JP2008231587A - Composition for coating paper and coated paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composition for coating paper, excellent in coating operability of a high speed flowability (high shear viscosity) of the composition for coating the paper, also excellent in printing aptitude such as surface strength, white paper gloss, printing gloss, etc., and further capable of obtaining the coated paper having the above excellent printing aptitude over a wide printing speed range, and to provide the coated paper. <P>SOLUTION: This composition for coating the paper containing a pigment and binder is provided by containing the pigment containing fine particle kaolin or fine particle calcium carbonate having ≥95% particle size distribution of ≤2 μm, containing latex in the binder, and containing 4-10 pts.mass copolymer contained in the latex and having 50-100 nm number-average particle diameter, based on 100 pts.mass pigment. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a paper coating composition and coated paper, and more particularly to a paper coating composition suitable for high-speed coating and high concentration and a coated paper coated with the composition.

In recent years, high-speed coating of coaters, particularly blade coaters, has been attempted with the increase in the speed of paper machines. However, in the so-called high-speed coating region where the coating speed exceeds 1000 m / min, when trying to produce a coated paper having a coating amount of 10 g / m ² or more, the coating amount control is difficult, The rough surface of the coating surface occurred and became an obstacle to the improvement of the coating speed. In order to solve these problems, solutions from the hardware side such as coaters have been studied. However, the previous problem is a phenomenological paper coating paint (hereinafter referred to as coating). Since it is strongly derived from the rheological behavior of the coating color, studies have been conducted to make the coating color suitable for high-speed coating. As a result, attempts have been made to improve the above problems in high-speed coating by lowering the solid content concentration of the coating color and lowering the viscosity of the coating color. However, with this method, the physical properties of the coated paper are deteriorated, and further, a capital investment such as making the drying zone longer in the coater or improving the drying capacity is unavoidable. In addition, there is a problem that it becomes difficult to control the coating amount at 10 g / m ² or more.

For high solid differentiation, coating with a high solid content concentration of the coating color increases the bulk of the coating layer, resulting in improved ink acceptability and improved white paper gloss. Furthermore, binder migration is suppressed, resulting in a uniform binder distribution and an improvement in the peel strength of the coating layer. Furthermore, it leads to reduction of energy cost at the time of drying and suppression of backing roll dirt which may be caused by insufficient drying, and high solid content coating 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. For this purpose, 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 limitations in increasing the density, and further, the high-speed fluidity is remarkably lowered, causing problems such as the occurrence of streak and stratite during the operation of preparing the 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, preferably 1500 m / min practical, it is possible to achieve a higher level of coating color and a higher level of coating color high-speed fluidity. It is necessary to satisfy both of the following two points. There is a technique disclosed in Patent Document 1 as a technique for making these compatible.
JP-A-6-173198

  However, there has been a demand for a paper coating composition that has the above performance at a higher level. The present invention has been made in view of such problems of the prior art, and the subject is excellent in coating operability such as high-speed fluidity (high shear viscosity) of the paper coating composition. In addition, a composition for paper coating and a coated paper, which are excellent in printability such as surface strength, white paper gloss, and print gloss, and can obtain a coated paper having the above-mentioned excellent printability over a wide printing speed range. Is to provide.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be achieved by the specific paper coating composition and coated paper of the present invention. It came to be completed.

  That is, according to the present invention, the following paper coating composition and coated paper are provided.

[1] A paper coating composition containing a pigment and a binder, wherein the pigment contains fine kaolin or fine calcium carbonate having a particle size distribution of 2% or less of 95 μm or more, and the binder contains latex, A paper coating composition containing 4 to 10 parts by mass of a copolymer having a number average particle diameter of 50 to 100 nm contained in latex with respect to 100 parts by mass of pigment.

[2] The paper coating composition according to the above [1], containing 25 parts by mass or more of the fine kaolin or the fine calcium carbonate with respect to 100 parts by mass of the pigment.

[3] The copolymer contained in the latex is (a) 30 to 70% by mass of an aliphatic conjugated diene monomer, (b) 5 to 40% by mass of a vinyl cyanide monomer, and (c) ethylene. Is a copolymer obtained by emulsion polymerization of a monomer component consisting of 0.1 to 10% by weight of an unsaturated carboxylic acid monomer, and has a glass transition temperature of at least in the range of −100 to 60 ° C. The paper according to the above [1] or [2], which is a copolymer having a single point and having a difference (ΔT) between the minimum temperature T1 and the maximum temperature T2 of the transition region of 30 ° C. or higher in the differential calorimetric curve Composition for coating.

