JP2007247081A - Organic pigment dispersion for paper coating, coated paper and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic pigment dispersion for paper coating, which is preferably used in production of coated paper satisfying each characteristic required for coated paper for offset printing and coated paper for electrophotography. <P>SOLUTION: The organic pigment dispersion for paper coating comprises an aqueous medium, and an organic pigment, wherein the organic pigment is a solid organic pigment and includes a polymer having a glass transition temperature of ≥50°C and a number average particle size of ≥110 nm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic pigment dispersion for paper coating, a coated paper, and a method for producing the same. More specifically, the properties of the offset printing coated paper and the electrophotographic printing coated paper can be satisfied. Organic pigment dispersion for paper coating that can be suitably used in producing a possible coated paper, and coated paper having a coating layer comprising such an organic pigment dispersion for paper coating and its It relates to a manufacturing method.

  In order to improve the appearance and printability of coated paper for offset printing and electrophotographic printing, white pigments such as kaolin and calcium carbonate (heavy and light) and water-soluble It is obtained by applying a paper coating composition mainly composed of a binder (starch, latex, etc.). In particular, there is a demand for improvements in printability such as white paper gloss, improved printing strength (dry strength) and printing gloss in offset printing, and further suppression of toner blistering during electrophotographic printing and improved toner fixability. Yes. In order to meet such demands, the formulation in the paper coating composition is optimized.

  Specifically, attempts have been made to optimize inorganic pigments and use organic pigments (also called plastic pigments). It is known that by optimizing the formulation in the paper coating composition, it is possible to increase the printing gloss of the coated paper for offset printing and to improve the printing strength (dry strength). Furthermore, calendering under low-pressure conditions is possible. By forming a bulky coating layer, the glossiness of blank paper can be improved. Furthermore, by increasing the air permeability of the coated paper, electrophotographic printing can be achieved. It is known that toner blistering at the time can be suppressed and image quality can be improved. In order to make it difficult for toner blisters to occur during printing on coated paper for electrophotographic printing, the air permeability (JIS P8117) according to the Oken formula is required to be low, for example, 4000 seconds or less. It is said that. In addition, as means for improving the gloss and image quality of coated paper, attempts have been made to use hollow organic pigments having voids in the interior and latex having a high glass transition point (Tg) (for example, Patent Document 1, 2). On the other hand, as a method for producing coated paper for offset printing, only the organic pigment is overcoated and a surface layer is provided on the primed coated paper. Manufacturing methods exhibiting excellent offset printability are known (see, for example, Patent Document 3).

Japanese Patent No. 2676291 JP 2004-239960 A Japanese Patent No. 2940851

  However, since the required properties differ between the offset printing coated paper and the electrophotographic printing coated paper, the conventional paper coating composition is used for the offset printing coated paper and the electrophotographic printing coating. It was a problem that the respective characteristics of the craft paper could not be satisfied. Moreover, it is extremely difficult to satisfy the above-mentioned characteristics without calendering the coating composition.

  The present invention has been made in view of the above-described problems of the prior art, and manufactures a coated paper that can satisfy the respective characteristics of the offset printing coated paper and the electrophotographic printing coated paper. An organic pigment dispersion for paper coating that can be suitably used in the process, a coated paper provided with a coating layer comprising such an organic pigment dispersion for paper coating, and a method for producing the same.

  As a result of intensive studies to achieve the above-mentioned problems, the inventors of the present invention are composed of a polymer having a glass transition point of 60 ° C. or higher, its number average particle diameter is 110 nm or more, and its inside is clogged (solid) It has been found that the above-mentioned problems can be achieved by using an organic pigment dispersion for paper coating in which a dense organic pigment is dispersed in an aqueous medium, and the present invention has been completed.

  That is, according to the present invention, the following organic pigment dispersion for paper coating, coated paper and a method for producing the same are provided.

[1] An organic pigment dispersion containing an aqueous medium and an organic pigment, wherein the organic pigment is made of a polymer having a glass transition point of 60 ° C. or higher and a number average particle diameter of 110 nm or higher. An organic pigment dispersion for paper coating.

[2] The organic material for paper coating according to [1], wherein the polymer constituting the dense organic pigment contains 2 to 40% by mass of a structural unit derived from an ethylenically unsaturated carboxylic acid monomer. Pigment dispersion.

[3] The organic pigment dispersion for paper coating according to the above [1] or [2], which contains 0 to 100 parts by mass of a binder with respect to 100 parts by mass of the solid organic pigment.

[4] The organic pigment dispersion for paper coating according to [3], wherein the binder is latex.

[5] The paper coating organic pigment dispersion according to any one of [1] to [4], wherein the solid content concentration of the paper coating organic pigment dispersion is 10 to 55% by mass.

[6] The paper according to any one of [1] to [5], wherein an undercoat layer is formed by applying a paper coating composition for undercoat on the coated base paper, and the undercoat layer is formed on the undercoat layer. By applying the organic pigment dispersion for coating to form a coating layer, the white paper gloss comprising the coating base paper, the undercoat layer, and the coating layer, measured according to JIS P8142. Is 50% or more, and the manufacturing method of the coated paper which obtains the coated paper whose air permeability measured based on JISP8117 is 4000 second or less.

[7] The method for producing a coated paper according to [6], wherein the coating layer is formed without performing a calendering treatment after coating the organic pigment dispersion for paper coating on the undercoat layer.

