JPH10226993A - Paper coating solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a paper coating solution, which, although containing a high proportion of solid(s), shows stable paper coating operability at a high coating speed, i.e., at a shear rate of 1×10<5> /s or higher. SOLUTION: This paper coating solution comprises a pigment for paper coating, macromolecular latex, cellulose (e.g. pulp hyrolyzed in the presence of an acid or oxidatively decomposed in the presence of an alkali), sodium salt of carboxymethyl cellulose, thickening agent and water, causing no bleeding even when it contains 50 to 75wt.% of solid(s) and is coated at a shear rate of 1×10<5> /s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a composite material having a shear rate of 10 ^5.
The present invention relates to a paper coating liquid having improved coating operability at the time of high-speed coating at a rate of at least / sec.

[0002]

2. Description of the Related Art The production of coated paper for the purpose of improving printability and appearance has been growing in step with prints. In recent years, the speed of coating has been increased in order to increase productivity. Is coming. However, when high-speed coating is performed at a speed exceeding 1000 m / min, problems such as generation of staglamite and bleeding phenomena, which cause deterioration of coated paper quality such as streaks and scratches, occur. Thus, conventionally, an attempt has been made to improve the problem by lowering the solid content of the coating composition.

[0003] However, this method causes other operational problems such as backing roll contamination due to insufficient drying after coating, or an increase in equipment investment for increasing drying conditions. Will occur. On the other hand, the use of a method of changing the type and blending ratio of the pigment, the use of a modified polymer latex and the reduction of the latex particle diameter, etc.
No. 173198) or a method of compounding a thickener having a large water retention effect has been adopted, but a satisfactory product has not been obtained, and the solid content of the coating liquid is reduced in the production of coated paper. There has been a strong demand for a high-speed coating paper coating solution that can perform high-speed coating without causing stalagmite generation and bleeding phenomenon and has improved coating operability for a long time.

[0004]

SUMMARY OF THE INVENTION The present invention overcomes the problems of the prior art and suppresses the occurrence of staglamite and bleeding even under high-speed coating conditions using a coating solution having a high solid content. It is an object of the present invention to provide a high-speed coating paper coating liquid capable of improving coating operability such that a coated paper free from streaks or scratches can be obtained.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have accomplished the present invention. That is, the present invention is as follows. (1) Pigment for paper coating, polymer latex, cellulose,
A paper coating liquid comprising sodium carboxymethylcellulose, a thickener, and water, wherein the solid content of the paper coating liquid is 50 to 75% by weight, and the shearing rate is 1 × 10 ⁵ / sec. Paper coating liquid characterized by not generating. (2) The paper coating liquid according to the above (1), wherein the cellulose is 0.01 to 2 parts by dry weight and the carboxymethyl cellulose sodium salt is 0.005 to 1 dry parts by weight based on 100 parts by weight of the paper coating pigment. (3) The paper coating liquid according to the above (1) or (2), wherein the cellulose is obtained by subjecting pulp to acid hydrolysis or alkali oxidative decomposition, or obtained by mechanically treating pulp before or after acid hydrolysis or alkali oxidative decomposition. . (4) The paper coating liquid according to (1) or (2) above, wherein the cellulose is obtained by mechanically treating pulp.

Hereinafter, the present invention will be described in detail. As means for improving the coating operability in the related art, studies have been made focusing on a method for improving the water retention of the coating composition and a method for reducing the high shear viscosity. However, the high-speed coated paper coating composition of the present invention can obtain stable coating operability without causing stalagmite or bleeding phenomenon at the time of high-speed coating, even though water retention is not always improved and high shear viscosity is not reduced. There is a characteristic where it can be done.

The pigment for paper coating in the present invention is a white mineral pigment or organic pigment which is coated on the base paper surface for the purpose of improving printability and appearance, and examples of the mineral pigment include kaolin clay. , Calcium carbonate, talc, silica, titanium oxide, satin white, aluminum hydroxide and the like. As an organic pigment, for example,
Plastic pigment, urea resin, and the like. These pigments may be used alone or in combination of two or more, and the mixing ratio is arbitrarily determined.

[0008] The polymer latex in the present invention is an aqueous polymer latex used for fixing the above-mentioned pigment for paper coating on the paper surface, and includes a styrene-butadiene copolymer, a polystyrene copolymer, Polybutadiene-based copolymer, acrylonitrile-butadiene-based copolymer,
Polyurethane-based copolymer, polymethyl methacrylate-based copolymer, methyl methacrylate-butadiene-based copolymer, polyacrylate-based copolymer, styrene-acrylate-based copolymer, vinyl chloride-based copolymer, vinyl acetate-based copolymer Latexes such as coalesce, vinyl acetate-ethylene copolymer and the like. These polymer latexes having a number average particle diameter of 150 nm or less can be used. When the number average particle size exceeds 150 nm, the effect of improving the coating operability is not necessarily sufficient. The number average particle diameter is 50 to 130 from the viewpoint of industrial availability and practical use.
nm is preferred. These polymer latexes may be used alone or as a mixture of two or more kinds, and the mixing ratio is arbitrarily determined.

