JPS6138921B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a copolymer latex which provides coated paper with good ink gloss. Specifically, (a) 10 to 20% by weight of an ethylenically unsaturated carboxylic acid monomer, a monomer containing a hydroxyalkyl group.
10-20% by weight and vinyl cyanide monomer 60
Emulsion polymerization of 2 to 30 parts by weight of a monomer mixture consisting of ~80% by weight, (b) 30 to 70% by weight of aliphatic conjugated diene monomer, alkenyl aromatic in the presence of the obtained copolymer latex; 70 to 98 parts by weight of a monomer mixture consisting of 20 to 70% by weight of group monomers, 5 to 40% by weight of unsaturated carboxylic acid alkyl ester monomers, and 0 to 15% by weight of vinyl cyanide monomers. Provided is a method for producing a copolymer latex, which comprises adding and polymerizing a copolymer latex. BACKGROUND ART In recent years, with the rapid increase in the number of printed materials, the printing speed has increased, and printing technology has rapidly developed, with ink drying faster and at higher temperatures. Along with this, the performance requirements for coated paper have naturally become stricter, and adhesive strength and strength sufficient to withstand high-speed printing have become stricter.
Water resistance, etc. is required. In particular, there has been a demand for higher printing speeds and improved blister resistance of coated paper, and improvements have been made from the base paper surface and coating. There are various ways to improve blister resistance, such as lowering the moisture content of coated paper, making the coated layer more porous, or strengthening the internal bonding strength of paper fibers. If the water content of the coated paper is reduced, it becomes difficult to wind up the off-wheel paper. Furthermore, there is a limit to the strength of the internal bonding of paper fibers. From the above viewpoint, the best way to improve blister resistance is to make the coating layer porous. Porous coating layers can also be made by changing the pigment composition (for example, using large amounts of coarse pigments, spherical pigments, etc.) in the paper coating paint. Furthermore, as a method for improving copolymer latexes, a method has been proposed in which the gel content of the copolymer is reduced to improve the blister resistance. However, although the above-mentioned improvement method certainly improves blister resistance, it deteriorates printing suitability other than blister resistance (for example, ink gloss, water resistance, adhesion, etc.). In conventional methods, improving one will reduce the other, so it is necessary to first improve the performance that is most required for the printing (such as blister resistance) and tolerate the decline in other properties to some extent. I needed to. The present inventors have found a method for improving the above-mentioned blister resistance, ink gloss, water resistance, and adhesiveness in a well-balanced manner, and have completed the present invention. The copolymer latex produced according to the present invention has excellent stability when preparing paints for coated paper, that is, excellent pigment miscibility and chemical stability when mixed with various pigments including polyvalent cations. It also has excellent stability against mechanical shearing on a coating machine, so it can exhibit revolutionary performance as a pigment binder. Among the monomer mixtures used in the production of the synthetic copolymer latex of the present invention, the ethylenically unsaturated carboxylic acid monomers polymerized in the first stage include acrylic acid, methacrylic acid, maleic acid, and fumaric acid. , anhydrides or monoalkyl esters of itaconic acid and dicarboxylic acids, and these may be used alone or in combination of two or more. These ethylenically unsaturated carboxylic acid monomers improve the adhesion of the polymer through copolymerization and also improve the mechanical stability of the latex produced. These ethylenically unsaturated carboxylic acid monomers are preferably used in an amount of 10 to 20% by weight of the total monomers from the viewpoint of adhesion and mechanical stability. If it is less than 10% by weight, the adhesive strength and mechanical stability of the copolymer latex will decrease, and if it exceeds 20% by weight, the viscosity of the copolymer latex will become too high and the water resistance of the coated paper will also decrease. Undesirable. Examples of the unsaturated monomer containing a hydroxyalkyl group include β-hydroxyethyl acrylate,
β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate,
Hydroxybutyl methacrylate, 3-chloro-
Examples include 2-hydroxybutyl methacrylate, di-(ethylene glycol) maleate, di-(ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis(2-hydroxyethyl) maleate, and 2-hydroxyethylmethyl fumarate. Used alone or in combination of two or more. Among the monomers used in the first stage polymerization, the number of unsaturated monomers containing hydroxyalkyl groups is 10
Used at ~20% by weight. If it is less than 10% by weight, the stability of the final copolymer latex will be poor, and if it exceeds 20% by weight, the water resistance of the coated paper will be poor. The vinyl cyanide monomer polymerized in the first stage includes one or more aliphatic unsaturated nitriles such as acrylonitrile, α-chloroacrylonitrile, methacrylonitrile, and α-ethyl acrylonitrile. It is used in
