JPH0433919B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a paper coating composition, and particularly to a paper coating composition that is excellent in operability, adhesive strength, water resistance, blister resistance, and gloss. [Prior Art] Carboxy-modified butadiene-styrene copolymer latex has been widely used as a binder for pigment coating processing of paper, either alone or in combination with natural or synthetic binders such as casein, protein, starch, and polyvinyl alcohol. has been done. Pigment-coated papers (coated papers) treated with paper coating compositions containing these carboxy-modified butadiene-styrene copolymer latexes have various excellent properties such as whiteness and gloss, and are therefore used in a variety of applications. is used in large quantities. [Problem to be solved] In recent years, the growth of coated paper has been remarkable, and as a result, high-speed coating has progressed further, and color solid content has been increased to reduce costs by saving drying energy during coating. Concentration is also recommended. In high-speed coating, there is a strong demand for rolls to be clean from an operational standpoint. On the other hand, when increasing the concentration, the viscosity of the paper coating composition (color) is too high, resulting in deterioration of fluidity, resulting in a problem with operability.As a countermeasure for this problem, fine particles with good fluidity are used as pigments. The general method is to increase the usage ratio of heavy calcium carbonate, and to reduce the amount of natural water-soluble binders such as casein and starch, which have strong thickening effects, to make the binder relatively latex thick. (Ref.TAPPI Coating
Conference'79). However, the improvement effect is still not sufficient. For this reason, there is a growing demand for paper coating compositions that have better operability than ever before. In addition, with the recent rapid increase in the number of printed materials, there is a growing trend toward higher speed printing, especially in offset printing, and the following properties are now required of pigment-coated papers and pigment binders for offset printing. That is, it has the property of resisting the mechanical force applied to the surface of the pigment-coated paper during printing, allowing beautiful printing without causing the pigment to fall off or the coating layer to peel from the base paper. For this purpose, it is necessary to firmly adhere the pigment particles to each other and the pigment coating layer to the base paper that is its support. Such damage to the paper surface becomes more severe as the printing speed increases and the number of overprints increases, and pigment-coated paper that can withstand this damage is required, and for this purpose, a pigment binder with excellent adhesive strength is required. be done. In addition, offset printing uses a "dampening water" unique to the printing method, but it is required to have the strength (water resistance) to withstand the mechanical force of printing when wet. Moreover, in order to further exhibit the effect of a beautiful print finish, it is now required that the coated paper has excellent gloss and printing gloss. In addition, especially in the case of rotary offset printing, due to the nature of the printing method, high-speed printing and high-temperature and high-speed drying are required.
"Blistering" is likely to occur, and when this blistering occurs, the commercial value of the printing paper is greatly impaired. Since the pigment binder is a major factor in the occurrence of blisters, a pigment binder with excellent blister resistance is required. Various methods have been used to improve the above-mentioned required performance from the aspects of base paper and coated paper composition. Improvements in synthetic copolymer latexes are considered important because they have a large influence on operability and printability and have a degree of freedom in improvement. [Means for Solving the Problems] The present inventors have conducted intensive studies to improve the performance of conventional copolymer latexes, and as a result, they have developed a copolymer latex with excellent operability, adhesive strength, water resistance, blister resistance, and gloss. This invention was completed because we were able to produce a new copolymer latex that can be used as a binder. That is, the present invention includes a) aliphatic conjugated diene monomer 25 to 45% by weight b) unsaturated fatty acid glycidyl ester
0.5~10 〃 c Vinyl cyanide monomer 0~30 〃 d Alkenyl aromatic monomer 10~69 〃 e Ethylenically unsaturated carboxylic acid alkyl ester 5~40% by weight f Ethylenically unsaturated carboxylic acid 0.5~ A paper coating composition characterized by containing a copolymer latex consisting of 10 〃 and a pigment. The copolymer latex that can be used in the present invention can be produced by a known method, that is, by emulsion polymerization using an emulsifier, a polymerization initiator, a polymerization chain transfer agent, etc. in an aqueous medium. The aliphatic conjugated dienes used in the production of the copolymer latex of the present invention include butadiene, isoprene, 2-chloro-1,3-butadiene, and the like. These monomers should be in the range of 25-45% by weight to give the copolymer adequate elasticity and film hardness. If it is less than 25% by weight, the copolymer will be hard and brittle, while if it exceeds 45% by weight, it will be too soft and have poor water resistance. Examples of unsaturated fatty acid glycidyl esters include mono- or diglycidyl esters of monobasic unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, dibasic unsaturated carboxylic acids such as itaconic acid and maleic acid, and 2-methylglycidyl. esters,
Monoglycidyl ether monoacrylates or monomethacrylates of ethylene glycol, propylene glycol, and butylene glycol, and monoglycidyl ester monoacrylates or monomethacrylates of these glycols can be used. Preferably, glycidyl acrylate and glycidyl methacrylate are used. The amount used is 0.5 to 10% by weight, preferably 1 to 8% by weight. If the amount used is less than 0.5% by weight, the desired effect of the present invention will not be sufficiently achieved, while if it exceeds 10% by weight, polymerization stability will deteriorate. As the vinyl cyanide monomer, acrylonitrile, methacrylonitrile, etc. can be used. Effective in improving print gloss. The amount used is 0 to 30% by weight.
Preferably it is 3 to 20% by weight. If the amount used exceeds 30% by weight, the adhesive strength will decrease. Examples of alkenyl aromatic monomers include styrene, α
-Methylstyrene, vinyltoluene, etc. can be used in an amount of 10 to 69% by weight. Water resistance is less than 10% by weight, 69
If it exceeds % by weight, polymerization stability will deteriorate. Examples of ethylenically unsaturated carboxylic acid alkyl esters include alkyl acrylates, alkyl methacrylates, and hydroxyalkyl esters of ethylenically unsaturated carboxylic acids; examples of alkyl acrylates include methyl acrylate, ethyl acrylate, and butyl acrylate; examples of alkyl methacrylates include methyl acrylate; As methacrylate, ethyl methacrylate, and hydroxyalkyl esters of ethylenically unsaturated carboxylic acids, β-hydroxyethyl acrylate, β-hydroxy methacrylate, etc. can be used.
They can be used alone or in a mixture of two or more. The amount used is 5 to 40% by weight; if the amount used is less than 5% by weight, polymerization stability will be poor, and if it exceeds 40% by weight, water resistance will be poor. As the ethylenically unsaturated carboxylic acid, mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid can be used, but dicarboxylic acid anhydrides can also be used. Ethylenically unsaturated carboxylic acid 0.5-10% by weight,
Preferably it is used in an amount of 1 to 7% by weight. If it is less than 0.5% by weight, the adhesive strength and mechanical stability will decrease, and if it exceeds 10% by weight, the viscosity of the latex will become too high.
Handling becomes difficult. The copolymer latex used in the composition of the present invention can be produced by one-step copolymerization of the monomers (a) to (f) above. ) In the presence of a first-stage copolymer latex with Tg = -25 to 50°C obtained by first copolymerizing 10 to 40% by weight of the total monomers of monomers selected from (a) to (f) and their quantities, In the case of a two-stage copolymer latex in which the remaining monomers are copolymerized, the adhesive strength, water resistance, and blister resistance are particularly excellent. In the case of a two-stage copolymer latex in which the remaining monomers are copolymerized in the presence of a first-stage copolymer latex with a Tg of 50 to 95°C obtained by first copolymerizing ~40% by weight, white paper gloss is particularly low. Gives an excellent composition. The gel content of the copolymer latex of the present invention is 30~
When it is 70%, the coating composition for coated paper for offset rotary printing exhibits more excellent effects as the object of the present invention. The paper coating composition of the present invention combines mineral pigments commonly used for paper coating such as clay, barium sulfate, titanium oxide, calcium carbonate, and satin white, with the copolymer latex of the present invention as a pigment binder. Furthermore, a natural or synthetic binder such as casein, starch, polyvinyl alcohol, etc. can be added as necessary. The preferred ratio of the copolymer latex and pigment of the present invention is 3 to 30 parts by weight per 100 parts by weight of the pigment. Furthermore, various commonly used compounding agents such as water resistance improvers, water resistance reaction accelerators, pigment dispersants, viscosity modifiers, coloring pigments, fluorescent dyes, and PH regulators can also be optionally added. [Examples] Next, the present invention will be explained with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Note that in the examples, parts and % indicating percentages mean parts by weight and % by weight, respectively. Example 1 200 parts of water, 30 parts of butadiene in an autoclave,
Add 50 parts of styrene, 10 parts of methyl methacrylate, 5 parts of acrylonitrile, 2 parts of itaconic acid, 3 parts of glycidyl methacrylate, 0.5 parts of sodium dodecylbenzenesulfonate, 1.5 parts of potassium persulfate, and 6 parts of carbon tetrachloride, and heat at 60°C. After 13 hours of reaction, a copolymer latex with a polymerization conversion rate of 98% was obtained. This latex is called (A). Copolymer latex (B), (C), (A) with the composition shown in Table 1 under the same conditions as (A)
was manufactured. Comparative Example 1 Under the same conditions as in Example 1, copolymer latexes (E), (F), and (G) having the compositions shown in Table 1 were obtained. Example 2 200 parts of water, 10 parts of butadiene in an autoclave,
Add 10.5 parts of styrene, 5 parts of methyl methacrylate, 3 parts of acrylonitrile, 1.5 parts of itaconic acid, 0.5 parts of sodium dodecylbenzenesulfonate, 1.5 parts of potassium persulfate, and 5 parts of carbon tetrachloride.
A latex with a polymerization conversion rate of 95% was obtained by reacting for a period of time. In the presence of this latex, butadiene, 20 parts, styrene, 30 parts, methyl methacrylate, 13 parts, acrylonitrile, 4 parts, and 3 parts of glycidyl methacrylate were added sequentially over a period of 10 hours, during which time the reaction was continued, and after the monomer addition was completed, aging was performed for 2 hours, resulting in a polymerization conversion rate of 98%. of latex was obtained. This latex is called (H). Copolymer latexes (I) and (J) having the compositions shown in Table 2 were produced under the same conditions as (H). Example 3 200 parts of water, 2.5 parts of butadiene in an autoclave
parts, 14 parts of styrene, 6 parts of methyl methacrylate,
3 parts acrylonitrile, 1 part fumaric acid, 1 part acrylic acid, 0.5 parts sodium dodecylbenzenesulfonate
1.5 parts of potassium persulfate and 5.5 parts of carbon tetrachloride were added and reacted at 60°C for 4 hours to obtain a copolymer latex with a polymerization conversion rate of 97%. In the presence of this latex, 33.5 parts of butadiene, 16.5 parts of styrene, 15 methyl methacrylate, 7 acrylonitrile, and 4 glycidyl methacrylate were successively added over 10 hours to continue the reaction, and after the monomer addition was completed, aging was performed for 2 hours, resulting in a latex with a polymerization conversion rate of 97%. I got it. Let this latex be (K). Then, using the obtained latexes (A) to (K), paper coating paints were prepared according to the following method and were subjected to the following tests. Compounded clay 80 parts (contains 0.5% sodium pyrophosphate as a dispersant) Calcium carbonate 20 parts Copolymer latex 10 parts oxidized starch 5 parts water Added in sufficient amount to make the total solids content 60% Test method in Examples is as follows. 1 Gum up test: Indicator of roll fouling resistance (indicator of operability) The coating liquid is kneaded between rubber rolls using a gum up tester, and the time (minutes) until coagulation occurs on the rubber roll by applying mechanical shear. ) to measure.
The longer the time, the better. 2 RI Dry Picking: Indicator of Adhesive Strength The degree of picking when printed with an RI printing machine was visually determined and evaluated using a 5-step method. The higher the score, the better. Displayed as the average value of 6 measurements. 3 RI Wet Pick: Indicator of Water Resistance The degree of picking when applying dampening water using a Morton roll on an RI printing machine was visually judged and evaluated using a five-point scale. The higher the score, the better. Displayed as the average value of 6 measurements. 4. Wet Rub: Indicator of water resistance Test it on an Adams tester for 15 seconds and measure the transmittance of the cloudy water obtained at that time using a spectrophotometer. The higher the number, the better. 5 White paper gloss Measured using a Murakami gloss meter (75°-75°) 6 Print gloss Printed a solid sheet of web offset ink using an RI printing machine and measured using a Murakami gloss meter (75°) (゜-75゜) 7 Blister resistance A paper coated on both sides is placed in a heated oil bath with controlled humidity (approximately 6%), and the lowest temperature at which blisters occur is shown. 8 Gel content The obtained copolymer latex was adjusted to pH 8.0, coagulated with isopropanol, washed and dried, and then a predetermined amount (approximately 0.3 g) of the sample was immersed in a predetermined amount (100 ml) of toluene for 20 hours. Measure the insoluble matter,
Expressed in weight percent relative to the sample.

