JPS62215091A - Production of coated paper for double-surface printing - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing coated paper for printing, and particularly to a method for producing coated paper for double-sided printing having a cast coat layer on at least one side.

(Prior art) Manufacturing methods for highly glossy coated paper for printing called cast coated paper include the wet casting method, in which a wet coating layer is pressed against a heating drum surface having a mirror surface to give a glossy finish, and the wet coating method. A gel casting method in which the coated layer is brought into a gel state and brought into contact with the heated drum surface for a glossy finish.After the wet coated layer is once dried, it is plasticized with a re-wetting liquid and then pressed against the heated drum surface. A rewet cast method is known.

All of these methods share the same principle in that the coating layer, which is mainly composed of mineral pigments and adhesives, is pressed against a heated finished surface while it is in a plastic state due to water content, and is then dried. It is something to do.

Most of the cast-coated Gio produced according to these manufacturing methods are so-called single-sided cast-coated Gio, which has a highly glossy cast finish on one side and a high-quality paper-like surface on the other side. When printability is required, a pigment coating layer with good ink receptivity, retention, and plate reproducibility is provided on the back side. In this case, the basic method of cast finishing as described above is not changed; instead, a pigment coating layer is provided on the back side of the base paper, and if necessary, this is smoothed by calendering. While the pigment coating layer on the surface of the base paper contains water and is in a plastic state, it is pressed against the heated and finished surface and dried. In some cases, the cast coated paper thus obtained may be further subjected to super calendering.

In the conventional method of producing cast coated paper having a pigment coating layer on the back side as described above, the moisture in the wet pigment coating layer in contact with the heated finished surface passes through the base paper layer and evaporates and evaporates to the back side. However, in this case, the pigment coating layer on the back side blocks the evaporation of water, so a significant decrease in operating speed cannot be avoided.

In addition, the pigment coating layer on the back side swells and softens due to the rapid evaporation of water, resulting in a decrease in smoothness and gloss, so results are not always satisfactory for purposes that require a high degree of printability. It doesn't bring.

This tendency is particularly noticeable when the pigment coating layer on the back side lacks water resistance. This decrease in smoothness and gloss of the pigment coating layer on the back side can be recovered to some extent by calendering after finishing the cast. This method is not necessarily recommended because the advantages of high stiffness and low tensile strength unique to coated paper are lost.

Furthermore, the above is the same when producing double-sided cast coated paper, and when finishing the cast afterwards, water passes through the already finished cast coat layer on one side and evaporates. As a result, the cast surface swells and softens due to the passing moisture, resulting in a significant decrease in smoothness and gloss, resulting in a large difference in quality between the two surfaces. In order to improve these shortcomings, methods have been proposed to increase moisture permeability by using special adhesives in the coating layer or by applying corona discharge treatment to the base paper. At present, satisfactory improvement effects are not necessarily obtained.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for producing a coated paper for printing that does not reduce the quality characteristics of both sides of the coated paper that has a cast coat layer on at least one side. The purpose is to

(Means for Solving the Problem) As a result of intensive studies to achieve the above object, the present inventors have established a technique for producing coated paper for double-sided printing having the following configuration. That is, the present invention heat-melts a cast coated paper and a coated paper for printing using a bonding agent made of a thermoplastic polymer having a softening point of 180° C. or lower so that at least one side has a cast coat layer. It is characterized by this.

The bonding agent made of thermoplastic polymer used in the above configuration has a Vicat softening point of 180°C or less (ASTM
D-1525-707) is a thermoplastic polymer.

The type of thermoplastic polymer is not particularly limited as long as the Vicat softening point is 180°C or less, but from the viewpoint of bonding strength and ease of handling, ethylene resin, propylene resin, styrene resin, vinyl chloride, etc. Resin, vinylidene chloride resin, ethylene/vinyl acetate copolymer resin, butyral resin, ester resin, polyamide resin, acrylic resin, nitrile resin, butadiene resin, halogenated rubber, urethane resin, cellulose resin, gelatin or Copolymers of monomers constituting these resins are used in solid, sol, or gel states.

