Papermaking additive

Abstract

[Problem] The present invention addresses the problem of providing a papermaking additive that is capable of sufficiently exhibiting the effect required for additives for papermaking even in a deteriorated papermaking environment, and that does not cause a change in a liquid mixture such as gelation or an increase in the viscosity of the liquid mixture, or separation or deposition of components, particularly when the concentration of the liquid mixture is high. [Solution] This papermaking additive is characterized by: comprising (A) an amphoteric ion polymer having (a) a (meth)acrylamide monomer unit, (b) a cationic monomer unit, and (c) an anionic monomer unit, (B) a cationic polymer that is a hydrolysate of a polymer having a vinylformamide monomer unit, and (C) an oxoacid and / or oxoacid salt having a valence of two or more; and being an aqueous solution in which the total concentration of (A) and (B) is 10-25 mass%.

Description

Papermaking additives

[0001] The present invention relates to a papermaking additive.

[0002] In the papermaking process, various papermaking additives are used to improve operability and paper quality. For example, paper strength agents are additives that significantly contribute to improving paper strength and productivity. Several types of paper strength agents are known depending on the type of raw material, such as amphoteric acrylamide polymers.

[0003] In recent years, in the paper manufacturing process, fillers, resin components, starch, and other materials derived from waste paper have accumulated in the papermaking system due to factors such as the closed white water system imposed by wastewater regulations. These materials cause increases in the pH and electrical conductivity of papermaking water. Such changes in the environment within the papermaking system are one of the factors that reduce the effectiveness of conventional papermaking additives.

[0004] To solve these problems, a method has been reported in which a cationic polymer containing vinylamine monomer units, known as a resin with excellent flocculation properties and as a fixing aid for internally added chemicals, is used in combination with an amphoteric acrylamide polymer (Patent Document 1). Furthermore, a method has also been reported in which the two are mixed and used as a single additive to increase the efficiency of the combined use (Patent Document 2). However, significant deterioration in the papermaking system has occurred, and further improvements in performance are required.

[0005] Given this background, cationic polymers with higher cationic degree and molecular weight than conventional polymers, which have higher coagulation properties, are increasingly being used. However, when these cationic polymers are mixed with polymers having anionic groups, they are more likely to cause problems such as thickening and gelation due to ionic interactions. To avoid this problem, a method has been reported in which the pH of a mixture of a cationic polymer having vinylamine monomer units and an anionic substance is adjusted to 3 or less, thereby weakening the interaction between the two and improving stability (Patent Document 3). However, even with this technology, thickening, gelation, or component separation and precipitation cannot be sufficiently suppressed, especially when the concentration is increased to improve the effectiveness of the mixture. Therefore, a new method that can ensure storage stability even when mixed at high concentrations has been sought.

[0006] JP 2012-530196 A JP 2001-020198 A JP 2018-024760 A

[0007] An object of the present invention is to provide a papermaking additive that can fully exert the effects required of a papermaking additive even in the above-mentioned worsening papermaking environment, and that has excellent storage stability so that the mixed solution does not undergo changes such as an increase in viscosity, gelation, separation of components, or precipitation, particularly when the mixed solution has a concentration of 10% by mass or more.

[0008] The present inventors have discovered that a mixed solution can be obtained that does not impair drainage in the papermaking process or the paper strength effect of the resulting paper, and that has high storage stability even at a concentration of 10% by mass or more, by containing an amphoteric polymer (A) having (a) (meth)acrylamide monomer units, (b) cationic monomer units, and (c) anionic monomer units, a cationic polymer (B) that is a hydrolyzate of a polymer having vinylformamide monomer units, and a divalent or higher oxoacid or oxoacid salt (C), and thus completed the present invention.

[0009] That is, the present invention provides: <1> a papermaking additive comprising: (A) an amphoteric polymer having (a) (meth)acrylamide monomer units, (b) cationic monomer units, and (c) anionic monomer units; (B) a cationic polymer which is a hydrolyzate of a polymer having vinylformamide monomer units; and (C) a divalent or higher oxoacid and / or oxoacid salt, wherein the total concentration of (A) and (B) is an aqueous solution of 10 to 25% by mass; <2> the papermaking additive according to <1>, wherein the degree of cationization of (B) is 3.0 meq / g or more and 15 meq / g or less; <3> the papermaking additive according to <1>, wherein (C) is sulfuric acid and / or a sulfate; <4> the papermaking additive according to <3>, wherein the total concentration of sulfuric acid and the sulfate relative to (B) is 70 to 500% by mass calculated as a sulfate radical; <5> The papermaking additive according to <1>, characterized in that the blending ratio of (A) to (B) is (A):(B)=99:1 to 90:10. <6> The papermaking additive according to any one of <1> to <5>, characterized in that it further contains (D) a salt containing a monovalent anion that satisfies the following conditions: (1) it contains a metal ion selected from alkali metals and alkaline earth metals, and (2) the content ratio of (D) is 1 to 25 mass% of the total of (A) and (B).