[4] In addition to the monomer components (a) to (c), the copolymer contained in the latex further comprises (d) 0 to 64.9% by mass of other copolymerizable monomers. (However, the paper coating according to the above [3], which is a copolymer obtained by emulsion polymerization of a monomer component consisting of (a) + (b) + (c) + (d) = 100 mass%) Industrial composition.

[5] A coated paper using the paper coating composition according to any one of [1] to [3] as a coating liquid.

  The composition for paper coating of the present invention is excellent in high-speed fluidity (high shear viscosity) coating operability, and excellent in printability such as surface strength, white paper gloss, printing gloss, and the like over a wider printing speed range. Coated paper having excellent printability can be obtained.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiment, and is based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention. It should be understood that modifications and improvements as appropriate to the following embodiments also fall within the scope of the present invention.

[Composition for paper coating]
The paper coating composition of the present invention contains a pigment and a binder.

[1. Pigment]
In the paper coating composition of the present invention, as a pigment, an aqueous dispersion of the pigment is a fine particle having a particle size distribution of 2 μm or less measured with a laser fine particle counter (NP500T manufactured by Nippon Denshoku Industries Co., Ltd.) of 95% or more. Contains kaolin or fine calcium carbonate. Examples of the pigment include kaolin, calcium carbonate, satin white, talc, titanium oxide, and calcium hydroxide. Preferably, 20-100 parts by weight of kaolin and 0-80 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.

  Use of fine pigments improves the white paper gloss and printing gloss of the coated paper, but reduces the surface strength. In addition, when the small particle size latex is used, the surface strength of the coated paper is improved, but the white paper gloss is lowered. The inventors have found that a combination of a fine pigment and a specific small particle size latex can improve blank paper gloss and printing gloss while maintaining surface strength.

  In order to obtain 65% or more blank paper gloss, it is desirable to contain 25 parts by mass or more of the fine pigment with respect to 100 parts by mass of the pigment. Preferably, 35 parts by mass or more, more preferably 50 or more.

[2. binder]
In the present invention, a latex containing a copolymer having a specific particle size can be used as the binder. Latex containing a copolymer having a specific particle size that can be used in the present invention comprises a monomer component (a) 30 to 70% by mass of an aliphatic conjugated diene monomer, and (b) a vinyl cyanide monomer. A monomer comprising 5 to 40% by mass of a product, (c) 0.1 to 10% by mass of an ethylenically unsaturated carboxylic acid monomer, and (d) 0 to 64.9% by mass of another copolymerizable monomer. It is obtained by emulsion polymerization of a body component and contains a copolymer having a number average particle diameter of 50 to 100 nm.

  Examples of the (a) aliphatic conjugated diene monomer include 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene, chloroprene and the like. Of these, 1,3-butadiene is preferable. These (a) aliphatic conjugated diene monomers can be used singly or in combination of two or more. The (a) aliphatic conjugated diene monomer is a useful component for imparting appropriate flexibility and elongation to the resulting polymer and imparting impact resistance. (A) The amount of the aliphatic conjugated diene monomer used is 30 when the total amount of monomers for copolymerization ((a) + (b) + (c) + (d)) is 100% by mass. It is -70 mass%, Furthermore, it is preferable that it is 33-60 mass%, and it is still more preferable that it is 35-55 mass%. If it is less than 30% by mass, the copolymer tends to be too hard and the adhesive strength tends to deteriorate, and if it exceeds 70% by mass, it becomes too soft and the stickiness resistance tends to deteriorate.

  Examples of the (b) vinyl cyanide monomer include acrylonitrile and methacrylonitrile. Of these, acrylonitrile is preferable. These (b) vinyl cyanide monomers can be used individually by 1 type or in combination of 2 or more types. (B) The amount of vinyl cyanide monomer used is 5 to 40% by mass, preferably 10 to 35% by mass, more preferably 100% by mass when the total amount of monomers for copolymerization is 100% by mass. 15 to 33% by mass. When the amount is less than 5% by mass, the ink solvent resistance tends to decrease and the printing gloss tends to decrease. When the amount exceeds 70% by mass, the copolymer becomes too hard and the adhesive strength tends to deteriorate.

