JPH07173799A - Paper-coating composition and coated paper produced by coating with the composition - Google Patents

Abstract

PURPOSE:To obtain a paper-coating composition having excellent adhesive strength, wet strength and ink receptivity by emulsion-polymerizing a specific monomer composition using a specific chain transfer agent, adjusting the pH, adding an ethylenic unsaturated amine to the system and polymerizing the amine. CONSTITUTION:This paper-coating composition providing a coated paper having excellent adhesive strength and wet strength and high ink receptivity is produced by emulsion-polymerizing (A) 20-60 pts.wt. of an aliphatic conjugated diene monomer and (B) 0.5-8 pts.wt. of an ethylenic unsaturated acid monomer other than ethylenic unsaturated amine monomer in the presence of a chain transfer agent composed of 0.05-3 pts.wt. of alpha-methylstyrene dimer and 0.05-3 pts.wt. of a 4-12C alkylmercaptan, adjusting the pH of the emulsion to >=7 with an alkali metal compound, adding (C) 0.5-8 pts.wt. of an ethylenic unsaturated amine monomer, (D) 1-5 pts.wt. of methacrylamide and its N-substituted compound and (E) 19-78 pts.wt. of other copolymerizable monomer (e.g. styrene), polymerizing the monomers, using the obtained copolymer latex as an adhesive and adding a pigment, etc., to the latex.

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 capable of obtaining a coated paper for printing which is particularly excellent in adhesive strength (dry strength), water resistance strength (wet strength) and ink acceptability. Is.

[0002]

2. Description of the Related Art In recent years, due to the speeding up and high functionality of printing methods, it has been desired to improve the quality of coated paper, which is one of printing base papers, so as to withstand various printing conditions. In particular, among the physical properties of coated paper for printing, basic adhesive strength, water resistance, and ink acceptability are important items, and the demands thereof are increasing. The carboxyl-modified latex used as an adhesive in the paper coating composition has been conventionally improved in quality by adjusting the composition of the monomer, the gel content, the particle size, etc. Absent.

Next, an amphoteric latex obtained by adding a cation group to an anion-modified latex has been developed for the purpose of increasing the affinity with the pigment and increasing the adhesive strength. As these proposals, Japanese Examined Patent Publication No. 3-8643 and Japanese Examined Patent Publication No. 61-
Although there are Japanese Patent No. 39334, Japanese Patent Laid-Open No. 58-4894, etc., the inventors of the present invention have found that the coated paper using the latex obtained by these methods improves the ink acceptability and the water resistance, but does not adhere to the paper. It is not enough to improve the strength, and the mutual improvement of the adhesive strength and the water resistance strength is still insufficient.

[0004]

DISCLOSURE OF THE INVENTION In order to improve the mutual adhesive strength and water resistance of coated paper, as a result of earnest research, a combination of a specific monomer and a chain transfer agent with an amphoteric latex was found to be To solve the problem of
The present invention has been completed.

[0005]

The present invention is as follows. (A) In a paper coating composition containing a pigment and an adhesive as main components, (1) 20 to 60 parts by weight of an aliphatic conjugated diene monomer (2) an ethylenically unsaturated acid monomer 0.5 to 8 parts by weight (3) Ethylenically unsaturated amine monomer 0.5 to 8 parts by weight (4) Methacrylamide and its N-substituted product 1 to 5 parts by weight (5) Other copolymerizable monomers A paper coating composition comprising a copolymer latex containing 19 to 78 parts by weight of a composition as a main component as the adhesive,
The copolymer latex is emulsion-polymerized with monomers other than ethylenically unsaturated amine monomers using a specific chain transfer agent, and adjusted to pH 7 or higher with an alkali metal compound. And a composition for paper coating, which is produced by further adding and polymerizing an ethylenically unsaturated amine monomer. (B) The paper coating composition as described in (a) above, wherein the chain transfer agent comprises the following (5) and (6).

(6) α-Methylstyrene dimer 0.05 to 3 parts by weight (7) 0.05 to 3 parts by weight of alkyl mercaptan having 4 to 12 carbon atoms (c) Paper coating according to (a) and (b) A coated paper obtained by coating a composition for industrial use.

The present invention will be described in detail below. The latex used in the present invention is, in a broad sense, referred to as SBR latex, MBR latex, SMBR latex and the like produced by emulsion polymerization, and is used as an adhesive in a paper coating composition. It has the same composition as the latex for use.

