JP3362096B2 - Paper coating liquid and coated paper - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paper coating liquid having good water retention property and a coated paper having a coating layer formed on the surface thereof.

[0002]

2. Description of the Related Art Generally, a printing paper is provided with a coating layer of a coating liquid on its surface in order to improve smoothness, glossiness and printability. This coating solution is usually a slurry in which white pigments such as clay and ground calcium carbonate and latex or starch are dispersed in water as a binder. After diluting, it is supplied from a preparation tank to a coating machine and continuously coated on running paper, and the excess is removed by a coating head such as a blade to obtain a required film thickness.
The coating liquid removed from the paper is returned to the adjustment tank, mixed with a new coating liquid, and reused.

This coating liquid is applied to the surface of the paper base material as described above and then dried to form a coating layer. Depending on the paper base material, the coating layer is formed between the coating step and the drying step. Moisture in the coating liquid is absorbed, and ingredients such as clay, ground calcium carbonate, latex, and starch penetrate into the paper substrate, resulting in impaired smoothness and uneven layer thickness. It is known that printability is deteriorated, and such deterioration of surface properties is mainly due to insufficient water retention.

By the way, a small amount of a polymer substance such as carboxymethyl cellulose (CMC) or sodium alginate is usually added to the coating liquid in order to adjust the coating properties such as viscosity, fluidity and water retention. However, increasing the amount of these polymeric substances in order to prevent the deterioration of water retention, the viscosity of the coating liquid becomes extremely high and the fluidity deteriorates.As a result, high-speed coating becomes impossible and productivity decreases. In addition, the coated paper obtained is unavoidably deteriorated in surface properties such as picking resistance, printability, and smoothness.

In order to solve such a problem, a paper coating solution using an acrylic acid-methacrylic acid copolymer in place of carboxymethyl cellulose or sodium alginate has been proposed so far (Japanese Patent Laid-Open No. H2-1990). 53,996). Compared with those using carboxymethyl cellulose and sodium alginate, the water retention, viscosity and fluidity could be improved with a small amount,
It was not possible to obtain sufficient water retention yet, and it was not possible to suppress the above-mentioned deterioration of the surface characteristics.

[0006]

DISCLOSURE OF THE INVENTION The present invention is intended to improve the drawbacks of conventional paper coating solutions and to sufficiently compensate for the lack of water retention which causes the deterioration of the surface properties of coated paper. It was made for the purpose of providing a coating liquid capable of achieving the above.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies on a paper coating liquid having good water retention property, and as a result, have a pigment and a binder as basic components and have a specific composition and molecular weight. It has been found that the above object can be achieved by a coating liquid containing a methacrylic acid-ethyl acrylate copolymer in a predetermined ratio, and the present invention has been completed based on this finding.

That is, according to the present invention, in a paper coating liquid containing a pigment and a binder as basic components, the molar ratio of methacrylic acid units to ethyl acrylate units is 5:95 to 45:55 and the weight average molecular weight is 900. 1,000 ~
A methacrylic acid-ethyl acrylate copolymer within the range of 8,000,000 is added in an amount of 0.01 to 100 parts by weight of the pigment.
0.5 parts by weight of the coating liquid and the surface of the paper base, which are characterized by containing 0.5 parts by weight, so that the coating layer of the preceding paper coating liquid has a solid content of ² to 30 g / m ^2. The present invention provides a coated paper characterized by being provided in.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the paper coating liquid of the present invention, it is necessary to contain a methacrylic acid-ethyl acrylate copolymer together with a pigment and a binder as basic components. As the methacrylic acid-ethyl acrylate copolymer, one having a methacrylic acid unit / ethyl acrylate unit molar ratio of 5:95 to 45:55 is used. If the proportion of methacrylic acid units is higher than that of water, the fluidity under high shear will deteriorate and the B-type viscosity will increase. If it is lower than this, the water retention effect will be insufficient. Considering the fluidity and water retention effect under high shear, the preferable molar ratio of the methacrylic acid unit and the ethyl acrylate unit is in the range of 20:80 to 40:60.
The weight average molecular weight of the methacrylic acid-ethyl acrylate copolymer is in the range of 900,000 to 8,000,000. If the weight average molecular weight is less than 900,000, sufficient water retention cannot be obtained, and
If it exceeds the range, disadvantages such as an increase in the viscosity of the coating liquid occur. From the viewpoint of water retention and balance of viscosity, the preferable weight average molecular weight is 1,000,000 to 4,000,0.
The range is 00. The weight average molecular weight is a polystyrene equivalent value measured by a gel permeation chromatography method (GPC method).