  (C) As an ethylenically unsaturated carboxylic acid monomer, acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid etc. can be mentioned, for example. These (c) ethylenically unsaturated carboxylic acid monomers can be used singly or in combination of two or more. (C) The amount of the ethylenically unsaturated carboxylic acid monomer used is 0.1 to 10% by mass, preferably 0.7, when the total amount of monomers for copolymerization is 100% by mass. -7% by mass, more preferably 1-5% by mass. When the amount is less than 0.1% by mass, the polymerization stability and dispersion stability tend to decrease. When the amount exceeds 10% by mass, the viscosity of the copolymer becomes too high and the workability tends to decrease. .

  Examples of other monomers (d) copolymerizable with the above-mentioned monomers include aromatic vinyl monomers, alkyl (meth) acrylates, vinyl acetate, acrylamide compounds, N-methylol acrylamide and the like. be able to. Examples of the aromatic vinyl monomer include styrene, α-methyl styrene, p-methyl styrene, vinyl toluene, chlorostyrene, and the like. Of these, styrene is preferable. Alkyl (meth) acrylates include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, and benzyl (meth). Examples thereof include acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, and isobornyl (meth) acrylate. Of these, methyl methacrylate is preferable. Examples of the acrylamide compound include acrylamide, methacrylamide, N, N-dimethylacrylamide, N, N-dimethylaminopropyl (meth) acrylamide and the like. These (d) other monomers can be used individually by 1 type or in combination of 2 or more types. (D) The other monomer is used to give an appropriate glass transition temperature according to the purpose to the obtained copolymer. (D) It is preferable that the usage-amount of another monomer is 0-64.9 mass% when the sum total of the monomer for a copolymer is 100 mass%.

(Additive)
In the present invention, starch, polyvinyl alcohol, polyvinyl acetate and the like, preferably starch, can be added as the other adhesive in addition to the latex as the binder. The amount of the other adhesive used is 15 parts by mass or less, preferably 12 parts by mass or less, with respect to 100 parts by mass of the pigment.

  When preparing a composition for paper coating, for example, a dispersant, an antifoaming agent, a preservative, a water resistant agent, a lubricant, a fluorescent dye, and the like can be added as additives. The usage-amount is 0-10 mass parts with respect to 100 mass parts of pigments. When the amount exceeds 10 parts by mass, the physical properties of the coated paper are deteriorated, which is not preferable. As the dispersant, sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate and the like can be used alone or in combination, and the amount used is preferably 0 to 2 parts by mass with respect to 100 parts by mass of the pigment (A), More preferably, 0.05 to 1 part by mass can be used. When the amount exceeds 2 parts by mass, no improvement in the dispersion effect is observed, and conversely, an increase in viscosity is caused.

(Particle size)
The average particle size of the copolymer contained in the latex is 50 to 100 nm, and preferably 60 to 90 nm. If it is less than 50 nm, the viscosity of the latex becomes too high, and the workability tends to decrease. On the other hand, in the case of 100 nm or more, the surface strength tends to decrease. In particular, when acicular and long columnar light calcium carbonate is used, this tendency becomes remarkable. The average particle size of the latex is evaluated by a light scattering method or the like. This average particle size can be prepared by adjusting the amount of water, emulsifier, polymerization initiator and the like used in the known emulsion polymerization technique described below.

(Glass transition point)
The copolymer contained in the latex of the paper coating composition of the present invention has at least one glass transition temperature in the range of −100 to 60 ° C. The glass transition temperature is preferably −80 to 55 ° C., more preferably −70 to 50 ° C. When the temperature is lower than -100 ° C, the stickiness resistance tends to deteriorate. When the temperature is 60 ° C or higher, the copolymer becomes too hard and the adhesive strength tends to deteriorate.

(Glass-transition temperature)
In the copolymer contained in the latex of the paper coating composition of the present invention, the difference ΔT between the lowest temperature T1 and the highest temperature T2 in the transition region is 30 ° C. or higher in the differential calorimetric curve. Preferably, it is 35 ° C. or higher, more preferably 40 ° C. or higher. When the temperature is lower than 30 ° C., the printability cannot be maintained at a high level in a wide range of print speeds, so that there is a tendency that a sufficient print speed range cannot be secured. At the same time, the surface strength and impact resistance of the coated paper are lowered, and there is a tendency that the coated paper cannot withstand impact deformation with a large deformation speed in high-speed printing. In other words, the strength tends to decrease.

