water, tap water, industrial water, or the like. These may also be mixed. The diluted solution may also be further diluted a second or third time.
The anionic water-soluble polymer is added at a rate of 10 to 1000 ppm (pure polymer content) relative to the stock solids concentration. The cationic coagulant is added at a rate of 10 to 5000 ppm (solids content equivalent) relative to the stock solids concentration.

The anionic water-soluble polymer and cationic coagulant of the present 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 retention aids, but it is preferable to use only the retention aid system of the present invention, as this provides greater advantages.

The papermaking method of the papermaking raw material using the anionic water-soluble polymer and cationic coagulant of the present invention will be specifically described below, but the present invention is not limited to the following examples.

(Anionic water-soluble polymer sample)
The anionic water-soluble polymer samples A and B of the present invention were prepared by the usual methods of water-in-oil emulsion polymerization and dispersion polymerization in salt water, respectively. Anionic water-soluble polymer sample C outside the scope of the present invention was prepared by the usual method of water-in-oil emulsion polymerization. The compositions and physical properties of these are shown in Table 1.

単量体組成；ＡＡＣ：アクリル酸、ＡＡＭ：アクリルアミド
製品形態；Ｅ：油中水型エマルジョン、Ｄ：塩水液中分散重合液
固有粘度；水溶性高分子の２５℃において測定した０．５質量％における、４質量％食塩水溶液中の固有粘度。
０．２質量％水溶液粘度；高分子濃度が０．２質量％になるように水で溶解したときの２５℃において測定した粘度（ｍＰａ・ｓ）。 (Table 1)

Monomer composition: AAC: acrylic acid, AAM: acrylamide Product form: E: water-in-oil emulsion, D: dispersion in saline solution Intrinsic viscosity: intrinsic viscosity of water-soluble polymer in 4 mass% saline solution at 0.5 mass% measured at 25°C.
Viscosity of 0.2% by mass aqueous solution: Viscosity (mPa·s) measured at 25° C. when dissolved in water to give a polymer concentration of 0.2% by mass.

(Cationic retention aid sample)
As comparative samples, commercially available cationic retention aids D and E were prepared. Their compositions and physical properties are shown in Table 2.

製品形態；Ｅ：油中水型エマルジョン、Ｄ：塩水液中分散重合液
固有粘度；水溶性高分子の２５℃において測定した０．５質量％における、４質量％食塩水溶液中の固有粘度。 (Table 2)

Product form: E: water-in-oil emulsion, D: dispersion in saline solution Intrinsic viscosity of polymer solution: intrinsic viscosity of water-soluble polymer in 4 mass % saline solution at 0.5 mass % measured at 25°C.

(Cationic Coagulant Sample)
As the cationic coagulant in the present invention, organic coagulant samples were prepared or manufactured from commercially available products. Their compositions and physical properties are shown in Table 3. In addition, as inorganic coagulants, commercially available products PAC (polyaluminum chloride, alumina concentration 10% by mass, stock solution used as 100% by mass solids) and aluminum sulfate (aluminum sulfate, alumina concentration 8% by mass, stock solution used as 100% by mass solids) were prepared.

製品形態；ＡＱ：水溶性重合体液
０．５質量％塩水溶液粘度；４質量％食塩水中に高分子濃度が０．５質量％になるように溶解したときの２５℃において測定した粘度（ｍＰａ・ｓ）。 (Table 3)

Product form: AQ: water-soluble polymer solution 0.5% by weight saline solution viscosity: viscosity (mPa·s) measured at 25° C. when dissolved in 4% by weight saline solution to give a polymer concentration of 0.5% by weight.