[8] In the above [6] or [7], the organic pigment dispersion for paper coating is applied such that the coating amount after drying is 1 to 5 g / m ² per one side of the coating base paper. The manufacturing method of the coated paper of description.

[9] The above [6] to [8], wherein the undercoating paper coating composition is applied so that the coating amount after drying is ² to ²⁰ g / m ² per one side of the coating base paper. The manufacturing method of the coated paper in any one of.

[10] An undercoat layer composed of a coated base paper, a paper coating composition for undercoating coated on the coated base paper, and the above [1] to [5] coated on the undercoat layer And a coating layer made of an organic pigment dispersion for paper coating according to any one of the above, having a white paper gloss of 50% or more measured according to JIS P8142, and an air permeability measured according to JIS P8117 Coated paper whose is less than 4000 seconds.

[11] The coated paper according to [10], wherein the coating layer is formed without performing a calendar process.

[12] The coated paper according to [10] or [11], wherein a coating amount of the coating layer is 1 to 5 g / m ² per one side of the coating base paper.

[13] The coated paper according to any one of [10] to [12], wherein the coating amount of the undercoat layer is ² to ²⁰ g / m ² per one side of the coating base paper.

[14] The coated paper according to any one of [10] to [13], which is used for offset printing or electrophotographic printing.

  The organic pigment dispersion for paper coating of the present invention can be suitably used for producing coated paper that can satisfy the characteristics of offset coated paper and electrophotographic coated paper. In particular, the organic pigment dispersion for paper coating of the present invention can satisfy the above properties without calendering the formed coating layer.

  Further, the coated paper of the present invention has good white paper gloss and air permeability, and can be suitably used in any printing of offset printing and electrophotographic printing. Moreover, the manufacturing method of the coated paper of this invention can manufacture such a coated paper simply.

  Hereinafter, the organic pigment dispersion for paper coating of the present invention, and the coated paper and the manufacturing method thereof will be described based on specific embodiments, but the present invention is limited to the following embodiments. However, within the scope of the present invention, based on the ordinary knowledge of those skilled in the art, it is understood that modifications and improvements as appropriate to the following embodiments are also included in the scope of the present invention. It should be.

[1] Organic pigment dispersion for paper coating:
The organic pigment dispersion for paper coating of the present embodiment (hereinafter sometimes simply referred to as “organic pigment dispersion”) is an organic pigment dispersion containing an aqueous medium and an organic pigment. The organic pigment dispersion is a dense organic pigment made of a polymer having a glass transition point of 60 ° C. or higher, a number average particle diameter of 110 nm or more, and the inside thereof being clogged (solid).

  The organic pigment dispersion of this embodiment is a dispersion for forming a coating layer (overcoat layer) on a coating base paper on which an undercoat layer is formed. By using such an organic pigment dispersion of the present embodiment, a coated paper that can satisfy the respective characteristics of the coated paper for offset printing and the coated paper for electrophotographic printing is satisfactorily produced. be able to. In particular, in the organic pigment dispersion of the present embodiment, the above properties can be satisfied without calendering the formed coating layer.

  Specifically, the coated paper that can satisfy the characteristics of the offset printing coated paper and the electrophotographic printing coated paper has a white paper gloss (JIS P8142) of 50% or more. At the same time, in order to make it difficult for toner blisters to occur during electrophotographic printing, the air permeability (JIS P8117) according to the Oken formula is required to be low, for example, 4000 seconds or less. By using the organic pigment dispersion of the present embodiment to form a coating layer on a coated base paper on which an undercoat layer has been formed, the gloss of white paper is 50% or more and the air permeability is 4000 seconds or less. The coated paper can be produced satisfactorily. The white paper gloss (%) of the coated paper can be measured in accordance with JIS P8142, for example, using a gloss meter manufactured by Murakami Color Co., Ltd. Further, the air permeability (seconds) by the Oken type can be measured according to JIS P8117 using an Oken type air permeability meter manufactured by Asahi Seiko Co., Ltd.

  Further, in the organic pigment dispersion of the present embodiment, the content ratio of the dense organic pigment dispersed in the aqueous medium is not particularly limited, but from the viewpoint of reducing the drying load during coating and improving workability, for example, The solid content concentration of the organic pigment dispersion is preferably 10 to 55% by mass, more preferably 20 to 50% by mass. If the solid content concentration of the organic pigment dispersion is less than 10% by mass, the solid organic pigment is difficult to be placed on the coated base paper and it is difficult to adjust the coating amount when blade coating is performed. is there. On the other hand, if the solid content concentration exceeds 55% by mass, the viscosity of the dense organic pigment becomes too high, and it may be difficult to adjust the coating amount. Hereinafter, the organic pigment dispersion of the present embodiment will be described in more detail for each component.

[1-2] Dense organic pigment:
The solid organic pigment used in the organic pigment dispersion of the present embodiment is a solid having a glass transition point of 60 ° C. or more, a number average particle diameter of 110 nm or more, and a solid inside. Organic pigment. If the number average particle size of the dense organic pigment is less than 110 nm, the glossiness of the coated paper and the image quality during electrophotographic printing are degraded. In addition, dry strength and printing gloss during offset printing are also reduced. The “number average particle size” in the present specification is the number average particle size measured using a dynamic light scattering method. This measurement can be performed using, for example, a laser particle analyzer (trade name “Laser Particle Size Analysis System, LP-510 Model PAR-III”, manufactured by Otsuka Electronics Co., Ltd.).

