JPH0160115B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to cast coated paper. More specifically, the present invention uses a zwitterionic synthetic polymer copolymer with specific properties to greatly reduce the amount of natural protein adhesives such as casein and soy protein used. This is about cast coated paper, which has completely disappeared. Prior Art Conventional methods for producing cast coated paper include, for example, US Pat. No. 1,719,166 and Japanese Patent Publication No. 38
The wet method described in Japanese Patent No. 25160 is known. In this wet method, a coating layer of a wet water-based coating liquid applied to the surface of a support is directly brought into close contact with the heated mirror-like surface of a metal drum under pressure without coagulating.
The coating layer is dried in this adhered state, and then the dried cast coated paper is peeled off from the specular surface. By the above operation, a mirror surface replica is formed on the coated surface of the cast coated paper. In the conventional wet method, it is necessary that the coating liquid contains a natural protein adhesive in order to smoothly peel off the coating layer from the mirror-like surface. However, even if a paint containing a natural protein adhesive is used, in this wet method, if the temperature of the surface of the cast drum exceeds 100°C, bumping of the paint will occur when the coating layer contacts the drum surface. Because of this, the surface of the cast drum is generally kept at 80 to 90°C, resulting in significant damage to the coated surface. Also, US Patent No. 2919205, Japanese Patent Publication No. 38
-15751 Publication and Special Publication No. 1972-7207,
A method for producing cast coated paper called a gelling method is disclosed. In this gelling method, a water-based paint is applied to the surface of a support to form a coating layer, and this is immersed in a coagulation bath consisting of an aqueous solution containing a coagulant such as an acid to coagulate the coating layer. This method involves pressurizing and adhering this coagulated coating layer to the mirror-like surface of a heated drum, drying it, and peeling off the dried cast coated paper from the drum surface, so the surface temperature of the cast drum was kept at 100°C. The above conditions can be set. The inclusion of a natural protein adhesive in the water-based coating is considered essential for good release of the coating layer from the cast drum. However, natural protein adhesives have problems such as being very expensive and having variable quality.Furthermore, due to their uniform dissolution,
Disadvantages include a large amount of thermal energy, a long time required, and the phenomenon of agglomerates often forming during the paint preparation process, the so-called casein shock phenomenon. Several proposals have been made to solve the problems of natural protein adhesives as described above. For example, JP-A-53-94367, JP-A-57-
16996, US Pat. No. 4,048,380, and US Pat. No. 4,109,056, etc., it has been proposed to use starch or a modified product thereof instead of a natural protein adhesive. Further, US Pat. No. 3,832,216 and US Pat. No. 4,024,313 propose the use of synthetic polymer copolymers as adhesives for coating layers. However, the adhesive proposed above is inferior to natural protein adhesives in terms of releasability of the coated layer containing it from the specular surface of the drum. Particularly on an industrial scale, when the coating layer is dried continuously over a long period of time, the coating layer containing the adhesive has the fatal disadvantage that a portion of it adheres to the mirror-like surface of the drum. ing. Furthermore, the above adhesives are inferior to natural protein adhesives in terms of product quality, such as water resistance, coating strength, and other properties, and therefore have not yet been put into practical use industrially. In view of the above-mentioned state of the art, the cast-coated paper industry is seeking an application for a cast-coated paper that reduces the amount of natural protein adhesive used, eliminates its drawbacks, and has better quality. It was strongly requested. OBJECTS OF THE INVENTION An object of the present invention is to provide a cast coated paper that can reduce or eliminate the amount of natural protein adhesive used, has good processability, and has excellent product quality. Structure of the Invention The cast coated paper of the present invention has a support and a coating layer containing an adhesive formed on the support. A cast coated paper obtained by pressurizing and adhering a layer of a coating liquid containing a coating liquid without coagulating or after coagulating to a mirror-finished surface of a metal drum and drying the coated paper, the coating layer comprising: It is characterized in that the adhesive therein contains at least one zwitterionic synthetic polymer copolymer latex having an isoelectric point of pH 3 to 7. DETAILED DESCRIPTION OF THE INVENTION The coating layer adhesive used in the cast coated paper of the present invention contains a zwitterionic synthetic polymer copolymer latex having specific properties. This copolymer has both an anionic functional group and a cationic functional group, and is described in, for example, JP-A-54-30910 and US Pat. No. 3,671,472.
It can be manufactured by the method described in the specification. The copolymer used in the present invention has an isoelectric point of PH 3 to 7, preferably 4 to 6, and exhibits anionic properties at a PH higher than the isoelectric point, and exhibits anionic properties at a PH lower than the isoelectric point. Shows cationic properties. The main copolymer components of the amphoteric copolymer mentioned above include 1,3-butadiene, 2-methyl-1,3
- Aliphatic conjugated diolefin monomers such as butadiene, and aromatic vinyl compounds such as styrene, α-methylstyrene, monochlorostyrene, vinyltoluene; methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, etc. Included are alkyl esters of acrylic acid and methacrylic acid; and monoolefinic monomers such as ethylenically unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile. Furthermore, as a copolymerization component of the amphoteric copolymer, in addition to the monoolefin monomer used as the main component, β-hydroxyethyl acrylate, β-hydroxypropyl acrylate, β-hydroxyethyl methacrylate, and acrylamide are used. , methacrylamide, N-methylolacrylamide, diacetone acrylamide, glycidyl acrylate, glycidyl methacrylate, acrolein, and allyl alcohol. The anionic copolymerization component of the amphoteric copolymer includes unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butenetricarboxylic acid; itaconic acid monoethyl ester , monoalkyl esters of unsaturated dicarboxylic acids such as fumaric acid monobutyl ester, and maleic acid monobutyl ester; Ethylenically unsaturated acid monomers, such as alkali salts thereof, can be used. In addition, as the cationic copolymerization component of the amphoteric copolymer, as an unsaturated amine, (In the formula, R ₁ is H or a methyl group, R ₂ is a C ₂ to C ₁₂ alkylene group, R ₃ and R ₄ are H or a C ₁ to ₁₂ alkyl group, and A is

