阅读说明：本技术 造纸用添加剂、纸及纸的制造方法 (Additive for papermaking, paper and method for producing paper ) 是由 山本琢二 信国茂树 岩城直陶 茨木英夫 吉谷孝治 于 2019-08-28 设计创作，主要内容包括：本发明的课题在于提供一种纸力增强效果优异的聚丙烯酰胺系造纸用添加剂及使用了所述造纸用添加剂的纸、使用了所述造纸用添加剂的纸的制造方法。一种造纸用添加剂,含有两性聚丙烯酰胺,所述两性聚丙烯酰胺包含(A)(甲基)丙烯酰胺、(B)(甲基)烯丙基磺酸类、(C)具有羧基的阴离子性乙烯基单体、(D)具有季铵的阳离子性乙烯基单体作为共聚成分,且所述造纸用添加剂的特征在于,所述两性聚丙烯酰胺的阴离子等量与阳离子等量的比为0.05以上、1.7以下,所述两性聚丙烯酰胺的辛醇/水分配系数为-1.44以上、-0.60以下,所述两性聚丙烯酰胺的表面张力为66mN/m以上、未满74mN/m。(The invention provides a polyacrylamide papermaking additive with excellent paper strength enhancing effect, paper using the papermaking additive, and a method for manufacturing the paper using the papermaking additive. An additive for papermaking, comprising an amphoteric polyacrylamide which contains, as copolymerization components, (A) (meth) acrylamide, (B) (meth) allylsulfonic acid, (C) an anionic vinyl monomer having a carboxyl group, and (D) a cationic vinyl monomer having a quaternary ammonium, and is characterized in that the ratio of the equivalent amount of anions to the equivalent amount of cations in the amphoteric polyacrylamide is 0.05 or more and 1.7 or less, the octanol/water partition coefficient of the amphoteric polyacrylamide is-1.44 or more and-0.60 or less, and the surface tension of the amphoteric polyacrylamide is 66mN/m or more and less than 74 mN/m.)

1. An additive for papermaking, characterized by comprising an amphoteric polyacrylamide containing, as copolymerized components, (A) (meth) acrylamide, (B) (meth) allylsulfonic acid, (C) an anionic vinyl monomer having a carboxyl group, and (D) a cationic vinyl monomer having a quaternary ammonium,

the ratio of the equivalent amount of anions to the equivalent amount of cations in the amphoteric polyacrylamide is 0.05 to 1.7,

the amphoteric polyacrylamide has an octanol/water partition coefficient of-1.44 or more and-0.60 or less,

the surface tension of the amphoteric polyacrylamide is more than 66mN/m and less than 74 mN/m.

2. The additive for papermaking according to claim 1,

the amphoteric polyacrylamide has a peak top molecular weight Mp of 100 to 500 ten thousand,

a molecular weight distribution Mw/Mn of 2.5 to 8.0,

the ratio Mp/V of the peak top molecular weight Mp to the viscosity V of a 20 mass% aqueous solution (25 ℃) of the additive for papermaking is 200 to 800 inclusive.

3. A paper comprising the additive for papermaking according to claim 1 or 2.

4. A method for producing paper, characterized in that the additive for paper production according to claim 1 or 2 is used, and an aluminum compound is added to a pulp slurry in an amount of 0 to 0.3 mass% in terms of alumina relative to the dry mass of pulp, and papermaking is carried out at a papermaking pH of 5.0 to 8.5.

5. The method for producing paper according to claim 4, wherein the conductivity of the paper is more than 300 mS/m.

Technical Field

The present invention relates to an additive for papermaking having an excellent paper strength-enhancing effect, paper containing the additive for papermaking, and a method for producing the paper.

Background

Conventionally, various papermaking additives including a polyacrylamide-based papermaking agent have been used in the production of paper in order to improve productivity and paper strength.

As the polyacrylamide-based paper strength agent, for example, there are proposed: a paper strength enhancing agent which is an acrylamide polymer aqueous solution having a low viscosity despite a high concentration and a high molecular weight and is excellent in paper strength such as breaking strength and Z-axis strength or drainage (see patent document 1); a paper strength enhancing agent comprising an acrylamide polymer obtained by polymerizing a polymerization component containing (meth) acrylamide, a quaternary ammonium monomer and (meth) allylsulfonate and containing no nitrogen-containing crosslinkable monomer and no tertiary amino monomer (see patent document 2).

In recent years, from the viewpoint of environmental concerns and improvement of workability, in the production of paper, there have been advanced problems of deterioration of paper quality due to increase in ash content in paper making stock, increase in conductivity of paper making system, and the like, by utilizing old paper stock, saving water (recycling of white water), or by reducing aluminum sulfate in neutral paper making to no aluminum sulfate.

However, in the above-mentioned prior art, in a system in which only a small amount of an aluminum compound such as aluminum sulfate or polyaluminum chloride (PAC) as a fixing aid of a paper strength agent is added to a pulp slurry, or a papermaking system without aluminum; or a papermaking system with high conductivity having a high white water recirculation rate for water saving or a papermaking system in which the paper strength enhancing effect is limited even when a paper strength enhancing agent is added to a pulp slurry at a high level, a satisfactory paper strength enhancing effect cannot be obtained.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. Hei 08-067715

Patent document 2: japanese patent No. 6060314 (International publication No. WO 2016/092965)

Disclosure of Invention

Problems to be solved by the invention

The invention provides a polyacrylamide papermaking additive with excellent paper strength enhancing effect, paper containing the papermaking additive and a method for manufacturing the paper using the papermaking additive.

Means for solving the problems

The present inventors have made diligent studies and, as a result, have found that: by using the specific polyacrylamide-based papermaking additive, paper having satisfactory paper strength can be obtained even under the papermaking conditions (old paper utilization, white water recycling, no sulfation).