The polymer latex of the present invention can be used in an amount of 2 to 25 parts by weight, preferably 4 to 20 parts by weight, based on 100 parts by weight of the paper coating pigment (hereinafter, the dry part is simply referred to as part by weight). Parts by weight can be used. Cellulose in the present invention refers to cellulose obtained by subjecting pulp to acid hydrolysis or alkali oxidative degradation, pulp subjected to mechanical treatment such as grinding, pulverization, classification before or after acid hydrolysis or alkali oxidative degradation, or pulp obtained by simply grinding pulp. It refers to one that has been mechanically processed such as crushing, crushing, and classification. Specific examples of those obtained by subjecting pulp to acid hydrolysis or alkali oxidative decomposition, or those obtained by subjecting pulp to mechanical treatment such as grinding or pulverization before or after acid hydrolysis or alkali oxidative decomposition, such as "Theolus Cream" FP -03 (manufactured by Asahi Kasei Corporation) and the like are preferably used. As a specific example of the pulp obtained by mechanical treatment such as simply grinding, pulverizing, and classifying, "Serish" (manufactured by Daicel Chemical Industries, Ltd.) is preferably used. These celluloses can be used alone or as a mixture of two or more kinds, and the mixing ratio at that time is arbitrarily determined.

As the above mechanical treatment method, a ball mill, a jet mill, a high-pressure homogenizer or the like is suitably used. The cellulose in the present invention can be used in an amount of 0.01 to 2 parts by weight based on 100 parts by weight of the pigment for paper coating. Preferably, 0.03 to 1.5 parts by weight, more preferably 0.05 to 1 part by weight can be used. If the amount is less than 0.01 part by weight, the effect of the present invention is not always sufficiently exhibited. On the other hand, if it exceeds 2 parts by weight, the viscosity of the coating liquid may increase, and the pigment dispersibility, coating workability, etc. may decrease.

The carboxymethylcellulose sodium salt used in the present invention is a general-purpose sodium salt having a degree of etherification of about 0.6 to 1.5 and an average degree of polymerization of about 1200 or less. The sodium salt of carboxymethyl cellulose in the present invention is used in an amount of 0.1 to 100 parts by weight of the pigment for paper coating.
005 to 1 part by weight can be used, and preferably 0.01 to 1 part by weight.
0.5 parts by weight can be used. If the amount is less than 0.005 parts by weight, the effect of the present invention is not always sufficiently exhibited. On the other hand, if it exceeds 1.0 part by weight, the viscosity of the coating liquid increases, and the pigment dispersibility, coating workability, and the like may decrease.

The thickener in the present invention is used for the purpose of imparting water retention of a coating solution, adjusting the viscosity, and stabilizing the dispersion of a pigment. Starch, modified starch, casein, modified casein, polyvinyl alcohol, modified polyvinyl Alcohol, sodium polyacrylate, polyvinylpyrrolidone, alkali-soluble latex and the like are used. Examples of the modified starch include oxidized starch, etherified starch, enzyme-modified starch, phosphate esterified starch, and the like.

The thickener may be used in an amount of 0.1 part by weight or more, preferably 0.5 part by weight or more, based on 100 parts by weight of the pigment for paper coating. These thickeners can be used alone or as a mixture of two or more kinds, and the mixing ratio at that time is arbitrarily determined. When using a starch or a modified starch, it is usually used after being gelatinized by heating in water in advance. The high-speed coating paper coating liquid of the present invention includes sodium hydroxide, potassium hydroxide,
PH adjusters such as ammonia, pigment dispersants such as low molecular weight sodium polyacrylate and sodium tripolyphosphate, printability improvers such as water-proofing agents and meat improvers, dyes, preservatives, defoamers, and ultraviolet absorption Additives such as an agent commonly used in paper coating compositions can be used as needed.

The paper coating liquid of the present invention has a solid content of 50 to 75% by weight, preferably 53 to 72% by weight, more preferably 55 to 70% by weight, and has a high solid content at the time of high-speed coating. The coating operation stability was remarkably improved. 5 solids
If the amount is less than 0% by weight, sufficient drying cannot be performed, so that the backing roll becomes contaminated, and if an attempt is made to increase the drying capacity, an economic problem such as an increase in drying energy cost occurs. On the other hand, if the solid content exceeds 75% by weight, it becomes difficult to uniformly disperse the coating liquid, and it is not suitable as a paper coating liquid.