(Test Example 1, Drainage Performance Evaluation Test) (Examples 1 to 16)
Drainage performance was evaluated using a dynamic drainage tester DDA (Dynamic Drainage Analyzer, Matsubo). LBKP prepared to a beating degree of 350 mL was diluted with clean water, light calcium carbonate was added, and the pH was adjusted to prepare an inlet stock for testing. The physical properties of the prepared inlet stock were a solids concentration of 13215 ppm, a light calcium carbonate etc. ash solids concentration of 2771 ppm (relative to the stock solids), pH 8.5, and electrical conductivity 36.1 mS/m. The turbidity of the Whatman No. 41 filter paper filtrate of the prepared inlet stock was 299 NTU (using HACH's 2100P type), and the cation demand was 0.011 meq/L (using Mutec's PCD-05 type).
A predetermined amount of the prepared inlet stock was charged into a DDA stirred tank equipped with a 62 mesh wire at the bottom. After stirring for 5 seconds at 1000 rpm, 0.5% by mass of aluminum sulfate was added (relative to the stock solids), stirring was performed for 20 seconds at 1000 rpm, 0.3% by mass of commercially available cationized starch was added (relative to the stock solids), stirring was performed for 20 seconds at 1000 rpm, and then 300 ppm of a 0.1% by mass aqueous solution of sample A in Table 1 was added (pure polymer content) relative to the stock solids as the first liquid, stirring was performed for 20 seconds at 1000 rpm (assuming addition at the screen inlet), and 100 ppm of a 0.1% by mass aqueous solution of sample 1 in Table 3 was added (pure polymer content) as the second liquid, stirring was performed for 10 seconds at 1000 rpm (assuming addition at the screen outlet), and the stock was sucked under a reduced pressure of 300 mBar, and the drainage time and sheet moisture content were measured when a sheet was formed on the wire. This is Example 1. Similar tests were also carried out under similar conditions using the same prepared inlet paper stocks and inorganic coagulant samples shown in Tables 1 to 3 (Examples 2 to 16). The results are shown in Table 4.

(Test Example 1, Drainage Performance Evaluation Test) (Comparative Examples 1 to 14)
Using the same prepared inlet paper stock and inorganic coagulant samples as in Example 1, similar tests were carried out under similar conditions to those in Example 1, but with different samples and addition orders. The results are shown in Table 4.

(Table 4)

In the examples in which a cationic coagulant was added after the addition of the anionic water-soluble polymer of the present invention, the drainage time was shortened and the sheet moisture content was lower than in the comparative examples. In the comparative examples in which the addition method was different from that of the present invention, no results were obtained that showed both a shortened drainage time and a lower sheet moisture content. The addition method of the present invention confirmed the drainage performance and water squeezing performance.

(Test Example 2, Yield Measurement Test) (Examples 17 to 30)
In the retention rate measurement test, a Britt type dynamic jar tester was used (using 30 mesh wire).
A predetermined amount of the same inlet stock as in Example 1 was collected, 0.5% by mass of aluminum sulfate was added (relative to the stock solids), and the stirring speed was 1000 rpm for 20 seconds. 0.3% by mass of cationic starch was added (relative to the stock solids), and the stirring speed was 1000 rpm for 20 seconds. As the first liquid, 300 ppm of a 0.1% by mass aqueous solution of sample A in Table 1 was added (pure polymer content) relative to the stock solids, and the stirring speed was 1000 rpm for 20 seconds (assuming addition at the screen inlet). As the second liquid, 100 ppm of a 0.1% by mass aqueous solution of sample 1 in Table 3 was added (pure polymer content) and the stirring speed was 1000 rpm for 10 seconds (assuming addition at the screen outlet). The filtrate was collected for a certain period of time, filtered with ADVANTEC No. 2 filter paper, and the SS was measured to determine the total retention rate. The filter paper was incinerated at 525°C for 2 hours, and the ash retention rate was measured. This is Example 17. Similar tests were also carried out under similar conditions using the same prepared inlet paper stock and the inorganic coagulant samples shown in Tables 1 and 3 (Examples 18 to 30). The results are shown in Table 5.

