JP3166361B2 - Composition for paper coating - 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 composition suitable for high-speed coating and high concentration, and a method for producing the same.

[0002]

[Prior art]

(1) Regarding high-speed coating, in recent years, high-speed coating of a coater, particularly a blade coater, has been attempted with the speeding up of a paper machine. However, in a so-called high-speed coating region where the coating speed exceeds 1000 m / min, 10 g / m ²
When trying to produce coated paper with the above coating amount,
It is difficult to control the amount of coating or the coating surface is rough, which is an obstacle to improving the coating speed. In order to solve these problems, solutions from the hardware side, such as a coater, are being considered.
Because it is phenomenologically derived from the rheological behavior of paper coating paints (hereinafter referred to as coating colors) used for coating, it is necessary to make coating colors suitable for high-speed coating. Research has been intense. As a result, by lowering the solid content concentration of the coating color and lowering the viscosity of the coating color,
Attempts have been made to improve the above problems in high speed coating. However, in this method, the physical properties of the coated paper are reduced, and furthermore, the drying zone in the coater must be lengthened or equipment investment such as improvement of the drying capacity must be accompanied. In addition, there is a problem that it is difficult to control the coating amount at 10 g / m ² or more.

(2) With respect to high solid differentiation, when the coating is performed with a high solid content of the coating color, the coating layer becomes bulky, and as a result, the ink receptivity and the white paper gloss are improved. I do. Further, the binder migration is suppressed, and the distribution of the binder is made uniform and the peel strength of the coating layer is thereby improved. Furthermore, reduction of energy cost at the time of drying and suppression of backing roll dirt, which can be caused by insufficient drying, also lead to high solid content coating, which is a desirable direction in coated paper production. . Therefore, the conventional method of increasing the solid content concentration of the coating color is a method of reducing the water component in the coating color, and therefore the copolymer latex used as an adhesive is a high solid content copolymer latex. Has been addressed by using. However, increasing the density of the coating color by this method has a limit in increasing the density, and furthermore, the high-speed fluidity is remarkably reduced, causing problems such as generation of streaks and straktite during the operation of producing coated paper. Furthermore, there is a disadvantage that the coating amount increases and the coating amount cannot be controlled. Therefore, in order to make high-speed coating exceeding 1000 m / min, desirably 1500 m / min practical, it is necessary to achieve high density of the coating color while achieving high density.
In addition, it is necessary to balance the two points of maintaining the high-speed fluidity of the coating color at a better level.

[0004]

According to the present invention, there is provided a pigment (A) 1
5 parts by weight of the copolymer latex (B) to 100 parts by weight.
Contains 5 parts by weight (solid content) and has a solid content concentration of 65 to 75
Percent by weight, high shear viscosity of a shear rate of 10 ⁶ sec ^-1 is from 10 to 60 centipoise, an average particle diameter of the copolymer latex (B) is Ri 50~110nm der,
When the solid concentration of the copolymer latex (B) is 30 to 5
5% by weight and the copolymer latex (B)
Adjusted by adding pigment (A) in the presence of at least a part of
It is the, characterized in that.

Hereinafter, the present invention will be described in detail. (1) Description of Claim 1 First, the pigment (A) will be described. Examples of the pigment (A) include kaolin, calcium carbonate, satin white, talc, titanium oxide, calcium hydroxide and the like.
Preferably, 20 to 100 parts by weight of kaolin and 0 to 100 parts by weight
80 parts by weight of calcium carbonate are used. As calcium carbonate, heavy calcium carbonate and / or light calcium carbonate can be used alone or in combination. Next, the copolymer latex (B) will be described in detail. The composition of the copolymer latex (B) is usually as follows. (B-1) Conjugated diene monomer 20 to 60 parts by weight (B-2) Ethylenically unsaturated carboxylic acid monomer 0.5 to 7 parts by weight (B-3) (B-1) and (B- Ethylene unsaturated monomer other than 2) 33 to 79.5 parts by weight, provided that (B-1) + (B-2) + (B-3) = 100
Parts by weight.