That is, the present invention as means for solving the above problems is:

< 1 > an additive for papermaking, comprising an amphoteric polyacrylamide (ampholytic polyacrylamide) containing (A) (meth) acrylamide, (B) (meth) allylsulfonic acids, (C) an anionic vinyl monomer (anionic vinyl monomer) having a carboxyl group, (D) a cationic vinyl monomer (cationic monomer) having a quaternary ammonium (quaternary ammonium) as a copolymerization component, wherein the ratio of the equivalent amount of anions to the equivalent amount of cations of the amphoteric polyacrylamide is 0.05 or more and 1.7 or less, the octanol/water partition coefficient (partition coefficient) of the amphoteric polyacrylamide is-1.44 or more and-0.60 or less, the surface tension of the amphoteric polyacrylamide is 66mN/m or more and is less than 74mN/m,

< 2 > the additive for papermaking as described in < 1 >, wherein the amphoteric polyacrylamide has a peak top molecular weight (Mp) of 100 to 500 ten thousand, a molecular weight distribution Mw/Mn of 2.5 or more and 8.0 or less, a ratio Mp/V of the peak top molecular weight Mp to a viscosity V of a 20 mass% aqueous solution (25 ℃) of the additive for papermaking of 200 or more and 800 or less,

< 3 > a paper containing the papermaking additive described in < 1 > or < 2 >,

< 4 > A method for producing paper, characterized by using the additive for paper making described in < 1 > or < 2 >, adding 0 to 0.3 mass% of an aluminum compound (aluminum compound) in terms of alumina to a pulp slurry based on the dry mass of the pulp, and performing paper making (papermaking) at a paper making pH of 5.0 to 8.5,

< 5 > the method for producing paper according to < 4 >, wherein the conductivity of the paper is more than 300 mS/m.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, paper having excellent paper strength can be provided even under the conventional papermaking conditions.

Detailed Description

The amphoteric polyacrylamide contained in the papermaking additive of the present invention is obtained by copolymerizing monomers containing, as a copolymerization component, (a) (meth) acrylamide, (B) (meth) allylsulfonic acid, (C) an anionic vinyl monomer having a carboxyl group, and (D) a cationic vinyl monomer having a quaternary ammonium. The proportion of the amphoteric polyacrylamide in the total solid content of the papermaking additive is preferably 90 mass% or more and 100 mass% or less.

(A) The (meth) acrylamide is acrylamide or methacrylamide, and can be used alone or in combination.

(B) The (meth) allylsulfonic acid is at least one member selected from the group consisting of allylsulfonic acid, methallylsulfonic acid, and alkali metal salts and ammonium salts thereof such as sodium salts and potassium salts thereof. Among these, sodium methallyl sulfonate is preferable.

The anionic vinyl monomer having a carboxyl group (C) may be an anionic vinyl monomer having one or more carboxyl groups. Examples thereof include alkali metal salts and ammonium salts such as sodium salts and potassium salts of unsaturated monocarboxylic acids, unsaturated dicarboxylic acids, unsaturated tricarboxylic acids and unsaturated tetracarboxylic acids, and one kind of them may be used alone or two or more kinds thereof may be used in combination. Of these, alkali metal salts or ammonium salts of unsaturated monocarboxylic acids, unsaturated dicarboxylic acids, and sodium salts and potassium salts thereof are preferable from the viewpoint of paper strength-enhancing effect and economy.

Examples of the unsaturated monocarboxylic acid include: acrylic acid, methacrylic acid, 2- (meth) acrylamido-N-glycolic acid, N-acryloylglycine, 3-acrylamidopropionic acid, 4-acrylamidobutyric acid, and the like.

Examples of unsaturated dicarboxylic acids include: maleic acid, fumaric acid, itaconic acid, citraconic acid, and the like.

Among the anionic vinyl monomers having a carboxyl group (C), alkali metal salts or ammonium salts such as acrylic acid, 2-acrylamido-N-glycolic acid, itaconic acid, and sodium salts and potassium salts thereof are more preferable.

Examples of the cationic vinyl monomer having quaternary ammonium (D) include a vinyl monomer obtained by the reaction of a vinyl monomer having a tertiary amino group and a quaternizing agent, and a diallyldialkylammonium quaternary salt. Examples of the quaternary agent include: alkyl halides such as methyl chloride and methyl bromide; halogenated aromatic hydrocarbons (aryl halides) such as benzyl chloride (benzyl chloride) and benzyl bromide (benzyl bromide); dimethyl sulfate, diethyl sulfate, epichlorohydrin, 3-chloro-2-hydroxypropyltrimethylammonium chloride, glycidyltrialkylammonium chloride, and the like.

Examples of the cationic vinyl monomer having quaternary ammonium (D) include: dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate methyl sulfate quaternary salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl sulfate quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, dimethylaminopropyl acrylamide methyl sulfate quaternary salt, dimethylaminopropyl acrylamide benzyl chloride quaternary salt, dimethylaminopropyl methacrylamide methyl sulfate quaternary salt, dimethylaminopropyl methacrylamide methyl chloride quaternary salt, dimethylaminopropyl methacrylamide benzyl chloride quaternary salt, dimethylaminopropyl acrylamide 3-chloro-2-hydroxypropyl) trimethylammonium quaternary salt (N- (3-Acrylamidopropyl) -N, n, N '-pentamethyl-N, N' - (2-hydroxypropane-1,3-diyl) diammonium dichloride), diallyldimethylammonium chloride, diallyldiethylammonium chloride.

The cationic vinyl monomer having quaternary ammonium (D) may be used alone or in combination of two or more.

The amphoteric polyacrylamide contained in the papermaking additive of the present invention is preferably: the ratio of the components (A) to (D) constituting the amphoteric polyacrylamide is

(A) 62 to 99.2 mol% of (meth) acrylamide

(B) (meth) allylsulfonic acid 0.1 to 3 mol%

(C) 0.2 to 15 mol% of an anionic vinyl monomer having a carboxyl group

(D) 0.5 to 20 mol% of a cationic vinyl monomer having quaternary ammonium.

In the amphoteric polyacrylamide contained in the papermaking additive of the present invention, other monomers may be added in addition to the above-mentioned components (a) to (D) within the range not to impair the effects of the present invention. Examples of the monomers other than the monomers (A) to (D) include: other anionic vinyl monomer (C '), other cationic vinyl monomer (D'), crosslinking monomer (E), and nonionic vinyl monomer (F).

Examples of the other anionic vinyl monomer (C') include: and alkali metal or ammonium salts such as unsaturated sulfonic acids (excluding the (meth) allylsulfonic acids) and unsaturated phosphonic acids, and sodium salts and potassium salts thereof. Instead of a part of the anionic vinyl monomer (C) having a carboxyl group, another anionic vinyl monomer (C') is used, preferably 10 mol% or less, more preferably 5 mol% or less.