(Test Example 2: Yield Measurement Test) (Comparative Examples 15 to 22)
Using the same prepared inlet stock as in Example 1, and the inorganic coagulant samples in Tables 1 and 3, similar tests were carried out under the same conditions as in Example 1, but with different samples and addition orders. The results are shown in Table 5.

(Table 5)

The addition method of the present invention resulted in maintaining or improving the yield rate compared to the comparative example. This means that by applying the addition method of the present invention, the yield effect is equal to or greater than that of the comparative example, and the freeness and squeezing can be improved, and the addition rate of the system for further improving the yield can be increased. On the other hand, in a comparison between comparative examples 15 and 16, by changing the addition of sample A from the screen inlet to the screen outlet, the collapse of the formed flocs due to the stirring shear of the screen is suppressed, and the yield rate is improved, but from the results of comparative example 2 of (Test Example 1. Drainage Performance Evaluation Test), excessive water is taken into the flocs, and the freeness and squeezing are greatly reduced. In addition, adding a high molecular weight polymer to the screen outlet has a large effect on the formation. Therefore, the change to the screen outlet addition or the increase in the addition rate of the anionic water-soluble polymer cannot achieve an improvement in production efficiency. The same can be said for sample B. It was confirmed that the retention effect was relatively low when sample C was added, and even if it was increased, the retention effect of the same level as samples A and B was not obtained, and a certain molecular weight or more was required for the anionic water-soluble polymer.

(Test Example 3. Drainage Performance Evaluation Test) (Example 31)
Drainage performance was evaluated using a dynamic drainage tester (DDA, Matsubo). 2% by mass of aluminum sulfate and 0.2% by mass of paper strength agent (both based on the solid content of the paper) were added to the prepared inlet stock of the coated base paper sheet-making raw material obtained from a certain paper company and used for the test. The physical properties of the prepared inlet stock were a solid content concentration of 14811 ppm, a solid content concentration of light calcium carbonate etc. of ash content of 2727 ppm (based on the solid content of the paper stock), pH 7.7, and electrical conductivity 75.1 mS/m. The turbidity of the Whatman No. 41 filter paper filtrate of the prepared inlet stock was 19 NTU (using HACH's 2100P model), and the cation demand was 0.025 meq/L (using Mutec's PCD-05 model).
A predetermined amount of the prepared inlet stock was put into a DDA stirring tank with a 62 mesh wire at the bottom. After stirring for 5 seconds at 1000 rpm, 0.3% by mass of commercially available cationic starch was added (relative to the stock solids), and stirring was performed for 30 seconds at 1000 rpm. As the first liquid, a 0.1% by mass aqueous solution of sample A in Table 1 was added at 25 ppm (pure polymer content) relative to the stock solids, and after stirring for 20 seconds at 1000 rpm (assuming addition at the screen inlet), as the second liquid, a 0.1% by mass aqueous solution of sample 2 in Table 3 was added at 350 ppm (pure polymer content) relative to the stock solids or 2500 ppm of PAC was added, and after stirring for 10 seconds at 1000 rpm (assuming addition at the screen outlet), the stock was sucked under a reduced pressure of 300 mBar, and the drainage time and sheet moisture content were measured when a sheet was formed on the wire. This is Example 31. The results are shown in Table 6.

(Test Example 3, Drainage Performance Evaluation Test) (Comparative Example 23)
Using the same prepared inlet stock as in Example 31, a similar test was carried out under the same conditions as in Example 31, except that a commercially available anionic water-soluble polymer sample F [anionic polyacrylamide, anionic equivalent value 4.5 meq/g (pH 7), 0.5 mass% salt solution viscosity 143 mPa·s] was added to the first liquid (assuming addition to the screen inlet) at 50 ppm (pure polymer content) based on the stock solids, and 400 ppm of commercially available colloidal silica was added to the second liquid (assuming addition to the screen outlet). The results are shown in Table 6.

