JPH01246494A - Production of cast coated paper and coating composition therefor - 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 [Field of Industrial Application] The present invention relates to a coating composition for producing cast-coated paper and a method for producing cast-coated paper, particularly improvements in the rewet casting method.

[Conventional technology and its problems]

The methods for producing highly glossy coated paper for printing, called cast coated paper, include the contact casting method, in which a wet coating layer is pressed against the surface of a heated drum to give a glossy finish, and the wet coating layer is coated in a coagulant solution. A coagulation casting method in which the wet coating layer is dried or semi-dried, plasticized by rewetting, and then pressed against the heating drum surface. A rewetting cast method is known.

All of these cast finishing methods have in common that the coating layer in a plastic state is pressed against the surface of a heated drum and then released from the mold, but the differences in the plasticity of the coating layer affect operability and yield. There is a difference in the quality of cast coated paper.

That is, in the direct method, if the surface temperature of the heating drum exceeds 100C, the coating composition will boil and the coating layer will be destroyed, so the drum temperature Fi must be kept below 100C and the casting speed must be low. Become.

In the coagulation method, since the coating layer is gelled, it is possible to raise the temperature of the heating drum surface to over 100C, but the coating layer contains a lot of water and has poor peelability from the drum. In addition, it is difficult to control the degree of coagulation of the coated layer, so it is actually not possible to finish at a high speed of 90%.

In the rewet casting method, it is possible to raise the temperature of the heating drum surface to 90 to 180C in order to dry the coating layer once.Force ζ - To rewet the coating layer once dried The degree of plasticization is significantly lower than other methods. Containing an amide compound in a rounding rewetting solution that facilitates plasticization by rewetting (Japanese Patent Application Laid-Open No. 59-1927
However, the degree of plasticization is still low, and as a result, the coating layer is not evenly adhered to the heating drum surface, and the coating layer is relatively homogeneous when operating at low speeds. Although highly glossy coated paper can be obtained, as the speed of operation increases, uneven gloss and pinhole-like spots occur, and the uniformity of the coated surface is rapidly lost.

In addition, in order to improve the adhesion of the coating layer to the heated drum, there is a method of smoothing the coating layer by applying a super calender before rewetting it, and a method of smoothing the coating layer before it is re-wetted, and a method of using a press roll when pressing the coating layer to the finished surface. Methods of increasing the pressure to high pressure have also been proposed, but on the other hand, these methods significantly impair the advantages of low tension and high bulk, which are characteristics of cast coated paper.

Additionally, a method of adding salts of zinc, aluminum, and magnesium to the coating composition to make the coating layer porous and improve adhesion to the heating drum (Japanese Patent Application Laid-Open No. 146097/1983)
(No. 2) has also been proposed, but this method weakens the surface strength of the finished cast-coated paper and requires an increase in the amount of adhesive, so the plasticization of the coated layer is not as good. .

[Purpose of the invention]

In the beam wet casting method of the present invention, the coating layer is easily plasticized by the rewetting solution, and therefore, high speed operation is possible without the occurrence of pinhole-like spots, uneven gloss, etc., and the surface The purpose is to produce cast-coated paper with high strength.

[Structure of the invention]

As a result of intensive research into a method for producing high-quality cast-coated paper at high speed, the present inventors have determined that the coating layer temperature is the glass transition point of the outer layer of the double-layered latex added to the cast coating composition. (T-G-) Dry the coated layer at a temperature not exceeding +20 C, rewet with a rewetting solution, and then heat the outer layer of the double-layer latex T, G, to a temperature exceeding +20 C. The present inventors have discovered that it is possible to produce cast-coated paper of high quality with high surface strength at high speed by press-contacting it on a cast drum and finishing it by casting, thereby leading to the present invention.

The present invention provides a method for producing cast-coated paper, in which a coated layer mainly composed of pigments, adhesives, and auxiliary agents is re-wetted after drying, and is pressed against a heated mirror drum for a high-gloss finish.
The adhesive has a double structure (core-shell structure), and the outer layer (shell part) has T and G higher than 40℃ and the inner layer (part of the core) has T and G lower than 20℃. m-A coating composition containing as an active ingredient, and after coating the base paper with the composition, the temperature of the coating film is r of the outer layer part (shell part) of the latex having a double structure,
After drying and rewetting under conditions not exceeding o+2Oct-
This is a method for producing cast coated paper in which the outer layer (shell part) is finished by being pressed against a cast drum heated to a temperature higher than T, G + 20C, preferably 'r, G + 40C or higher.

