JP2005133009A - Organic pigment, paper-coating composition and coated paper using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic pigment suitable for coated paper excellent in blank paper gloss and printing gloss and having good ink set properties and blocking resistance, a paper-coating composition containing the organic pigment and coated paper coated with the paper-coating composition. <P>SOLUTION: The organic pigment is obtained by emulsion copolymerizing 100 pts.wt. of a monomer mixture having a specific composition, has 150-400 nm volume average particle diameter and 40 wt.% or more of tetrahydrofuran-insoluble component, and is characterized in that it is obtained by emulsion copolymerizing 10-60 pts.wt. of a monomer mixture (B) having a specific composition comprised of a conjugated diene monomer, an ethylenically unsaturated carboxylic acid monomer, an ethylenically unsaturated nitrile monomer, and another monomer that is copolymerizable with these monomers in the presence of a copolymer latex obtained by emulsion copolymerizing 40-90 pts.wt. of a monomer mixture (A) having a specific composition comprised of a conjugated diene monomer, an ethylenically unsaturated carboxylic acid monomer, and another monomer % that is copolymerizable with these monomers. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an organic pigment, a paper coating composition, and a coated paper using the same, and particularly suitable for coated paper board that is calendered to improve glossiness and smoothness of blank paper. The present invention relates to a composition for coating and a coated paper using the same.

2. Description of the Related Art Conventionally, a paper coating composition containing an organic pigment is applied to paper to improve the white paper gloss and printing gloss of the coated paper.
As a paper coating composition containing an organic pigment, for example, a glass transition temperature obtained by emulsion copolymerization of a monomer mixture containing 20% by weight or less of a conjugated diene monomer is 30 to 105 ° C., An organic pigment having an average particle size of 150 to 400 nm and a copolymer latex obtained by emulsion copolymerization of a monomer mixture containing 25 to 55% by weight of a conjugated diene monomer, and the organic pigment and the copolymer A paper coating composition containing a combined latex in a weight ratio of 10/90 to 60/40 has been proposed (see Patent Document 1). When such a paper coating composition is used, a coated paper excellent in blocking resistance can be obtained while suppressing the occurrence of calendar roll stains, but it tends to cause problems in multicolor printing due to poor ink setting. Moreover, the gloss of the coated paper that is actually confirmed is only about 70% at most.

  Moreover, as an organic pigment contained in the composition for paper coating, for example, in the presence of 20 to 60 parts by weight of a polymer obtained by polymerizing a monomer containing 80% by weight or more of a conjugated diene monomer. An organic pigment obtained by polymerizing 80 to 40 parts by weight of a monomer containing an aromatic vinyl monomer and (meth) acrylonitrile has been proposed (see Patent Document 2). However, when such an organic pigment is used, a coated paper having excellent printing gloss can be obtained, but the level of blank paper gloss is insufficient and ink setability is poor.

Furthermore, as the organic pigment to be contained in the paper coating composition, for example, polymers 30 to 30 obtained by polymerizing a monomer containing an aromatic vinyl monomer and an ethylenically unsaturated carboxylic acid monomer. An organic pigment having a microdomain structure obtained by polymerizing 70 to 30 parts by weight of a monomer containing 30 to 80% by weight of a conjugated diene monomer in the presence of 70 parts by weight (patent) Reference 3). When such an organic pigment is used, a coated paper having a relatively excellent ink setting property, white paper gloss and printing gloss can be obtained, but it is inferior in blocking resistance and easily causes calendar roll stains when subjected to calendar treatment. There's a problem.
In particular, with the conventional method, it is difficult to obtain an organic pigment with improved white paper gloss and printing gloss, and excellent ink setability and blocking resistance, especially when calendering coated paper at high temperatures. This trend was great.

JP 61-225395 A JP-A-63-303195 Japanese Patent Laid-Open No. 3-167398

  An object of the present invention is to improve coated paper gloss and printing gloss, have good ink setting properties, and is suitable for producing a coated paper having excellent blocking resistance even in high temperature calendar processing. An object of the present invention is to provide an organic pigment, a paper coating composition containing the organic pigment, and a coated paper obtained by coating the base paper with the paper coating composition.

  As a result of intensive investigations to achieve the above-mentioned problems, the inventors of the present invention are organic pigments having a specific composition, tetrahydrofuran-insoluble matter, and volume average particle diameter. It has been found that the above object can be achieved by using an organic pigment obtained by emulsion copolymerization in a stage and emulsion copolymerization of a monomer mixture containing a specific amount of an ethylenically unsaturated nitrile monomer in the second stage, Based on this finding, the present invention has been completed.

