JP7571996B2 - A papermaking additive that enhances the effectiveness of paper strength agents - Google Patents

Description

The present invention relates to a papermaking additive that enhances the effect of paper strength agents in the papermaking process and a method for enhancing the effect of paper strength agents.

Polyacrylamide-based paper strength agents are used as paper strength enhancers that impart strength to paper. Polyacrylamide-based paper strength enhancers are classified into anionic, cationic, and amphoteric types according to their ionicity. Currently, amphoteric paper strength enhancers are the mainstream in terms of performance. Amphoteric polyacrylamide-based paper strength enhancers are made of amphoteric acrylamide-based water-soluble polymers obtained by copolymerizing acrylamide with various polymerization components such as cationic monomers and anionic monomers (Patent Document 1). Amphoteric acrylamide-based water-soluble polymers form polyion complexes. Polyion complexes are formed by electrostatic interactions between cationic and anionic groups. It is known that amphoteric acrylamide-based water-soluble polymers exert a paper strength enhancing effect by forming polyion complexes.
In recent years, with the advancement of recycling waste paper and closed systems, fine fibers and dissolved electrolytes have accumulated in the papermaking system, and the electrical conductivity of the papermaking system has tended to increase. As a result, amphoteric paper strength agents in particular are prevented from forming ion complexes, and are unable to exert their full effect. However, increasing the amount of paper strength agents added leads to deterioration of water quality, which is undesirable from an environmental perspective. Therefore, from an environmental perspective, there is a need to improve the effect of paper strength agents without increasing the amount added.
As a method for improving the effect of a paper strength agent used in the papermaking process, for example, a method of contacting a paper strength agent with an oxidizing agent at a specific concentration has been disclosed (Patent Document 2). However, this method has undesirable effects such as adverse effects on equipment due to the use of the oxidizing agent and reduced effects of papermaking chemicals such as retention aids.

JP 2012-251252 A Patent No. 6664627

The present invention aims to provide a papermaking additive that can improve the effectiveness of paper strength agents without adversely affecting the environment or equipment during the papermaking process.

As a result of intensive research to solve the above problems, it was discovered that by using a polymer having a specific composition together with a paper strength enhancer, the paper strength enhancing effect of the paper strength enhancer is enhanced, and the amount of paper strength enhancer used can be reduced.

According to the present invention, by using a polymer having a specific composition together with a paper strength enhancer, the paper strength-increasing effect of the paper strength enhancer is promoted, and the amount of paper strength enhancer used can be reduced.

The present invention will be described in detail below.
The polymer of the present invention can be obtained by any method such as aqueous solution polymerization, emulsion polymerization, dispersion polymerization, suspension polymerization, etc. The aqueous solution polymerization will be described below.
The polymer of the present invention can be obtained by polymerizing a monomer component having a cationic monomer as an essential component. The polymerization can be carried out by adding a monomer mixture, water, a radical polymerization initiator, and optionally a surfactant to a predetermined reaction vessel, stirring and heating the mixture in an inert gas atmosphere such as nitrogen gas, to obtain the target polymer.

Among the cationic monomers, examples of the tertiary amino group-containing cationic monomers include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide, diethylaminopropyl (meth)acrylamide, and salts thereof.
Examples of the quaternary ammonium base-containing cationic monomer 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, etc. Also included are diallyl methyl amine, diallyl benzyl amine, diallyl dimethyl ammonium chloride, diallyl methyl benzyl ammonium chloride, etc.
The content of the cationic monomer is 50 to 100% by mass, preferably 60 to 100% by mass, and more preferably 60 to 99% by mass, based on the total amount of the monomers.

The polymer in the present invention may further contain nonionic monomers, hydrophobic monomers, etc. as polymerization components.

Examples of nonionic monomers include acrylamide, dimethylacrylamide, diethylacrylamide, isopropylacrylamide, hydroxyethylacrylamide, vinylpyrrolidone, vinylformamide, glycerol (meth)acrylate, hydroxyethyl (meth)acrylate, etc. Two or more of these may be used in combination.
The amount of the nonionic monomer is 0 to 50% by mass, preferably 0 to 30% by mass, based on the total amount of the monomers.