(Latex preparation method)
Latex can be easily prepared by emulsion polymerization. In the emulsion polymerization, an emulsifier, a polymerization initiator, a molecular weight regulator and the like are used in an aqueous medium. As an emulsifier, an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, etc. can be used individually by 1 type or in combination of 2 or more types. Examples of the anionic surfactants include higher alcohol sulfates, alkylbenzene sulfonates, aliphatic sulfonates, and polyethylene glycol alkyl ether sulfates. As the nonionic surfactant, an ordinary polyethylene glycol alkyl ester type, alkyl ether type, alkylphenyl ether type, or the like is used. Examples of the amphoteric surfactant include those having a carboxylate salt, sulfate ester salt, sulfonate salt, and phosphate ester salt as an anion portion, and an amine salt and a quaternary ammonium salt as a cation portion. Specifically, betaines such as lauryl betaine and stearyl betaine; amino acid types such as lauryl-β-alanine, stearyl-β-alanine, lauryl di (aminoethyl) glycine, octyldi (aminoethyl) glycine, and the like are used. .

  As the polymerization method, a method in which a part of the monomer is polymerized and then the remainder is continuously or intermittently added, or a method in which the monomer is continuously added from the beginning of the polymerization is usually employed. . The polymerization temperature is usually 20 to 85 ° C, preferably 25 to 80 ° C. The polymerization time is usually 5 to 30 hours, preferably 8 to 25 hours.

[3. Pigment and latex content]
In the composition for paper coating of this invention, the copolymer contained in latex is 4-10 mass parts with respect to 100 mass parts of pigments, Preferably, it is 5-9 mass parts. When the amount is less than 4 parts by mass, the surface strength tends to decrease, and when the amount exceeds 10 parts by mass, the gloss of white paper and the print gloss tend to decrease.

(Method for preparing paper coating composition)
The preparation method of the composition for paper coating of this invention is demonstrated. As the dispersing apparatus, the paper coating composition of the present invention can be prepared by using a general mechanical dispersing apparatus such as a Kedymill-Coreless disperser, but the dispersing apparatus is not limited to this. Absent. Using these dispersing devices, first, latex is charged, and pigment is added with stirring to disperse and mix them. If necessary, 0 to 15 parts by mass, preferably 2 to 10 parts by mass of another adhesive such as starch is added. Moreover, when adding and dispersing a pigment in latex, 0 to 10 parts by mass of an additive can be used as necessary before and after the pigment and other adhesives are added. When a dispersant is used as the additive, it is preferably added before or simultaneously with the addition of the pigment. The latex used when dispersing the pigment can be used in an amount of 50% or more, preferably 70% or more of the total amount used, and the remaining amount after adding the pigment or after adding other adhesives and additives, Or you may add simultaneously.

Water can be added to the paper coating composition prepared in this way as necessary to obtain the desired solid content concentration. The solid content concentration of the paper coating composition is 50 to 75% by mass, preferably 65 to 72% by mass, and more preferably 67 to 70% by mass. When it exceeds 75% by mass, it becomes impossible to disperse, and when it is less than 50% by mass, 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 becomes possible to replace water, which is a medium at the time of pigment dispersion, with water in the copolymer latex, and a high solid content composition up to 75% by mass can be easily obtained. . In addition, the composition obtained by the production method of the present invention is excellent in high-speed fluidity and can achieve both high solid-state differentiation and high-speed coating, and therefore exhibits a remarkable effect as a coated paper.

(Method for producing coated paper)
Application of the paper coating composition of the present invention to the base paper for coating can be carried out using known techniques, but a blade coater is preferred. In particular, when high-speed coating of 1200 m / min or 1500 m / min or more is performed, the fluidity and coated paper properties are excellent as compared with conventional paper coating compositions. When a high speed coating of 1500 m / min is performed, the paper coating composition undergoes a shear rate deformation 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 60 centipoise, preferably 10 to 50 centipoise, more preferably 10 to 40 centipoise, measured at 8800 rpm. The maximum Hercules torque is usually 350 × 10 ⁴ dyn · cm or less, preferably 300 × 10 ⁴ dyn · cm or less, more preferably 250 × 10 ⁴ dyn · cm or less. If it exceeds 60 centipoise, problems such as the occurrence of streaks and stratites occur during the production of coated paper, and the amount of coating cannot be controlled, which is inappropriate. Moreover, even if it is less than 10 centipoise, it becomes difficult to control the coating amount of 10 g / m ² or more, which is not preferable. The high shear viscosity of the present invention is measured using a slit direometer. Slit rheometers 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 is not preferable in coating operation, and it is preferable to take a thixotropic behavior in which the high shear viscosity is uniformly reduced depending on the shear rate.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