Examples of the unsaturated sulfonic acid include: vinylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and the like.

Examples of the unsaturated phosphonic acid include vinylphosphonic acid and α -phenylvinylphosphonic acid.

Examples of the other cationic vinyl monomer (D') include vinyl monomers having a tertiary amino group, a secondary amino group, and a primary amino group, such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide, alkyldiallylamine, diallylamine, and allylamine, and salts of inorganic acids or organic acids, such as hydrochloric acid, sulfuric acid, formic acid, acetic acid, and phosphoric acid, thereof. Instead of a part of the cationic vinyl monomer (D) having quaternary ammonium, another cationic vinyl monomer (D') may be used.

Examples of the crosslinkable monomer (E) include: n-substituted (meth) acrylamides such as N, N-dimethyl (meth) acrylamide, N-methylolacrylamide, and N, N' -methylenebis (meth) acrylamide; polyfunctional (meth) acrylates such as ethylene glycol di (meth) acrylate and triacetyl formal; divinyl esters such as divinyl adipate. These may be used alone or in combination of two or more. It is preferable to use 0.001 to 2.0 mol% of a crosslinkable monomer (E) as a copolymerization component of the amphoteric polyacrylamide in place of a part of the components (A) to (D).

Examples of the nonionic vinyl monomer (F) include: (meth) acrylate, (meth) acrylonitrile, styrene derivatives, vinyl acetate, vinyl propionate, and methyl vinyl ether. These may be used alone or in combination of two or more. The amphoteric polyacrylamide may be used as a copolymerization component thereof, preferably 10 mol% or less, more preferably 5 mol% or less, of a nonionic vinyl monomer (F) in place of a part of the components (a) to (D).

The method for producing the amphoteric polyacrylamide is not particularly limited, and various methods known in the art can be used. For example, the pH is adjusted by using the monomer, water as a solvent (an organic solvent may be used in combination as needed), and an acid such as sulfuric acid or hydrochloric acid or a pH adjuster such as a base such as sodium hydroxide, potassium hydroxide, or ammonium as needed, in a reaction vessel including a stirrer and a thermometer under an inert gas atmosphere such as nitrogen. Then, a polymerization initiator is added to carry out the reaction in a temperature range in which the reaction can be controlled, and the objective amphoteric polyacrylamide can be obtained. Further, if necessary, polymerization may be carried out while dropping a part or all of the monomers, water, chain transfer agent, pH adjuster, and polymerization initiator into the reaction vessel. In terms of expanding the degree of freedom in designing the molecular structure of the copolymer, it is preferable to carry out polymerization by dividing and/or dropping the monomer.

The polymerization initiator used in the present invention is not particularly limited, and a known polymerization initiator can be used. For example, one may exemplify: persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; peroxides such as hydrogen peroxide, benzoyl peroxide, t-butyl hydroperoxide, and di-t-butyl peroxide; bromates such as sodium bromate and potassium bromate; perborates such as sodium perborate, potassium perborate, and ammonium perborate; percarbonate such as sodium percarbonate, potassium percarbonate, and ammonium percarbonate; perphosphates such as sodium perphosphate, potassium perphosphate, ammonium perphosphate and the like. In this case, the redox polymerization initiator may be used alone, or may be used in combination with a reducing agent.

Examples of the reducing agent include: organic amines such as sulfite, bisulfite and N, N, N ', N ' -tetramethylethylenediamine, azo compounds such as 2,2' -azobis-2-amidinopropane hydrochloride, and reducing sugars such as aldose. Azo compounds such as azobisisobutyronitrile, 2' -azobis-2-amidinopropane hydrochloride, 2' -azobis-2, 4-dimethylvaleronitrile, 4' -azobis-4-cyanovaleric acid and salts thereof can also be used. Two or more of these initiators may be used in combination.

The amount of the polymerization initiator used in the polymerization is not particularly limited, but is usually 0.005 to 5 parts by mass, preferably 0.01 to 2.5 parts by mass, based on 100 parts by mass of the polymerization components, in order to sufficiently perform the polymerization reaction of the polymerization components.

The papermaking additive of the present invention is required to contain the amphoteric polyacrylamide such that the ratio of the equivalent amount of anions to the equivalent amount of cations is 0.05 to 1.7. Here, the ratio of the equivalent amount of anion to the equivalent amount of cation is a value obtained by dividing the total of the equivalent amounts of anion of all the monomers exhibiting anion constituting the amphoteric polyacrylamide by the total of the equivalent amounts of cation of all the monomers exhibiting cation. When the ratio of the equivalent amount of anions to the equivalent amount of cations of the amphoteric polyacrylamide is less than 0.05, ionic bonding sites with the aluminum compound added to the pulp slurry or the aluminum compound in the old paper are small, and therefore, fixation to the pulp fibers is difficult, and the paper strength-enhancing effect is reduced.

When the ratio of the equivalent amount of anions to the equivalent amount of cations exceeds 1.7, the pulp fibers having negative charges have fewer ionic bonding sites, or anionic groups neutralize cationic groups in the molecules, and thus the pulp fibers are difficult to fix to the paper, and the paper strength-enhancing effect is reduced.

The amphoteric polyacrylamide required to be contained in the papermaking additive of the present invention has an octanol/water partition coefficient (hereinafter, sometimes referred to as LogP (Poly)) of-1.44 or more and-0.60 or less. Here, the octanol/water partition coefficient (LogP) can be determined by Howard method (journal of Pharmaceutical Sciences) Vol84, No. 11995. The octanol/water partition coefficient (LogP (poly)) of the amphoteric polyacrylamide can be calculated by the Howard method, by calculating the octanol/water partition coefficient (LogP) of each copolymerization component of the amphoteric polyacrylamide, and by multiplying the obtained value by the sum of the mole fractions of the copolymerization components.

The octanol/water partition coefficient (LogP) of each copolymerization component was determined by the following calculation formula.

LogP＝Σ(fi×ni)+Σ(cj×nj)+0.229

Here, fi and cj are a fragment constant and a correction coefficient corresponding to each copolymerizability, respectively, and examples are shown in table 1. The fragment refers to a product obtained by arbitrarily dividing a chemical structure.

