JPH09209296A - Production of cast-coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a cast-coated paper having excellent surface gloss and printability in high operability. SOLUTION: A cast-coated paper is produced by coating at least one surface of a base paper with an aqueous coating composition composed mainly of pigment and adhesive, drying the applied coating material to obtain an undercoating layer, applying a cast-coating layer to the surface of the undercoating layer and subjecting the coating layer to glazed finish treatment comprising the pressing of the layer against a mirror-finished hot roll followed by the peeling of the layer after drying. The coating rate of the undercoating layer to the base paper is especially >=12g/m<2> . A soybean protein synthetic graft copolymer is used as a main component of the coating layer for casting. As necessary, an inorganic pigment may be included in the coating layer in an amount of <=60wt.% based on the total solid content of the coating layer for casting. The dry coat weight of the coating layer for casting is 0.1-5g/m<2> .

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing cast coated paper, and more particularly to a method for producing cast coated paper having excellent surface gloss and printability and excellent operability.

[0002]

2. Description of the Related Art Cast coated paper is one of printing coated papers.
It is a typical coated paper with high gloss and high smoothness, and its application is also used in various fields such as general book text paper, cover, book cover cosmetic case, calendar paper, etc. ing. As a general method for producing a cast coated paper, a coating composition for casting mainly composed of a pigment and an adhesive is coated on a base paper, and then while the coating composition is in a wet plastic state. Wet casting method in which a heated drum surface having a mirror surface is pressed, dried, and then peeled off to obtain a high gloss finish, a cast coating composition mainly composed of a pigment and an adhesive is once coated on a base paper, dried and then coated. After the coating layer is wet-plasticized with a rewetting liquid, a rewet cast method in which it is pressed against a heating drum surface and dried to obtain a high gloss finish, and the coating layer in a wet state is gelled There is known a gelling casting method in which the surface of the heating drum is pressed to obtain a gloss finish. In the method for producing the cast coated paper, the coating composition provided on the base paper is pressed against a mirror surface drum heated while the plastic composition is in a wet plastic state, and dried and peeled to give a strong gloss finish. Have in common.

However, in recent years, along with the trend toward higher quality printed matter, paper containers, etc., transparent resin is printed on ordinary coated paper or cast coated paper for the purpose of adding higher gloss, gloss, or smoothness. Widely used are varnished paper coated by the above method, press-coated paper that is coated with a large amount of resin on the surface of the paper and has a gloss finish, and laminated paper in which a plastic film such as polyethylene is attached to the surface.

By the way, varnished paper, press coated paper,
Or, since laminated paper cannot be printed on it normally, it must be printed before processing and then varnished or laminated to add a sense of quality. In addition to being disadvantageous, the high-gloss paper processed as described above spends a great deal of time and energy on the disaggregation performed for reprocessing, and has a problem in terms of recycling broke. ing. In view of the above situation, there is a strong demand for the development of cast coated paper having a high degree of gloss and gloss without the need for special processing such as varnishing and laminating.

To improve the gloss and shine of cast coated paper, it is possible to some extent by increasing the amount of the adhesive in the cast coating composition, but at present it is as good as press coated paper or laminated paper. Is not improved. Originally, the coating composition was mainly composed of a pigment and an adhesive, and 1
A large amount of solid content coating such as 0 to 40 g / m ² is provided on the base paper, and by increasing the amount of adhesive in the coating composition, the porosity of the coating layer is lost, resulting in As a result, the vapor permeability of the coating layer and the releasability from the cast drum are deteriorated, the production speed is significantly reduced, and the printability, especially the ink setting and ink drying characteristics of cast coated paper, are extremely low. There are difficulties such as deterioration.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for producing cast coated paper, and particularly, to efficiently and stably produce cast coated paper having high gloss comparable to that of laminated paper and having excellent printability. The present invention provides a possible manufacturing method.