An effective ink gloss can be obtained using these nitriles in a range of 60 to 80% by weight. The monomer mixture polymerized in the first stage above includes all the monomers used in the first and second stage polymerizations.
2 to 30 parts by weight are used as 100 parts by weight. If it is less than 2 parts by weight, a stable copolymer latex cannot be obtained, and if it exceeds 30 parts by weight, the water resistance of coated paper using the obtained copolymer latex will decrease. The aliphatic conjugated diolefin monomers polymerized in the second stage include 1.3-butadiene, 2-methyl-1.3-butadiene, 2.3-dimethyl-1.3-butadiene, 2-neopentyl-1.3-butadiene,
2-chloro-1.3-butadiene, 2-cyano-1.3
-butadiene, substituted linear conjugated pentadienes, conjugated hexadiene with linear and side chains, and the like. These monomers are used in amounts of 30 to 70% by weight, but adhesive strength is poor at less than 30% by weight;
Exceeding this will reduce water resistance. Examples of the alkenyl aromatic monomer used in the second stage include styrene, alphamethylstyrene, methylalphamethylstyrene, and vinyltoluene. These monomers are used in amounts of 20 to 70% by weight, but if less than 20% by weight, water resistance decreases.
If it exceeds 70% by weight, the adhesive strength will decrease. The unsaturated carboxylic acid alkyl ester monomers used in the second stage include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate,
Dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and the like. These monomers are used in an amount of 5 to 40% by weight, but if the amount is less than 5% by weight, the stability of the latex will be poor. Moreover, if it exceeds 40% by weight, adhesive strength and water resistance will decrease. The vinyl cyanide monomer used in the second stage is selected from the same group as the monomer used in the first stage, but is used in an amount of 15% by weight or less. If it exceeds 15% by weight, water resistance and blister resistance will deteriorate. The monomers used in the second stage described above may be used alone or in combination of two or more. The monomer mixture to be polymerized in the second stage is used in an amount of 70 to 98 parts by weight based on 100 parts by weight of the total monomers used in the first and second stage polymerizations. If it is less than 70 parts by weight, the water resistance of coated paper using the obtained copolymer latex will be poor, and if it exceeds 98 parts by weight, a stable copolymer latex cannot be obtained. When starting the second stage emulsion copolymerization, if the first stage reaction has completely completed, that is, if the polymerizable radicals have completely disappeared, it is necessary to add a reaction initiator, etc. Therefore, it is necessary to start a new reaction. There is no particular restriction on the method of adding the various components in the first stage emulsion copolymerization, and any of a batch addition method, a divided addition method, and a continuous addition method may be used. As in the case of the first stage, the method of adding the monomer in the second stage of emulsion adhesion is not particularly limited, and may be any one of a batch addition method, a divided addition method, and a continuous addition method. Further, it is preferable that the conversion of the monomers polymerized in the first stage is 70% or more, and if it is less than 70%, the water resistance and adhesive properties will be poorer than if it is 70% or more. Examples of emulsifiers include anionic surfactants such as higher alcohol sulfate esters, alkynebenzene sulfonates, and aliphatic sulfonates, and nonionic surfactants such as polyethylene glycol alkyl esters, alkyl phenyl ethers, and alkyl ethers. One or more types of agents are used. When considering the water resistance of the obtained copolymer latex, it is preferable to use 2 parts by weight or less per 100 parts by weight of the monomer. Examples of initiators include water-soluble initiators such as potassium persulfate, ammonium persulfate, and sodium persulfate;
Alternatively, a redox initiator or an oil-soluble initiator such as benzoyl peroxide is used. As the chain transfer agent, mercaptans, halogenated hydrocarbons, etc. can be used. Examples are shown below, but the present invention is not limited in any way by the examples. Note that all parts and % in the examples mean parts by weight and % by weight unless otherwise specified. Example 1 In a pressure-resistant container, 5 parts of sodium dodecylbenzenesulfonate, 3 parts of potassium persulfate, and 4 parts of potassium persulfate were added to 100 parts of the monomers used in the first stage emulsion polymerization shown in Tables 1 and 2. 20 parts carbon, 1 part tertiary dodecyl mercaptan, 3 parts sodium bicarbonate, water
The mixture was mixed at a ratio of 400 parts and stirred with the monomer to be subjected to emulsion polymerization in the first stage, and the temperature was raised to 65°C to carry out polymerization. Next, 0.5 parts of sodium dodecylbenzenesulfonate, 0.5 parts of potassium persulfate, 2 parts of carbon tetrachloride, and Mix 0.1 part of grade dodecyl mercaptan and 60 parts of water,
The mixture was mixed and stirred with the monomers to be subjected to emulsion polymerization in the step, and then continuously added to a pressure vessel for polymerization. The final polymerization conversion rate was 99% or more in all cases. After removing unreacted monomer by stripping
Copolymer latexes A to J were obtained by passing through a 200-mesh wire mesh.