  Further, although not particularly limited, the substantial maximum value of the number average particle diameter of the dense organic pigment is preferably 500 nm. If the number average particle diameter of the dense organic pigment exceeds 500 nm, it may be difficult to form a coating layer, or the white paper gloss, printing gloss, image quality, toner fixability, and coating layer strength may decrease. . For this reason, in the organic pigment dispersion of the present embodiment, the number average particle size of the dense organic pigment is preferably 110 to 500 nm, and more preferably 130 to 400 nm.

  In addition, when the glass transition point of the polymer constituting the dense organic pigment is less than 60 ° C., the polymer constituting the dense organic pigment is welded to develop the adhesive strength. In the coated paper on which the coated layer is formed, since the formed coated layer is formed, the air permeability of the coated paper is increased to over 4000 seconds and toner blisters are generated. Further, since the toner stays on the coating layer and is not embedded in the coating layer at the time of electrophotographic printing, the smoothness of the surface of the printed material is lowered and the image quality is lowered. The more preferable glass transition point of the polymer constituting the dense organic pigment is preferably 60 ° C. or higher, and more preferably 70 ° C. or higher.

  The “glass transition point (Tg)” in the present specification is a film prepared by heating and drying a latex containing the above polymer at 130 ° C. for 30 minutes, and the glass transition point (Tg) of this dry film is expressed as a differential. It is a value measured using a scanning calorimeter (trade name “DSC-220C”, manufactured by Seiko Electronics Co., Ltd.) under a temperature rising rate of 15 ° C./min.

  In addition, as described above, the dense organic pigment used in the organic pigment dispersion of the present embodiment is made of a polymer having a glass transition point of 60 ° C. or higher, its number average particle diameter is 110 nm or more, and its internal Is dense, the composition is not particularly limited. For example, the polymer constituting the solid organic pigment contains 2 to 40 mass of structural units derived from an ethylenically unsaturated carboxylic acid monomer. % Content is preferable.

  By comprising in this way, coating layer intensity | strength expresses by the hydrogen bond of an undercoat coating layer and the ethylenically unsaturated carboxylic acid polymerized by the solid organic pigment. Furthermore, when obtaining such a dense organic pigment, it is obtained by emulsion polymerization of a monomer component containing an ethylenically unsaturated carboxylic acid monomer and then adjusting the pH to 6.0 or higher. It is preferable that the pH is 7.0 or more. In particular, by adjusting the pH of the dense organic pigment to 7.0 or more, the ethylenically unsaturated carboxylic acid is alkali-soluble in the particle surface layer or the water layer portion, It is thought that it contributes to the adhesion of the paper and expresses the strength of the coating layer and improves the gloss of the white paper.

  In addition, as a more specific structure of the polymer which comprises a dense organic pigment, the structural unit 50-100 mass% derived from (a) aromatic vinyl monomer ((a ') monomer), ( b) Structural unit derived from aliphatic conjugated diene monomer ((b ′) monomer) 0 to 20% by mass, (c) derived from ethylenically unsaturated carboxylic acid monomer ((c ′) monomer) (D) vinyl cyanide monomer ((d ′) monomer) 0 to 40% by mass, and (e) these (a ′) to (d ′) monomer 0 to 48% by mass of a structural unit derived from another monomer (((e ′) monomer)) copolymerizable with the product (provided that (a) + (b) + (c) + (d) + (E) = 100% by mass), a dense organic pigment.

  In addition, when the structural unit derived from the (a) aromatic vinyl monomer ((a ′) monomer) is less than 50% by mass, the production cost may increase or the polymerization stability may decrease. Examples of the aromatic vinyl monomer ((a ′) monomer) include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, and chlorostyrene. Among these, styrene is preferable. These aromatic vinyl monomers can be used alone or in combination of two or more. In addition, it is more preferable that the structural unit derived from the (a) aromatic vinyl monomer ((a ′) monomer) is 55 to 95% by mass, and 60 to 90% by mass. Is particularly preferred.

  In addition, when the structural unit derived from the (b) aliphatic conjugated diene monomer exceeds 20% by mass, the glass transition point of the polymer constituting the dense organic pigment is lowered, and the film is formed to increase the air permeability. It is not preferable. Examples of the aliphatic conjugated diene monomer ((b ′) monomer) include butadiene, isoprene, 1,3-hexadiene, 2,3-dimethylbutadiene, 2-trimethoxysilyl-1,3-butadiene, Examples include 1,3-pentadiene and 2,4-dimethyl-1,3-butadiene. Of these, butadiene is preferred. These aliphatic conjugated diene monomers can be used alone or in combination of two or more. The structural unit derived from the (b) aliphatic conjugated diene monomer ((b ′) monomer) is an optional component, but it is more preferable to contain, for example, 2 to 18% by mass.

  Examples of the ethylenically unsaturated carboxylic acid monomer ((c ′) monomer) include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and itaconic acid. These ethylenically unsaturated carboxylic acid monomers can be used singly or in combination of two or more. In addition, it is more preferable that the structural unit derived from (c) the ethylenically unsaturated carboxylic acid monomer ((c ′) monomer) is contained in an amount of 5 to 30% by mass.