  Thus, according to the present invention, the conjugated diene monomer (a) 5 to 20% by weight, the ethylenically unsaturated carboxylic acid monomer (b) 0.5 to 10% by weight, the ethylenically unsaturated nitrile monomer (C) Volume obtained by emulsion copolymerization of 100 parts by weight of a monomer mixture consisting of 5 to 20% by weight and other monomers copolymerizable therewith (d) 50 to 89.5% by weight An organic pigment having an average particle diameter of 150 to 400 nm and an insoluble content of tetrahydrofuran of 40% by weight or more, comprising 5 to 50% by weight of a conjugated diene monomer (a1) and an ethylenically unsaturated carboxylic acid monomer (b1) Emulsion copolymerization of 40 to 90 parts by weight of a monomer mixture (A) composed of 0.5 to 10% by weight and other monomer (d1) 40 to 94.5% by weight copolymerizable therewith. In the presence of a copolymer latex, a conjugated diene Monomer (a2) 0 to 10 wt%, ethylenically unsaturated carboxylic acid monomer (b2) 0.5 to 10 wt%, ethylenically unsaturated nitrile monomer (c2) 15 to 50 wt%, and these 10-60 parts by weight of a monomer mixture (B) comprising 30 to 84.5% by weight of another monomer (d2) copolymerizable with the monomer (provided that the monomer mixture (A) and the monomer mixture ( The total amount with B) is 100 parts by weight.) An organic pigment obtained by emulsion copolymerization is provided.

  Moreover, according to this invention, the composition for paper coating containing an organic pigment is provided.

  Furthermore, according to this invention, the coated paper formed by apply | coating the said composition for paper coating to a base paper is provided.

  According to the present invention, an organic pigment suitable for coated paper having excellent white paper gloss and printing gloss and having good ink setting properties and blocking resistance, a paper coating composition containing the organic pigment, and the A coated paper obtained by coating the paper coating composition is obtained.

(Organic pigment)
The organic pigment of the present invention comprises conjugated diene monomer (a) 5 to 20% by weight, ethylenically unsaturated carboxylic acid monomer (b) 0.5 to 10% by weight, ethylenically unsaturated nitrile monomer ( c) Volume average obtained by emulsion copolymerization of 100 parts by weight of a monomer mixture comprising 5 to 20% by weight and other monomers copolymerizable therewith (d) 50 to 89.5% by weight The particle size is 150 to 400 nm and the tetrahydrofuran insoluble matter is 40% by weight or more.

Examples of the conjugated diene monomer (a) include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene. Etc. Of these, 1,3-butadiene is preferred. These can be used alone or in combination of two or more.
The usage-amount of a conjugated diene monomer (a) is 5 to 20 weight% with respect to all the monomers, Preferably it is 8 to 16 weight%. When this amount is small, the glossiness of the coated paper is inferior, and conversely, when it is large, the blocking resistance of the coated paper is inferior.

Examples of the ethylenically unsaturated carboxylic acid monomer (b) include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; unsaturated polycarboxylic acids such as fumaric acid, maleic acid, itaconic acid, and butenetricarboxylic acid. And a partially esterified product of an ethylenically unsaturated polyvalent carboxylic acid such as monoethyl maleate and monomethyl itaconate. These ethylenically unsaturated carboxylic acid monomers can also be used as alkali metal salts or ammonium salts. These ethylenically unsaturated carboxylic acid monomers can be used alone or in combination of two or more.
The usage-amount of an ethylenically unsaturated carboxylic acid monomer is 0.5 to 10 weight% with respect to all the monomers, Preferably it is 1 to 5 weight%. If this amount is small, there is a problem that a large amount of coarse agglomerates are generated during emulsion copolymerization or the surface strength of the coated paper is reduced. Conversely, if the amount is large, the viscosity of the latex containing the organic pigment is low. It becomes too expensive to handle.

Examples of the ethylenically unsaturated nitrile monomer (c) include acrylonitrile, methacrylonitrile, fumaronitrile, α-chloroacrylonitrile, α-cyanoethylacrylonitrile, and acrylonitrile is particularly preferable.
The amount of the ethylenically unsaturated nitrile monomer used is 5 to 20% by weight, preferably 5 to 16% by weight, based on the total monomers. If the amount is small, the printed paper has poor print gloss and blocking resistance, and conversely if the amount is large, the ink set property of the coated paper is poor.

  Other monomers (d) that can be copolymerized with the above monomers are not particularly limited, and examples thereof include aromatic vinyl monomers, ethylenically unsaturated carboxylic acid ester monomers, Examples include ethylenically unsaturated carboxylic acid amide monomers, ethylenically unsaturated acid monomers other than ethylenically unsaturated carboxylic acid monomers, and crosslinkable monomers.

  Examples of the aromatic vinyl monomer include styrene, α-methyl styrene, p-methyl styrene, hydroxymethyl styrene and the like, and styrene is particularly preferable.

  Examples of the ethylenically unsaturated carboxylic acid ester monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and (meth) acrylic acid-2. -Ethylhexyl, trifluoroethyl (meth) acrylate, tetrafluoropropyl (meth) acrylate, methoxymethyl (meth) acrylate, ethoxyethyl (meth) acrylate, methoxyethoxyethyl (meth) acrylate, (meth) acrylic Ethylenically unsaturated monocarboxylic acid ester monomers such as cyanomethyl acid, 2-cyanoethyl (meth) acrylate, hydroxyethyl acrylate, glycidyl methacrylate; ethylenic acid such as dibutyl maleate, dibutyl fumarate, diethyl maleate Saturated polycarboxylic acid ester Body; and the like. Among these, ethylenically unsaturated monocarboxylic acid ester monomers can be preferably used.

