JPH07119089A - Copolymer latex for paper coating - Google Patents

Abstract

PURPOSE:To provide a paper-coating copolymer latex especially having excellent adhesive strength and giving a coated paper having excellent white paper gloss, printing gloss, etc. CONSTITUTION:This copolymer latex for paper coating is produced by the emulsion polymerization of a monomer mixture composed of (A) 10-60wt.% of an aliphatic conjugated diene monomer, (B) 0.2-15wt.% of an ethylenically unsaturated carboxylic acid monomer and (C) 25-89.8wt.% of other monoolefinic monomer copolymerizable with the above monomers. The Mooney viscosity (MS1+4, 100 deg.C) of the solid component of the copolymer latex is 40-195.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copolymer latex for paper coating, and more specifically, it has excellent dry pick strength and is particularly useful as a binder of a coating liquid for lithographic sheet offset printing. It relates to a copolymer latex for coating.

[0002]

2. Description of the Related Art In recent years, a large amount of pigment-coated paper has been used for publication or commercial printing. Most of the printing of coated paper is performed by lithographic printing (offset printing), and the tendency of high-speed printing is increasing to increase the demand or reduce the production cost. The demand is increasing.

When performing high-speed printing by this lithographic printing, the energy at the time of cleavage of the printing ink exceeds the surface strength of the paper, and picking easily occurs, which causes a problem that the commercial value of the printed matter is significantly impaired. Therefore, among the qualities of coated paper, there is a strong demand for improvement in dry pick strength.

As a method for improving the dry pick strength, a method of increasing the toluene insoluble content of the paper coating latex or reducing the particle size to make the coating layer dense is known.

However, in this case, white paper gloss, printing gloss and inking property were deteriorated, and it was difficult to improve the dry pick strength without sacrificing the physical properties of these coated papers.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. In particular, the dry pick strength is good, and the blank paper has a contradictory relationship with the dry pick strength. An object of the present invention is to provide a copolymer latex for paper coating which is excellent in other physical properties of the coated paper such as gloss, printing gloss and ink receptivity.

[0007]

That is, the present invention is
(A) 10 to 60% by weight of an aliphatic conjugated diene monomer,
(B) 0.2-15 ethylenically unsaturated carboxylic acid monomer
%, And (c) a copolymer latex obtained by emulsion-polymerizing a monomer consisting of 25 to 89.8% by weight of another monoolefin-based monomer copolymerizable therewith, Mooney viscosity (M
S _{1 + 4} , 100 ° C.) is 40 to 195, to provide a copolymer latex for paper coating. (Structure of the Invention) Hereinafter, the present invention will be described in detail.

Examples of the aliphatic conjugated diene-based monomer (hereinafter referred to as "component (a)") used in the present invention include 1,3-butadiene, 2-methyl-1,3-butadiene and 2,3. -Dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, linear and side chain conjugated hexadienes and the like can be mentioned. The component (a) is necessary for imparting appropriate elasticity to the copolymer and appropriate softness to the resulting coating film, and the amount thereof is 10 to 60% by weight, preferably 20 to 20% by weight based on the whole monomer. 55% by weight. If the amount of component (a) used is less than 10% by weight, the copolymer obtained will be hard and brittle, while if it exceeds 60% by weight, the copolymer obtained will be too soft and will have poor water resistance.

The ethylenically unsaturated carboxylic acid monomer used in the present invention (hereinafter referred to as "component (b)") is
For example, mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid can be mentioned. Moreover, a dicarboxylic acid anhydride can also be used. The amount of the component (b) used is 0.2 to 15% by weight, preferably 0.5 to 13% by weight based on the whole monomer.
%, More preferably 1 to 10% by weight. If the amount of component (b) used is less than 0.2% by weight, the adhesive strength and mechanical stability of the resulting copolymer will decrease, whereas if it exceeds 15% by weight, the viscosity of the copolymer latex will be too high. Difficult to handle.

Other monoolefin-based monomers (hereinafter referred to as "component (c)") copolymerizable with the components (a) and (b) used in the present invention include styrene and α-
Aromatic vinyl compounds such as methylstyrene, vinyltoluene, and dimethylstyrene; methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, β acrylate
-Hydroxyethyl, acrylic acid or methacrylic acid esters such as β-hydroxyethyl methacrylate; acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-chloroacrylonitrile, α
Examples thereof include vinyl cyanide-based monomers such as ethylacrylonitrile.

The amount of the component (c) used is 25 to the total amount of the monomers.
It is 89.8% by weight, preferably 32 to 79.5% by weight. If the amount of the component (c) used is less than 25% by weight, the water resistant adhesive strength is poor, while if it exceeds 89.8% by weight, the adhesive strength is poor.

The copolymer latex of the present invention is obtained by emulsion-polymerizing the monomers of the component (a), the component (b) and the component (c), and the Mooney viscosity of the solid content of the copolymer latex. (MS _{1 + 4} , 100 ° C.) is 40 to 195, preferably 80 to 180, more preferably 90 to 170.
Is. When the Mooney viscosity (MS _{1 + 4} , 100 ° C.) is less than 40, the dry pick strength is inferior, while when it exceeds 195, the obtained copolymer latex is hard and brittle and inferior in adhesive strength and water resistance.