[ Table 1]

More than two cases

From table 1, for example, acrylamide can be found as the sum of the fragment constants shown in table 2. Further, for example, itaconic acid can be obtained as the sum of the fragment constant and the correction coefficient shown in table 3.

[ Table 2]

[ Table 3]

More than two cases

The smaller the value of the octanol/water partition coefficient, the more hydrophilic the structure, and the larger the value, the more hydrophobic the structure. When the octanol/water partition coefficient (logp (poly)) of the amphoteric polyacrylamide is larger than-0.60, the amphoteric polyacrylamide is adsorbed on hydrophobic inclusions (resin acids, pitch, etc.) in the pulp slurry, and accordingly, the fixing amount on the pulp fibers becomes small, and the paper strength improving effect is lowered. When the LogP (Poly) value is less than-1.44, the hydrophilicity is high, and hence the amphoteric polyacrylamide in the aqueous solution is adsorbed and detached from the pulp fiber, whereby the fixing is difficult to be performed, and the paper strength-enhancing effect is lowered.

The amphoteric polyacrylamide to be contained in the papermaking additive of the present invention has a surface tension of 66mN/m or more and less than 74 mN/m. Here, the surface tension of amphoteric polyacrylamide means the following value: the SURFACE tension of a 0.2M ammonium acetate/0.6M NaCl aqueous solution containing 0.2 mass% of amphoteric polyacrylamide at 25 ℃ and adjusted to pH7.0 was measured by using a SURFACE TENSIOMETER (CBVP SURFACTANSUNSOMETER A3, Kyowa scientific Co., Ltd.). When the papermaking additive does not contain an amphiphilic additive that affects the surface tension of the defoaming agent or the like, the surface tension defined in the present invention can be determined as a value measured by adjusting the amphoteric polyacrylamide concentration to 0.2 mass% in the papermaking additive as it is with a buffer solution. On the other hand, in the case of an additive for papermaking containing an amphiphilic additive which affects the surface tension of a defoaming agent or the like, the surface tension of a 0.2 mass% buffer solution of the following amphoteric polyacrylamide is measured: amphoteric polyacrylamide is precipitated with acetone and the additives are removed by vacuum drying.

Surface tension is free energy per unit area, and the surface tension of cellulose is 68.7mN/m (reference: Japanese TAPPI JOURNAL (JAPAN TAPPI JOURNAL) No. 39, No. 8 p 733-746). Further, the surface tension of the pulp fiber of BKP was 71.3mN/m (reference: J.F.49No. 6 (1993)).

The amphoteric polyacrylamide contained in the papermaking additive of the present invention is preferably fixed to pulp fibers quickly when added to a papermaking system. Therefore, when the surface tension of the amphoteric polyacrylamide is 66mN/m or more and less than 74mN/m, the amphoteric polyacrylamide is close to the surface tension of cellulose or pulp fibers, and therefore is likely to wet and spread in the pulp fibers and to be surface-bonded, and thus is fixed to the pulp fibers and is likely to exhibit a paper strength-enhancing effect. When the surface tension of the amphoteric polyacrylamide is less than 66mN/m, the amphoteric polyacrylamide is more likely to wet and spread in the pulp fibers, moves into the pores of the pulp fibers, and is fixed to the pulp fibers, but does not contribute to the paper strength-improving effect. When the surface tension is 74mN/m or more, the paper strength-enhancing effect is difficult to be exhibited because the paper is not wet-spread in pulp fibers and is point-bonded.

The papermaking additive of the present invention preferably contains amphoteric polyacrylamide having a peak top molecular weight (Mp) of 100 to 500 ten thousand, and more preferably 150 to 400 ten thousand. Here, the peak top molecular weight can be determined from the position of the peak top of the molecular weight distribution. As an index of the molecular weight, a weight average molecular weight obtained by a Gel Permeation Chromatography (GPC) method is generally used, but a weight average molecular weight (Mw) in which a relationship between a dissolution time and a molecular weight is obtained and the molecular weight is used as a weight is easily affected by the presence of a high molecular weight. Therefore, even if the polyacrylamide has a weight average molecular weight (Mw) within a range that is generally considered to exhibit the paper strength-enhancing effect, the following may occur: the peak top molecular weight (Mp) was low, and the paper strength-enhancing effect was insufficient. When the peak top molecular weight (Mp) is 100 ten thousand or more, the paper strength-enhancing effect can be sufficiently obtained, and when it is 500 ten thousand or less, the aggregation is less likely to occur, and the paper strength-enhancing effect is excellent.

The papermaking additive of the present invention preferably contains amphoteric polyacrylamide such that the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 2.5 or more and 8.0 or less. When the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 2.5 or more, the capability of coping with the fluctuation of the paper making system increases due to the diversity of the amphoteric polyacrylamide, and when it is 8.0 or less, the content of the amphoteric polyacrylamide having a low molecular weight and causing the excessive aggregation decreases, and thus the paper strength-enhancing effect is excellent.

The viscosity of the additive for papermaking of the present invention is not particularly limited, and in terms of the ease with which the ratio Mp/V of peak top molecular weight (Mp)/viscosity (V) becomes 200 or more, it is preferable that the B-type viscosity (V) at 25 ℃ when diluted or concentrated so that the solid content concentration of the additive for papermaking becomes 20.0 mass% be 1,000mPa · s to 15,000mPa · s.

The ratio Mp/V of weight average molecular weight (Mp)/viscosity (V) is preferably 200 or more and 800 or less. When the amount is 200 or more, moderate cohesion is generated, and when the amount is 800 or less, excessive cohesion is not easily caused, so that the paper strength-enhancing effect can be improved. Here, the viscosity is a B-type viscosity at 25 ℃ when the solid content concentration of the additive for papermaking is 20.0 mass% and the pH of the additive for papermaking adjusted to 20.0 mass% by sulfuric acid or sodium hydroxide is 3.0, and the rotational speed of the rotor is appropriately adjusted from 12rpm to 60rpm according to the viscosity by using a rotor of No.4 as a rotor of a B-type viscometer. The unit is mPas.

The papermaking additive of the present invention is usually supplied in the form of an aqueous solution. The concentration is not particularly limited, and is preferably 10 to 40% by mass from the viewpoint of transportation cost and handling.

