JP2020139252A - Surface sizing agent for papermaking and coated paper - Google Patents

Abstract

To provide a surface sizing agent for papermaking that has excellent mechanical stability at high temperatures and also exhibits an excellent sizing effect, and a coated paper.SOLUTION: A surface sizing agent for papermaking containing an emulsion polymer of a polysaccharide (A) having a (meth)acryloyl group in the molecule and a monomer (B) having an ethylenic unsaturated group is used.SELECTED DRAWING: None

Description

The present invention relates to a surface sizing agent for papermaking and coated paper.

In paper made by adding various paper-making chemicals from pulp slurry, a surface sizing agent is applied to the surface of the base paper in order to further reinforce the sizing effect. As the form, an aqueous dispersion of a polymer having a low viscosity or an emulsion polymer (emulsion) is widely used from the viewpoint of product handling and workability of pump transfer.

For example, an aqueous polymer dispersion obtained by emulsion polymerization using specific amounts of styrene, alkyl (meth) acrylate and ethylene-based unsaturated monomer in the presence of reduced starch is disclosed, and hydrogen peroxide is used as the reduced treatment. It is used (Patent Document 1). However, in the present invention, the mechanical stability is required as the speed of the paper machine is increased, and the stability is inferior.

The applicant also obtained by emulsion polymerization of an unsaturated monomer mixture consisting of styrenes and (meth) acrylic acid esters in starch prepared to have a specific intrinsic viscosity using an inorganic peroxide. Although a surface sizing agent for papermaking containing an aqueous polymer emulsion is disclosed (Patent Document 2), there is a problem that the mechanical stability at high temperature is inferior and the machine is soiled.

Special Table 2002-504563 JP-A-2014-163002

An object of the present invention is to provide a surface sizing agent for papermaking and coated paper which are excellent in mechanical stability at high temperature and also exhibit excellent sizing effect.

The present inventor considered that the factor inferior in mechanical stability in the prior art was the composition of polysaccharides such as starch, and as a result of diligent studies, the monomer components were found in the presence of polysaccharides incorporating specific reactive groups. We have found that a surface sizing agent for papermaking containing an emulsion polymer obtained by polymerization solves the problem, and have completed the present invention. That is, the present invention relates to the following surface sizing agents for papermaking and coated paper.

1. 1. A surface sizing agent for papermaking, which comprises an emulsion polymer of a polysaccharide (A) having a (meth) acryloyl group in the molecule and a monomer (B) having an ethylenically unsaturated group.

2. 2. The surface sizing agent for papermaking according to item 1 above, wherein the component (A) is a reaction product of the raw material polysaccharide (a1) and the (meth) acrylic compound (a2).

3. 3. The surface sizing agent for papermaking according to item 1 or 2 above, wherein the introduction rate of the (meth) acryloyl group in the component (A) is 0.05 to 2 in terms of the degree of substitution (DS).

4. The surface sizing agent for papermaking according to item 2 above, wherein the component (a1) has a weight average molecular weight of 500 to 1,000,000.

5. The surface sizing agent for papermaking according to item 2 above, wherein the component (a2) is one selected from the group consisting of a carboxylic acid anhydride, a carboxylic acid bromide, a compound having an epoxy group, and a compound having an isocyanate group.

6. The surface sizing agent for papermaking according to any one of the above items 1 to 5, wherein the component (B) contains styrenes (b1) and / or an alkyl (meth) acrylate (b2) having no hydroxy group.

7. A coated paper obtained by coating a base paper with the surface sizing agent for papermaking according to any one of the above items 1 to 6.

According to the surface sizing agent for papermaking of the present invention, the mechanical stability at high temperature is excellent. In addition, the coated paper obtained by applying the surface sizing agent to the base paper also exhibits a good sizing effect.

The surface sizing agent for papermaking of the present invention has a polysaccharide (A) having a (meth) acryloyl group in the molecule (hereinafter referred to as a component (A)) and a monomer (B) having an ethylenically unsaturated group (hereinafter referred to as a component). It contains an emulsion polymer (referred to as component).

Examples of the component (A) include reaction products of the raw material polysaccharide (a1) (hereinafter referred to as the component (a1)) and the (meth) acrylic compound (a2) (hereinafter referred to as the component (a2)). Be done.

The component (a1) is not particularly limited, and examples thereof include starches, celluloses, disaccharides, oligosaccharides, amylose, and amylopectin. These may be used alone or in combination of two or more.

The starches are not particularly limited, and are, for example, unmodified starches such as corn starch, potato starch, tapioca starch, wheat starch, rice starch, sago starch, and high amylose starch; cationized starch, oxidized starch, phosphate-modified starch, and the like. Examples thereof include modified starches such as carboxymethylated starch, amine-modified starch, hydroxyethylated starch, carbamylethylated starch, cyanoethylated starch, dialdehyde-modified starch, acetic acid-modified starch, and TEMPO-oxidized starch. These may be used alone or in combination of two or more. Further, a commercially available product may be used.