[0007]

According to the present invention, an aqueous undercoating composition containing a pigment and an adhesive as a main component is applied to at least one side of a base paper and dried to form an undercoating coating layer.
A cast coated paper is provided on which a cast coating layer is provided on the undercoat coating layer, and while the cast coating layer is in a wet plastic state, press-contacts with a heated mirror surface drum and peels after drying to obtain a high gloss finish. In the production method, the coating amount of the undercoat coating layer on the base paper is 12 g / m ² or more, and the soybean protein synthetic graft copolymer is the main component as a component of the coating layer for casting, and if necessary, an inorganic pigment Can be contained up to 60% by weight with respect to the total solid content of the coating layer for casting,
And the dry coating amount of the coating layer for casting is 0.1 to 5 g / m.
^The method for producing cast coated paper is characterized in that coating is performed so as to be ² .

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Based on the above-mentioned circumstances, the inventors of the present invention have conducted earnest studies to obtain a cast coated paper which has a high gloss and gloss comparable to those of laminated paper and has excellent printability. . As a result, by providing a cast coating layer having a soy protein synthetic graft copolymer as an essential component on the undercoat layer provided on the base paper, it has an extremely excellent gloss desired by the present invention, and printability. The inventors have found that an excellent cast coated paper can be efficiently obtained and have completed the present invention.

Regarding the application of the soybean protein synthetic graft copolymer to cast coated paper, JP-A-3-45 is known.
Although it has been disclosed in Japanese Patent No. 797 that relatively good operability and gloss can be obtained, it has not reached the target of the present invention to obtain gloss comparable to that of press-coated paper or laminated paper.

That is, the present invention is provided on at least one side of the base paper,
An aqueous coating composition containing a pigment and an adhesive as a main component is coated so that the solid content is 12 g / m ² or more, dried to form an undercoating layer, and then cast on the undercoating layer. In the method for producing a cast coated paper, wherein a coating layer for coating is provided, while the coating layer for casting is in a wet plastic state, pressure-contacted with a heated mirror surface drum, and peeling after drying to obtain a high gloss finish,
As the composition of the coating layer for casting, soybean protein synthetic graft copolymer is contained as an essential component, and the inorganic pigment is contained in an amount of 60% by weight or less based on the total solid content of the coating layer for casting, or inorganic. A method for producing cast-coated paper, comprising coating composition containing no pigment, and further coating the cast coating composition so that the dry coating amount is 5 g / m ² or less. .

In the present invention, the soybean protein synthetic graft copolymer used as a main component of the coating layer for casting is a soybean protein coating for general printing as disclosed in JP-A-2-123170. Used as a monomer during the polymerization of polymer latex used for paper,
For example, it is a copolymer obtained by graft-copolymerizing monomers such as styrene, butadiene, methyl acrylate, and methyl methacrylate. And as a monomer to be copolymerized, styrene and butadiene are preferably used.
The amount of the soybean protein synthetic graft copolymer contained in the coating layer for casting is 10 to 1 with respect to 100 parts by weight of the coating layer for casting (solid content).
It is adjusted in the range of 00 parts by weight. Incidentally, if it is less than 10 parts by weight, excellent releasability cannot be obtained, and stable cast coating may not be possible.

The soybean protein synthetic graft copolymer used in the present invention, as disclosed in Japanese Patent Application Laid-Open No. 3-45797, has a relatively excellent peeling property from the metal mirror drum in the portion acting as a synthetic binder. Since it is surrounded by and protected by the soybean protein shell, it is possible to obtain a good peeling property as compared with the case of using the ordinary synthetic binder alone. On the other hand, in the method proposed in JP-A-3-45797, since 10 to 25 parts by weight of the soybean protein synthetic graft copolymer is used as a binder per 100 parts by weight of the pigment, the pigment ratio is high, and Due to the porosity of the pigment itself, the high gloss desired by the present invention cannot be obtained. By the way, although gloss can be increased by increasing the ratio of the binder to the pigment, on the other hand, problems of poor ink drying property and poor releasability occur.

In the present invention, by using the above-mentioned soybean protein synthetic graft copolymer as the main component of the coating layer for casting, it is possible to improve the releasability from the metal drum surface and at the same time maintain the printability and to obtain an excellent whiteness. The inventors have found a method for effectively obtaining a cast coated paper having extremely high gloss by combining the requirements described in detail below in order to obtain the gloss on the paper surface.