Specific examples of the conjugated diene monomer (B-1) used in the production of the copolymer latex of the present invention include butadiene, isoprene, 2-chloro-1,3-butadiene and 2-methyl-1. , 3-butadiene and the like. These can be used alone or in combination, but butadiene is particularly preferred. The conjugated diene monomer is used for imparting appropriate elasticity and film hardness to the obtained copolymer. The amount used is usually 20 to 60 parts by weight, particularly preferably 25 to 55 parts by weight, based on 100 parts by weight of all monomers. If the amount is less than 20 parts by weight, the adhesive strength is not sufficient, while
If it exceeds 60 parts by weight, water resistance and adhesive strength are undesirably reduced.

The ethylenically unsaturated carboxylic acid monomer (B-
Specific examples of 2) include acrylic acid, methacrylic acid,
Monocarboxylic acids such as crotonic acid; and dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid. These can be used alone or in combination of two or more. The amount of the ethylenically unsaturated carboxylic acid monomer used is
Usually, it is 0.5 to 7 parts by weight, preferably 0.5 to 4 parts by weight. If the amount is less than 0.5 part by weight, the adhesive strength and mechanical stability decrease. If the amount exceeds 7 parts by weight, the viscosity of the latex becomes too high to make it difficult to handle, and the fluidity of the coating liquid is deteriorated.

Specific examples of the ethylenically unsaturated monomer (B-3) include aromatic vinyl compounds such as styrene, α-methylstyrene and vinyltoluene, methyl acrylate,
Alkyl or methacrylic acid alkyl ester compounds such as methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, Acrylamide,
Examples include unsaturated amide compounds such as methacrylamide, N, N-dimethylacrylamide and N-methylolacrylamide, and unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile.
These can be used alone or in combination of two or more. Of these, styrene is preferably used as the aromatic vinyl compound, methyl methacrylate is preferably used as the alkyl ester compound, and acrylonitrile is preferably used as the unsaturated nitrile compound. The eletin-based unsaturated monomer is used for imparting appropriate hardness, elasticity and water resistance to the obtained copolymer, and its use amount is usually 33 to 79.5 parts by weight, preferably Is 38
７４74.5 parts by weight. If the amount is less than 33 parts by weight, the water resistance is not sufficient. On the other hand, if it exceeds 79.5 parts by weight, the copolymer becomes too hard and the adhesive strength is undesirably reduced.

The average particle size of the copolymer latex (B) is
This is a very important requirement in the configuration of the present invention.
It must be in the range of 0 nm. Preferably 10
0 to 60 nm. If it exceeds 110 nm, the fluidity of the coating liquid will deteriorate. This tendency is particularly remarkable when needle-like or long columnar light calcium carbonate is used. On the other hand, when it is smaller than 50 nm, the fluidity of the coating liquid is no longer improved, the glossiness of white paper and the ink transfer property are significantly reduced, and the light calcium carbonate cannot be sufficiently compensated for. The average particle size of the copolymer latex (B) is evaluated by a light scattering method or the like. This average particle size is
It can be prepared by adjusting the amounts of water, emulsifier, polymerization initiator and the like in the known emulsion polymerization techniques described below.

In the present invention, a copolymer latex is obtained by emulsion-polymerizing the components (B-1) to (B-3). In the emulsion polymerization, a known emulsifier, a polymerization initiator, And a molecular weight regulator. As the emulsifier, an anionic emulsifier, a nonionic emulsifier, and an amphoteric emulsifier can be used. Examples of the anionic emulsifier include a higher alcohol sulfate, an alkylbenzene sulfonate, and a fatty acid sulfonate. As the nonionic emulsifier, an alkyl ester type, an alkyl ether type, an alkyl phenyl ether type or the like of polyoxyethylene glycol is used. As the amphoteric emulsifier, an alkylbentain type is used. As the initiator, a water-soluble initiator such as sodium persulfate, potassium persulfate, and ammonium persulfate, and an oil-soluble initiator such as benzoyl peroxide can be used. Known molecular weight regulators, chelating agents, inorganic salts and the like can be used for emulsion polymerization. As the molecular regulator, alkyl mercaptans, dimers of α-methylstyrene, and the like can be used.

