JP7629633B2 - Method for producing paper sizing agent - Google Patents

Description

The present invention relates to a method for producing a paper sizing agent, and more specifically, to a method for producing a paper sizing agent that imparts excellent sizing performance by coating the surface of base paper.

Conventional paper sizing agents include cationic solution-type paper sizing agents, such as quaternized styrene-dimethylaminoethyl (meth)acrylate copolymers and quaternized styrene-dimethylaminopropylacrylamide copolymers, which dissolve resins consisting of hydrophobic and hydrophilic parts, and anionic solution-type paper sizing agents, such as alkali metal salts of styrene-maleic acid copolymers, alkali metal salts of styrene-(meth)acrylic acid copolymers, and alkali metal salts of α-olefin maleic acid copolymers. These solution-type paper sizing agents have high viscosity at concentrations that can be sold commercially, making it difficult to increase the concentration, which is a cost problem. In addition, the sizing agent foams a lot, which is a drawback in that it is prone to problems with operability during papermaking. Therefore, it is necessary to use a large amount of defoamer in combination to improve operability in actual machines, and they are not satisfactory in terms of cost and sizing performance.

Recently, emulsion types incorporating hydrophobic particles that are an improvement over these have become common. By incorporating hydrophobic particles, it is possible to reduce the viscosity of the product, and it is possible to reduce costs or foaming by increasing the concentration, which was difficult with solution types. These emulsion types include cationic emulsion types and anionic emulsion types. Examples of cationic emulsion types include an internal sizing agent for papermaking, which is obtained by emulsion-polymerizing a polymerizable hydrophobic monomer, preferably styrene and 2-ethylhexyl acrylate, in the presence of an epihalohydrin quaternary product of a styrene-dimethylaminoalkyl (meth)acrylate copolymer (see, for example, Patent Document 1), and an internal sizing agent for papermaking, which is obtained by emulsion-polymerizing a styrene-based compound and a (meth)acrylic acid ester having an alkyl group with 3 to 6 carbon atoms in the presence of a quaternary product of a copolymer consisting of a styrene-based compound and a dialkylaminoalkyl (meth)acrylate. Surface sizing agents (see, for example, Patent Document 2), surface sizing agents for papermaking obtained by emulsion polymerization of a polymerizable hydrophobic monomer, preferably a styrene-based compound and a (meth)acrylic acid ester, in the presence of a quaternized product of a copolymer consisting of a styrene-based compound and a dialkylaminoalkyl (meth)acrylamide (see, for example, Patent Document 3), and surface sizing agents for papermaking containing an emulsion obtained by emulsion polymerization of 10 to 500 parts by weight of a hydrophobic unsaturated monomer in an aqueous solution containing 100 parts by weight of a water-soluble copolymer containing a carboxyl group-containing unsaturated monomer and a hydrophobic unsaturated monomer (see, for example, Patent Document 4) are known as anionic emulsion types.

However, the size effect was not satisfactory.

Japanese Unexamined Patent Publication No. 54-006902 Japanese Patent Application Publication No. 11-256496 Japanese Patent Application Publication No. 11-279983 Japanese Patent Application Publication No. 08-246391

The problem that this invention aims to solve is to provide a method for producing a paper sizing agent that has a better sizing effect than conventional methods.

As a result of intensive research to solve the above problems, the inventors discovered that a sizing agent obtained by polymerization in the presence of iodine and/or an iodine compound has excellent sizing effect, and thus completed the present invention.

That is, the present invention, which is a means for solving the above problems,
<1> A method for producing a paper sizing agent, characterized in that in the following steps (I) and/or (II), iodine and/or an iodine compound are used in an amount of 50 ppm or more in terms of iodine atoms relative to the total amount of monomers used as polymerization components:
(I): A step of polymerizing a copolymer (A) containing a hydrophobic monomer (a1) and a hydrophilic monomer (a2) as polymerization components; (II): A step of polymerizing a hydrophobic monomer (b) in the presence of the copolymer (A) and/or a surfactant; <2> A method for producing a papermaking sizing agent according to <1> above, characterized in that the mass ratio of the hydrophobic monomer (a1) to the hydrophilic monomer (a2) is hydrophobic monomer (a1):hydrophilic monomer (a2)=(50-85):(15-50);
<3> The method for producing a papermaking sizing agent according to <1> or <2>, characterized in that the mass ratio of the copolymer (A) to the hydrophobic monomer (b) is copolymer (A):hydrophobic monomer (b)=(10-100):(0-90);
<4> The method for producing a paper sizing agent according to any one of <1> to <3>, wherein the hydrophilic monomer (a2) of the copolymer (A) contains one or more selected from a vinyl monomer containing a tertiary amino group and a vinyl monomer containing a carboxylic acid group.
It is.

By using the paper sizing agent obtained by the method for producing a paper sizing agent of the present invention, paper with excellent sizing performance can be obtained, and the sizing performance of paperboard in particular can be improved.

