JPH10226992A - Paper coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a paper coating composition, 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 composition 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), 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 composition 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 composition which is capable of high-speed coating without causing stalagmite generation and bleeding phenomenon and has improved coating operability for a long time.

[0004] The coating composition for coated paper described in Japanese Patent Publication No. 49-36044 is improved in coating operation efficiency by improving the viscosity behavior of the coating composition for coated paper containing a cellulose crystallite composite. However, the effect of the coating composition described in this publication is exhibited when the coating speed is up to 180.
m / min and a low coating speed of less than 900 / sec.

[0005] The coating liquid composition for paper coating described in JP-A-6-136593 reduces the viscosity of the coating liquid composition for paper coating under a high shear rate by incorporating microcrystalline cellulose. It is characterized in that the coating liquid shown in the examples has a low solid content of 44.2% by weight, and the operation at the time of high-speed coating at a solid content concentration of 50% by weight or more which is the object of the present invention. No gender is mentioned.

JP-A-53-28712 and JP-A-5-28712
JP-A-865598 and JP-A-5-321195 disclose the use of cellulose in the coating composition, and have found an effect of improving the quality of the coated paper. No mention is made of the operability improvement effect. JP-A-8-151504 describes a coating liquid containing an aqueous dispersion comprising an epoxy resin, microcrystalline cellulose, and a surfactant, and has found an effect of improving the printability of coated paper. The effect of improving operability during high-speed coating is not known.

[0007]

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 coated paper coating composition capable of improving coating operability such that a coated paper having no streaks or scratches can be obtained.

[0008]

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 composition comprising a thickener and water, wherein the solid content of the paper coating composition is 50 to 75% by weight, and the shear rate is 1 ×.
A paper coating composition characterized in that bleeding does not occur at a coating rate of 10 ⁵ / sec. (2) The paper coating composition according to the above (1), wherein the cellulose is 0.01 to 2 parts by weight based on 100 parts by weight of the pigment for paper coating. (3) The paper coating composition according to (1) or (2) above, 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. Stuff. (4) The paper coating composition 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.

[0010] The paper coating pigment in the present invention is a white mineral pigment or organic pigment which is coated on the surface of base paper 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.

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 in the present invention can be used in an amount of 2 to 25 parts by weight, preferably 4 to 20 parts by weight, per 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 in combination of two or more, and the mixing ratio at that time can be 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 thickener in the present invention is used for the purpose of imparting water retention of the coating composition, adjusting the viscosity, stabilizing the dispersion of the pigment, etc., and includes starch, modified starch, casein, modified casein, polyvinyl alcohol, Polyvinyl alcohol, sodium polyacrylate, polyvinyl pyrrolidone, 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 can be used in an amount of 0.1 part by weight or more based on 100 parts by weight of the pigment for paper coating.
More than parts by weight can be used. These thickeners may be used alone or
Mixtures of more than one species can be used, and the mixing ratio at that time can be 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 composition of the present invention, sodium hydroxide,
PH adjusters such as potassium hydroxide and ammonia; pigment dispersants such as low molecular weight sodium polyacrylate and sodium tripolyphosphate; water-proofing agents;
Additives usually used in paper coating compositions, such as dyes, preservatives, defoamers, and ultraviolet absorbers, can be used as needed.

In the paper coating composition of the present invention, the solid content of the paper coating composition is 50 to 75% by weight, preferably 53 to 72% by weight, more preferably 55 to 70% by weight. The coating operation stability at the time is remarkably improved. If the solid content is less than 50% by weight, economical problems such as insufficient backing roll contamination due to insufficient drying, and an increase in drying energy cost when trying to increase the drying capacity arise. On the other hand, when the solid content exceeds 75% by weight, it is difficult to uniformly disperse the coating composition, and the composition is not suitable as a paper coating composition.