In addition, the present invention provides a method of manufacturing paper. The method for producing paper of the present invention is characterized in that the paper making additive is used to add 0 to 0.3 mass% of an aluminum compound in terms of alumina to a pulp slurry based on the dry mass of the pulp, and the paper is made at a paper making pH of 5.0 to 8.5.

The pulp slurry is prepared by diluting pulp with water to obtain a slurry, and any of bleached or unbleached chemical pulp such as kraft pulp and sulfite pulp, bleached or unbleached high-yield pulp such as wood pulp, mechanical pulp and thermomechanical pulp, and used paper pulp such as used newspaper, used magazine paper, used corrugated paper and deinked used paper can be used as the pulp.

In the method for producing paper of the present invention, the papermaking additive is added to the pulp slurry in an amount of usually 0.01 to 5.0% by mass of solid content, preferably 0.05 to 3.0% by mass of solid content, and more preferably 0.5 to 3.0% by mass of solid content, based on the dry mass of the pulp. Although paper having excellent paper strength can be obtained without using an aluminum compound such as aluminum sulfate or polyaluminum chloride, when the aluminum compound is added, it is preferably added in an amount of 0.1 to 0.3% by mass in terms of alumina.

Further, as a method of adding the papermaking additive to the pulp slurry, for example, a method of adding the papermaking additive without using any aluminum compound; a method of adding an additive for papermaking after adding the aluminum compound; a method of adding an aluminum compound after the addition of the papermaking additive; the method of adding the aluminum compound and the papermaking additive at the same time may be any method.

In general, when NaCl or MgCl is used₂When the electrolyte of inorganic salts is dissolved in water, the electrolyte is distributed in the water solution, the interface surface is close to fresh water to generate negative adsorption, and the surface tension of the water solution is improved. The surface tension of pure water at 25 ℃ was 72.0mN/M, but the 0.2M-NaCl aqueous solution was 72.9mN/M, the 0.6M-NaCl aqueous solution was 73.0mN/M, and the 1.2M-NaCl aqueous solution was 73.6 mN/M. On the other hand, in the paper-making system, various inorganic salts are dissolved, and therefore, an electrolyte such as amphoteric polyacrylamide suppresses dissociation of ionic functional groups by a shielding effect by the inorganic salts, and the hydrophobicity of cationic groups becomes strong, and the surface tension is lowered. Presume that: when the deviation of the surface tension of the amphoteric polyacrylamide from the surface tension of cellulose or pulp fiber becomes large, the amphoteric polyacrylamide is easily adsorbed to the hydrophobic inclusions in the pulp slurry.

Similarly, it is presumed that when the papermaking pH is increased to be equal to or more than neutral, the hydrophobic property of the amphoteric polyacrylamide is increased, so that the surface tension is decreased, and the hydrophobic inclusions in the pulp slurry are easily wetted and spread, and as a result, the fixation on the pulp fibers is decreased, and the paper strength-improving effect is insufficient.

The amphoteric polyacrylamide contained in the additive for papermaking of the present invention contains a quaternary cationic vinyl monomer as a cationic vinyl monomer, and the ratio of the equivalent amount of anions to the equivalent amount of cations is 0.05 or more and 1.7 or less, and therefore it is presumed that the effect of strengthening paper strength is good due to an appropriate ion balance without losing the cationic property by the masking effect or high pH. On the other hand, in the strongly anionic polyacrylamide having a ratio of the equivalent amount of the anion to the equivalent amount of the cation exceeding 1.7, an aluminum compound such as aluminum sulfate or polyaluminum chloride is required as a fixing aid for the paper strength enhancer, and therefore, a sufficient paper strength enhancing effect cannot be obtained in a papermaking system in which only a small amount or no amount of the aluminum compound is added to the pulp slurry.

As described above, when the papermaking additive of the present invention is used, even in a papermaking system in which a sufficient paper strength-enhancing effect cannot be obtained by the conventional papermaking additive, the surface tension at which wet spread surfaces are easily adhered to pulp fibers is maintained, and therefore, an excellent paper strength-enhancing effect is exhibited. The conductivity of the paper is preferably at most 5000 mS/m.

In the method for producing paper of the present invention, an acidic rosin-based sizing agent (acidic rosin-based sizing agent), a neutral rosin-based sizing agent, an alkyl ketene dimer-based sizing agent, an alkenyl or alkyl succinic anhydride-based sizing agent, a polycarboxylic acid and an aliphatic alcohol having an alkyl group or an alkenyl group, an aliphatic amine-based condensation-based sizing agent having an alkyl group or an alkenyl group, or the like may be added to the pulp slurry. Examples of methods for adding these sizing agents include: a method of adding an additive for papermaking after adding a sizing agent to a pulp slurry; a method of adding a sizing agent after adding an additive for papermaking; a method of diluting the papermaking additive, mixing the diluted additive with a sizing agent in advance, and then adding the diluted additive. In addition to the above, the pulp slurry may also contain a size fixing agent, an additive for papermaking other than the one of the present invention, a defoaming agent, a filler such as clay, kaolin, calcium carbonate, barium sulfate or titanium oxide, a pH adjuster, a dye, a fluorescent whitening agent, and the like. Further, the basis weight of the paper obtained by the production method of the present invention is usually 10g/m²～750g/m²Left and right.

Further, if necessary, starch, surface paper strength agents such as polyvinyl alcohol and acrylamide polymers, surface sizing agents, dyes, paints (coating colors), and anti-slip agents may be coated by a size press, a horizontal roll coater (gate roll coater), a Bill blade coater (roll coater), a calender, or the like.

In the method for producing paper of the present invention, the papermaking pH of the pulp slurry to which the papermaking additive of the present invention and the like are added is preferably 5.0 to 8.5, and more preferably 6.5 to 8.5 in terms of the paper strength enhancing effect. The paper pH in the present invention is the pH of the pulp slurry immediately before dewatering with the paper machine, and the pH of the pulp slurry immediately before dewatering with the paper machine corresponds to the pH at the inlet in a normal actual machine.

