JPH0790798A - Production of cast coated paper - Google Patents

Abstract

PURPOSE:To provide cast coated paper having high gloss and excellent printability (surface strength), also excellent in releasability. CONSTITUTION:The objective cast coated paper can be obtained by providing a substrate with a water-based composition for the aimed paper comprising a pigment and an adhesive followed by pressure contact of the resultant substrate with a hot drum with specular surface while said composition is in a wet, plastic state and then drying. In particular, the adhesive is a latex of a copolymer having core-shell structure and composed of (1) core consisting mainly of a copolymer essentially made up of styrene monomer unit and butadiene monomer unit and (2) shell consisting mainly of a copolymer essentially made up of methyl methacrylate monomer unit and butadiene monomer unit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing cast coated paper, and more particularly to a method for producing cast coated paper which has high gloss and excellent printability and can be produced at high speed. .

[0002]

2. Description of the Related Art Cast coated papers are widely used as high-grade printing papers because they have very high smoothness and gloss on the paper surface and excellent printability. By the way, as a method for producing a cast coated paper, a wet coating method in which a coating layer in a wet state is pressed against the surface of a heating drum having a mirror surface and dried to give a gloss finish, a coating layer in a wet state provided on a support After being dried once, the coating layer is wet-plasticized with a re-wetting liquid, and then pressed against a heating drum surface having a mirror surface, a rewet cast method for drying and gloss finishing, and a coating layer in a wet state is further formed. A gelling casting method in which a gel state is brought into pressure contact with a heating drum surface having a mirror surface, followed by drying and gloss finishing is generally known. All of these cast finishing methods are common in that the surface of the coating layer in the wet plastic state is pressed against a heating drum and dried to copy the mirror surface. However, due to the difference in the wet plastic state of the cast coating layer, there are the following problems in operability and the quality of the cast coated paper obtained.

That is, in the wet cast method, when the temperature of the heating drum surface is set to 100 ° C. or higher, the coating liquid boils and the coating layer is destroyed, so that the low speed operation at 100 ° C. or lower is unavoidable. In addition, gel cast method,
In the rewet casting method, since the cast coating layer is gelled or dried before being pressed against the heated mirror surface drum, the surface temperature is 9% in any method.
Cast finish is possible even when pressed against a mirror drum of relatively high temperature of 0 ° C or higher. Therefore, these casting methods can improve the drying speed as compared with the wet casting method, and are excellent in productivity.

In these cast finishing methods, casein and synthetic resin latex are generally used in combination as an adhesive for the aqueous composition for cast coated paper. And the important physical properties required for these adhesives are
It has a white paper gloss and an adhesive strength that can withstand printing. On the other hand, at the time of production, when the coating layer that is a mirror surface of the drum is released from the heated mirror surface drum, part of the coating layer remains on the mirror surface drum. It must be an adhesive that does not cause paper breaks due to mold defects.

Therefore, as the synthetic resin latex, a styrene-butadiene copolymer, a carboxy-modified styrene-butadiene copolymer, a methylmethacrylate-butadiene copolymer and the like are generally used. Then, in order to improve the glossiness of white paper, the adhesive strength, and the releasability, it has been proposed to devise the ratio of materials to be copolymerized, or to copolymerize by adding other monomer in addition to the main monomer as a modifier. ing.

However, when the releasability is generally emphasized, there is a contradictory tendency that the glossiness of the white paper is inferior and the adhesive strength is lowered, and a synthetic resin (adhesive agent that simultaneously satisfies the releasability, the glossiness of the white paper and the adhesive strength) The current situation is that) is not yet available.

[0007]

Under the circumstances as described above, the present inventors have earnestly conducted research on a manufacturing method for manufacturing high quality cast coated paper at high speed. As a result, according to the present invention, by using a specific copolymer latex, a cast coated paper having excellent printability can be efficiently obtained at a high speed, and a cast having an extremely excellent surface gloss desired by the present invention. A method for manufacturing coated paper is provided.

[0008]

SUMMARY OF THE INVENTION The present invention comprises:
After providing an aqueous composition for cast coated paper containing a pigment and an adhesive as a main component, while the aqueous composition is in a wet plastic state, it is pressed against a heating drum having a mirror surface and dried to finish the cast coated paper. In the production method, as the adhesive, a copolymer in which the main component of the core part is styrene and butadiene as essential monomer units, and the main component of the shell part is methyl methacrylate and butadiene as essential monomer units Is a copolymer latex having a core-shell structure composed of the above-mentioned copolymer.