The present invention will be explained in detail below.

In the present invention, T and G of the outer layer part (shell part) are 40C with latex having a double structure (core shell structure).
A latex with higher inner layer T and G lower than 20tll' is used. Structural materials for the outer and inner layers of the latex having a double structure include styrene-butadiene polymers, conjugated diene polymers such as methyl methacrylate-butadiene copolymers, and polymers of acrylic esters and/or methacrylic esters. or acrylic polymers such as copolymers, vinyl polymers such as ethylene-vinyl acetate copolymers, or alkaline polymers obtained by functionally modifying these polymers with monomers containing functional groups such as carboxyl groups. A soluble or alkali-insoluble polymer can be used.

The above-mentioned latex having a double structure with T and G higher than 40°C in the outer layer and lower T and G lower than 20C in the inner layer can be used alone or in combination with other adhesives to form a coating composition for cast coated paper. Use as an additive to things.

Adhesives used in combination with the above latex include casein,
Proteins such as soybean protein and synthetic proteins, starches such as positive starch and oxidized starch, cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose, synthetic resin adhesives such as polyvinyl alcohol, olefin-maleic anhydride copolymer resin, and melamine resin. , conjugated diene polymer latex such as styrene-butadiene polymer, methyl methacrylate-butadiene copolymer, acrylic polymer latex such as acrylic acid ester and/or methacrylic acid ester polymer or copolymer, ethylene- Vinyl polymer latex such as vinyl acetate copolymer, or alkali-soluble or alkali-insoluble polymer latex modified by functional group-containing monomers such as carboxyl groups, or various polymers thereof with functional group-containing monomers such as carboxyl groups. It has a double structure,
T and G of the outer layer are higher than 40℃, T and G of the inner layer are 2
It can be used without latex at a temperature lower than 0°C. A latex that has a double structure and has T and G higher than 40C in the outer layer and lower T and G lower than 20℃ in the inner layer with other latex and/or casein, protein such as soybean protein, starch, etc. When used together, it is desirable that the latex has a double structure, with T and G of the outer layer being higher than 40C and lower than DT and (ki120C) of the inner layer, at a ratio of f'i50 weight X or more.

In addition, T and G for other latex are 20C.
It is recommended to use the following:

The adhesive is used in an amount of 5 to 50 parts by weight per 100 parts by weight of pigment, generally in a Vi range of 10 to 30 parts by weight.

In addition, the present invention includes at least one sulfate, nitrate, acetate, or formate of aluminum, magnesium, or zinc as an auxiliary agent in the coating liquid containing the latex,
T, G of outer layer of latex with double structure +20
After drying and rewetting at a temperature lower than C, the latex T,
G to a temperature higher than +20C, preferably r, G+4o
This also includes a method of finishing by pressing onto a cast drum heated to a temperature higher than °C. Furthermore, the present invention exhibits its effects regardless of the composition of the rewetting liquid.

In the rewet casting method, the MY solution is coated and dried, then rewetted with a rewetting solution and finished by pressing against a heated drum. Also, the problem is how to make the adhesion to the drum easier, and as mentioned above, it is necessary to change the ingredients of the rewetting liquid, smoothen the coating layer after drying, or change the coating composition. It has been considered to solve the problem by adding a coagulant to the latex, but in order to fundamentally solve this problem, the present inventors investigated the film-forming properties of latex and found an effective solution. I found a way.

In other words, latex ° has its own film-forming temperature, and we focused on the property that it does not form a film below the film-forming temperature.

The glass transition temperature (T,G) of latex is the point at which the segments of the polymer transition from a glassy state to a rubbery state. ,
When latex is dried at a temperature exceeding G, dry strength and water resistance begin to develop, and a film is partially formed. T,
As the temperature is further increased beyond G, the dry strength and water resistance increase, and film formation progresses, but it is thought that temperature, pressure, and the time required are influential in forming a complete film. Therefore, the coating layer is latex T, G +
If the coating layer is dried under drying conditions such that the temperature is below 20 C, the latex in the coating layer will not form a complete film and the dry strength will be weak if the drying time is normal for manufacturing cast coated paper. It is presumed that the coating layer does not exhibit water resistance and is therefore easily plasticized when rewetting with a rewetting solution.

