JPH04332701A - Production of copolymer latex and composition for coating paper using the same latex - Google Patents

Abstract

PURPOSE:To stably obtain a latex providing coated paper having high strength, bond strength and blister resistance by adding a chain transfer agent previously adjusted to an emulsion state to an aliphatic conjugated diene monomer and a copolymerizable monomer and subjecting to emulsion polymerization. CONSTITUTION:A chain transfer agent (e.g. n-hexylmercaptan) previously adjusted to an emulsion state is added to a monomer mixture of 10-80wt.% aliphatic conjugated diene monomer (e.g. 1,3butadiene), 0-10wt.% ethylenic unsaturated carboxylic acid (e.g. acrylic acid) as a monomer copolymerizable with the aliphatic conjugated diene monomer and 10-90wt.% monoolefinic monomer (e.g. styrene) and the mixture is copolymerized in the presence of an emulsifying agent (e.g. sodium dodecylbenzenesulfonate) and a radical polymerization initiator (e.g. ammonium persulfate) to give the objective copolymer latex. The copolymer latex is mixed with pigment to give a paper coating composition.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a method for producing a copolymer latex which is less likely to generate fine coagulates and has excellent polymerization stability, as well as a method for producing a copolymer latex that exhibits mechanical stability, adhesive strength, and This invention relates to a paper coating composition that has excellent blister resistance and the like.

0002

[Prior Art] So-called butadiene-based copolymer latex, which has butadiene as its main component, is used in the paper processing field and
It is well known that it is widely used as a binder in carpet backsizing and the like.

[0003] The performance required of the binder for each application is wide-ranging, and the composition and structure of the butadiene copolymer latex are generally changed accordingly.

[0004] These copolymer latexes are generally produced by emulsion polymerization, but at this time, slight differences are observed depending on the composition of the monomer mixture constituting the copolymer latex and the types and amounts of various additives. However, there is a problem in that fine coagulation occurs in the copolymer latex.

[0005] In addition, in recent years, increasing the speed of paper coating and printing has been promoted from the viewpoint of labor saving and rationalization, and there is a need for coating colors that can withstand high speed coating and coated paper that can withstand high speed printing. It is being

That is, coating colors are required to have stability against mechanical shearing as a performance during coating, and coated papers are required to have excellent adhesive strength and blister resistance.

[0007] It is known that the copolymer latex, which is one component of the coating color, has a great influence on these performances.

[0008] Fine coagulates in copolymer latex are known to be a factor that impairs the mechanical stability of coating colors, and if there are many such coagulates, streak troubles during blade coating, applicator stains, and calender processing may occur. Problems such as stains during printing and blanket piling occur during printing.

[0009] Furthermore, the adhesive strength and blister resistance of coated paper are contradictory properties, and for example, the gel content of the copolymer latex (insolubility of the latex film in solvents) has a strong influence on these properties. It is known that when a latex with a high gel content is used, the adhesive strength is excellent, whereas when a latex with a low gel content is used, the blister resistance is excellent. Therefore, it has been difficult to simultaneously improve adhesive strength and blister resistance.

0010

[Problems to be Solved by the Invention] As described above, fine coagulates in the copolymer latex cause fouling of the reactor, and
Particularly in high-speed coating, this impairs the mechanical stability of the coating color, so it is usually removed by a filtration process or the like.

[0011] However, this filtration process is also complicated, and there is a limit to the amount of fine coagulum that can be removed, so it is difficult to completely remove the fine coagulum, and productivity is inevitably reduced. was. Furthermore, coated paper is required to have adhesive strength and blister resistance that can withstand high-speed printing.

0012

[Means for Solving the Problem] As a result of intensive study on the problem, the present inventors have found that when emulsion polymerizing an aliphatic conjugated diene monomer and other monomers that can be copolymerized with the aliphatic conjugated diene monomer, By polymerizing with the addition of a chain transfer agent that has been adjusted to an emulsified state in advance, it is possible to suppress the generation of fine coagulates and efficiently obtain a copolymer latex with good polymerization stability. We have discovered that by using a polymer latex, it is possible to obtain a paper coating composition that has improved mechanical stability during paper coating, adhesive strength during printing, and blister resistance, and has arrived at the present invention.

That is, in the present invention, when emulsion polymerizing an aliphatic conjugated diene monomer and other monomers copolymerizable therewith, a chain transfer agent which has been adjusted to an emulsified state in advance is added. The present invention provides a method for producing a copolymer latex characterized by polymerization, and a paper coating composition containing the copolymer latex obtained by the method and a pigment.

The present invention will be explained in detail below.

[0015] As the aliphatic conjugated diene monomer in the present invention, 1,3-butadiene, 2-methyl-1,3-
Butadiene, 2,3-dimethyl-1,3-butadiene,
Examples include 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and one or more types can be used. Particularly preferred is 1,3-butadiene.

