JP3116597B2 - Copolymer latex for paper coating - Google Patents

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 particularly, to a paper coating having particularly excellent blister resistance and other coated paper properties such as dry pick strength and print gloss. It relates to a copolymer latex for industrial use.

[0002]

2. Description of the Related Art In recent years, a large amount of pigment coated paper has been used for publication or packaging. Most of the coated paper printing is performed by offset rotary printing, and the trend of high-speed printing is increasing in order to increase demand or reduce production cost, and therefore, the demand for coated paper capable of high-speed printing is increasing. ing.

In order to perform high-speed printing by the offset rotary printing, high-temperature and high-speed drying is required, so that so-called "blisters" are apt to occur, and when the blisters occur, the commercial value of the printed matter is significantly impaired. Will be. Therefore, among the quality of coated paper, improvement of blister resistance has been strongly demanded.

As a method of improving blister resistance,
There are known methods for lowering the toluene-insoluble content of paper coating latex and increasing the particle diameter to improve air permeability.

[0005] However, in this case, the dry pick strength and the print gloss are reduced, and it is difficult to improve the blister resistance without sacrificing the physical properties of the coated paper.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has particularly good blister resistance, and has a reciprocal relationship with the blister resistance. An object of the present invention is to provide a copolymer latex for paper coating which is excellent in other coated paper properties such as dry pick strength and print gloss.

[0007]

That is, the present invention provides:
(A) 10 to 50% by weight of an aliphatic conjugated diene monomer,
(B) ethylenically unsaturated carboxylic acid monomer 0.2 to 15
And a copolymer latex obtained by emulsion polymerization of 45 to 89.8% by weight of another monoolefin monomer copolymerizable therewith, the solid content of the copolymer latex being methanol. The soluble component is 5 to 40% by weight, the tetrahydrofuran (THF) soluble component is in the range of 80% by weight or more, and the weight average molecular weight of the THF soluble component copolymer is 80,000 or more. The present invention provides a copolymer latex for paper coating.

Hereinafter, the present invention will be described in detail.

As the aliphatic conjugated diene monomer (hereinafter referred to as "component (a)") used in the present invention, for example, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3 -Dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted straight-chain conjugated pentadienes, straight-chain and side-chain conjugated hexadienes, and the like. The component (a) is necessary for imparting appropriate elasticity to the copolymer and appropriate softness to the obtained coating film. The amount of the component (a) is 10 to 50% by weight, preferably 15 to 50% by weight of the whole monomer. 40% by weight, more preferably 20-43
% By weight. If the amount of the component (a) is less than 10% by weight, the obtained copolymer is hard and brittle, while if it exceeds 50% by weight, the obtained copolymer becomes too soft and has poor water resistance.

The ethylenically unsaturated carboxylic acid monomer (hereinafter referred to as “component (b)”) used in the present invention includes:
For example, mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid can be mentioned. Also, dicarboxylic anhydrides can be used. Component (b) is used in an amount of 0.2 to 15% by weight, preferably 0.5 to 13% by weight, and more preferably 1 to 10% by weight, based on the whole monomer. When the amount of the component (b) is less than 0.2% by weight, the adhesive strength and mechanical stability of the obtained copolymer decrease, while when it exceeds 15% by weight, the viscosity of the copolymer latex becomes too high. Handling becomes difficult.

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

The amount of component (c) used is 45 to 45
It is 89.8% by weight, preferably 54.5 to 72% by weight, more preferably 47 to 79% by weight. When the amount of the component (c) is less than 45% by weight, the water-resistant adhesive strength is inferior. On the other hand, when the amount exceeds 89.8% by weight, the adhesive strength is inferior.

The copolymer latex of the present invention is obtained by emulsion-polymerizing the monomers of the components (a), (b) and (c), and has a solid content of the following: It has the condition of. Methanol soluble content is 5 to 40% by weight. The THF-soluble component is 80% by weight or more, and the weight-average molecular weight of the THF-soluble component copolymer is 80,000 or more.