[0009]

As described above, the present inventors have found that the main component of the core portion (inner layer) of the copolymer latex particles is an monomer for which styrene and butadiene are essential as an adhesive for the aqueous composition for cast coated paper. Use a copolymer latex having a core-shell structure, which is a copolymer having units and whose main components in the shell portion (outer layer) are methyl methacrylate and butadiene as essential monomer units. As a result, the inventors have found that the drawbacks of the conventional water-based composition for cast coated paper can be solved, and that cast coated paper excellent in white paper gloss and printability can be efficiently produced, thereby completing the present invention.

The reason why the above-mentioned copolymer latex having the core-shell structure exhibits the desired action and effect of the present invention is not always clear, but it is presumed as follows. That is, a copolymer having styrene and butadiene as an essential monomer unit generally has high adhesive strength, but relatively low releasability, depending on the composition ratio of styrene and butadiene. The tendency is strong when the amount of is large. On the other hand, a copolymer containing methyl methacrylate and butadiene as essential monomers has relatively high gloss and excellent releasability, but tends to have weak adhesive strength. From the above characteristics, with respect to the white paper gloss and releasability required for the aqueous composition for cast coated paper, a copolymer containing methyl methacrylate and butadiene in the shell portion as essential monomer units is mainly desired. On the other hand, regarding the printing strength required at the time of printing, on the other hand, regarding the printing strength required at the time of printing, it is presumed that the copolymer having styrene and butadiene as essential monomer units in the core part is involved in the desired effect. To be done. In short, it is assumed that the advantages of both will be synergistically exerted.

In the present invention, the aqueous composition for cast coated paper, which is a coating layer for cast coated paper, contains a pigment and an adhesive as main components, and particularly, a core which is a feature of the present invention.・ Describe the shell structure latex. As described above, in the present invention, the main component of the core part is a copolymer composed of monomer units indispensable for styrene and butadiene, and the main component of the shell part is methyl methacrylate and butadiene indispensable monomer. It is essential to use a copolymer latex having a core-shell structure composed of a copolymer as a body unit. In the copolymer constituting the core part or the shell part, other monomers than butadiene, styrene or methyl methacrylate can be used. Other monomers include, for example, methyl acrylate, ethyl acrylate,
Alkyl ester of unsaturated carboxylic acid such as butyl acrylate, ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid and itaconic acid, ethylenically unsaturated carboxylic acid such as acrylamide, methacrylamide, N-methylol acrylamide and diacetone acrylamide One or more kinds of amides and unsaturated nitrile-based monomers such as acrylonitrile and methacrylonitrile can be further copolymerized.

In the copolymer latex used in the present invention, the polymer of the core portion has a styrene unit constituting the core portion, and generally 20 to 20 of all monomer units of the polymer constituting the core portion and the shell portion. 55% by weight, preferably 25-50
% By weight, usually 15 to 25% by weight, preferably 15 to 20% by weight, based on the total monomer units of the polymer in which the butadiene unit constitutes the core part and the shell part, a monomer other than the styrene unit and the butadiene unit. The unit is usually 40% by weight or less, and preferably 35% by weight or less, of all the monomer units of the polymer constituting the core part and the shell part.

The polymer of the shell portion is usually 15 to 35% by weight, preferably 25 to 35% by weight of all the monomer units of the polymer constituting the core portion and the shell portion. 35% by weight, usually 10 to 25% by weight, preferably 10 to 20% by weight, based on the total monomer units of the polymer in which the butadiene unit constitutes the core part and the shell part, a unit other than the methyl methacrylate unit and the butadiene unit. The monomer unit is usually 30% by weight or less, and preferably 25% by weight or less, based on the total monomer units of the polymer constituting the core portion and the shell portion.

Incidentally, when each monomer unit of the polymer constituting the core part or the shell part is out of the above range, the white paper gloss, surface strength or releasability of the coated paper is deteriorated. The weight ratio of the core part and the shell part is usually 8/2 to 2/8, preferably 7/3 to 3/7.

The particle size of the above-mentioned copolymer latex having a core / shell structure is not particularly limited, but it is preferable to use one having a particle size of about 600 to 2500Å. Incidentally, if it is less than 600 Å, the air permeability of the cast coating layer on the mirror-drum is lowered during the cast finishing, and as a result, the drying speed tends to be lowered. On the other hand, if it is larger than 2500 Å, the adhesive strength tends to decrease. The amount of the specific copolymer latex used is determined by the balance between releasability from the mirror surface drum and surface strength, but is generally 5 to 50% by weight, more preferably 10 to 30% by weight, based on the pigment. Adjusted in range.