The paper produced using the papermaking additive of the present invention includes: examples of the Paper include information papers such as Plain Paper Copier (PPC), art papers (art Paper), cast-coated papers (cast-coated Paper), coated papers such as high-grade coated papers, tissue papers (tissue Paper), sanitary papers such as hand towels and napkin papers, fruit bag papers, laundry label papers, decorative sheet papers/wallpaper papers, printing papers, laminate papers, processed papers such as food container papers, packaging papers such as double-layer kraft papers/single-ply kraft papers for weight bags, electrical insulating papers, box board papers, corrugated papers, Paper tube papers, white board papers, gypsum board papers, newspaper papers, and cardboard papers for Paper machines.

Examples

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as the invention does not depart from the gist thereof. Hereinafter,% represents mass% unless otherwise specified.

The peak top molecular weight (Mp), the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (Mw/Mn) of the amphoteric polyacrylamide was determined by a GPC-Multi Angle Light Scattering (MALS) method in which a Multi Angle Light Scattering detector was attached to a Gel Permeation Chromatograph (GPC). The measurement conditions are as follows.

GPC Main body: LC1100 series column manufactured by Agilent Technology: soidex (SHODEX) SB806MHQ manufactured by Showa Denko K.K. (Strand)

Eluent: n/15 phosphate buffer containing N/10 sodium nitrate (pH3)

Flow rate: 1.0 ml/min

The detector 1: multi-angle light scatter detector DAWN manufactured by Wyatt Techogy Corporation

The detector 2: difference refractive index detector RI-101 manufactured by Showa electrician (Strand)

The polymerization rate of the amphoteric polyacrylamide is determined by¹H-Nuclear Magnetic Resonance (NMR) was carried out. The polymerization ratio here means the ratio (molar ratio) of the polymer to the total amount of monomers to be reacted with the amphoteric polyacrylamide.

The LogP value of each copolymerization component of amphoteric polyacrylamide used for synthesizing the additive for papermaking, which is determined by Howard method, is as follows.

Acrylamide: -0.8569

Sodium methallylsulfonate: 1.3949

Itaconic acid: -0.4867

Acrylic acid: 0.3920

2-acrylamido-N-glycolic acid: -2.6750

Dimethylaminoethyl methacrylate methyl chloride quaternary salt: -3.3914

Dimethylaminoethyl acrylate methyl chloride quaternary salt: -3.8449

Dimethylaminoethyl methacrylate benzyl chloride quaternary: -1.6836

Dimethylaminoethylacrylate benzyl chloride quaternary: -2.1371

Methyl aminopropyl acrylamide methyl chloride quaternary salt: -4.4231

Diallyl dimethyl ammonium chloride: -2.5892

Dimethylaminoethyl methacrylate: 0.8290

Dimethylaminoethyl acrylate: 0.3755

N, N-dimethylacrylamide: -0.1798

N, N' -methylenebisacrylamide: -1.6145

< Synthesis of additive for papermaking >

Example 1

A1 liter four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet was charged with 323.60g of water, 136.13g of a 50% acrylamide aqueous solution as a monomer (1), 36.35g of 80% dimethylaminoethylmethacrylate methyl chloride quaternary salt, 3.06g of sodium methallylsulfonate (methallylsulfonate), 0.28g of N, N-dimethylacrylamide and 4.32g of 1% N, N' -methylenebisacrylamide, and adjusted to pH3.0 with a 30% sulfuric acid aqueous solution. Subsequently, the temperature was raised to 65 ℃ under a nitrogen atmosphere, ammonium persulfate as a polymerization initiator was added to start polymerization, and the reaction temperature was raised to 90 ℃. Then, ammonium persulfate was added, and when the polymerization rate reached 95%, monomer (2) comprising water 274.0g, a 50% acrylamide aqueous solution 229.48g, itaconic acid 7.29g, sodium methallylsulfonate 1.11g, N-dimethylacrylamide 0.28g, and 1% N, N' -methylenebisacrylamide 4.32g was added, and ammonium persulfate was further added. Then, ammonium persulfate was further added, and 105.0g of water was added to the mixture at a point when the viscosity at 25 ℃ reached 6000 mPas to complete the reaction, thereby obtaining an additive for papermaking having a solid content of 20.1%. The obtained papermaking additive was adjusted to 20.0% of solid content and ph3.0, and the results of measurement of viscosity, peak top molecular weight, molecular weight distribution and surface tension, the ratio of peak top molecular weight to viscosity calculated from the measurement results, the ratio of equivalent anion to equivalent cation calculated from the monomer composition, and the octanol/water distribution coefficient are shown in table 6.

Examples 2 to 4, examples 6 to 16, 18 and 21 comparative examples 1 to 4, 6, 7, 9 and 10

A polyacrylamide-based additive for papermaking was obtained in the same manner as in example 1, except that the monomer composition was changed as shown in tables 4 and 5 and the viscosity of the additive for papermaking was changed as shown in table 6.

The obtained papermaking additive was adjusted to 20.0% of solid content and ph3.0 in the same manner as in example 1, and the results obtained by measuring viscosity, peak top molecular weight, molecular weight distribution and surface tension, the ratio of peak top molecular weight to viscosity calculated from the measurement results, the ratio of equivalent amount of anion to equivalent amount of cation calculated from the monomer composition, and the octanol/water distribution coefficient are shown in table 6.

Example 5

A1 liter four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet was charged with 753.0g of water, 329.07g of a 50% acrylamide aqueous solution, 32.45g of 80% dimethylaminoethylmethacrylate methyl chloride quaternary salt, 6.51g of itaconic acid, 1.38g of sodium methallylsulfonate and 23.13g of 1% N, N' -methylenebisacrylamide, and then adjusted to pH3.0 with a 30% sulfuric acid aqueous solution. Heating to 60 ℃ in a nitrogen environment, adding ammonium persulfate serving as a polymerization initiator, heating to 85 ℃ in the nitrogen environment, and preserving heat. Ammonium persulfate was additionally added after 1 hour from the start of the polymerization, and the polymerization was stopped after 2 hours from the start of the reaction. After cooling, an additive for papermaking having a solid content of 20.1% was obtained. The obtained papermaking additive was adjusted to 20.0% of solid content and ph3.0 in the same manner as in example 1, and the results obtained by measuring viscosity, peak top molecular weight, molecular weight distribution and surface tension, the ratio of peak top molecular weight to viscosity calculated from the measurement results, the ratio of equivalent amount of anion to equivalent amount of cation calculated from the monomer composition, and the octanol/water distribution coefficient are shown in table 6.

