JPH0381379A - Coating composition for web offset paper - Google Patents

Abstract

PURPOSE:To obtain the title composition which is excellent in water retention and flowability and gives a coated paper excellent in blister resistance, printing luster, adhesive strength and water resistance by compounding a specified alkali- insoluble copolymer latex and a specified alkali-soluble copolymer latex. CONSTITUTION:The title composition comprises 100 pts.wt. pigment and 5-20 pts.wt. mixture of an alkali-insoluble copolymer latex A and an alkali-soluble copolymer latex B in a weight ratio of A to B of 99/1 to 80/20 in terms of solid content. The latex A is one prepared by the emulsion polymerization of (a) in aliphatic conjugated diene, (b) a vinyl cyanide monomer, (c) an ethylenically unsaturated carboxylic acid monomer, and (d) another comonomer, wherein first a monomer mixture comprising the whole of components (a) and (b), 60-90% of component (c) and part of component (d) is emulsion-polymerized to give a copolymer and then a monomer mixture comprising 40-10% of component (c) and the rest of component (c) is emulsion-polymerized in the presence of the above copolymer. The latex B is one prepared by the emulsion polymerization of component (b), an alkyl ester of an unsaturated carboxylic acid and a cross-linking monomer.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a coating composition for rotary offset printing paper. The present invention relates to a coating composition for rotary offset printing paper that has excellent paper blister resistance, printing gloss, adhesive strength, and water resistance.

<Prior Art> In recent years, as the number of printed materials has increased, rotary offset printing presses, which are capable of high-speed printing and improved printing efficiency, have become rapidly popular. Blister resistance is one of the important printability requirements for coated paper used in rotary offset printing. Generally, after rotary offset printing, when the ink is dried at high temperatures, the moisture contained in the coated paper evaporates and expands, causing blisters on the surface of the paper, which is called blister. Blister resistance in coated papers for rotary offset printing is important.

Methods for improving this blister resistance include the use of pigments with good air permeability (for example, fine particle size calcium carbonate, satin white), and the reduction of natural polymers such as starch used as binders.

However, the use of pigments with good air permeability lowers adhesive strength, and the reduction of natural polymers has the problem of lowering the water retention properties of the composition and lowering adhesive strength.

On the other hand, recent trends in coating technology include increasing the speed of coaters and increasing the density of coating colors in order to improve operational efficiency, reduce drying energy costs, and improve coated paper quality. Good fluidity of the coating color is also required. In this respect as well, reducing the natural polymer can improve fluidity under high shear rates, but as described above, reducing the natural polymer reduces the water retention and adhesive strength of the composition. Therefore, the use of an alkali-sensitive latex, which is a synthetic copolymer latex that imparts water retention and thickening properties to the coating composition, has been proposed, for example, in JP-A-57-16749.
It is proposed in No. 0.

However, the use of these latexes is still not satisfactory in terms of water retention and fluidity.
Furthermore, the blister resistance is also poor.

<Problems to be Solved by the Invention> The objects of the present invention are to improve the water retention and fluidity of a coating composition and the blister resistance of coated paper for offset rotary printing obtained by coating the composition; The purpose is to improve printing gloss, adhesive strength, and water resistance.

Means for Solving the Problems> As a result of intensive studies to achieve the above-mentioned object, the present inventors have developed an alkali-insoluble copolymer latex obtained through a specific two-step polymerization, a specific composition and It has been discovered that this objective can be achieved by using a specific proportion of an alkali-soluble copolymer latex having an average molecular weight,
The present invention has now been completed.

That is, the present invention comprises 25 to 40% by weight of aliphatic conjugated diene monomers, 1 to 40% by weight of vinyl cyanide monomers, 1 to 10% by weight of ethylenically unsaturated carboxylic acid monomers, and other co-monomers. In emulsion polymerization of 10 to 73% by weight of polymerizable monomers, in the first stage, the total amount of aliphatic conjugated diene monomers, the total amount of vinyl cyanide monomers, and the amount of ethylenically unsaturated carboxylic acid monomers are added. 60 to 90 M% of the total amount of monomers used, and a part of other copolymerizable monomers, and the total amount is 45% of the total monomers used.
In the presence of a copolymer obtained by emulsion polymerization of a monomer mixture of ~99% by weight, as a second stage, ethylenically unsaturated carboxylic acid monomer 4
A monomer mixture consisting of 0 to 10% by weight and the balance of other copolymerizable monomers, the total amount of which is 1 to 55% by weight of the total monomers used, is added and emulsion polymerized. alkali-insoluble copolymer latex (6) obtained by
Unsaturated carboxylic acid alkyl ester monomer 49.9-8
The average molecular weight obtained by emulsion polymerization of 0% by weight and 0.01 to 0.1% by weight of a crosslinkable monomer is 15,000 to 50.
0,000 alkali-soluble copolymer latex (
(b) and mixed in a ratio of (6)/(b) in a weight ratio (solid content) of 99/l to 80/20 to 100 parts by weight of pigment. 2
The present invention provides a coating composition for rotary offset printing paper, characterized in that it contains 0 parts by weight (in terms of solid content).