Further, as the starches, unmodified starch, modified starch or the like treated with a modifier (hereinafter referred to as “modified starch”) can be used. The modified starch is not particularly limited, and examples thereof include peroxide-modified starch obtained by treating the raw material starch with an inorganic peroxide; and enzyme-modified starch obtained by treating the raw material starch with an enzyme. The reduced starch can be produced by heating and stirring an aqueous solution composed of starch and a reducing agent at 60 to 100 ° C. for 30 to 60 minutes.

The inorganic peroxide used for producing the peroxide-modified starch is not particularly limited, and is, for example, hypochlorite, peroxodisulfate (ammonium persulfate, potassium persulfate, sodium persulfate, etc.), peroxide. Examples include hydrogen peroxide. The peroxide may be used alone or in combination of two or more. Further, hydrogen peroxide may be combined with at least one water-soluble heavy metal salt of iron sulfate and copper sulfate. Among these, ammonium persulfate, potassium persulfate, and sodium persulfate can be preferably used. The amount of the inorganic peroxide used is not particularly limited, but is preferably about 0.5 to 5 parts by weight with respect to 100 parts by weight of the component (a1) in terms of solid content weight.

As the enzyme used for producing the enzyme-reduced starch, for example, α-amylase produced by various bacteria, animals and plants is preferably used. Examples of commercially available products include "Krystase SD80", "Kokugen SD-A", and "Kokugen L" (manufactured by Amano Enzyme Co., Ltd.). The amount of the enzyme used is not particularly limited, but is preferably about 0.005 to 1 part by weight with respect to 100 parts by weight of the component (a1) in terms of solid content weight.

The celluloses are not particularly limited, and examples thereof include cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl methyl cellulose. These may be used alone or in combination of two or more.

The disaccharide is not particularly limited, and examples thereof include trehalose, isotorehalose, maltose, cellobiose, isomaltose, lactose, and sucrose. These may be used alone or in combination of two or more.

The oligosaccharide is not particularly limited, and examples thereof include fluquoligosaccharide, galactooligosaccharide, α-cyclodextrin, and β-cyclodextrin. These may be used alone or in combination of two or more.

Among the components (a1), starches and oligosaccharides are preferable because the surface sizing agent for papermaking is excellent in mechanical stability at high temperatures, and the starches are peroxide-decomposed starch and enzyme-decomposed. Starch is more preferred.

The weight average molecular weight of the component (a1) is not particularly limited, but is preferably about 500 to 1,000,000 to 1,000 to 1,000,000 because the surface sizing agent for papermaking is excellent in mechanical stability at high temperatures. About 100,000 is more preferable. The weight average molecular weight refers to a value obtained by a polyethylene oxide conversion value obtained by a gel permeation chromatography (GPC) method.

The component (a2) is a (meth) acrylic compound, and includes a compound having a (meth) acryloyl group (CH2 = CH-C (O)-) and a skeleton of acrylic acid or methacrylic acid. Is done. By using the component (a2), the hydrophobicity of the component (A) obtained by reacting with the component (a1) is increased, and as a result, the surface sizing agent for papermaking is excellent in mechanical stability at high temperature. It also has a better size effect. The component (a2) is not particularly limited, and for example, carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, and isocrotonic acid; carboxylic acids such as acrylic acid anhydride, methacrylic acid anhydride, crotonic acid anhydride, and isocrotonic acid anhydride are anhydrous. (Meta) acrylate having halogen such as chloromethyl acrylate, chloromethyl methacrylate, 2-chloroethyl acrylate, 2-chloroethyl methacrylate, 2-bromoethyl acrylate, 2-bromoethyl methacrylate, bromoglycidyl acrylate; glycidyl methacrylate, Compounds having an epoxy group such as glycidyl acrylate; compounds having an isocyanate group such as isocyanate ethyl acrylate, isocyanate ethyl methacrylate, and 1,1- (bisacryloyloxymethyl) ethyl isocyanate can be mentioned. These may be used alone or in combination of two or more.

As the component (a2), the obtained component (A) can be sufficiently polymerized with the component (B), and the surface sizing agent for papermaking has excellent mechanical stability at high temperatures. One selected from the group consisting of an acid anhydride, a carboxylic acid anhydride, a compound having an epoxy group and a compound having an isocyanate group is preferable, and one selected from the group consisting of acrylic anhydride, methacrylic anhydride, glycidyl methacrylate and bromoethyl methacrylate. One is more preferable.

The amount of the component (a2) used is not particularly limited, but from the viewpoint of the reactivity between the component (a1) and the component (a2), the solid content weight is 50 to 50 to 100 parts by weight of the component (a1). About 1000 parts by weight is preferable, and about 200 to 400 parts by weight is more preferable.