That is, first, in order to obtain a high gloss, it is necessary that the surface of the cast coating layer sufficiently copies the surface gloss of the mirror surface drum. In the present invention, as described above,
It is an essential requirement to use a soy protein synthetic graft copolymer, but in addition to that, a synthetic polymer latex used in general coated paper can be used as a film-forming binder in combination, and furthermore, it is usually cast coated. Inorganic pigments used in paper and coated paper for general printing can be used in an amount of up to 60% by weight, if necessary, with respect to the entire coating layer for coating (coating composition). 20 pigments
It is a more preferable embodiment from the viewpoint of printability and releasability that it is used in an amount of 50 to 50% by weight. Incidentally, if the blending ratio of the inorganic pigment exceeds 60% by weight, the excellent high gloss desired by the present invention cannot be obtained.

Examples of the inorganic pigment include clay,
Kaolin, aluminum hydroxide, calcium carbonate, titanium dioxide, barium sulfate, zinc oxide, satin white,
Examples include calcium sulfate, talc, plastic pigment, colloidal silica and the like. Further, as the synthetic latex binder that can be used in combination with the soybean protein synthetic graft copolymer, a conjugated diene copolymer latex such as styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, a polymer of acrylic acid ester and methacrylic acid ester is used. Alternatively, an acrylic polymer latex such as a copolymer, a vinyl polymer latex such as an ethylene-vinyl acetate copolymer, or these various polymers or copolymers may be prepared by using a monomer containing a functional group such as a carboxyl group. , Functional group-modified alkali-soluble or alkali-insoluble (co) polymer latex, polyvinyl alcohol, olefin-maleic anhydride resin, and the like.

Further, in the coating composition (hereinafter, simply referred to as a coating) constituting the coating layer for casting in the present invention, a releasing agent may be used in combination for improving the releasability, if necessary. You can also Examples of the release agent in that case include fatty acids such as stearic acid and oleic acid and metal salts thereof,
Hydrocarbons such as microcrystalline wax and polyethylene emulsion, higher alcohols such as cetyl alcohol and stearyl alcohol, various surfactants such as fluorine-containing surfactants, funnel oil, lecithin, tetrafluoroethylene polymer and ethylene tetrafluoride. Fluoropolymers such as ethylene polymers are exemplified. Further, in order to adjust the whiteness, ink acceptability, blocking suitability, fluidity, etc., pigments, dispersants, defoamers, which are used in the production of general printing coated paper and cast coated paper, Various auxiliaries such as colorants, antistatic agents and preservatives are appropriately added.

Thus, as a coating material for casting composed of the above-mentioned materials, the solid content concentration is generally adjusted to about 10 to 65% by weight, and dried on the undercoating layer mainly composed of pigment and adhesive. 0.1-5 g / m ² by weight, and preferably after coated so that 0.5 to 2 g / m ^2, cast finished by immediately heated pressed against the mirror surface drum, dried, and peeled . By the way, the coating amount is 5g /
If it exceeds m ² , the releasability and the ink drying property deteriorate, which is not preferable. If it is less than 0.1 g / m ² , the desired gloss may not be obtained.

The coating device used for coating the above-mentioned paint is, for example, a blade coater,
Known publicly-used devices such as an air knife coater, roll coater, brush coater, champlex coater, bar coater and gravure coater are appropriately used. Particularly in the case of the present invention, immediately after (in the wet plasticized state) a gloss finish is applied by wet casting after coating the casting coating on the undercoat coating to obtain a coating for casting.

Next, the undercoating aqueous coating composition (hereinafter simply referred to as paint) used in the present invention is mainly composed of a pigment and an adhesive which are generally used in the field of producing cast coated paper. The paint used is not particularly limited. Incidentally, examples of the pigment include kaolin, aluminum hydroxide, satin white, barium sulfate, heavy calcium carbonate, light calcium carbonate, talc, hectorite, plastic pigment, calcined clay, titanium dioxide, alumina, amorphous silica, mica, etc. Are exemplified, and at least one of them is appropriately selected and used.

