JP2000239992A - Surface sizing and production of coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface sizing excellent in mechanical stability, low foaming properties and sizing effect on acidic paper and neutral paper by emulsion polymerizing a hydrophobic monomer or with an anionic monomer in the presence of a specific salt of a water-soluble copolymer. SOLUTION: This surface sizing is prepared from a copolymer obtained by emulsion polymerization of the hydrophobic monomers such as styrene or the like or with the anionic monomers such as (meth)acrylic acid or the like in the presence of the salt of the water-soluble copolymer comprising 35-75 wt.% of the hydrophobic monomers such as styrenes and alkyl (meth)acrylates as the monomer units, 15-55% of the anionic monomer such as the salt of the (meth)acrylic acid or the like in which at least a part exists as a salt and 5-20% of a nonionic N-substituted mono alkyl (meth)acryl amide expressed by formula (R1 is H or methyl, R2 is a 4<=C alkyl). Coated paper is obtained by coating 0.01-1 g/m2 of this sizing on a paper base.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface sizing agent and a method for producing a coated paper, and more particularly, to a paper sizing agent obtained by emulsion polymerization using a specific polymer emulsifying and dispersing agent, and The present invention relates to a method for producing a coated paper for applying a coating liquid containing the surface sizing agent to paper.

[0002]

Conventional surface sizing agents for papermaking include styrene-maleic acid copolymers, styrene- (meth) acrylic acid copolymers, and α-olefin-maleic acid copolymers. Aqueous solutions of metal salts are known.

[0003] A surface sizing agent containing a styrene-maleic acid copolymer as a component can exhibit a good sizing effect on acid paper containing a large amount of a sulfuric acid band. Neutral paper with a small amount of water significantly deteriorates the size performance.

[0004] In addition, when the surface is coated, since the surface sizing agent itself often foams, it is necessary to add a large amount of an antifoaming agent to the coating liquid.

[0005] A surface sizing agent containing a styrene- (meth) acrylic acid copolymer as a component can exhibit a relatively good Steckigt sizing degree with respect to the neutral paper, but is inferior in pen writing sizing degree. Therefore, there is a problem that characters are blurred at the time of writing.

Further, since the stability of the coating solution to metal ions is remarkably poor, there are many operational problems such as generation of large amounts of impurities and foaming.

A surface sizing agent containing an α-olefin-maleic acid copolymer as a component shows a good pen writing size, but when used for PPC paper, has low toner fixability,
When used for printing paper, there is a problem that ink adhesion is low.

Some patents have already been reported as prior art as surface sizing agents obtained by carrying out emulsion polymerization in the presence of a polymeric emulsifier.

For example, Japanese Patent Application Laid-Open No. Hei 8-246391 discloses that
"(A) In an aqueous solution containing 100 parts by weight of a water-soluble copolymer containing (1) a carboxyl group-containing unsaturated monomer and (2) a hydrophobic unsaturated monomer, A papermaking surface sizing agent comprising an emulsion obtained by emulsion polymerization of 10 to 500 parts by weight of an unsaturated monomer "is disclosed.

[0010] This surface sizing agent has a higher compatibility with other concomitant chemicals, stability against dissolved metal ions in the coating solution or foaming property in the coating solution as compared with the conventional solution type surface sizing agent. Although improved, its effect is still inadequate.

Further, Japanese Patent Application Laid-Open No. 8-158292 discloses "Acrylamide polymer having an anionic group (A), hydrophobic vinyl monomer (b1), anionic vinyl monomer and / or salts thereof (b2). A copolymer (B) obtained by polymerizing as an essential component,
And the compounding weight ratio is (A) :( B) = 100: 0.1
To 100, which is a surface paper quality improver.

However, the surface paper quality improver is a mixture of an anionic polyacrylamide conventionally used as a surface strength improver at the time of coating and a styrene-methacrylic acid type aqueous solution conventionally used as a surface sizing agent. By selecting the mixing ratio, the paper surface properties such as size, ink receptivity and smoothness are improved, but the stability to dissolved metal ions in the coating liquid and the low Foamability cannot be satisfied.

[0013] More recently, not only ink-jet specialty papers but also PPC papers have been required to have ink-jet suitability, and a surface sizing agent capable of obtaining paper satisfying the suitability has been desired.

[0014] Ink jet suitability includes print density, feathering, and the like required for an image printed by an ink jet method using monochrome or color ink.
Characteristics such as strikethrough and boundary bleeding can be given.

[0015]

DISCLOSURE OF THE INVENTION The present invention relates to a surface sizing agent which is excellent in mechanical stability and storage stability.
It can improve sizing performance, has excellent inkjet suitability for information paper, especially inkjet paper, and improves foaming (reduces foaming) of a coating liquid containing a surface sizing agent. An object of the present invention is to provide a papermaking surface sizing agent that is compatible with other concomitant drugs and stable against dissolved metal ions.

[0016]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a hydrophobic monomer, an anionic monomer and a specific nonionic N-substituted monoalkyl (meth) acrylamide are used. In the presence of a water-soluble copolymer salt obtained by copolymerization, it has been found that the above problem can be overcome by emulsion polymerization of a hydrophobic monomer alone or a monomer component containing a hydrophobic monomer and an anionic monomer. The present invention was completed as an opportunity.

That is, the invention according to claim 1 is:
As a monomer unit, a hydrophobic monomer (a1) and an anionic monomer (a at least partially having a salt form)
2) and the following formula

[0018]

Embedded image (R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkyl group having 4 or more carbon atoms.) Nonionic N-substituted monoalkyl (meth) acrylamide (a
3) a surface sizing agent comprising a copolymer obtained by emulsion polymerization of a hydrophobic monomer (b1) in the presence of a water-soluble copolymer salt [A] containing The invention according to claim 2, wherein the monomer component containing a hydrophobic monomer (b1) and an anionic monomer (b2) is emulsion-polymerized in the presence of the water-soluble copolymer salt [A]. The surface sizing agent according to claim 3, wherein the surface sizing agent comprises the copolymer obtained by the method described in claim 1 or 2. A] The component has a monomer unit of 35 to 75
% By weight of the hydrophobic monomer (a1) and 15 to 55% by weight of the anionic monomer (a2) and 5 to 20% by weight.
And the nonionic N-substituted monoalkyl (meth) acrylamide (a3) of the present invention is a surface sizing agent. 3. A method for producing a coated paper, which comprises applying a coating liquid containing the surface sizing agent according to any one of items 3 to paper.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the hydrophobic monomer (a1) as a monomer unit constituting the water-soluble copolymer salt [A] include a vinyl monomer which is substantially insoluble in water. Are 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)
Examples include acrylates and alkyl (meth) acrylates such as decyl (meth) acrylate, dialkyl esters of unsaturated dicarboxylic acids such as maleic acid and fumaric acid, and vinyl esters such as vinyl acetate and vinyl propionate.