After that, when the latex is pressed against a cast drum heated to a temperature higher than T, G +200 of the outer layer of the latex, a film is formed on the latex due to the action of heat, resulting in cast coated paper with good surface quality.

On the other hand, when looking at the surface strength of finished cast-coated paper, latex with a single structure and high T and G values generally have difficulty developing strength unless given sufficient temperature, pressure, and the time required. However, in the present invention, as a method that allows easy plasticization during rewetting and gives the surface strength of the product to the cast finished layer, it has a double structure (core-shell structure), and the T and G of the outer layer are from 40r. High, inner T,
A latex having a G lower than 20° C. is used in a coating composition for cast coated paper. That is, the above latex having a double structure is used in the coating composition for cast coated paper, and the temperature of the coating layer and coating film on the base paper does not exceed T, G + 20 C of the outer layer of the double structure latex. In the method of drying at a temperature and press-contacting the outer layer part to a cast drum heated to a temperature higher than T, G +20 C after rewetting, the latex, which has a double structure after drying but before rewetting, forms a coating. The outer layer does not form a film during the process of being pressed against a cast drum heated to a temperature higher than T, G + 20C of the outer layer. At the same time, film formation is promoted in the inner layer, and since T and G of the inner layer are much lower than those of the outer layer, it becomes more effective in developing coating film strength.

As the pigment, for example, general pigments for coated paper such as clay, kaolin, aluminum hydroxide, rhusium carbonate, titanium oxide, barium sulfate, zinc oxide, satin white, and plastic pigments are used.

Further, as an auxiliary agent, salts such as sulfates, nitrates, acetates, or formates of zinc, aluminum, and magnesium may be used.

In addition, various auxiliary agents such as antifoaming agents, coloring agents, flow modifiers, and mold release agents can be used as appropriate.

In the present invention, the coating composition is coated using a blade coater, an air knife coater, a roll coater, a brush coater, a curtain coater, a champlex coater, a bar coater, a gravure coater, a size press coater, etc., which are generally used in the production of coated paper. The base paper is coated in one layer or in multiple layers using an on-machine or off-machine coater equipped with a device.

At that time, the solid content concentration of the coating composition is generally 35 to 70.
The weight is X, but considering the operability, the weight is 45 to 65
Amounts in the range are preferred.

As the base paper, a paper pace or board base paper having a weight of 30 to 400.9/cm, which is used for general printing coated paper or cast coated paper, is used. these are,
Of course, it is also possible to use a medium-quality base paper that is made by an acidic or alkaline paper-making method and contains high-yield pulp of about 10% by weight or more. In addition, it is also possible to use as a base paper a coated paper having a preliminary coating layer or a coated paper having a general pigment coating layer on the back side of a cast coating layer.

The coating amount of the coating composition on such base paper is 10
~50117m2, but it is 1st in terms of improving the blank quality of the cast coated paper obtained and the cast coating speed.
Most preferably, it is adjusted within the range of 5 to 35 Jl/1n2.

In the rewet casting method, the coating composition coated on the base paper is once dried. For drying, a conventional dryer such as a hot air dryer, air foil dryer, air camp dryer, cylinder dryer, infrared dryer, or electron beam dryer is used. A coated paper dryer is used.

The degree of drying of coated paper varies depending on the type of base paper, the type of coating composition, etc., but it is generally dried to a paper moisture content of about 1 to 15X, preferably about 5 to 10%.

What is the temperature of the coating layer during drying of the outer layer of the latex, which has a double structure as described above? , G +20 C.

After drying, the coated paper is smoothed using a machine calender, super calender, etc. as necessary.
Of course, it is necessary to avoid excessive processing that significantly impairs the bulk and hardness characteristic of cast coated paper.

The coating layer is then re-wetted according to the usual glue wet casting method and pressed onto a heated mirror drum to achieve a strong gloss finish.In the method of the present invention, in particular, the mirror drum is coated with a coating composition. The outer layer of the double-layered latex used for
Finish casting at a temperature of C or higher.

Note that the rewetting liquid is not particularly limited, and includes, for example, fresh water, warm water, hot water, an aqueous solution containing a mold release agent,
Conventional rewetting fluids such as aqueous solutions containing amines such as dicyandiamide urea are used.

〔Example〕

The present invention will be specifically explained below with reference to Examples, but it is of course not limited to these. Note that parts and % in the examples indicate parts by weight and % by weight, respectively, unless otherwise specified.