The copolymer latex (B) has a solid content of 30 to 55% by weight, preferably 45 to 52% by weight.
It is. When the solid concentration of the copolymer latex (B) is 55
If the amount is more than 10% by weight, the viscosity of the latex rises remarkably, and handling becomes difficult. When the content is less than 30% by weight,
Even when the method for producing a paper coating composition of the present invention is used, high solid differentiation cannot be achieved. The solid content concentration can be adjusted by heating or concentrating the polymer obtained by emulsion polymerization under reduced pressure. The composition of the present invention contains the pigment (A) 100
It is necessary to include 5 to 25 parts by weight, preferably 8 to 20 parts by weight of the copolymer (B) as a binder for binding the parts by weight. When the amount of the copolymer (B) is less than 5 parts by weight, the adhesive strength is not sufficient. When the amount exceeds 25 parts by weight, the glossiness of white paper and the ink transfer property are deteriorated. In the present invention, in addition to the copolymer (B) as a binder, starch, polyvinyl alcohol, polyvinyl acetate and the like, preferably starch, can be added as another adhesive (C). When the other adhesive (C) is used, the amount is 15 parts by weight or less, preferably 12 parts by weight or less based on 100 parts by weight of the pigment (A).

When adjusting the composition for paper coating, additives (D) such as dispersants, defoamers, preservatives, water-proofing agents, lubricants, fluorescent dyes and the like can be added.
The amount used is from 0 to 1 based on 100 parts by weight of the pigment (A).
0 parts by weight. If it is used in an amount exceeding 10 parts by weight, the physical properties of the coated paper are undesirably reduced. As a dispersant,
Sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate and the like can be used alone or in combination, and the amount is preferably 0 to 2 parts by weight, more preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the pigment (A). 0
5 to 1 part by weight can be used. If it exceeds 2 parts by weight, no improvement in the dispersing effect is observed, and conversely, an increase in viscosity is caused.

[0013] The paper coating composition of the present invention can be applied to a base paper for coating using a known technique, but a blade coater is preferred. Especially 1200
When a high-speed coating at m / min or 1500 m / min or more is performed, the fluidity and physical properties of the coated paper are superior to those of a conventional paper coating composition. When performing high speed coating at 1500 m / min, the paper coating composition undergoes deformation at a shear rate of about 10 ⁶ sec ^-1 . The high shear viscosity of the paper coating composition of the present invention at a shear rate of 10 ⁶ sec ^-1 is 10 to 10 sec.
60 centipoise, preferably 10 to 50 to centipoise, more preferably 10 to 40 centipoise,
Hercules maximum torque measured at 8800 rpm is
Usually 350 × 10 ⁴ dyn · cm or less, preferably 30
0 × 10 ⁴ dyn · cm or less, more preferably 250
× 10 ⁴ dyn · cm or less. When it exceeds 60 centipoise, problems such as generation of streaks and structite occur during the production of coated paper, and it becomes impossible to control the amount of coating, which is unsuitable. Further, even if it is less than 10 centipoise, it is difficult to control the coating amount of 10 g / m ² or more, which is not preferable. The measurement of the high shear viscosity of the present invention is performed using a slit die rheometer. A slit die rheometer can measure high shear viscosity as a function of shear rate. A dilatant behavior in which the shear rate dependence of the high shear viscosity becomes convex upward is not preferable in the coating operation, and it is preferable to take a thixotropic behavior in which the high shear viscosity decreases uniformly depending on the shear rate.