The method for producing the component (A) is not particularly limited, and for example, after the component (a1) is dispersed in a solvent, the component (a2) is mixed and the temperature is about 5 to 90 ° C. (preferably 30 to 80). The reaction may be carried out at a temperature of about 1 to 7 hours (preferably about 3 to 5 hours). The component (a2) may be added by dropping. Since the component (A) obtained by this production method has a (meth) acryloyl group in the molecule, the surface sizing agent for papermaking is excellent in mechanical stability and sizing effect at high temperature.

The solvent is not particularly limited, and water (ion-exchanged water, pure water, tap water, etc.), an organic solvent, or the like can be appropriately used. The organic solvent is not particularly limited as long as the component (a1) can be easily dissolved or dispersed at room temperature or heating, and is not particularly limited. For example, dimethyl sulfoxide, N-2-methylpyrrolidone, N, N-dimethylformamide, N. , N-Dimethylacetamide, acetonitrile and the like. These may be used alone or in combination of two or more. The amount of the solvent used is not particularly limited, but it is preferable to adjust the solid content concentration to about 0.1 to 60% by weight in order to react with a uniform solution. In the present invention, the component (a2) may be sprayed onto the powdery component (a1) without a solvent, but it is preferable to use the solvent, and water is particularly preferable.

The structure of the obtained component (A) is not clear, but if the hydrogen atom of the hydroxy group of the component (a1) is replaced with the (meth) acryloyl group of the component (a2), the introduction rate below It is inferred from the measurement of.

The physical properties of the component (A) of the present invention are not particularly limited, and one of them is the introduction rate of the (meth) acryloyl group in the component (A). The introduction rate indicates the degree to which the (meth) acryloyl group derived from the component (a2) is bound to the component (a1). The higher the introduction rate, the more hydrophobic the surface sizing agent for papermaking is due to the (meth) acryloyl group introduced into the component (a1), and the sizing agent has excellent mechanical stability at high temperatures. ..

The method for measuring the introduction rate is not particularly limited, but in the present invention, the ¹ H-NMR spectrum of the component (A) is measured, and the degree of substitution is calculated from the ratio of the integrated values of specific peaks in the obtained spectrum. The method of calculating DS) is applied.

The above-mentioned degree of substitution (DS) is derived from the peak integrated value (T1) of the hydrogen atom bonded to the anomer carbon of the component (a1) and the component (a2) bonded to the component (a1) in the obtained component (A). It can be calculated by substituting the peak integrated value (T2) of methyl hydrogen of the (meth) acryloyl group into the following (Equation 1).
(Equation 1) Degree of substitution (DS) = T2 / T1

As an example of the integrated value to be read, when oxidized starch is used as the component (a1) and glycidyl methacrylate is used as the component (a2), T1 is the integrated value of the signal on the low magnetic field side of 5.0 to 5.2 ppm. T2 is the integral value of the signal on the high magnetic field side of 1.7 to 1.9 ppm.

The introduction rate is preferably about 0.05 to 2 and more preferably about 0.2 to 2 in terms of degree of substitution (DS) because the surface sizing agent for papermaking is excellent in mechanical stability at high temperatures.

Other physical properties of the component (A) are not particularly limited, and for example, the viscosity at a solid content concentration of 20% by weight and a temperature of 25 ° C. is usually about 10 to 1000 mPa · s, preferably 100 to 500 mPa · s. Degree.

The component (B) is a monomer having an ethylenically unsaturated group, and the surface sizing agent for papermaking obtained by emulsion polymerization exhibits an excellent sizing effect.

The component (B) can be distinguished by a nonionic unsaturated monomer, a cationic unsaturated monomer, and an anionic unsaturated monomer. These may be used alone or in combination of two or more.

The nonionic unsaturated monomer is not particularly limited, and for example, styrenes such as styrene, α-methylstyrene and vinyltoluene; diisobutylene (2,4,4-trimethyl-1-pentene, 2,4,4-). A mixture of trimethyl-2-pentene, 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene), 3-methyl-1-butene, 3-methyl-1-pentene, 4 Branched α-olefins such as −methyl-1-pentene; 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, 1-tetracosene and the like. Linear α-olefins; alicyclic α-olefins such as cyclohexene, methylcyclohexene, vinylcyclohexane, 4-vinylcyclohexene, cyclopentene, methylcyclopentene; methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl ( Meta) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, n-pentyl (meth) acrylate, n-hexyl (meth) acrylate, n- Octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) Alkyl (meth) acrylates having no hydroxy group such as acrylate; diethyl maleate, di n-butyl maleate, isobutyl maleate, di n-octyl maleate, di n-decyl maleate, di n-dodecyl maleate, di Unsaturated dicarboxylic acid dialkyl ester such as n-hexadecyl maleate; N-substituted (meth) such as N, N-dimethyl (meth) acrylamide, N, N-diacetone (meth) acrylamide, N-isopropyl (meth) acrylamide, etc. Acrylate; N, N'-alkylene bis (meth) acrylamide such as N, N'-methylenebis (meth) acrylamide, N, N'-ethylenebis (meth) acrylamide; vinyl ester such as vinyl propionate, vinyl acetate; acrylonitrile , Metaacrylonitrile and other ditrils; 1-butene, 2-butene, 1-hexene, 2-hexene, 1 -Alkenes such as octene and 2-octene can be mentioned. These may be used alone or in combination of two or more.