The present invention relates to a method for producing a paper sizing agent, characterized in that the paper sizing agent is obtained by using iodine and/or an iodine compound in an amount of 50 ppm or more, calculated as iodine atoms, based on the total amount of monomers used as polymerization components in the following steps (I) and/or (II):
(I): A step of polymerizing a copolymer (A) containing a hydrophobic monomer (a1) and a hydrophilic monomer (a2) as polymerization components. (II): A step of polymerizing a hydrophobic monomer (b) in the presence of the copolymer (A) and/or a surfactant.

The method for producing a paper sizing agent of the present invention can produce two types of paper sizing agents, broadly classified as (1) solution type and (2) emulsion type, as follows.

(1) Solution type A solution type paper sizing agent is obtained through the above-mentioned process (I). Specifically, it is a paper sizing agent containing, as a sizing agent component, a copolymer (A) obtained by using a hydrophobic monomer (a1) and a hydrophilic monomer (a2) as polymerization components, polymerizing the monomers in a suitable solvent described below using a radical polymerization initiator, and distilling off the solvent as necessary after the polymerization is completed.

(2) Emulsion type Emulsion type paper sizing agents are obtained by the above-mentioned step (II) alone or by the steps (I) and (II). These paper sizing agents contain hydrophobic particles as a sizing agent component obtained by emulsion polymerization of a hydrophobic monomer (b) as a polymerization component in the presence of a copolymer (A) and/or a surfactant. In this case, the copolymer (A) may be one obtained by the above-mentioned step (I) or a commercially available one, so long as it is a copolymer containing a hydrophobic monomer (a1) and a hydrophilic monomer (a2) as polymerization components.

In the method for producing a paper sizing agent of the present invention, iodine and/or iodine compounds are used in the above steps (I) and/or (II) in an amount of 50 ppm or more in terms of iodine atoms relative to the total amount of monomers used as polymerization components. In other words, iodine and/or iodine compounds may be used in at least one of steps (I) or (II), and may be used in both steps (I) and (II). However, from the viewpoint of improving sizing properties compared to conventional paper sizing agents that do not use iodine and/or iodine compounds, the amount of iodine atoms must be 50 ppm or more relative to the total amount of monomers used in each step.

Examples of iodine and/or iodine compounds include iodine, as well as iodine compounds such as iodoform, potassium iodide, and iodoacetic acid. Iodine and/or iodine compounds may be used alone or in combination of two or more.

The amount of iodine and/or iodine compounds used can be determined appropriately depending on the molecular weight of the polymer to be obtained, but if the amount is too large, the polymer cannot be obtained, so the amount is preferably 50 to 50,000 ppm, and more preferably 50 to 20,000 ppm, relative to the monomer.

Examples of the hydrophobic monomer (a1) that can be used in step (I) include styrenes such as styrene, α-methylstyrene, vinyltoluene, and divinylbenzene; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, normal butyl (meth)acrylate, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl ( Examples of the monomers include alkyl (meth)acrylates such as methacrylate; dialkyl esters of maleic acid and fumaric acid; vinyl esters such as vinyl acetate and vinyl propionate; nitriles such as acrylonitrile and methacrylonitrile; linear α-olefins such as 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene; cyclic olefins such as cyclohexene; N-alkyl (meth)acrylamides; and alkyl vinyl ethers such as methyl vinyl ether. One of these monomers can be used alone, or two or more can be used in combination. Among these, styrenes and/or alkyl (meth)acrylates are preferred, and more preferred are styrene and/or butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate.

The hydrophilic monomer (a2) that can be used in step (I) includes cationic monomers, anionic monomers, and nonionic monomers, and among these, cationic monomers and anionic monomers are preferred. These hydrophilic monomers can be used alone or in combination of two or more.

The cationic monomer may be any vinyl monomer having cationic properties, and specific examples thereof include primary amines such as allylamine; secondary amines such as diallylamine; dialkylaminoalkyl (meth)acrylates such as dimethylaminoethyl (meth)acrylate and dimethylaminopropyl (meth)acrylate; tertiary amines such as (dialkyl)aminoalkyl (meth)acrylamides such as dimethylaminopropyl (meth)acrylamide; and quaternary ammonium salts obtained by quaternizing the above cationic monomers with a quaternizing agent or the like. One or more of these cationic monomers can be used.

It is preferable to use a tertiary amine as the cationic monomer, as this is expected to improve the stability and sizing performance of the sizing agent, and among these, dimethylaminoethyl (meth)acrylate and dimethylaminopropyl (meth)acrylamide are more preferable.

When using the above-mentioned primary, secondary and tertiary amines, it is preferable to make them into salts using a neutralizing agent such as formic acid, acetic acid, or other carboxylic acid, malic acid, tartaric acid, citric acid, or other oxycarboxylic acid, or sulfuric acid, hydrochloric acid, or other inorganic acid before or after polymerization in order to impart hydrophilicity.