The method for preparing the paper coating composition of the present invention will be described. As a dispersing device, a paper coating composition of the present invention can be prepared by using a general mechanical dispersing device such as a Kedimill / Corless dispersing device, but the dispersing device is not limited thereto. Absent. Using these dispersing devices, the copolymer latex (B) is initially charged, and the pigment (A) is added with stirring, and these are dispersed and mixed. If necessary, another adhesive (C) such as starch is added in an amount of 0 to 15 parts by weight, preferably 2 to 10 parts by weight.
Add by weight. When the pigment (A) is added to and dispersed in the copolymer (B), before and after adding the pigment (A) and the other adhesive (C), 0 to 10 parts by weight of Additive (D) can be used. Additive (D)
When a dispersant is used, it is preferable to add it before or simultaneously with the addition of the pigment (A). Claim 1 relates to the other adhesive (C) and the additive (D).
The compounds described in (1) can be used within the range of the amount used.
The copolymer latex (B) used when dispersing the pigment (A) is at least 50%, preferably 70%, of the total amount used.
% Or more, and the remaining amount may be added after the addition of the pigment (A) or after the addition of the other adhesive (C) and the additive (D), or simultaneously.

[0015] If necessary, water can be added to the thus prepared paper coating composition to adjust it to a desired solid content concentration. The solid content concentration of the paper coating composition is 50 to
It is 75% by weight, preferably 65-72% by weight, more preferably 67-70% by weight. If it exceeds 75% by weight, dispersion becomes impossible. If it is less than 50% by weight, it is difficult to increase the drying zone of the coating machine or to control the coating amount of 10 g / m ² or more. By using the production method of the present invention, it is possible to replace water as a medium at the time of pigment dispersion with water in the copolymer latex, and it is possible to easily obtain a high solid content composition of up to 75% by weight. . Further, the composition obtained by the production method of the present invention is also excellent in high-speed fluidity, high solid differentiation, because it can be compatible with high-speed coating, has been found to exhibit a remarkable effect as coated paper, the present invention. Reached.

Hereinafter, specific examples of the present invention will be described with reference to examples. In Examples, “%” indicates “% by weight” and “parts” indicates “parts by weight”.

【Example】

1. Method for Producing Copolymer Latex A temperature-controllable pressurized reaction vessel equipped with a stirrer having an internal volume of 100 liters was replaced with nitrogen, and 300 parts of water, 1.5 parts of maleic acid, 0.5 parts of acrylic acid, Potassium persulfate 1
Parts, sodium alkylbenzene sulfonate 2 parts, n-
0.2 part of dodecyl mercaptan, 4 parts of butadiene, 10 parts of styrene and 6 parts of methyl methacrylate were charged,
The temperature was raised with stirring, and polymerization was performed at 70 ° C. for 4 hours. At this time, the conversion was 99%. Then butadiene 34
Parts, 30 parts of styrene, and 14 parts of methyl methacrylate were mixed, and the addition polymerization was continuously continued at a uniform speed from 4 hours to 20 hours after the polymerization reaction. During this time, the temperature of the polymerization system was maintained at 70 ° C., and the polymerization was further maintained at this temperature for 6 hours. The polymerization rate at the end of the polymerization was 98%. The copolymer latex obtained as described above was adjusted to pH 7.0 by adding an aqueous solution of sodium hydroxide having a concentration of 5%, the residual monomer was removed by steam distillation, and further concentrated under reduced pressure by heating to obtain a solid. The content was adjusted to 50% to obtain a copolymer latex A. In addition, the amounts of the emulsifier, the amount of water, the amount of each monomer, the amount of the initiator, the molecular regulator and the like were appropriately varied to obtain copolymer latexes B and ac. About the obtained copolymer latex, a laser particle analyzer system, LPA-3000 / 3100 [Otsuka Electronics Co., Ltd.
Was used to measure the average particle size. Table 1 shows the results.
Shown in

[0017]

[Table 1]