Examples 1 to 7, Comparative Examples 1 to 3 80 parts of kaolin, 20 parts of light coal, and 0.4 parts of sodium polyacrylate were dispersed in water using a splitter manufactured by Serini Co., Ltd. to give a solid content concentration of 55%. A pigment slurry was prepared.

The resulting round pigment slurry! J-100 parts by weight, 0.4 parts of tributyl phosphate as an antifoaming agent, 8 parts of a 15% casein aqueous solution (solid content) dissolved using ammonia as an adhesive, and the latex shown in Tables 1 and 2. In addition, polyethylene wax emulsion 1.
5 parts (solid content) were added, and finally ammonia and water were added to adjust the solid content concentration to 43% and -9.5 to obtain 10 types of coating compositions.

Using this coating composition, rewet casting was carried out using the apparatus shown in FIG. That is, Yonetsubo 609/ln2
The dry weight of base paper 1 is 25 I/! The above coating composition was coated with a roll coater 2 to give a2, and dried in a dryer 3 under the conditions shown in Tables 1 and 2 so that the moisture content was 6%. The paper was then passed through a breath nip 6 formed by a rubber roll 4 and a chrome-plated cast drum 5, where the surface of the coated layer was rewetted with a rewetting liquid supplied from a nozzle 7, and then the drum temperature conditions shown in Table 1 were applied. Press pressure 150k)/c on cast drum 5 with rotational speed 100771/min! The paper was pressed with IL, and after drying, it was peeled off from the cast drum with a take-off roll 8 to produce cast coated paper 9.

The quality of the cast coated paper obtained is shown in Tables 1 and 2.

Table 1 shows the effect of drying temperature on the quality of cast-coated paper when the paper is coated with the same dual-layer latex coating composition and the drying conditions are varied. Table 2 shows the quality of cast coated paper when dual structure latex and single structure latex were used alone and in combination.

Surface properties and white paper gloss were measured as follows.

[Surface]

Sensory evaluation: The best score was 10 points and the worst score was 1 point, with scores of 10 to 6 being a passing level, and scores of 5 to 1 being a failing level.

[White paper gloss]

Measured with a crossmeter (75°). (To Nippon Denshoku Kogyo,
) V Ck -j O-type glossmeter) [Effects of the Invention] As is clear from the results of each example, in the method of the present invention, as described above, the rewetting liquid is applied during rewetting. The coating is easily plasticized and has good adhesion to the cast drum, resulting in a cast surface with few defects.

In addition, in the process of being pressed against a cast drum heated to a temperature higher than T, G + 20 C of the outer layer, the inner layer is also encouraged to form a film at the same time as the outer layer forms a film. Since T and G are much lower than those of the outer layer, they are effective in developing coating film strength. Therefore, rewet casting can be easily carried out according to the present invention, and cast coated paper with good surface properties, glossiness and surface strength can be obtained at high speed.

[Brief explanation of the drawing]

FIG. 1 shows a flow diagram of an apparatus for carrying out the invention. 1... Base paper, 2... Roll coater 13... Dryer, 4... Press roll, 5... Cast drum,
6... Press nip, 8... Take-off roll, 9
・・・Cast coated paper

Claims (1)

[Scope of Claims] 1. Used in the production of cast-coated paper, which has a coating layer mainly composed of pigments, adhesives, and auxiliary agents, which is re-wetted after drying and is pressed against a heated mirror drum to give a strong gloss finish. A coating composition for cast-coated paper containing a latex as an active ingredient, which has a double structure as an adhesive and has a glass transition point higher than 40°C in the outer layer and lower than 20°C in the inner layer. A coating composition for cast coated paper, characterized in that: 2. In the method for manufacturing cast coated paper, in which the coating layer, which is mainly composed of pigments, adhesives, and auxiliary agents, is dried, re-wetted, and pressed against a heated mirror drum to give a high gloss finish, double coated paper is used as an adhesive. structure, the glass transition point of the outer layer is 40℃
After coating a base paper with a coating composition containing a latex whose inner layer has a glass transition point higher than 20°C, the temperature of the coating film reaches the glass transition point of the outer layer of the latex having a double structure +20°C. After drying and rewetting under conditions that do not exceed
Glass transition point + of the outer layer of latex with double structure
A method for producing cast coated paper, the method comprising press-contacting it to a cast drum heated to a temperature higher than 20°C.