The methanol-soluble content of the solid content of the latex means that the solid content of the copolymer latex is adjusted to 10% by weight, a cation exchange resin is added to the latex, and ion exchange is performed. The whole amount is weighed accurately, absorbed in a filter paper and dried. The filter paper is cut finely, extracted twice with 100 ml of methanol, and the extracts are combined and evaporated to obtain the amount of the residue. This is the value calculated for the methanol-soluble matter.

The methanol-soluble component is 5 to 40% by weight, preferably 5 to 30% by weight, and more preferably 8 to 20% by weight, based on the solid content of the copolymer latex. When the methanol-soluble content is less than 5% by weight, when the copolymer latex is used as a paper coating composition, the blister resistance decreases, whereas when it exceeds 40% by weight, the strength of the coating layer decreases. I do.

The THF-soluble matter is measured as follows. A cation exchange resin was added to about 0.3 g of the copolymer latex adjusted to a solid content of 50% by weight, ion exchange was performed, 50 ml of THF was added, and the mixture was allowed to stand for 1 hour.

Next, No. This is a value obtained by filtering using a qualitative filter paper, evaporating the filtrate to dryness, determining the amount of residue, and calculating the THF-soluble content based on the total solid content.

The soluble matter in THF is at least 80% by weight, preferably at least 90% by weight, more preferably at least 95% by weight of the solid content of the copolymer latex. If the THF-soluble component is less than 80% by weight, the blister resistance deteriorates.

The weight-average molecular weight of the copolymer soluble in THF is 80,000 or more, preferably 90,000 to 1,000.
200,000. This weight average molecular weight is 80,0
If it is less than 00, the adhesive strength of the obtained copolymer is inferior.

The weight average molecular weight is a value determined by gel permeation chromatography in terms of polystyrene.

Generally, in order to increase the amount of methanol-soluble components, there is a method in which the amounts and types of an emulsifier, a molecular weight regulator, a monomer composition, an initiator and the like are appropriately selected.

The molecular weight is also controlled by a polymerization formulation such as the amount and type of a molecular weight regulator and an initiator.

In general, the conditions for increasing the methanol-soluble content and the conditions for increasing the molecular weight of the THF-soluble component are opposite to each other. Therefore, it is technically very difficult to polymerize the latex to satisfy the above conditions by appropriately combining an initiator, a molecular weight modifier and other polymerization conditions. If a latex satisfying the conditions of the present invention can be synthesized, the reciprocal properties of adhesive strength and blister resistance can be improved in a well-balanced manner.

In the present invention, the toluene insoluble content of the copolymer latex is desirably 3 to 60% by weight. If the toluene-insoluble content is less than 3% by weight, the strength and printing gloss of the obtained coating layer become insufficient, while if it exceeds 60% by weight, the strength and water resistance of the coating layer tend to decrease. The toluene-insoluble content was measured as follows.

The pH of the copolymer latex sample was adjusted to 8.0, and the copolymer in the latex was coagulated with isopropanol, and the obtained solid was washed and dried. About 0.3 g of this solid content (total solid content A) was added to 100 ml of toluene.
After being immersed at room temperature for 20 hours, The mixture was filtered using a bi-qualitative filter paper. A part of the filtrate (Cml) is accurately collected,
Evaporate to dryness and obtain residual solids (toluene solubles)
(Toluene soluble content B) was weighed, and the toluene insoluble content was determined by the following equation.

{(AB × (100 / C)) / A} × 100 (%) The chain transfer agent used in the present invention is a conventionally known one such as t-dodecyl mercaptan, carbon tetrachloride, octyl mercaptan. , N-dodecyl mercaptan, n-tetradecyl mercaptan, t-tetradecyl mercaptan, n
-Hexadecyl mercaptan, t-hexadecyl mercaptan, tetraethylthiuram sulfide, methylene chloride, ethylene bromide, dipentamethylenethiuram hexasulfide, diisopropylpropyl xanthogen disulfide,
A molecular regulator generally used for controlling a molecular weight in an emulsion polymerization reaction such as α-methylstyrene dimer can be used. Also, a combination of two or more of these can be used.