【formula】

[Formula] or -O -), for example, methylaminoethyl (meth)acrylate,
of ethylenically unsaturated carboxylic acids such as t-butylaminoethyl (meth)acrylate, dimethyl-aminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and dibutylaminoethyl (meth)acrylate. Aminoalkyl esters; aminoalkylamides of ethylenically unsaturated carboxylic acids such as methylaminoethyl (meth)acrylamide, dimethylaminoethyl (meth)acrylamide, and dimethylaminopropyl (meth)acrylamide:
Aminoalkyl vinyl ethers such as aminoethyl vinyl ether, methylaminoethyl vinyl ether, dimethylaminoethyl vinyl ether, etc., and 2-vinylpyridine, 4-vinylpyridine,
Ethylenically unsaturated amines such as vinylpyridines such as 2-methyl-5-vinylpyridine and 2,4-diethyl-5-vinylpyridine can be used. However, the resulting copolymer has a pH of 3~
It is necessary to indicate an isoelectric point within the range of 7. Typical amphoteric copolymers used in the present invention include 20-50% by weight of aliphatic conjugated diolefin monomer, 0.5-20% by weight of ethylenically unsaturated acid monomer (anionic component), and ethylene-based There is a copolymer containing 0.5 to 20% by weight of an unsaturated amine monomer (cationic component) and 10 to 74% by weight of a monoolefin compound monomer. The ethylenically unsaturated acid monomer and ethylenically unsaturated amine monomer in the above-mentioned amphoteric copolymer serve as an anionic component and a cationic component, respectively, to improve the isoelectricity of the resulting amphoteric polymer latex. It is an essential ingredient for adjusting points. Both components are each 0.5 to 20% by weight, preferably 1 to 20% by weight.
The amount of each used is adjusted to give the resulting amphoteric copolymerizable latex a desired isoelectric point. The pH of the coating solution prepared using the amphoteric copolymer latex is preferably adjusted to 8 to 10, more preferably 8.5 to 9.5, and then applied to the surface of the support. When ammonia is used to adjust the pH of the above coating liquid, the ammonia volatilizes on the heating drum during the drying process of the coating layer using the wet method, and as the pH of the coating layer approaches its isoelectric point, the coating layer It hardens and peels the coating layer off the drum cast surface smoothly, giving excellent results. In addition, especially excellent results can be obtained when a coating liquid whose pH has been adjusted with ammonia is gelled in a coagulating liquid whose pH is in the acidic range. In the synthetic polymer copolymer latex used in the present invention, when its isoelectric point PH is on the acidic side lower than 3, in the wet method, the coating layer is In gelation or the gelation method, the gelation of the coating layer in an aqueous coagulation solution containing acids or inorganic salts does not proceed sufficiently, and therefore the peelability from the mirror-finished cast surface is also insufficient. Otherwise, good results cannot be obtained. Further, when the isoelectric point PH of the copolymer latex is higher than 7 and on the alkaline side, the dispersion state of the coating liquid components becomes unstable. In addition, if the pH of the paint liquid is lower than 8, the dispersion state of the paint liquid tends to become unstable;
If it is higher than 10, the coagulation performance of the coating liquid tends to be insufficient, so it is not preferable. The amphoteric copolymer latex used in the present invention has amphoteric ionic properties, so when the coating layer containing it is immersed in a coagulating solution in the acidic PH range and gelled, the copolymer has the property of a positive substance. Because it can electrostatically bond with pigment particles that have a negative surface charge, compared to ordinary anionic latex or nonionic latex,
A more effective welding point can be generated. In the present invention, clay, aluminum hydroxide, calcium carbonate, titanium oxide, barium sulfate, zinc oxide, satin white, plastic pigments, etc. can be used as pigments contained in the coating liquid. In addition, dispersants such as polyphosphates, sulfated castor oil, higher fatty acids or their salts,
A release agent such as a wax emulsion, an antifoaming agent such as tributyl phosphate, etc. can be added to the coating liquid as needed. The adhesive used in the coating layer of the cast coated paper of the present invention may consist only of one or more of the amphoteric copolymer latexes mentioned above, but may also be made of natural proteins, such as casein and/or soybean. There is absolutely no problem with the fact that it contains protein. EXAMPLES The present invention will be specifically explained below with reference to Examples, but the scope of the present invention is of course not limited to these. Unless otherwise specified, the blending ratios of coating components in the examples are expressed in parts by weight based on the total solid content. Example 1 Kaolinite clay for coating 76.8 parts, casein 4
(contains 5% ammonia based on casein),
16 parts of the following amphoteric copolymer latex, 1 part of polyphosphate dispersant, 2 parts of sulfated castor oil as a mold release agent, and 0.2 parts of tributyl phosphate as an antifoaming agent.
An aqueous coating solution with a concentration of 45% and a pH of 8.8 was prepared. The amphoteric copolymer latex of this example was