【table】

[Table] Example 2 Using the copolymer latex obtained in Example 1, a coating liquid was prepared according to the following formulation. Composition of coating liquid Kaolin clay 70 parts (solid content) Calcium carbonate 30 parts (〃) Modified starch 8 parts (〃) Emulsion copolymer latex 12 parts (〃) (Total solid content 62%) Obtained coating liquid A high-quality base paper for coated paper was coated on one and both sides using a blade coater and dried. (Coating amount is 10g/ ^m2 on one side)1
Adjustments were made under conditions of day and night relative humidity of 65% and temperature of 20°C, then linear pressure of 80 kg/cm, temperature of 60°C, and speed of 5 m/cm.
The sample was subjected to supercalender treatment under the conditions of min and 2 nip. The performance of the obtained coated paper is shown in Tables 3 and 4. The performance of the coated paper was measured using the following test method. o RI Dry Picking: The degree of picking when printed with an RI printing machine was visually judged and evaluated on a five-point scale from grade 1 (best) to grade 5 (worst).
The average value of 6 times is shown. o RI Wet Pick: The degree of picking when printing with dampening water on an RI printing machine is visually judged and graded on a five-point scale from Grade 1 (best) to Grade 5 (worst). evaluated. The average value of 6 times is shown. o Blistering resistance: Double-sided printed coated paper is humidity-controlled (approximately 6%) and thrown into a heated oil bath, and the lowest temperature at which blistering occurs is indicated. o Ink gloss: Print once using 0.4cc of commercially available offset printing ink using an RI type printing machine.
Leave it at room temperature for one day and night. The test paper that was left for one day and night was measured using a gloss meter and evaluated using a 5-step method.

【table】

【table】

Claims (1)

[Claims] 1 (a) Ethylenically unsaturated carboxylic acid monomer 10-
emulsion polymerization of 2 to 30 parts by weight of a monomer mixture consisting of 20% by weight, 10 to 20% by weight of a monomer containing a hydroxyalkyl group, and 60 to 80% by weight of a vinyl cyanide monomer, (b) In the presence of the obtained copolymer latex, 30 to 70% by weight of aliphatic conjugated diene monomer, 20 to 70% by weight of alkenyl aromatic monomer, and 5 to 40% by weight of unsaturated carboxylic acid alkyl ester monomer. % and 70 to 98 parts by weight of a monomer mixture consisting of 0 to 15% by weight of a vinyl cyanide monomer.