JPH0241495A - Production of cast coated paper - Google Patents

Abstract

PURPOSE:To obtain the title paper freed from pinholes by treating the surface of a base paper with an aqueous solution of metallic salt followed by application of a cast coated layer thereon using an aqueous pigment coating an by pressure contact of the resulting product with a metallic drum to provide the final cast coated layer. CONSTITUTION:The surface of a base paper is treated with an aqueous solution of metallic salt of zinc, calcium, aluminum or magnesium followed by drying. The resultant paper is then coated with an aqueous pigment coating comprising a pigment such as clay or kaolin and an adhesive such as synthetic resin latex- casein followed by drying to provide a case coated layer. Thence, this layer is moistened again and brought to pressure contact with a heated metallic specular drum followed by drying to provide the final cast coated layer, thus obtaining the objective paper freed from pinholes without impairing high gloss nature and other qualities.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing cast coated paper. In particular, the present invention relates to a method for producing cast coated paper that eliminates pinholes without impairing the high gloss and other qualities characteristic of cast coated paper.

[Conventional technology]

Cast coated paper has extremely high print reproducibility due to its high gloss and smooth surface, and is used for precise high-end printing, and is used for fine art prints, high-end catalogs, magazine covers, labels, wrapping paper, etc. Widely used.

Cast-coated paper is made by coating the surface of base paper with a water-based pigment coating mainly composed of pigments and adhesives to form a cast coating layer, and then applying the cast coating layer to a heated metal mirror drum. Manufactured by pressing and drying.

The method for producing cast coated paper involves pressing the cast coating layer onto a heated metal mirror drum and drying it to obtain a glossy finish.
It is broadly divided into wet method (direct method), gelling method (coagulation method) and rewetting method (indirect method).

That is, in the wet method, the cast coating layer is pressed onto a heated metal mirror drum while it is in a wet state, and then dried to give a glossy finish.

In addition, the gelling method involves passing the wet cast coating layer through a coagulation system to gel it, then pressing it onto a heated metal mirror drum and drying to give it a glossy finish. After drying the wet cast coating layer, the cast coating layer is re-wetted with a wetting liquid either as it is or after being treated with a super calender to make it plastic, and then it is pressed onto a heated metal mirror drum. The rewetting method produces a glossy finish.

[Problem to be solved by the invention]

In all of these methods for producing cast-coated paper, the cast coating layer is pressed onto a specular drum while it is in a wet or plastic state and dried.

Therefore, the water in the cast coating layer evaporates through the base paper layer. On the other hand, part of the water in the cast coating layer evaporates toward the specular drum through the cast coating layer. If the evaporation rate increases beyond a certain limit, pinholes will occur on the surface of the resulting cast coat layer, making it impossible to print as a product and causing a decrease in productivity. This phenomenon is noticeable in the wet method, where the amount of evaporated water is relatively large, and for this reason, CAST1
~C1- The rewetting method is suitable for increasing the speed of paper production.

However, on the other hand, the rewetting method has the disadvantage that the plasticity of the cast coating layer is low compared to other wet methods and gelling methods. Therefore, in the rewetting method, it is important to select the water-based pigment paint formulation for the cast coating layer, the selection of the rewetting liquid, and the selection of working conditions such as work speed, temperature of the mirror drum, and press pressure on the mirror drum. If incorrectly applied, there is a drawback that so-called casting surface defects such as pinholes and uneven adhesion on the surface of the cast coating layer are likely to occur.

On the other hand, in the gelling method, the coated layer is gelled by treatment with a coagulating liquid, and although relatively high temperature cast drum processing is possible, it generally does not involve drying, so the drying load on the cast drum is It is higher than the beam wet method, or because the coagulation process is performed just before casting, a sufficient coagulation effect cannot be obtained, and there is also a concern that the coagulant may reduce gloss. Various methods have been implemented in which a coagulant is added to the water-based pigment paint in advance, but in this case, the viscosity of the water-based pigment paint tends to fluctuate, making stable coating difficult. It is also difficult to expect a sufficient coagulation effect.

[Means to solve the problem]

The inventors of the present invention conducted intensive studies to solve these drawbacks of various casting methods, and as a result, succeeded in solving the problems by treating the surface of the base paper with a specific metal salt aqueous solution, and completed the present invention. I let it happen.

That is, in the present invention, the surface of base paper is coated with zinc, calcium,
Treated with an aqueous solution of metal salts such as aluminum and magnesium,
It is dried, calendered if necessary, and then coated with a water-based pigment paint mainly composed of pigment and adhesive, dried to form a cast coating layer, and then the cast coating layer is re-wetted. , crimped onto a heated metal mirror drum,
This is a method for producing cast coated paper by drying and providing a cast coat layer.