Among them, low-density polyethylene, atactic polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-isobutyl acrylate copolymer , vinyl acetate-crotonic acid copolymer, vinyl acetate-phthalic anhydride copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butadiene-styrene block copolymer Soc copolymer, nylon-12, terephthalic acid-1.4-butanediol copolymer, etc. are more preferably used because sheets can be joined without deteriorating the quality characteristics as coated paper for printing. It is of course possible to use such thermoplastic polymers alone or in combination of two or more.

In addition, tackifiers, liquid or solid plasticizers, softeners, organic solvents, water,
Various auxiliary agents such as petroleum resins, pigments, fillers, metal compounds, crosslinking agents, waxes, surfactants, antioxidants, ultraviolet absorbers, and anti-aging agents can also be included in the bonding agent.

The reason why the thermoplastic polymers used in the present invention are limited to those with a Vikaft softening point of 180°C or lower is that when the temperature exceeds 180°C, small bumps occur on the surface of the printing coating layer.
This is because the quality characteristics as a coated paper for printing will be impaired. In particular, the occurrence of such irregularities on the surface of the cast coat layer has a fatal negative effect on the quality of the cast coat paper, which is characterized by high smoothness and high gloss.

Furthermore, the reason why water-soluble or solvent-based binders are not included in the binders used in the present invention is that water or organic solvents of these binders pass through the coating layer and evaporate when drying. This is because the coating layer swells and softens, resulting in a decrease in smoothness and gloss.

Therefore, cast coated paper and other coated papers for printing are bonded together by heat melting, but other coated papers for printing here are cast coated paper, art paper, coated paper, synthetic paper, etc. This refers to coated paper for printing, etc.

Examples of bonding methods include, for example, when bonding cast-coated paper and other coated paper for printing, a bonding agent may be applied to the back side of each or any of the sheets in a hot molten state, or a bonding agent may be applied in the form of a film or powder. Examples include a method in which a bonding agent is inserted between a cast coated paper and another coated paper for printing, and heated and melted to provide a bonding agent layer and simultaneously bond the two coated papers for printing.

However, in consideration of bonding stability, work efficiency, etc., the most preferable method is to apply a bonding agent by hot melting at the time of bonding.

Application of bonding agents to cast-coated papers or other coated papers for printing is generally done by coating, spraying, Meyer bar, screen printing, kiss roll coater, or direct roll coater.
, offset roll coater, Clavier roll coater
, a reverse roll coater, a bar coater, a blade coater, a curtain coater, a die slot coater, an extrusion coater, and an extrusion laminator.

The coating amount of the bonding agent may generally be about 3 to 60 g/d in terms of dry weight, but if the coating amount is too large, the smoothness of the cast coated paper after bonding will deteriorate, so 3 to 30 g/r+? degree is desirable. Note that the bonding agent can also be partially applied to cast coated paper or other coated paper for printing to bond the sheets.

In addition, when using a film bonding agent, vacuum method, low-temperature lamination method using thermal primer treatment, etc. are adopted, and when using powder bonding agent, electrostatic coating, mesh roll type scattering method, thermal spraying method, spray method, etc. are used. , screen printing, etc. are used.

The bonding agent can be heated and melted using steam, electric heat, flame hot air, hot plate,
Heat roller, or infrared, low frequency, high frequency, ultrasonic,
The crimping is performed using electromagnetic waves such as a laser at the time of crimping or before or after crimping. Furthermore, heating, cooling, electron beam irradiation, and other means may be used to supplement bonding as necessary.

(Effects) According to the method for producing coated paper for double-sided printing of the present invention, there is no evaporation of water or solvent even when cast coated paper and other coated paper for printing including cast coated paper are joined. The coating layers on both sides did not swell or soften, so the smoothness and gloss of the cast-coated paper after joining did not decrease, and the quality when finished separately was maintained. It is possible to obtain coated paper for double-sided printing of high quality.