  Examples of the ethylenically unsaturated carboxylic acid amide monomer include (meth) acrylamide, N-methylol (meth) acrylamide, N, N-dimethylol (meth) acrylamide, and the like.

  Examples of the ethylenically unsaturated acid monomer other than the ethylenically unsaturated carboxylic acid monomer include vinyl sulfonic acid, methyl vinyl sulfonic acid, styrene sulfonic acid, (meth) allyl sulfonic acid, (meth) acrylic acid- Sulfonic acid group-containing monomers such as ethyl 2-sulfonate and 2-acrylamido-2-hydroxypropanesulfonic acid; (meth) acrylic acid-3-chloro-2-phosphate propyl, (meth) acrylic acid-2- And phosphoric acid group-containing monomers such as ethyl phosphate and 3-allyloxy-2-hydroxypropane phosphoric acid.

  Examples of the crosslinkable monomer include conjugated divinyl compounds such as divinylbenzene; di (meth) acrylates such as polyethylene glycol di (meth) acrylate and polypropylene glycol di (meth) acrylate; trimethylolpropane tri (meth) acrylate And poly (meth) acrylates such as pentaerythritol tri (meth) acrylate.

  These other monomers (d) can be used alone or in combination of two or more. Of these other monomers (d), aromatic vinyl monomers, ethylenically unsaturated carboxylic acid ester monomers, and ethylenically unsaturated carboxylic acid amide monomers are preferably used.

  The usage-amount of another monomer (d) is 50-89.5 weight% with respect to all the monomers, Preferably it is 63-86 weight%. If the amount used is small, the coated paper is inferior in blocking resistance, and if it is large, the coated paper is inferior in white paper gloss.

When the organic pigment of the present invention emulsion-copolymerizes 100 parts by weight of the monomer mixture,
Conjugated diene monomer (a1) 5 to 50% by weight, ethylenically unsaturated carboxylic acid monomer (b1) 0.5 to 10% by weight, and other monomer (d1) 40 copolymerizable therewith In the presence of a copolymer latex formed by emulsion copolymerization of 40 to 90 parts by weight of a monomer mixture (A) comprising ˜94.5% by weight, 0 to 10% by weight of the conjugated diene monomer (a2), Ethylenically unsaturated carboxylic acid monomer (b2) 0.5 to 10% by weight, ethylenically unsaturated nitrile monomer (c2) 15 to 50% by weight, and other monomers copolymerizable therewith ( d2) 10 to 60 parts by weight of the monomer mixture (B) comprising 30 to 84.5% by weight (however, the total amount of the monomer mixture (A) and the monomer mixture (B) is 100 parts by weight) It is obtained by emulsion copolymerization.

  Examples of the conjugated diene monomer (a1) include those exemplified for the conjugated diene monomer (a). The amount used is 5 to 50% by weight, preferably 10 to 35% by weight in the monomer mixture (A). If the amount used is small, the glossiness of the white paper and the printing gloss is inferior, and conversely if it is large, the blocking resistance is poor.

  Examples of the ethylenically unsaturated carboxylic acid monomer (b1) include those exemplified for the ethylenically unsaturated carboxylic acid monomer (b). The amount used is 0.5 to 10% by weight, preferably 1 to 5% by weight in the monomer mixture (A). If the amount used is small, a large amount of coarse aggregates may be generated during the emulsion polymerization. Conversely, if the amount is large, the viscosity of the latex containing the organic pigment increases, making it difficult to handle.

Examples of the other monomer (d1) copolymerizable with the conjugated diene monomer (a1) and the ethylenically unsaturated carboxylic acid monomer (b1) include the ethylenically unsaturated nitrile monomer (c) and others. And those exemplified for the monomer (d). As the other monomer (d1), those not including those exemplified for the ethylenically unsaturated nitrile monomer (c) are particularly preferable. When the other monomer (d1) includes those exemplified for the ethylenically unsaturated nitrile monomer (c), the content thereof is 10% by weight or less, preferably 5% by weight based on the total amount of the monomer mixture (A). It is preferable to set the weight% or less.
The usage-amount of another monomer (d1) is 40-94.5 weight% in a monomer mixture (A), Preferably it is 60-89 weight%. If the amount used is small, the blocking resistance is poor, and conversely if it is large, the printing gloss is poor.

  The usage-amount of a monomer mixture (A) is 40-90 weight part with respect to 100 weight part of all the monomer mixtures, Preferably it is 50-80 weight part. If the amount used is small, the glossiness of white paper is poor, and conversely if it is large, the blocking resistance and ink setting properties are poor.