The method for preparing the paper coating composition 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 a base paper for applying the paper coating composition of the present invention, paper, plastic film, synthetic paper, or the like is used, and one-sided or two-sided coating can be performed.

As a method for coating these base papers, known techniques can be used, but the effect when a blade coater is used is remarkable and preferable. Coating speed is 100
0 m / min or more, preferably 1300 m / min or more, more preferably 1500 m / min or more.

[0019]

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 Co., a 67% by weight paper coating composition was measured under the conditions of F Bob and 6600 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 the tip blade, using a microscope, observe the blade edge when the coating solution is directly applied to the backing roll without using paper, 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 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.

[0022]

Example 1 10% by weight fine cellulose ("Theolus Cream") obtained by subjecting pulp to acid hydrolysis and grinding
FP-03; 0.5 parts by weight, manufactured by Asahi Kasei Kogyo Co., Ltd., clay (Ultra White 90; manufactured by Engelhard) 70
Parts by weight, 30 parts by weight of calcium carbonate (Carbital 90; manufactured by Fuji Kaolin Co., Ltd.), 0.2 parts by weight of sodium polyacrylate (Aron T-40; manufactured by Toagosei Co., Ltd.), 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 were added to adjust the solid content to 67% by weight. And a color disperser to obtain a paper coating composition.

[0023]

Example 2 0.1% of "Ceolas cream" FP-03
Except having changed to the weight part, it carried out similarly to Example 1, and obtained the paper coating composition.

[0024]

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 composition 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 size of 100 nm in parts by weight.

[0025]

Example 4 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 composition was obtained in the same manner as in Example 1 except that 0.3 parts by weight was used.

[0026]

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 composition was obtained in the same manner as in Example 1, except that 1.0 part by weight was used.

[0027]

Example 6 A paper coating composition 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 an SB latex having a number average particle diameter of 130 nm.

[0028]

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 composition.

[0029]

Comparative Example 2 A paper coating composition 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.

[0030]

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

[0031]

[Comparative Example 4] SB latex having a number average particle diameter of 200 nm
The cellulose fine powder (KC Floc W-
400; manufactured by Nippon Paper Industries Co., Ltd.), and a paper coating composition was obtained in the same manner as in Comparative Example 1, except that 2.5 parts by weight were added.

[0032]

Comparative Example 5 100 parts by weight of calcined clay, 0.5 part by weight of sodium polyacrylate (Alon T-40; manufactured by Toagosei Co., Ltd.), 1 part by weight of sodium pyrophosphate, 0.2 part by weight of sodium hydroxide, Crystalline cellulose composite (Avicel® R
0.1 parts by weight of C-591; manufactured by Asahi Kasei Corporation, 6 parts by weight of polyvinyl alcohol, SB latex (L-15
37 number average particle diameter 210 nm; manufactured by Asahi Kasei Corporation
2 parts by weight and water were further added to adjust the solid content to 50% by weight, and mixed with a color disperser to obtain a paper coating composition.

Using these paper coating compositions, a high shear viscosity measurement and a coating operation stability evaluation test were conducted. Table 1 shows the results.

[0034]

[Table 1]

[0035]

[Effect of the Invention] Even when high-speed coating at a shear rate of 10 ⁵ / sec or more is performed using a paper coating composition having a high solid content, stable paper coating operability without generation of stalagmite, bleeding, etc. is obtained. can get.

Claims (4)

[Claims] 1. A paper coating composition comprising a pigment for paper coating, a polymer latex, cellulose, a thickener, and water, wherein the solid content of the paper coating composition is 50 to 75% by weight, and the shear is A paper coating composition wherein bleeding does not occur at a coating speed of 1 × 10 ⁵ / sec. 2. 100 parts by weight of dry pigment for paper coating,
2. The paper coating composition according to claim 1, wherein the cellulose is 0.01 to 2 parts 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 composition. 4. The paper coating composition according to claim 1, wherein the cellulose is obtained by mechanically treating pulp.