[Operation and mode of the invention]

There are various possible causes for the formation of pinholes in cast coated paper, but it is known that rapid evaporation of water destroys the cast coating layer, causing pinholes and blisters. It is also well known that if the cast coating layer is coagulated with formic acid or calcium formate, the cast coating layer will be less likely to be destroyed even if it comes into contact with a high-temperature casting drum, and therefore speeds can be increased. However, as already mentioned, problems such as viscosity and gloss arise if the cast coating layer is simply coagulated or a coagulant is added to the water-based pigment coating. Efforts have been made to improve the air permeability of the cast coating layer by increasing the air permeability of the base paper or by improving the pigment and latex formulations, but there are limits to the degree of improvement, and there is a significant increase in the air permeability of water-based pigment paints. Such changes often have an adverse effect on the viscosity of the paint, the quality of the cast coated paper, etc., and therefore, fully satisfactory results have not been obtained.

The inventors of the present invention have investigated various methods of manufacturing paper that produce high quality paper, especially those that do not generate pinholes and have high productivity (immediately before casting). After treating the surface of base paper with an aqueous solution of a specific metal salt, It has been found that the objective can be achieved by providing a cast coat layer using a method.

In the present invention, since the surface of the base paper is treated in advance with a coagulation treatment agent using a metal salt, the viscosity of the paint does not change during coating, and the cast coating layer is coated with a water-based pigment paint. Since the coagulation effect is promoted and ensured by the subsequent heat drying, the purpose can be achieved with a small amount of coagulant. Furthermore, by rewetting after drying, high gloss, which is an advantage of the rewetting method, can be obtained.

This improvement effect is not much different when using general water-based pigment paints for paper coating, and there is no deterioration in the properties of cast coated paper, and pinholes and uneven adhesion are reduced when a glossy finish is achieved using the rewetting method. It was possible to obtain a cast-coated paper that was significantly improved, and also to increase the speed of the cast-coating operation.

Next, the method for producing cast coated paper of the present invention will be described in detail.

First, examples of metal salts that can be used to treat the surface of base paper include nitric acid, sulfuric acid, formic acid, and acetate of zinc, calcium, aluminum, magnesium, and the like.

Among these, zinc salts are the most effective. To treat the surface of base paper with these metal salts,
A treatment solution having a concentration of 2 to 50% is prepared and used. Furthermore, if necessary, starch, polyvinyl alcohol, cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and methyl cellulose, water-soluble polymers such as polyacrylamide and polyacrylates, or viscosity modifiers can be used in combination.

If the concentration of the treatment liquid is too low, the effect on air permeability will be insufficient, and if it is too high, the surface strength of the resulting cast coated paper will deteriorate, which is not preferable.

To treat the paper surface with a metal salt treatment solution, on-machine size press, impregnation with gate rolls, blades, etc., application or off-machine roll coating,
Equipment such as kiss coating, air knife coating, bar coating, and spray atomization is used. The coating amount of the metal salt is desirably adjusted to 1 to 20 gr/n+2. The base paper treated with such a metal salt treatment solution is dried and, if necessary, calendered, and then immediately subjected to a casting process, or it is first wound up and used as a base paper for cast coating.

The pigments used in providing the cast coating layer may then be those commonly used for aqueous pigment coatings of paper. Therefore, as pigments, clay, kaolin, aluminum hydroxide, calcium carbonate, titanium oxide, barium sulfate, satin white, various plastic pigments, etc. are used. In addition, as an adhesive,
Synthetic resin latexes such as styrene-butadiene latex and methyl methacrylate-butadiene latex, and water-soluble adhesives such as casein, soybean protein, oxidized starch, modified starch, and polyvinyl alcohol are used. These adhesives are blended in a total amount of 15 to 30 parts by weight based on 100 parts by weight of the pigment. and,
In preparing the water-based pigment paint, additives such as a mold release agent, an antifoaming agent, a coloring agent, a viscosity modifier, and a waterproofing agent can be added as necessary.

Water-based pigment paints with a solid content concentration of 40 to 70%, which are prepared using pigments and adhesives as main components and additives as necessary, can be used with air knife coaters, blade coaters, roll coaters, and rod coaters. etc., basis weight 40
~350gr/m2 base paper surface with a coating weight of 5
A cast coating layer is provided to provide a coating of ~30gr/m2.

The cast-coated paper obtained in this way is first dried and then given a cast gloss finish in accordance with the rewetting method commonly used in cast coating, thereby eliminating pinholes without impairing its high gloss or other qualities. It is possible to produce cast-coated paper that eliminates the problem at high speed. The rewetting liquid is not particularly limited, but water, a mixture of water and a mold release agent, an aqueous solution of a plasticization accelerator, and the like can be used as appropriate.