  Examples of the vinyl cyanide monomer ((d ′) monomer) include acrylonitrile and methacrylonitrile. These vinyl cyanide monomers can be used individually by 1 type or in combination of 2 or more types. The structural unit derived from this (d) vinyl cyanide monomer ((d ′) monomer) is an optional component, but it is more preferable to contain, for example, 0 to 30% by mass.

  Examples of other monomers ((e ′) monomer) copolymerizable with these (a ′) to (d ′) monomers include methyl acrylate and methyl methacrylate. These other monomers ((e ′) monomers)) can be used alone or in combination of two or more.

  In addition, the dense organic pigment having such a composition is obtained by polymerizing a monomer component containing a predetermined amount of the above-described monomers (a ′) to (e ′) by adjusting the particle diameter according to the number of used emulsifiers. It can be obtained by emulsion polymerization using an initiator or the like.

  As the emulsifier, anionic surfactants, nonionic surfactants, amphoteric surfactants and the like can be used alone or in combination of two or more. Here, examples of the anionic surfactant include sulfates of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, and sulfates of polyethylene glycol alkyl ethers. As the nonionic surfactant, an ordinary polyethylene glycol alkyl ester type, alkyl ether type, alkylphenyl ether type, or the like is used. Examples of amphoteric surfactants include those having a carboxylate, sulfate, sulfonate, and phosphate ester salt as the anion moiety, and an amine salt and quaternary ammonium salt as the cation moiety. 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.

  Examples of the polymerization initiator include water-soluble polymerization initiators such as sodium persulfate, potassium persulfate, and ammonium persulfate, and oil-soluble polymerization initiators such as benzoyl peroxide, lauryl peroxide, and 2,2′-azobisisobutyronitrile. Redox polymerization initiators in combination with reducing agents can be used alone or in combination of two or more.

  Further, known molecular weight regulators, chelating agents, inorganic electrolytes and the like can be used. Examples of molecular weight regulators include halogenated hydrocarbons such as chloroform and carbon tetrabromide, mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and thioglycolic acid, dimethylxanthogen Xanthogens such as disulfide and diisopropylxanthogen disulfide, terpinolene (trade name), α-methylstyrene dimer, 1,1-diphenylethylene and the like which can be used in usual emulsion polymerization can be used.

[1-3] Aqueous medium:
The aqueous medium used in the organic pigment dispersion of the present embodiment is a solvent for dispersing the above-described dense organic pigment, and specifically includes water. As this aqueous medium, water used as a medium in the emulsion polymerization for obtaining the above-described dense organic pigment can be used as it is.

[1-4] Binder:
In addition, the organic pigment dispersion of the present embodiment contains 0 to 100 parts by mass of a binder with respect to 100 parts by mass of the dense organic pigment in addition to the dense pigment dispersed in the aqueous medium. May be.

  By containing such a binder, the high-speed fluidity of the organic pigment dispersion is improved, and the coating layer strength is also improved, so that the coating operability during coating can be improved. For example, it is possible to suppress streak during blade coating and to prevent dirt on the backing roll and guide roll. By adjusting the glass transition point (Tg) and particle diameter of the binder, problems such as white paper gloss, double feeding and sticking during printing can be suppressed. As such a binder, latex such as styrene butadiene latex and acrylic latex can be used. As such a latex, for example, Tg is −50 to 55 ° C., and the particle diameter is preferably 50 nm to 400 nm, and more preferably 80 nm to 300 nm. When the binder has a core / shell structure, the average Tg is preferably within the range of the Tg. In addition to the latex described above, a binder such as starch, casein, soy protein, carboxymethylcellulose, PVA and the like may be contained, and these may be used for adjusting the viscosity of the organic pigment dispersion in addition to the function as a binder. it can.

[2] Method for producing coated paper:
Next, an embodiment of a method for producing a coated paper of the present invention will be described. The method for producing a coated paper according to the present embodiment is such that a paper coating composition for undercoating is applied onto a base paper to form an undercoating layer, and the above-described paper of the present invention is formed on the undercoating layer. By applying an organic pigment dispersion for coating (hereinafter sometimes simply referred to as “organic pigment dispersion”) to form a coating layer, a coating base paper, an undercoat layer, and a coating layer are formed. And a coated paper manufacturing method for obtaining a coated paper having a white paper gloss of 50% or more measured according to JIS P8142 and an air permeability measured according to JIS P8117 of 4000 seconds or less.

  Thus, in the coated paper manufacturing method of the present embodiment, by forming the coating layer using the organic pigment dispersion of the present invention described so far, the coated paper for offset printing and the electronic Coated paper capable of satisfying the characteristics of coated paper for photographic printing, that is, a white paper gloss measured according to JIS P8142 is 50% or more, and air permeability measured according to JIS P8117 It is possible to form a coated paper having an air permeability according to the Oken formula of 4000 seconds or less. The white paper gloss (%) can be measured according to JIS P8142, for example, using a gloss meter manufactured by Murakami Color Co., Ltd., and the air permeability (seconds) is measured by Oken manufactured by Asahi Seiko Co., Ltd. It can measure according to JIS P8117 using a type air permeability meter.

  Note that the coated paper obtained by the coated paper manufacturing method of the present embodiment can be particularly preferably used as a paper for offset printing and electrophotographic printing as described above, as well as gravure printing, etc. It can also be suitably used as a coated paper for intaglio printing and letterpress printing.