The method for producing the methacrylic acid-ethyl acrylate copolymer is not particularly limited, and a known method such as emulsion polymerization method in an aqueous medium can be preferably adopted. At this time, as the polymerization initiator, a water-soluble one such as hydrogen peroxide, a water-soluble inorganic peroxide, or a combination of a water-soluble reducing agent with a water-soluble inorganic peroxide or an organic peroxide is used. Examples of water-soluble inorganic peroxides include potassium persulfate and ammonium persulfate. As the water-soluble reducing agent, for example, a reducing agent used as a water-soluble ordinary radical redox polymerization catalyst component, for example, ethylenediaminetetraacetic acid or its sodium salt or potassium salt, or iron with these,
Complex compounds with heavy metals such as copper and chromium, sulfinic acid or its sodium salt or potassium salt, L-ascorbic acid or its sodium salt, potassium salt, calcium salt, ferrous pyrophosphate, ferrous sulfate, ferrous sulfate Examples include ammonium iron, sodium sulfite, acidic sodium sulfite, sodium formaldehyde sulfoxylate, reducing sugars and the like. On the other hand, examples of the water-soluble organic peroxide include cumene hydroperoxide, p-cymene hydroperoxide, t-butylisopropylbenzene hydroperoxide, diisopropylbenzene hydroperoxide,
Hydroperoxides such as p-menthane hydroperoxide, decalin hydroperoxide, t-amyl hydroperoxide, t-butyl hydroperoxide, isopropyl hydroperoxide and the like can be mentioned.

In this emulsion polymerization, an emulsifier is used, and as the emulsifier, an anionic surfactant or a combination of the anionic surfactant and a nonionic surfactant is usually used. As the anionic surfactant, known ones usually used in emulsion polymerization, for example, alkylbenzene sulfonate, alkyl sulfonate, alkyl sulfate ester salt, fatty acid metal salt, polyoxyalkyl ether sulfate ester salt, polyoxyethylene carboxylic acid salt are used. Examples thereof include acid ester sulfate ester salts, polyoxyethylene alkylphenyl ether sulfate ester salts, and succinic acid dialkyl ester sulfonates. Examples of the nonionic surfactant include polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene alkyl ether glycerin borate ester, polyoxyethylene. A compound having a polyoxyethylene chain in the molecule, such as an alkyl ether phosphate, polyoxyethylene, etc., and having surface-active ability, and the polyoxyethylene chain of the compound is replaced with a copolymer of oxyethylene and oxypropylene. Examples thereof include sorbitan fatty acid ester, fatty acid glycerin ester, glycerin fatty acid ester, pentaerythritol fatty acid ester, and the like.

Methacrylic acid-acrylic acid ester is prepared by polymerizing methacrylic acid and ethyl acrylate at a predetermined ratio in an aqueous medium containing the above-mentioned polymerization initiator and emulsifier, usually at a temperature in the range of 30 to 80 ° C. An emulsion in which the fine particles of the copolymer are uniformly dispersed is obtained. This emulsion may be used as it is for the preparation of a paper coating liquid, or may be subjected to a known treatment such as salting out or spray drying, taken out as a solid, and used for the preparation of a paper coating liquid. Good.

In the coating liquid of the present invention, the methacrylic acid-ethyl acrylate copolymer should be blended in a proportion of 0.01 to 0.5 parts by weight per 100 parts by weight of the pigment. If this amount is less than 0.01 parts by weight, sufficient water retention cannot be obtained, and if it exceeds 0.5 parts by weight, the viscosity of the coating liquid becomes too high and gelation occurs. From the viewpoint of water retention and viscosity and fluidity of the coating liquid, the preferable blending amount of this methacrylic acid-ethyl acrylate copolymer is pigment 100
It is in the range of 0.05 to 0.3 parts by weight per part by weight.