[0010] The amphoteric polymer (A) contributes to improving the strength of paper produced using the papermaking additive of the present invention, and the components constituting the amphoteric polymer (A) include at least (meth)acrylamide monomer units (a), cationic monomer units (b), and anionic monomer units (c).

[0011] The (meth)acrylamide monomer (a) is acrylamide or methacrylamide, preferably acrylamide, and may be used alone or in combination.

[0012] Examples of the cationic monomer (b) include dialkylaminoalkyl (meth)acrylates, which are esters of dialkylaminoalkyl alcohols and (meth)acrylic acid, such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, and diethylaminopropyl (meth)acrylate; dialkylaminoalkyl (meth)acrylamides, such as dimethylaminopropyl (meth)acrylamide and diethylaminopropyl (meth)acrylamide; and allylamines, such as alkyldiallylamine, dialkylallylamine, diallylamine, and allylamine; and salts and quaternized products of the above-mentioned cationic monomers. These may be used alone or in combination of two or more.

[0013] Of these cationic monomers (b), dimethylaminoethyl (meth)acrylate, its quaternized methyl chloride and quaternized benzyl chloride, and diallyldimethylammonium chloride are preferred.

[0014] Examples of the anionic monomer (c) include carboxy group-containing vinyl monomers, sulfonic acid group-containing vinyl monomers (excluding (meth)allylsulfonic acid and salts thereof), and phosphonic acid group-containing vinyl monomers, and these may be used alone or in combination of two or more.

[0015] Examples of the carboxy group-containing vinyl monomer include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, 2-(meth)acrylamide-N-glycolic acid, 3-acrylamidopropanoic acid, and 4-acrylamidobutanoic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid; unsaturated tricarboxylic acids such as aconitic acid, 3-butene-1,2,3-tricarboxylic acid, and 4-pentene-1,2,4-tricarboxylic acid; and salts of the above-mentioned carboxy group-containing vinyl monomers.

[0016] Examples of the sulfonic acid group-containing vinyl monomer (excluding (meth)allylsulfonic acid and its salts) include vinylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and salts thereof.

[0017] The phosphonic acid group-containing vinyl monomers include vinylphosphonic acid and α-phenylvinylphosphonic acid and salts thereof.

[0018] Among these anionic monomers described above, carboxy group-containing vinyl monomers are preferred, and specifically, from the viewpoints of availability and versatility, acrylic acid, methacrylic acid, 2-(meth)acrylamide-N-glycolic acid, maleic acid, and itaconic acid are preferred, with acrylic acid, 2-(meth)acrylamide-N-glycolic acid, and itaconic acid being more preferred.

[0019] The proportions of the (meth)acrylamide monomer units (a), the cationic monomer units (b), and the anionic monomer units (c) constituting the amphoteric polymer (A) are preferably 60 to 99.8 mol % for (a), 0.1 to 20 mol % for (b), and 0.1 to 20 mol % for (c).

[0020] The amphoteric polymer (A) may contain a structure derived from a monomer other than the above-mentioned monomers. Examples of the other monomer include copolymerizable monomers such as chain transfer monomers, crosslinkable monomers, and nonionic vinyl monomers other than (a).

[0021] Examples of the chain transfer monomer include (meth)allyl alcohol and its ester derivatives, (meth)allyl sulfonic acid and its salts, allyl sulfides, and allyl mercaptans, and it is preferable to use (meth)allyl sulfonic acid and its salts.

[0022] Examples of the crosslinkable monomer include N-substituted (meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N-methylolacrylamide, and N,N'-methylenebis(meth)acrylamide; and polyfunctional vinyl monomers such as ethylene glycol di(meth)acrylate, triacrylformal, and divinyl adipate, with N,N-dimethyl(meth)acrylamide being preferred.