As the adhesive, the above-mentioned specific core
A copolymer latex having a shell structure is mainly used. In addition to such a copolymer latex, proteins such as casein, soybean protein, methanol, acetic acid, and other proteins extracted from monocytoplasmic cells are also used. , Polyvinyl alcohol, olefin maleic anhydride resin, melamine resin and other synthetic resin adhesives, positive starch, oxidized starch and other starches, carboxymethyl cellulose, hydroxyethyl cellulose and other cellulose derivatives, etc. One or more kinds may be used in combination as appropriate. However, these adhesives must be used within a range that does not impair the desired effects of the present invention, and generally 1 to the pigment.
It is adjusted to 20% by weight, more preferably 5 to 15% by weight.

As the pigment used in the aqueous composition for cast coated paper, pigments for coated paper generally used in the field of coated paper production such as kaolin and aluminum hydroxide,
Satin white, barium sulfate, ground calcium carbonate,
Light calcium carbonate, talc, plastic pigment, calcined clay, titanium dioxide and the like are exemplified, and one or more kinds are selected and used from these.

In the aqueous composition, in addition to the above-mentioned pigment and adhesive, sodium chloride, ammonium chloride, zinc chloride, magnesium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, zinc sulfate, magnesium sulfate,
Ammonium nitrate, sodium monophosphate, ammonium phosphate, calcium phosphate, sodium polyphosphate, sodium hexametaphosphate, sodium formate, ammonium formate, sodium acetate, potassium acetate, sodium monochlorate, sodium malonate, sodium tartrate, potassium tartrate, sodium citrate , Potassium citrate, sodium lactate, sodium gluconate, sodium adipate, ammonium salts of inorganic or organic acids such as sodium dioctylsulfosuccinate and metal salts, methylamine, diethanolamine, diethylenetriamine,
Various additives such as diisopropylamine can be appropriately used. Further, as an auxiliary agent, a defoaming agent, a coloring agent, a release agent, a flow modifier, a water-proofing agent, a preservative and the like can be used if necessary.

The support for the cast coated paper is not particularly limited, and an acidic base paper or a neutral base paper generally used in the coated paper field is applied. It should be noted that an undercoat base paper obtained by preliminarily coating a general pigment coating composition on one or both sides of the base paper can also be appropriately used. In this case, the coating amount is preferably about 5 to 30 g / m ^{2 on a} dry basis per one side. Further, if necessary, this pre-coated base paper may be subjected in advance to smoothing treatment such as super calendering, brushing and cast finishing.

An aqueous composition for cast coated paper comprising the above materials is prepared to have a solid content concentration of about 45 to 65% by weight so that the solid coating amount is about 5 to 30 g / m ^2. Generally, a publicly known and publicly used coating device such as a blade coater, an air knife coater, a roll coater, a brush coater, a chanplex coater, a bar coater or a gravure coater is used.

After applying the aqueous composition for casting by the above-mentioned method, the casting finish may be carried out by any of the usual wet casting method, rewetting casting method and gelling casting method, but especially casting The rewet casting method is preferable because it has an excellent effect of improving the releasability from the drum and the obtained cast coated paper surface has extremely high surface gloss. In this rewet casting method, the aqueous coating liquid for cast coated paper is once dried, and then the dried coating layer is rewetted and pressed against a heated mirror surface drum to give a strong gloss finish. The rewetting liquid is not particularly limited, and for example, a release agent such as polyethylene emulsion, fatty acid soap, calcium stearate, microcrystalline wax, surfactant, and funnel oil is used in an amount of about 0.01 to 3% by weight. A normal rewetting liquid such as an aqueous solution or emulsion containing the same is used. Further, it is of course possible to use a phosphate such as alkali or sodium hexametaphosphate, urea, an organic acid or the like in combination for promoting plasticization of the dry coating layer. It is also effective to perform smoothing treatment such as super calendering or brushing before rewetting the coated layer.

[0022]

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the examples, parts and% are parts by weight and% by weight, respectively, unless otherwise specified.