Examples of anionic monomers include carboxyl group-containing monomers, sulfonic acid group-containing monomers, phosphate ester group-containing monomers, and salts thereof. These anionic monomers can be used alone or in combination. It is preferable to convert the anionic monomers into salts using alkalis such as alkali metal hydroxides (e.g., sodium hydroxide and potassium hydroxide), ammonia, and amine bases (e.g., methylamine and dimethylamine) as neutralizing agents before or after polymerization, since this can impart hydrophilicity to the anionic monomers.

Examples of carboxyl group-containing monomers include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, their acid anhydrides, neutralized salts, and half esters. Examples of sulfonic acid group-containing monomers include vinyl sulfonic acid, (meth)allyl sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and sulfonated styrene. Examples of phosphate ester group-containing monomers include phosphate esters of hydroxyalkyl (meth)acrylates. Of these, it is preferable to use carboxyl group-containing monomers, and more preferably acrylic acid, methacrylic acid, maleic acid, and salts thereof. One or more of these anionic monomers can be used.

Examples of nonionic monomers include (meth)acrylamide; hydroxyl group-containing (meth)acrylates such as hydroxyethyl acrylate and hydroxyethyl methacrylate. These nonionic monomers can be used alone or in combination.

From the viewpoint of emulsion stability and sizing performance during production, the mass ratio of hydrophobic monomer (a1) to hydrophilic monomer (a2) is preferably 50-85:15-50, and more preferably 70-85:15-30.

In addition, copolymerizable vinyl monomers other than the hydrophobic monomer (a1) and the hydrophilic monomer (a2) may be used as polymerization components of the copolymer (A) as long as the effect of the papermaking sizing agent is not impaired. It is preferable that the amount of such a monomer is less than 10% by mass of the polymerization components constituting the copolymer (A).

Examples of radical polymerization initiators include oil-soluble azo initiators such as 2,2'-azobisisobutyronitrile and dimethyl 2,2'-azobis-(2-methylpropionate); oil-soluble organic peroxides such as benzyl peroxide, tertiary butyl peroxybenzoate and tertiary butyl peroxy-2-ethylhexanoate; persulfates such as ammonium persulfate, potassium persulfate and sodium persulfate; water-soluble peroxides such as hydrogen peroxide; redox polymerization initiators formed by combining these persulfates and peroxides with a reducing agent; water-soluble azo initiators such as 2,2'-azobis(2-amidinopropane)dihydrochloride; and water-soluble organic peroxides such as tertiary butyl hydroperoxide. However, the radical polymerization initiator is not limited to these, and other known and commonly used polymerization initiators can also be used. Two or more of these polymerization initiators may be used in combination.

The amount of the polymerization initiator used is usually 0.5 to 10% by mass based on the total amount of the monomers used in the present invention. The polymerization initiator may be charged together with the monomers in a reaction vessel all at once, or may be added dropwise continuously.

In addition, known chain transfer agents can be used, such as α-methylstyrene dimer; alkyl mercaptan compounds such as normal octyl mercaptan, tertiary dodecyl mercaptan, and normal dodecyl mercaptan; mercaptan derivatives such as thioglycolic acid derivatives, mercaptopropionic acid derivatives, mercaptoethanol, thiomalic acid, and thiosalicylic acid; and alcohols such as ethanol and isopropyl alcohol.

These chain transfer agents may be charged together with the monomers in a reaction vessel at once, or may be added dropwise continuously. Two or more of these chain transfer agents may be used in combination. The amount of chain transfer agent used depends on the chain transfer agent used, but is preferably in the range of 0 to 200% by mass based on the total amount of monomers used in the present invention.

Examples of solvents that can be used in step (I) include water; lower alcohol-based organic solvents such as methyl alcohol, ethyl alcohol, and isopropyl alcohol; aromatic organic solvents such as benzene, toluene, and xylene; ketone-based organic solvents such as acetone and methyl ethyl ketone; and acetic acid-based organic solvents such as acetic anhydride and glacial acetic acid. These organic solvents can be used alone or in combination of two or more. Usually, after polymerization, water and an appropriate amount of a neutralizing agent for the copolymer (A) are mixed together to prepare an aqueous solution, but as a paper sizing agent, it is preferable that no organic solvent, which is a hazardous material, remains. For this reason, lower alcohol-based solvents and ketone-based organic solvents with a boiling point of less than 100°C that can be easily distilled off after polymerization, and toluene that can be distilled off by azeotropy with water are preferably used.

The polymerization method in step (I) can be, for example, a batch addition polymerization method in which all the monomers are charged into a reaction vessel at once and polymerized, a divided addition polymerization method in which some or all of the monomers are divided and added to the reaction vessel and polymerized, and a continuous drop polymerization method in which some or all of the monomers are continuously dropped into the reaction vessel and polymerized.

The aqueous solution containing copolymer (A) obtained in step (I) can be used as a solution-type paper sizing agent as is, but the aqueous solution can also be used in step (II).

When a cationic monomer having a tertiary amino group is used as the hydrophilic monomer (a2), it is preferable to quaternize the tertiary amino group of the copolymer by a known, conventional method. Examples of quaternizing agents that can be used for the quaternization include alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide, and oxides such as styrene oxide; organic halides such as methyl chloride, ethyl chloride, benzyl chloride, epichlorohydrin, glycidyl trimethyl ammonium chloride, and 3-chloro-2-hydroxypropyl trimethyl ammonium chloride; dimethyl sulfate, and diethyl sulfate.