The pigment used in the coating liquid of the present invention is not particularly limited, and those conventionally used in paper coating liquids can be used. Examples of such substances include clay, calcium carbonate, kaolin, talc, titanium oxide, silica, zinc oxide, aluminum hydroxide, clay, lake, and synthetic plastic pigment.
These may be used alone or in combination of two or more, and the compounding amount thereof is usually selected in the range of 40 to 70% by weight based on the total amount of the coating liquid.

The binder used in the coating liquid of the present invention is not particularly limited, and a latex or solution of synthetic or natural polymer conventionally used in paper coating liquids can be used. Examples of such polymer substances include styrene-butadiene copolymers, styrene-acrylic copolymers, vinyl acetate-acrylic copolymers, ethylene-vinyl acetate copolymers, butadiene-methyl methacrylate copolymers. Polymer, vinyl acetate-butyl acrylate-based copolymer, styrene-maleic anhydride-based copolymer, isobutene-maleic anhydride-based copolymer, acrylic acid-methyl methacrylate-based copolymer, oxidized starch,
Examples thereof include esterified starch, etherified starch, enzyme-modified starch, casein, soybean protein and the like. These may be used alone or in combination of two or more, and the compounding amount thereof is usually 3 to 30 parts by weight, preferably 5 to 20 parts by weight, per 100 parts by weight of the pigment. Is selected in.

The coating liquid of the present invention may contain a dispersant, a thickener, a defoaming agent, and a defoaming agent, if necessary, within a range that does not impair the object of the present invention.
A waterproofing agent, a coloring agent, etc. can be appropriately contained.
Examples of the dispersant include sodium polyacrylate,
Sodium hexametaphosphate, sodium pyrophosphate,
Examples thereof include sodium salt of acrylic acid-maleic acid copolymer.

The coated paper of the present invention has a coating layer of the above-mentioned paper coating liquid provided on the surface of a paper base material so that the amount of solids deposited becomes ² to 30 g / m ^2. Examples of the material include high-quality paper, medium-quality paper and paperboard. Further, the coating layer is formed by applying the paper coating solution on one or both sides of these paper base materials by a usual method using a blade coater, a roll coater, an air knife coater, etc., and performing a drying treatment. You can

[0018]

EFFECT OF THE INVENTION The paper coating liquid of the present invention has a good water retention property and can give a coated paper excellent in surface smoothness, printability, picking resistance and gloss.

[0019]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The physical properties of the paper coating liquid and the coated paper in each example were determined according to the following methods.

(1) Water retention of paper coating liquid (A) S & D Warren method (S & D W
Arren). The larger the value, the better the water retention. (B) Retention meter-AA-
GWR [Kaltec Scientific (Kalt
ec Scientific) was used to measure the amount of dehydration of the coating color on the filter paper under the conditions of coating color of 10 cc, pressure of 1.5 bar, pressurizing time of 15 seconds, and temperature of 20 ° C. The smaller the value, the better the water retention. (2) B-type viscosity (cps) of paper coating liquid According to TAPPI standard T648 Su-72, the B-type viscosity at 20 ° C was measured at a rotation speed of 60 rpm. (3) High shear (HS) viscosity (cps) of paper coating liquid A high shear viscometer [manufactured by Nippon Seiki Co., Ltd.] was used to measure the high shear viscosity at 20 ° C. at a rotation speed of 8800 rpm. (4) Fluidity of paper coating solution After the coating solution is subjected to centrifugal separation to separate it into an aqueous phase (liquid phase) and a solid phase, the viscosity of the aqueous phase is measured, and the formula: fluidity = coating solution viscosity / The fluidity at 20 ° C was determined according to the viscosity of the aqueous phase. (5) Glossiness of coated paper It was measured according to JIS P8142-1965. (6) Whiteness of coated paper It was measured according to JIS P8123-1961. (7) Smoothness of coated paper It was measured according to JIS P8119-1976. (8) Dry pick of coated paper, wet pick We printed on the surface of the coated paper using RI printer (manufactured by Meisei Co., Ltd.) and observed picking occurrence situation by 5 point method (the higher the value, the better) evaluated. (9) Gravure halftone dot drop test of coated paper It was measured using a printing station type gravure printing suitability tester (manufactured by Kumagai Riki Kogyo, serial number 8608189). The smaller the value, the less the gravure halftone dots are missing.