[Methods of analysis, measurement, evaluation, etc.]
[Analysis and measurement of copolymer contained in latex]
(Average particle size of copolymer contained in latex)
The average particle size of the copolymer contained in the latex was determined by a conventional method using a particle size measuring device (FPAR-1000: manufactured by Otsuka Electronics Co., Ltd.).

(Toluene insoluble matter)
The latex was adjusted to pH 8.0, then coagulated with isopropanol, the coagulated product was washed and dried, and a predetermined amount (about 0.03 g) of the sample was immersed in a predetermined amount (100 ml) of toluene for 20 hours. Then, it filtered with a 120 mesh wire net | network, and calculated | required the mass% with respect to the total solid of the preparation of the residual solid content obtained.

(Glass transition temperature (Tg))
The latex was vacuum dried at 100 ° C. for 20 hours to produce a film. This dry film was measured according to the ASTM method using a differential scanning calorimeter (DSC6100: manufactured by Seiko Instruments Inc.).

(Differential calorific curve)
Using a differential scanning calorimeter (DSC6100: manufactured by Seiko Instruments Inc.), measurement was performed according to the ASTM method, and a differential calorimetric curve was obtained. Thereby, the difference ΔT (° C.) between the minimum temperature T1 and the maximum temperature T2 of the transition region of the copolymer contained in each latex was determined.

[Preparation of coating composition]
The raw material was uniformly mixed using a mixer as in the blending prescription to prepare a paper coating composition.
(Combination prescription)
Kaolin clay 50.0 parts Calcium carbonate 50.0 parts Dispersant (sodium polyacrylate) 0.05 parts Sodium hydroxide 0.1 parts Starch 3.0 parts Latex (as solids) 10.0 parts Water Total solids Appropriate amount added to make 65%

  As fine kaolin, J. Org. M.M. Hubbell's JAPANGLOSS, a large particle size kaolin, M.M. HYDRACOTE-B manufactured by Huber, IMERYS Carbital 95 was used as fine calcium carbonate, and IMERYS Carbital 60 was used as large particle size calcium carbonate.

[Evaluation of coating composition]
(PH)
Using a pH meter (HORIBA Co., Ltd. M-7) adjusted with a pH standard solution, it was measured by a conventional method.

(High shear viscosity)
The high shear viscosity of the coating composition was determined by a conventional method using a Hercules high shear viscometer “HR-801C” (manufactured by Kumagai Riki Kogyo Co., Ltd.) after adjusting the coating composition. The measurement conditions were Bob type F, rotational speed 6600 rpm, and sweep time 10 seconds. The lower the viscosity, the better the fluidity of the coating liquid during high-speed coating, indicating that the coating operability is excellent.

[Manufacture of coated paper]
The coating composition was coated on the coated base paper with an electric blade coater (manufactured by Kumagai Riki Kogyo Co., Ltd.) so that the coating amount was 15.0 ± 0.5 g / m ^{2 on} one side. 150 It dried for 5 second with the electric hot air dryer of ° C. The obtained coated paper is left in a constant temperature and humidity chamber at a temperature of 23 ° C. and a humidity of 60% for one day, and then subjected to a super calender treatment twice under the conditions of a linear pressure of 130 kg / cm and a roll temperature of 50 ° C. Paper was manufactured.

[Evaluation of coated paper]
(Dry pick strength)
The degree of picking when printing with an RI printer was judged with the naked eye and evaluated in five stages. Higher scores were obtained with less picking. The numerical value was shown as an average value of 6 measurements.

(Wet pick strength)
The surface of the coated paper was moistened with a water absorbing roll using an RI printing machine, and the degree of picking when printed with the RI printing machine was judged with the naked eye, and evaluated in five stages. Higher scores were obtained with less picking. The numerical value was shown as an average value of 6 measurements.

(White paper gloss)
The coated paper was measured at an angle of 75 degrees using a Murakami gloss meter. The larger the number, the higher the gloss.