In step (II), hydrophobic monomer (b) is emulsion-polymerized in water in the presence of copolymer (A) and/or a surfactant to form hydrophobic particles and prepare an emulsion.

In the present invention, the surfactant refers to a known low molecular weight surfactant, and examples of such surfactants include cationic, nonionic, amphoteric or anionic surfactants and surfactants capable of radical polymerization. At least one selected from these groups can be used. The amount of the surfactant used is usually 0 to 10 mass % based on the total amount of monomers used in the present invention. The surfactant may be charged in a reaction vessel together with the monomers all at once, or may be added dropwise continuously together with the monomers.

Examples of cationic surfactants include acetates and epichlorohydrin-modified primary and secondary amines, tetraalkylammonium chloride, trialkylbenzylammonium chloride, epichlorohydrin-modified rosinamine acetate, monooxyethylene alkylamines, and polyoxyethylene alkylamines.

Examples of anionic surfactants include alkyl sulfates, alkyl ether sulfates, alkylbenzene sulfonates, and alkali salts of naphthalenesulfonic acid-formaldehyde condensates.

Nonionic surfactants include polyoxyalkylene alkyl ethers, polyoxyalkylene alkyl phenyl ethers, polyoxyalkylene fatty acid esters, sorbitan fatty acid esters, etc.

Furthermore, examples of radically polymerizable surfactants include polyoxyalkylene alkyl ethers, polyoxyalkylene phenyl ethers, and polyoxyalkylene mono- or distyryl phenyl ethers, each of which has one or more functional groups with a carbon-carbon double bond in the molecule, such as (meth)allyl groups, 1-propenyl groups, 2-methyl-1-propenyl groups, isopropenyl groups, vinyl groups, and (meth)acryloyl groups, as well as sulfonates and sulfate ester salts derived therefrom.

As the hydrophobic monomer (b), any of the monomers listed as the hydrophobic monomer (a1) used in step (I) can be used, and these monomers can be used alone or in a mixture of two or more. Among these, styrenes and alkyl (meth)acrylates are preferred from the viewpoint of sizing performance and emulsion stability during emulsion polymerization, and styrene and/or butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are more preferred. Note that a portion of the hydrophobic monomer (b) can also be replaced with a vinyl monomer copolymerizable with the hydrophobic monomer (b) within a range that does not impair the effects of the present invention.

When copolymer (A) is used in step (II), the mass ratio of copolymer (A) to hydrophobic monomer (b) is preferably (10-100):(0-90) from the viewpoint of the stability and size performance of the resulting copolymer, and more preferably (20-100):(0-80).

In step (II), the hydrophobic monomer (b) component is emulsion-polymerized in water using a radical polymerization initiator, and the polymerization method can be any of the conventionally known polymerization methods that can be applied in step (I). In this case, the radical polymerization initiator can be the same as that which can be used in step (I).

Additives such as antioxidants, defoamers, preservatives, chelating agents, and water-soluble aluminum compounds may be added to the paper sizing agent obtained by the method for producing a paper sizing agent of the present invention, as necessary.

Paper sizing agents can be used as surface sizing agents or internal sizing agents for papermaking, but it is preferable to use them as surface sizing agents.

Surface sizing agents are applied to base paper to produce a sizing effect mainly on the surface of the paper, while internal sizing agents are added to the pulp slurry before paper is manufactured to produce a sizing effect throughout the paper.

When used as a papermaking sizing agent, the pulp used in the base paper or paper to which it is applied may be bleached or unbleached chemical pulp such as kraft pulp or sulfite pulp, bleached or unbleached high-yield pulp such as groundwood pulp, mechanical pulp or thermomechanical pulp, or waste paper pulp such as recycled newspapers, magazines, cardboard or deinked waste paper.

Additives such as water-soluble aluminum compounds such as aluminum sulfate, fillers, dyes, rosin-based sizing agents for acidic papermaking, alkyl ketene dimer and alkenyl succinic anhydride-based sizing agents for neutral papermaking, rosin-based sizing agents for neutral papermaking, dry strength agents, wet strength agents, retention agents, drainage agents, coagulants, and defoamers may be added as necessary to the slurry obtained by dispersing the pulp in water to obtain base paper or paper in order to achieve the physical properties required for each paper type. When used as an internal sizing agent, they are added to the pulp slurry. Examples of fillers include clay, talc, titanium oxide, and heavy and light calcium carbonate. These may be used alone or in combination.

When used as a surface sizing agent, the coating machine that can be used is a size press, a film press, a gate roll coater, a rod metering coater, a blade coater, a calendar, a bar coater, a knife coater, an air knife coater, a curtain coater, etc. It can also be applied to the surface of the base paper by a spray coater.

When applied as a surface sizing agent, the sizing agent may be used as is or diluted with water, etc., but it may also be used by mixing at least one selected from the group consisting of starches such as oxidized starch, phosphate esterified starch, enzyme-modified starch, ammonium persulfate-modified starch, cationic starch, and amphoteric starch, celluloses such as carboxymethylcellulose, polyvinyl alcohols, polyacrylamides, and water-soluble polymers such as sodium alginate, into the coating liquid. In addition, additives such as other surface sizing agents, pH adjusters such as aluminum sulfate, conductive agents such as sodium chloride and sodium sulfate, anti-slip agents, preservatives, rust inhibitors, defoamers, viscosity adjusters, dyes, and pigments may also be used in combination.

Examples of sized papers that can be obtained using paper sizing agents include various types of paper and paperboard. For example, recording papers such as PPC paper, inkjet recording paper, laser printer paper, form paper, thermal transfer paper, and thermal recording paper; coated papers such as art paper, cast coated paper, and fine coated paper; wrapping papers such as kraft paper and pure white roll paper; Western papers such as notebook paper and book paper; newsprint; paperboards for paper containers such as manila cardboard, white cardboard, and chipboard; paperboards such as liners and corrugated cores, etc.

The concentration of the coating liquid when applied as a surface sizing agent is usually 0.1 to 5% by mass, preferably 0.2 to 1% by mass. If it is less than 0.1% by mass, the sizing effect may be insufficient, and even if it is used in excess of 5% by mass, there is little further improvement in the sizing effect and it may be economically disadvantageous, so it is not preferred.

Usually, the coating amount is 0.01 to 1 g/m ² in terms of solid content, and preferably 0.02 to 0.2 g/m ^2. When the amount is within the above range, the sizing effect is particularly good.

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 these examples. In the following, "parts" and "%" mean parts by mass and % by mass, respectively, unless otherwise specified.

1-1. Production of paper sizing agent (cationic copolymer) (1) Production of solution type (Example 1)
A 1-liter four-neck flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was charged with 75 parts of styrene as a hydrophobic monomer (a1), 25 parts of dimethylaminoethyl methacrylate as a hydrophilic monomer (a2), 1.0 part of iodine as an iodine compound (10,000 ppm relative to the monomer as an iodine atom), 2.0 parts of azobisisobutyronitrile and 50 parts of toluene, and held at 80° C. for 7 hours, then charged with 0.7 parts of azobisisobutyronitrile and held at the same temperature for 3 hours. Next, 10.6 parts of 90% acetic acid was added as a neutralizing agent, and then 200 parts of water was added to obtain an emulsion, and the temperature was further increased to distill off toluene.
Next, 14.7 parts of epichlorohydrin (100 mol % based on dimethylaminoethyl methacrylate) was added as a quaternizing agent, and the mixture was reacted at 60° C. for 4 hours. 258 parts of water was then added to obtain a solution-type paper sizing agent containing 20.1% of copolymer (A-1) as a solid content.

(Comparative Example 1)
A comparative solution-type paper sizing agent containing copolymer (A-2) was obtained in the same manner as in Example 1, except that iodine and/or an iodine compound was not used.

(Comparative Example 2)
To the solution containing the copolymer (A-2) obtained in Comparative Example 1, iodine dissolved in isopropyl alcohol was added in an amount of 10,000 ppm based on the mass of the copolymer before neutralization and quaternization to obtain a solution containing the copolymer (A-3), thereby obtaining a solution-type comparative papermaking sizing agent.

(Explanation of abbreviations in the table)
St: styrene DMEM: dimethylaminoethyl methacrylate Epi: epichlorohydrin

*Added to the solution containing copolymer (A-2) after polymerization.

(2) Production of emulsion type (Example 2)
Into the same reactor as in Example 1, 500 parts of the aqueous solution of the copolymer (A-1) produced in Example 1 (100 parts as solids) was placed, 192 parts of water, 50 parts of isobutyl methacrylate and 50 parts of normal butyl acrylate as hydrophobic monomers (b), 0.10 parts of iodine as an iodine compound (as iodine atoms, relative to monomer 1000 ppm) and 10 parts by weight of 5% 2,2'-azobis (2-methylpropiondiamidine) dihydrochloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.: water-soluble azo polymerization initiator V-50) aqueous solution (hereinafter, sometimes simply abbreviated as "5% V-50 aqueous solution") were added, and the temperature was raised to 80 ° C. while mixing and stirring under a nitrogen stream. The emulsion polymerization reaction was completed by holding at 80 ° C. for 4 hours, and an emulsion-type papermaking sizing agent (E-1) with a solids concentration of 25% was obtained.

(Examples 3 to 16, Comparative Examples 3 to 4)
Solutions containing copolymers (A-4) to (A-9) were obtained in the same manner as in Example 1, except that the type and amount of hydrophobic monomer (a1), the type and amount of hydrophilic monomer (a2), the amount of quaternizing agent, and the type and amount of iodine and/or iodine compound were changed as shown in Table 2, and were used in polymerizing the paper sizing agents of Examples 5 to 8, 11, and 12.
Next, the type and amount of copolymer (A), the type and amount of hydrophobic monomer (b), and the type and amount of iodine and/or iodine compound were changed as shown in Table 3, and emulsion-type paper sizing agents (E-2) to (E-17) were obtained in the same manner as in Example 2.

