JPH0197298A - Coating composition for press processing - Google Patents

Abstract

PURPOSE: To obtain the subject composition, composed of, as the major ingredients, an aqueous resin dispersion having a glass transition temperature in a specific range and an inorganic filler, and excellent in gloss, smoothness, resistance to wear, adhesion, resistance to blocking, workability, suitability for corrugation and resistance to heat. CONSTITUTION: This composition contains, as the major ingredients, (A) an aqueous resin dispersion having a glass transition temperature of 60 to 130 deg.C, e.g. dispersion of acrylic acid, methacrylic acid or the like as the monomer which is emulsion-polymerized in the presence of ammonium persulfate or the like as the catalyst, and (B) an inorganic filler, e.g. powdered silica, quartz powder, alumina or the like, preferably at 0.5 to 3.0 wt.%.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a coating material for press working, which has particularly excellent gloss, smoothness, abrasion resistance, adhesion and blocking resistance, and workability, and which is suitable for corrugators. - It is an object of the present invention to provide a coating composition for press processing that has excellent suitability and heat resistance.

<Conventional technology> In recent years, in order to make printed matter more beautiful and more sophisticated, it has become common practice to apply a resin solution onto the printed surface, dry it, and then hot press it using a mirror plate to impart gloss. It is being done.

Traditionally, this type of press processing was mainly used for the production of book and Matsushi covers, calendars, and gift boxes.
In the field of corrugated cardboard as well, there is an increasing demand for decorative and high-grade corrugated cardboard, and the use of highly glossy decorative corrugated cardboard is expanding.

The press processing method involves applying a resin solution to the printed paper.
After drying, the surface liner is applied with a flat press or an endless press to give it gloss.
In the case of corrugated board after pasting together the core and back liner, undulations occur and press processing cannot be performed.

Therefore, if you want to obtain corrugated board with a high level of gloss, you can either attach pre-pressed printed matter to the corrugated board, or press the front liner printed matter and then use a corrugator machine to attach the center core and back liner. There was no choice but to use one of two methods: pasting it together.

However, in the former case, a special pasting machine is required because printed materials are pasted together by press processing on cardboard, and the problem of low work efficiency is expected; in the latter case, corrugator - Bonding temperature in the machine (usually done at 160-190°C)
or contact friction with a hot plate.

In conventional press processing, a mirror plate made of stainless steel or the like is layered on the resin surface obtained by applying it onto printing paper, and flat pressure pressing is performed, or hot printing is performed using an endless belt etc. that has been subjected to mirror finishing. By passing it between rollers,
Press processing is performed continuously to impart gloss, but the temperature at this time is usually in the range of 90 to 130°C, which is far lower than the corrugator bonding temperature mentioned above. , and a resin solution that softens within this temperature range was used.

Conventional coating materials for press processing include solvent-based vinyl chloride-vinyl acetate resins.
-12312, etc.), but due to work environment problems and fire hazards, recently it has been changed to water-based types, and water-based dispersions of acrylic or styrene copolymers or , a coating agent in which a water-soluble polymer of Ike was mixed (JP-A-50-148607, 51-
No. 82010, No. 51-82011), etc. are known. In addition to the above-mentioned resins, leveling agents, plasticizers, etc. are added to these coating materials as necessary to improve gloss, or release agents are added to facilitate peeling. Inorganic fillers such as silica
It was not used because it had a negative effect on improving gloss.

<Problems to be Solved by the Invention> A conventional water-based press coating is applied to the front liner of a pre-printed corrugated board, and after drying,
When using a front liner that has been pressed using a roll press and laminating it with the core and back liner using a corrugator machine, the lamination temperature is 160 to 190°C.
It has been found that there are problems in that the re-softened resin deteriorates the gloss and the re-softened resin stains the hot plate, significantly reducing the commercial value of the corrugated board. Therefore, conventional coating materials for press working cannot withstand the high heat of corrugator machines and the like.

As a countermeasure to this problem, it may be possible to improve the heat resistance of the corrugator machine by using a resin with a high softening point for the coating material, but in this case, the temperature of the press roller should also be raised accordingly. Not only that, but the high temperature during press processing causes the paper to shrink, causing paper to shift during cutting, deteriorating the strength of the paper, and even warping the sheets. This was a problem.

The present invention provides a coating for press processing that can be applied at conventional temperatures without raising the temperature during press processing to a particularly high temperature, and that does not cause problems such as reduction in gloss even when laminated using a corrugator machine. The purpose of the present invention is to provide a drug composition.