Examples of the adhesive include proteins such as casein and soybean protein, conjugated diene polymer latex such as styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer, acrylic acid ester and / or methacrylic acid ester. Of acrylic polymer latex such as polymer or copolymer of (1), vinyl polymer latex such as ethylene-vinyl acetate copolymer, or these various polymers are functionalized with a functional group-containing monomer such as carboxyl group. Group-modified alkali-soluble or alkali-insoluble polymer latex, polyvinyl alcohol, olefin-maleic anhydride resins, synthetic resin adhesives such as melamine resins, starches such as positive starch, oxidized starch, esterified starch, etc. , Carboxymethyl cellulose, hydroxyethyl cellulose Like cellulose derivatives, one or more adhesives known for general coated paper is appropriately selected and used. The amount of the adhesive used is 5 to 50 parts by weight, generally 10 to 100 parts by weight of the pigment, based on the solid content.
It is adjusted in the range of 30 parts by weight. In addition to the pigments and adhesives as described above, antifoaming agents, colorants, mold release agents, flow modifiers, water resistance agents, preservatives, etc. are used as necessary in the paint. .

Thus, the undercoating paint comprising the above materials is generally adjusted to a solid content concentration of about 10 to 65% by weight, and has a dry weight on a base paper having a weight of about 35 to 400 g / m ^2. Of 12 to 50 g / m ² , more preferably 2
It is generally coated using a publicly known and used coating device so as to have a weight of 0 to 35 g / m ² . After applying the coating material, it can be used as an undercoat coating layer in a dried or semi-dried state. By the way, when the coating amount is less than 12 g / m ² , even if the coating material for casting is applied thereon, the unevenness of the surface of the undercoat coating layer is not sufficiently covered, resulting in uneven gloss or pinholes. Not preferable. Further, when the coating amount exceeds 50 g / m ² , there is a concern that the coating layer may be broken when the cast coated paper is inadvertently folded after finishing the product, that is, so-called crevice cracking may occur. It

The smoothness of the coating layer surface after the base paper is coated with the undercoating paint and dried is 300 seconds as measured by a Beck's smoothness meter (the larger the value, the better the smoothness).
The above is a more preferable embodiment because excellent high gloss is exhibited. As a means for improving the smoothness, a pressure means such as a super calender is usually used as appropriate. The upper limit of smoothness is not particularly limited, but 5000 seconds is sufficient for practical use. If the smoothness is further increased, the breathability and the like will be deteriorated, and there is a risk that productivity will decrease and a new problem in terms of quality such as paper habit will occur.

The base paper used in the present invention is not particularly limited, and acidic base paper, neutral base paper and the like generally used in the field of manufacturing cast coated paper are appropriately used.

[0024]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In the examples, parts and% are parts by weight and% by weight, respectively, unless otherwise specified.

Example 1 As a soybean protein synthetic graft copolymer, RXP-5
35 (Protein Technologies International Inc./USA) 50 parts, Kaolin (trade name: U
W-90 / EC) (48 parts), and 2 parts of calcium oleate as a releasing agent, a coating composition for casting having a solid content concentration of 47% was prepared and cast-finished by a wet casting method.

That is, 65 parts of kaolin (trade name: UW in advance
-90 / EC), heavy calcium carbonate (trade name: Carbital 90 / ECC) 35 parts, styrene-butadiene copolymer latex (trade name: DL-636 / Asahi Kasei) 15 parts, and oxidized starch. of 3 parts (each, in terms of solid content), so that the solid content becomes dry weight of 50% of the undercoat paint a blade coater and 25 g / m ^2, coated on basis weight 95 g / m ² on quality base paper Then, it was dried to obtain a base paper for cast coated paper (Beck smoothness: 120 seconds) having a basis weight of 120 g / m ² . Then, the coating layer surface of the base paper for cast coated paper is coated with the above-prepared coating material for casting with a roll coater so that the dry weight is 2 g / m ² .
Immediately, the coated surface is cast drum (surface temperature 80 ℃)
After press contacting, drying and peeling from the cast drum surface, a cast coated paper was obtained.