[0023] Examples of nonionic vinyl monomers other than (a) include hydrophilic vinyl monomers such as acryloylmorpholine and N-vinylpyrrolidone, and hydrophobic vinyl monomers such as (meth)acrylic acid esters, (meth)acrylonitrile, styrene, styrene derivatives, vinyl acetate, vinyl propionate, and methyl vinyl ether.

[0024] The method for producing component (A) is not particularly limited, and any method for polymerizing the above-mentioned monomers by a conventionally known method can be used. Since this method allows for greater freedom in designing the molecular structure of component (A), it is preferable to polymerize the monomers in portions and / or dropwise.

[0025] Examples of cationic polymers (B) that are hydrolyzates of polymers containing vinylformamide monomer units include polyvinylamine, poly(vinylamine-vinylformamide), poly(vinylamine-vinylformamide-acrylamide), poly(vinylamine-vinylformamide-acrylonitrile), poly(vinylamine-vinylformamide-diallyldialkylammonium salt), and polyamidine. The cationic polymers (B) may also contain cationic or nonionic monomer units. By hydrolyzing polyvinylformamide or a polymer containing vinylformamide monomer units, cationic polymers with a degree of cationization and molecular weight suitable for use as raw materials for the papermaking additive of the present invention can be obtained.

[0026] From the viewpoint of improving paper strength, the cationic polymer (B) preferably has a degree of cationization of 3.0 meq / g or more and 15 meq / g or less. Of these, a degree of cationization of 4.0 meq / g or more and 11 meq / g or less is particularly preferred. In the present application, the degree of cationization is a value measured using a Mutek Particle Charge Detector 05 with potassium polyvinyl sulfonate (PVSK) at a point where the streaming potential becomes zero as the end point.

[0027] Furthermore, poly(vinylamine-vinylformamide) and polyamidine are more preferred as the cationic polymer (B). The polymer can be synthesized, for example, by hydrolysis of a polymer containing N-vinylformamide monomer units or a copolymer of N-vinylformamide and acrylonitrile, but commercially available products can also be used. Examples of commercially available products include "KP8040 (poly(vinylamine-vinylformamide))" manufactured by Mitsubishi Chemical Corporation and "Himoc ZP700 (polyamidine)" manufactured by Hymo Co., Ltd.

[0028] The present invention contains, in addition to the above-described amphoteric polymer (A) and cationic polymer (B), which is a hydrolyzate of a polymer having vinylformamide monomer units, a divalent or higher oxoacid or oxoacid salt (C), and thereby achieves a dramatic improvement in storage stability even when the total concentration of (A) and (B) is 10% by mass or more. Examples of the divalent or higher oxoacid or oxoacid salt (C) include sulfuric acid, phosphoric acid, carbonic acid, and neutralized salts thereof. The oxoacid or oxoacid salt used can be selected depending on the circumstances, but sulfuric acid, which is a strong acid, and neutralized salts of sulfuric acid are more preferred.

[0029] As the oxoacid salt, a normal salt with a monovalent or divalent metal cation is particularly preferred. Examples of the metal salt include sodium salt, potassium salt, calcium salt, etc., with sodium salt being more preferred.

[0030] It is believed that when mixed with the cationic polymer (B), the divalent or higher valent oxoacid or oxoacid salt (C) reduces the solubility of the cationic polymer (B), thereby suppressing thickening and gelation of the mixed solution with the amphoteric polymer (A), thereby contributing to improved stability.

[0031] In the papermaking additive of the present invention, the concentration of the divalent or higher oxoacid or oxoacid salt (C), calculated as the oxoacid radical in the oxoacid or oxoacid salt (weight excluding components other than the oxoacid radical in the oxoacid salt), is preferably 70% by mass or more, more preferably 90% by mass or more, relative to the cationic polymer (B). A concentration of 70% by mass or more is believed to facilitate the reduction of the solubility of the cationic polymer (B) and inhibit ionic bonding with the amphoteric polymer (A), thereby improving the stability of the mixed solution. Furthermore, the divalent or higher oxoacid or oxoacid salt (C) is preferably sulfuric acid, a strong acid, or a neutralized salt of sulfuric acid. It is particularly preferred that the combined concentration of sulfuric acid and sulfate relative to (B), calculated as sulfate radical, is 70 to 500% by mass.