The amount of the nonionic unsaturated monomer used is not particularly limited, and in order to obtain an excellent size effect of the coated paper, the component (B) is 100% by weight, and usually 60 to 100% by weight, preferably 70. ~ 100% by weight, more preferably 80-100% by weight.

The cationic unsaturated monomer is not particularly limited, and for example, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, Tertiary amino group-containing unsaturated monomers such as N, N-diethylaminopropyl (meth) acrylamide or salts thereof (potassium, sodium, ammonium, etc.) and the above-mentioned tertiary amino group-containing unsaturated monomers and quaternizing agents ( Examples thereof include a quaternary ammonium salt obtained by reacting methyl chloride, benzyl chloride, etc.). These may be used alone or in combination of two or more.

The amount of the cationic unsaturated monomer used is not particularly limited, and in order to obtain an excellent size effect of the coated paper, the component (B) is set to 100% by weight, and usually 20% by weight or less, preferably 15% by weight. % Or less, more preferably 10% by weight or less.

The anionic unsaturated monomer is not particularly limited, and for example, an unsaturated carboxylic acid such as (meth) acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, muconic acid, and citraconic acid; 2-hydroxymethyl ( Meta) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 3-hydroxybutyl (meth) acrylate, 4-hydroxybutyl acrylate, 5-hydroxypentyl Alkyl (meth) acrylate having a hydroxy group such as (meth) acrylate and 6-hydroxyhexyl (meth) acrylate; diethylene glycol mono (meth) acrylate, triethylene glycol mono (meth) acrylate, tetraethylene glycol mono (meth) acrylate, Polyalkylene glycol-based unsaturated monomers such as dipropylene glycol mono (meth) acrylate, tripropylene glycol mono (meth) acrylate, tetrapropylene glycol mono (meth) acrylate; vinyl sulfonic acid, sodium styrene sulfonate, (meth) allyl sulfone. Examples thereof include unsaturated monomers having a sulfonic acid group such as sodium acid, potassium (meth) allyl sulfonate, and ammonium (meth) allyl sulfonate. These may be used alone or in combination of two or more.

The amount of the anionic unsaturated monomer used is not particularly limited, and since the surface sizing agent for papermaking is excellent in mechanical stability and size effect at high temperature, the component (B) is usually 20% by weight. By weight or less, preferably 15% by weight or less, more preferably 10% by weight or less.

Among these (B) components, styrenes (b1) (hereinafter referred to as (b1) component) and alkyl (meth) acrylates (b2) having no hydroxy group are obtained from the viewpoint of obtaining an excellent size effect of coated paper. ) (Hereinafter referred to as the component (b2)).

The component (b1) and the component (b2) can be used alone, but when used in combination, the amounts used are (b1) / (b2) = 50/50 to 95 / in the ratio of the solid content weight. It is preferably about 5, and more preferably 55/45 to 80/20.

In the component (B), if necessary, mercaptans such as 2-mercaptoethanol and n-dodecyl mercaptan; saturated aliphatic alcohols such as ethanol, isopropyl alcohol and pentanol; carbon tetrachloride, ethylbenzene and isopropylbenzene, Chain transfer agents such as cumene, α-methylstyrene dimer and 2,4-diphenyl-4-methyl-1-pentene may be contained.

The amount of the chain transfer agent used is not particularly limited, but it is preferable that the component (A) is 100% by weight and is about 0.1 to 4% by weight.

The surface sizing agent for papermaking of the present invention contains an emulsion polymer, and the emulsion polymer can be obtained by emulsion polymerization of component (B) in the presence of component (A).

The amount of the component (B) used with respect to 100 parts by weight of the component (A) is not particularly limited, and is usually 50 to 1000 parts by weight, preferably 50 in order to emulsify well and obtain an excellent size effect of the coated paper. It is ~ 500 parts by weight, more preferably 100 to 300 parts by weight.

The conditions for the emulsion polymerization are not particularly limited, and the polymerization is usually carried out at a temperature of about 75 to 95 ° C. for about 1 to 5 hours, preferably at a temperature of about 80 to 85 ° C. for about 2 to 3 hours. The polymerization initiator is not particularly limited, and examples thereof include peroxodisulfate such as ammonium persulfate, potassium persulfate, and sodium persulfate; hydrogen peroxide and the like. These may be used alone or in combination of two or more. Among these, ammonium persulfate, potassium persulfate, sodium persulfate, and hydrogen peroxide are preferable. Further, although optional, a reducing agent may be used in combination because it facilitates the generation of radicals of the organic peroxide and promotes the hydrogen abstraction effect. The reducing agent is not particularly limited, and examples thereof include sulfites such as sodium sulfite; hydrogen sulfites such as sodium hydrogen sulfite; triethanolamine and ferrous sulfate; ferric ferric sulfate heptahydrate and the like.