In the water-soluble copolymer salt [A],
One or more of these are contained as monomer units.

Among such hydrophobic monomers (a1), styrenes and alkyl (meth) acrylates are particularly preferred in view of the effect of improving the size. Among the alkyl (meth) acrylates, those having 1 to 6 carbon atoms are preferable.

Examples of the anionic monomer (a2) as a monomer unit constituting the water-soluble copolymer salt [A] include monomers having an anionic group such as a carboxyl group, a sulfonic group, and a phosphate group. be able to. Here, the anionic group can be rephrased as a group that forms a salt with an alkali compound described below.

Examples of the anionic monomer (a2) include α, β-unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid and citraconic acid; Monomethyl maleate, Monoethyl maleate, Monopropyl maleate, Monobutyl maleate, Monomethyl fumarate, Monoethyl fumarate, Monopropyl fumarate, Monobutyl fumarate, Monomethyl itaconate, Monoethyl itaconate, Monopropyl itaconate, and Itaconic acid Carboxyl group-containing monomers such as α, β-unsaturated dicarboxylic acid half esters such as monobutyl, vinyl sulfonic acid,
(Meth) allylsulfonic acid, 2-acrylamide-2-
Sulfonic acid group-containing monomers such as methylpropane sulfonic acid and sulfonated styrene; phosphate ester group-containing monomers such as hydroxyalkyl (meth) acrylate phosphate; and salts of these alkali compounds. The anionic monomer (a2) in the water-soluble copolymer salt [A] in the present invention is partially or entirely a salt of an alkali compound in the polymer.

In the water-soluble copolymer salt [A],
One or more of these are contained as monomer units.

Among such anionic monomers (a2), monomers having a carboxyl group are preferred in that the foamability of the finally obtained surface sizing agent is low.

The nonionic N-substituted monoalkyl (meth) acrylamide (a3) as a monomer unit constituting the water-soluble copolymer salt [A] includes N-tert-butyl (meth) acrylamide, N-lauryl N-substituted monoalkyl (meth) acrylamides having 4 or more carbon atoms in the alkyl group such as (meth) acrylamide, N-tert-octyl (meth) acrylamide, and N-cyclohexyl (meth) acrylamide can be exemplified. .

In the water-soluble copolymer salt [A],
One or more of these may be contained as a monomer unit. In such a nonionic N-substituted monoalkyl (meth) acrylamide (a3), the alkyl group has 4 or more carbon atoms, and preferably 4 to 12 carbon atoms. As the nonionic N-substituted monoalkyl (meth) acrylamide (a3), N-tert-octyl (meth) acrylamide is particularly preferred. In the water-soluble copolymer [A], one of these
Species or two or more species are contained.

The water-soluble copolymer salt [A] includes, as monomer units, 35 to 75% by weight of a hydrophobic monomer (a1) and 15 to 55% by weight of an anionic monomer (a).
A water-soluble copolymer salt containing 2) and 5 to 20% by weight of a nonionic N-substituted monoalkyl (meth) acrylamide (a3) is preferred. A surface sizing agent in which the ratio of the monomer units in the water-soluble copolymer salt is in the above range,
The size effect is remarkably improved, and the coating liquid has little foaming when coated on paper.

In the present invention, if necessary, the water-soluble copolymer salt [A] contained in the obtained water-soluble copolymer salt [A] may be any of the above-mentioned monomers (a1), (a) as long as the effects thereof can be maintained without departing from the object of the present invention. A monomer copolymerizable with a2) and (a3) may be contained as a monomer unit.

Examples of such a monomer include, for example,
(Meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, and N-
Nonionic N-substituted monoalkyl (meth) acrylamide having an alkyl group having 3 or less carbon atoms such as isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N-diisopropyl (meth) acrylamide,
N, N-ditertiarybutyl (meth) acrylamide, N, N-dilauryl (meth) acrylamide,
N-ditertiary octyl (meth) acrylamide,
And N-substituted dialkyl (meth) acrylamides such as N, N-dicyclohexyl (meth) acrylamide, nonacetone monomers such as diacetone acrylamide and vinylpyrrolidone, and (mono- or di-alkyl) aminoalkyl (meth) acrylate (Mono- or di-alkyl) aminohydroxylalkyl (meth) acrylate, (mono- or di-alkyl) aminoalkyl (meth) acrylamide, vinylpyridine,
Examples thereof include cationic monomers such as vinylimidazole and diallylamine.

The amount of the monomer used is within a range that does not decrease the size performance and emulsification performance of the obtained water-soluble copolymer salt, and is usually 5% by weight or less, preferably 2% by weight or less.

As the method for producing the water-soluble copolymer salt [A] in the present invention, conventionally known polymerization methods can be applied, for example, solution polymerization using an organic solvent, or polymerization without using a solvent. Bulk polymerization and emulsion polymerization in which polymerization is carried out in an aqueous system using a low-molecular or high-molecular emulsifier can be applied.

The water-soluble copolymer is obtained by polymerizing the hydrophobic monomer (a1), the anionic monomer (a2) at least partially in a salt form, and the nonionic N-substituted monoalkyl (meth) acrylamide (a3). Salt can be obtained.

The hydrophobic monomer (a1), the non-salt anionic monomer (a2) and the nonionic N-substituted monoalkyl (meth) acrylamide (a3)
And the resulting copolymer is neutralized with an alkali compound to obtain a water-soluble copolymer salt. It is preferable to obtain a water-soluble copolymer salt in this way.