Example 1 70 parts by weight of clay, 30 parts by weight of heavy calcium carbonate, 10 parts by weight of styrene-butadiene copolymer latex (as solid content), 3 parts by weight of oxidized starch and dispersant (SDA-made by Somar). 40 K) 0.1 part by weight (as solid content) was mixed and water was added so that the total solid content concentration was 62%, and then the molar ratio of methacrylic acid unit and ethyl acrylate was 39:61. And the weight average molecular weight is 30,
Methacrylic acid-ethyl acrylate copolymer emulsion of 0,000 (solid content 35.3% by weight, viscosity at 20 ° C. 5
A paper coating solution was prepared by adding 0.2 parts by weight (as solid content) of 4 mPa · s and average particle diameter of 71 nm based on the copolymer and mixing them homogeneously. The physical properties of this product are shown in Table 1. The weight average molecular weight is a polystyrene equivalent value measured by the GPC method. Next, this paper coating liquid was applied and dried on one surface of a high-quality paper (basis weight 60 g / m ² ) so that the amount of solids deposited was 15 g / m ² , to prepare a coated paper. Table 1 shows the physical properties of the coated paper.

Comparative Example 1 In Example 1, as a methacrylic acid-ethyl acrylate copolymer emulsion, the molar ratio of methacrylic acid units to ethyl acrylate units was 60:40 and the weight average molecular weight was 2,500,000. Methacrylic acid-ethyl acrylate copolymer emulsion (solid content 35.0% by weight, viscosity at 20 ° C. 125 mPa · s, average particle diameter 65 n
A paper coating solution was prepared in the same manner as in Example 1 except that m) was used, and a coated paper was prepared. Table 1 shows the physical properties of the paper coating liquid and the coated paper.

Comparative Example 2 In Example 1, as a methacrylic acid-ethyl acrylate copolymer emulsion, the molar ratio of methacrylic acid units to ethyl acrylate units was 50:50 and the weight average molecular weight was 3,000,000. Methacrylic acid-ethyl acrylate copolymer emulsion (solid content 35.0% by weight, 20 ° C. viscosity 86 mPa · s, average particle diameter 68 nm)
A paper coating liquid was prepared in the same manner as in Example 1 except that was used to prepare coated paper. Table 1 shows the physical properties of the paper coating liquid and the coated paper.

Comparative Example 3 In Example 1, as a methacrylic acid-ethyl acrylate copolymer emulsion, methacrylic acid having a molar ratio of methacrylic acid units to ethyl acrylate units of 39:61 and a weight average molecular weight of 70,000. Acid-ethyl acrylate copolymer emulsion (solid content 35.2% by weight, 20
A paper coating liquid was prepared in the same manner as in Example 1 except that a viscosity of 30 mPa · s at a temperature of 65 nm and an average particle diameter of 65 nm was used, and a coated paper was prepared. Table 1 shows the physical properties of the paper coating liquid and the coated paper.

[0025]

[Table 1]

From this table, it is apparent that the paper coating liquid of the present invention is superior in water retention as compared with the comparative example. Further, the coated paper prepared using the paper coating liquid of the present invention has glossiness, whiteness, smoothness and printability better than those of the coated paper prepared using the paper coating liquid of Comparative Example. You can see that the balance is high.