  The organic pigment of the present invention contains 0 to 10% by weight of conjugated diene monomer (a2) in the presence of a copolymer latex obtained by emulsion copolymerization of the monomer mixture (A). Carboxylic acid monomer (b2) 0.5 to 10% by weight, ethylenically unsaturated nitrile monomer (c2) 15 to 50% by weight, and other monomers copolymerizable with these (d2) 30 to 30% 10 to 60 parts by weight of a monomer mixture (B) comprising 84.5% by weight (provided that the total amount of the monomer mixture (A) and the monomer mixture (B) is 100 parts by weight). It is obtained by emulsion copolymerization.

Examples of the conjugated diene monomer (a2) include those exemplified for the conjugated diene monomer (a). The usage-amount is 0 to 10 weight% in a monomer mixture (B), Preferably it is 0 to 5 weight%. If this amount is large, the blocking resistance is poor.
In addition, the content rate (Wa1: wt%) of the conjugated diene monomer (a1) in the monomer mixture (A) is the content rate of the conjugated diene monomer (a2) in the monomer mixture (B). More than (Wa2: wt%), it is more preferable that the relationship of (Wa1-5)> Wa2 is satisfied.

  Examples of the ethylenically unsaturated carboxylic acid monomer (b2) include those exemplified for the ethylenically unsaturated carboxylic acid monomer (b2). The amount used is 0.5 to 10% by weight, preferably 1 to 5% by weight in the monomer mixture (B). If the amount used is small, there is a problem that a large amount of coarse agglomerates are generated during the emulsion copolymerization or the surface strength of the coated paper is lowered. Conversely, if the amount is large, the viscosity of the latex containing the organic pigment is low. It becomes too expensive to handle, and the coated paper is inferior in gloss.

  Examples of the ethylenically unsaturated nitrile monomer (c2) include those exemplified for the ethylenically unsaturated nitrile monomer (c). The amount used is 15 to 50% by weight, preferably 15 to 45% by weight in the monomer mixture (B). If the amount used is small, the blocking resistance and printing gloss are poor, and conversely if it is large, the blank paper gloss and ink setting properties are poor.

  Other monomers (d1) copolymerizable with the conjugated diene monomer (a2), the ethylenically unsaturated carboxylic acid monomer (b2) and the ethylenically unsaturated nitrile monomer (c2) And those exemplified for the monomer (d). The amount used is 30 to 84.5% by weight, preferably 45 to 84% by weight in the monomer mixture (B). If the amount used is small, the blocking resistance is poor, and conversely if it is large, the printing gloss is poor.

The usage-amount of a monomer mixture (B) is 10-60 weight part with respect to 100 weight part of all the monomers, Preferably it is 20-50 weight part. If the amount used is small, the blocking resistance and ink setting properties are poor, and conversely if it is large, the printing gloss is poor.
The total amount of the monomer mixture (A) and the monomer mixture (B) is 100 parts by weight.

  The method for emulsion copolymerization of the monomer mixture is not particularly limited, and conventionally known methods can be employed in emulsion polymerization.

Examples of the monomer addition method include a method in which the monomers to be used are added all at once to the reactor, a method in which the monomer is added continuously or intermittently as the polymerization proceeds, and a part of the monomer is added. And a method of polymerizing by reacting to a specific polymerization conversion rate and then adding the remaining monomers continuously or intermittently, and any method may be employed. When the monomers are mixed and added continuously or intermittently, the composition of the mixture may be constant or may be changed.
Each monomer may be added to the reaction vessel after previously mixing various monomers to be used, or may be added separately to the reaction vessel.

  In the emulsion copolymerization, a seed polymerization method can also be employed. Employing this method is preferable in that the volume average particle diameter of the organic pigment can be easily controlled and the polymerization reaction can be performed more stably. When employing the seed polymerization method, the composition of the seed latex is not particularly limited, and may be the same as or different from the composition of the monomer mixture used for the production of the organic pigment described above. What is necessary is just to adjust the particle diameter and usage-amount of seed latex suitably so that the weight average particle diameter of the organic pigment finally obtained may become a desired value.

  In the emulsion copolymerization, commonly used polymerization auxiliary materials such as emulsifiers, polymerization initiators, molecular weight regulators, chelating agent dispersants, oxygen scavengers, pH regulators, and builders can be used. The addition method of these polymerization auxiliary materials is not particularly limited, and any method such as an initial batch addition method, a divided addition method, or a continuous addition method can be employed.

  As a medium, water is usually used. The amount used is usually 80 to 300 parts by weight with respect to 100 parts by weight of all monomers.

Although it does not specifically limit as an emulsifier, For example, Anionic emulsifiers, such as an alkylbenzene sulfonate, an aliphatic sulfonate, a sulfate ester salt of a higher alcohol; Polyethylene glycol alkyl ether type, polyethylene glycol alkyl ester type, polyethylene glycol alkylphenyl Nonionic emulsifier such as ether type; amphoteric emulsifier having carboxylate, sulfate, sulfonate, phosphate or phosphate as anion moiety and amine or quaternary ammonium salt as cation moiety Etc. Among these, an anionic emulsifier can be preferably used.
The usage-amount of an emulsifier is 0.1-5 weight part normally with respect to 100 weight part of all monomers, Preferably it is 0.1-2 weight part, More preferably, it is 0.15-1 weight part.