Means for Solving the Problems> The present inventors have developed a method that does not cause problems such as a decrease in gloss or staining of hot plates even if it is passed through the lamination process of a corrugator machine after imparting gloss through press working. As a result of extensive research into a coating composition for press processing suitable for producing highly glossy corrugated board, we have developed an aqueous resin dispersion with a glass transition temperature within a specific range, mixed with an inorganic filler in a specific range of proportions. We discovered that this method enables a high level of gloss to be imparted, and at the same time does not cause problems such as loss of gloss even when exposed to extreme conditions such as temperature, hot plate contact, and friction as in the above-mentioned lamination process. This led to the completion of the invention.

That is, the present invention has a glass transition temperature (Tg) of 60 to
It is an object of the present invention to provide a coating composition for press processing which contains an aqueous resin dispersion having a temperature range of 130°C and an inorganic filler as main components.

First, when obtaining an aqueous resin dispersion having a specific glass transition temperature to be used in the composition according to the present invention, consider the glass transition temperature of the vinyl monomer homopolymer shown below, and use the conventionally known approximate formula etc. By setting the polymerization ratio of each vinyl monomer based on the above, an aqueous resin dispersion having a desired glass transition temperature can be obtained. On the other hand, a so-called polymer blend, which is a mixture of an aqueous resin dispersion made of a polymer with a relatively high Tg and an aqueous resin dispersion made of a polymer with a relatively low Tg, can also be used to obtain an aqueous resin dispersion with a desired Tg. can be obtained. Examples of vinyl monomers that can be used to produce the aqueous resin dispersion according to the present invention include the following.

Vinyl monomers from which homopolymers with relatively high Tg can be obtained include acrylic vinyl monomers such as acrylic acid, methacrylic acid, methacrylate, and ethyl methacrylate, and styrene vinyl monomers such as styrene and α-methylstyrene. Examples of vinyl monomers with relatively low Tg include acrylic acid or methacrylic acid alkyl esters other than methyl methacrylate and ethyl methacrylate, such as methyl, ethyl, propyl, isopropyl, n-butyl, S-butyl, t-butyl, hexyl, Examples include esters having a linear or side chain alkyl group such as 2-ethylhexyl, decyl, and lauryl. In addition to the above-mentioned monomers, it is also possible to copolymerize other vinyl monomers, such as unsaturated monocarboxylic acids such as crotonic acid, itaconic acid, fumaric acid,
alpha, beta unsaturated dicarboxylic acids such as maleic acid, acrylamide derivatives containing at least one N-substituted methylol group such as N-methylol acrylamide, N-butoxymethyl acrylamide, ethylene glycol,
Mono- or diesters of acrylic acid or methacrylic acid of glycols such as diethylene glycol, propylene glycol, and dipropylene glycol, or monomers such as glycidyl ether of acrylic acid and methacrylic acid, acrylonitrile, vinyl chloride,
Examples include vinyl acetate, vinyl propionate, and vinylidene chloride.

Among these exemplified vinyl monomers, those whose main components are acrylic acid, methacrylic acid, or their alkyl esters, and styrene vinyl monomers are preferred.

To obtain an aqueous resin dispersion from these vinyl monomers, the above-mentioned polymers are stabilized by emulsion polymerization using a hydrophilic catalyst such as ammonium persulfate, potassium persulfate, hydrogen peroxide, or a redox catalyst using a generally known method. What is necessary is to disperse the emulsifier into a mixture, and if necessary, an emulsifier can be added.

As an emulsifier, a mixture of vinyl monomers can be copolymerized in an emulsified state in the presence of an anionic or nonionic surfactant, but in general, the use of low-molecular-weight surfactants is bad for the water resistance of the resulting film. Therefore, when water resistance is particularly required, polymeric anionic activators are suitable as emulsifiers.

The aqueous resin dispersion according to the present invention also has excellent performance by using the emulsifier. Such polymer emulsifiers include shellac, (meth)acrylic acid-based or maleic acid-based copolymers having carboxyl groups, etc.
Conventional aqueous solutions of alkali-soluble resins can be used.

Regarding the coating composition for press processing according to the present invention, it is necessary to use an aqueous resin dispersion having a relatively high glass transition temperature (60 to 130°C). As a dispersant used in this process, a relatively large amount of an aqueous solution of an alkali-soluble resin composed of a vinyl monomer that forms a homopolymer with a high glass transition temperature, such as acrylic acid, methacrylic acid, or styrene, is used, and other It is preferable to emulsion polymerize vinyl monomers.