In the present invention, the hydrophobic monomer means a monomer having a solubility of 2% by mass or less in water at 20° C. Examples of hydrophobic monomers include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, octyl (meth)acrylate, stearyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, styrene, ethylstyrene, etc. Two or more of these may be used in combination.
The amount of the hydrophobic monomer is 0 to 50% by mass, preferably 0 to 40% by mass, and more preferably 1 to 40% by mass, based on the total amount of the monomers.

Furthermore, an anionic monomer and a crosslinking monomer may be contained to the extent that the effect is not impaired.
Examples of the anionic monomer include (meth)acrylic acid, itaconic acid, maleic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and salts thereof. Two or more of these may be used in combination.
Examples of the crosslinkable monomer include methylenebisacrylamide, ethylene glycol di(meth)acrylate, N-methylolacrylamide, triallyl isocyanate, and divinylbenzene. Two or more of these may be combined. The addition rate of the crosslinkable monomer is preferably 1% by mass or less based on the total monomers.

When using a hydrophobic monomer during polymerization, a surfactant can be used. The surfactant is a substance having a hydrophilic group and a hydrophobic group in the molecule. Neutral surfactants include polyoxyalkylene alkyl ethers, polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate, polyoxyethylene alkyl ethers such as polyoxyethylene cetyl ether, polyoxyethylene oleyl ether and polyoxyethylene lauryl ether, sorbitan fatty acid esters such as sorbitan monooleate and sorbitan monostearate, and polyoxyethylene higher alcohol ethers such as pentaoxyethylene oleyl alcohol ether. Anionic surfactants include sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and naphthalenesulfonate-formalin condensates. Cationic surfactants include dodecyltrimethylammonium chloride, stearyltrimethylammonium chloride, and distearyldimethylammonium chloride. Two or more of these can also be combined. Polymerization in water in the presence of a surfactant acts to finely disperse the hydrophobic monomer, promoting copolymerization. If the amount of surfactant is small, the effect of finely dispersing the monomer is small, and if the amount is too large, it can cause foaming when dissolved or used. The surfactant addition rate is 0.01% to 5% by mass, preferably 0.05% to 3% by mass, and more preferably 0.1% to 1% by mass, based on the total monomer.

In the present invention, a chain transfer agent can be used. Examples of the chain transfer agent include alkyl mercaptans, thioglycolic acid and its esters, isopropyl alcohol, allyl alcohol, allylamine, sodium hypophosphite, etc. Also included are monomers such as methallylsulfonates, such as sodium methallylsulfonate, potassium methallylsulfonate, and ammonium methallylsulfonate.

The polymerization initiator may be, for example, an azo-based polymerization initiator such as 2,2'-azobis[2-(5-methyl-imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, or 2,2'-azobis-2-amidinopropanedihydrochloride. Other examples include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate, and peroxides such as hydrogen peroxide and benzoyl peroxide. These may be used alone, or may be used as a redox-based polymerization initiator in combination with a reducing agent such as a sulfite or hydrogen sulfite. The addition rate of the polymerization initiator is 0.01% to 2% by mass, preferably 0.1% to 1% by mass, based on the total monomer.

The polymerization concentration is 10% by mass to 80% by mass in terms of monomer concentration, and preferably 15% by mass to 60% by mass.
The polymerization reaction is usually carried out at a temperature of 30° C. to 100° C. for a time of 0.5 to 20 hours.

The viscosity of the obtained polymer in a 1% by weight aqueous solution is preferably 5 to 200 mPa·s. More preferably, it is 15 to 170 mPa·s. The viscosity is measured with a B-type viscometer at 60 rpm and 25°C. If the viscosity is lower than this range, the paper strength enhancing effect will be insufficient. If the viscosity is higher than this range, the solubility will decrease and handling will be difficult. As the B-type viscometer, a general-purpose product such as the B8M model or TVB-10M model manufactured by Toki Sangyo Co., Ltd. is appropriately used. If the viscosity is 100 mPa·s or less, a No. 1 rotor is used.