[2-1] Coated base paper:
The type of the coating base paper used in the method for producing the coated paper of the present embodiment is not particularly limited as long as it can be used as the coated paper by applying the organic pigment dispersion described above. Good.

  The kind of raw material pulp of the coating base paper is not particularly limited, and examples thereof include mechanical pulp, chemical pulp, and waste paper pulp (DIP). In addition, for coated base papers, pigments such as calcium carbonate, clay and talc as internal additives, sizing agents such as alkyl ketene dimer, rosin acid soap, and sulfuric acid band, cationic starch, and paper strength enhancement such as polyacrylamide An agent, a bulking agent, etc. can also be used. Further, a surface sizing agent such as acrylamide or acrylic-styrene polymer can be applied to the surface of the coated base paper using a size press, a gate roll coater, a metered size press, or the like.

[2-2] Composition for paper coating (for undercoating):
In the method for producing a coated paper according to the present embodiment, first, an undercoat layer is formed by applying a paper coating composition for undercoating onto the above-described coated base paper.

  Although it does not specifically limit as this paper coating composition for undercoat, For example, what contains an inorganic pigment, starch, polyvinyl alcohol, and latex can be used conveniently. Starch and polyvinyl alcohol may be used alone. Examples of such a paper coating composition for undercoating include, for example, 50 parts of kaolin clay (trade name “Miragros J”, manufactured by Engelhard), heavy calcium carbonate (trade name “Pimatech 90”, Pimatech). 50 parts, starch (trade name “MS4600”, manufactured by Japan Food Industry Co., Ltd.) 4 parts, latex (trade name “0696”, manufactured by JSR) 8 parts, dispersant (polyacrylic acid dispersant; trade name) It can be prepared using 0.2 part of “Aron-T40” (manufactured by Toagosei Co., Ltd.) and 0.1 part of sodium hydroxide (trade name “sodium hydroxide grade 1”, manufactured by Wako Pure Chemical Industries, Ltd.). .

When an undercoat layer is formed by applying a paper coating composition for undercoating onto a coating base paper, the coating amount after drying is ² to ²⁰ g / m ² per side of the coating base paper. It is preferable to apply to. When the coating amount of the paper coating composition for undercoating is less than 2 g / m ² , there is a tendency that it becomes difficult to sufficiently cover the coated base paper and sufficient smoothness cannot be obtained. On the other hand, the upper limit does not lead to a serious disadvantage in terms of quality and operation, but is usually applied more than 20 g / m ² in view of material cost, production efficiency, quality, etc. with respect to the final product price. There are few things.

  As a method of applying the paper coating composition for the undercoat, a conventionally known coating method can be used. If a coating method in which coating is performed by a blade coater and a bar coater is adopted, the coated surface is smoothed. This is preferable.

[2-3] Organic pigment dispersion:
The organic pigment dispersion used in the method for producing the coated paper of the present embodiment is the organic pigment dispersion of the present invention described so far.

  In the coated paper manufacturing method of the present embodiment, such an organic pigment dispersion is applied onto an undercoat layer made of the above-described undercoat paper coating composition to form a coated layer. Thus, a coated paper having a coated base paper, an undercoat layer, and a coating layer can be produced.

In addition, when the organic pigment dispersion is applied onto the undercoat layer to form a coating layer, the coating amount after drying is 1 to 5 g / m ² per side of the coated base paper. It is preferable to carry out coating so as to be 1.5 to 4 g / m ² . When the coating amount of the organic pigment dispersion is less than 1 g / m ² , it becomes difficult to form a continuous coating layer, and it is not possible to obtain a coated paper in which the coating layer is favorably formed on the undercoat layer. Sometimes. On the other hand, if it exceeds 5 g / m ² , it is difficult to adjust the coating amount, and the drying load becomes large, making production difficult.

  In addition, as a method for coating the organic pigment dispersion, a conventionally known coating method can be used. However, when a coating method in which coating is performed using a blade coater and a bar coater is employed, the coated surface can be smoothed and blank paper is used. It is preferable because gloss is improved.

  In the method for producing coated paper of the present embodiment, in addition to the above-described steps of forming the undercoat layer and the coating layer by a coating method, a paper coating composition for undercoating or an organic pigment dispersion is applied. After the processing, it is preferable to have a drying step of drying the undried undercoat layer or coating layer. The drying method in the drying step is not particularly limited, and a method used in a general coated paper manufacturing method can be employed. For example, hot air drying, infrared drying, microwave drying, or the like can be employed. These can be used individually by 1 type or in combination of 2 or more types.

  Further, in the method for producing a coated paper of the present embodiment, after coating the organic pigment dispersion on the undercoat layer, the coating layer may be formed without performing a calendar treatment, or a conventionally known method You may perform a calendar process according to the method. When the coating layer is formed without performing the calendar process, a bulky coating layer can be formed, and the rigidity (paper stiffness) of the coated paper and the white paper gloss can be improved. On the other hand, for example, by performing a calender treatment at a temperature equal to or lower than the crow transition point (Tg) of the solid organic pigment contained in the organic pigment dispersion, it is possible to further bring out the blank gloss and print gloss of the obtained coated paper. Examples of the calendar process include a super calendar, a machine calendar, and a soft nip calendar. These may give only 1 type and may give 2 or more types. In addition, when manufacturing the coated paper of this Embodiment, you may have a desired process suitably other than the above-mentioned process.