As the alkali compound used in the neutralization reaction, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, and amine bases such as methylamine and dimethylamine can be used. The use amount of these alkali compounds is preferably 0.6 to 1 equivalent to the equivalent of the anionic group of the anionic monomer (a2) used in the present invention, that is, the equivalent of anion. When the use amount of the alkali compound is less than 0.6 equivalent or more than 1 equivalent, sufficient dispersibility cannot be obtained, and when the hydrophobic monomer (b1) is emulsion-polymerized and the hydrophobic monomer (b
Emulsion polymerization of the monomer component containing 1) and the anionic monomer (b2) is not preferred because emulsion polymerization may be poor. Even if it is used in excess of 1 equivalent, no further improvement in water solubility is seen and it is not efficient.

In the production of the water-soluble copolymer salt [A], a monomer may be added by a batch addition polymerization method in which all the monomers are charged into a reaction vessel at a time, and a part or all of the monomers are reacted. A division addition polymerization method in which polymerization is carried out by dividing and adding to a vessel, a continuous drop polymerization method in which polymerization is performed while continuously or partially dropping a part or all of a monomer into a reaction vessel, and the like can be used.

The monomer concentration during polymerization is usually 15 to 50
% By weight. It is possible to obtain a copolymer having a concentration of 15% by weight or more by polymerizing at a monomer concentration of less than 15% by weight and performing a concentration operation, but this is not preferable in terms of economy. When the polymerization is carried out at a monomer concentration exceeding 50% by weight, it is difficult to control the heat of polymerization. The polymerization reaction temperature is usually 40 to 120 ° C, preferably 50 to 100 ° C, and the reaction time is 1 to 20 hours. The neutralization reaction of the copolymer usually has a reaction temperature of 60 to 100 ° C. and a reaction time of 0.5 to 4 hours.

The polymerization initiator used for producing the water-soluble copolymer salt [A] of the present invention includes persulfates such as ammonium persulfate, potassium persulfate and sodium persulfate, and tertiary butyl hydroperoxide. And the like, a redox polymerization catalyst obtained by combining these persulfates or peroxides with a reducing agent, and 2,
Examples include azo catalysts such as 2'-azobisisobutyronitrile and 2,2'-azobis-2-methylpropionamidine dihydrochloride, but are not particularly limited thereto. 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 0.01 to 5 mol% based on the total amount of the monomers used in the present invention. Further, the polymerization initiator may be charged together with the monomer into the reaction vessel, or may be continuously dropped.

In preparing the water-soluble copolymer salt [A] of the present invention, known chain transfer agents can be used. Specifically, for example, normal octyl mercaptan, tertiary decyl mercaptan, normal dodecyl Alkyl mercaptan compounds such as mercaptan, normal octadecyl mercaptan, and normal hexadecyl mercaptan, and chain transfer agents such as mercaptan derivatives such as thioglycolic acid derivative, mercaptopropionic acid derivative, mercaptoethanol, thioethanol, thiomalic acid, and thiosalicylic acid (Molecular weight modifier).

These chain transfer agents may be charged together with the monomer into the reaction vessel, or may be continuously dropped. These chain transfer agents may be used in combination of two or more.
The use amount of the chain transfer agent is preferably in the range of 0.01 to 2% by weight based on the total amount of the monomers used in the present invention.

As the emulsifier used for producing the water-soluble copolymer salt [A], a known emulsifier or dispersant can be used, for example, a low molecular surfactant, a surfactant having a polymerizable group, and a high molecular weight surfactant. And a molecular dispersant.

As the low molecular surfactant, those which can be generally applied to emulsion polymerization can be used, and nonionic, anionic and amphoteric low molecular surfactants, and surfactants having a polymerizable group can be used. Can be used.

Examples of the nonionic low molecular surfactant include polyoxyalkylene alkyl phenyl ether,
Polyoxyalkylene alkyl ether, polyoxyalkylene fatty acid ester, polyoxypropylene polyoxyethylene glycol glycerin fatty acid ester, sorbitan fatty acid ester, polyethylene glycol fatty acid ester, polyoxyethylene sorbitan fatty acid ester, sucrose fatty acid ester, pentaerythritol fatty acid ester, propylene Glycol fatty acid esters,
Fatty acid diethanolamide, polyoxypropylene polyoxyethylene glycol, and the like.

In the present invention, one of the nonionic low-molecular surfactants may be used alone, or two or more of them may be used in combination.

Examples of the anionic surfactant include compounds such as polyoxyalkylene alkylphenyl ether, polyoxyalkylene monostyryl phenyl ether, polyoxyalkylene distyryl phenyl ether, polyoxyalkylene alkyl ether, and polyoxyalkylene fatty acid ester. A phosphate salt, a sulfonate, a succinate, and a sulfosuccinate, an alkylbenzene sulfonate, a naphthalenesulfonic acid formalin condensate, an alkenyl succinate,
Examples thereof include rosin salts, fortified rosin salts, and alkyl diphenyl ether disulfonic acid compounds such as hexyl diphenyl ether disulfonic acid, decyl diphenyl ether disulfonic acid, dodecyl diphenyl ether disulfonic acid, and hexadecyl diphenyl ether disulfonic acid, and salts of the above compounds. As the salt, alkali metal salts such as sodium salt and potassium salt,
Examples thereof include ammonium salts and amine salts.

In the present invention, one of the above-mentioned anionic low molecular surfactants can be used alone, or two or more of them can be used in combination.

The amphoteric surfactant has an anionic group and a cationic group, and can be used alone.
Two or more types can be used.

The surfactant having a polymerizable group is generally called a reactive emulsifier, and examples thereof include compounds having a hydrophobic group, a hydrophilic group and a polymerizable group in the molecule.

The polymerizable group may be, for example, a carbon-carbon double such as a (meth) allyl group, a 1-propenyl group, a 2-methyl-1-propenyl group, an isopropenyl group, a vinyl group, and a (meth) acryloyl group. Contains a functional group having a bond.