2. Preparation of Paper Coating Composition [Examples 1 to 8] Using the copolymer latexes A and B, a paper coating composition was prepared by the following method. The copolymer latex and the dispersant were placed in a Cores disperser, clay and calcium carbonate were gradually added, and the mixture was stirred and dispersed.
Separately, the oxidized starch was cooked and dissolved to a solid content of 34%, and added to the dispersion. Adjusted water was appropriately added thereto and dispersed to obtain a paper coating composition having a final solid content of 75%. Similarly, the amount of conditioning water was adjusted to obtain a paper coating composition having a solid content of 72%, 70%, and 67%. As the compounding formulation, the following clay, calcium carbonate, oxidized starch, dispersant and the like were used in combination. As for the composition, 100 parts by weight of the pigment (clay and calcium carbonate) was used, and the copolymer latex 12 was used.
Parts by weight (solid content), 3 parts by weight of oxidized starch, 0.
2 parts by weight. Clay: Amazon 88 (made by Kadam) Ultra White-90 (UW-90) [made by Engelhard Mineral Chemical Phillips] Heavy calcium carbonate: Carbital-90 (CA-90)
[Made by Fuji Kaolin Co., Ltd.] (Slurry having a solid content of 75%) Needle-like light calcium carbonate: Tamapearl-123 (TP-
123) [Okutama Industry Co., Ltd.] Oxidized starch: Egg Ace B [Egg Co., Ltd. Starch Co., Ltd.] Dispersant: Alon T-40 [Toa Gosei Co., Ltd.]

Comparative Example 9 A composition for paper coating was prepared using copolymer latex A by the following method. First, after dissolving a dispersant in a certain amount of water, clay and calcium carbonate were gradually added and dispersed by stirring with a Coreless disperser. On the other hand, the oxidized starch was dissolved by cooking, and this was added to the dispersion and dispersed.
The solid content of the oxidized starch was 34% by weight, as in Example 1. Finally, copolymer latex A was added to obtain a paper coating composition. Further, when the copolymer latex was added, adjusted water was added to obtain a predetermined solid content concentration. However, in this method, in the preparation of a dispersion of clay and calcium carbonate, the dispersion could be performed only at a solid content concentration of 72% or less. As a result, it was possible to prepare only a final paper coating composition having a concentration of less than 70%. The formulation was performed in the same manner as in Example 1.

Comparative Examples 1 to 7 A paper coating composition was prepared in the same manner as in Example 1 using the latexes A and a to c of the copolymer. For the copolymer latexes b and c, the preparation at a solid content of 75% by weight could not be stirred and could not be prepared.
A composition of 0.67% by weight was obtained. Copolymer latex a
Was able to prepare 75, 72, 70, and 67% by weight of the composition. Comparative Example 8 A paper coating composition was prepared in the same manner as in Comparative Example 9, using the copolymer latex c.

3. 3. Fluidity evaluation of paper coating composition 3-1 Viscosity Immediately after preparation of the paper coating composition, it was measured at 60 rpm using a Brookfield viscometer. 3-2 High-speed fluidity 0-8800r using Hercules high shear viscometer
The maximum torque of the paper coating composition was measured at pm. 1.0 × 10 ⁶ sec ⁻¹ using a slit die rheometer
The viscosity at the shear rate of was evaluated. As a material having a known viscosity and showing Newtonian flow, silicone oil [T
SF451-100, manufactured by Toshiba Silicone Co., Ltd.], and the absolute value of the viscosity was corrected.
Table 2 shows the fluidity evaluation results of the compositions obtained in the examples and comparative examples.

[0022]

[Table 2]

4. Coating For a paper coating composition having a solid content of 67% or 70%, a cylindrical laboratory coater (CLC6) was used.
000) [manufactured by Warehauser Co., Ltd.]
Coating was performed on a commercial high-quality paper at a coating speed of 1 minute to produce a coated paper. The coating amount was controlled by adjusting the pushing distance of the blade so as to be 12.0 ± 0.5 g / m ² . The coated paper was subjected to lab super calender treatment twice at 70 ° C. and a linear pressure of 100 kg / cm to obtain a test sample.