Hereinafter, the present invention will be explained in detail.

The aliphatic conjugated diene monomer constituting the alkali-insoluble copolymer latex of the present invention is selected from those having 4 to 10 carbon atoms, and specifically, 1,8-butadiene, 2- Methyl-1,3-butadiene, 2,3-
Examples include dimethyl-1,3-butadiene, halogen-substituted butadienes, substituted linear conjugated pentadines, and conjugated hexadienes having a straight chain or a side chain, and one type or two or more types thereof can be used.

Examples of vinyl cyanide monomers include acrylonitrile,
Examples include methacrylonitrile, and one or more types can be used.

Examples of ethylenically unsaturated carboxylic acid monomers include monocarboxylic acids such as acrylic acid and methacrylic acid, dicarboxylic acids such as itaconic acid, fumaric acid, and maleic acid, and maleic anhydride. The above can be used.

Monomers that can be copolymerized with these include aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, and dimethylstyrene, methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. , lauryl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and other unsaturated carboxylic acid alkyl ester monomers, as well as acrylamide, N Examples include methylol acrylamide, glycidyl acrylate, and glycidyl methacrylate, and one or more types of each can be used.

The aliphatic conjugated diene monomer is used in an amount of 25 to 40% by weight, but if it is less than 25% by weight, the adhesive strength decreases and 40% by weight is used.
If it exceeds % by weight, the blister resistance will decrease. Preferably it is in the range of 27 to 38% by weight.

The vinyl cyanide monomer is used in an amount of 1 to 40% by weight, but if it is less than 1% by weight, the gloss decreases, and if it exceeds 40% by weight, a stable copolymerized latex cannot be obtained. Preferably it is 5 to 35% by weight.

The ethylenically unsaturated carboxylic acid monomer is used in an amount of 1 to 10% by weight, but if it is less than 1% by weight, the stability of the copolymer latex will be insufficient and the adhesive strength will also decrease.

Moreover, if it exceeds 10% by weight, the viscosity of the copolymer latex produced becomes high, making it difficult to handle. Preferably it is 1 to 7% by weight.

The copolymerizable monomer is used in an amount of 10 to 73% by weight, but if it is less than IO% by weight, the blister resistance decreases and 78% by weight is used.
If it exceeds % by weight, the adhesive strength will decrease. Preferably 20
~67% by weight.

The alkali-insoluble copolymer latex (6) of the present invention is
In emulsion polymerization of monomers having the above composition, in the first stage, the total amount of aliphatic conjugated diene monomers, the total amount of vinyl cyanide monomers, and 60% of the ethylenically unsaturated carboxylic acid monomers are ~90% by weight, consisting of a part of other copolymerizable monomers, and whose total amount is 45% by weight of the total monomers used.
In the presence of a copolymer obtained by emulsion polymerization of a monomer mixture of ~99% by weight, as a second stage, ethylenically unsaturated carboxylic acid monomer 4
A monomer mixture consisting of 0 to 10% by weight and the balance of other copolymerizable monomers, the total amount of which is 1 to 55% by weight of the total monomers used, is added and emulsion polymerized. This is what you get.

It is essential that the aliphatic conjugated diene monomer and vinyl cyanide monomer be used in their entirety in the first stage. If an aliphatic conjugated diene monomer is used in the second stage, a stable copolymer latex cannot be obtained. Furthermore, if vinyl cyanide monomer is used in the second stage, sufficient printing gloss cannot be obtained.

The ethylenically unsaturated carboxylic acid monomer is 60 to 60% in the first stage.
90% by weight is used. If the amount used in the first stage is less than 60% by weight, good fluidity cannot be obtained, and if it exceeds 90% by weight, the necessary viscosity during coating cannot be obtained. Preferably 60-8
It is 5% by weight.

In addition, the amount of monomer mixture used for emulsion polymerization in the first stage is:
It is 45 to 99% by weight of the total monomers used. The usage amount is 4
If it is less than 5% by weight, water resistance and adhesive strength will decrease, and 99% by weight.
If it exceeds % by weight, satisfactory blister resistance and printing gloss cannot be obtained. Preferably it is 50 to 90% by weight.

The ethylenically unsaturated carboxylic acid monomers and unsaturated carboxylic acid alkyl ester monomers constituting the alkali-soluble copolymer latex (b) of the present invention are those described in the alkali-insoluble copolymer latex (f). Those similar to the above can be mentioned, and one type or two or more types of each can be used.