Example 2 In Example 1, in preparing the cast paint,
Soybean protein synthetic graft copolymer (RXP-535)
And a coating composition for casting having a solid content concentration of 40%, which comprises 98 parts of
A cast coated paper was obtained in the same manner as in Example 1 except that the coating weight of the coating material for casting was 1 g / m ² on a dry basis.

Example 3 In Example 1, in preparing the cast paint,
Soybean protein synthetic graft copolymer (RXP-535)
40 parts, styrene-butadiene copolymer latex (Asahi Kasei L-1392) 20 parts, kaolin (UW-90) 3
8 parts, and 2 parts of calcium oleate as a release agent (each solid content), a coating composition for casting having a solid content concentration of 45% was prepared, and the coating weight of the coating composition for casting was 1 g / m 2 dry weight. ^A cast coated paper was obtained in the same manner as in Example 1 except that the number ² was used.

Example 4 In Example 1, the solid content concentration of the coating material for casting was 45
%, And a cast coated paper was obtained in the same manner as in Example 1 except that the coating amount was 1 g / m ² in terms of dry weight.

Example 5 In Example 1, the solid content concentration of the casting paint was 40%.
%, And cast coated paper was obtained in the same manner as in Example 1 except that the coating weight was 0.5 g / m ² in terms of dry weight.

Example 6 In Example 1, in preparing the coating composition for casting,
Soybean protein synthetic graft copolymer (RXP-535)
A coating composition for casting having a solid content concentration of 52%, which comprises 40 parts, 58 parts of kaolin (UW-90), and 2 parts of polyethylene wax emulsion (each solid content) as a mold release agent, and is coated with the coating composition for casting. 4 g dry weight
A cast coated paper was obtained in the same manner as in Example 1 except that / m ² was used.

Example 7 In Example 1, the undercoat coating amount was 15 by dry weight.
A cast coated paper was obtained in the same manner as in Example 1 except that the amount was changed to g / m ² . The Bekk smoothness of the base paper for cast coated paper in this case was 180 seconds.

Example 8 The base paper for cast coated paper (undercoated paper) used in Example 1 was placed in a super calender at a linear pressure of 300 kg.
/ Cm, paper is passed twice, and the Bekk smoothness of the undercoat layer is 3
A cast coated paper was obtained in the same manner as in Example 1 except that the base paper having a time of 80 seconds was used.

Example 9 In Example 1, instead of kaolin in the coating composition for casting, precipitated calcium carbonate (trade name: Brilliant S) was used.
15 / manufactured by Shiraishi Industry Co., Ltd.) to make the solid content concentration of the coating 44%, and the dry coating amount of the coating 1.5g.
The coated paper was coated so as to be / m ² , dried, and then peeled to obtain a cast-coated paper in the same manner as in Example 1.

Comparative Example 1 In Example 1, in preparing the coating material for casting,
Soybean protein synthetic graft copolymer (RXP-535)
A coating composition for casting having a solid content of 47% was prepared, which was composed of 30 parts, 68 parts of kaolin (UW-90), and 2 parts of calcium oleate as a release agent, and the dry coating amount of the coating material was 4 g / A cast-coated paper was obtained in the same manner as in Example 1 except that the coating was carried out so as to give m ² .

Comparative Example 2 In Comparative Example 1, the solid content concentration of the casting paint was 52
%, And cast coated paper was obtained in the same manner as in Comparative Example 1 except that the coating amount was 12 g / m ² in terms of dry weight.

Comparative Example 3 In Example 1, in preparing the coating composition for casting,
Instead of the soy protein synthetic graft copolymer, styrene-butadiene copolymer latex (Asahi Kasei L-139
A cast coated paper was obtained in the same manner as in Example 1 except that the same amount of 2) was used.

Comparative Example 4 In Example 1, the coating amount of the undercoat paint was 1 by dry weight.
A cast coated paper was obtained in the same manner as in Example 1 except that the coating was performed so that the coating amount became 0 g / m ² . At this time, the Bekk smoothness of the surface of the undercoat coating layer was 200 seconds.

Comparative Example 5 In Example 1, the solid content concentration of the casting paint was 10
%, And cast coated paper was obtained in the same manner as in Example 1 except that the coating weight was 0.08 g / m ² in terms of dry weight.