The effect of enhancing the effect of the polymeric paper strength agent in the present invention will now be described.
It is believed that the cationic group portion of the strength agent interacts with the carboxyl group of the pulp to exert the paper strength enhancing effect. However, the distribution of the carboxyl group of the pulp is not uniform, and the strength agent is preferentially distributed in the area with a high density of carboxyl groups, and the distribution of the strength agent on the pulp is also uneven, and it is believed that the paper strength enhancing effect cannot be fully exerted. It is believed that by adding the polymer with a high density of cationic groups in the present invention, the polymer is preferentially adsorbed to the area with a high density of carboxyl groups, uniformizing the distribution of the strength agent on the pulp and promoting the paper strength enhancing effect.
It is known that cationic polymers copolymerized with hydrophobic monomers form micelles in water. Cationic polymers copolymerized with hydrophobic monomers are believed to effectively block localized carboxymethyl groups on the pulp, uniformly distribute the paper strength agent on the pulp, and further promote the paper strength enhancement effect. In addition, micellar cationic polymers have an increased cationic group density, which is believed to contribute to improving the adhesion between pulps.

The location where the polymer in the present invention is added is the vicinity of the location where the paper strength agent is added. Generally, the paper strength agent is added to the raw paper material before papermaking where the pulp dry solid content is 2.0 mass% or more upstream of the papermaking process, such as a refiner, a raw material blending chest, a mixing chest, a machine chest, a seed box, etc. In this case, the polymer in the present invention is also added to the raw paper material.
In the papermaking process, high-concentration papermaking raw material with a pulp dry solids concentration of 2.0% or more is transferred from upstream and diluted with white water or fresh 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 material or headbox raw material. In some cases, a paper strength agent is added to these raw materials (hereinafter referred to as inlet raw material), and in this case, the polymer of the present invention is also added to the papermaking raw material. In this case, the location of addition in the process is before or after the fan pump or before or after the screen, which is the shearing process.
The order of addition of the paper strength enhancer may be before or after the paper strength enhancer, or they may be added simultaneously. In view of the mechanism of the paper strength enhancing effect in the present invention, it is preferable to add the paper strength enhancer before or simultaneously with the addition of the paper strength enhancer.

The types of paper to which the polymer-based papermaking additive of the present invention is applied include newsprint, wood-free printing paper, medium-quality printing paper, gravure printing paper, PPC paper, coated base paper, lightly coated paper, packaging paper, liner and core base paper boards, etc. Among these, liner and core base paper boards, which require a stronger effect from the paper strength enhancer, are preferred. The addition rate is 1% to 100% by mass (polymer pure content) of the paper strength enhancer (pure content). The polymer pure content is 0.003 to 1% by mass, preferably 0.005 to 0.5% by mass, based on the dry solid content of the pulp. It can also be used in combination with other papermaking chemicals such as sizing agents, aluminum sulfate, pitch control agents, retention aids, and drainage aids.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not exceed the gist of the invention.

(Production Example 1)
In a 500 mL four-neck flask, 62.5 g of 80% by mass methacryloyloxyethyl trimethylammonium chloride, 187.5 g of demineralized water, and 0.1 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044 manufactured by Wako Pure Chemical Industries, Ltd.) were charged and nitrogen gas was passed through while stirring at 150 rpm. After 30 minutes, the temperature was raised to 50°C and maintained for 3 hours. Then, the temperature was maintained at 70°C for 2 hours. Then, the mixture was cooled to obtain an aqueous polymer solution. The viscosity of the 1% by mass aqueous solution of the obtained polymer was 16.4 mPa·s. The results are shown in Table 1.

(Production Example 2)
In a 500 mL four-neck flask, 10.0 g of styrene, 50.0 g of 80% by mass methacryloyloxyethyl trimethylammonium chloride, 189.1 g of demineralized water, 0.5 g of sodium dodecyl sulfate, and 0.01 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044 manufactured by Wako Pure Chemical Industries) were charged and nitrogen gas was passed through while stirring at 150 rpm. After 30 minutes, the temperature was raised to 50°C and maintained for 3 hours. Then, the temperature was maintained at 70°C for 2 hours. Then, the mixture was cooled to obtain an aqueous polymer solution. The viscosity of the 1% by mass aqueous solution of the obtained polymer was 20.2 mPa·s. The results are shown in Table 1.