Among the monomers constituting the copolymer latex used in the paper coating composition of the present invention, the aliphatic conjugated diene-based monomers include 1.3-butadiene and 2-methyl-1.
3-butadiene, 2-chloro-1.3-butadiene and the like can be mentioned, and these can be used alone or in combination of two or more kinds. These monomers impart appropriate elasticity to the copolymer, and the amount thereof used is 20 to 60 parts by weight based on 100 parts by weight of the total monomer mixture. If it is less than 20 parts by weight, the glass transition temperature of the copolymer latex becomes high and the adhesive strength is lowered, and if it exceeds 60 parts by weight, the rigidity and water resistance are lowered. It is preferably 25 to 50 parts by weight. It is more preferably 28 to 45 parts by weight.

The ethylenically unsaturated acid monomers include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid and maleic acid, and further itaconic acid monoethyl ester and fumaric acid monoacid. Examples thereof include monoalkyl esters of unsaturated dicarboxylic acids such as butyl ester and maleic acid monopropyl ester, and unsaturated sulfonic acids such as 2-sulfoethyl acrylate, styrene sulfonic acid and acrylamidopropane sulfonic acid. These are used alone or in combination of two or more. The amount used is 0.5 to 8 parts by weight based on 100 parts by weight of the total monomer mixture, and if it is less than 0.5 parts by weight, not only the mechanical and chemical stability of the latex is lowered, but also the resulting coating composition is obtained. The adhesive strength of the craft paper decreases. If it exceeds 8 parts by weight, the viscosity of the latex becomes abnormally high, making it difficult to use, and the viscosity of the paper coating composition also becomes high, which is a problem.

As the ethylenically unsaturated amine monomer,
Methylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, diethylaminoethyl (meth)
Ethylenically unsaturated carboxylic acid aminoalkyl ester such as acrylate, aminoalkyl vinyl ether such as aminoethyl vinyl ether, methylaminoethyl vinyl ether, dimethylaminoethyl vinyl ether, 2-
Vinyl pyridine, 4-vinyl pyridine, 2-methyl-4
-Vinyl pyridines such as vinyl pyridine, etc., which are used alone or in combination of two or more. The amount used is 0.5 to 8 parts by weight, preferably 1 to 4 parts by weight, based on 100 parts by weight of the total monomer mixture. If it is less than 0.5 part by weight, the effect of the present invention cannot be obtained, and if it exceeds 8 parts by weight, the stability of the latex is lowered and the viscosity of the paper coating composition is abnormally increased, which makes it difficult to use. Is. It is preferably 1 to 5 parts by weight. Methacrylamide and N-substituted compounds are essential components of the present invention, and include N-methylolmethacrylamide, N-methoxymethacrylamide, N-butoxymethacrylamide and the like in addition to methacrylamide. The amount used is 1 to 5 parts by weight based on 100 parts by weight of the total monomer mixture, and the effect of the present invention is not obtained when the amount is less than 1 part by weight, and the viscosity of the latex and the paper coating composition is more than 5 parts by weight. Is too high to be suitable. It is preferably 1 to 3 parts by weight.

Aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, etc., as other copolymerizable monoolefin monomers; methyl acrylate,
Acrylic esters such as ethyl acrylate, methacrylic acid esters such as methyl methacrylic acid, ethylenically unsaturated carboxylic acid alkyl ester compounds such as diethyl fumarate and dimethyl itaconate; acrylonitrile, α-chloroacrylonitrile, methacrylic acid Vinyl cyanide compounds such as ronitrile; ethylenically unsaturated carboxylic acid amides such as acrylamide and N-methyl acrylamide and N-substituted compounds thereof, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylic acid The
Examples thereof include functional alkyl ester compounds such as glycidyl methacrylate, vinyl esters such as vinyl acetate, and the like, which impart appropriate hardness to the copolymer, and may be used alone or in combination of two or more kinds. I can.

When the pH of the above-mentioned monomer is adjusted with an alkali metal compound before the polymerization of the ethylenically unsaturated amine monomer, neutralizing agents used include sodium hydroxide, potassium hydroxide and lithium hydroxide. , Trisodium phosphate, disodium phosphate, tripotassium phosphate, dipotassium phosphate and the like, and these can be used alone or in combination of two or more kinds. When an amine-based neutralizing agent is used as the neutralizing agent, although coated paper having excellent ink acceptability can be obtained,
Adhesive strength and water resistance are insufficient. Further, if the adjusted pH is less than 7, the addition of an ethylenically unsaturated amine monomer causes polymerization and is insufficient. Preferably pH 7-10, more preferably pH 8-9.

As the emulsifier, anionic surfactants such as higher alcohol sulfate, alkylbenzene sulfonate, and aliphatic sulfonate, alkyl ester type of polyethylene glycol, alkyl phenyl ether type,
Nonionic surfactants such as alkyl ether type and amphoteric surfactants such as betaine type are used alone or in combination of two or more kinds. Considering the water resistance of the resulting copolymer latex, the amount of these surfactants is preferably 1 part by weight or less per 100 parts by weight of the total monomer mixture. As the polymerization initiator, potassium persulfate, ammonium persulfate, water-soluble initiators such as sodium persulfate, benzoyl peroxide, oil-soluble initiators such as azobisisobutyronitrile, or redox initiators. Can be used. These are used alone or in combination of two or more.