Comparative Example 6 As a paint for casting, 12 parts of soybean protein synthetic graft copolymer (RXP-535) and kaolin (UW-9) were used.
0) A coating composition for casting having a solid content concentration of 58% was prepared which was composed of 76 parts, 10 parts of heavy calcium carbonate, and 2 parts of calcium oleate (a solid content) as a release agent. Immediately after coating on a high quality base paper of 120 g / m ² so that the dry weight was 25 g / m ² , cast finishing was carried out in the same manner as in Example 1.

Comparative Example 7 Kaolin (UW-90) 70 was used as a paint for casting.
Part, light calcium carbonate (trade name: PX / Shiraishi Kogyo)
30 parts, styrene-butadiene latex (DL-63
6) 12 parts, 10 parts casein dissolved in aqueous ammonia,
As a mold release agent, a coating composition for casting comprising 1 part of calcium stearate (each calculated as solid content) and having a solid content of 50% was prepared. A cast finish was applied to the base paper for cast coated paper (on the base coated paper) used in Example 1 in the same manner as in Example 1 so that the coating amount was 12 g / m ^{2 in} dry weight. went.

The cast coated paper thus obtained was evaluated for white paper gloss, ink setting property and releasability from the drum according to the following methods, and the results are shown in Table 1.

[White Paper Gloss] The 75-degree gloss and 20-degree gloss according to JIS P8142 were measured.

[Ink settability] Ink for sheet offset by RI printing tester (Gr.
af-G black) 0.6 cc was used to print the surface of the cast coated paper once, and immediately after the printing, 2 minutes after the printing, and 4 minutes later, the high-quality paper was superposed on the surface of the cast coated paper (printing). The ink density transferred to the high-quality paper was pressed under a constant pressure, and the ink density was observed and judged according to the following criteria. ⊚: Ink hardly transferred to the high-quality paper after 2 minutes. ◯: Ink hardly transferred to the high-quality paper after 4 minutes. Δ: The transfer density after 4 minutes was about half of the ink transfer density immediately after printing, and the drying speed was slightly slow. X: The transfer density after 4 minutes was slightly thin with respect to the ink transfer density immediately after printing, and the drying speed was considerably slow.

[Operability (Releasability)] Continuous production operation (10
After a lapse of time), the releasability was evaluated as follows by determining the presence or absence of a drum pick. ◎: Continuous operation is possible without drum picking. ○: Continuous operation is possible although some drum picks occur. ×: Paper stuck to the drum surface, making operation impossible.

[0046]

[Table 1]

[0047]

As is clear from the results shown in Table 1, the method of the present invention can produce cast coated paper which is excellent in releasability (productivity) from the drum and has no problem in operability. The cast coated paper obtained had no gloss unevenness and was extremely excellent in white paper gloss, printing strength and ink setting property.

Claims (4)

[Claims] 1. A pigment and an adhesive on at least one side of a base paper.
Apply the water-based coating composition containing the agent as the main component and dry it.
After providing the undercoat layer, for casting on the undercoat layer
A coating layer is provided and the casting coating layer is in a wet plastic state
In between, pressure contact with the heated mirror surface drum, peeling after drying, and strong
In the manufacturing method of cast coated paper with gloss finish,
12g / m coating amount of undercoat coating layer on paper^TwoAnd above,
In addition, the soybean protein content is used as the composition of the coating layer for casting.
Made of graft graft copolymer as the main component, if necessary inorganic
Pigment up to 60% by weight based on the total solid content of the cast coating layer
Can be included and the coating layer for casting is dried
Coating amount is 0.1-5g / m ^TwoTo be coated
A method for producing a cast coated paper, which comprises: 2. The method for producing cast coated paper according to claim 1, wherein the inorganic pigment is contained in an amount of 20 to 50% by weight based on the total solid content of the cast coating layer. 3. The dry coating amount of the coating layer for casting is 0.5-.
The method for producing cast coated paper according to claim 1 or ² , wherein the amount is ² g / m ² . 4. The method for producing a cast coated paper according to claim 1, wherein the undercoat coated layer has a smoothness of 300 seconds or more as measured by a Beck's smoothness meter.