[3] Coated paper:
Next, an embodiment of the coated paper of the present invention will be described. The coated paper of the present embodiment is a coated paper produced by the above-described method for producing a coated paper of the present invention, and the coated base paper and the undercoat paper coating applied on the coated base paper. An undercoat layer made of a working composition, and a coating layer made of the above organic pigment dispersion coated on the undercoat layer, having a blank gloss of 50% or more measured according to JIS P8142, JIS P8117 This is a coated paper having an air permeability measured in accordance with JIS of 4000 seconds or less.

  Such coated paper can be particularly suitably used as a paper for offset printing and electrophotographic printing. It can also be used for other intaglio printing such as gravure printing and letterpress printing. In the coated paper of the present embodiment, it is preferable that the coating layer and the undercoat layer are formed so as to have the coating amount described in the above-described coated paper manufacturing method. Moreover, the coating base paper demonstrated with the manufacturing method of the above-mentioned coated paper can be used suitably also about a coating base paper. Moreover, this coating layer may be formed without performing calendar processing, or may be subjected to calendar processing according to a conventionally known method.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In the examples and comparative examples, “parts” and “%” are based on mass unless otherwise specified. Moreover, the measuring method and evaluation method of various physical property values are shown below.

  [Glass transition point (Tg)]: A dense organic pigment was heated and dried at 130 ° C. for 30 minutes to produce a film, and using a differential scanning calorimeter (trade name “DSC-220C”, manufactured by Seiko Electronics Co., Ltd.) The measurement was performed under the condition of a heating rate of 15 ° C./min.

  [Number average particle diameter]: The number average particle diameter was measured by a light scattering method using a laser particle analyzer (trade name “Laser Particle Size Analysis System, LP-510 Model PAR-III”, manufactured by Otsuka Electronics Co., Ltd.).

  [Blank gloss]: A gloss meter (Murakami Color Co., Ltd.) was used and measured according to JIS P8142.

  [Air permeability]: Measured according to JIS P8117 using an Oken type air permeability meter (manufactured by Asahi Seiko Co., Ltd.).

[Toner fixing property] Using a laser printer (trade name “IRC3220”, manufactured by Canon Inc.), a solid surface of black, indigo, red, and yellow and a patch of characters were prepared as a printing surface. Next, after sticking an adhesive tape (trade name “Cellophane Tape”, manufactured by Nichiban Co., Ltd.) evenly on the printed surface, check the degree of toner peeling when slowly peeled by hand, and follow the criteria below. It evaluated by x.
○: Toner does not peel off.
X: Toner peeling is confirmed even a little.

[Image quality (image quality in electrophotographic printing)]: Using a laser printer (trade name “IRC3220”, manufactured by Canon Inc.), print black, solid, indigo, red, and yellow solid parts and characters on the print surface. The feeling was evaluated using a loupe. The presence / absence of gloss unevenness, printing unevenness, and unevenness was evaluated according to the following criteria: ○ to ×.
○: No gloss unevenness, printing unevenness, or uneven feeling.
(Triangle | delta): Gloss unevenness, printing unevenness, and a feeling of unevenness are somewhat seen.
X: Gloss unevenness, printing unevenness, and unevenness are clearly seen.

[Dry Strength]: Paper test ink (trade name “SD50 Red BT-13”, manufactured by TOKA Co., Ltd.) is kneaded in a printing roll by 0.6 cc with a RI printing machine (manufactured by Meisei Co., Ltd.) and once at a rotation speed of 60 rpm The degree of picking at the time of printing was judged with the naked eye, and the printing strength was evaluated.
○: No picking occurred.
Δ: Slight picking occurred.
X: A large amount of picking occurs.

  [Glossy printing (printing gloss in offset printing)]: Using the above RI printing machine, 0.6 cc of offset ink (trade name “Values-G black”, manufactured by Dainippon Ink & Chemicals, Inc.) is solid on coated paper. After printing, it was measured with a gloss meter (Murakami Color Co., Ltd.) at an incident angle of 60 ° and a reflection angle of 60 °.

(Production of dense organic pigment A)
In an autoclave equipped with a stirrer and capable of temperature adjustment, 150 parts of water, 0.2 part of sodium dodecylbenzenesulfonate, 1.0 part of potassium persulfate, and 0.5 part of sodium bisulfite were charged in advance.

  Next, as the first stage component, 1.0 part of 1,3-butadiene and 18.4 parts of styrene were charged all together and reacted at 55 ° C. for 3 hours to confirm that the polymerization conversion was 90% or more. (First stage polymerization).

  Thereafter, polymerization was continued at 65 ° C. while continuously adding 4.0 parts of 1,3-butadiene, 73.6 parts of styrene, 1 part of itaconic acid, and 2 parts of acrylic acid as the second stage component over 12 hours. . After completion of the continuous addition, the reaction was further continued at 70 ° C. for 3 hours (second stage polymerization), and then sodium hydroxide was added to adjust the pH to 8.0. Thereafter, a dense organic pigment A concentrated to a solid content of 50% by a concentrator was obtained (this dense organic pigment is referred to as “dense organic pigment A”). The final polymerization conversion of the dense organic pigment A was 99.5%. Table 1 shows the polymerization composition of the dense organic pigment A.