The chain transfer agent used in the present invention is an α-methylstyrene dimer essential for the present invention and a mercaptan having 4 to 12 carbon atoms such as octyl mercaptan, n-dodecyl mercaptan and t-dodecyl mercaptan. Are used together. The amount of α-methylstyrene dimer used is 0.05 based on 100 parts by weight of the total monomer mixture.
To 3 parts by weight, If it is less than 05 parts by weight, the water resistance of the coated paper obtained will decrease, and if it exceeds 3 parts by weight, the stability of the latex during polymerization will decrease, or the adhesive strength of the obtained coated paper will decrease. It is preferably 0.1 to 2 parts by weight. The amount of the mercaptans used is 0.05 to 3 parts by weight based on 100 parts by weight of the total monomer mixture. If the amount is less than 05 parts by weight, the water resistance of the obtained coated paper is lowered, and if it exceeds 3 parts by weight, the adhesive strength of the obtained coated paper is lowered. It is preferably 0.1 to 2 parts by weight.

In the production of the copolymer latex used in the paper coating composition of the present invention, it is particularly limited according to the known emulsion polymerization method except that the monomers are polymerized under the above-mentioned conditions. Not done. Further, for the purpose of stabilizing the particles during polymerization, as a protective colloid agent, for example, hydroxyethyl cellulose, carboxymethyl cellulose,
Polyvinyl alcohol or the like may be added. When pH is adjusted again with an alkali metal compound after polymerization of the above-mentioned monomers, examples of the neutralizing agent used include sodium hydroxide, potassium hydroxide, lithium hydroxide, trisodium phosphate, and phosphoric acid 2 Sodium, tripotassium phosphate, dipotassium phosphate and the like can be used alone or in combination of two or more kinds.

The paper coating composition of the present invention may contain various additives such as a dispersant, a water-proofing agent, a viscosity modifier and a defoaming agent, in addition to the copolymer latex and the pigment. Examples of pigments that can be used in the present invention include inorganic pigments such as clay, calcium carbonate, aluminum hydroxide, titanium white, satin white, and talc, and organic pigments such as polystyrene and phenol resin. In addition to the copolymer latex of the present invention, a latex of water-soluble polymer such as starch, casein, polyvinyl alcohol, polyvinyl acetate, acrylate copolymer, etc. can be used in combination, if necessary.

The copolymer latex used in the present invention is
Usually 5 to 30 parts by weight (solid content) with respect to the pigment (solid content)
Used in the range of. The thus obtained paper coating composition is coated in the same manner as in general coated paper production, for example, by a coating device such as an air knife coater, a blade coater, a roll coater and a bar coater. The solid content of the composition for coated paper is usually 40 to 70% by weight. In addition, as the coated paper, a high-quality paper, a medium-quality paper, a paperboard having a basis weight of 40 to 300 g / m ² , or a coated paper in which a paper coating composition is previously coated on one or both sides as a base paper is used. Used. The present invention will be specifically described below with reference to examples. In addition, the number of parts in Examples and Comparative Examples means parts by weight unless otherwise specified.

[0018]

Examples Production Example of Latex A An autoclave equipped with a stirrer and having an internal volume of 100 liters was charged with the following composition and thoroughly mixed, deoxidized by nitrogen substitution, and then heated to 70 ° C. Water 100 parts Sodium bicarbonate 0.1 part Sodium lauryl sulphate 0.1 part Potassium persulfate 1 part Itaconic acid 1.5 parts Immediately after the completion of temperature increase, among the monomer compositions shown in Table-1, butadiene 25 of the first stage composition Part, 49.5 parts of styrene, 18 parts of methyl methacrylate, a hydrophobic monomer mixture of 0.5 part of n-dodecyl mercaptan and 0.2 part of α-methylstyrene dimer, and 2 parts of acrylic acid and methacrylic acid. A water-soluble mixture of 2 parts of the amide, 40 parts by weight of pure water, and 0.3 part by weight of sodium lauryl sulfate was added to the autoclave at a constant rate for 4 hours. After the addition of the raw materials was completed, when the polymerization rate reached 98%, the pH was adjusted to 8.0 with a caustic soda aqueous solution, and 2 parts by weight of the ethylenically unsaturated amine monomer of the second stage composition shown in Table 1 was further adjusted. Was added at a constant rate of 30 minutes. After the addition, the mixture was reacted for 3 hours and then cooled to complete the reaction.