The amount of the polymerization initiator used is also not particularly limited, and is usually about 0.03 to 5 parts by weight, preferably about 0.05 to 3 parts by weight, based on 100 parts by weight of the component (B).

The method for charging the component (B) may be any method such as batch charging, divided dropping, or the like, and the polymerization initiator may also be dropped.

In addition, in emulsion polymerization, various known nonionic, anionic or cationic surfactants and reactive emulsifiers can be used alone or in combination as long as the object of the present invention is not impaired.

The nonionic surfactant is not particularly limited, and examples thereof include polyethylene glycol, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene styryl phenyl ether, and polyoxyethylene sorbitan fatty acid ester.

The anionic surfactant is not particularly limited, and is, for example, an alkyl sulfate, an alkylbenzene sulfonate, a polyoxyethylene alkyl ether sulfate, a polyoxyethylene alkyl phenyl ether sulfate, a dialkyl sulfosuccinic acid ester salt, and an alkyl sulfonic acid. Salt, polyoxyethylene alkyl ether sulfosuccinate, polyoxyethylene styrylphenyl ether sulfosuccinate salt, polyoxyethylene alkyl ether phosphate, α-olefin sulfonate, naphthalin sulfonate formalin condensate, polyoxyethylene alkyl Examples thereof include phenyl ether sulfate ester salts.

The cationic surfactant is not particularly limited, and for example, lauryltrimethylammonium chloride, cetyltrimethylammonium chloride (cetrimonium chloride), stearyltrimethylammonium chloride (stealtrimonium chloride), alkyltrimethylammonium chloride, distearyldimethyl chloride. Ammonium, behenyltrimethylaluminum chloride (behentrimonium chloride), distearyldimethylammonium chloride (dystearyldimonium chloride), cetyltrimethylammonium bromide, stearyltrimethylammonium bromide, lanolin sulfate fatty acid aminopropylethyldimethylammonium, stearyltrimethyl Examples thereof include ammonium saccharin, cetyltrimethylammonium saccharin, methacryloyloxyethyltrimethylammonium chloride, behenyltrimethylammonium methylsulfate, and quaternium-91.

The reactive emulsifier is not particularly limited, and examples thereof include those having a polymerizable functional group in the molecule described in JP-A-2003-293288.

The amount of these surfactants and the reactive emulsifier used is not particularly limited, and is usually 5 parts by weight or less, preferably 3 parts by weight or less, based on 100 parts by weight of the component (B).

The surface sizing agent for papermaking of the present invention is characterized by being excellent in mechanical stability at high temperatures. The method for measuring the mechanical stability is not particularly limited, but in the present invention, a container containing a constant amount of a surface sizing agent for papermaking is heated to a constant temperature, and then strongly stirred under pressure while keeping the temperature warm. Then, the agglomerates formed are filtered out, and the weight of the agglomerates after drying with a circulation dryer or the like is measured and calculated using (Equation 2). The heating method is not particularly limited, and examples thereof include a hot water bath.
(Equation 2) = [Weight of agglomerates after drying (g)] / [Solid weight of surface sizing agent for papermaking (g)] x 100

In the papermaking surface sizing agent, the weight ratio of the agglomerates generated by the above measuring method is usually 5% by weight or less, preferably 2% by weight or less, more preferably with respect to the solid content weight of the papermaking surface sizing agent. Is 1% by weight or less. When the weight ratio of the agglomerates is within the above range, the surface sizing agent for papermaking is expected to have excellent mechanical stability at high temperatures and reduce machine stains in the coating process.

Other physical properties of the surface sizing agent for papermaking are not particularly limited, and for example, the particle size is usually about 50 to 500 nm, preferably about 70 to 120 nm. The "particle size" refers to the average primary particle size of the emulsion particles, and can be measured by, for example, a dynamic light scattering method. The particle size measuring device is not particularly limited, and for example, a light scattering particle size analyzer (product name "ELSZ-2", manufactured by Otsuka Electronics Co., Ltd.) can be used.

The other physical properties of the surface sizing agent for papermaking are not particularly limited, and for example, the Brookfield viscosity is usually about 1 to 1500 mPa · s, preferably 1 to 200 mPa · s at a solid content concentration of 20% by weight and a temperature of 25 ° C. It is about s.

The pH of the surface sizing agent for papermaking is usually about 2 to 7 at a temperature of 25 ° C., preferably about 3 to 6. The pH may be adjusted before, during, or after the polymerization. The pH adjuster is not particularly limited, and for example, inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; metal hydroxides such as sodium hydroxide, potassium hydroxide, and calcium hydroxide; sodium carbonate, potassium carbonate, and carbonic acid. Metallic carbon oxides such as calcium; metal hydrides such as sodium hydrogen carbonate, potassium hydrogen carbonate and calcium hydrogen carbonate; amines such as trimethylamine and triethylamine; ammonia and the like.