5. Evaluation of Physical Properties of Coated Paper 5-1 Dry Pick Strength (Adhesive Strength) The degree of picking occurrence when printed with an RI printing machine was visually determined, and evaluated by a five-step method. The higher the score, the better. 5-2 Wet Pick Strength (Water Resistance) The degree of picking when printing was performed by applying dampening water using a Molton roll with an RI printer was visually determined, and evaluated on a scale of 1 to 5. The higher the score, the better. 5-3 Ink Filling Property (Ink Acceptability) Printing is performed by using a moltroll with a RI printing machine, applying dampening water, and using a printing ink having a tack value that does not cause pinking. Measure the transferred ink density with a densitometer,
evaluated. The higher the numerical value, the better. 5-4 Gloss on White Paper Gloss was measured using a gloss meter at an incident angle of 75 ° and a reflection angle of 75 °. The larger the gloss value, the better. 5-5 Printing Gloss Printing was performed using a fixed amount of ink with an RI printing machine, and the gloss of the printed surface was measured and evaluated in the same manner as in the case of blank paper gloss. 5-6 Burnout test Apply 10% ammonium chloride solution to coated paper,
It was placed in a gear oven at 0 ° C., and the coating state was visually judged from the coloring state. (○; good to ×; bad) The results of evaluation of the physical properties of the coated paper are shown in Table 3.

[0025]

[Table 3]

Examples 1 to 9 are the paper coating compositions of the present invention, and the desired effects of the present invention were obtained. Example 1
Among 9 to 9, 1 to 8 are those prepared by the method of claim 2, which enable higher solid differentiation than Example 9 prepared by the conventional method, and have generally excellent coated paper properties. I have. In Comparative Examples 1 and 2, the average particle diameter of the copolymer latex is less than the range of the present invention, and although the fluidity is good, the inking property and the gloss of white paper are remarkably reduced, and are not suitable as coated paper. In Comparative Example 3, the average particle diameter of the copolymer latex was large, coating unevenness was observed in a burnout test, and the white paper gloss was poor. Comparative Example 4 is an example in which the solid content of Comparative Example 3 was lowered, and although coating was possible, the strength was reduced and the balance as coated paper properties was poor. Comparative Examples 5 and 6 are examples in which the average particle size of the copolymer latex was further increased as compared with Comparative Examples 3 and 4. In this case, the coating amount could not be controlled to a predetermined amount. Paper properties could not be evaluated.
In the burnout test, coating unevenness was remarkable.
Comparative Example 8 is an example prepared by a conventional method using a copolymer latex having a large average particle diameter. However, similarly to Comparative Example 6, control of the coating amount was impossible, and coating unevenness was remarkable. .

[0027]

Industrial Applicability The paper coating composition of the present invention can achieve a high solids concentration of 70% or more, has excellent high-speed fluidity under a high shear rate of 10 ⁶ sec ⁻¹ , and has a high speed and a high flow rate. It is suitable for solid content coating and has good coated paper properties such as white paper gloss and inking property. Further, by performing the high solid content coating, it is possible to avoid problems such as cost reduction due to reduction of drying load and operational problems such as backing roll contamination in the production of coated paper.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takashi Matsui 2--11-24 Tsukiji, Chuo-ku, Tokyo Japan Synthetic Rubber Co., Ltd. (56) References JP-A-58-54096 (JP, A) JP-A Sho 57-161193 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D21H 19/56-19/60

Claims (4)

(57) [Claims] 1. A pigment (A) containing 100 parts by weight of a copolymer latex (B) in an amount of 5 to 25 parts by weight (solid content), a solid content of 65 to 75% by weight, and a shearing rate. 1
0 high shear viscosity of ⁶ sec ^-1 is 10 to 60 centipoise, an average particle diameter of the copolymer latex (B) is the 50～110Nm, solid concentration of the copolymer latex (B) is 30 to 55% by weight, and
A paper coating composition, which is prepared by adding a pigment (A) in the presence of at least a part of the copolymer latex (B). 2. The composition according to claim 1, wherein the copolymer latex (B) has a solid content of 45 to 5%.
A composition for paper coating characterized by being 2% by weight. 3. The paper coating according to claim 1, wherein the copolymer latex (B) used when dispersing the pigment (A) uses 50% or more of the total amount of the copolymer latex (B). Industrial composition. 4. The paper coating composition according to claim 1, wherein the solid content concentration is 67 to 70% by weight.
A paper coating composition, characterized in that: