JPS6353320B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel paper coating liquid base composition that provides gravure printing paper with good printability. More specifically, the present invention provides copolymer layers with two or more different compositions prepared by sequentially polymerizing specific heterolayer structure copolymers, that is, monomer mixtures with different components or mixing ratios. The present invention relates to a coating liquid base composition for gravure printing paper, which is made of a latex containing a granular copolymer having the following properties and has excellent gravure halftone reproducibility. In recent years, with the rapid increase in the number of printed materials, the number of gravure printed materials such as gravure magazines has also increased.The most important physical property required of this gravure printing paper is that the halftone dots of the printing plate can be accurately restored on the printed paper. , that is, excellent gravure halftone reproducibility,
The printing paper has excellent printing gloss. If the printing gloss is high, the aesthetic appearance of the printed matter will improve, and as a result, the commercial value of the printed matter can be significantly increased. In order to increase this printing gloss, it is known that using Sachin White as part of the pigment and increasing the amount of adhesive are effective. Lines appear on the surface of the paper, so-called streaks, which deteriorate the quality of the printing paper, and when the amount of adhesive is increased,
Printing gloss is improved, but gravure halftone reproducibility is inevitably reduced. Next, in order to improve gravure halftone dot reproducibility, strict control of supercalender conditions is carried out to improve smoothness. However, the stiffness, which is one of the physical properties required for printing paper, decreases, resulting in the disadvantage that the so-called stiffness of coated paper becomes weak. On the other hand, as a copolymer latex that can provide excellent water resistance and adhesive strength when used in coated paper, the styrene-butadiene copolymer or styrene-butadiene-olefinic unsaturated compound obtained in the first stage polymerization is used. A heterolayer structure copolymer latex obtained by polymerizing a small amount of an ethylenically unsaturated monocarboxylic acid, an ethylenically monocarboxylic acid ester, or an N-substituted ethylenically unsaturated amide in the second stage polymerization of the copolymer is obtained. Although it has been proposed (Special Public Interest Publication 1973
38924), the coated paper obtained from this is suitable for offset printing, and for gravure printing, it does not necessarily give sufficiently satisfactory results in terms of gravure halftone reproducibility and printing gloss. isn't it. In addition, in the first stage polymerization, a monomer composition consisting of styrene, butadiene, acrylonitrile, and α,β-ethylenically unsaturated carboxylic acid was added to the second stage polymerization.
In step polymerization, a monomer composition consisting of styrene, butadiene and acrylic ester, or a mixture of two or more thereof, a neutral ethylenically unsaturated monomer and an α,β-ethylenically unsaturated carboxylic acid,
By polymerizing the former and the latter in a ratio of 5:95 to 25:75, a heterolayer structure copolymer latex containing stable large particles and irregularly shaped particles is produced. It is also known (Special Publication No. 47-36024). However, the latex obtained by this method contains large particles with an average particle size of 0.2 to 0.6μ, and is not necessarily suitable for coated paper.
When applied to gravure printing paper, it has the disadvantages of low printing gloss, adhesive strength, and gravure halftone reproducibility. Therefore, until now, no paper has been realized in which printing gloss and gravure halftone reproducibility are sufficiently improved without impairing physical properties desirable for gravure printing paper. The inventors of the present invention have conducted extensive research in order to develop a gravure printing paper with improved print gloss and gravure halftone dot reproducibility without undesirable phenomena such as the occurrence of streaks or a decrease in stiffness. We have discovered that this objective can be achieved by using a heterolayer structure copolymer latex with a composition of He came up with an invention. That is, the present invention provides a secondary transition temperature of 60°C or higher obtained by emulsion polymerization of two or more monomers selected from ethylenically unsaturated carboxylic acids, their esters, and styrene monomers. At least one monomer selected from ethylenically unsaturated carboxylic acids, their esters, and styrene monomers and aliphatic conjugated diolefin monomers are added to the aqueous dispersion of the copolymer (A) having Adding a monomer mixture (B) containing A and B as essential components at a weight ratio of (A) and (B) in the range of 3:7 to 7:3, and further emulsion polymerization. The present invention provides a coating liquid base composition for gravure printing paper comprising a latex containing a different layer structure copolymer with a minimum film forming temperature of 25° C. or less and an average particle size of 0.1 to 0.27μ, prepared by be. In the production of a copolymer latex with a different layer structure in the present invention, for example, a copolymer latex with a secondary transition temperature of 60°C or higher is formed by an emulsion polymerization method, and when the polymerization rate exceeds 90% in the polymerization reaction. ,
This is carried out by adding a monomer mixture having a different composition and then polymerizing another copolymer on top of the above copolymer by emulsion polymerization. In this emulsion polymerization method, an anionic emulsifier is usually used as the emulsifier, but a nonionic emulsifier can be used alone or in combination with an anionic emulsifier. Examples of such emulsifiers include higher alcohol sulfate ester salts, alkyl sulfonate salts, and fatty acid esters of polyethylene glycol or polypropylene glycol. As the catalyst, inorganic peroxides such as persulfate and hydrogen peroxide, or organic peroxides such as benzoyl peroxide and cumene hydroperoxide are used. Furthermore, so-called redox catalysts in which a peroxide and a reducing agent are combined can also be used. Further, if necessary, mercabutanes, halogenated hydrocarbons, etc. can also be used as a chain transfer agent according to a conventional method. The polymerization temperature of this emulsion polymerization is usually 60°C to 90°C, and batch, semi-batch and continuous polymerization methods are possible. A copolymer having a secondary transition temperature of 60°C or higher formed by the first stage emulsion polymerization in the present invention