Additives such as antioxidants, antifoaming agents, preservatives, chelating agents, and water-soluble aluminum compounds may be added to the surface sizing agent for papermaking of the present invention, if necessary.

As the coating liquid containing the surface sizing agent for papermaking of the present invention, the sizing agent may be used as it is or diluted with water or the like, but an additive may also be added if necessary. Examples of the additive include starches such as oxidized starch, phosphate esterified starch, self-modified starch, cationized starch and amphoteric starch; celluloses such as carboxymethyl cellulose; polyvinyl alcohols, polyacrylamides, sodium alginate and the like. Water-soluble polymers; anti-slip agents, preservatives, rust preventives, pH adjusters, antifoaming agents, thickeners, fillers, antioxidants, water resistant agents, film-forming aids, pigments, dyes, etc. Be done.

The solid content concentration of the coating liquid containing the surface sizing agent for papermaking of the present invention is not particularly limited, and is usually put into practical use in the range of about 0.5 to 30% by weight, preferably 1 to 20% by weight. ..

The present invention also relates to coated paper. The coated paper is obtained by applying a coating liquid containing a surface sizing agent for papermaking to the surface of the base paper.

The base paper is not particularly limited, and usually uncoated paper and paperboard made from wood cellulose fibers can be used. The base paper is obtained from paper-making pulp, and the paper-making pulp is not particularly limited, and chemical pulp such as broadleaf pulp (LBKP) and coniferous pulp (NBKP); crushed wood pulp (GP), Mechanical pulp such as refiner ground pulp (RGP) and thermomechanical pulp (TMP); used paper pulp such as used cardboard paper and the like can be mentioned. These may be used alone or in combination of two or more. Further, various chemicals such as fillers, sizing agents, and paper strength enhancers to be added to the papermaking pulp are not particularly limited.

The coating means of the coating liquid is not particularly limited, and for example, an impregnation method, a size press method, a gate roll method, a bar coater method, a calendar method, a spray method and the like can be applied. Further, the coating amount of papermaking surface sizing agent not limited (solids) in particular, usually, 0.005~1g / ^{m 2} approximately, and preferably from 0.01 to 0.5 g / ^{m 2} approximately.

The paper coated with the surface sizing agent of the present invention is not particularly limited, and for example, recording paper such as foam paper, PPC paper, and heat-sensitive recording paper: coating of art paper, cast-coated paper, high-quality coated paper, and the like. Paper; Wrapping paper such as kraft paper and pure white roll paper; Various types of paper (Western paper) such as notebook paper, book paper, printing paper and newspaper paper; Paperboard for paper containers such as Manila balls, white balls and chip balls; Liner, core Such as paperboard.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to these examples. Further, in the examples, "%" and "part" are expressed in terms of weight unless otherwise specified.

<Weight average molecular weight of component (a1)>
The molecular weight was measured by the gel permeation chromatography (GPC) method under the following measurement conditions.
GPC body: Tosoh Co., Ltd. column: Tosoh Co., Ltd. guard column TSK gel guard column α 1 and TSK-GEL α-M 2 (temperature 40 ° C)
Eluent: 0.2 mol / L sodium nitrate buffer (sodium nitrate (manufactured by Wako Pure Chemical Industries, Ltd.)
Flow velocity: 1.0 mL / min Detector:
Viscotec TDA MODEL 301 (concentration detector and 90 ° light scattering detector and viscosity detector (temperature 40 ° C.)) RALLS method measurement sample: (a1) The above so that the component has a solid content concentration of 0.5%. Eluent was added to prepare the measurement sample.

Synthesis example 1
Oxidized starch (trade name: "Oji Ace A", manufactured by Oji Corn Starch Co., Ltd., solid content concentration 88%) 63 parts, α in a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas introduction tube. -Amylase (trade name "Kokugen L", manufactured by Amano Enzyme Co., Ltd.) 5000 ppm (for 100 parts by weight of solid content of oxidized starch) and 185 parts of ion-exchanged water were added, and the temperature was raised to 75 ° C. to 40. After stirring for minutes, the temperature was raised to 90 ° C. and the mixture was further stirred for 10 minutes. After cooling to 65 ° C., the pH was adjusted to 11 with an aqueous sodium hydroxide solution (solid content concentration: 48%) to obtain an enzyme-modified starch (a1-1) having a weight average molecular weight of 50,000. Then, 222 parts of glycidyl methacrylate was added, and the mixture was further stirred at 65 ° C. for 4 hours, and an aqueous sulfuric acid solution (solid content concentration: 60%) was added so that the pH became 5.5 to 6.0. The obtained emulsion polymer was added to 3000 parts of ethanol for reprecipitation, filtered through a glass fiber filter (trade name: "GA200", ADVANTEC, size: 30 cm x 30 cm, thickness: 70 mm), and then on the filter. Was washed with 600 parts of ethanol. Ion-exchanged water was added to the washed polymer so that the solid content concentration was 10%, and the mixture was stirred to obtain the component (A-1). The composition is shown in Table 1 (the same applies hereinafter).