(Production Example 3)
In a 500 mL four-neck flask, 50.0 g of 50% acrylamide, 31.8 g of 80% methacryloyloxyethyl trimethylammonium chloride, 167.3 g of demineralized water, 0.05 g of sodium hypophosphite, and 0.05 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044 manufactured by Wako Pure Chemical Industries) were charged and nitrogen gas was passed through while stirring at 150 rpm. After 30 minutes, the temperature was raised to 50°C and maintained for 3 hours. Then, the temperature was maintained at 70°C for 2 hours. Then, the mixture was cooled to obtain an aqueous polymer solution. The viscosity of the 1% by mass aqueous solution of the obtained polymer was 42.0 mPa·s. The results are shown in Table 1.

(Production Example 4)
In a 500 mL four-neck flask, 30.0 g of 50% acrylamide, 43.9 g of 80% methacryloyloxyethyl trimethylammonium chloride, 175.1 g of demineralized water, 0.05 g of sodium hypophosphite, and 0.05 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044 manufactured by Wako Pure Chemical Industries) were charged and nitrogen gas was passed through while stirring at 150 rpm. After 30 minutes, the temperature was raised to 50°C and maintained for 3 hours. Then, the temperature was maintained at 70°C for 2 hours. Then, the mixture was cooled to obtain an aqueous polymer solution. The viscosity of the 1% by mass aqueous solution of the obtained polymer was 24.0 mPa·s. The results are shown in Table 1.

(Production Example 5)
In a 500 mL four-neck flask, 0.5 g of dodecyl methacrylate, 61.9 g of 80% by mass methacryloyloxyethyl trimethylammonium chloride, 187.3 g of demineralized water, 0.5 g of sodium dodecyl sulfate, and 0.05 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044 manufactured by Wako Pure Chemical Industries) were charged and nitrogen gas was passed through while stirring at 150 rpm. After 30 minutes, the temperature was raised to 50°C and maintained for 3 hours. Then, the temperature was maintained at 70°C for 2 hours. Then, the mixture was cooled to obtain an aqueous polymer solution. The viscosity of the 1% by mass aqueous solution of the obtained polymer was 26.5 mPa·s. The results are shown in Table 1.

(Production Example 6)
In a 500 mL four-neck flask, 0.5 g of dodecyl methacrylate, 1.0 g of styrene, 60.6 g of 80% by mass methacryloyloxyethyl trimethylammonium chloride, 187.2 g of demineralized water, 0.5 g of sodium dodecyl sulfate, and 0.05 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044 manufactured by Wako Pure Chemical Industries) were charged and nitrogen gas was passed through while stirring at 150 rpm. After 30 minutes, the temperature was raised to 50°C and maintained for 3 hours. Then, the temperature was maintained at 70°C for 2 hours. Then, the mixture was cooled to obtain an aqueous polymer solution. The viscosity of the 1% by mass aqueous solution of the obtained polymer was 112.0 mPa·s. The results are shown in Table 1.

(Production Example 7)
In a 500 mL four-neck flask, 20.0 g of styrene, 24.7 g of dimethylaminoethyl methacrylate, 15.8 g of 35% by mass hydrochloric acid, 187.2 g of demineralized water, 0.5 g of sodium dodecyl sulfate, and 0.05 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044 manufactured by Wako Pure Chemical Industries, Ltd.) were charged and nitrogen gas was passed through while stirring at 150 rpm. After 30 minutes, the temperature was raised to 50°C and maintained for 3 hours. Then, the temperature was maintained at 70°C for 2 hours. Then, the mixture was cooled to obtain an aqueous polymer solution. The viscosity of the 1% by mass aqueous solution of the obtained polymer was 23.4 mPa·s. The results are shown in Table 1.