In addition, the crosslinkable monomer is a monomer containing two or more polymerizable non-conjugated double bonds, such as allyl acrylate,
Diallyl maleate, diallyl phthalate, diallyl isophthalate, diallyl itaconic acid, triallyl cyanurate, diallylbenzene phosphonate, diethylene glycol bisallyl carbonate, diallyl tetrachlorophthalate, diallyl hetate, ethylene glycol dimethacrylate, allyl methacrylate, diallyl Cyanamide, diarylidenepentaerythritol, divinylbenzene, divinylxylene, diacrylic acid, ethylene glycol dimethacrylate, 2-ethylhexane-1,
3-dimethacrylate, divinylxylene, divinylethylbenzene, divinyl ether, divinyl sulfone, N-N'-methylene diacrylamide, 1,2-di(
Examples include α-methylmethylenesulfonamide)-ethylene, and one or more types can be used.

Ethylenically unsaturated carboxylic acid monomers increase the viscosity of the resulting copolymer latex, making it difficult to handle. Preferably it is 24.9 to 45% by weight.

In addition, the unsaturated carboxylic acid alkyl ester monomer is 49
．． It is used at 9 to 80% by weight, but if it is less than 49.9% by weight, a stable copolymer latex cannot be obtained, and 80% by weight is used.
If it exceeds this, the adhesive strength will decrease. Preferably 54.9~
It is 75% by weight.

The crosslinkable monomer is used in an amount of 0.01 to 0.1% by weight, but if it is less than 0.01% by weight, the viscosity of the coating liquid decreases and
．． If it exceeds 1% by weight, the fluidity of the coating liquid will decrease and the blister resistance of the coated paper will also decrease.

The alkali-soluble copolymer latex (b) needs to have a weight average molecular weight in the range of 15,000 to 500,000. If the molecular weight is less than 15,000, the water retention of the coating liquid will be poor, and the adhesive strength of the coated paper will also be poor.
! If it exceeds this, the blister resistance will decrease. Preferably 5
It is 0.000 to 400,000.

The weight average molecular weight of the alkali-soluble copolymer latex (b) was measured using a water-based column under conditions of pH 9 to 10 based on polyethylene glycol.

The above-mentioned alkali-insoluble copolymer latex (c) and alkali-soluble copolymer latex (b) have a weight ratio (
(solid content equivalent) (A)/(Bl = 99/1 to 80/20
They are mixed in the following proportions. If (6) exceeds 99% by weight of the total of (9) and (b), satisfactory water retention will not be obtained, and if it is less than 80% by weight, fluidity, adhesive strength and blister resistance will decrease.

The alkali-insoluble copolymer latex (6) and the alkali-soluble copolymer latex (b) are each obtained by emulsion polymerization, and known emulsifiers, polymerization initiators, chain transfer agents, etc. are used during the polymerization.

As the emulsifier, anionic surfactants such as higher alcohol sulfate esters, alkylbenzene sulfonates, aliphatic sulfonates, etc., or nonionic surfactants such as polyethylene glycol alkyl ester types, alkylphenyl ether types, and alkyl ether types are used. Type 1 or 2
Used in more than one species.

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

As the chain transfer agent, mercaptans, halogenated hydrocarbons, etc. are used.

Furthermore, the alkali-soluble copolymer latex 0 is usually produced in a separate glue actor from the alkali-insoluble copolymer latex (c), but after polymerizing the alkali-insoluble copolymer latex (c), the same It is also possible to polymerize in a reactor.

Examples of pigments constituting the coating composition of the present invention include known pigments such as kaolin, heavy calcium carbonate, light calcium carbonate, clay talc, titanium oxide, aluminum hydroxide, silica, zinc oxide, and plastic pigments. One type or two or more types can be used.

The composition ratio of the above-mentioned copolymer latex (mixture) and pigment is 5 to 20 parts by weight of copolymer latex per 100 parts by weight of pigment.
Parts by weight (in terms of solid content), and the copolymer latex is 5
If the amount is less than 20 parts by weight, the adhesive strength will be insufficient, and if it exceeds 20 parts by weight, the blister resistance will decrease.

In the coating composition of the present invention, in addition to the above copolymer latex, natural binders such as oxidized starch, etherified starch, esterified starch, enzyme-modified starch, and soybean protein are used in combination with the copolymer latex. You can also. Furthermore, known additives and auxiliaries such as a dispersant, thickener, preservative, pH adjuster, mold release agent, water retention agent, water resistance agent, antifoaming agent, coloring agent, etc. can be used as necessary.

〔Example〕

Examples of the present invention are shown below, but the present invention is not limited to these Examples in any way.

Note that parts and percentages in the examples are based on weight.

