JP2961206B2 - Composition 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 paper coating composition, and more particularly, to a paper coating composition having excellent mechanical stability and providing a coated paper having good printability.

[0002]

2. Description of the Related Art Problems Solved by the Prior Art and the Invention
A carboxy-modified butadiene-based copolymer latex is used alone or together with a water-soluble polymer such as casein, starch, or polyvinyl alcohol as a paper coating binder.

However, there has been a remarkable recent increase in the speed of coating and printing, and a paper coating composition containing a binder for paper coating is required to be able to withstand these speed increases.

[0004] That is, in coating, a paper coating composition having excellent mechanical stability is required in order to maintain stability during operation, and in high-speed printing, the adhesive strength and the anti-strength property are required. Good blister properties and the like are required.

[0005] In particular, it is known that the adhesive strength and the blister resistance are in conflict with each other, and for example, the gel content of the latex (the insolubility of the latex film in the solvent) has a strong influence on these properties. Have been.

That is, when a latex having a high gel content is used, the adhesive strength is excellent, and when a latex having a low gel content is used, the blister resistance is good.

[0007] Therefore, it is difficult to simultaneously improve the adhesive strength and the blister resistance, and in addition, a paper coating composition having excellent mechanical stability has been demanded.

[0008]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that a copolymer obtained by emulsion-copolymerizing a monomer mixture having a specific composition in the presence of a polyphosphate. By using a polymer latex, it has been found that a paper coating composition having excellent mechanical stability and excellent adhesive strength and blister resistance can be obtained, and the present invention has been achieved.

That is, the present invention relates to an aliphatic conjugated diene monomer of 20 to 60% by weight, an ethylenically unsaturated carboxylic acid monomer of 0.5 to 5% by weight, and an ethylenically unsaturated carboxylic acid alkyl ester monomer. A monomer mixture consisting of 3 to 30% by weight, 0.5 to 5% by weight of an ethylenically unsaturated carboxylic acid amide monomer and 0 to 76% by weight of another copolymerizable monomer is added to the presence of a polyphosphate. The present invention provides a paper coating composition characterized by mainly containing a pigment and a copolymer latex obtained by emulsion copolymerization below.

Hereinafter, the present invention will be described in detail.

The aliphatic conjugated diene monomer used in the present invention includes 1,3-butadiene and 2-methyl-
Examples thereof include 1,3-butadiene and 2-chloro-1,3-butadiene, and one or more kinds can be used. In particular, 1,3-butadiene is preferred.

[0012] The aliphatic conjugated diene monomer is preferably from 20 to 60.
When the amount is less than 20% by weight, the dry pick strength decreases, and when the amount exceeds 60% by weight, the wet pick strength decreases.

The ethylenically unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, glycidyl methacrylate, dimethyl fumarate, dimethyl maleate, diethyl Maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate and the like can be mentioned, and one or more kinds can be used. Particularly, methyl methacrylate is preferred.

The unsaturated carboxylic acid alkyl ester-based monomer is used in the range of 3 to 30% by weight.
If it is less than 30%, the dry pick strength decreases and the weight is 30% by weight.
Exceeding the range is not preferred because the wet pick strength decreases.

The ethylenically unsaturated carboxylic acid monomer used in the present invention includes acrylic acid, methacrylic acid,
Examples thereof include fumaric acid, maleic acid, and itaconic acid, and one or more of these can be used. The ethylenically unsaturated carboxylic acid monomer is used in the range of 0.5 to 5% by weight, but if the amount is less than 0.5% by weight, the dry pick strength and the mechanical stability of the latex decrease, and Exceeding the weight percent is not preferred because the viscosity of the latex becomes too high.

The ethylenically unsaturated carboxylic amide monomers used in the present invention include acrylamide, methacrylamide, N-methylolacrylamide, N-
Methylol methacrylamide, N, N-dimethylacrylamide and the like can be mentioned, and one or more of these can be used. Acrylamide is particularly preferred.