As the surfactant having a polymerizable group, those which can be generally applied to emulsion polymerization can be used and are not particularly limited. Specific examples include one or more of the above-mentioned polymerizable groups in the molecule. Having a polymerizable group-containing polyoxyalkylene ether-based compound such as polyoxyalkylene alkyl ether, polyoxyalkylene aralkyl ether, and polyoxyalkylene phenyl ether; and polyoxyalkylene monostyryl phenyl ether and polyoxyalkylene distyryl phenyl ether. Of polyoxyalkylenestyryl phenyl ether compounds.

Examples of the surfactant having a polymerizable group include a sulfonate, a sulfate and a sulfonate derived from the polyoxyalkylene ether compound containing the polymerizable group and the polyoxyalkylenestyrylphenyl ether compound. Phosphate and sulfosuccinate, aliphatic carboxylate and aromatic carboxylate derived from the polymerizable group-containing polyoxyalkylene ether compound, acidic phosphoric acid (meth) acrylate compound, and rosin -Glycidyl (meth) acrylate compounds and the like can be exemplified.

In the present invention, one of the above-mentioned surfactants having a polymerizable group can be used alone, or two or more thereof can be used in combination.

The polymer dispersant is not particularly limited, but is basically a synthetic polymer having a hydrophobic group, a nonionic group and / or an ionic group, and a general natural polymer dispersant. it can.

As an example of a synthetic polymer, polyvinyl alcohol and its modified product, anionic styrene-
Examples thereof include partially or completely neutralized (meth) acrylic acid copolymers, and anionic or cationic (meth) acrylic ester copolymers and (meth) acrylamide copolymers.

Examples of the natural polymer dispersant include casein, lecithin, cellulose derivatives such as hydroxyethylcellulose, starch, and processed starch.

In the present invention, the polymer dispersant is
A single species can be used, or two or more species can be used in combination.

The water-soluble copolymer salt [A] in the present invention.
Is usually obtained as a solid content concentration of 15 to 50% by weight in a polymerization product liquid. The polymerization product liquid containing the water-soluble copolymer salt [A] usually has a viscosity at a solid content of 15% by weight (Brookfield rotational viscometer: 25 ° C.)
Is 10 to 1,000 cps, and the pH is 6 to 10.

The surface sizing agent of the present invention contains the hydrophobic monomer (b1) alone or the hydrophobic monomer (b1) and the anionic monomer (b2) in the presence of the water-soluble copolymer salt [A]. It can be obtained by subjecting the monomer component to be emulsion-polymerized. Here, as an embodiment of “emulsion-polymerizing a monomer component containing a hydrophobic monomer (b1) and an anionic monomer (b2)”, the monomer component containing the hydrophobic monomer (b1) and the anionic monomer (b2) is contained. In addition to the embodiment in which the monomer mixture is emulsion-polymerized, first, one of the hydrophobic monomer (b1) and the anionic monomer (b2) is emulsion-polymerized, and then the hydrophobic monomer (b1) and the anionic monomer ( An embodiment in which the emulsion polymerization is continued by adding the other monomer, if necessary, and the other monomer in b2).

In the production of the surface sizing agent of the present invention, when the hydrophobic monomer (b1) is used alone, the hydrophobic monomer (b1) and the anionic monomer (b2) are used in an amount of 100 parts by weight alone. ) Is used in combination with 20 to 500 parts by weight of the water-soluble copolymer salt [A] based on the total weight of 100 parts by weight, from the viewpoint of the stability of the emulsion, and in particular, the size performance. Therefore, it is preferable to contain 100 to 200 parts by weight of the water-soluble copolymer salt [A].

When the hydrophobic monomer (b1) and the anionic monomer (b2) are used, the amount of the hydrophobic monomer (b1) used is at least 95% by weight in view of size performance and mechanical stability. Preferably 98 to 99.
9% by weight, and the amount of the anionic monomer (b2) used is at most 5% by weight, preferably 0.1 to 2% by weight.

As the hydrophobic monomer (b1), the same monomers as the hydrophobic monomer (a1) described in connection with the water-soluble copolymer salt [A] can be used. Specifically, styrene, α-methyl Styrenes such as styrene, vinyltoluene and divinylbenzene, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, normal butyl (meth) acrylate, isobutyl (meth) acrylate, tertiary butyl (meth) Alkyl (meth) acrylates such as acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and decyl (meth) acrylate; dialkyl esters of unsaturated dicarboxylic acids such as maleic acid and fumaric acid; and vinyl acetate And vinyl propionate And vinyl esters of. The hydrophobic monomers (b1) are used alone or in combination of two or more. Among such hydrophobic monomers (b1), styrenes and alkyl (meth) acrylates are particularly preferred in view of the effect of improving the size.

As the anionic monomer (b2), the same monomer as the anionic monomer (a2) described in connection with the water-soluble copolymer salt [A] can be used. Specifically, (meth) acrylic acid, Maleic acid, fumaric acid, itaconic acid, citraconic acid, crotonic acid, monomethyl maleate, monoethyl maleate, monopropyl maleate, monobutyl maleate, monomethyl fumarate, monoethyl fumarate, monopropyl fumarate, monobutyl fumarate, itacon Monomers having a carboxyl group such as monomethyl acrylate, monoethyl itaconate, monopropyl itaconate and monobutyl itaconate, vinyl sulfonic acid, (meth) allyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, sulfonated styrene and the like Has a sulfonic acid group of That monomer include monomers having a phosphoric acid ester group and phosphoric acid esters of hydroxyalkyl (meth) acrylate. These can be used alone or in combination of two or more. Among such anionic monomers (b2), (meth) acrylic acid, maleic acid and fumaric acid are preferred, and (meth) acrylic acid is particularly preferred in that the foamability of the obtained surface sizing agent is low.

In the present invention, if necessary, a monomer copolymerizable with the hydrophobic monomer (b1) and the anionic monomer (b2) may be used as far as it does not depart from the object of the present invention and still maintain its effect. Can be used.