Synthesis Examples 2 to 13, Comparative Synthesis Examples 1 to 4
The compositions shown in Table 1 were synthesized in the same manner as in Example 1 to obtain components (A-2) to (A-13) and components (D-1) to (D-4), respectively.

* All parts by weight are indicated by solid content.

The abbreviations in Table 1 represent the following compounds.
-GMA: glycidyl methacrylate-Aan: methacrylic anhydride-MAan: methacrylic anhydride-BrEMA: bromoethyl methacrylate-IEMA: isocyanate ethyl methacrylate-PO: propylene oxide

Example 1
In a reaction vessel equipped with a stirrer, a cooling pipe, a nitrogen introduction pipe, a thermometer and a dropping funnel, 240 parts (24 parts of solid content) of (A-1) component having a solid content concentration of 10% was charged, and oxygen in the reaction vessel was charged. Was sufficiently replaced with nitrogen, and then the temperature inside the system was raised to 80 ° C. with stirring. Next, a polymerization initiator prepared by dissolving 32 parts of styrene and 16 parts of n-butyl acrylate and 5 parts of 30% aqueous hydrogen peroxide solution (3 parts of solid content with respect to all the monomer components) in 19 parts of ion-exchanged water. 3.2 parts of an aqueous solution and an aqueous solution of 0.83% iron (II) sulfate (II) heptahydrate (0.055 parts of solid content for all monomer components) were added dropwise into the system over about 1.5 hours, and further 0. The reaction was completed by keeping warm for 5 hours. Then, after cooling, 2.6 parts of a 48% aqueous sodium hydroxide solution was added, and the concentration was adjusted to 20% with ion-exchanged water to obtain an emulsion polymer having a pH of 5.0. Table 2 shows the composition and physical properties (the same applies hereinafter).

Examples 2-19, Comparative Examples 1-4
The composition shown in Table 2 was synthesized in the same manner as in Example 1 to obtain emulsion polymers. Hereinafter, the emulsion polymers obtained in each Example and Comparative Example were used as they were as a surface sizing agent for papermaking.

<Viscosity (Brookfield viscosity)>
The viscosity of the sample adjusted to 25 ° C. was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.).

<Particle diameter>
The measurement was performed using a light scattering particle size analyzer (product name "ELSZ-2", manufactured by Otsuka Electronics Co., Ltd.).

<Mechanical stability at high temperature>
50 g of each papermaking surface sizing agent diluted in advance with ion-exchanged water so as to have a solid content concentration of 20% was weighed in a metal container. While keeping the surface sizing agent for papermaking in the container warm with hot water so that it reaches 70 ° C, using a Marlon stability tester [manufactured by Kumagaya Riki Kogyo Co., Ltd.] under a load of 30 kg, 30 at a rotation speed of 1000 rpm. The paper surface sizing agent was vigorously stirred for minutes. It was filtered in advance with a weighed 350 mesh wire mesh (manufactured by SUS). After the filtered wire mesh was dried in a circulation dryer at 105 ° C. for 3 hours, the weight of the remaining agglomerates was determined, and from (Equation 2), the weight of the agglomerates generated with respect to the solid content of the surface sizing agent for papermaking. The mechanical stability under high temperature was evaluated by the ratio (E) (%). The smaller the weight ratio, the better the mechanical stability at high temperature.
(Formula 2) Weight ratio (E) (%) = [Weight of aggregates after drying (g)] / [Solid weight of surface sizing agent for papermaking (g)] x 100

<Preparation of coating liquid>
Corn starch (trade name: "corn starch", manufactured by Japan Corn Starch Co., Ltd.) is diluted with ion-exchanged water so that the solid content concentration is 12%, and ammonium persulfate (hereinafter referred to as APS) is added to 1 of the starch solid. It was added at 0.6% and kept warm at 90 ° C. for 20 minutes. The mixture was diluted with ion-exchanged water so that the solid content concentration was 7.5%, and adjusted to pH 5.0 with a 48% aqueous sodium hydroxide solution to obtain APS-modified starch. 0.16 parts of each surface sizing agent for papermaking was mixed with 50 parts of the modified starch to prepare a coating liquid. The solid content concentration of the surface sizing agent for papermaking in the coating liquid is 0.10%.

<Making coated paper>
Using a bar coater, each coating liquid whose liquid temperature was adjusted to 50 ° C. was double-sided coated on the surface of high-quality acid-free paper (Sutekihito size: 0.5 seconds, basis weight: 70 g / m ² ). After that, it was dried with a rotary dryer at 105 ° C. for 1 minute to prepare a coated paper. The amount of the surface sizing agent for papermaking attached to the base paper was about 0.08 g / m ² in terms of solid content, and the amount of starch attached was about 2 g / m ² in terms of solid content.

<Stunning human size>
According to JIS P 8122, the degree of nice human size of the coated paper was measured. The larger the value, the better the size effect.

* 1: The weight% of each component in the component (B) is expressed so that the total weight of the component (B) is 100% by weight.