Other monomers copolymerizable with the aliphatic conjugated diene monomer include ethylenically unsaturated carboxylic acid monomers, alkenyl aromatic monomers, and unsaturated carboxylic acid alkyl ester monomers. Examples include unsaturated monomers containing monomers, hydroxyalkyl groups, vinyl cyanide monomers, and unsaturated carboxylic acid amide monomers.

Examples of ethylenically unsaturated carboxylic acid monomers include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl α-methylstyrene, vinyltoluene, and divinylbenzene, and one or more of them can be used. Styrene is particularly preferred.

Examples of the unsaturated carboxylic acid alkyl ester monomer include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate,
Examples include diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate, and one or more of them can be used. Particularly preferred is methyl methacrylate.

Examples of the unsaturated monomer containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl acrylate, and β-hydroxyethyl acrylate.
-Hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate,
Hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di-(ethylene glycol) maleate,
Di-(ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis(2-hydroxyethyl)
Examples include maleate and 2-hydroxyethylmethyl fumarate, and one or more types can be used. Particularly preferred is β-hydroxyethyl acrylate.

Examples of vinyl cyanide monomers include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethyl acrylonitrile, etc.
One type or two or more types can be used. Acrylonitrile is particularly preferred.

[0021] As the unsaturated carboxylic acid amide monomer,
Acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N,
Examples include N-dimethylacrylamide, and one or more types can be used. Acrylamide is particularly preferred. Each of these monomers may be used alone or in combination.

[0022] There are no restrictions on the above monomer composition, but 10 to 80% by weight of aliphatic conjugated diene monomer, 0 to 10% by weight of ethylenically unsaturated carboxylic acid monomer, and alkenyl aromatic monomer. unsaturated carboxylic acid alkyl ester, unsaturated monomer containing a hydroxyalkyl group,
10 to 90% by weight of monoolefin monomer selected from vinyl cyanide monomer and unsaturated carboxylic acid amide monomer
It is preferable that

If the content of the aliphatic conjugated diene monomer is less than 10% by weight, the adhesiveness tends to be poor, and if it exceeds 80% by weight, the water resistance tends to be poor, which is not preferable. If the content of the ethylenically unsaturated carboxylic acid monomer exceeds 10% by weight, the viscosity of the latex tends to increase, which is not preferable. If the monoolefin monomer content is less than 10% by weight, water resistance tends to be poor, and if it exceeds 90% by weight, adhesiveness tends to be poor, which is not preferable.

The chain transfer agent used in the present invention is as follows:
Alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan, xanthogen compounds such as dimethyl xanthogen disulfide, diisopropyl xanthogen disulfide, α- Methylstyrene dimer, terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide,
Thiuram compounds such as tetramethylthiuram monosulfide, phenolic compounds such as 2,6-di-t-butyl-4-methylphenol and 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, 2-ethylhexylthioglycolate, etc., and one or more types can be used. can.

[0025] In the present invention, it is necessary to adjust the chain transfer agent to an emulsified state in advance, and a general emulsification method can be used to adjust the chain transfer agent to an emulsified state. . For example, there is a method in which an aqueous emulsifier solution and a chain transfer agent are brought into an emulsified state using a homogenizer, or a method in which a mixture of an aqueous emulsifier solution and a chain transfer agent is irradiated with ultrasonic waves to be brought into an emulsified state. There are no restrictions on the type of emulsifier used to emulsify the chain transfer agent.
Emulsifiers commonly used in emulsion polymerization can be used.

[0026] The method of adding the various components in the present invention is not particularly limited, and any of a batch addition method, a divided addition method, and a continuous addition method can be employed. Furthermore, in emulsion polymerization, commonly used emulsifiers, polymerization initiators, electrolytes, polymerization promoters, chelating agents, etc. can be used.

Examples of emulsifiers include anionic surfactants such as sulfate ester salts of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, aliphatic carboxylates, sulfate ester salts of nonionic surfactants, or polyethylene glycol. Nonionic surfactants such as alkyl ester type, alkylphenyl ether type, and alkyl ether type may be used alone or in combination of two or more.

As the initiator, water-soluble initiators such as potassium persulfate, ammonium persulfate, and sodium persulfate, redox initiators, and oil-soluble initiators 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 amount of the copolymer latex of the present invention is 2 to 100 parts by weight, preferably 5 to 30 parts by weight, and the other binder is 0 to 3 parts by weight, based on 100 parts by weight of the pigment in terms of solid content.
0 parts by weight can be used.

[0031] Here, as the pigment, kaolin clay,
Talc, barium sulfate, titanium oxide, calcium carbonate,
Examples include inorganic pigments such as aluminum hydroxide, zinc oxide, and satin white, and organic pigments such as polystyrene latex, which may be used alone or in combination.