The ethylenically unsaturated carboxylic acid amide monomer is used in the range of 0.5 to 5% by weight, but if the amount is less than 0.5% by weight, the dry pick strength and the mechanical stability of the latex are deteriorated. If it is lowered and exceeds 5% by weight, the viscosity of the latex becomes too high, which is not preferred.

Other copolymerizable monomers used in the present invention include alkenyl aromatic monomers, unsaturated monomers containing a hydroxyalkyl group, vinyl cyanide monomers and the like. .

Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl-α-methylstyrene, vinyltoluene, etc., with styrene being particularly preferred.

Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate and β-hydroxyethyl acrylate.
-Hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl methacrylate, 3
-Chloro-2-hydroxybutyl methacrylate, di-
(Ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis- (2-hydroxyethyl) maleate, 2
-Hydroxyethyl fumarate and the like.

Examples of the vinyl cyanide monomer include acrylonitrile, α-chloroacrylonitrile, methacrylonitrile, α-ethylacrylonitrile and the like.

These other copolymerizable monomers can be used alone or in combination of two or more.

The other copolymerizable monomer is 0 to 7
It is used in the range of 6% by weight. However, if the amount exceeds 76% by weight, the dry pick strength is undesirably reduced.

The polyphosphate used in the present invention includes pyrophosphate, tripolyphosphate, tetrapolyphosphate,
Examples thereof include sodium salts, potassium salts and ammonium salts of metaphosphoric acid and the like, and these can be used alone or in combination of two or more.

These polyphosphates are preferably used in the range of 0.05 to 2 parts by weight based on 100 parts by weight of the monomer mixture from the viewpoint of water resistance. From the viewpoint of stability during polymerization, it is preferable to add the copolymer latex at a conversion of 30% or less.

The method of adding the various components in the present invention is not particularly limited, and any of a batch addition method, a split addition method, and a continuous addition method can be employed. Further, in the emulsion polymerization, commonly used emulsifiers, chain transfer agents, polymerization initiators, electrolytes, polymerization accelerators, chelating agents and the like can be used.

Examples of the emulsifier include anionic surfactants such as sulfates of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, aliphatic carboxylates, sulfates of nonionic surfactants, and polyethylene glycol. Nonionic surfactants such as alkyl ester type, alkyl phenyl ether type and alkyl ether type are used alone or in combination of two or more.

The chain transfer agent used in the present invention includes:
alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan, dimethyl xanthogen disulfide, diethyl xanthogen disulfide, diisopropyl xanthogen disulfide and the like Xanthogen compounds, α-methylstyrene dimer, terpinolene, thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide, 2,
6-di-t-butyl-4-methylphenol, phenolic compounds such as styrenated phenol, allyl compounds such as allyl alcohol, dichloromethane, dibromomethane, carbon tetrachloride, halogenated hydrocarbon compounds such as carbon tetrabromide, Triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid,
-Ethylhexylthioglycolate and the like, and one or more kinds can be used.

As the initiator, a water-soluble initiator such as potassium persulfate, ammonium persulfate, and sodium persulfate, a redox-based initiator, or an oil-soluble initiator such as benzoyl peroxide can be used.

The paper coating composition of the present invention is prepared as an aqueous dispersion of the copolymer latex, together with a pigment and, if necessary, other binders.

At this time, the copolymer latex of the present invention is 2 to 100 parts by weight, preferably 5 to 30 parts by weight, and other binders are 0 to 100 parts by weight of solids in terms of solid content.
30 parts by weight can be used.

Here, as the pigment, kaolin clay,
Talc, barium sulfate, titanium oxide, calcium carbonate,
Examples thereof include inorganic pigments such as aluminum hydroxide, zinc oxide and satin white, and organic pigments such as polystyrene latex, and these are used alone or in combination.

Other binders include modified starches such as starch, oxidized starch and esterified starch, natural binders such as soybean protein and casein, and synthetic latexes such as polyvinyl alcohol, polyvinyl acetate latex and acrylic latex. Is used.