The polymerization initiator is not particularly limited, and examples thereof include inorganic peroxides such as sodium persulfate, potassium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; t-butyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, benzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide Organic peroxides such as oxide and t-butylperoxyisobutyrate; azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, methyl azobisisobutyrate, etc. This Can. Among these, inorganic peroxides are preferable, and persulfates can be used more preferably. These polymerization initiators can be used alone or in combination of two or more. The peroxide can also be used as a redox polymerization initiator in combination with a reducing agent such as sodium bisulfite.
The usage-amount of a polymerization initiator is 0.1-2 weight part normally with respect to 100 weight part of all the monomers, Preferably it is 0.5-1.5 weight part.

In the present invention, it is preferable to use a molecular weight modifier for the purpose of adjusting the insoluble content of the organic pigment in tetrahydrofuran.
Although it does not specifically limit as a molecular weight modifier, For example, α-methylstyrene dimer; Mercaptans, such as t-dodecyl mercaptan, n-dodecyl mercaptan, octyl mercaptan; Halogenation, such as carbon tetrachloride, a methylene chloride, a methylene bromide Hydrocarbons; sulfur-containing compounds such as tetraethylthiuram disulfide, dipentamethylene thiuram disulfide, diisopropylxanthogen disulfide, and the like. These may be used alone or in combination of two or more. Among these, mercaptans are preferable, and t-dodecyl mercaptan can be more preferably used.
The amount of the molecular weight modifier used varies depending on the type, but is preferably 0.1 to 0.8 parts by weight, more preferably 0.2 to 0.7 parts by weight with respect to 100 parts by weight of all monomers. It is a range.

Although polymerization temperature is not specifically limited, Usually, it is 0-100 degreeC, Preferably it is 40-90 degreeC.
After the polymerization is started, the polymerization reaction is stopped by cooling the polymerization system or adding a polymerization terminator at a predetermined polymerization conversion rate. The polymerization conversion rate when stopping the polymerization reaction is preferably 90% by weight or more, more preferably 95% by weight or more.

  After emulsion copolymerization as described above, if desired, unreacted monomers are removed to obtain a latex containing an organic pigment.

  The volume average particle diameter of the organic pigment of the present invention is 150 to 400 nm, preferably 180 to 320 nm. If the particle size is too small or too large, the balance between the white paper gloss and the surface strength of the coated paper is lowered. The particle size can be controlled to a desired value by adjusting the amount of emulsifier and polymerization initiator used, or by adjusting the particle size of the seed latex and the amount used.

  The organic pigment of the present invention has an insoluble content of tetrahydrofuran of 40% by weight or more, preferably 50 to 95% by weight. When this amount is small, the printing gloss and ink setting property of the coated paper are lowered, and the blocking resistance is remarkably lowered. On the other hand, if the amount of insoluble tetrahydrofuran is too much, the glossiness of the white paper tends to decrease or the surface strength tends to decrease.

  The glass transition temperature of the organic pigment of the present invention is preferably 40 to 95 ° C, more preferably 50 to 90 ° C. When the glass transition temperature is in the above range, a coated paper having an excellent balance between white paper gloss and blocking resistance can be obtained.

  The latex containing the organic pigment may further contain additives such as a dispersant, a pH adjuster, an antifoaming agent, an antiseptic, an antibacterial agent, an anti-aging agent, and an ultraviolet absorber, if necessary. . There are no particular limitations on the type and amount used.

(Composition for paper coating)
The composition for paper coating of this invention contains the said organic pigment.
In the paper coating composition of the present invention, a copolymer latex having a glass transition temperature of −50 to + 25 ° C. as an adhesive is preferably added to 100 parts by weight of the pigment containing the organic pigment in terms of solid content. It is formed by blending ~ 20 parts by weight.

Examples of the pigment other than the organic pigment of the present invention include organic pigments other than the above-described organic pigments such as binder pigments, plastic pigments, and hollow polymer particles; clay, barium sulfate, calcium carbonate, talc, titanium oxide, satin white, And inorganic pigments such as aluminum hydroxide, silica and mica. As the pigment used in addition to the organic pigment of the present invention, inorganic pigments are preferable, and among them, clay and calcium carbonate are preferably used.
The content of the organic pigment of the present invention in the pigment is preferably 3 to 50 parts by weight, more preferably 5 to 30 parts by weight with respect to 100 parts by weight of the total pigment. If the content is too small, the coated paper tends to be inferior in white paper gloss and printed gloss, and conversely if it is too much, the coated paper tends to be inferior in blocking resistance and ink setting.