(Production of dense organic pigment B)
A dense organic pigment B was obtained in the same manner as in the above-mentioned “Preparation of dense organic pigment A” except that 0.5 part of sodium dodecylbenzenesulfonate was used.

(Manufacture of dense organic pigment C)
A dense organic pigment C was obtained in the same manner as in the above-mentioned “Production of dense organic pigment A” except that 0.05 part of sodium dodecylbenzenesulfonate was used.

(Manufacture of dense organic pigments D to K)
Except for the polymerization composition shown in Table 1, dense organic pigments D to K were obtained in the same manner as in “Production of dense organic pigment A” described above. The particle diameter of the dense organic pigment obtained was adjusted mainly by adjusting the amount of the emulsifier (sodium dodecylbenzenesulfonate).

(Manufacture of dense organic pigment L)
A dense organic pigment L was obtained in the same manner as in the above-mentioned “Production of dense organic pigment A” except that 0.9 part of sodium dodecylbenzenesulfonate was used. The particle diameter of the dense organic pigment obtained was adjusted mainly by adjusting the amount of the emulsifier (sodium dodecylbenzenesulfonate).

  In the dense organic pigments B to L, sodium hydroxide was added to adjust the pH to 8.0 after the second stage polymerization. Moreover, the glass transition point and number average particle diameter of obtained dense organic pigments A to L were measured. The measurement results are shown in Tables 1 and 2.

(Preparation of organic pigment dispersion (formulation (1)))
Aqueous medium (water) so that the solid content concentration of the obtained organic pigment dispersion is 35% in 100 parts (solid content) of the dense organic pigment A concentrated so that the solid content concentration becomes 50% as described above. Was added to prepare an organic pigment dispersion (formulation (1)). Table 2 shows the formulation of the organic pigment dispersion (formulation (1)).

(Preparation of organic pigment dispersion (compounds (2) to (13)))
The organic pigment dispersions (compounds (2) to (2) having a solids concentration of 35% were prepared in the same manner as in “Preparation of organic pigment dispersion (formulation (1))” described above except that the formulation shown in Table 2 was used. 13)) was prepared. In addition, in the organic pigment dispersions (formulations (4) and (5)), 5 parts each of latex (trade names “0696”, “0640”, manufactured by JSR Corporation) having a solid content concentration of 48.0% as a binder are used. (Solid content) and 70 parts (solid content) were further added to prepare.

Example 1
In this example, a commercially available fine base paper (81 g / m ² ) was coated with the following undercoat coating composition to form an undercoat layer, and then an organic pigment dispersion (formulation (1)) was applied. To form a coating layer to form a coated paper.

[1-1] Preparation of undercoat coating composition:
Kaolin clay (trade name “Miragros J”, manufactured by Engelhard) 50 parts heavy calcium carbonate (trade name “Pimatech 90”, manufactured by Pimatech), starch (trade name “MS4600”, Japan Food Industry) 3 parts, latex (trade name “0696”, manufactured by JSR) 8 parts, dispersant (polyacrylic acid type dispersant; trade name “Aron-T40”, manufactured by Toagosei Co., Ltd.) 0.2 part, and An undercoat coating composition for a solid content of 65% was prepared using 0.1 part of sodium hydroxide (trade name “sodium hydroxide grade 1”, manufactured by Wako Pure Chemical Industries, Ltd.).

  A specific method for producing an undercoat coating composition was as follows. First, adjustment water, a dispersant, and sodium hydroxide were charged in a SUS container, and the rotation speed of a coreless disperser (manufactured by Shimazaki Seisakusho) was set to 2000 rpm. . Next, kaolin was gradually added into the SUS container, and after complete addition, the rotational speed of the disperser was set at 6000 rpm and stirring was continued for 30 minutes. Next, calcium carbonate was added, and then starch and sodium hydroxide were added, followed by further stirring for 15 minutes. Next, the number of revolutions of the coreless disperser was set to 2000 rpm, latex was added, and the mixture was stirred for 10 minutes. The starch was prepared in advance in a SUS container with a concentration adjusted with cold water so as to have a concentration of 30%, and the starch was dissolved at 95 ° C. for 1 hour using an apparatus with stirring capable of adjusting the temperature.

[1-2] Formation of undercoat layer:
Using the above-mentioned composition for undercoat coating, blade coating was performed on a commercially available high-quality base paper (81 g / m ² ) so that the coating amount was 10 ± 0.2 g / m ² per side. An undercoat layer was formed on both sides by drying with hot air for 10 seconds. The blade coater was coated using a single wafer coater (manufactured by SMT).

[1-3] Formation of coating layer:
An organic pigment dispersion (formulation (1)) (solid content concentration: 35%) is coated on the undercoated paper by wire bar coating and dried with hot air at 150 ° C. for 10 seconds to form a coating layer (top coating). Layer) was formed on both sides to obtain a coated paper of this example. The coating amount of the organic pigment dispersion was adjusted so that the coating layer after drying was 2.5 ± 0.1 g / m ² . The blade coater was coated using a single wafer coater (manufactured by SMT). Further, the obtained coated paper was subjected to the above-described various evaluations without being subjected to the super calendar process. The evaluation results are shown in Table 3.

(Examples 2 to 11)
A coated paper was obtained in the same manner as in Example 1 except that an organic pigment dispersion (formulations (2) to (11)) was used to form a coating layer (overcoating layer). went. The evaluation results are shown in Table 3.