In preparing the paper coating composition of the present invention, other auxiliaries such as dispersants (sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate) and defoamers (polyglycol, Fatty acid esters, phosphate esters, silicone oils, 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 dyes, color water retention A performance improver (carboxymethylcellulose, sodium alginate, etc.) is added as necessary.

[0035]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to the examples. The percentages and parts used in the examples all mean% by weight and parts by weight unless otherwise specified.

Example 1 (Production method of copolymer latex) In a 10 l autoclave, the composition of the number of parts shown in Table 1 and potassium persulfate were added.
0.8 part was charged and emulsion polymerization was carried out at 65 ° C. while stirring. The polymerization conversion of each of the obtained copolymer latexes was 97% or more. Next, after adjusting the pH of the copolymer latex to 7 with an aqueous sodium hydroxide solution, unreacted monomers were removed by steam distillation.
~ L was obtained. Table 1 shows the gel content and particle size of the obtained copolymer latex.

In addition to the results shown in Table 2, all of Example-1
The same operation as described above was performed to obtain copolymer latexes a to h. Here, a to h are copolymer latexes for comparison.

(Method of Measuring Gel Content in Copolymer Latex) a) A film of the copolymer latex is prepared by drying at room temperature, and the film is put in about 200 to 800 times toluene and left for 48 hours. No. 2 Filter using filter paper. b) The filtrate is dried under reduced pressure at 70 ° C., weighed, and the toluene liquid content (%) of the copolymer latex film is determined. c) A value obtained by subtracting the toluene-soluble component (%) from 100%, that is, the toluene-insoluble component (%) is calculated as the gel content.

(Method for Measuring Particle Size of Copolymer Latex)
It was measured from an electron micrograph.

Example 2 (Adjustment and Performance Evaluation of Composition for Paper Coating) Using the copolymer latexes A to L and a to h obtained in Example 1,
Create a paper coating composition based on each of the following prescription,
The mechanical stability was tested. Further, each composition was applied to base paper to prepare coated papers (1) to (20). After calendering the obtained coated paper, tests for RI wet pick strength, RI dry pick strength, and blister resistance were performed. The results are shown in Table-3.

(Prescription) Kaolin clay 70 parts Calcium carbonate 30 parts Modified starch 4 parts Copolymer latex 12 parts (solid content)

(Measurement method) Mechanical stability The solid content of the paper coating composition was adjusted to 40%, filtered through a 200-mesh wire gauze, and measured with a Maron stability tester using 50 g (measurement conditions). 1000 rpm, 10 kg / cm ² , 10
Minutes). After completion of the measurement, the amount of solidified matter remaining on the 200 mesh wire net was measured, and the weight% based on the solid content was determined.

RI wet pick strength The degree of picking when printing with a fountain solution by an RI printing machine is visually judged, and the degree of picking is determined from the first grade (best) to the fifth grade (worst). It was evaluated by the grade method. The average value of 6 times is shown.

RI dry pick strength Evaluation was made in the same manner as in the above-mentioned RI wet pick strength measuring method except that no fountain solution was used.

Blister resistance The humidity of a double-sided printing coated paper is adjusted to about 6%, and then, the paper is put into a heated oil bath to indicate a minimum temperature at which blisters are generated.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

As described above, the paper coating composition of the present invention has excellent mechanical stability, and the coated paper obtained by using the composition has wet topic strength, dry pick strength and Various performances such as blister resistance have been comprehensively improved.

Claims (1)

(57) [Claims] 1. An aliphatic conjugated diene monomer 20 to 60% by weight, an ethylenically unsaturated carboxylic acid monomer 0.5 to 5% by weight, and an ethylenically unsaturated carboxylic acid alkyl ester monomer 3 to 30% by weight. %, 0.5 to 5% by weight of an ethylenically unsaturated carboxylic acid amide monomer and 0 to 76% by weight of another copolymerizable monomer in the presence of a polyphosphate. A paper coating composition mainly comprising a copolymer latex and a pigment obtained by copolymerization.