Ethylenically unsaturated carboxylic acids used in (A) include acrylic acid, methacrylic acid, maleic acid,
Examples of esters of itaconic acid and fumaric acid include methyl ester, ethyl ester, propyl ester, butyl ester, hexyl ester, and 2-ethylhexyl ester. In addition, styrene monomers include styrene,
α-methylstyrene, 4-methylstyrene, 2-
Hydroxymethylstyrene, 4-ethylstyrene, 4-ethoxystyrene, 3,4-dimethylstyrene, 2-chlorostyrene, 3-chlorostyrene, 4-chloro-3-methylstyrene, divinylbenzene, 2,4-dichlorostyrene, etc. There is. Next, in the second stage of emulsion polymerization, an aliphatic conjugated diolefin monomer is added together with at least one monomer selected from the above ethylenically unsaturated carboxylic acids, their esters, and styrene monomers. Examples include 1,3-butadiene, 2-chloro-1,3-butadiene, 2-
Examples include methyl-1,3-butadiene and 2,3-dimethyl-1,3-butadiene. Suitable monomer combinations for this second stage emulsion polymerization include styrene-butadiene, butadiene-
Methyl methacrylate, butadiene-styrene-
Methyl methacrylate mixture or acrylic acid, methacrylic acid, maleic acid,
It is a mixture containing itaconic acid, fumaric acid, etc. Such a monomer mixture may optionally contain further monomers such as ethylene, propylene,
Vinyl acetate and the like can also be included. If the secondary transition temperature of the pre-emulsion-polymerized copolymer of the present invention is less than 60°C, printing paper with high printing gloss cannot be obtained. Further, the weight ratio of the preformed copolymer to the copolymer layered thereon must be in the range of 3:7 to 7:3. If the amount of the pre-formed copolymer is less than the above lower limit, not only will a high level of printing gloss not be achieved, but the gravure halftone reproducibility will also deteriorate. Moreover, if it exceeds the upper limit, the adhesive force of the different layer structure copolymer latex will be significantly reduced. On the other hand, the minimum film-forming temperature of this heterolayer structure copolymer latex must be 25°C or lower. The minimum film forming temperature here refers to the lowest temperature at which continuous film formation is possible. If this temperature exceeds 25°C, the adhesive strength will be insufficient. Furthermore, the average particle size of this latex is 0.1~
It needs to be 0.27μ. Average particle size is 0.27
If it becomes larger, not only the adhesive strength tends to decrease, but also the printing gloss, which is one of the features of the present invention, decreases considerably. Furthermore, the viscosity of the coating composition has poor rheological properties under high shear stress, causing problems such as streaks on the coated surface during blade coating. On the other hand, if it is smaller than 0.1μ, it is not preferable in terms of the stability of the latex, and moreover, it is difficult to obtain the high level of print gloss that is the object of the present invention, and the opacity decreases. This average particle size can be adjusted by selecting the amount of seed latex used and the type and amount of surfactant used in combination. The coating liquid base made of the heterolayer structure copolymer latex of the present invention contains, as at least a part of the adhesive,
It is usually added in an amount of 7 to 30 parts by weight based on 100 parts by weight of the total mineral pigment in the coating liquid for gravure printing paper. In this case, if it is less than 7 parts by weight, the adhesive strength tends to be insufficient, and if it exceeds 30 parts by weight,
A so-called blocking phenomenon occurs in which coated surfaces adhere to each other. The coating base composition of the present invention can also be used in combination with other adhesive components. Such adhesives include natural adhesives such as raw starch, modified starch, soy protein, milk casein, and the like. It can also be mixed with ordinary polymer latexes used for paper coating, such as styrene-butadiene latexes containing carboxylated modifications, methyl methacrylate-butadiene latexes, vinyl acetate emulsions, and acrylic ester emulsions. be. In addition, various auxiliary agents such as a dispersant, a preservative, a dye, an antifoaming agent, and a mold release agent may be added to the coating liquid as desired. The coating liquid base composition of the present invention is prepared by mixing it with the necessary components and then applying it on a machine usually equipped with a coating device such as an air knife coater, blade coater, roll coater, plush coater, bar coater, or size press coater. Alternatively, it is coated in a single layer or in multiple layers on base paper using an off-machine coater.
The coating amount is suitably in the range of 3 to 18 g/m ² (one side) in terms of dry weight, and it is possible to coat both one side and both sides. Next, the present invention will be explained in more detail based on examples. Note that parts and percentages shown in the examples are based on weight, unless otherwise specified. Example: Initially, 70 ml of water was added to a reaction vessel purged with nitrogen gas.
parts, sodium dodecylbenzenesulfonate 0.1
parts, 0.2 parts of sodium hydroxide and potassium persulfate
Add 0.3 parts of styrene component with an average particle size of 0.03μ.
0.26 part of styrene-acrylic acid copolymer latex consisting of 96% acrylic acid component and 4% acrylic acid component and 20% styrene.
1 part, 21 parts of methyl methacrylate, and 2 parts of acrylic acid were reacted at 80°C for 3 hours, and when the polymerization rate reached 90%, 28 parts of styrene, 28 parts of butadiene, 1 part of itaconic acid, 1 part of dodecyl mercaptan, and hydroxide were added. Add 0.2 parts of sodium, 0.3 parts of potassium persulfate, and 0.3 parts of sodium dodecylbenzenesulfonate to 80
The reaction was carried out at ℃ for 4 hours. The copolymer latex thus obtained was PH-PHENED with sodium hydroxide.
Adjusted to 8.0. As a comparative experiment, samples A to F shown in Table 1 were polymerized in the same manner as above, and these latexes were also PH-treated with sodium hydroxide.
Adjusted to 8.0. Furthermore, a single-layer copolymer latex having the same composition as in the example was prepared and designated as G. The above is summarized in Table 1.