When emulsion-polymerizing the monomers (a) to (c) used in the present invention, a chain transfer agent, a molecular weight modifier, an emulsifier, a polymerization initiator and the like may be added, if necessary, by a known method. Can be used.

The chain transfer agent used in the polymerization of the copolymer latex of the present invention is a conventionally known one, for example, t-dodecyl mercaptan, octyl mercaptan, n-dodecyl mercaptan, n-tetradecyl mercaptan, t-
Molecular weight of tetradecyl mercaptan, n-hexadecyl mercaptan, t-hexadecyl mercaptan, tetraethyl thiuram sulfide, methylene chloride, ethylene bromide, dipentamethylene thiuram hexasulfide, diisopropylxanthogen disulfide, α-methylstyrene dimer, etc. Molecular weight regulators commonly used for regulation can be used. Also, two or more of these can be used in combination.

As the emulsifier, anionic surfactants such as sulfuric acid esters of higher alcohols, alkylbenzelsphonates and aliphatic sulfonates, or alkyl ester type of polyethylene glycol, alkyl phenyl ether type, alkyl ether type are used. These nonionic surfactants can be used alone or in combination of two or more.

The polymerization initiator is a radical-decomposable monomer in the presence of heat or a reducing substance to cause addition polymerization of a monomer, and is a water-soluble or oil-soluble peroxodisulfate, peroxide or azobis. Compounds such as potassium peroxodisulfate, sodium peroxodisulfate,
Ammonium peroxodisulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, 2,2
-Azobisisobutyronitrile, cumene hydroperoxide, etc. In the present invention, it is preferable to use at least one water-soluble initiator, which can increase the stability of the polymer latex. Among them, peroxodisulfate is most preferably used.
Two or more polymerization initiators may be used, and an oil-soluble initiator may be used in combination. The proportion of the polymerization initiator used is usually 0.05 to 1.5% by weight based on the monomers. The polymerization temperature is usually in the range of 35 to 90 ° C., but when it is desired to accelerate the polymerization rate or to carry out the polymerization at a lower temperature, sodium bisulfite, ascorbic acid or a salt thereof, ersorbic acid or a salt thereof, Rongalit sulfuric acid is used. A so-called redox polymerization method in which a reducing agent such as iron is used in combination with a polymerization initiator can also be used.

In addition, as the chelating agent, the inorganic salt and the like, those known as emulsion polymerization are used.

The copolymerization method may be, for example, a method in which the monomer mixture is charged all at once, or a part of the monomer mixture is polymerized, and then the rest is added intermittently or continuously as the polymerization progresses. It is also possible to adopt a method in which the monomer mixture is continuously added from the beginning of the polymerization.

The paper coating composition in which the copolymer latex of the present invention is used comprises an inorganic pigment or an organic pigment, preferably an inorganic pigment, and the above-mentioned copolymer latex and, if necessary, other binder. Prepared. The blending amount of the above copolymer latex is preferably 5 to 30 parts by weight, more preferably 5 to 20 parts by weight, and more preferably 5 to 20 parts by weight, based on 100 parts by weight of the pigment in terms of solid content. The compounding amount of the agent is preferably 10 parts by weight or less, more preferably 2 to 5 parts by weight, based on 100 parts by weight of the pigment in terms of solid content.

Examples of the inorganic pigment include kaolin clay,
Talc, barium sulfate, titanium oxide, (rutile anatase), calcium carbonate, aluminum hydroxide, zinc oxide, satin white and the like, and organic pigments such as polystyrene latex are used. These may be used alone or in combination of two or more.

As the other binder, a natural binder such as starch, oxidized starch, soybean protein and casein, or a synthetic latex such as polyvinyl alcohol, polyvinyl acetate latex and acrylic latex is used.

Further, various auxiliaries generally used in this paper coating composition, for example, dispersants (sodium pyrophosphate, sodium hexametaphosphate, etc.), antifoaming agents (polyglycol, fatty acid ester, phosphorus). Acid ester,
Silicone oil, etc., Leveling agent (funnel oil, dicyandiamide, urea, etc.), antiseptic, water resistance agent (formalin, hexamine, melamine resin, urea resin glyoxal, etc.), mold release agent (calcium stearate, paraffin emulsion, etc.), bud If necessary, a photo dye, a color water retention improver (carboxymethyl cellulose, sodium alginate, etc.) can be added.

This paper coating composition can be applied by a conventionally known method using, for example, an air knife coater, a blade coater, a roll coater or an applicator.

In addition to the pigment binder, the copolymer latex of the present invention can be used as a paper coating agent, a carpet backing agent adhesive, various other adhesives, and a paint.