Examples of the emulsifier include anionic surfactants such as sulfates of higher alcohols, alkylbenzenesulfonates and aliphatic sulfonates, and alkyl ester, alkyl phenyl ether and alkyl ether types of polyethylene glycol. Such nonionic surfactants can be used alone or in combination of two or more.

[0028] The polymerization initiator is a compound which undergoes radical decomposition in the presence of heat or a reducing substance to cause addition polymerization of the monomer. The polymerization initiator is water-soluble or oil-soluble peroxodisulfate, peroxide, azobis. Compounds, such as potassium peroxodisulfate, sodium peroxodisulfate,
Examples include ammonium perdisulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, 2,2-azobisisobutyronitrile, cumene hydroperoxide and the like. In the present invention, it is preferable to use at least one water-soluble initiator, whereby the stability of the polymer latex can be increased. Of these, peroxodisulfate is most preferably used. Two or more polymerization initiators may be used, and an oil-soluble initiator may be used in combination. The usage ratio of the polymerization initiator is usually 0.2 to 1.5% by weight based on the monomer. The polymerization temperature is generally in the range of 50 to 90 ° C., but if it is desired to accelerate the polymerization rate or to carry out the polymerization at a lower temperature, sodium bisulfite, ascorbic acid or its salt, ersorbic acid or its salt, Rongalit sulfate 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, known chelating agents, inorganic salts and the like are also used as emulsion polymerization.

The copolymerization method may be, for example, a method in which the monomer mixture is charged at once, or a part of the monomer mixture is polymerized, and then the remaining portion is added intermittently or continuously as the polymerization proceeds. Further, a method in which the monomer mixture is continuously added from the beginning of the polymerization may be employed.

The paper coating composition using the copolymer latex of the present invention comprises an inorganic pigment or an organic pigment, preferably an inorganic pigment, and the above copolymer latex, and if necessary, other binders. It is prepared by The amount of the copolymer latex to be added is preferably 5 to 30 parts by weight, more preferably 5 to 20 parts by weight, based on 100 parts by weight of the pigment in terms of solid content, and other bonds added as necessary. 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.

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

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

Further, various auxiliaries generally used in the paper coating composition, for example, dispersants (sodium pyrophosphate, sodium hexametaphosphate), defoamers (polyglycol, fatty acid ester, phosphorus Acid esters,
Silicone oil, etc.), leveling agents (funnel oil, dicyandiamide, urea, etc.), preservatives, waterproofing agents (formalin, hexamine, melamine resin, urea resin glyoxal, etc.), mold release agents (calcium stearate, paraffin emulsion, etc.), fluorescent A light dye, a color water retention improver (carboxymethyl cellulose, sodium alginate, etc.) and the like can be added as required.

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

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

[0037]

EXAMPLES Hereinafter, the present invention will be described more specifically 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 6) [Production of copolymer latex] In an autoclave equipped with a stirrer, 150 parts of water, 2 parts of butadiene, 3 parts of styrene, 2 parts of methyl methacrylate, 1 part of acrylonitrile, 3 parts of itaconic acid, acrylic acid 1 part, t-dodecyl mercaptan 0.3 part, sodium dodecylbenzenesulfonate 0.1 part.
15 parts and 1.0 part of potassium persulfate
For 1 hour. Next, a monomer mixture comprising 28 parts of butadiene, 32 parts of styrene, 23 parts of methyl methacrylate, 5 parts of acrylonitrile, and 1 part of t-dodecyl mercaptan was continuously added to the polymerization system in the autoclave over 10 hours. . During this time, the temperature in the polymerization system was 6
The temperature was kept at 5 ° C., and the reaction was carried out at 70 ° C. for 6 hours to complete the polymerization at a polymerization conversion of 98%. As a result, a copolymer latex according to Example 1 was obtained.