Examples 1 to 4, Comparative Examples 1 to 4 70 parts of kaolin, 30 parts of calcium carbonate, and 0.5 parts of sodium polyacrylate were stirred and dispersed in water using a Choles disperser, and the solid content concentration was 65%. A pigment slurry of was prepared. Into this slurry, 0.5 parts of tributyl phosphate as an antifoaming agent, 1.0 part of ammonium stearate as a releasing agent, and 10 parts of a 15% casein aqueous solution (as a solid content) dissolved using ammonia water as an adhesive are shown. 1
16 parts of the copolymer latex shown in Example 1 (Example 1 ... A, Example 2 ... B, Example 3 ... C, Example 4 ... D, respectively).
Comparative Example 1 ... E, Comparative Example 2 ... F, Comparative Example 3 ... G, Comparative Example 4
(H corresponds), 2 parts of ZnSO ₄ and water were further added, and the pH was adjusted to 8 with aqueous ammonia to prepare a coating liquid for casting with a solid content concentration of 45%. The casting coated liquid, dry weight using an air knife coater on a rice basis 64 g / m ² base paper after coated such that 20 g / m ^2, and dried by air flow Tay ring drier. Next, the coated paper is passed through a press nip formed by a press roll and a cast drum, and the rewetting liquid (1.0% concentration) composed of polyethylene emulsion supplied from a nozzle is applied to the surface of the coated layer. After rewetting,
Pressing pressure 200Kg on cast drum with surface temperature 105 ℃
A cast coated paper was obtained by press-contacting with / cm and drying.

Example 5 As a pigment, 80 parts of kaolin, 20 of heavy calcium carbonate
Parts, 4 parts of oxidized starch as an adhesive and 15 parts of a monolayer styrene-butadiene copolymer latex (as a solid content), and zirconium ammonium carbonate 0.5 as a waterproofing agent.
Parts by stirring with a Choles disperser, mixing, solid content concentration 55%
A coating liquid for undercoat was prepared. The base paper on the dry weight of the undercoating coated liquid Beitsubo 60 g / m ² is coated with a blade coater so that the 12 g / m ^2, and dried to obtain an undercoat base paper for the cast coated paper.

Next, 80 parts of kaolin, 20 parts of light calcium carbonate, 12 parts of 15% aqueous casein solution (solid content) dissolved in aqueous ammonia, 1 part of ammonium stearate as a release agent, and the copolymers shown in Table 1. 15 parts of latex (latex B) was stirred and mixed using a stirrer to prepare a cast coating liquid having a solid content concentration of 45%. This coating solution was applied to the above base paper for cast coated paper with a dry weight of 1
It was coated with a roll coater so as to have a weight of ² g / m ² , pressed against a cast drum having a surface temperature of 90 ° C. at a pressing pressure of 30 kg / cm, and dried to obtain a cast coated paper by a wet casting method.

Table 2 shows the evaluation results of the thus obtained cast coated paper with respect to white paper gloss, surface strength, and releasability from the drum during casting. The above evaluation method was performed as follows.

[Glossiness of White Paper] It was measured according to JIS-P-8142.

[Surface Strength] The surface of the cast coated paper was printed 5 times with 0.4 cc of sheet offset ink (trade name: Graf-G ink / Dainippon Ink and Chemicals) using an RI type printing tester. The surface peeling state of the printed surface was observed and judged according to the following criteria. ◯: Excellent in surface strength and no peeling of the coat layer on the surface of the cast coated paper. Δ: A slight peeling of the coat layer on the surface of the cast coated paper is recognized, but there is no problem in practical use. X: The peeling of the coat layer on the surface of the cast coated paper is remarkable.

[Releasability] In the continuous production operation, the releasability was evaluated as follows depending on the presence or absence of the drum pick. ◎: Continuous production is possible without drum picking. ○: Some drum picks occur, but continuous production is possible. ×: Drum picks occur frequently and continuous production is impossible

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

As is apparent from the results of Table 2, the cast coated paper obtained by the method of the present invention has excellent releasability (operability) from the cast drum, and the cast coated paper obtained. The paper had excellent white gloss and printing strength.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Koike 1-2-1, Yokou, Kawasaki-ku, Kawasaki-shi, Kanagawa Japan Zeon Corporation Research and Development Center

Claims (2)

[Claims] 1. An aqueous composition for cast coated paper, which comprises a pigment and an adhesive as main components, is provided on a support, and then pressed against a heating drum having a mirror surface while the aqueous composition is in a wet plastic state. In the method for producing a cast coated paper which is finished by drying, as the adhesive, a copolymer in which the main component of the core portion is styrene and butadiene as essential monomer units, and the main component of the shell portion are methyl methacrylate And a copolymer latex having a core-shell structure composed of a copolymer containing butadiene as an essential monomer unit. 2. The aqueous composition for cast coated paper provided on a support is once dried, and then the dried aqueous composition is brought into a wet plastic state again by pressure contact with a heating drum having a mirror surface to dry the composition. Item 2. A method for producing a cast coated paper according to item 1.