JPS6039800B2 - How to give paper surface gloss - Google Patents

Description

[Detailed Description of the Invention] Nowadays, cosmetic cases, covers of books and matches, calendars, etc. are coated with a resin solution over the printed surface, dried, and then hot-pressed using a mirror plate to give gloss and deluxe appearance. It is widely practiced to give a sense of feeling.

In the past, vinyl chloride-vinyl acetate copolymer was mainly used as a resin for such coatings, but since this resin is soft, although it is suitable for batch processing, it is not suitable for continuous pressing using an endless stainless steel belt. The drawback is that peeling from the belt surface is not smooth, and in recent years, acrylic copolymers, which are resins with higher glass transition points, have been used in continuous methods.
However, since the above-mentioned resins are used as a solvent solution in the work process, they can harm the health of workers due to the solvent scattering, pose a fire risk, and become a source of pollution when mixed into wastewater. This is a situation where it is becoming legally regulated. The present inventors thought that the above problems could be solved by processing paper using an aqueous dispersion of an acrylic copolymer, but in reality, an aqueous dispersion of an acrylic copolymer was applied to paper. This causes cracks, making it difficult to obtain a uniform coating, and even if it appears to be applied evenly, the adhesion is so poor that it peels off as soon as you rub your fingers or nails on the coating. Therefore, it was not something that could be put to practical use at all.

However, as a result of further studies, the present inventors found that polyvinyl alcohol was added to an aqueous dispersion of a polymer that contains an alkyl methacrylate having an alkyl group of 2 to 4 carbon atoms as an essential component and does not contain either methyl methacrylate or styrene. When applying a mixture of resins in a specific ratio to printing paper, a uniform coating with great adhesion can be obtained, and if the coated surface is hot-pressed using a mirror plate, it can be coated with an extremely beautiful gloss. The present inventors have discovered that a processed paper rich in oxidation can be obtained, and that the adhesion of the coating film to the substrate is so strong that it causes delamination between the paper layers in a peel test using an adhesive tape, leading to the completion of the present invention.

Since the present invention is water-based, the pollution problem caused by the brightness of the solvent, which has been a problem in the past, is completely solved. In the present invention, an aqueous dispersion of a polymer containing an alkyl methacrylate having an alkyl group of 2 to 4 carbon atoms as an essential component and containing neither methyl methacrylate nor styrene is used. Examples of such alkyl groups include ethyl group, n-propyl group, isopropyl group, n-butyl group, n-isobutyl group, and t-butyl group. It is preferable that the content of the alkyl methacrylate ester accounts for 5% by weight or more of the polymer; if it is less than 5% by weight, the softening temperature of the polymer will decrease and the peelability between the mirror plate and the mirror plate during hot pressing will be poor, and the specific The surface gloss becomes difficult to obtain. In addition to the above-described alkyl taacrylate esters, the polymer may also contain acrylic esters, other methacrylic esters, acrylonitrile, methacrylonitrile, vinyl chloride, vinyl acetate, and the like. However, in this application, methyl methacrylate and/or styrene are not included as constituents of the polymer. Regarding the case containing these comonomer components, it has already been reported in Tsubakiren Sho 49-5762.
This is because the application is filed as No. 7. Such polymers can be used as aqueous dispersions. The resin concentration in the dispersion can vary widely depending on the purpose, but is usually selected from a range of about 20 to 6% by weight. As the polyvinyl alcohol resin, resins having a wide range of compositions can be used regardless of their degree of polymerization and degree of saponification, such as those having a degree of polymerization of about 200 to 3000 and a degree of saponification of about 75 mol % or more.

However, in general, those with an extremely high degree of polymerization or those with an extremely low degree of saponification are limited in terms of solubility in water. Note that the polyvinyl alcohol resin mentioned here is not limited to saponified homopolymers of vinyl acetate, but also contains vinyl acetate as its main component, with small amounts of other copolymerizable monomers, such as ethylene, propylene, crotonic acid, and acrylic acid. , methacrylic acid, maleic acid, or saponified copolymers with esters of these unsaturated acids. It also includes modified products in which polyvinyl alcohol is partially acetalized with formaldehyde, acetaldehyde, butyraldehyde, etc., and modified products in which polyvinyl alcohol is converted into urethane, within a range that does not impede water solubility.
The polyvinyl alcohol resin is mixed with the aqueous dispersion of the above polymer in the form of a powder or an aqueous solution.

In the present invention, the blending ratio of polyvinyl alcohol resin is 5 to 5 parts by weight for 10 parts by weight of resin in the aqueous dispersion.
It must be within the range of 20 parts by weight.

If the blending amount of the polyvinyl alcohol resin is less than 5 parts by weight, the coating will lack uniformity, such as cracking when applied to a substrate, and will also lack adhesion. On the other hand, if the amount of the polyvinyl alcohol resin exceeds 20 parts by weight, the surface gloss and adhesion to the substrate will be insufficient, and sufficient water resistance will not be obtained even when a crosslinking agent described below is used in combination. Here, if the amount of polyvinyl alcohol resin blended is relatively large within the above range (approximately 20 to 3 anchor parts or more), there is an advantage that film formation progresses more smoothly, but on the other hand, water resistance is slightly impaired. It may happen.

Therefore, when used in applications that require particularly water resistance,
It has been found that if a crosslinking agent for polyvinyl alcohol resin is further added to the mixture consisting of the aqueous dispersion of the above polymer and polyvinyl alcohol resin, sufficient satisfaction can be obtained in terms of water resistance. Such crosslinking agents are water-soluble or water-friendly and have a crosslinking effect on polyvinyl alcohol resins, examples of which include urea,
Examples include methylol compounds such as melamine, and compounds containing two or more glycidyl groups, N-methylol groups, carboxyl groups, or isocyanate groups in the molecule. The amount of crosslinking agent to be used varies depending on the type of crosslinking agent and the degree of water resistance desired, so it cannot be determined unconditionally, but it is usually about 8% by weight or less based on the polyvinyl alcohol resin, especially 5% by weight or less based on the polyvinyl alcohol resin. It is often set at about 5% by weight.

