JPH0826274B2 - Coating composition and cast-coated paper obtained by applying the composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a composition for cast coated paper, which can be produced at high speed, and a cast coated paper obtained by coating the composition.

{Prior Art} As methods for producing cast coated paper, there are a wet casting method, a gelling casting method, a rewetting method and the like. The wet cast method is a method in which a water-based paint containing a pigment and an adhesive is applied to a base paper and then adhered to a high-temperature mirror drum (hereinafter referred to as a cast drum) in a wet state and dried. It is a method of adding a coating agent to the base paper and then contacting and drying it on a cast drum in a wet state, or a method of applying an aqueous coating material to a base paper and then applying a coagulant and then contacting and drying on a cast drum in a wet state. The rewetting method is a method in which a water-based paint is applied to a base paper, dried once, re-wet, and then adhered and dried on a cast drum. Therefore, while high-gloss art paper is supercalendered in a dry state, cast coated paper is smoothed in any of the methods in a wet state, that is, a coating layer having high plasticity,
A coated surface with high smoothness and higher gloss can be obtained.

However, after the coated surface containing a large amount of water is brought into close contact with the cast drum surface and dried, it is possible to release the coated surface from the cast drum surface without resistance to obtain a coated surface with high gloss and no defect. This is an important requirement. Conventionally, good adhesion to the cast drum to impart high gloss causes a problem that releasability is greatly reduced, so cast with high gloss and few coating surface defects such as pinholes Obtaining coated paper at high speed required advanced technology.
In particular, when the release speed of the coating surface from the cast drum is increased for high-speed production, the release resistance increases, and sometimes the coating film adheres to the drum and is partially picked up (hereinafter, the resulting coating surface defect). Are referred to as pits), and a coated surface having no defect and uniform gloss was not obtained. Another problem during high-speed production is that it is necessary to quickly evaporate the water on the cast drum, but the higher the speed of operation, the shorter the time the coated paper stays on the drum. Is a new problem that arises due to the requirement for high water vapor movement speed. That is, especially in the rewetting method, the surface is formed under high pressure on the cast drum for surface formation, but during high speed operation, water often forms a pool between the drum surface and the coating film. It was difficult to sufficiently remove water through the voids in the coating film. As a result, pits of a different type from the pits formed by the pickup were formed in the coating film, and defects were remarkably generated on the surface of the cast coated paper.

{Problems to be solved by the invention} Therefore, in order to solve the above problems of cast coated paper even a little and enable high-speed production while maintaining the coated surface quality, a pigment and an unsaturated carboxylic acid are contained as monomer components. Also proposed is a method of adding zinc, aluminum, magnesium, etc. sulfates, nitrates, formates, acetates, etc. as coagulants to paints containing adhesives such as latex and casein as a coagulant (Japanese Patent Publication 60-146097). However, even with this method, the production rate was still low and unsatisfactory.

Therefore, an object of the present invention is to produce a cast coated paper, particularly in a rewet method which has a relatively high production rate, and has excellent releasability, high shine and good surface strength with no pits even at high speed production which has not been hitherto known. It is intended to provide a coating composition capable of obtaining the cast coated paper having the above and a cast coated paper obtained by applying the composition.

{Means for Solving the Problems} In order to solve the above problems, in a paint for cast coated paper containing a pigment and an adhesive as main components, a rubber having a gel content of 50% or more as the adhesive. Provided are a coating composition for cast coated paper, which comprises a system latex (A) and an acrylic emulsion (B) having a gel content of 50% or more, and a cast coated paper obtained by coating the composition.

The present invention uses a rubber latex (hereinafter simply referred to as a latex) and an acrylic emulsion as the adhesive in a coating material for cast coated paper containing a pigment and an adhesive as main components, and the molecular weight of the polymer of the latex and the acrylic emulsion. The inclusion of a certain percentage by weight (usually referred to as the gel content) of the toluene insoluble matter in the dry film, which is related to the degree of crosslinking and the polarity, enables high-speed production of cast coated paper.

In the present invention, the reason why the combined use of the latex (A) and the acrylic emulsion (B) as the adhesive is defined when the latex (A) is used alone or the acrylic emulsion (B) is used alone as the synthetic binder. In the case of use, the cast coat obtained using the coating composition according to the above has a poor releasability from the drum surface during production of the cast coat paper, which makes the high-speed production which is the object of the present invention difficult, or the obtained cast coat. This is because the paper has low surface strength and cannot withstand practical printing.