【table】

[Table] * Copolymer (A) was dried and the resulting sample was measured using a thermal dilatometer.
** Measured by temperature gradient plate method.
Using the latex obtained in the above Examples and Comparative Examples A to G and the Comparative Example 6 of Japanese Patent Publication No. 47-36024, a coating liquid was prepared according to the formulation described below, and its performance was tested. Ivy. First, 80 parts of clay [Ultracoat (trade name), manufactured by Engelhard Minerals and Chemicals], light calcium carbonate [PZ (trade name),
Add 20 parts of Shiraishi Kogyo Co., Ltd., 0.2 parts of a dispersant [Aron T-40 (trade name), manufactured by Toagosei Co., Ltd.] and a predetermined amount of water to uniformly disperse the various latexes listed above.
% and further oxidized starch [Oji Ace B
(Product name), Oji Cornstarch Co., Ltd.] 5 parts,
A coating liquid with a solid content of 60% by weight was produced. These coating solutions are applied to medium base paper with a basis weight of 60 g/m ² and a solid content of 10 g/m ^{2 .}
(One side) was applied with a wire bar, and immediately after application, it was placed in a hot air dryer for 60 seconds at 105°C.
%RH) for 24 hours. Table 2 shows the results of a quality test performed on this sample. The results show that the coating compositions of Examples provide satisfactory gravure printing paper with excellent opacity and printing gloss, and excellent gravure halftone reproducibility. It can also be seen that the adhesive force is also good.

【table】

[Table] As can be seen from Tables 1 and 2, Comparative Example A
is a copolymer latex with a different layer structure that has a second-order transition temperature of 60°C or less, and has poor white paper gloss, printing gloss, and adhesive strength. Comparative Example B is a copolymer latex with a different layer structure having a minimum film forming temperature of 25° C. or higher, and is particularly poor in printing gloss and adhesive strength. Comparative Example C is a copolymer latex with a different layer structure having an average particle size of 0.1 μm or less, and is inferior in white paper gloss, print gloss, opacity, and gravure halftone dot reproducibility. Comparative example D
In this case, the content of the (A) portion of the different layer structure copolymer latex is 30% by weight or less, and the print gloss and gravure halftone dot reproducibility are poor. In Comparative Example E, the portion (A) of the different layer structure copolymer latex was 70% by weight or more, and the print gloss, gravure halftone reproducibility, and adhesive strength were poor. Comparative example F
is a different layer structure copolymer latex with an average particle size of 0.27μ or more, and has poor printing gloss and adhesive strength.
Comparative Example G is a single-layer latex, and is inferior in white paper gloss, printing gloss, gravure halftone reproducibility, and adhesive strength. Finally, Example 6 of Japanese Patent Publication No. 47-36024 not only has poor adhesive strength, but also poor white paper gloss and print gloss. In any case, single-layer structure and heterolayer structure copolymer latexes other than those of the present invention have many drawbacks. The gravure printing paper obtained using the coating liquid base composition using the heterolayer structure copolymer latex of the present invention has good gravure halftone reproducibility and good printing gloss. Furthermore, the coated paper has excellent opacity, making it very useful industrially.

Claims (1)

[Claims] 1 Obtained by emulsion polymerization of two or more monomers selected from ethylenically unsaturated carboxylic acids, their esters, and styrene monomers. At least one monomer selected from ethylenically unsaturated carboxylic acids, their esters, and styrene monomers is added to the aqueous dispersion of the copolymer (A) having a second-order transition temperature of 60°C or higher. and an aliphatic conjugated diolefin monomer as essential components (B)
is added in a weight ratio of (A) and (B) in the range of 3:7 to 7:3, and further emulsion polymerization is carried out. A coating liquid base composition for gravure printing comprising a latex containing a copolymer with a different layer structure having a particle size of 0.1 to 0.27μ.