[0025]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. "Part" and "%" in these examples
Means parts by weight and% by weight, respectively. Examples 1 to 5 (Production of copolymer latex) In an autoclave with a stirrer, 200 parts of water, 5 parts of butadiene, 2 parts of styrene, 2 parts of methyl methacrylate, 2 parts of acrylonitrile, 3 parts of acrylic acid, 1 part of fumaric acid. , T-dodecyl mercaptan 0.3 parts, sodium dodecylbenzene sulfonate 0.
5 parts and 1.5 parts of potassium peroxodisulfate were charged and reacted at 60 ° C. for 2 hours. Then butadiene 3
A monomer mixture consisting of 8 parts, 15 parts of styrene, 20 parts of methyl methacrylate, 10 parts of acrylonitrile, 2 parts of acrylic acid and 0.5 part of t-dodecyl mercaptan was placed in the polymerization system in the autoclave for 10 hours. Added continuously. During this time, the temperature in the polymerization system was kept at 65 ° C., and then the reaction was carried out at 75 ° C. for 5 hours to complete the polymerization at a polymerization conversion rate of 98%. As a result, a copolymer latex according to Example 1 was obtained.

Examples 2 to 2 were conducted in the same manner as in Example 1 except that the monomers and other substances having the compositions shown in Table 1 were used.
A copolymer latex of No. 5 was obtained. Furthermore, the Mooney viscosity (MS _{1 + 4} , 1
(00 ° C.) was measured by the method specified in the present invention, and the results are shown in Table 1.

[Table 1] Further, the copolymer for each example was used to prepare a paper coating composition having the following formulation. (Preparation of composition for paper coating) Using each of the above copolymer latexes, a composition (color) for paper coating was prepared according to the following formulation.

Clay 80 parts (containing 0.5 part of sodium pyrophosphate as a dispersant) Calcium carbonate 20 parts Copolymer latex 10 parts (solid content) Oxidized starch 5 parts Water (amount in which total solid content is 60%) Obtained The obtained color was evaluated by the following test method. The coated paper used in the test had a color of base paper of 64 g / m ^{2 with} a coating blade and a coating weight of 20 g / m 2.
It was obtained by coating with ² . (1) RI Dry Pick: Index of Adhesive Strength The degree of picking when printed with an RI printing machine was judged with the naked eye and evaluated in 5 levels. The higher the score, the better. The score is an average value of 6 times of measurement. (2) RI Wet Pick: Index of Water Resistance A Molton roll was used in an RI printing machine to visually determine the degree of picking when dampening water was applied, and was evaluated on a five-point scale. The higher the score, the better. The score was displayed as an average value of 6 times of measurement. (3) White paper gloss: Incident angle 75 ° using Murakami gloss meter
The glossiness of the coated paper was measured with. (4) Printing gloss: A web offset ink was solidly coated using an RI printer and the glossiness was measured at an incident angle of 60 ° using a Murakami gloss meter.

The results are shown in Table 2.

[Table 2] Examples 1 to 5 are examples in which a copolymer latex for paper coating within the scope of the present invention was used, and the obtained paper coating compositions have the effects of the object of the present invention. Comparative Examples 1 and 2 Copolymer latexes according to Comparative Examples 1 and 2 were obtained in the same manner as in Example 1 except that the composition was changed as shown in Table 3.

The Mooney viscosity (MS _{1 + 4} , 100 ° C.) of these copolymer latices was measured, and a paper coating composition was prepared in the same manner as in Examples to evaluate the physical properties of the coated paper. The results are shown in Tables 3 and 4.

[Table 3]

[Table 4] In Comparative Example 1, the Mooney viscosity (MS _{1 + 4} , 100 ° C.) of the solid content of the copolymer latex is less than the range of the present invention,
Poor RI dry pick (adhesive strength).

In Comparative Example 2, the Mooney viscosity (MS _{1 + 4} , 100 ° C.) of the solid content of the copolymer latex exceeds the range of the present invention, and RI dry pick (adhesive strength) and R are used.
I Inferior in wet pick (water resistance).

[0031]

EFFECT OF THE INVENTION The copolymer latex for paper coating of the present invention is not only excellent in adhesive strength, but also excellent in other physical properties of coated paper such as white paper gloss and printing gloss. as a result,
The copolymer latex for paper coating of the present invention can be suitably used for producing a coating liquid for planographic sheet-fed (sheet) offset printing.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takashi Matsui 2-11-24 Tsukiji, Chuo-ku, Tokyo Japan Synthetic Rubber Co., Ltd.

Claims (1)

[Claims] 1. (a) 10 to 60% by weight of aliphatic conjugated diene-based monomer, (b) 0.2 to 15% by weight of ethylenically unsaturated carboxylic acid monomer, (c) copolymerizable with these A copolymer latex obtained by emulsion-polymerizing a monomer consisting of 25 to 89.8% by weight of another monoolefin monomer, which has a Mooney viscosity (MS) of a solid content of the copolymer latex. _{1 + 4} , 100 ° C.) is 40 to 195, a copolymer latex for paper coating.