The copolymer latex to be blended as an adhesive is not particularly limited as long as it is usually used in the field of coated paper, but its glass transition temperature is −50 to + 25 ° C., preferably −40 to + 20 ° C. is there. If the glass transition temperature is within the above range, a coated paper that is superior in balance between surface strength and blocking resistance can be obtained.
Moreover, the volume average particle diameter of the copolymer latex blended as an adhesive is preferably 30 to 120 nm, more preferably 50 to 110 nm. When the volume average particle diameter is in the above range, a coated paper that is superior in balance between surface strength and ink setting property can be obtained.

Copolymer latex blended as an adhesive is conjugated diene monomer 24 to 60% by weight, ethylenically unsaturated carboxylic acid monomer 1 to 5% by weight, ethylenically unsaturated nitrile monomer 5 to 25% by weight. It is also preferable to emulsion-copolymerize a monomer mixture comprising 34 to 70% by weight of other monomers copolymerizable therewith.
Conjugated diene monomer, ethylenically unsaturated carboxylic acid monomer, ethylenically unsaturated nitrile monomer and other monomers copolymerizable therewith are conjugated diene monomer (a) and ethylene, respectively. Examples of the unsaturated unsaturated carboxylic acid monomer (b), the ethylenically unsaturated nitrile monomer (c), and other monomers (d) copolymerizable therewith can be used.

  The usage-amount of the copolymer latex mix | blended as an adhesive agent is 3-20 weight part with respect to 100 weight part of all the pigments, Preferably it is 5-17 weight part. If the amount used is small, the surface strength of the coated paper tends to be reduced, and conversely if it is large, the blocking resistance and ink setting properties of the coated paper tend to be lowered.

  The weight ratio of the copolymer latex to be blended as the adhesive and the organic pigment of the present invention is preferably 20/80 to 90/10, more preferably 50/50 to 85/15, particularly preferably in terms of solid content. 65/35 to 80/20.

  A water-soluble adhesive generally used in a paper coating composition may be used in combination with the paper coating composition of the present invention. Examples of the water-soluble adhesive include starch, oxidized starch, casein, soy protein, and polyvinyl alcohol. The amount of the water-soluble adhesive used is usually 1 part by weight or more, preferably 3 to 20 parts by weight with respect to 100 parts by weight of the total pigment.

  In the paper coating composition of the present invention, if necessary, a pH adjuster, a pigment dispersant, a water resistance agent, an antifoaming agent, a dye, a lubricant, a water retention improver, a fluidity improver, a preservative, Additives such as antibacterial agents and organic solvents can be blended.

(Coated paper)
The coated paper of the present invention is obtained by coating the above paper coating composition on a base paper.
The base paper is not particularly limited, and base paper made of pulp such as mechanical pulp, chemical pulp, and waste paper pulp can be used. Moreover, as the base paper, a coated paper obtained by previously coating the undercoat composition can be used.
The basis weight of the base paper is not particularly limited, but usually, paper of 40 to 130 g / m ² and paperboard of 160 to 420 g / m ² are used.

The coating method is not particularly limited. For example, the coating can be performed using a coating apparatus such as a blade coater, a roll coater, an air knife coater, or a short dwell coater. The coating amount is usually in the range of ³ to 30 g / m ² , preferably 5 to 25 g / m ² , in terms of solid content after drying.
A coated paper can be obtained by coating a paper coating composition on a base paper and then drying. The drying temperature is usually 50 ° C. or higher.
Furthermore, when the coated paper is passed through a finishing device such as a soft nip calender, a super calender, or a gloss calender, the smoothness of the surface of the coated layer is improved, and a higher white paper gloss is exhibited.
The organic pigment of the present invention has excellent ink setting properties and anti-blocking properties on coated paper, as well as high white paper gloss and printing gloss, especially when surface treatment is performed at a high temperature of 110 to 170 ° C. with a soft nip calender or gloss calender. Sex can be imparted.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples. In addition, the part and% in an Example are a basis of weight unless there is particular notice.
Evaluation was performed by the method shown below.
(1) Volume average particle diameter The volume average particle diameter of the organic pigment and the copolymer latex was measured using a light scattering particle diameter measuring device (LS230: Coulter).
(2) Tetrahydrofuran (THF) insoluble content A latex containing an organic pigment is cast on a glass plate with a frame and left in a constant temperature and humidity chamber at a temperature of 20 ° C. and a relative humidity of 65% for 12 hours. The film was dried for 1 hour to obtain an organic pigment film. The film was cut into a size of 2 mm × 2 mm or less to prepare a sample. 0.3g of this sample was placed in a 150 mesh wire mesh basket, immersed in 100ml of tetrahydrofuran at 20 ° C for 48 hours, then the film remaining on the wire mesh without dissolving was dried at 100 ° C under reduced pressure, and the residual rate was calculated. The THF-insoluble content (%) was determined.
(3) Glass transition temperature A latex containing an organic pigment is cast on a glass plate with a frame, left in a constant temperature and humidity chamber at a temperature of 20 ° C. and a relative humidity of 65% for 12 hours, and further dried at 105 ° C. for 1 hour. Thus, an organic pigment film was obtained. About this film, the glass transition temperature was measured with the temperature increase rate of 20 degree-C / min and measurement temperature range-100-100 degreeC using the differential scanning calorimeter.