The abbreviations in Table 2 mean the following compounds.
-St: Styrene-BA: n-Butyl acrylate-IBMA: Isobutyl methacrylate-2-HEMA: 2-Hydroxyethyl methacrylate

From the results in Table 2, it was found that the surface sizing agents for papermaking of Examples 1 to 19 were superior in mechanical stability and sizing effect at high temperatures as compared with Comparative Examples 1 to 4. It is presumed that this was effective because the (meth) acryloyl group was introduced into the polysaccharide.

In order to confirm the above speculation, the ¹ H-NMR spectra of the components (A-1), (A-6) to (A-13) and (D-4) prepared in the synthetic example were measured and replaced. The degree (DS) was calculated. The method is described below.

<Introduction rate of (meth) acryloyl group (degree of substitution (DS))>
( ¹ Measurement of ¹ H-NMR spectrum)
A measurement sample (solid content concentration of component (A): 0.5%) was prepared by mixing 5.0 mg of component (A-1) and 0.9 ml of deuterated dimethyl sulfoxide (DMSO-d6) in a measurement solvent. Then, ¹ H-NMR spectrum was measured under the following conditions.

(Measurement condition)
NMR measuring instrument: 400MR Made by Agilent Technologies 400MHz
Probe: AutoX PFG probe (5 mm)
Probe temperature: 25 ° C
Measurement frequency: 399.75 MHz
Measuring solvent: Deuterated dimethyl sulfoxide (DMSO-d6)
Pulse sequence: Presaturation standard parameter usage integration count: 16 times

(Calculation method of degree of substitution (DS))
From the obtained ¹ H-NMR spectrum data, the peak integrated value (T1) of the hydrogen atom bonded to the anomer carbon of the oxidized starch and the peak integrated value of the methyl hydrogen of the (meth) acryloyl group derived from GMA bonded to the oxidized starch. Each value (T2) was read and substituted into Equation 1 to calculate the degree of substitution (DS). For the components (A-6) to (A-13) and (D-4), the ¹ H-NMR spectrum was measured by the same method to calculate the degree of substitution (DS). The results are shown in Table 3.

(Equation 1) Degree of substitution (DS) = T2 / T1
T1: Integral value of the peak appearing at the hydrogen atom bonded to the anomeric carbon of the oxidized starch T2: Integrated value of the peak appearing at the methyl hydrogen of the (meth) acryloyl group derived from GMA bonded to the oxidized starch

For T1, the integral value of the peak appearing in the following chemical shift (δ) was read according to the component (a1) used. For T2, the integrated value of the peaks appearing at δ = 1.7 to 1.9 ppm was read.
[Position where anomeric hydrogen peak appears (chemical shift (δ))]
* When oxidized starch is used as the component (a1): 5.0 to 5.2 ppm
* When tapioca starch is used as the component (a1): 5.0 to 5.2 ppm
* When β-cyclodextrin is used as the component (a1): 4.8 to 4.9 ppm
* When glucose is used as a monosaccharide: 4.8 to 5.0 ppm

From the above, it was found that the (meth) acryloyl group was introduced in the components (A-1) and (A-6) to (A-13). It was confirmed that the (meth) acryloyl group was also introduced in the component (D-4), but since the mechanical stability and size effect at high temperature were inferior, the (meth) acryloyl group was introduced into the raw material polysaccharide. It turned out to be effective by being done.

Further, since the components (A-2) to (A-5) and (D-1) are synthesized by the same method as in Synthesis Example 1, they are reacting with the compounds shown in Table 1. Furthermore, since the components (A-2) to (A-5) have good mechanical stability and size effect at high temperatures, the (meth) acryloyl group is almost the same as the component (A-1). It is considered that they are introduced with the same degree of substitution (DS).

Claims (7)

A surface sizing agent for papermaking, which comprises an emulsion polymer of a polysaccharide (A) having a (meth) acryloyl group in the molecule and a monomer (B) having an ethylenically unsaturated group. The surface sizing agent for papermaking according to claim 1, wherein the component (A) is a reaction product of the raw material polysaccharide (a1) and the (meth) acrylic compound (a2). The surface sizing agent for papermaking according to claim 1 or 2, wherein the introduction rate of the (meth) acryloyl group in the component (A) is 0.05 to 2 in terms of the degree of substitution (DS). The surface sizing agent for papermaking according to claim 2, wherein the component (a1) has a weight average molecular weight of 500 to 1,000,000. The surface sizing agent for papermaking according to claim 2, wherein the component (a2) is one selected from the group consisting of a carboxylic acid anhydride, a carboxylic acid bromide, a compound having an epoxy group, and a compound having an isocyanate group. The surface sizing agent for papermaking according to any one of claims 1 to 5, wherein the component (B) contains styrenes (b1) and / or an alkyl (meth) acrylate (b2) having no hydroxy group. A coated paper obtained by coating a base paper with the surface sizing agent for papermaking according to any one of claims 1 to 6.