As the alkali used for water-solubilizing the alkali-soluble resin, any known alkali can be used, such as ammonia, organic amines such as triethanolamine, monoethanolamine, etc. However, after drying the water-soluble resin, volatile High alkalinity is good.

Here, if the Tg of the obtained water-soluble resin dispersion is less than 60°C, the heat resistance will not be sufficient, and during lamination with a corrugator machine, gloss will decrease or hot plate stains will occur. C
Those with super gloss are 80 to 85
Say something at ℃. ) becomes difficult to obtain.

Examples of the inorganic filler which is the other essential component include silica powder, silica gel, quartz powder, alumina, glass powder, talc, clay, calcium carbonate, magnesium carbonate, zinc white, barium sulfate, etc. In the coating composition, 0.1 to 5.0% by weight, more preferably,
It is necessary to contain it in a range of 0.5 to 3.0% by weight. If the content of the inorganic filler is less than 0.1% by weight, the heat resistance will not be sufficient, and if it exceeds 5.0%, there will be a problem that high gloss cannot be obtained. It is something.

When producing the coating composition for press processing according to the present invention, the inorganic filler may be mixed into the aqueous resin dispersion, or finely dispersed using a conventional dispersion machine. It can be obtained by

In addition, the following additives can be added to the composition as necessary, and these additives include water-soluble face to assist in adhesion to the printed surface, acrylic resin, An aqueous solution of an alkali-soluble resin such as a rosin-modified maleic resin, a styrene-maleic resin, or shellac can be added. In addition, waxes such as polyethylene waxes are used to improve abrasion resistance, higher fatty acids such as stearic acid, higher alcohols such as cetyl alcohol, and surfactants such as phosphoric acid esters are used to improve peelability during press processing. Agents etc. can be used.

It is also possible to add colorants such as dyes and pigments as additives, making it possible to obtain a colored glossy film.

The material to which the press processing coating consisting of the above-mentioned components is applied may be liner paper used in normal corrugated board manufacturing, such as jute liner or K liner, but coated cardboard with excellent surface smoothness is preferable. , these are printed in roll format using flexo ink, planographic ink, gravure ink, etc., and are printed on the entire surface using means such as roll coating, curtain coating, spray coating, or gravure printing machine. Or apply it to the necessary areas. After application, it is dried and then glossed using a hot roller used for press processing.

The temperature of the hot roller should be between 90 and 130 degrees Celsius, and the pressure should be within the range of 90 to 130 degrees. 50~350 Kg/crr? It can be done with.

The front liner, which has been given a gloss by pressing, is installed on the mill stand for the front liner of a corrugator machine for manufacturing corrugated board, and is bonded to the core and back liner using the same method as before to achieve high gloss. It is possible to obtain corrugated cardboard having the following characteristics.

The glossy corrugated board bonded to the core and back liner is cut according to the printed pattern or the size of the corrugated board, and then subjected to necessary die-cutting and the like to be used as a corrugated box.

Hereinafter, the press working coating composition according to the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

<Example> Dispersion production example 1 Methacrylic acid, 53% by weight of lactic acid, methyl methacrylate 23%
Using an ammonia aqueous solution of an alkali-soluble resin containing 24% by weight of styrene as a dispersant, 34 parts by weight of styrene was added to 66 parts by weight of the resin content of the dispersant, and 4'AL polymerization was carried out in a conventional manner. Aqueous resin dispersion A is obtained. The obtained dispersion A has a solid content of 37% by weight and a glass transition temperature of the dispersion of about 125°C.

Dispersion Production Example 2 Same as Production Example 1, 36% by weight of methacrylic acid, 49% by weight of methyl methacrylate, 15% by weight of butyl acrylate.
Using an ammonia aqueous solution of an alkali-soluble resin consisting of as a dispersant, with respect to 60 parts by weight of the resin content of the dispersant,
Aqueous resin dispersion B is obtained by emulsion polymerization of 33 parts by weight of styrene and 7 parts by weight of butyl acrylate by a conventional method. The resulting dispersion A has a solid content of 39% by weight and a glass transition temperature of about 76°C.

Dispersion Production Example 3 As in Production Example 1, an ammonia aqueous solution of an alkali-soluble resin consisting of 28% by weight of methacrylic acid, 4% by weight of acrylic acid, 7% by weight of methacrylate, and 4% by weight of ethyl acrylate was used as a dispersant. It is a dispersion with a styrene transition temperature of about 89°C based on 12 parts by weight of the resin content of the dispersant.