(Explanation of abbreviations in the table)
St: styrene IBMA: isobutyl methacrylate TBA: t-butyl acrylate DMEM: dimethylaminoethyl methacrylate DMPMA: dimethylaminopropyl methacrylamide Epi: epichlorohydrin

*As iodine atoms

(Explanation of abbreviations in the table)
IBMA: isobutyl methacrylate BA: n-butyl acrylate St: styrene EHA: 2-ethylhexyl acrylate

*As iodine atoms

1-2. Evaluation test of papermaking sizing agent as surface sizing agent (Test Example 1) Evaluation of sizing performance on paperboard (1) Papermaking of paperboard base paper Using recycled corrugated cardboard pulp with 380 ml Canadian Standard Freeness, ash content of 10.0%, and pH of 7.0, 1.0% (absolute dry weight basis) of aluminum sulfate was added to the pulp, 0.3% of a PAM-based strength agent (manufactured by Seiko PMC Co., Ltd.; DS4433) was added as a strength agent, and 0.1% of a rosin-based sizing agent (manufactured by Seiko PMC Co., Ltd.; CC1401) was added as a strength agent, and the mixture was diluted to 0.8% with water having an electrical conductivity of 170 mS/m. Then, 0.01% (absolute dry weight basis) of a retention aid (manufactured by Heimo Co., Ltd.; Heimolock ND300) was added to the diluted pulp slurry, and paper was made on a Noble and Wood papermaking machine to a basis weight of 120 g/ ^m2 . The pH of the paper at this time was 7.3. The wet paper was dried using a drum dryer at 100° C. for 160 seconds.

(2) Method for preparing coating liquid Corn starch (Corn Starch Y, manufactured by Nihon Shokuhin Kako Co., Ltd.) was diluted with water to a concentration of 10%, and 1% ammonium persulfate based on the solid content of the starch was added thereto. The mixture was gelatinized at 95° C. for 20 minutes and adjusted to pH 6.0 using sodium hydroxide. Thereafter, the paper sizing agents obtained in Examples 1 to 16 and Comparative Examples 1 to 4 were added thereto so as to have the following solid content concentrations to prepare coating liquids.
Solids concentration of coating liquid: Ammonium persulfate modified starch...6%, paper sizing agent...0.3%

(3) Manufacture of paperboard and evaluation of sizing performance The coating liquid prepared in (2) above was applied to the base paper produced in (1) above using a size press. The solid coating amount of the surface sizing agent on this coated paper was 0.06 g/ ^m2 . After coating, the paper was dried at 100°C for 80 seconds using a drum dryer. The obtained test paper was conditioned for 24 hours in a constant temperature and humidity environment (23°C, 50% relative humidity), and the Cobb water absorbency (120 seconds) (based on JIS P8140) was measured. The smaller the Cobb water absorbency value, the better the sizing performance. The evaluation results are shown in Table 4.

The evaluation results show that the papers in Evaluation Examples 1 to 16 in Table 4, which were produced using the papermaking sizing agent of the present invention, have superior sizing performance (Cobb water absorbency) compared to the papers in Comparative Evaluation Examples 1 to 4, which were produced using a papermaking sizing agent different from the papermaking sizing agent of the present invention.

2-1. Production of paper sizing agent (anionic copolymer) (1) Production of solution type (Example 17)
In a reactor similar to that of Example 1, 70 parts of styrene as the hydrophobic monomer (a1), 30 parts of methacrylic acid as the hydrophilic monomer (a2), 1.2 parts of iodine as an iodine compound (as iodine atoms, relative to the monomer 12000 ppm), 2.0 parts of azobisisobutyronitrile and 100 parts of isopropyl alcohol were charged, and the mixture was held at 80 ° C. for 7 hours, and then 1.0 part of azobisisobutyronitrile was charged and further held at the same temperature for 3 hours. Next, 65.2 parts of 30% potassium hydroxide was added as a neutralizing agent, and then 300 parts of water was added, and the temperature was further increased to distill off the isopropyl alcohol. Water was added to obtain a solution-type papermaking sizing agent containing 20.2% of copolymer (A-10) as a solid content.

(Comparative Example 5)
A comparative solution-type paper sizing agent containing copolymer (A-11) was obtained in the same manner as in Example 17, except that iodine was not used.

(Comparative Example 6)
To the solution containing the copolymer (A-11) obtained in Comparative Example 5, iodine dissolved in isopropyl alcohol was added in an amount of 12,000 ppm based on the mass of the copolymer before neutralization to obtain a solution containing the copolymer (A-12), thereby obtaining a solution-type comparative papermaking sizing agent.

(Explanation of abbreviations in the table)
St: styrene MAA: methacrylic acid KOH: potassium hydroxide

*Added to the solution containing copolymer (A-11) after polymerization.