(Production Example 8)
In a 500 mL four-neck flask, 1.0 g of 2-ethylhexyl acrylate, 61.3 g of 80% by mass methacryloyloxyethyl trimethylammonium chloride, 187.3 g of demineralized water, 0.5 g of sodium dodecyl sulfate, and 0.05 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044 manufactured by Wako Pure Chemical Industries) were charged and nitrogen gas was passed through while stirring at 150 rpm. After 30 minutes, the temperature was raised to 50°C and maintained for 3 hours. Then, the temperature was maintained at 70°C for 2 hours. Then, the mixture was cooled to obtain an aqueous polymer solution. The viscosity of the 1% by mass aqueous solution of the obtained polymer was 155.5 mPa·s. The results are shown in Table 1.

(Production Example 9)
In a 500 mL four-neck flask, 0.5 g of stearyl methacrylate, 2.5 g of styrene, 59.0 g of 80% by mass methacryloyloxyethyl trimethylammonium chloride, 188.2 g of demineralized water, 0.5 g of sodium dodecyl sulfate, and 0.05 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044 manufactured by Wako Pure Chemical Industries) were charged and nitrogen gas was passed through while stirring at 150 rpm. After 30 minutes, the temperature was raised to 50°C and maintained for 3 hours. Then, the temperature was maintained at 70°C for 2 hours. Then, the mixture was cooled to obtain an aqueous polymer solution. The viscosity of the 1% by mass aqueous solution of the obtained polymer was 164.0 mPa·s. The results are shown in Table 1.

(Production Example 10)
In a 500 mL four-neck flask, 2.5 g of dodecyl methacrylate, 5.1 g of styrene, 53.1 g of 80% by mass methacryloyloxyethyl trimethylammonium chloride, 188.2 g of demineralized water, 0.5 g of sodium dodecyl sulfate, and 0.05 g of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (VA-044 manufactured by Wako Pure Chemical Industries) were charged and nitrogen gas was passed through while stirring at 150 rpm. After 30 minutes, the temperature was raised to 50°C and maintained for 3 hours. Then, the temperature was maintained at 70°C for 2 hours. Then, the mixture was cooled to obtain an aqueous polymer solution. The viscosity of the 1% by mass aqueous solution of the obtained polymer was 67.5 mPa·s. The results are shown in Table 1.

カチオン性単量体；ＤＭＭ：ジメチルアミノエチルメタクリレート、
ＤＭＣ：メタクリロイルオキシエチルトリメチルアンモニウムクロライド
疎水性単量体；Ｓｔ：スチレン、ＤＤＭ：ドデシルメタクリレート、２ＥＨＡ：２－エチルへキシルアクリレート、ＳＭＡ：ステアリルメタクリレート
ノ二オン性単量体；ＡＡＭ：アクリルアミド
１質量％水溶液粘度；Ｂ型粘度計を使用、回転数６０ｒｐｍ、２５℃で測定。 (Table 1)

Cationic monomer; DMM: dimethylaminoethyl methacrylate,
DMC: methacryloyloxyethyltrimethylammonium chloride hydrophobic monomer; St: styrene, DDM: dodecyl methacrylate, 2EHA: 2-ethylhexyl acrylate, SMA: stearyl methacrylate nonionic monomer; AAM: acrylamide. Viscosity of 1% by mass aqueous solution: measured using a B-type viscometer at a rotation speed of 60 rpm and 25° C.

In addition, commercially available paper strength agents 1 to 3 were prepared. Their compositions and physical properties are shown in Table 2.