Dispersion Production Example 4 Acrylic resin (Joncryl 67) is used as the alkali-soluble resin, and its alkaline aqueous solution is used as the dispersant. To 10 parts by weight of the resin component of the dispersant, 54 parts by weight of isobutyl methacrylate and 36 parts by weight of styrene are emulsion polymerized by a conventional method to obtain an aqueous resin dispersion.

The solids content of the dispersion is 40% by weight and the glass transition temperature is about 67°C.

Dispersion Production Example 5 An ammonia aqueous solution of an alkali-soluble resin consisting of 29% by weight of acrylic acid, 12% by weight of styrene, 56% by weight of α-methylstyrene, and 3% by weight of ethyldiglycol acrylate was used as a dispersant, and the resin content of the dispersant was Aqueous resin dispersion E is obtained by emulsion polymerization of 20 parts by weight of styrene and 50 parts by weight of 2-ethylhexyl acrylate with respect to 30 parts by weight. The obtained dispersion E had a solid content of 45 times,
It is a dispersion with a glass transition temperature of about 40°C.

Examples 1 to 10, Comparative Examples 1 to 5 Using dispersions A to E obtained in Dispersion Production Examples 1 to 5, Table-
A coating material for press processing is prepared based on the formulation shown in 1.

In addition, the numbers in the table indicate parts by weight, and as wax,
A phosphoric acid ester mold release agent is used as a mold release agent for polyethylene wax.

Evaluation Test Using a two-color printing machine for printing corrugated board liners, water-based flexographic ink was applied as the first color to Honshu Paper Industries' UF Manila paper (230 g/m'') for Examples 1 to 1O1 and Comparative Examples 1 to 5.
Continuous printing and application are performed using each coating material as the second color. After drying, use an endless press at a temperature of 130°C.
The gloss was imparted by pressing with a hot roller at a speed of 30 m/min under a pressure of 3007 cm'' and a speed of 30 m/min.The gloss after pressing was measured with a gloss meter, and the measured values were added to Table 1.

Using a glossy liner as the front liner, it is laminated with the core and back liner using a corrugator machine.
Manufactured from cardboard.

The obtained corrugated board is similarly measured using a crossmeter to measure the gloss ratio after pressing, that is, the degree of gloss reduction.

In addition, we visually judged the presence of surface scratches caused by the corrugator machine and the presence of hot plate stains, and also examined the presence or absence of blocking caused by stacking cut cardboard, and added the results to Table 1. Na.

Notes in Table-1 indicate the following.

Note 1 Thyroid 63 as silica gel
(manufactured by Fuji Davison).

Note 2: Snowtex N (manufactured by 8 San Kagaku Co., Ltd.) (solid content 20%) is used as colloidal silica.

Note 3: Shiroenka T- as calcium carbonate
DD (manufactured by Shiraishi Calcium Co., Ltd.) (charcoal calcium content 50%) is used.

Note 4: Gloss ratio indicates the value obtained by dividing the gloss value after passing through a corrugator machine by the gloss value after pressing.

Note 5 Regarding Comparative Examples 1.2.4, scratches occurred on the surface and gloss measurement could not be performed.

Effects> As shown in the Examples above, the coating composition for press processing according to the present invention does not cause any peeling and has a high It can be seen that the composition is suitable for producing glossy corrugated board.

On the other hand, it can be seen that conventional press working coatings are not suitable for corrugators and are unsuitable for corrugated board manufacturing.

Note that the corrugated board using the coating material for press processing according to the present invention is effective not only for imparting gloss but also for improving water resistance and strength of the corrugated board.

Applicant: Sakata Inx Co., Ltd.

Claims (4)

[Claims] (1) A coating composition for press processing whose main components are an aqueous resin dispersion and an inorganic filler having a glass transition temperature in the range of 60 to 130°C. (2) The coating composition for press working according to claim 1, which contains an inorganic filler in an amount of 0.1 to 5.0% by weight. (3) The aqueous resin dispersion contains an acrylic vinyl monomer,
The coating composition for press processing according to claim 1, which is an aqueous resin dispersion obtained by emulsion polymerization, which contains a vinyl monomer selected from styrenic vinyl monomers as a main component. (4) The aqueous resin dispersion is an aqueous resin dispersion obtained by emulsion polymerization using a water-soluble acrylic resin or a water-soluble styrene-acrylic resin as an emulsifier and containing a vinyl monomer selected from acrylic vinyl monomers and styrene-based vinyl monomers as the main component. The coating composition for press processing according to claim 3, which is a resin dispersion.