(4) Gloss of white paper For coated paper, using a gloss meter (GM-26D, manufactured by Murakami Color Co., Ltd.), the light reflectance (%) of the coated paper under the conditions of an incident angle of 75 degrees and a reflection angle of 75 degrees Was measured. Larger numbers are better.
(5) Printing Gloss After applying indigo color ink to the coated paper using an RI printing tester (manufactured by Akashi Seisakusho), it was measured by the same method as the measuring method of white paper gloss. Larger numbers are better.

(6) Ink setting properties Immediately after printing 0.6 cm ³ of printing ink (manufactured by Toyo Ink Co., Ltd., Mark V indigo) on a coated paper using an RI printing tester, the coated paper is overlaid and pressure-bonded. Ink was transferred from the printed surface to the coated paper. The transfer amount of the ink transferred to the coated paper is measured with a reflection densitometer (GRETAG D196D19C; manufactured by Gretag Macbeth AG), and indicated by an ink density value. The smaller this value is, the better the ink setting property is, and it is suitable for multicolor printing.
(7) Blocking resistance A commercially available medium quality paper was layered on the coated surface of the coated paper and passed through a gloss calendar at 160 ° C. and 75 MPa three times. Thereafter, the coated paper and the medium quality paper were peeled off, and the degree of adhesion of the medium quality paper to the coated surface was observed. The score was 5 according to the degree of adhesion of the medium quality paper to the coated surface, with a score of 5 for those not adhered at all and 1 for those adhered to the entire surface. The higher the score, the better the blocking resistance.

(Example 1)
In a pressure vessel, 50 parts of a monomer mixture having the first-stage monomer composition shown in Table 1, t-dodecyl mercaptan corresponding to 0.6% of the monomer mixture, 25 parts of ion-exchanged water, alkyl 0.1 parts of sodium diphenyl ether disulfonate and 0.2 parts of sodium hydrogen carbonate were added to obtain a monomer emulsion (I).
In a separate pressure vessel, 50 parts of a monomer mixture having the second-stage monomer composition shown in Table 1, t-dodecyl mercaptan corresponding to 0.6% of the monomer mixture, and 25 parts of ion-exchanged water Then, 0.1 part of sodium alkyldiphenyl ether disulfonate and 0.2 part of sodium bicarbonate were added to obtain a monomer emulsion (II).
Solid content conversion of seed latex (copolymer latex having a volume average particle diameter of 55 nm obtained by emulsion polymerization of a monomer mixture consisting of 40% styrene, 56% butadiene and 4% methacrylic acid) in a pressure-resistant reactor 2 parts, 50 parts of ion-exchanged water, 0.2 part of sodium alkyldiphenyl ether disulfonate and 0.05 part of ethylenediaminetetraacetic acid tetrasodium salt were added, and the temperature was raised to 80 ° C. with stirring.

Subsequently, 0.5 part of potassium persulfate was added to the reactor, and the above-mentioned monomer emulsion (I) was subjected to emulsion copolymerization while being continuously added to the reactor over 150 minutes. Subsequently, the above monomer mixture (II) was subjected to emulsion copolymerization while being continuously added to the reactor for 150 minutes. A 3% aqueous solution containing 0.5 part of potassium persulfate was continuously added to the reactor over 300 minutes from the time when continuous addition of the monomer emulsion (I) was started.
After the addition of the monomer mixture (II) was completed, the reaction was further continued at 85 ° C. for 5 hours, and then 0.025 part of sodium nitrite was added to stop the polymerization reaction. The polymerization conversion rate at this time was 98%.
An aqueous sodium hydroxide solution was added to adjust the pH of the latex to 8.2, and then unreacted monomers were removed by steam distillation. Concentrate to a solids concentration of 52%, add 0.15 parts of preservative, further adjust the solids concentration to 50% and pH to 8 to obtain latex A containing organic pigment It was. The latex was measured for the volume average particle diameter, glass transition temperature and THF-insoluble matter of the organic pigment, and the results are shown in Table 1.

(Examples 2 to 4 and Comparative Examples 1 to 3)
Latex B to G containing an organic pigment were obtained in the same manner as in Example 1 except that the polymerization recipe shown in Table 1 was changed. The volume average particle diameter, glass transition temperature and THF insoluble matter of the organic pigment in the latex B to G were measured, and the results are shown in Table 1.