The composition thus obtained is in a state intermediate between an aqueous dispersion and an aqueous solution.

In addition, known additives such as organic solvent-based staining agents such as ethanol and isopropanol, dyes, and plasticizers may be added to the above composition as required.

As the application method, any method such as roll coating, brush coating, curtain flow coating, spray coating, doctor coating, etc. can be employed.

After application, it is dried, but that alone will reduce the luster, so hot pressing is also performed.

For hot pressing, mirror plates made of stainless steel, aluminum, etc. are layered on the resin surface obtained by coating on printing paper, and an appropriate number of plates are piled up alternately and hot pressed at about 70 to 15,000 yen, or mirror plates are Hot in the form of an endless belt. It is possible to perform continuous processing by passing the material between the rollers. Next, the method of the present invention will be further explained with reference to Examples.

In the following, "parts" and "%" are based on weight unless otherwise specified. Example 1 90% ethyl methacrylate and 10% butyl acrylate
% copolymer emulsion (resin content 50
%) 1 part 1 Copolymerization degree 500 Add 5 parts of a 20% aqueous solution of polypynyl alcohol with a saponification degree of 97 mol% and 1 part of isopropanol, mix well, and apply this to a thick layer using a hand applicator. 0.5 sails printed on cardboard 12
It was coated with a powder coater (solid content) and dried with hot air at 100°C.

The film formation was uniform and did not peel off even when rubbed with a fingernail. Next, the coated paper was placed on a stainless steel mirror plate and heated to a temperature of 80°C.
00, and hot pressed for 1 minute at a pressure of 200 k9/. The peeling of the paper from the mirror plate after hot pressing proceeded extremely smoothly, and there were no problems even during the continuous hot pressing of 10 years. The decorative paper thus obtained was highly glossy, and in an adhesive tape peel test in which an adhesive tape was attached to the surface and then vigorously peeled off, the adhesiveness was so great that the paper layer, which was the base material, was broken.

On the other hand, as a control example, when coating was carried out in the same manner as in Example 1 except that only the aqueous polyvinyl alcohol solution was not added, cracks appeared and the film formation itself was not uniform, and the coated surface could be easily rubbed with a finger. The paper peeled off, the gloss was significantly inferior even after hot pressing, and in the adhesive tape test, it peeled between the paper and the resin film surface, making it completely unusable.

Example 2 To the mixture of the emulsion of ethyl methacrylate-butyl acrylate copolymer, polyvinyl alcohol aqueous solution and isopropanol in Example 1, a trimethylolmelamine crosslinking agent (Sumitex M-3,
A mixture prepared by Sumitomo Chemical Co., Ltd.) was coated on printing paper using the same machine as in Example 1, dried and hot pressed, resulting in good gloss and adhesion as well as high water resistance.

Example 3 Emulsion of polybutyl methacrylate (50% concentration)
10 parts of a 20% aqueous solution of polyvinyl alcohol with a degree of polymerization of 500 and a total degree of saponification of mol %, 9 parts of an ethylene glycol diglycidyl ether crosslinking agent (Eporite 4 trays, manufactured by Kyoeisha Yushi Kagaku Kogyo Co., Ltd.) and A mixture of 1 part sopropanol and 1 part sopropanol was coated on printing paper, dried and hot pressed in the same manner as in Example 1, and the paper had good releasability from the mirror plate, gloss, adhesion, and water resistance.

Example 4 60% ethyl methacrylate and 40% methyl acrylate
Emulsion of copolymer with composition (50% concentration)
A mixture consisting of 100 parts of a 10% aqueous solution of polyvinyl alcohol with a degree of polymerization of 1,400 and a degree of saponification of 96 mol %, consisting of 10 parts of polyvinyl alcohol and 1 part of isopropanol was applied to printing paper using the same machine as in Example 1, dried, and hot pressed. The resulting product had good releasability, gloss, adhesion, and water resistance from the mirror plate.

Example 5 10 parts of an emulsion (50% concentration) of a copolymer having a composition of 70% butyl methacrylate and 30% vinyl acetate, and 25 parts of a 20% aqueous solution of polyvinyl alcohol with a degree of polymerization of 80% and a degree of resaponification of 98% by mole. The mixture was applied to printing paper in the same manner as in Example 1, dried, and hot-pressed, and the product had good releasability from the mirror plate, gloss, adhesion, and water resistance.

Control Example A mixture consisting of 10 parts of the butyl methacrylate-vinyl acetate copolymer emulsion used in Example 5, 600 parts of the polyvinyl alcohol aqueous solution used in Example 5, 4 parts of Eporite and 3 parts of isopropanol. When used, the peelability from the mirror plate was good, but the gloss, adhesion and water resistance were poor.

Claims (1)

[Claims] 1. A polyvinyl alcohol resin is mixed with an aqueous dispersion of a polymer containing an alkyl methacrylate having an alkyl group of 2 to 4 carbon atoms as an essential component and containing neither methyl methacrylate nor styrene, and at this time, in the aqueous dispersion. The blending amount of the polyvinyl alcohol resin is selected to be 5 to 200 parts by weight based on 100 parts by weight of the polymer, and then the mixture is applied to printing paper and dried, and then hot pressed using a mirror plate. A method for imparting surface gloss to paper.