〔Example〕

Further, the present invention will be explained by examples.

Example 1 Zinc sulfate 20% on one side of a base paper with a basis weight of 100g/m"
Apply vt% aqueous solution to 10g/ni2,
A base paper was obtained which was dried to a moisture content of 4% and treated with zinc sulfate.

Cast coating layer composition Part by weight Kaolin
80 light calcium carbonate
20 Sodium polyacrylate 0.7 Casein 8 Styrene-butadiene latex
14 Ammonium stearate
0.5 Then, with the above cast coating layer composition, the solid content was 4.
An 8% water-based pigment paint was prepared and applied to the surface of base paper treated with zinc sulfate to a dry weight of 20g/m'', dried to a moisture content of 6%, and a cast coating layer was formed. Then, the cast coated layer was surface-treated with a rewetting solution consisting of water and a surfactant, and immediately pressed onto a cast drum heated to 120°C and dried to obtain a cast coated paper of the present invention.

Example 2 Cast-coated paper of the present invention was obtained in the same manner as in Example 1, except that a treatment solution containing 20 wt % zinc nitrate was used to treat the surface of the base paper.

Example 3 Cast-coated paper of the present invention was obtained in the same manner as in Example 1, except that a treatment solution containing 20 wt % zinc acetate was used to treat the surface of the base paper.

Example 4 Cast-coated paper of the present invention was obtained in the same manner as in Example 1, except that a treatment solution containing 10 wt % zinc formate was used to treat the surface of the base paper.

Example 5 In treating the surface of base paper, aluminum sulfate 15
Cast coated paper of the present invention was obtained in the same manner as in Example 1, except that a treatment liquid of wt % was used.

Example 6 In treating the surface of base paper, calcium formate low
Cast coated paper of the present invention was obtained in the same manner as in Example 1, except that t% of the treatment liquid was used.

Example 7 In treating the surface of base paper, magnesium nitrate 20
Cast coated paper of the present invention was obtained in the same manner as in Example 1, except that a treatment liquid of wt % was used.

Example 8 Cast-coated paper of the present invention was prepared in the same manner as in Example 1, except that the surface of the base paper was treated using a treatment solution containing 20w% zinc sulfate and coated to 15g/m''. Obtained.

Example 9 Cast-coated paper of the present invention was obtained in the same manner as in Example 1, except that a treatment solution containing 20 wt% zinc sulfate was used to treat the surface of the base paper at a coating density of 5 gr/m2. Na.

Comparative Example 1 A comparative cast coated paper was obtained in the same manner as in Example 1, except that the base paper was not treated with the treatment liquid.

Comparative Example 2 A comparative cast-coated paper was obtained in the same manner as in Example 1, except that a treatment liquid containing 1 wt % zinc sulfate was used as the treatment liquid for the base paper.

Comparative Example 3 A comparative cast coated paper was obtained in the same manner as in Example 1, except that a treatment liquid containing 1 wt % zinc nitrate was used as the treatment liquid for the base paper.

Comparative Example 4 A comparative cast-coated paper was obtained in the same manner as in Example 1, except that a treatment liquid containing 1 wt% aluminum sulfate was used as the treatment liquid for the base paper.

Comparative Example 5 A comparative cast coated paper was obtained in the same manner as in Example 1, except that a treatment liquid containing 1 wt % magnesium nitrate was used as the treatment liquid for the base paper.

A quality test was conducted on the cast coated paper obtained in each Example and Comparative Example. The quality test results are shown in the table below, and it can be seen that the cast-coated paper of the present invention has no problems with white paper gloss or other qualities, and the cast-coated paper is free from pinholes. .

Test method and evaluation criteria White paper gloss: (%) according to JIS P-8142 Print gloss: (%) according to JIS P-8142 dry,
Wet surface strength (according to R1 tester) O: Very good, no bumps Δ: Occasional bumps ×: Many bumps, pinholes ○: Hardly any, very good Δ: Slightly generated ×: All over the surface Unusable quality test results [Effects of the invention] According to the method for manufacturing cast coated paper using the glue wet method of the present invention, the obtained cast coated paper has high gloss and other qualities unique to cast coated paper, Moreover, it is possible to efficiently produce cast-coated paper free of pinholes.Therefore, the effects are immeasurable.

Patent applicant: Nippon Kako Paper Co., Ltd. Representative Kenbetsu Toto

Claims (1)

[Claims] The surface of the base paper is treated with an aqueous solution of metal salts such as zinc, calcium, aluminum, magnesium, etc. and dried. Next, a water-based pigment paint containing pigments and adhesives as main components is applied and dried to form a cast coating layer. The cast coated paper is then re-wetted, pressed onto a heated metal mirror drum, and dried to form a cast coated paper.