Example 17

A1 liter four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet was charged with 262.40g of water, 147.24g of a 50% acrylamide aqueous solution as a monomer (1), 7.29g of itaconic acid, 3.99g of sodium methallylsulfonate, 0.28g of N, N-dimethylacrylamide and 4.32g of 1% N, N' -methylenebisacrylamide, and adjusted to pH3.0 with a 30% NaOH aqueous solution. Subsequently, the temperature was raised to 65 ℃ under a nitrogen atmosphere, ammonium persulfate as a polymerization initiator was added to start polymerization, and the reaction temperature was raised to 90 ℃. Then, 333.20g of water, 218.33g of a 50% aqueous acrylamide solution, 36.35g of 80% dimethylaminoethylmethacrylate methyl chloride quaternary salt, 0.18g of sodium methallylsulfonate, 0.28g of N, N-dimethylacrylamide and 4.32g of 1% N, N' -methylenebisacrylamide were added to the mixture when the polymerization rate reached 97%, and ammonium persulfate was further added. Thereafter, ammonium persulfate was further added, and 111.3g of water was added to the mixture at a point when the viscosity at 25 ℃ became 9000 mPas to complete the reaction, thereby obtaining an additive for papermaking having a solid content of 20.5%. The obtained papermaking additive was adjusted to 20.0% of solid content and ph3.0 in the same manner as in example 1, and the results obtained by measuring viscosity, peak top molecular weight, molecular weight distribution and surface tension, the ratio of peak top molecular weight to viscosity calculated from the measurement results, the ratio of equivalent amount of anion to equivalent amount of cation calculated from the monomer composition, and the octanol/water distribution coefficient are shown in table 6.

Example 19

A papermaking additive having a solid content of 20.6% was obtained in the same manner as in example 17, except that the monomer composition was changed as shown in table 4 and the viscosity of the papermaking additive was changed as shown in table 6.

The obtained papermaking additive was adjusted to 20.0% of solid content and ph3.0 in the same manner as in example 1, and the results obtained by measuring viscosity, peak top molecular weight, molecular weight distribution and surface tension, the ratio of peak top molecular weight to viscosity calculated from the measurement results, the ratio of equivalent amount of anion to equivalent amount of cation calculated from the monomer composition, and the octanol/water distribution coefficient are shown in table 6.

Example 20

A papermaking additive having a solid content of 20.8% was obtained in the same manner as in example 5, except that the monomer composition was changed as shown in table 4 and the viscosity of the papermaking additive was changed as shown in table 6. The obtained papermaking additive was adjusted to 20.0% of solid content and ph3.0 in the same manner as in example 1, and the results obtained by measuring viscosity, peak top molecular weight, molecular weight distribution and surface tension, the ratio of peak top molecular weight to viscosity calculated from the measurement results, the ratio of equivalent amount of anion to equivalent amount of cation calculated from the monomer composition, and the octanol/water distribution coefficient are shown in table 6.

Example 22

An additive for papermaking was obtained in the same manner as in example 1, except that the composition of monomers was changed as shown in table 4, the viscosity of the additive for papermaking was changed as shown in table 6, and the monomers (2) were added when the polymerization rate reached 99%.

The obtained papermaking additive was adjusted to 20.0% of solid content and ph3.0 in the same manner as in example 1, and the results obtained by measuring viscosity, peak top molecular weight, molecular weight distribution and surface tension, the ratio of peak top molecular weight to viscosity calculated from the measurement results, the ratio of equivalent amount of anion to equivalent amount of cation calculated from the monomer composition, and the octanol/water distribution coefficient are shown in table 6.

Example 23

An additive for papermaking having a solid content of 21.2% was obtained in the same manner as in example 1 except that the monomer (2) was added and ammonium persulfate was further added, except that the monomer composition was changed as shown in table 4 and the viscosity of the additive for papermaking was changed as shown in table 4, except that the additional ammonium persulfate was not added.

The obtained papermaking additive was adjusted to 20.0% of solid content and ph3.0 in the same manner as in example 1, and the results obtained by measuring viscosity, peak top molecular weight, molecular weight distribution and surface tension, the ratio of peak top molecular weight to viscosity calculated from the measurement results, the ratio of equivalent amount of anion to equivalent amount of cation calculated from the monomer composition, and the octanol/water distribution coefficient are shown in table 6.

Comparative example 5

In a 1-liter four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas inlet, 70 mol% of the total amount of the monomers having the compositions shown in Table 5 was charged as a part of the polymerization components, and the mixture was diluted with water so that the concentration thereof became 30 mass%. Specifically, 219.60g of water, 255.51g of a 50% acrylamide aqueous solution as the monomer (1), 4.59g of itaconic acid, 3.10g of sodium methallylsulfonate, and 26.81g of 65% diallyldimethylammonium chloride were charged, and the pH was adjusted to 2.5 with a 30% sulfuric acid aqueous solution. Then, the temperature was raised to 60 ℃ in a nitrogen atmosphere, and ammonium persulfate as a polymerization initiator was added dropwise and polymerized. Further, after 5 minutes elapsed from the temperature rise accompanied by polymerization to the maximum temperature of 95 ℃ the remaining part (30 mol%) of the polymerization component was added dropwise. Specifically, 95.50g of water, 109.50g of a 50% acrylamide aqueous solution, 1.97g of itaconic acid, 1.33g of sodium methallylsulfonate, and 11.49g of 65% diallyldimethylammonium chloride were added dropwise to the reaction mixture (2). The polymerization rate at the start of dropping of the monomers (2) was 97%.

Then, after the completion of the dropwise addition of the remaining part of the polymerization components, ammonium persulfate as a polymerization initiator was added twice, and the reaction was continued at about 85 ℃ for 150 minutes. Then, sodium sulfite and water 363.00g as a polymerization stopper (reducing agent) were added, and cooling was performed, thereby obtaining an additive for papermaking having a solid content of 20.5%.

The obtained papermaking additive was adjusted to 20.0% in solid content, pH3.0 and viscosity (25 ℃ C.) of 581 mPas in the same manner as in example 1.

The results of measuring the viscosity, peak top molecular weight, molecular weight distribution and surface tension of the obtained papermaking additive, the ratio of peak top molecular weight to viscosity calculated from the measurement results, the ratio of equivalent anion to equivalent cation calculated from the monomer composition, and the octanol/water distribution coefficient are shown in table 6.