The method for preparing the paper coating liquid of the present invention can use a general mechanical dispersing device such as a Coreless disperser or a color disperser, but is not particularly limited thereto. As the base paper on which the paper coating liquid of the present invention is applied, paper, plastic film, synthetic paper, or the like is used, and one-sided or two-sided coating can be performed. As a method of coating these base papers, a known technique can be used, but the effect when a blade coater is used is remarkable and preferable. The coating speed is 1000 m / min or more, preferably 130 m / min.
It is at least 0 m / min, more preferably at least 1500 m / min.

[0016]

The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the invention. The parts by weight mean parts by dry weight. The measuring method is as follows. (1) Number average particle diameter Particles when the integrated number becomes 50% of the total number of particles when measured using an ultrafine particle size analyzer (model: 9230 Microtrac UPA, manufactured by Nikkiso Co., Ltd.) Refers to the spherical equivalent diameter, and is appropriately dispersed in water for measurement. (2) High Shear Viscosity Measurement Using a Hercules High Shear Viscometer manufactured by Kumagai Riki, a 67% by weight paper coating solution was measured under the conditions of F Bob at 6,600 rpm (shear rate 1.8 × 10 ⁵ / sec). (3) Coating operation stability evaluation test The coating operation stability evaluation test was performed by the method described in Japanese Patent Application No. 7-97681. The outline is shown below.

Using a bench coater capable of coating with a blade, observe the blade edge when the coating liquid is directly coated on a backing roll without using paper with a microscope and observe the stability of the coating process (bleeding). Whether there is a phenomenon)
Was evaluated. The shear rate during coating was calculated from the coating thickness and the coating rate. The coating thickness was determined from the difference between before and during coating on the backing roll surface using a laser displacement meter.
Further, in order to prevent the blade from hitting the heel, the deflection of the blade was detected with a laser displacement meter, and the coating was performed by adjusting the blade so that the blade always hit the toe (the blade tip angle at the blade tip plus the angle of 5 degrees).

With respect to each shear rate, a case where bleeding occurred less than 3 times out of 10 times was evaluated as ○, and a case where bleeding occurred more than 3 times out of 10 times was evaluated as x.

[0019]

Example 1 10% by weight fine cellulose ("Theolus Cream") obtained by subjecting pulp to acid hydrolysis and grinding
FP-03; 0.1 parts by weight (hereinafter referred to as parts by weight), carboxymethylcellulose sodium salt (cellogen; manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 0.0
1 part by weight, 70 parts by weight of clay (Ultra White 90; manufactured by Engelhard Co.), calcium carbonate (Carbital 9)
0; manufactured by Fuji Kaolin Co., Ltd.) 30 parts by weight, sodium polyacrylate (Alon T-40; manufactured by Toagosei Co., Ltd.) 0.2
Parts by weight, 0.2 parts by weight of sodium hydroxide, 3 parts by weight of pregelatinized oxidized starch (Oji Ace B; manufactured by Oji Cornstarch Co., Ltd.), 11 parts by weight of SB latex having a number average particle diameter of 130 nm, and water In addition, the solid content was adjusted to 67% by weight and mixed with a color disperser to obtain a paper coating liquid.

[0020]

Example 2 A paper coating liquid was obtained in the same manner as in Example 1 except that the carboxymethylcellulose sodium salt was changed to 0.1 part by weight.

[0021]

Example 3 Cellulose fine powder (Selish FD-100E; manufactured by Daicel Chemical Industries, Ltd.) obtained by subjecting pulp to high-pressure dispersion treatment in water and replacing it with "Seolas Cream" FP-03 1.8 A paper coating liquid was obtained in the same manner as in Example 1, except that the SB latex was replaced by SB latex having a number average particle diameter of 100 nm in parts by weight.

[0022]

Example 4 Instead of "Theolus Cream" FP-03, 0.27 parts by weight of crystalline cellulose obtained by acid hydrolysis of pulp and 0.03 parts by weight of sodium salt of carboxymethylcellulose were previously kneaded and dried. A paper coating liquid was obtained in the same manner as in Example 1 except that was used.

[0023]

Example 5 Microcrystalline cellulose obtained by subjecting pulp to acid hydrolysis, drying and mechanical treatment in place of "Theolus Cream" FP-03 ("Avicel"FD-F20; manufactured by Asahi Kasei Corporation) A paper coating liquid was obtained in the same manner as in Example 1, except that 1.0 part by weight and carboxymethylcellulose sodium salt were changed to 0.2 part by weight.