(2) Production of emulsion type (Examples 18 to 32, Comparative Examples 7 to 8)
Solutions containing copolymers (A-13) to (A-18) were obtained in the same manner as in Example 17, except that the type and amount of hydrophobic monomer (a1), the type and amount of hydrophilic monomer (a2), and the type and amount of iodine and/or iodine compound used were changed as shown in Table 6. These solutions were used in polymerizing the sizing agents of Examples 21 to 24, 28, and 29.
Next, emulsion-type paper sizing agents (E-18) to (E-34) were obtained in the same manner as in Example 2, except that the type and amount of copolymer (A), the type and amount of hydrophobic monomer (b), and the type and amount of iodine and/or iodine compound were changed as shown in Table 7, and the 5% V-50 aqueous solution was changed to 5% ammonium persulfate.

(Explanation of abbreviations in the table)
St: styrene IBMA: isobutyl methacrylate EHA: 2-ethylhexyl acrylate MAA: methacrylic acid MAn: maleic anhydride AA: acrylic acid IA: itaconic acid KOH: potassium hydroxide

*As iodine atoms

(Explanation of abbreviations in the table)
IBMA: isobutyl methacrylate BA: n-butyl acrylate St: styrene EHA: 2-ethylhexyl acrylate

*As iodine atoms

2-2. Evaluation test of papermaking sizing agents as surface sizing agents (Test Example 2) Evaluation of sizing performance on neutral wood-free paper (1) Papermaking of neutral wood-free base paper
Pulp (mixed pulp with a pulp ratio of hardwood to softwood of 9:1) beaten to 380 ml Canadian Standard Freeness was made into a 2.5% slurry, to which 2% (bone dry weight basis) of calcium carbonate (TP121S, manufactured by Okutama Kogyo Co., Ltd.) was added. Next, 0.5% (bone dry weight basis) of aluminum sulfate, 0.5% (bone dry weight basis) of cationic starch (Cato304, manufactured by National Starch Co., Ltd.) and 0.03% (bone dry weight basis) of an alkyl ketene dimer sizing agent (AD1602, manufactured by Seiko PMC Co., Ltd.) were added in sequence, and the pulp slurry was diluted to a concentration of 0.25% with dilution water of pH 7.5. Thereafter, calcium carbonate (TP121S, manufactured by Okutama Kogyo Co., Ltd.) was added to the diluted pulp slurry in an amount of 15% (bone dry weight basis) based on the pulp, and a retention aid (NR12MLS, manufactured by Hymo Co., Ltd.) was added in an amount of 0.01% (bone dry weight basis) based on the pulp, and the mixture was made into paper with a basis weight of 65 g/ ^m2 using a Noble and Wood papermaking machine. The pH of the paper was 7.5 at this time. The wet paper was dried using a drum dryer at 100°C for 80 seconds.

(2) Method for preparing coating solution Oxidized starch (MS3800, manufactured by Nihon Shokuhin Kako Co., Ltd.) was diluted with water to a concentration of 10%, and gelatinized at 95° C. for 20 minutes. Thereafter, the paper sizing agents obtained in Examples 17 to 32 and Comparative Examples 5 to 8 and sodium chloride (NaCl) were added to the coating solution so as to obtain the solid content concentrations shown below.
Solid concentration of coating liquid: oxidized starch...6%, paper sizing agent...0.3%, NaCl...0.5%

(3) Manufacture of neutral wood-free paper and evaluation of sizing performance The coating liquid prepared in (2) above was applied to the base paper prepared in (1) above using a size press to obtain a neutral wood-free paper. The solid content of the paper sizing agent in this coated paper was 0.05 g/ ^m2 . After coating, the paper was dried at 100°C for 80 seconds using a drum dryer. The obtained test paper was conditioned for 24 hours in a constant temperature and humidity environment (23°C, 50% relative humidity), and the Stockigt sizing degree was measured in accordance with JIS P8122. The larger the Stockigt sizing degree value, the better the sizing performance. The results are shown in Table 8.

The evaluation results show that the papers in Evaluation Examples 17 to 32 in Table 8, which were produced using the papermaking sizing agent of the present invention, have superior sizing performance (Stöckigt sizing degree) compared to the papers in Comparative Evaluation Examples 5 to 8, which were produced using a papermaking sizing agent different from the papermaking sizing agent of the present invention.

3-1. Production of paper sizing agent (emulsion type using surfactant) (Example 33)
In a reactor similar to that of Example 1, 10 parts (3 parts as solids) of Lipocard T-30 (surfactant manufactured by Lion Corporation, stearyl trimethyl ammonium chloride) as a surfactant, 292 parts of water, 50 parts of isobutyl methacrylate and 50 parts of normal butyl acrylate as hydrophobic monomers (b), 0.10 parts of iodine as an iodine compound (1000 ppm as iodine atoms relative to monomer) and 10 parts by weight of a 5% V-50 aqueous solution were added, and the mixture was heated to 80° C. while being stirred under a nitrogen stream. The emulsion polymerization reaction was completed by holding at 80° C. for 4 hours, and an emulsion-type papermaking sizing agent (E-35) with a solids concentration of 25% was obtained.