Preparation of alkali-insoluble copolymer latex (2) In an autoclave that had been purged with nitrogen in advance,
A mixture of the monomer mixture of step 1, 1 part of sodium alkylbenzene sulfonate, 0.5 part of potassium persulfate, 0.5 part of t-dodecylmercaptan, and 100 parts of pure water was charged;
Polymerization was carried out at 65° C. with stirring. After the polymerization conversion rate in the first stage reaches 90%, the monomer mixture in the second stage is added and polymerized to form an alkali-insoluble copolymer latex (
C) to U) were obtained.

Preparation of alkali-soluble copolymer latex (b) In an autoclave that had been purged with nitrogen in advance, the monomer mixture shown in Table 2, t-dodecyl mercaptan, 0.5 part of sodium alkylbenzenesulfonate, and 0.5 part of sodium bicarbonate were added.
5 parts of potassium persulfate, 0.5 parts of potassium persulfate, and 100 parts of pure water were added, and polymerization was carried out at 70° C. for 8 hours with stirring to obtain latexes (I) to (A).

Preparation of coating composition The above alkali-insoluble copolymer latex (9) and alkali-soluble copolymer latex (b) were mixed in the proportions shown in Table 3, and the latex mixture was mixed in the amounts shown in Table 3. 80 parts of kaolin, 20 parts of ground calcium carbonate, and 5 parts of phosphated starch (not used in Example 8)
A coating composition was adjusted to a solid content concentration of 60% using adjusted water according to the formulation.

During the adjustment, a dispersant (sodium polyacrylate) and a pH adjuster (ammonia, caustic soda) were used as appropriate.

Examples 1 to 8 and Comparative Examples 1 to 16 Using the obtained coating liquid, high-quality coated base paper (64?/
The coated paper was coated on both sides using a blade, and after drying, it was subjected to a super calender treatment. The test results of the obtained coated paper are shown in Table 3.

In addition, the coated paper test was measured by the following method.

(1) Viscosity of the composition: 5Qr, p, m by BL type viscometer
Measurement was carried out at 20°C using a No. 3 rotor and a No. 4 rotor.

(2) Water retention of the composition: Measured according to S, D, Warren method to determine quality.

◎ (Excellent) ← × (Poor) (3) Fluidity of composition: 20°C using a Hercules viscometer
, BobE, and determined from the flow pattern at 6000 p.m. ◎ (Good with no turbulence) × (Poor with turbulence) (4) Dry pick strength of coated paper: R■ Judging the degree of picking during printing with the printing machine with the naked eye.

5 (Excellent) Ol (Poor) (5) Wet pick strength of coated paper: The degree of picking during printing using dampening water on an R printing machine was judged by the naked eye.

5 (excellent) ol (poor) (6) Coated paper printing gloss near 5°-75° Measured using a Murakami color gloss meter.

The ink is manufactured by Toyo Ink Co., Ltd. I used Tsubu Shine.

(7) Blister resistance of coated paper: Using a Motoya Riki Kogyo (To) blister tester, the coated paper was printed, then humidity conditioned, and the degree of blistering was determined after heating at 200°C.

5 (Excellent) 01 (Poor) <Effects of the Invention> As described above, the coating composition of the present invention has excellent water retention and fluidity, and the coating composition for offset rotary printing obtained by coating the composition The coated paper has excellent blister resistance, print gloss, adhesive strength and water resistance.

Claims (1)

[Claims] 25 to 40% by weight of aliphatic conjugated diene monomer, 1 to 40% by weight of vinyl cyanide monomer, 1 to 10% by weight of ethylenically unsaturated carboxylic acid monomer, and other In emulsion polymerization of 10 to 73% by weight of copolymerizable monomers, in the first stage, the total amount of aliphatic conjugated diene monomers, the total amount of vinyl cyanide monomers, and the ethylenically unsaturated carboxylic acid monomers are and a part of other copolymerizable monomers, and the total amount is 45% by weight of the total monomers used.
In the presence of a copolymer obtained by emulsion polymerization of a monomer mixture of ~99% by weight, as a second stage, ethylenically unsaturated carboxylic acid monomer 4
A monomer mixture consisting of 0 to 10% by weight and the balance of other copolymerizable monomers, the total amount of which is 1 to 55% by weight of the total monomers used, is added and emulsion polymerized. Alkali-insoluble copolymer latex (A) obtained by
The weight average molecular weight obtained by emulsion polymerization of ~80% by weight and 0.01 to 0.1% by weight of a crosslinkable monomer is 15,00%.
It consists of an alkali-soluble copolymer latex (B) having a molecular weight of 0 to 500,000, and is mixed at a weight ratio (in terms of solid content) of (A)/(B) of 99/1 to 80/20. 1. A coating composition for rotary offset printing paper, comprising 5 to 20 parts by weight (in terms of solid content) of a latex mixture consisting of 100 parts by weight of a pigment.