(Test Example 4, Yield Measurement Test) (Example 32)
In the retention rate measurement test, a Britt type dynamic jar tester was used (using 30 mesh wire).
A predetermined amount of the same inlet stock as in Example 31 was collected, 0.3% by mass of cationic starch was added (relative to the stock solids), and the mixture was stirred at 500 rpm for 30 seconds. As the first liquid, 25 ppm of a 0.1% by mass aqueous solution of sample A in Table 1 was added to the stock solids (pure polymer content), and after stirring at 500 rpm for 20 seconds (assuming addition to the screen inlet), 350 ppm of a 0.1% by mass aqueous solution of sample 2 was added to the stock solids (pure polymer content) or 2500 ppm of PAC was added to the second liquid, and after stirring at 500 rpm for 10 seconds (assuming addition to the screen outlet), the filtrate was collected for a certain period of time, filtered with ADVANTEC No. 2 filter paper, and the SS was measured to determine the total retention rate. The filter paper was incinerated at 525°C for 2 hours, and the ash retention rate was measured. This is Example 32. These results are shown in Table 6.

(Test Example 4, Yield Measurement Test) (Comparative Example 24)
Using the same prepared inlet stock as in Example 31, a similar test was carried out under the same conditions as in Example 32, except that 50 ppm of commercially available anionic water-soluble polymer sample F [anionic polyacrylamide, product form: water-in-oil emulsion, anion equivalent value: 4.5 meq/g (pH 7), 0.5 mass% salt solution viscosity: 143 mPa·s] was added to the first liquid (assuming addition to the screen inlet) based on the stock solids (pure polymer content), and 400 ppm of commercially available colloidal silica was added to the second liquid (assuming addition to the screen outlet). The results are shown in Table 6.

Table 6

For this papermaking raw material, the anionic PAM + colloidal silica retention improvement system of Comparative Examples 23 and 24 was applied, but it was found that the retention improvement system of the present invention can maintain or improve the yield rate at a lower chemical addition cost than the comparative examples, and can improve drainage and dewatering properties.

Claims (5)

A papermaking method comprising the steps of: adding, to a papermaking raw material prior to papermaking in a papermaking process , an anionic water-soluble polymer having as constituent units 5 to 80 mol % of one or more selected from vinyl sulfonic acid, vinylbenzenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, methacrylic acid, acrylic acid, itaconic acid, maleic acid, or salts thereof , and 20 to 95 mol % of a nonionic monomer, as a monomer represented by the following general formula (1), and having an intrinsic viscosity of 10 to 30 dl/g in a 4 mass % saline solution at 0.5 mass % of the anionic water-soluble polymer measured at 25°C: and then adding a cationic coagulant.

General formula (1)
R ₁ represents hydrogen, a methyl group or a carboxymethyl group, Q represents SO ₃ ^-- , C ₆ H ₄ SO ₃ ^-- , CONHC(CH ₃ ) ₂ CH ₂ SO ₃ ^-- or COO ^-- , R ₂ represents hydrogen or COOY ₂ , and Y ₁ and Y ₂ each represent hydrogen or a cation. The papermaking method according to claim 1, characterized in that the cationic coagulant is one or more selected from organic coagulants such as dialkylaminoalkyl (meth)acrylate polymers, vinylamine polymers, ethyleneimine polymers, condensation amine polymers, amidine polymers, diallylamine polymers, and dicyandiamide polymers. The papermaking method according to claim 1, characterized in that the cationic coagulant is one or more selected from inorganic coagulants such as polyaluminum chloride, aluminum sulfate, aluminum chloride, ferric chloride, ferric sulfate, and polyferric sulfate. The papermaking method according to claim 2, characterized in that the cationic equivalent value of the organic coagulant at pH 7 is 3.0 to 22.0 meq/g. The papermaking method according to claim 2, characterized in that the viscosity measured at 25°C when the organic coagulant is dissolved in a 4% by mass saline solution so that the polymer concentration is 0.5% by mass is 10 mPa·s or less.