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

To prepare the paper coating composition of the present invention,
Furthermore, other auxiliary agents such as dispersants (sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate, etc.), antifoaming agents (polyglycol, fatty acid ester, phosphate ester, silicone oil, etc.), leveling agents (funnel oil, dicyandiamide, urea, etc.),
Preservatives, water resistance agents (formalin, hexamine, melamine resin, urea resin, glyoxal, etc.), mold release agents (calcium stearate, paraffin emulsion, etc.), fluorescent dyes, color water retention improvers (carboxymethylcellulose, sodium alginate, etc.) Added as needed.

The paper coating composition of the present invention can be applied to coated paper using known techniques such as air knife coater,
This is done using a coating machine such as a blade coater, roll coater, or bar coater. After application, the surface is dried and finished by calendering, etc.

Furthermore, since the copolymer latex obtained by the production method of the present invention has a small amount of fine coagulation, it can be used in other applications such as fiber processing applications such as carpets, tire cords, rock fibers, wood applications, and leather applications. It can also be suitably used as an adhesive.

[Examples] The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is exceeded. In the examples, parts and percentages are based on weight. In addition, measurements of various physical properties in Examples were based on the following methods.

- Observing fine coagulates of several μm to 50 μm using a microcoagulate microscope,
○: Very much △: Few ×: Many This is done in three stages.

・Gel content A copolymer latex film was prepared by drying at room temperature,
The film was placed in toluene of about 200 to 800 times the concentration and left for 48 hours. 2. Filter using filter paper. The filtrate is dried under reduced pressure at 70°C and weighed to determine the toluene soluble content (%) of the copolymer latex film. 10
The value obtained by subtracting the above toluene soluble content from 0%, that is,
The toluene insoluble content (%) was calculated as the gel content.

- Mechanical stability The coating color is kneaded between a metal roll and a rubber roll using patter stability, mechanical shear is applied, and the time (minutes) until a coagulum appears on the rubber roll is measured.

- RI Dry Pick Strength The degree of picking when printed with an RI printing machine without using dampening water is judged visually, and is ranked from grade 1 (best) to grade 5.
Evaluation was made on a five-point scale (worst).

- Blister resistance Double-sided printed coated paper was placed in a heated oil bath after adjusting the humidity to about 6%, and the lowest temperature at which blisters occurred was measured.

<Preparation of copolymer latex> Ten types of latex shown in Table 1 were prepared. Copolymer latexes 1 to 7 are examples, and copolymer latexes 8 to 10 are comparative examples.

For Examples 1 to 7, 0.2 parts of sodium dodecylbenzenesulfonate, 3 parts of water, and the chain transfer agent shown in Table 1 were emulsified using a homogenizer.

Furthermore, in an autoclave, add the monomers shown in Table 1 and sodium dodecylbenzenesulfonate 0
．． 3 parts of sodium bicarbonate, 0.5 parts of ammonium persulfate, 100 parts of water, and an emulsion of the above chain transfer agent were charged and polymerized at 65° C. with stirring.

For Comparative Examples 8 to 10, add the monomers shown in Table 1, 0.5 parts of sodium dodecylbenzenesulfonate, and 0.5 parts of sodium bicarbonate to a 10 liter autoclave.
1 part, 0.9 parts of ammonium persulfate, 100 parts of water, and an unemulsified chain transfer agent, and polymerization was carried out at 65° C. with stirring.

The polymerization conversion rates of the obtained latexes were all 97% or higher. After adjusting the pH of these latexes to 6.0 with ammonia, unreacted monomers were removed by steam distillation to obtain copolymer latexes 1 to 10.

The fine coagulum and gel content of the copolymer latexes 1 to 10 obtained were measured. The results are shown in Table-1.

<Preparation of Paper Coating Composition> Using the above copolymer latexes 1 to 10, paper coating compositions were prepared according to the following formulation, and their mechanical stability was measured. Also,
Coated on commercially available high-quality paper at a density of 10 g/m2 on one side,
A coated paper was obtained.

The RI dry pick strength and blister resistance of the obtained coated paper were measured. The results are shown in Table-1.

(Prescription) Kaolin clay 80
Part calcium carbonate 2
Part 0 modified starch
8-part copolymer latex
12 parts (solid content)

[0051]

[Table 1]

Claims (2)

[Claims] [Claim 1] When emulsion polymerizing an aliphatic conjugated diene monomer and other monomers copolymerizable with it, it is possible to add a chain transfer agent that has been prepared in advance to an emulsified state. A method for producing characteristic copolymer latex. 2. A paper coating composition comprising a copolymer latex obtained by the production method according to claim 1 and a pigment.