(Table 2)

Example 1
As a paper stock, waste cardboard was beaten with a Niagara beater to a degree of beating of 300 mL. This was used as a pulp slurry with a pulp concentration of 1% by mass (pH 7.3, electrical conductivity 117.1 mS/m). To 500 mL of this pulp slurry, 0.01% by mass of the polymer sample production example 1 in the present invention in Table 1 and 0.3% by mass of the paper strength enhancer 1 in Table 2 were added based on the pulp solid content, and the mixture was stirred at 800 rpm for 1 minute, after which paper was made with a TAPPI standard paper machine (using 80 mesh wire), followed by pressing for 5 minutes at a pressure of 410 kPa, and then drying for 3 minutes at 105°C using a rotary drum wire. The paper was conditioned for 24 hours under conditions of a temperature of 23°C and a humidity of 50%, to obtain a paper with a basis weight of 80 g/ ^cm2 . The burst strength and compression strength of the obtained paper were measured and expressed as specific burst strength and specific compression strength, respectively. The burst strength was measured using a Mullen burst tester (manufactured by Kumagai Riki Kogyo Co., Ltd.) in accordance with JIS P 8131, and the compressive strength was measured using a short span compression tester (Compressive Strength Tester STFI, manufactured by L&W Co., Ltd.) in accordance with JIS P 8126. The same tests were also carried out for Production Examples 2 to 4. The results are shown in Table 3.

(Comparative Example 1)
Using the same pulp slurry as in Example 1, the same test as in Example 1 was carried out without using the polymer sample of the present invention. The results are shown in Table 3.

(Table 3)

Compared to adding a paper strength agent alone, the use of the polymer sample of the present invention in combination was found to enhance the effect of the paper strength agent. Polymer sample production example 2 obtained using a cationic monomer and a hydrophobic monomer was the most effective.

Example 2
Using the same pulp slurry as in Example 1, tests similar to those in Example 1 were carried out using the polymer sample preparation examples 5 to 7 of the present invention. The results are shown in Table 4.

(Comparative Example 2)
Using the same pulp slurry as in Example 1, the same test as in Example 1 was carried out without using the polymer sample of the present invention. The results are shown in Table 4.

(Table 4)

Compared to adding a paper strength agent alone, the use of the polymer sample of the present invention in combination with the paper strength agent was found to promote the effect of the paper strength agent. It was found that the effect tends to be greater when the hydrophobic monomer content is high and the viscosity of the 1% by mass aqueous solution is high.

Example 3
Using the same pulp slurry as in Example 1, the same test as in Example 1 was carried out using the polymer sample of the present invention, Example 8. The effective addition ratio of the paper strength agent and the polymer sample of the present invention was investigated. The results are shown in Table 5.

(Comparative Example 3)
Using the same pulp slurry as in Example 1, tests similar to those in Example 1 were carried out using the paper strength agent alone or the polymer sample of the present invention alone. The results are shown in Table 5.

(Table 5)

When comparing the same total addition rate, it was found that the addition of a small amount of the polymer sample of the present invention in combination with the paper strength agent alone was more effective at promoting paper strength.

Example 4
Using the same pulp slurry as in Example 1, tests similar to those in Example 1 were carried out using paper strength agents 2 and 3. The results are shown in Table 6.

(Comparative Example 4)
Using the same pulp slurry as in Example 1, the same test as in Example 1 was carried out without using the polymer sample of the present invention. The results are shown in Table 6.

Table 6

Addition of a small amount of the polymer sample of the present invention to any of the paper strength agents was found to have a significant effect of promoting the paper strength agent.

Claims (4)

The papermaking additive is a polymer obtained by polymerizing a monomer component containing 30% by mass to 100% by mass of a cationic monomer based on the total monomers, and the method for enhancing the effect of a paper strength agent is characterized in that the papermaking additive is added to a papermaking raw material prior to papermaking in an amount of 1% by mass to 100% by mass (pure polymer content) of the paper strength agent (pure content) before or simultaneously with the addition of the paper strength agent . 2. The method for enhancing the effect of a paper strength agent according to claim 1, wherein the polymer is obtained by polymerizing a monomer component containing a hydrophobic monomer. The method for enhancing the effect of a paper strength agent according to claim 2, characterized in that the polymer is obtained by polymerizing a monomer component containing more than 0% by mass to 50% by mass of hydrophobic monomers relative to the total monomers. The method for enhancing the effect of a paper strength agent according to any one of claims 1 to 3, characterized in that the viscosity (25°C) of a 1% by mass aqueous solution of the polymer is 5 to 200 mPa·s when measured with a B-type viscometer at a rotation speed of 60 rpm.