【table】

【table】

[Table] Measured using a type differential calorimeter.

[Table] Example 4 Copolymer latexes (L) and (M) were produced under the same conditions as in Example 1 except that the composition of the monomers was as shown in Table 4. Using the obtained copolymer latexes (L) and (M), a paper coating paint was prepared according to the same formulation as in Example 1, and was subjected to the same tests as in Example 1. The results are shown in Table 5.

【table】

〔Effect of the invention〕

As is clear from the results in Table 3, the copolymer latex of the present invention has excellent operability, adhesion during printing on coated paper, and water resistance, which were not sufficiently obtained with conventional copolymer latexes. It can be seen that it has excellent performance in terms of gloss, gloss, and blister resistance.

Claims (1)

[Claims] 1 (a) Aliphatic vinyl conjugated diene monomer
25-45% by weight b Unsaturated fatty acid glycidyl ester
0.5-10% by weight c Vinyl cyanide monomer 0-30% by weight d Alkenyl aromatic monomer 10-69% by weight e Ethylenically unsaturated carboxylic acid alkyl ester 5-40% by weight f Ethylenically unsaturated carboxylic acid A paper coating composition comprising a copolymer latex composed of 0.5 to 10% by weight of an acid and a pigment. 2. In the presence of a first-stage copolymer latex with a Tg of -25 to 50°C, the copolymer latex is obtained by copolymerizing monomers selected from (a) to (f) in an amount of 10 to 40% by weight of the total monomers. The paper coating composition according to claim 1, which is a copolymer latex obtained by copolymerizing the remaining monomers. 3. In the presence of a first stage copolymer latex with a Tg of 50 to 95°C, the copolymer latex is obtained by copolymerizing monomers selected from (a) to (f) in an amount of 10 to 40% by weight of the total monomers, The paper coating composition according to claim 1, which is a copolymer latex obtained by copolymerizing the remaining monomers.