Comparative example 8

A1 liter four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet was charged with 269.70g of water, 145.25g of a 50% acrylamide aqueous solution as a monomer (1), 13.93g of 65% diallyldimethylammonium chloride, 2.91g of itaconic acid, 2.66g of sodium methallylsulfonate, 0.28g of N, N-dimethylacrylamide and 4.32g of 1% N, N' -methylenebisacrylamide, and adjusted to pH3.0 with a 30% sulfuric acid aqueous solution. Then, the temperature was raised to 60 ℃ in a nitrogen atmosphere, ammonium persulfate as a polymerization initiator was added to start polymerization, and the reaction temperature was raised to 85 ℃. Then, 298.80g of water, 220.80g of a 50% acrylamide aqueous solution, 20.89g of 65% diallyldimethylammonium chloride, 4.37g of itaconic acid, 0.97g of sodium methallylsulfonate, 0.28g of N, N-dimethylacrylamide and 4.32g of 1% N, N' -methylenebisacrylamide were added when the polymerization rate reached 90%, and ammonium persulfate was further added. Then, ammonium persulfate was further added, and 100.7g of water was added to the mixture when the viscosity at 25 ℃ became 5000 mPas to complete the reaction, thereby obtaining an additive for papermaking having a solid content of 20.7%. The obtained papermaking additive was adjusted to 20.0% of solid content and ph3.0, and the results of measurement of viscosity, peak top molecular weight, molecular weight distribution and surface tension, the ratio of peak top molecular weight to viscosity calculated from the measurement results, the ratio of equivalent anion to equivalent cation calculated from the monomer composition, and the octanol/water partition coefficient were shown in table 6.

[ Table 4]

The abbreviations in tables 4 and 5 are as follows.

AAm: acrylamide

SMAS: sodium methallyl sulfonate

IAc: itaconic acid (itaconic acid)

AGAc: 2-acrylamido-N-glycolic acid

AAc: acrylic acid

DMAEM-MCQ: dimethylaminoethyl methacrylate methyl chloride quaternary salt (ethylene methyl methacrylate)

DMAEA-MCQ: dimethylaminoethyl acrylate methyl chloride quaternary salt (dimethyl methacrylate chloride quaternary salt)

DMAEM-BZQ: dimethylaminoethyl methacrylate benzyl chloride quaternary product

DMAEA-BZQ: dimethylaminoethyl acrylate benzyl chloride quaternary product

DMAPA-MCQ: dimethyl aminopropyl acrylamide methyl chloride quaternary salt

DADMACQ: diallyl dimethyl ammonium chloride (diallyl dimethyl ammonium chloride)

DMAEM: dimethylaminoethyl methacrylate (dimethylamino ethyl methacrylate)

DMAEA: dimethylaminoethyl acrylate (dimethylamino acrylate)

DMAAm: n, N-dimethylacrylamide (N, N-dimethylacrylamide)

MBAAm: n, N '-methylenebisacrylamide (N, N' -methylenebisacrylamide)

[ Table 6]

< evaluation of additive for papermaking based on handsheet test >

Application example 1

To old corrugated paper pulp slurry having a concentration of 2.4%, a Freeness (Canadian Standard Freeness) of 330 and a conductivity of 350mS/m, 1.0% of aluminum sulfate (0.153% in terms of alumina) based on the solid content of the pulp and 0.4% of the additive for papermaking obtained in example 1 based on the solid content of the pulp were added. Stirring The pulp slurry, diluting The pulp slurry to 0.8% with water having a pH of 6.7, and then diluting The pulp slurry with Nubru and Wood (The Noble)&Wood) was used for papermaking, and after pressing, the sheet was dried at 100 ℃ for 100 seconds by means of a drum dryer (dry dryer) to obtain a basis weight of 80g/m²The paper of (1). The obtained paper was evaluated for specific breaking strength as described below. The results are shown in Table 7.

Specific rupture strength: the method was carried out in accordance with Japanese Industrial Standards (JIS) P8112.

Application example 2 to application example 23, and application comparative example 1 to application comparative example 10

The same operation as in application example 1 was carried out, except that in application example 1, the kind of papermaking additive was changed as shown in Table 7To obtain a basis weight of 80g/m²The paper of (1). The obtained paper was evaluated in the same manner as in application example 1. The results are shown in Table 7.

[ Table 7]

Application example 24

To an old corrugated paper pulp slurry having a consistency of 2.4%, a freeness (canadian standard freeness) of 330 and a conductivity of 350mS/m, the additive for papermaking obtained in example 1 was added in an amount of 0.4% with respect to the solid content of the pulp. Stirring The pulp slurry, diluting The pulp slurry to 0.8% with water of pH7.5, and then using Nubru and wood (The Noble)&Wood) was used, and after pressing, the sheet was dried at 100 ℃ for 100 seconds by a drum dryer to obtain a basis weight of 80g/m²The paper of (1). The obtained paper was evaluated for specific breaking strength as described below. The results are shown in Table 8.

Application example 25, application comparative example 11 to application comparative example 12

In application example 24, the same operation as in application example 24 was carried out except that the kind of papermaking additive was changed as shown in Table 8, thereby obtaining a basis weight of 80g/m²The paper of (1). The obtained paper was evaluated in the same manner as in application example 24. The results are shown in Table 8.

[ Table 8]

As can be seen from tables 7 and 8: the papermaking additive of the present invention is superior in paper strength to comparative examples that do not satisfy any of the specifications of the present invention.

According to application example 1, application example 17, and application example 20: the papermaking additive has a peak top molecular weight (Mp) of 100 to 500 ten thousand, and is more excellent in paper strength-enhancing effect than the papermaking additive outside the above range.

According to application example 1, application example 5, and application example 22, it can be seen that: the papermaking additive has a ratio Mp/V of peak top molecular weight (Mp)/viscosity (V) of 200 to 800, and is more excellent in paper strength-enhancing effect than the papermaking additive outside the above range.

According to application example 1, application example 21, and application example 23: the molecular weight distribution Mw/Mn of the additive for papermaking is 2.5 or more and 8.0 or less, and the paper strength-enhancing effect is more excellent than that of the additive for papermaking outside the above range.