[Table 1] Five kinds of copolymer latexes according to the examples were obtained in the same manner as in the example 1 except that the monomers having the compositions shown in Table 1 and other substances were used. Further, the methanol-soluble content, the THF-soluble content and the weight average molecular weight of each of these copolymer latexes were measured by the method defined in the present invention,
The results are shown in Table 2.

[Table 2] Using the copolymer latex according to each example, a paper coating composition was prepared according to the following formulation. [Preparation of Paper Coating Composition] A paper coating composition (color) was prepared using the above copolymer latexes according to the following formulation.

80 parts of clay (containing 0.5 parts of sodium pyrophosphate as a dispersant) 20 parts of calcium carbonate 10 parts of a copolymer latex (solid content) 5 parts of oxidized starch 5 parts of water (a total solid content of 60%) is obtained The obtained color was evaluated by the following test method. The coated paper used in the test was coated on a base paper having a basis weight of 64 g / m ² using a coating blade, and a coating amount of 20 g / m ² was used.
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 visually judged, and evaluated on a scale of 1 to 5. The higher the score, the better. The score was indicated by an average value of six measurements. (2) RI Wet Pick: Index of Hydrophobicity The degree of picking when dampening water was applied was visually determined using a Molton roll in an RI printing machine, and evaluated on a five-point scale. The higher the score, the better. The score was indicated by an average value of six measurements. (3) Printing gloss: The ink for web offset was solid-coated using an RI printing machine and measured using a Murakami gloss meter (incident angle: 60 °). (4) Blister resistance: Humidity control (approximately 6
%), And then thrown into a heated oil bath to indicate the lowest temperature at which blisters occur.

The results are shown in Table 2. (Comparative Examples 1 to 4) Four kinds of copolymer latexes according to Comparative Examples were obtained in the same manner as in Example except that the composition was changed as shown in Table 3.

[Table 3] The methanol-soluble content of these copolymer latexes, TH
The F-soluble matter and its weight average molecular weight were measured by the method specified in the present invention, and a paper coating composition was prepared in the same manner as in the examples, and the coated paper properties were evaluated. Table 4 shows the results.

[Table 4] In Comparative Example 1, the methanol-soluble content of the copolymer latex was less than the range of the present invention, and the blister resistance was poor.

In Comparative Example 2, the methanol-soluble content of the copolymer latex exceeded the range of the present invention, and was inferior in RI dry pick (adhesive strength) and RI wet pick (water resistance strength). Comparative Example 3 is a copolymer latex THF
The soluble content is less than the range of the present invention, and the blister resistance is poor.

Comparative Example 4 is a copolymer latex of THF
The weight average molecular weight of the soluble component is less than the range of the present invention, and the adhesive strength and the water resistance are poor.

[0042]

The copolymer latex for paper coating of the present invention is not only particularly excellent in blister resistance, but also excellent in other coated paper properties such as adhesive strength and print gloss. As a result, the copolymer latex for paper coating of the present invention can be suitably used for production of coated paper, especially coated paper for offset rotary printing.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takashi Matsui 2--11-24 Tsukiji, Chuo-ku, Tokyo Japan Synthetic Rubber Co., Ltd. (56) References JP-A-50-107030 (JP, A) JP-A-2-250495 (JP, A) JP-A-62-231097 (JP, A) JP-A-62-231096 (JP, A) JP-A-58-32649 (JP, A) JP-A-2-70714 (JP, A) A) (58) Field surveyed (Int. Cl. ⁷ , DB name) D21H 19/58

Claims (1)

(57) [Claims] 1. (a) 10 to 50% by weight of an aliphatic conjugated diene monomer, (b) 0.2 to 15% by weight of an ethylenically unsaturated carboxylic acid monomer, (c) Copolymerizable therewith. A copolymer latex obtained by emulsion-polymerizing a monomer consisting of 45 to 89.8% by weight of a monomer soluble in methanol and a solid soluble in methanol of the copolymer latex. Is 5 to 40% by weight, and the tetrahydrofuran-soluble content of the solid is 80% by weight or more, and
A copolymer latex for paper coating, wherein the weight average molecular weight of the copolymer soluble in tetrahydrofuran is 80,000 or more.