Examples of such a monomer include, for example,
Nonionic monomers such as (meth) acrylamide, monoalkyl (meth) acrylamide, dialkyl (meth) acrylamide, diacetone acrylamide, and vinylpyrrolidone, and (mono- or di-alkyl) aminoalkyl (meth) acrylate, (mono- Or cationic monomers such as (di-alkyl) aminohydroxylalkyl (meth) acrylate, (mono- or di-alkyl) aminoalkyl (meth) acrylamide, vinylpyridine, vinylimidazole, and diallylamine.

The amount of the monomer used is within a range that does not decrease the sizing performance of the surface sizing agent of the present invention.
It can be used in combination at not more than 2% by weight, preferably not more than 2% by weight. When the monomer is used in an amount exceeding 5% by weight, the viscosity of the surface sizing agent of the present invention increases, the mechanical stability of the surface sizing agent of the present invention deteriorates, and the foaming of the coating liquid increases. Problem arises.

In the emulsion polymerization of the hydrophobic monomer (b1) alone or in the monomer component containing the hydrophobic monomer (b1) and the anionic monomer (b2), a conventionally known emulsion polymerization method is applied. For example, the hydrophobic monomer (b1) and the anionic monomer (b2) can be combined with each other in the presence of the water-soluble copolymer salt [A].
A method of performing emulsion polymerization in water with a radical polymerization catalyst can be employed. In the emulsion polymerization, substantially all of the monomers are polymerized. In the case of the emulsion polymerization of the hydrophobic monomer (b1) alone, a homopolymer of the hydrophobic monomer (b1) is formed, and the hydrophobic polymer (b1) is formed. In the emulsion polymerization of a monomer component containing a monomer (b1) and an anionic monomer (b2), a copolymer having the hydrophobic monomer (b1) and the anionic monomer (b2) as monomer units is formed. .

As the radical polymerization catalyst in the emulsion polymerization, for example, ammonium persulfate, potassium persulfate,
And persulfates such as sodium persulfate, peroxides such as tertiary butyl hydroperoxide, redox polymerization catalysts obtained by combining these persulfates or peroxides with reducing agents, and 2,2'-azo Examples include azo-based catalysts such as bisisobutyronitrile and 2,2'-azobis-2-methylpropionamidine dihydrochloride, but are not particularly limited thereto, and may be other known and commonly used polymerizations. Initiators can also be used. Two or more of these polymerization initiators may be used. Further, if necessary, a known chain transfer agent may be appropriately used in combination.

Emulsion polymerization of the hydrophobic monomer (b1),
The amount of the water-soluble copolymer salt [A] used in the emulsion polymerization of a monomer component containing the hydrophobic monomer (b1) and the anionic monomer (b2) is as follows. That is, in the emulsion polymerization of the hydrophobic monomer (b1) alone, the water-soluble copolymer salt [A] is usually added in a solid content of 20 parts by weight to 100 parts by weight of the hydrophobic monomer (b1).
Use up to 500 parts by weight. On the other hand, the hydrophobic monomer (b
In the emulsion polymerization of a monomer component containing 1) and an anionic monomer (b2), a water-soluble copolymer salt [A] is added as a solid component to 100 parts by weight of the total amount of the monomers used as the monomer component. Usually, 20 to 500 parts by weight are used. If the amount of the water-soluble copolymer salt [A] is less than 20 parts by weight, the particle size of the obtained surface sizing agent may be too large, which is not preferable. On the other hand, when the amount of the water-soluble copolymer salt [A] used is more than 500 parts by weight, the particle size of the obtained surface sizing agent is not further reduced, and the surface sizing agent is not coated when coated on paper. It is not preferable because the sizing agent may foam.

When the hydrophobic monomer (b1) is emulsion-polymerized, and when the monomer component containing the hydrophobic monomer (b1) and the anionic monomer (b2) is emulsion-polymerized, the surface sizing agent of the present invention is used. As long as the performance is not impaired, a known low-molecular surfactant and a high-molecular dispersant used at the time of production of the water-soluble copolymer salt [A] may be used in combination. When the hydrophobic monomer (b1) is emulsion-polymerized, the amount of the low molecular surfactant and the high molecular dispersant is 10% by weight or less, preferably 5% by weight or less based on the hydrophobic monomer. When emulsion-polymerizing a monomer component containing a hydrophobic monomer (b1) and an anionic monomer (b2), the amount is 10% by weight or less, preferably 5% by weight, based on the total amount of monomers in the monomer component. % By weight or less. If the amount of the low molecular surfactant and the high molecular dispersant exceeds 10% by weight, the foaming property of the obtained surface sizing agent becomes strong, which may cause troubles due to bubbles when used as a coating liquid. is there.

The surface sizing agent of the present invention is obtained by emulsion-polymerizing a hydrophobic monomer (b1) in the presence of a specific water-soluble copolymer salt [A] obtained by copolymerizing the above-mentioned specific monomer. Alternatively, it can be used as a polymerization product liquid containing a copolymer obtained by emulsion polymerization of a monomer component containing a hydrophobic monomer (b1) and an anionic monomer (b2).

The surface sizing agent of the present invention usually has a solid content of 25 to 50% by weight and a viscosity (Brookfield rotational viscometer: 25 ° C.) of 1 at a solid content of 25% by weight.
It is preferable to adjust the pH to 0 to 1,000 cps and the pH to 6 to 10.

The pulp used for the base paper to which the surface sizing agent of the present invention is applied may be bleached or unbleached chemical pulp such as kraft pulp and sulfite pulp, bleached pulp such as groundwood pulp, mechanical pulp and thermomechanical pulp. Examples include unbleached high-yield pulp, waste newspaper pulp, magazine waste paper, and waste paper pulp such as cardboard waste paper and deinked waste paper.

In order to obtain base paper, fillers, dyes, rosin-based sizing agents for acidic papermaking, alkylketene dimer-based or alkenylsuccinic anhydride-based sizing agents for neutral papermaking, rosin-based sizing agents for neutral papermaking, etc. Additives such as a dry paper strength enhancer, a wet strength enhancer, a retention improver, a drainage improver, and an antifoaming agent are also used as needed to develop the physical properties required for each paper type. May be used. Fillers include clay, talc, titanium oxide, heavy or light calcium carbonate, and the like. These may be used alone or in combination of two or more.