[Table] This product was produced by copolymerizing 50% carbonate with an isoelectric point of PH5.6 according to the method described in JP-A No. 54-30910.
% concentration (weight) latex emulsion. The above coating liquid was applied to the felt surface of base paper with a basis weight of 60 g/m ² at a coating weight of 22 g/m ² , and then 3
% formic acid aqueous solution to coagulate the coating liquid layer, and then the formed coating layer was pressed onto the chrome plating surface of a cast drum heated to 95°C and dried to a sheet moisture content of 5.5%. The above operation was carried out continuously over several hours, and the state of peeling of the coating layer from the cast drum was observed. the result,
The releasability of the coating layer was determined by the combination of 10 parts of casein and 10 parts of anionic styrene-butadiene latex (not showing amphoteric properties), despite the low casein content of 4 parts in the coating liquid. The result was exactly the same as when a coating liquid containing the same additives as described above was used. Moreover, no peeling sound indicating poor peeling was detected during peeling, and no coating pieces were observed to adhere to the drum surface. The resulting cast-coated paper has an excellent mirror surface, no surface defects, and a gloss level of 85%.
(75 degrees), showing excellent printability. On the other hand, as a comparative example, an anionic styrene-butadiene latex with no amphoteric properties was applied, and a cast paint with the same composition as above except for containing 4 parts of casein and 16 parts of latex was applied. A loud sound was made when the sheet was peeled off, a coating film was deposited on the drum surface, and numerous pinholes were generated on the surface of the resulting cast-coated paper. Example 2 An aqueous coating liquid having the same composition as in Example-1 except that it contained 79.8 parts of kaolinite clay for coating and 17 parts of the same zwitterionic latex as described in Example 1 and did not contain casein was used. Prepared. The pH of the paint was adjusted to 8.6 by adding ammonia, and the paint concentration at the time of application was 52%. The above coating liquid was applied at a coating weight of 23 g/m ² to the felt surface of base paper with a 60 g/m ² basis, and immersed in a coagulation bath consisting of a 10% calcium formate aqueous solution to form a coagulated coating layer. After that, the same casting process as in Example-1 was performed. As a result, although this cast coating layer did not contain casein, it had excellent releasability from the cast drum, and the obtained product had no surface defects. Cast coated paper with good blank paper quality and printing quality was obtained. On the other hand, as a comparative example, a cast paint liquid having the same composition as above was applied, except that a normal anionic styrene-butadiene latex having no isoelectric point was used instead of the amphoteric latex.
Significant paint film adhesion was observed on the surface of the cast drum.
It was not possible to continue processing. Example 3 Zwitterionic copolymer latex, anionic copolymer latex, and cationic copolymer latex having the following copolymer components and compositions were prepared as adhesives for cast paints by the method described in JP-A-54-30910. did.

[Table] Acid

[Table] Using these latexes, coating liquids were prepared in the same manner as in Example 2, and cast processing was performed under the same operating conditions. As a result, when using zwitterionic latexes (1), (2), and (3) with an isoelectric point PH of 3 to 7, the resulting coating layer was released from the cast drum. The cast-coated paper had excellent properties, had no surface defects, and had good blank paper quality and printing quality. When an amphoteric copolymer latex (4) with an isoelectric point PH exceeding 7 and a latex (5) and (6) without an isoelectric point were used as comparative examples, the resulting coating layer The mold releasability from the cast drum was poor, and a significant amount of paint film adhered to the drum surface, making it impossible to continue processing. Effects of the Invention According to the present invention, the use of expensive natural protein adhesives can be reduced or omitted, and cast-coated paper of excellent quality can be obtained using a coating liquid with excellent processability.

Claims (1)

[Scope of Claims] 1 Comprising a support and a coating layer containing an adhesive formed on the support, the coating layer being a layer of a coating liquid containing the adhesive coated on the support. In the cast coated paper obtained by pressurizing and adhering to the mirror-finished surface of a metal drum without coagulating or after coagulating and drying, the adhesive in the coating layer is PH3 A cast-coated paper comprising at least one zwitterionic synthetic polymer copolymer latex having an isoelectric point of ~7. 2. The cast coated paper according to claim 1, wherein the coating liquid has a pH adjusted to 8 to 10.