[0032] In producing the papermaking additive of the present invention, the method and order of adding the divalent or higher valent oxoacid or oxoacid salt (C) are not particularly limited. The divalent or higher valent oxoacid or oxoacid salt (C) may be added to the aqueous solution after mixing the amphoteric polymer (A) and the cationic polymer (B), or the divalent or higher valent oxoacid or oxoacid salt (C) may be added in advance to an aqueous solution of the amphoteric polymer (A) and / or the cationic polymer (B) and then mixed, or both may be used.

[0033] The papermaking additive of the present invention is an aqueous solution containing the amphoteric polymer (A) and the cationic polymer (B) at a total concentration of 10 to 25% by mass. By mixing the amphoteric polymer (A) and the cationic polymer (B) at a concentration of 10% by mass or more, the combined effect is enhanced, resulting in a papermaking additive that is more effective in improving drainage yield and paper strength.

[0034] In the present invention, the mixing ratio of the amphoteric polymer (A) and the cationic polymer (B) is arbitrary, but the effect varies depending on the mixing ratio. For example, when used as a paper strength agent, a ratio of (A):(B) = 99:1 to 90:10 is preferred. Furthermore, when the ratio of the cationic polymer (B) is 10% or more, it can also be used as a drainage yield aid and an operation improver.

[0035] When producing the papermaking additive, the order of adding the amphoteric polymer (A) and the cationic polymer (B) is not particularly limited.

[0036] The papermaking additive of the present invention preferably further contains a salt (D) containing a monovalent anion in addition to the above-mentioned (A), (B), and (C). Examples of the monovalent anion contained in the salt (D) include halide ions, carboxylate ions, and nitrate ions, with halides being preferred.

[0037] Examples of the corresponding cation include alkali metal ions, alkaline earth metal ions, transition metal ions, and ammonium ions, and among these, cations selected from alkali metal ions and alkaline earth metal ions are preferred. As the salt (D), lithium chloride, sodium chloride, potassium chloride, and cesium chloride are particularly preferred. Furthermore, the salt (D) is preferably contained in the papermaking additive of the present invention in a proportion of 1 to 25 mass% based on the total mass of the (A) and (B). By including the salt (D) in the aforementioned proportion, the synergistic effect of blending (A) and (B) is enhanced, contributing to an improvement in the paper strength of the resulting papermaking additive, as well as to an improvement in the drainage properties when added to pulp.

[0038] The papermaking additive of the present invention can be suitably used as a paper strength agent by adding it to pulp slurry during the production of paper (including paperboard). It can also be used as a drainage retention agent and an operation improvement agent. When paper is produced using the papermaking additive of the present invention, there are no particular restrictions on the use of other papermaking additives in combination, and aluminum sulfate, sizing agents, wet strength agents, etc. can be used in combination depending on the use of the resulting paper.

[0039] Synthesis examples and working examples used in the present invention will be described below, but the present invention is not limited thereto. Note that % is % by mass unless otherwise specified.

[0040] The degree of cationization of the cationic polymer (B) was measured using a Mutek Particle Charge Detector 05, with the endpoint being the point at which the streaming potential became zero in polyvinylsulfonate potassium (PVSK).

[0041] (Synthesis of amphoteric polymer (A)) A 1-liter four-neck flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was charged with 390.0 g of water, 152.0 g of a 50% (a) aqueous acrylamide solution as monomers (1), 23.7 g of 80% (b) trimethylammonium chloride ethyl methacrylate, 1.2 g of N,N-dimethylacrylamide as a crosslinkable monomer, 1.56 g of (c) itaconic acid, and 1.92 g of sodium methallylsulfonate as a chain transfer monomer. Next, the mixture was heated to 70°C under a nitrogen gas atmosphere, and ammonium persulfate was added as a polymerization initiator to initiate polymerization, and the reaction temperature was raised to 90°C. Thereafter, 150.0 g of water, 161.3 g of a 50% (a) aqueous acrylamide solution, 7.5 g of 80% (b) trimethylammonium chloride ethyl methacrylate, 0.36 g of (c) itaconic acid, 1.26 g of sodium methallylsulfonate as a chain transfer monomer, and 1.2 g of N,N-dimethylacrylamide as a crosslinkable monomer (monomers (2)) were added, and the reaction was carried out for 60 minutes. Thereafter, the reaction was terminated by cooling, and water was added, and the reaction mixture was adjusted to a concentration of 20% and a pH of 3.5 with an aqueous hydrochloric acid solution, thereby obtaining an aqueous solution of amphoteric polymer (A).