Examples of a coating machine for coating the surface sizing agent of the present invention include a size press, a film press, a gate roll coater, a shim sizer, a blade coater, a calender, a bar coater, a knife coater, an air knife coater, A curtain coater or the like can be used. Further, the surface sizing agent of the present invention can be applied to the base paper surface by a spray coating machine.

When applying the surface sizing agent of the present invention, starches such as oxidized starch, phosphorylated esterified starch, enzyme-modified starch, and cationized starch, celluloses such as carboxymethylcellulose, polyvinyl alcohols, Acrylamides and water-soluble polymers such as sodium alginate can also be used as mixed in the coating solution. Further, additives such as other surface sizing agents, anti-slip agents, preservatives, rust inhibitors, defoamers, viscosity modifiers, dyes, and pigments may be used in combination.

Examples of the sizing paper that can be obtained by applying the surface sizing agent of the present invention to the base paper include recording paper such as PPC paper, ink jet recording paper, laser printer paper, foam paper, heat transfer paper, and thermal recording paper. Paper, art paper, cast coated paper, coated paper such as high quality coated paper, packaging paper such as kraft paper and pure white roll paper, notebook paper, book paper, printing paper, newspaper paper and other Western paper, manila balls, white balls And various base papers obtained by acidic or neutral papermaking such as paperboard for paper containers such as chipboard and high-grade whiteboard, and paperboard such as liner.

The concentration of the surface sizing agent in the coating solution when applying the surface sizing agent of the present invention is usually 0.01 to 5% by weight, preferably 0.05 to 2% by weight. If the surface sizing agent concentration is less than 0.01% by weight, the sizing effect may be insufficient, and if the surface sizing agent concentration is more than 5% by weight, the sizing effect is hardly improved and it is economically disadvantageous. Absent.

Usually, the coating amount of the surface sizing agent is 0.01 to 1 g / m ² , preferably 0.01 to 0.1 g / m ² in terms of solids.
1 g / m ² . When it is within the above range, the size effect is particularly well exhibited.

[0080]

The present invention will be described in more detail with reference to Synthesis Examples, Examples and Comparative Examples below, but the present invention is not limited to these Examples. In the following, "parts" and "%" are based on weight.

<Method for Producing Water-Soluble Copolymer Salt [A]> (Synthesis Example 1) Water 49 was placed in a 1-liter four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube.
9.2 parts, styrene 100.6 parts, 80% methacrylic acid 23.6 parts, N-tert-octylacrylamide 6.3 parts, normal dodecyl mercaptan 0.64 parts,
47% dodecyl diphenyl ether disulfonic acid 0.6
3 parts were charged and heated to 70 ° C. Next, after sufficiently removing oxygen in the reaction system with nitrogen gas, 2.9 parts of ammonium persulfate was added. After 20 minutes, the temperature in the reaction system was raised to 80 ° C, and the reaction was further performed at 80 ° C for 2 hours. Then, 320 parts of water and 48.5% potassium hydroxide aqueous solution 2
2.8 parts (neutralization equivalent: 0.9) were added to obtain a water-soluble copolymer salt (A-1) solution having a pH of 8.7, a solid content of 15.2%, and a viscosity of 65 cps. The obtained water-soluble copolymer salt (A
-1) Table 1 shows the composition and properties of the solution.

(Synthesis Examples 2 to 13) In Synthesis Example 1, a hydrophobic monomer (a1), an anionic monomer (a2),
Nonionic N-substituted monoalkyl (meth) acrylamide (a3), a water-soluble copolymer salt (A-) was prepared in the same manner as in Synthesis Example 1 except that the neutralization equivalent was changed to the kind and the mixing ratio shown in Table 1. 2 to A-13) A solution was obtained. Table 1 shows the types and properties of the monomers in the obtained water-soluble copolymer salt solution.

[0083]

[Table 1] St: Styrene MMA: Methyl methacrylate MAA: Methacrylic acid NIPAM: N-isopropylacrylamide Nocta: N-tert-octylacrylamide DAAm: Diacetone acrylamide AAm: Acrylamide DMAAm: N, N-dimethylacrylamide tBAAm: N-tert-butylacrylamide Equivalent : Equivalent to the anionic group of the anionic monomer (a2).

Example 1 In the same reactor as in Synthesis Example 1,
54.4 parts of water, water-soluble copolymer salt of Synthesis Example 1 (A-1)
820.3 parts of an aqueous solution (124.7 parts as a solid content) of
62.3 parts of styrene, normal butyl acrylate 6
2.3 parts and 0.6 parts by weight of ammonium persulfate were added, and the mixture was heated to 80 ° C. while mixing and stirring under a nitrogen stream.

The emulsion polymerization reaction was completed by holding at 80 ° C. for 2 hours to obtain a surface sizing agent having a solid concentration of 25%.

(Examples 2 to 17, Comparative Examples 1 to 5) The type and amount of the water-soluble copolymer salt [A] (hereinafter referred to as “component [A])”, the hydrophobic monomer (b1) and A surface sizing agent was obtained in the same manner as in Example 1 except that the type and composition ratio of the anionic monomer (b2) (hereinafter, referred to as “[B] component)” were changed as shown in Tables 2 and 3.

[0087]

[Table 2] BA: butyl acrylate St: styrene MAA: methacrylic acid DM: dimethylaminoethyl methacrylate AAm: acrylamide

[0088]

[Table 3] BA: butyl acrylate St: styrene MAA: methacrylic acid

(Comparative Example 6) A commercially available styrene-acrylic surface sizing agent SS315 (manufactured by Nippon PMC) was used in place of the water-soluble copolymer salt [A] in Example 1. A surface sizing agent was prepared as in Example 1.