In the present invention, the reason why the gel contents of the latex (A) and the acrylic emulsion (B) are both limited to 50% or more is that the gel content of the latex (A) is 50%.
When it is less than 50%, even if the gel content of the acrylic emulsion (B) is 50% or more, the releasability from the cast drum surface of the coated paper due to it becomes poor and a smooth coated surface without pits is obtained. If the gel content of the acrylic emulsion (B) is less than 50%, even if the gel content of the latex (A) used in combination is 50% or more, cast coating of a coating composition depending on this is difficult. This is due to the fact that there are many pits on paper and high-speed production is difficult. The gel contents of the preferred latex (A) and acrylic emulsion (B) are both 60% or more.

In the present invention, the synthetic binder is preferably used in an amount of 5-19 parts by weight of the latex (A) and 3-13 parts by weight of the acrylic emulsion (B) with respect to 100 parts by weight of the pigment.

In the present invention, latex is a general term for rubber-based emulsions, and from that meaning, the components contained in latexes include diene-based monomers such as butadiene, isoprene, and 2-chlorobutadiene as essential components. Is a general term for a polymer emulsion which does not contain these diene-based monomers and has a monomer as described below as a main component. Aromatic alkenyl compounds such as styrene, α-methylstyrene, chlorostyrene and dimethylstyrene as the main monomer component in the acrylic emulsion as a copolymerization monomer component other than the diene monomer in the latex. And methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, glycidyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate , Glycidyl methacrylate, acrylamide, N-methylol acrylamide, N-methoxymethyl acrylamide, methacrylamide, N-methylol methacrylamide, N-methoxymethyl methacrylamide, acrylic acid, methacryl Monoolefinic unsaturated compounds such as acid, crotonic acid, fumaric acid alkyl ester, itaconic acid alkyl ester, acrylonitrile, methacrylonitrile, vinyl acetate, etc. are used as monomers, but these monomer components are a combination of two or more kinds. Can also be used in.

The gel content of the latex can be adjusted by using mercaptans such as alkyl mercaptans and tertiary mercaptans and chain transfer agents such as carbon tetrachloride and higher alcohols. It is effective to use not only one of these but also two or more of them in combination, and the amount used of these is usually relative to all monomers.
It is 5.0% by weight or less. The gel content of the acrylic emulsion is intramolecular using a monomer having a carboxyl group, a monomer having a hydroxyl group, a monomer having a methylol group, a monomer having a glycidyl group, etc. as a sub-monomer component. Alternatively, there are a method of adjusting by intermolecular crosslinking reaction and a method of adjusting by using a monomer having a divinyl group as an auxiliary monomer component. Either method is effective, and both methods can be used in combination.

In the above, the monomer having a carboxyl group is acrylic acid, methacrylic acid, itaconic acid, maleic acid, aconitic acid, citraconic acid, etc., and the monomer having a hydroxyl group is hydroxyethyl (meth) acrylate, ( A monomer having a methylol group such as hydroxypropyl (meth) acrylate is methylol (meth) acrylamide, methoxymethyl (meth) acrylamide, etc., and a monomer having a glycidyl group is glycidyl (meth) acrylate. It is preferable to use two or more kinds of these functional group-containing monomers in combination, and the amount of the functional group-containing monomer used relative to all the monomers is usually 1.0 to 10% by weight. Further, the monomer having a divinyl group is allyl (meth) acrylate, ethylene di (meth) acrylate, phenylenediacrylonitrile, divinylbenzene and the like. These may be used alone or in combination of two or more. Incidentally, the monomer having a functional group and the monomer having a divinyl group mentioned above are examples, and a monomer having a reactive functional group and a monomer having a polymerizable vinyl group are similarly exemplified. Can be used.

In the production of the synthetic binder of the present invention, a monomer as a main component and a chain transfer agent or a monomer as a gel content controlling agent as described above are used, and an ordinary initiator such as potassium persulfate or peroxide is used as a polymerization initiation catalyst. Water-soluble peroxides such as sodium sulfate and ammonium persulfate, or sodium bisulfite and these,
It is also possible to use it together with a water-soluble reducing agent such as sodium sulfite and sodium thiosulfate. Polymerization temperature of monomers is usually 50-100
In ° C, the pressure is in the range of 0-10 Kg / cm ^{2 in} gauge pressure. The addition of all the monomers used can be carried out by any of batch addition, divisional addition and continuous addition. Further, for stabilizing the particles during the polymerization, for example, an emulsifier such as sodium alkylbenzenesulfonate, sodium alkylsulfate, sodium alkylalcohol sulfate and the like, or a protective colloid agent such as hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol and the like can be added.