(Comparative Examples 1 and 2)
A coated paper was obtained in the same manner as in Example 1 except that an organic pigment dispersion (formulations (12) and (13)) was used to form a coating layer (overcoat layer). went. The evaluation results are shown in Table 3.

(Comparative Example 3)
Without applying the organic pigment dispersion, a coated paper on which only an undercoat layer composed of the undercoat coating composition was formed was formed. In this comparative example, various evaluations were performed without performing the super calendar process on the undercoat layer. The evaluation results are shown in Table 3.

(Comparative Example 4)
Without coating the organic pigment dispersion, the coated paper on which only the undercoat layer composed of the undercoat coating composition is formed is left in a constant temperature and humidity room at a temperature of 23 ° C. and a humidity of 55% for 24 hours, and then , Using the product name “Double Test Calendar” manufactured by Yuri Roll Co., Ltd. under the conditions of a linear pressure of 60 kg / cm and a roll temperature of 40 ° C., the super calender treatment was performed twice per side and the white paper gloss was adjusted to 50%. Various evaluations were performed. The evaluation results are shown in Table 3.

(Discussion)
The coated paper produced in Comparative Example 1 has a very high air permeability (measured value is infinite), and the air permeability is extremely poor, so that the occurrence of toner blisters is predicted. Also, the image quality in electrophotographic printing was poor because of its unevenness. The coated paper produced in Comparative Example 2 has a high air permeability, a high air permeability of over 4000 seconds, and the air permeability is poor, and toner blisters are predicted to occur. Also, the glossiness of blank paper was poor, the image quality in electrophotographic printing was slightly poor, and the dry strength in offset printing was also slightly bad. The coated paper produced by Comparative Example 3 had very poor white paper gloss, poor image quality in electrophotographic printing, and poor print gloss in offset printing. The coated paper produced in Comparative Example 4 has a high air permeability of over 4000 seconds, and the air permeability is poor, so that the occurrence of toner blisters is predicted. Also, the image quality in electrophotographic printing was somewhat poor.

  The coated paper produced in Examples 1 to 11 has a white paper gloss, air permeability (air permeability), image quality in electrophotographic printing, and offset printing, compared to the coated paper produced in Comparative Examples 1 to 4. The printing gloss and dry strength were all good.

  The organic pigment dispersion for paper coating of the present invention is preferably used when producing coated paper capable of satisfying the respective characteristics of offset printing coated paper and electrophotographic printing coated paper. Can do. The coated paper of the present invention can be particularly suitably used as a paper for offset printing and electrophotographic printing. Moreover, the manufacturing method of the coated paper of this invention can manufacture such a coated paper simply.

Claims (14)

An organic pigment dispersion containing an aqueous medium and an organic pigment,
An organic pigment dispersion for paper coating, wherein the organic pigment is a dense organic pigment composed of a polymer having a glass transition point of 60 ° C or higher and a number average particle diameter of 110 nm or higher.   The organic pigment dispersion for paper coating according to claim 1, wherein the polymer constituting the dense organic pigment contains 2 to 40% by mass of a structural unit derived from an ethylenically unsaturated carboxylic acid monomer.   The organic pigment dispersion for paper coating according to claim 1 or 2, comprising 0 to 100 parts by mass of a binder with respect to 100 parts by mass of the dense organic pigment.   The organic pigment dispersion for paper coating according to claim 3, wherein the binder is latex.   The organic pigment dispersion for paper coating according to any one of claims 1 to 4, wherein a solid content concentration of the organic pigment dispersion for paper coating is 10 to 55 mass%. On the coated base paper, a paper coating composition for undercoating is applied to form an undercoat layer,
On the undercoat layer, by applying the organic pigment dispersion for paper coating according to any one of claims 1 to 5 to form a coating layer,
The coated base paper, the undercoat layer, and the coating layer are provided. The gloss of the white paper measured according to JIS P8142 is 50% or more, and the air permeability measured according to JIS P8117 is 4000 seconds or less. The manufacturing method of the coated paper which obtains the coated paper which is.   The method for producing a coated paper according to claim 6, wherein the coating layer is formed without performing a calendering treatment after coating the organic pigment dispersion for paper coating on the undercoat layer. The coated paper according to claim 6 or 7, wherein the organic pigment dispersion for paper coating is applied such that the coating amount after drying is 1 to 5 g / m ² per one side of the coating base paper. Production method. The paper coating composition for undercoating is applied such that the coating amount after drying is ² to ²⁰ g / m ² per one side of the coating base paper. The manufacturing method of the coated paper of description. In any one of Claims 1-5 coated on the undercoat layer which consists of a coating base paper, the paper coating composition for the undercoat coated on the said coating base paper, and the said undercoat layer. A coating layer comprising the organic pigment dispersion for paper coating described above,
Coated paper having a white paper gloss of 50% or more measured according to JIS P8142 and an air permeability measured according to JIS P8117 of 4000 seconds or less.   The coated paper according to claim 10, wherein the coating layer is formed without performing a calendar process. The coated paper according to claim 10 or 11, wherein a coating amount of the coating layer is 1 to 5 g / m ² per one side of the coated base paper. The coated paper according to any one of claims 10 to 12, wherein a coating amount of the undercoat layer is ² to ²⁰ g / m ² per one side of the coated base paper.   The coated paper according to any one of claims 10 to 13, which is used for offset printing or electrophotographic printing.