(Example 34, Comparative Examples 9 and 10)
Next, the type of surfactant and the amount of iodine and/or iodine compound used were changed as shown in Table 9, and emulsion-type paper sizing agents (E-36) to (E-38) were obtained in the same manner as in Example 33.

(Explanation of abbreviations in the table)
T-30: Lipocard T-30 (surfactant manufactured by Lion Corporation, stearyl trimethyl ammonium chloride)
N210: Newcol 210 (surfactant manufactured by Nippon Nyukazai Co., Ltd., alkylbenzene sulfonate)
IBMA: isobutyl methacrylate BA: n-butyl acrylate

*As iodine atoms

3-2. Evaluation test of papermaking sizing agents as surface sizing agents (Test Example 3) Evaluation of sizing performance on neutral wood-free paper (1) Papermaking of neutral wood-free base paper
Pulp (mixed pulp with a 9:1 ratio of hardwood to softwood pulp) beaten to 380 ml Canadian Standard Freeness was made into a 2.5% slurry, to which 2% (bone dry weight basis) of calcium carbonate (TP121S, manufactured by Okutama Kogyo Co., Ltd.) was added. Next, 0.5% (bone dry weight basis) of aluminum sulfate, 0.8% (bone dry weight basis) of cationic starch (Cato304, manufactured by National Starch Co., Ltd.) and 0.03% (bone dry weight basis) of an alkyl ketene dimer sizing agent (AD1638, manufactured by Seiko PMC Co., Ltd.) were added in sequence, and the pulp slurry was diluted to a concentration of 0.25% with dilution water of pH 7.5. Thereafter, calcium carbonate (TP121S manufactured by Okutama Kogyo Co., Ltd.) was added in an amount of 15% (bone dry weight basis) based on the pulp, and a PAM-based paper strength agent (DS4431 manufactured by Seiko PMC Co., Ltd.) in an amount of 0.1% (bone dry weight basis) based on the pulp was added to the diluted pulp slurry, and paper was made using a Noble and Wood papermaking machine to a basis weight of 65 g/ ^m2 . The papermaking pH at this time was 7.5. The wet paper was dried using a drum dryer at 100°C for 80 seconds.

(2) Method for preparing coating liquid Tapioca starch (MKK-100, Matsutani Chemical Industry Co., Ltd.) was diluted with water to a concentration of 10%, and 0.1% of Kleistase E5CC (Amano Enzyme Inc.) was added based on the solid content of the starch to prepare an enzyme-modified starch, which was then gelatinized at 95° C. for 20 minutes. Thereafter, the paper sizing agents obtained in Examples 33 to 34 and Comparative Examples 9 to 10 were added to the coating liquid to give the following solid content concentrations.
Solids concentration of coating liquid: Enzyme-modified starch...7%, paper sizing agent...0.5%

(3) Manufacture of neutral wood-free paper and evaluation of sizing performance The coating liquid prepared in (2) above was applied to the base paper prepared in (1) above using a size press to obtain a neutral wood-free paper. The solid content of the paper sizing agent in this coated paper was 0.08 g/ ^m2 . After coating, the paper was dried at 100°C for 80 seconds using a drum dryer. The obtained test paper was conditioned for 24 hours in a constant temperature and humidity environment (23°C, 50% relative humidity), and the Stockigt sizing degree was measured in accordance with JIS P8122. The results are shown in Table 10.

The evaluation results show that the papers in Evaluation Examples 33 and 34 in Table 10, which were produced using the papermaking sizing agent of the present invention, have superior sizing performance (Stöckigt sizing degree) compared to the papers in Comparative Evaluation Examples 9 and 10, which were produced using a papermaking sizing agent different from the papermaking sizing agent of the present invention.

Claims (4)

A method for producing a paper sizing agent, characterized in that in the following steps (I) and/or (II), iodine and/or an iodine compound are used in an amount of 50 ppm or more in terms of iodine atoms relative to the total amount of monomers used as polymerization components:
(I): A step of polymerizing a copolymer (A) containing a hydrophobic monomer (a1) and a hydrophilic monomer (a2) as polymerization components. (II): A step of polymerizing a hydrophobic monomer (b) in the presence of the copolymer (A) and/or a surfactant. The method for producing a paper sizing agent according to claim 1, characterized in that the mass ratio of hydrophobic monomer (a1) to hydrophilic monomer (a2) is hydrophobic monomer (a1):hydrophilic monomer (a2) = (50-85):(15-50). The method for producing a paper sizing agent according to claim 1 or 2, characterized in that the mass ratio of copolymer (A) to hydrophobic monomer (b) is copolymer (A):hydrophobic monomer (b)=(10-100):(0-90). The method for producing a paper sizing agent according to any one of claims 1 to 3, characterized in that the hydrophilic monomer (a2) of the copolymer (A) contains one or more selected from a vinyl monomer containing a tertiary amino group and a vinyl monomer containing a carboxylic acid group.