(Test Example 1) Evaluation on acidic woodfree paper (1) Production of base paper for acid woodfree paper Pulp beaten to 380 ml Canadian Standard Freeness (pulp ratio of hardwood to softwood is 9: 1)
Was mixed with 2.5% aqueous slurry, and talc (manufactured by Fuji Talc Kogyo Co., Ltd .; ND talc) with a pulp content of 15% (on a dry basis) was added thereto. Then
After sequentially adding a sulfuric acid band of 2% (based on absolute dry weight) to pulp and a rosin sizing agent for acidic paper (manufactured by Nippon PMC Co., Ltd .; AL120) of 0.3% (based on absolute dry weight) relative to pulp, pH 4 was obtained. The pulp slurry was diluted to a concentration of 0.25% with 0.5 dilution water. After that, 0.01% against pulp
(Absolutely dry weight basis) retention improver (manufactured by Hymo; NR1)
2MLS), and on a Noble and Wood paper machine,
Paper was made to have a basis weight of 65 g / m ² . The papermaking pH at this time was 4.5. Drying of the wet paper was performed using a drum dryer at 100 ° C. for 80 seconds.

(2) Preparation method of coating solution Oxidized starch (MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) was diluted with water to a concentration of 10%, and gelatinized at 95 ° C. Any one of the surface sizing agents of Comparative Examples 1 to 6 was blended so that the solid content concentration of the oxidized starch became 6% and the solid content concentration of the surface sizing agent became 0.3%, and a coating liquid was prepared. The prepared coating solution was adjusted to pH 8 or pH 6 with caustic soda or sulfuric acid.

(3) Production and evaluation of acidic woodfree paper The coating liquid blended in the above (2) was applied to the base paper made in the above (1) with a size press to obtain acidic woodfree paper. The obtained test paper was conditioned for 24 hours in a constant temperature and constant humidity (20 ° C., 65% relative humidity) environment, and the Stekigto sizing degree (J
IS P8122) and measurement of pen writing size (J TAPPI paper pulp test method No. 12-76)
).

Tables 4 and 5 show the evaluation results. It should be noted that the higher the value of both the Steckigt sizing degree and the pen writing sizing degree, the better.

[0094]

[Table 4]

[0095]

[Table 5]

Test Example 2 Evaluation with Neutral Fine Paper (1) Papermaking of Neutral Fine Base Paper Pulp beaten to 380 ml Canadian Standard Freeness (pulp ratio of hardwood to softwood is 9: 1)
Was mixed with 2.5% aqueous slurry, and calcium carbonate (TP121S, manufactured by Okutama Kogyo Co., Ltd.) having a pulp content of 2% (on a dry basis) was added. Subsequently, an amphoteric starch (manufactured by National Starch; Cato3210) having a pulp content of 0.5% (based on absolute dry weight) and an alkyl ketene dimer sizing agent having a content of pulp of 0.08% (based on absolute dry weight) (Nippon PMC (Japan)) AS26
After 3) was added sequentially, the pulp slurry was diluted to a concentration of 0.25% with dilution water having a pH of 7.5. afterwards,
The diluted pulp slurry is made of calcium carbonate (manufactured by Okutama Industry Co., Ltd .; TP12) of 8% (based on absolute dry weight) based on pulp.
1S), a yield improver (NR12MLS, manufactured by Hymo Co., Ltd.) with a pulp content of 0.01% (on a dry basis) was added, and paper was made with a Noble & Wood paper machine so as to have a basis weight of 65 g / m ² . The papermaking pH at this time was 7.5. Dry the wet paper at 100 ° C using a drum dryer.
For 80 seconds.

(2) Preparation method of coating liquid Oxidized starch (MS3800 manufactured by Nippon Shokuhin Kako Co., Ltd.) was diluted with water to a concentration of 10%, and gelatinized at 95 ° C. A coating liquid was prepared by blending any of the surface sizing agents of Examples 1 to 6 such that the solid content concentration of the oxidized starch became 6% and the solid content concentration of the surface sizing agent became 0.3%. Then, the pH of the obtained coating solution was adjusted to pH 8 with caustic soda or sulfuric acid.

(3) Production and Evaluation of Neutral Fine Paper The coating liquid blended in (2) was applied to the base paper made in (1) using a size press, and the neutral fine paper was produced. Obtained. The obtained test paper was conditioned for 24 hours in a constant temperature and constant humidity (20 ° C., 65% relative humidity) environment, and the degree of Stigecht sizing and the degree of pen writing sizing were measured in the same manner as in Test Example 1. The results are shown in Tables 6 and 7.

[0099]

[Table 6]

[0100]

[Table 7]

Test Example 3 Evaluation with Inkjet Recording Paper (1) Preparation of Neutral Base Paper for Recording Paper Pulp beaten to 380 ml Canadian Standard Freeness (pulp ratio of hardwood to softwood is 9: 1)
Is a 2.5% aqueous slurry, and 1% (based on an absolute dry weight) calcium carbonate (manufactured by Okutama Industry Co., Ltd .; TP121S) and 5% talc (Fuji Talc Kogyo Co., Ltd.) And ND talc).

Then, a sulfuric acid band of 1.0% (based on absolute dry weight) with respect to pulp and 0.5% (based on absolute dry weight) with respect to pulp.
Amphoteric starch (National Starch; Cato3)
210) and 0.3% (based on absolute dry weight) of pulp to rosin for neutral paper (manufactured by Nippon PMC; CC16)
After the addition of 7) in order, the pulp slurry was diluted to a concentration of 0.25% with dilution water having a pH of 7.5. afterwards,
4% (based on absolute dry weight) calcium carbonate (Okutama Kogyo Co., Ltd .; TP12)
1S), a yield improver (NR12MLS, manufactured by Hymo Co., Ltd.) with a pulp content of 0.01% (on a dry basis) was added, and paper was made with a Noble & Wood paper machine so as to have a basis weight of 65 g / m ² . The papermaking pH at this time was 7.5. Dry the wet paper at 100 ° C using a drum dryer.
For 80 seconds.

(2) Preparation method of coating liquid Oxidized starch (MS3800 manufactured by Nippon Shokuhin Kako Co., Ltd.) was diluted with water to a concentration of 10%, gelatinized at 95 ° C. 1 to 17 and any of the surface sizing agents of Comparative Examples 1 to 6 and sodium chloride, and the solid content concentration of the oxidized starch was 5%.
%, And the solid content concentration of the surface sizing agent is 0.25%.
And the salt concentration was adjusted to be 0.25%.