[0024]

Example 6 A paper coating liquid was obtained in the same manner as in Example 1, except that an SB latex having a number average particle diameter of 70 nm was used instead of the SB latex having a number average particle diameter of 130 nm.

[0025]

Example 7 Microcrystalline cellulose obtained by acid hydrolysis of pulp ("Avicel"TG-101; manufactured by Asahi Kasei Kogyo Co., Ltd.) instead of "Theolus Cream" FP-03
A paper coating liquid was obtained in the same manner as in Example 1, except that 0.5 parts by weight and carboxymethylcellulose sodium salt were changed to 0.05 parts by weight.

[0026]

Example 8 In place of "Theolas Cream" FP-03, except that 0.2 parts by weight of crystalline cellulose obtained by acid hydrolysis of pulp and 0.5 parts by weight of sodium carboxymethylcellulose were used. A paper coating liquid was obtained in the same manner as in Example 1.

[0027]

Comparative Example 1 70 parts by weight of clay (Ultra White 90; manufactured by Engelhard Co.), 30 parts by weight of calcium carbonate (Carbital 90; manufactured by Fuji Kaolin Co., Ltd.), sodium polyacrylate (Alon T-40; Toa Gosei Co., Ltd.) Co., Ltd.) 0.
2 parts by weight, 0.2 parts by weight of sodium hydroxide, 3 parts by weight of pregelatinized oxidized starch (Oji Ace B; manufactured by Oji Cornstarch Co., Ltd.), 11 parts by weight of SB latex having a number average particle diameter of 130 nm, and water Was adjusted to a solid content of 67% by weight, and mixed with a color disperser to obtain a paper coating liquid.

[0028]

Comparative Example 2 A paper coating liquid was obtained in the same manner as in Comparative Example 1, except that the SB latex was changed to an SB latex having a number average particle diameter of 70 nm.

[0029]

[Comparative Example 3] SB latex having a number average particle diameter of 170 nm
A paper coating liquid was obtained in the same manner as in Example 3 except that SB latex was used.

[0030]

[Comparative Example 4] SB latex having a number average particle diameter of 200 nm
"Seolas Cream" FP-
Comparative Example 1 except that pulp was hydrolyzed with an acid and then mechanically treated, and 1.5 parts by weight of cellulose fine powder (KC Floc W-400; manufactured by Nippon Paper Industries Co., Ltd.) was added in place of Example No. 03. A paper coating liquid was obtained in the same manner as described above.

[0031]

Comparative Example 5 Microcrystalline cellulose obtained by acid hydrolysis of pulp ("Avicel"TG-101; manufactured by Asahi Kasei Kogyo Co., Ltd.) instead of "Theolus Cream" FP-03
A paper coating liquid was obtained in the same manner as in Example 1, except that 3.0 parts by weight and carboxymethylcellulose sodium salt were changed to 0.15 parts by weight.

[0032]

Comparative Example 6 A paper coating liquid was obtained in the same manner as in Comparative Example 5, except that 2.5 parts by weight of crystalline cellulose and 0.5 part by weight of sodium carboxymethylcellulose were used.

[0033]

[Comparative Example 7] "Ceolas cream" FP-03 was added to 1.0
A paper coating liquid was obtained in the same manner as in Example 1, except that the parts by weight and carboxymethylcellulose sodium salt were changed to 1.2 parts by weight. Using these paper coating solutions, a high shear viscosity measurement and a coating operation stability evaluation test were performed. Table 1 shows the results.

[0034]

[Table 1]

[0035]

[Effect of the Invention] Even when high-speed coating with a shear rate of 10 ⁵ / sec or more is performed using a paper coating liquid having a high solid content, stable paper coating operability without generation of staglamite or bleeding is obtained. Can be

Claims (4)

[Claims] 1. A paper coating liquid comprising a paper coating pigment, a polymer latex, cellulose, sodium carboxymethylcellulose, a thickener, and water, wherein the solid content of the paper coating liquid is 50 to 75% by weight. %, A bleeding does not occur in a coating at a shear rate of 1 × 10 ⁵ / sec. 2. 100 parts by weight of dry pigment for paper coating,
The paper coating liquid according to claim 1, wherein the cellulose is 0.01 to 2 parts by dry weight and the carboxymethylcellulose sodium salt is 0.005 to 1 part by dry weight. 3. The paper according to claim 1, wherein the cellulose is obtained by subjecting pulp to acid hydrolysis or alkali oxidative degradation, or obtained by mechanically treating pulp before or after acid hydrolysis or alkali oxidative degradation. Coating liquid. 4. The paper coating liquid according to claim 1, wherein the cellulose is obtained by mechanically treating pulp.