(Print gloss)
A commercially available black ink for offset printing was applied once using an RI printer, and measured at an angle of 60 degrees using a Murakami gloss meter. The larger the number, the higher the gloss.

[Latex production]
(Synthesis Examples 1-4)
The first-stage component shown in Table 1 was charged into a pressure-resistant reaction vessel equipped with a stirrer and a temperature controller, and the inside of the polymerization system was replaced with nitrogen. Thereafter, the temperature in the polymerization system was raised to 45 ° C., and polymerization was carried out at this temperature for 2.5 hours. Next, the second stage component was continuously added to the polymerization system over 2 hours to proceed the polymerization. Further, the third stage component was continuously added into the polymerization system over 4 hours. Thereafter, the temperature in the polymerization system was raised to 50 ° C., and the fourth stage component excluding sodium bisulfite was continuously added to the polymerization system over 2.5 hours, and sodium bisulfite was continuously added to the polymerization system over 5 hours. The final polymerization conversion was 98%.

  After adjusting the obtained latex to pH 7.5 using sodium hydroxide, water vapor was blown to remove unreacted monomers, and a latex having a solid content concentration of 52% was obtained by heating steam distillation.

  About the copolymer contained in the obtained latex, average particle diameter, toluene insoluble matter, glass transition temperature, and the difference ΔT between the lowest temperature and the highest temperature of the transition region in the differential calorimetric curve were determined. The results are shown in Table 1.

[Preparation of composition for paper coating]
Using the latex and pigment shown in Table 2, a composition for paper coating was prepared according to the above-mentioned formulation, and performance evaluation was performed according to the method described above. These results are shown in Table 2. In Table 2, the amount of the latex copolymer indicates the solid content of the copolymer contained in the latex. Furthermore, this coating composition was applied to paper to produce a coated paper. The performance of the coated paper was also evaluated according to the above method. These results are shown in Table 2.

[Explanation of evaluation results]
Examples 1 to 8 are examples of the composition for paper coating within the scope of the present invention, and the characteristics of the paper coating composition and coated paper targeted by the present invention are obtained. In particular, when Examples 1 to 10 and Comparative Examples 1 to 3 are compared, it can be clearly seen that the high shear viscosity is low and the white paper gloss and the print gloss are excellent while maintaining the surface strength. Examples 2, 7, 8 and Comparative Example 2 differ in the particle diameter of the copolymer contained in the latex. When the particle size is large, the high shear viscosity becomes high, and when it exceeds the range of the present invention, the surface strength, white paper gloss, and print gloss are lowered. In Comparative Example 4, since the content of the copolymer contained in the latex exceeds the range of the present invention, the surface strength and the print gloss are improved, but the white paper gloss is lowered.

  The coated paper of the present invention is excellent in printing gloss, ink acceptability, ink setting, and blank paper gloss, and is suitable as a sheet for sheet-fed offset printing or rotary offset printing.

Claims (5)

A composition for paper coating containing a pigment and a binder,
The pigment contains fine kaolin or fine calcium carbonate having a particle size distribution of 2 μm or less and 95% or more,
The binder comprises latex;
A paper coating composition containing 4 to 10 parts by mass of a copolymer having a number average particle diameter of 50 to 100 nm contained in the latex with respect to 100 parts by mass of the pigment.   The composition for paper coating of Claim 1 which contains 25 mass parts or more of the said fine kaolin or the said fine calcium carbonate with respect to 100 mass parts of said pigments. The copolymer contained in the latex is
(A) Aliphatic conjugated diene monomer 30 to 70% by mass,
(B) 5-40% by weight of vinyl cyanide monomer,
(C) 0.1 to 10% by mass of an ethylenically unsaturated carboxylic acid monomer,
And a glass transition temperature at least one point in the range of −100 to 60 ° C., and the lowest temperature of the transition region in the differential calorimetric curve. The paper coating composition according to claim 1 or 2, which is a copolymer having a difference (ΔT) between T1 and maximum temperature T2 of 30 ° C or higher. In addition to the monomer components (a) to (c), the copolymer contained in the latex is further
(D) 0 to 64.9% by mass of other copolymerizable monomers
(However, (a) + (b) + (c) + (d) = 100 mass%)
The composition for paper coating of Claim 3 which is a copolymer obtained by emulsion-polymerizing the monomer component which consists of this.   Coated paper using the paper coating composition according to any one of claims 1 to 3 as a coating liquid.