(3) Production of Recording Paper The coating liquid mixed in (2) was applied to the base paper for recording paper made in (1) by a size press to obtain a recording paper.
The obtained test paper is kept at a constant temperature and humidity (20 ° C., 65% relative humidity).
It was conditioned for 24 hours in an environment.

(4) Evaluation of Recording Paper The test paper obtained in the above (3) was subjected to a sizing test and an inkjet suitability test.

(I) Evaluation of sizing degree In the same manner as in the measurement of the sizing degree in Test Example 1, the Stigecht sizing degree and the pen writing sizing degree were measured. The results are shown in Tables 8 and 9.

(Ii) Ink Jet Suitability Test Method The ink jet suitability was evaluated by subjecting the test paper obtained in the above (3) to a calendering treatment, followed by constant temperature and humidity (20 ° C., 65 ° C.).
% Relative humidity) under an environment for 24 hours or more, and then a BJ-Bubble Jet Printer manufactured by Canon Inc.
It carried out by the following method using 220JC. Table 8 shows the results.
And Table 9 below.

(A) Print density test A solid print was printed on a test paper, and the print density of the solid portion was measured with a Macbeth ink densitometer. The higher the value, the higher the print density.

(B) Feathering test A straight line and a character having a constant line width perpendicular to the test paper were printed, and the bleeding of the outer edge of the straight line and the character was visually evaluated on a five-point scale. The sample having no feathering was designated as 5, and the sample having ink bleeding and the characters could not be identified was designated as 1.
The print quality that can withstand normal use is 4 or more.

(C) Run-through test Solid printing was performed on test paper, and the degree of bleeding of the ink on the back side of the solid printed portion was visually evaluated on a scale of 5 levels. The sample with no ink bleeding on the back was designated as 5, and the sample with the solid portion completely penetrated was designated as 1. The print quality that can withstand normal use is 4 or more.

[0111]

[Table 8]

[0112]

[Table 9]

(Test Example 4) Foamability test (1) Preparation of test solution for foamability evaluation Oxidized starch (MS3800 manufactured by Nippon Shokuhin Kako Co., Ltd.) was diluted to a concentration of 10% with water, and gelatinized at 95 ° C. Then, the oxidized starch, any one of the surface sizing agents of Examples 1 to 17 and Comparative Examples 1 to 6, and common salt were mixed at a solid content of 5%.
%, And the solid content concentration of the surface sizing agent is 0.25%.
And the salt concentration was adjusted to be 0.25%.

(2) Evaluation of foaming property of coating liquid 600 g of the coating liquid mixed in the above (1) was put into a foam cell having an inner diameter of 7 cm and a length of 50 cm, and circulated under the following conditions.
The height (mm) of the foam was measured. Tables 10 and 11 show the results.
Shown in Coating liquid temperature 60 ° C, circulation pump flow rate 9 l / min, circulation time 3 minutes.

In Tables 10 and 11, the lower the foam height, the better the foamability (the smaller the foaming amount).

(Test Example 5) Mechanical Stability Test 50 g of the coating liquid prepared in the above (1) was put in a cup, and heated at a temperature of 60 ° C., a load of 20 kg, and a rotation speed of 800 rpm.
A Marlon stability test was performed for one minute. The formed aggregate was filtered through a 325 mesh wire net, and the amount of the precipitate relative to the total solid content was measured and expressed as a percentage. The results are shown in Tables 10 and 11.

[0117]

[Table 10]

[0118]

[Table 11]

Evaluation results on the acidic high-quality papers in Tables 4 and 5
From the evaluation results on neutral high-quality papers in Tables 6 and 7, the surface sizing agents of Examples have a small effect on the change in the pH of the coating solution, and the surface sizing degree and pen writing sizing degree are comparatively small. It was found to be better than the agent.

From the evaluation results of the ink jet recording papers shown in Tables 8 and 9, the surface sizing agents of the examples showed that the print density, feathering, strike-through evaluation, Stecht sizing degree and pen writing sizing degree were the same as those of the comparative examples. It was found to be better than the agent.

From the evaluation results in Tables 10 and 11, the surface sizing agent of the example was lower in foaming property than the surface sizing agent of the comparative example, and the mechanical stability was superior to that of the surface sizing agent of the comparative example. It was found that the amount of lees was smaller than that of the sizing agent and was superior.

[0122]

According to the present invention, the sizing agent itself is excellent in mechanical stability, low foaming property and storage stability, and when used as a surface sizing agent, improves sizing performance from acidic paper to neutral paper. To provide a surface sizing agent which imparts excellent ink jet suitability to information paper, especially ink jet paper, has low foaming property in a coating liquid, and has good compatibility with other concomitant chemicals. be able to.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4L055 AG63 AG71 AG72 AG73 AH13 EA32 GA05 GA06 GA08 GA09 GA11 GA12 GA13 GA16 GA17 GA19 GA20

Claims (4)

[Claims] 1. A monomer unit comprising a hydrophobic monomer (a1), an anionic monomer (a2) having at least a part thereof in the form of a salt, and a compound represented by the following formula: (R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkyl group having 4 or more carbon atoms.) Nonionic N-substituted monoalkyl (meth) acrylamide (a
3) a surface sizing agent comprising a copolymer obtained by emulsion polymerization of a hydrophobic monomer (b1) in the presence of a water-soluble copolymer salt [A] containing . 2. Emulsion polymerization of a monomer component comprising a hydrophobic monomer (b1) and an anionic monomer (b2) in the presence of the water-soluble copolymer salt [A] according to claim 1. A surface sizing agent comprising the obtained copolymer. 3. The water-soluble copolymer salt [A] comprises, as monomer units, 35 to 75% by weight of the hydrophobic monomer (a1) in the above item 1, and 15 to 55% by weight of the hydrophobic monomer (a1) in the above item 1. Anionic monomer (a2), 5 to 20
3. The surface sizing agent according to claim 1, wherein the surface sizing agent comprises the nonionic N-substituted monoalkyl (meth) acrylamide (a3) according to claim 1. 4. A method for producing a coated paper, comprising applying a coating liquid containing the surface sizing agent according to claim 1 to paper.