Examples will be described below to explain the present invention more specifically, but the present invention is of course not limited to these. In addition,
Unless otherwise specified, parts and percentages in the examples refer to parts by weight and percentages by weight, respectively.

Example 1 A paint for cast coating was prepared consisting of 80 parts of kaolin, 20 parts of light calcium carbonate, 10 parts of casein, 10 parts of butadiene methyl methacrylate latex, and 1.0 part of ammonium stearate. This paint is coated onto the surface of the base paper using a first coating device to give a dry weight of 11 g/rrr, and then, while this coated layer is in a wet state, a second coating device is applied on top of it. After applying the same paint as above to a dry weight of 9 g/rd, immediately press it onto a chrome-plated cast drum with a surface temperature of 90°C.
A wet cast coated paper was obtained by drying. The glossiness of the cast coated surface was 83%, and the visual smoothness was also good.

Polyethylene resin (softening point: 80° C.) was melt-coated as a bonding agent on the back side of the obtained cast-coated paper using an extrusion laminator so that the coating amount was 10 g/rrr. The back side of the same cast-coated paper as above was placed on this bonding agent surface, and the two sides were bonded together using a press roll to obtain a double-sided cast-coated paper. The gloss of both surfaces of the obtained double-sided cast coated paper was 83% each, with no change at all compared to before lamination, and the visual smoothness did not change at all compared to before lamination, and the quality was excellent. However, no difference was observed between the two sides. Furthermore, the bonded double-sided cast-coated paper had far better curl resistance against humidity changes than the single-sided cast-coated paper.

Comparative Example 1 The reverse side (original paper side) of the single-sided cast-coated paper obtained in Example 1 was further cast-coated by the wet casting method in the same manner as in Example 1 to obtain double-sided cast-coated paper. In the obtained double-sided cast-coated paper, the second cast-coated side had a gloss of 85% and visual smoothness was good, but the first cast-coated side had a gloss of 70%. The visual smoothness also became very poor, resulting in a double-sided cast paper with a large difference in quality on both sides.

Example 2 A paint for cast coating with a concentration of 45% was obtained, consisting of 50 parts of kaolin, 50 parts of light calcium carbonate, 6 parts of casein, 18 parts of styrene-butadiene copolymer latex, and 1.0 part of potassium oleate.

This paint was finished by casting using the wet casting method described in JP-A-59-192797 to obtain cast coated paper with a weight of 128 g/rrr. (92% gloss) On the other hand, one-sided art paper (Kanzaki Paper Il
(manufactured by Kinto, single-sided art paper) with a gloss level of 68% and an ethylene-vinyl acetate copolymer binder (softening point 43) on the back side (original paper side).
℃) with a die slot coater at a melting temperature of 150℃! It was coated at a concentration of 30 g/nf. The back side of the above cast coated paper was laminated onto this bonding agent surface using a press roll to obtain coated paper for double-sided printing with cast coated paper on the front side and art paper on the back side. The glossiness of the cast coated side of the obtained coated paper for double-sided printing was 92%, and the glossiness of the art paper side was ℃
was 68%, no change at all compared to before bonding, and visual smoothness was also good with no change at all compared to before bonding.

Comparative Example 2 In Example 2, dextrin was used as a bonding agent for bonding cast paper and art paper. That is,
Add dextrin to the back side of art paper using roll caulk.
Coat itl with 0% aqueous solution.

The film was coated so that it was dry (glrd), immediately laminated with cast coated paper, dried in a drier to a moisture content of 5%, and rolled up. The glossiness of the cast coated side of the obtained coated paper for double-sided printing was 68%, and the glossiness of the art paper side was 62%, and the visual smoothness of both the cast coated side and the art paper side was also deteriorated. Moreover, small scratches were observed on both coated layers, and the entire printing paper had a damp feel.

Claims (1)

[Claims] A coating for double-sided printing having a cast coat layer on at least one side, characterized in that cast coat paper and coated paper for printing are bonded by heat melting using a bonding agent made of a thermoplastic polymer having a softening point of 180°C or less. Paper manufacturing method.