Example 2 80 parts by weight of clay, 20 parts by weight of heavy calcium carbonate, 6 parts by weight of styrene-butadiene copolymer latex (as solid content), dispersant (SDA-40K manufactured by Somar).
0.3 parts by weight (as solid content) was mixed, and water was added so that the total solid content concentration became 64%, and then the molar ratio of methacrylic acid unit and ethyl acrylate unit was 3
Methacrylic acid-ethyl acrylate copolymer emulsion having a weight average molecular weight of 3,000,000 at 9:61 (solid content 35.3% by weight, viscosity at 20 ° C. 54 mPa · s,
0.2 parts by weight (as a solid content) of an average particle diameter of 71 nm) was added based on the copolymer and mixed homogeneously to prepare a paper coating solution. The physical properties of this product are shown in Table 2. The weight average molecular weight is a polystyrene equivalent value measured by the GPC method. Next, apply this paper coating solution to high-quality paper (basis weight 60 g / m
^The coated paper was prepared by applying and drying the solid content of 15 g / m ² on one surface of ² ). Table 2 shows the physical properties of the coated paper.

Comparative Example 4 In Example 2, the methacrylic acid-ethyl acrylate copolymer emulsion was a 60:40 molar ratio of methacrylic acid units to ethyl acrylate units and had a weight average molecular weight of 2,500,000. Methacrylic acid-ethyl acrylate copolymer emulsion (solid content 35.0% by weight, viscosity at 20 ° C. 125 mPa · s, average particle diameter 65 n
A paper coating liquid was prepared in the same manner as in Example 2 except that m) was used, and this was used to prepare a coated paper. Table 2 shows the physical properties of the paper coating liquid and the coated paper.

Comparative Example 5 In Example 2, the methacrylic acid-ethyl acrylate copolymer emulsion was a 50:50 molar ratio of methacrylic acid units to ethyl acrylate units and had a weight average molecular weight of 3,000,000. Methacrylic acid-ethyl acrylate copolymer emulsion (solid content 35.0% by weight, 20 ° C. viscosity 86 mPa · s, average particle diameter 68 nm)
A paper coating solution was prepared in the same manner as in Example 2 except that the above was used, and this was used to prepare a coated paper. Table 2 shows the physical properties of the paper coating liquid and the coated paper.

Comparative Example 6 The methacrylic acid-ethyl acrylate copolymer emulsion of Example 2 was prepared as a methacrylic acid emulsion having a methacrylic acid unit / ethyl acrylate unit molar ratio of 39:61 and a weight average molecular weight of 70,000. Acid-ethyl acrylate copolymer emulsion (solid content 35.2% by weight, 20
A paper coating liquid was prepared in the same manner as in Example 2 except that the viscosity at 30 ° C. and the average particle diameter of 65 nm was used, and a coated paper was prepared using this. Table 2 shows the physical properties of the paper coating liquid and the coated paper.

[0031]

[Table 2]

As is clear from this table, the paper coating liquid of the present invention is superior in water retention as compared with that of the comparative example, and when the coated paper prepared using the same is used for gravure printing. Has few missing dots.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuyuki Kono 5-8 Nishimitabicho Suita City, Osaka Prefecture Nippon Shokubai (72) Inventor Takahiro Miwa 5-8 Nishimitabicho Suita City, Osaka Prefecture Stock Incorporated by Nippon Shokubai Co., Ltd. (56) Reference JP-A-56-125749 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) D21H 19/00-27/42

Claims (2)

(57) [Claims] 1. In a paper coating liquid containing a pigment and a binder as basic components, the molar ratio of methacrylic acid units to ethyl acrylate units is 5:95 to 45:55,
Weight average molecular weight of 900,000 to 8,000,000
A methacrylic acid-ethyl acrylate copolymer within the range of 0.01 to 0.5 parts by weight per 100 parts by weight of the pigment is contained in the paper coating liquid. 2. A surface of a paper base material, which comprises a pigment and a binder as basic components, a methacrylic acid unit / ethyl acrylate unit molar ratio of 5:95 to 45:55, and a weight average molecular weight of 900,000 to 8,000. Methacrylic acid-ethyl acrylate copolymer within the range of 1,000 in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the pigment, a coating layer of a paper coating solution, and a solid content of 2 A coated paper, characterized in that the coated paper is provided to be ~ 30 g / m ² .