In the present invention, the pigment used in the paint is clay, calcium carbonate, titanium white, ordinarily used for coated paper,
Satin white, aluminum hydroxide, barium sulfate,
Inorganic pigments such as zinc oxide and magnesium oxide and organic pigments such as plastic pigments and white urea resin pigments can all be used, and there is no particular limitation on the selection of pigments for the purpose of the present invention.

In the present invention, in addition to the synthetic binders of the latex (A) and the acrylic emulsion (B), these and a water-soluble polymer such as casein or modified starch are usually used as pigments in the paint.
It is effective to use 2-15 parts by weight per 100 parts by weight.

Further, a known coagulant such as calcium formate, magnesium formate, zinc formate, calcium acetate, magnesium acetate, zinc acetate or a release agent such as magnesium stearate or zinc stearate may be appropriately used in the coating composition of the present invention. Can be done.

The cast coated paper of the present invention is a known coating apparatus generally used for producing pigment-coated paper such as an air knife coater, roll coater, blade coater, etc., in which the coating composition of the present invention thus obtained is used as a base paper. It is obtained by applying pressure once to a cast drum which has been coated with the above-mentioned material and once dried and then rewetted with wet water and heated to 60 ° C. or higher at a linear pressure of 10 Kg / cm or higher. The base paper used is not particularly limited, and any of those usually used for pigment-coated paper may be used.

{Action} As described in the above detailed description, in the coating composition obtained by the present invention, that is, the coating material for cast coated paper mainly containing the pigment and the adhesive, the latex (A) having a gel content of 50% or more, The cast-coated paper obtained by applying the coating composition prepared by using the acrylic emulsion (B) by a known method and contact-drying it on a cast drum has excellent surface gloss and uniform surface quality without pits. In addition, since it has excellent air permeability and releasability, high-speed productivity is also possible. The coating composition of the present invention is also useful as a coating material for cast-coated paper by a wet casting method other than the rewetting method, a gelling casting method or the like as in the rewetting method.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited by these Examples. Parts and% in these are based on weight unless otherwise specified.

First, production examples of the latex (A) and acrylic emulsion (B) used in this example are shown, and then examples and application examples of preparation of coating materials are shown.

Production Example 1 of Latex- (A) 120 parts of deionized water in an autoclave purged with nitrogen,
Sodium dodecylbenzene sulfonate 0.2 parts, potassium persulfate 0.8 parts, tertiary dodecyl mercaptan (hereinafter TDM
0.6 part) and 40 parts of butadiene as a monomer composition,
A total of 100 parts of 45 parts of styrene, 8 parts of methyl methacrylate and 2 parts of acrylic acid as a functional group monomer, 2 parts of acrylamide and 3 parts of hydroxyethyl methacrylate were charged and polymerized at 70 ° C.
Since it exceeded 98%, the reaction was stopped, and after cooling, the pH was adjusted to 7 with sodium hydroxide to obtain latex (A). The gel content was 75% (hereinafter referred to as latex A-1).

Production Example 2-6 of Latex (A) In Production Example 1 of Latex (A), latexes having different gel contents are prepared in exactly the same manner and operation as in Production Example 1 of Latex (A) except that only the amount of TDM used is changed. A
-2 to A-6 were obtained. The amount of TDM used and the gel content of the obtained latex (A) are shown in Table 1.

Comparative Production Example of Latex A latex having a gel content of 40% was obtained by exactly the same procedure and operation as in Production Example 1 of latex (A) except that the amount of TDM used was changed (hereinafter, latex ratio a-
1).

Production Example 1 of Acrylic Emulsion (B) Deionized water 12
A total of 100 parts of 0 part, 0.1 part of sodium dodecylbenzene sulfonate, 0.8 part of ammonium persulfate, 0.5 part of divinylbenzene and 40 parts of butyl acrylate as a monomer composition, 40 parts of styrene, 17 parts of acrylonitrile, and 3 parts of methacrylic acid were charged. Polymerization is carried out at ℃, and the polymerization rate is 97 after 8 hours.
%, The reaction was stopped, and after cooling, the pH was adjusted to 7 with an aqueous ammonia solution to obtain an acrylic emulsion (B) having a gel content of 75% (hereinafter referred to as acrylic emulsion B-1) Acrylic emulsion (B) Production Example 2-6 of Acrylic Emulsion (B) In Production Example 1 of the acrylic emulsion (B), except that the amount of divinylbenzene used is changed, acrylics having different gel contents are prepared by exactly the same procedure and operation as in Production Example 1 of the acrylic emulsion (B). Emulsion B-2 to B
I got up to -6. The amount of divinylbenzene used and the gel content of the resulting acrylic emulsion (B) are shown in Table 2.