The internal temperature of the autoclave was maintained at 70 ° C. from the start of addition of the raw materials to the end of the polymerization and cooling. After the completion of cooling, unreacted monomers were removed from the obtained latex by steam stripping, and this latex was designated as Latex A of the present invention. Production Examples of Latex B to L Latex B to L were produced in the same manner as Latex A of Production Example 1 except for the conditions shown in Table 1. Latex B, C, and D are latexes of the present invention, and E to L are comparative latexes.

[0020]

[Table 1] The latex was used in the following examples.

(Production of Coated Paper) Examples 1 to 4 and Comparative Examples 1 to 8 Using the latex produced above, a composition for paper coating was prepared according to the following formulation.

(Formulation) Kaolin clay 70 parts Calcium carbonate 30 parts Dispersant 0.3 parts Oxidized starch 2 parts Latex 13 parts Total solid content 60% Kaolin clay, calcium carbonate and dispersant, caustic soda are prepared using a Cowles disperser. After being dispersed in water, a heated and dissolved aqueous solution of oxidized starch and latex were added to adjust the solid content to 60% to obtain a paper coating composition.

The results of Examples and Comparative Examples are summarized in Table 2. The numbers of Examples and Comparative Examples shown in Table 2 correspond to the numbers of Production Examples and Production Comparative Examples of latex, respectively, and the formulation of the paper coating composition other than latex is all under the same conditions. is there. Using the paper coating compositions obtained in the above Examples and Comparative Examples, test coated paper was prepared by the following method.

The above-mentioned composition for paper coating is coated on a high-quality paper with an applicator bar having an appropriate clearance so that the dry coating amount on one side is 15 g / m ^2, and the box type hot air is immediately applied. Dry in a dryer at 120 ° C for 20 seconds. The coated paper obtained was further seasoned at 20 ° C. and 65% relative humidity for one day and then seasoned at 60 ° C. and a linear pressure of 1%.
The super calender treatment was performed twice under the condition of 00 kg / cm, and the coated paper thus obtained was subjected to a printing surface strength test and the like. The coated paper obtained was evaluated according to the test methods shown below, and the results are shown in Table 2 together with the results of the viscosity of the paper coating composition.

[0025]

[Table 2]

(1) Viscosity of color (composition for paper coating) 25 ° C., 60 rpm, No. It was measured by a BM type viscometer under the condition of 3 rotors. (2) Dry strength test Using a RI printing aptitude tester (manufactured by Akira Seisakusho Co., Ltd.), the paper peeling state was visually judged by printing of Tack Ink (Toyo Ink SMX Tack 15), and a 10-point method (10 points were excellent). 1 point was inferior). (3) Wet strength test A RI printing aptitude tester was used to give dampening water using a molton roll, and the tacking ink (Toyo Ink SMX Tuck 10) was printed to visually judge the state of paper peeling, and a 10-point method was used. (1
The evaluation was 0 (excellent) and 1 (poor). (4) Inking of ink Using an RI printability tester, offset ink (Toyo Ink New Bright Indigo) and water were kneaded, this was printed, and the ink density was measured with a Macbeth densitometer. (5) Swimsuit meat Using an RI printability tester, water was applied to the test piece with a molton roll, and after printing with a printing ink (Toyo Ink New Bright Indigo) under the condition that no paper peeling occurred, Macbeth density The ink density was measured with a meter.

[0027]

INDUSTRIAL APPLICABILITY In the examples, the coated papers obtained from the paper coating composition of the present invention have good adhesive strength, and also have good water resistance and ink acceptability such as ink inking and swimwear meat. This suggests that the quality of the coated paper has been greatly improved.

Claims (3)

[Claims] 1. A composition for paper coating comprising a pigment and an adhesive as main components, comprising: (1) 20 to 60 parts by weight of an aliphatic conjugated diene monomer (2) a single amount of an ethylenically unsaturated acid Body 0.5 to 8 parts by weight (3) Ethylenically unsaturated amine monomer 0.5 to 8 parts by weight (4) Methacrylamide and its N-substituted product 1 to 5 parts by weight (5) Other copolymerizable monomer A paper coating composition comprising a copolymer latex containing a composition of 19 to 78 parts by weight as a main component as the adhesive,
The copolymer latex is emulsion-polymerized with monomers other than ethylenically unsaturated amine monomers using a specific chain transfer agent, and adjusted to pH 7 or higher with an alkali metal compound. And a composition for paper coating, which is produced by further adding and polymerizing an ethylenically unsaturated amine monomer. 2. The above-mentioned chain transfer agent is one of the following (5) and (6):
The composition for paper coating according to claim 1, which comprises: (6) α-Methylstyrene dimer 0.05 to 3 parts by weight (7) Alkyl mercaptan having 4 to 12 carbon atoms 0.05 to 3 parts by weight 3. A coated paper obtained by coating the paper coating composition according to claim 1.