[0042] (Synthesis of (B) Cationic Polymer) Synthesis Example B-1 475 g of water was added to a 1-liter four-neck flask equipped with a stirrer, a thermometer, and a reflux condenser. Next, 25.0 g of powdered poly-N-vinylformamide (Diaflock PNVF7000: manufactured by Hymo Co., Ltd.) was slowly added under stirring to prepare a 5% aqueous solution. Next, 50.0 g of a 25% aqueous NaOH solution was added, and the temperature was raised to 80°C and stirred for 3 hours to carry out hydrolysis. Thereafter, after cooling, the pH was adjusted to 3.5 with 35% hydrochloric acid to obtain an aqueous solution of cationic polymer (B-1) having the degree of cationization shown in Table 1.

[0043] Synthesis Examples B-2 and B-3 Aqueous solutions of cationic polymers (B-2 and B-3) having the degrees of cationization shown in Table 1 were obtained in the same manner as in Synthesis Example B-1, except that the amounts of 25% NaOH aqueous solution used in the hydrolysis were changed to 64.0 g and 70.0 g, respectively.

[0044] Synthesis Example B-4: 475 g of water was placed in a 1-liter four-neck flask equipped with a stirrer, and then 25.0 g of polyamidine (Himloc ZP700, manufactured by Hymo Co., Ltd.) serving as the cationic polymer (B) was slowly added thereto with stirring to prepare a 5% aqueous solution of cationic polymer (B-4).

[0045] Synthesis Example B-5: 500 g of an acrylamide polymer having a weight average molecular weight of 100,000 and a concentration of 15% was charged into a 1-liter four-neck flask equipped with a stirrer and a thermometer. Next, a mixture of 330 g of an aqueous sodium hypochlorite solution having an effective chlorine concentration of 12% and 52 g of 25% sodium hydroxide was added dropwise over 60 minutes while cooling and stirring. The pH was then adjusted to 4.5 with 35% hydrochloric acid, yielding an aqueous solution of cationic polymer (B-5), which was a Hoffmann degradation product of the acrylamide polymer.

[0046]

[0047] Explanation of terms in the table: p(NVF-VAm): Poly(vinylamine-vinylformamide) Hoffmann-modified PAM: Hoffmann degradation product of acrylamide polymer

[0048] Example 1: 89.7 g of the aqueous solution of the amphoteric polymer (A) synthesized in Synthesis Example 1, 9.2 g of the aqueous solution of the cationic polymer (B-1) prepared in Synthesis Example 2, and 1.1 g of water were mixed to obtain 100 g of a mixed solution. The blending ratio of (A) to (B-1) was 96:4. Next, to 100 g of the mixed solution, 70% by weight of (C) sodium sulfate, a divalent oxoacid salt, calculated as sulfate radical relative to (B), and 5.3% by weight of (D) sodium chloride relative to the total of (A) and (B) were added and thoroughly mixed. Finally, the pH was adjusted to 3.5 with aqueous hydrochloric acid to obtain a papermaking additive. The final total concentration of (A) and (B) was 18.2% by weight, and the total concentration of (A), (B), (C), and (D) was 19.4% by weight.

[0049] Reference Example 1 In Reference Example 1, the aqueous solution of the amphoteric polymer (A) synthesized in Synthesis Example 1 was used as a papermaking additive as it was.

[0050] Examples 2 to 23 and Comparative Examples 1 to 4 Papermaking additives were prepared in the same manner as in Example 1, except that the types and blending ratios of the cationic polymer (B), oxoacid or oxoacid salt (C), and monovalent anion-containing salt (D) added were changed as shown in Table 2. However, the amount of water added was adjusted appropriately so that the total concentration of (A) and (B) would be the value shown in Table 2. For Comparative Example 2, aqueous hydrochloric acid solution was added until the pH shown in Table 2 was reached.