Comparative Production Example of Acrylic Emulsion In Production Example 1 of Acrylic Emulsion (B), divinylbenzene was not used, but lauryl mercaptan was used instead.
An acrylic emulsion having a gel content of 40% was obtained by exactly the same procedure and operation except that 2 parts were used (hereinafter referred to as acrylic emulsion ratio b-1).

Example 1 An aqueous casein solution obtained by heating and dissolving 5 parts of 0.8% 28% ammonia water, 8 parts of milk casein and 44.5 parts of water.
3.3 parts (equivalent to 8 parts in terms of solid content) and 100 parts of water are put into a cowless mixer, and 40 parts of calcium carbonate (TP-222HS made by Okutama Kogyo) and kaolin (UW-90 made by EMC) while stirring.
After adding 60 parts and mixing and dispersing, 20% calcium acetate aqueous solution 3.
After adding 5 parts (equivalent to 0.7 part in terms of solid content), 12 parts of latex A-1 in solid content and acrylic emulsion B-1
Was added in a solid content of 7 parts. Finally, the coating solid content was adjusted to 40% to obtain a coating composition-1 for cast coated paper of the present invention.

Example 2-13 As shown in Table 3 for the combination of the latex A-1 and the acrylic emulsion B-1 used in Example-1, the latex (A) used A-1 to A-5, and the acrylic Emulsion (B) was prepared in the same manner and operation as in Example 1 except that B-1 to B-5 were combined to obtain coating compositions 2 to 13 for cast coated paper.

Comparative Example 1-3 A latex or an acrylic emulsion containing a gel component outside the limited range of the present invention in place of either or both of the latex A-1 and the acrylic emulsion B-1 used in Example-1. Comparative coating compositions 1 to 3 were obtained under the same procedure and conditions as in Example 1 except that they were used. The combinations of synthetic binders of these comparative coating compositions are shown in Table 3.

Comparative Examples 4 and 5 In this comparative example, in order to further clarify the usefulness of the combined use of the latex (A) and the acrylic emulsion (B), the case where the latex (A) and the acrylic emulsion (B) were used alone was used. To illustrate. That is, as shown in Table 3, comparison was made under the same conditions and conditions as in Example-1, except that the latex A-1 and the acrylic emulsion B-1 used in Example-1 were used alone and in the same amount as the total amount. A coating composition-4 and a comparative coating composition-5 were obtained.

Application Examples The coating compositions obtained in the above-mentioned Examples and Comparative Examples were prepared using a basis weight of 6
Using 4.0 g / m ² of base paper, each coating composition was coated with an air knife coater so that the dry weight was 25 g / m ^2, and after drying, a rewetting liquid was applied and passed through a cast drum. The diameter of the casting is 1200 mm, the pressing pressure is 50 kg / cm, the surface temperature is 95-1.
Using a drum at 00 ° C., the maximum casting speed at which good releasability and good pits were not found on the coated paper surface was determined. The air permeability of the coated paper before casting was measured, and the resulting cast coated paper was evaluated for glossiness and surface strength. The results are shown in Table 2. The air permeability was measured by an Oken type air permeability tester, and the glossiness was measured according to JIS P-8142. The surface strength was printed with an RI printing tester (manufactured by Ming Seisakusho) and visually evaluated for picking condition on a 10-point scale (10 being the best without picking on the surface, 1 being the most picking on the entire surface) It was judged as defective, and this period was divided into 10 levels for evaluation).

{Effect of the Invention} As shown in the numerical values in Table 3, the coating compositions of Examples within the limited range of the invention of the present application were not limited to high-speed production, but the cast-coated papers produced thereby had gloss, surface strength and transparency. Has excellent quality balanced in temper. From this, it is clear that the present invention is a very useful coating composition which has never been used as a coating composition for cast-coated paper.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location D21H 25/00 (72) Inventor Akio Hyugaji 3-14-14 Shodo, Sakae-ku, Yokohama-shi, Kanagawa (72) Inventor Akio Tanaka 21-12 Kaminocho, Sakae-ku, Yokohama-shi, Kanagawa (56) Reference JP-A-60-139762 (JP, A) JP-A-62-215091 (JP, A) JP-A-62-85094 (JP, A) ) JP-A-57-117694 (JP, A)

Claims (2)

[Claims] 1. A paint for cast coated paper, which comprises a pigment and an adhesive as main components, wherein the adhesive is a rubber latex (A) having a gel content of 50% or more and an acrylic having a gel content of 50% or more. A coating composition for cast coated paper, which comprises the emulsion (B). 2. A cast-coated paper coated with the composition according to claim 1.