[0051] (Evaluation of storage stability) The papermaking additives obtained in Examples 1 to 23 and Comparative Examples 1 to 4 were allowed to stand in an incubator at 40°C, and the viscosity increase rate was calculated using the following formula. A lower viscosity increase rate indicates higher viscosity stability. In addition, separation stability after a certain number of days was visually observed. The results are shown in Table 2. (Formula) Viscosity increase rate = viscosity measured after 7 days / viscosity immediately after production Viscosity measurement conditions: Brookfield viscometer No. 4 rotor, 60 rpm, 25°C

[0052] (Hand-made paper evaluation) Aluminum sulfate was added to a slurry of recycled liner paper pulp adjusted to a consistency of 2.4%, a beating degree (Canadian Standard freeness) of 360, and an electrical conductivity of 800 mS / m, in an amount of 0.5% relative to the pulp solids, and each of the papermaking additives obtained in Examples 1 to 23, Reference Examples 1 and 2, and Comparative Examples 1 to 3 was added in an amount of 0.4% relative to the pulp solids, and the mixture was stirred. The pulp was then diluted to a consistency of 0.8% with water having a pH of 6.5 and an electrical conductivity of 800 mS / m, after which the paper was made using a Noble & Wood sheet machine and dried in a drum dryer at 100°C for 100 seconds to give a paper with a basis weight of 100 g / m. ２ The resulting handsheets were conditioned for 24 hours at 23°C and 50% RH, after which the burst strength index (hereinafter sometimes referred to as paper strength) was measured using the following method. Furthermore, pulp slurries were prepared in the same manner as above until the pulp concentration reached 0.8%, and then the freeness test (DDT) was performed. The results are shown in Table 2.

[0053] Burst strength index: Based on JIS P-8112. Freeness: 500 mL of diluted pulp slurry (concentration 0.8%) was poured into a 7.5 cm diameter jar, and while stirring at 600 rpm, the bottom cock was opened and the slurry was filtered through a 100 mesh wire mesh. The time until a certain amount of filtrate was reached was measured, and this can be used to evaluate freeness. The time until the amount of filtrate reached 150 g was measured. The smaller the value, the better the freeness.

[0054]

[0055] Evaluation items in Table 2 Separation stability: ○...No separation for 180 days or more, △...No separation for 90 days or more.

[0056] Comparative Example 1, in which the total concentration of (A) and (B) was less than 10%, and Comparative Example 4, in which a cationic polymer that is a Hoffmann degradation product was used, were unable to exhibit the same paper strength effect as the Examples.

[0057] Examples 1 to 23, in which an oxo acid or oxo acid salt (C) was blended, had improved viscosity stability as a papermaking additive compared to Comparative Examples 2 and 3, in which no oxo acid or oxo acid salt (C) was blended. Furthermore, a comparison of Examples 1, 3, 6, 8, and 19 with Examples 20 and 21 shows that by setting the concentration of oxo acid or oxo acid salt (C) relative to (B) within a preferred range, it is possible to achieve both good viscosity stability and separation stability.

[0058] Comparison of Examples 3, 14, and 15 with Examples 22 and 23 shows that the paper strength is improved by setting the compounding ratio of (A) and (B) within a preferred range.

[0059] A comparison between Example 3 and Example 2 shows that the addition of the salt (D) containing a monovalent anion to the mixture of (A), (B) and (C) improves paper strength and drainage.

[0060] From the above, the papermaking additive of the present invention can fully exert the required paper strength effect and drainage effect, and also has excellent viscosity stability.

Claims

1. A papermaking additive comprising: (A) an amphoteric polymer having (a) (meth)acrylamide monomer units, (b) cationic monomer units, and (c) anionic monomer units; (B) a cationic polymer which is a hydrolyzate of a polymer having vinylformamide monomer units; and (C) a divalent or higher valent oxoacid and / or oxoacid salt, wherein the total concentration of (A) and (B) is 10 to 25% by mass.

2. The papermaking additive according to claim 1, wherein the degree of cationization of (B) is 3.0 meq / g or more and 15 meq / g or less.

3. The papermaking additive according to claim 1, wherein (C) is sulfuric acid and / or a sulfate salt.

4. The papermaking additive according to claim 3, wherein the total concentration of sulfuric acid and sulfate salts in (B) is 70 to 500% by mass in terms of sulfate radicals.

5. The papermaking additive according to claim 1, wherein the blending ratio of (A) to (B) is (A):(B)=99:1 to 90:

10.

6. The papermaking additive according to any one of claims 1 to 5, further comprising (D) a salt containing a monovalent anion that satisfies the following condition: (1) Contains a metal ion selected from alkali metals and alkaline earth metals. (2) The content of (D) is 1 to 25 mass % of the total of (A) and (B).

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