(Synthesis Example 1)
In a pressure vessel, 40 parts of ion exchange water, 0.3 part of sodium alkyldiphenyl ether disulfonate, 19 parts of styrene, 40 parts of 1,3-butadiene, 19 parts of methyl methacrylate, 18 parts of acrylonitrile, 2 parts of itaconic acid, 1 part of acrylamide , 0.7 parts of t-dodecyl mercaptan and 1 part of α-methylstyrene dimer were added and stirred to obtain a monomer emulsion.
A volume average particle diameter of 35 nm obtained by emulsion copolymerization of a seed latex (38% styrene, 30% 1,3-butadiene, 28% methyl methacrylate and 4% methacrylic acid) in a pressure-resistant reactor. 4 parts in terms of solid content, 60 parts of ion-exchanged water, 0.3 part of sodium alkyldiphenyl ether disulfonate, 1 part of itaconic acid, 0.05 part of ethylenediaminetetraacetic acid tetrasodium salt, The temperature was raised to 80 ° C. while stirring.
A 3% aqueous potassium persulfate solution containing 1 part of potassium persulfate was continuously added to the reactor over 210 minutes. For 210 minutes from the start of the addition of the aqueous potassium persulfate solution, emulsion copolymerization was carried out while continuously adding the above monomer emulsion to the reactor.

After completing the addition of the monomer emulsion, the reaction was further continued at 85 ° C. for 6 hours.
After the polymerization system was cooled to terminate the polymerization reaction, the pH was adjusted to 8.5 with sodium hydroxide, and unreacted monomers were removed by steam distillation to obtain a copolymer latex for adhesive. This copolymer latex had a glass transition temperature of 0 ° C. and a volume average particle size of 80 nm.

(Example 5)
Based on the formulation shown in Table 2, an undercoat composition and a paper coating composition were prepared. Note that latex A was used as the organic pigment in the paper coating composition.

The undercoat composition was blade-coated on a coated white ball base paper (310 g / m ² ) so that the solid content after drying was 10 g / m ² per side, and dried with hot air at 160 ° C. for 10 seconds. . Next, the paper coating composition was blade-coated so that the solid content after drying was 10 g / m ² per side, and was dried with hot air at 160 ° C. for 10 seconds immediately after coating. The obtained coated paper was subjected to gloss calendar treatment twice under the conditions of a temperature of 120 ° C. and a linear pressure of 75 MPa to obtain a coated paper as a final product.
The resulting coated paper was measured for white paper gloss, printing gloss, ink setting properties and blocking resistance, and the results are shown in Table 3.

(Examples 6-8 and Comparative Examples 4-6)
Coated paper was obtained in the same manner as in Example 5 except that latexes B to G were used in place of latex A used in the paper coating composition. The resulting coated paper was measured for white paper gloss, printing gloss, ink setting property and blocking resistance, and the results are shown in Table 3.

The following can be seen from the above results.
When the organic pigment of Comparative Example 1 obtained by emulsion copolymerization of a monomer mixture containing no ethylenically unsaturated nitrile monomer was used, printing gloss, ink setting property and anti-blocking property of the obtained coated paper (Comparative Example 4).
When the organic pigment of Comparative Example 2 obtained by emulsion copolymerization of a monomer mixture containing an ethylenically unsaturated nitrile monomer but not containing it in the second stage is used, The gloss of white paper is lowered, and the ink setting property and blocking resistance are inferior (Comparative Example 5).
When the organic pigment of Comparative Example 3 in which the amount of tetrahydrofuran insolubles is lower than the lower limit specified in the present invention is used, the resulting coated paper is inferior in ink setting properties and blocking resistance (Comparative Example 6).
In contrast to these comparative examples, when the organic pigments of Examples 1 to 4 of the present invention are used, coated paper having excellent white paper gloss and printing gloss, and good ink setting properties and blocking resistance can be obtained ( Examples 5-8).

The organic pigment of the present invention improves coated paper gloss and printing gloss, and provides coated paper with improved ink setting and blocking resistance at a high level, and is therefore suitable for coating various base papers such as western paper and paperboard. Therefore, it is possible to provide a coated paper with good quality.

Claims (7)

Conjugated diene monomer (a) 5-20% by weight, ethylenically unsaturated carboxylic acid monomer (b) 0.5-10% by weight, ethylenically unsaturated nitrile monomer (c) 5-20% by weight , And other monomers (d) copolymerizable therewith, obtained by emulsion copolymerization of 100 parts by weight of a monomer mixture comprising 50 to 89.5% by weight, having a volume average particle size of 150 to 400 nm, An organic pigment having a tetrahydrofuran insoluble content of 40% by weight or more, comprising 5 to 50% by weight of the conjugated diene monomer (a1), 0.5 to 10% by weight of the ethylenically unsaturated carboxylic acid monomer (b1), And in the presence of a copolymer latex obtained by emulsion copolymerization of 40 to 90 parts by weight of a monomer mixture (A) composed of 40 to 94.5% by weight of other monomer (d1) copolymerizable therewith. Conjugated diene monomer (a2) 0 to 10 weight , Ethylenically unsaturated carboxylic acid monomer (b2) 0.5 to 10% by weight, ethylenically unsaturated nitrile monomer (c2) 15 to 50% by weight, and other monomers copolymerizable therewith (D2) 10 to 60 parts by weight of the monomer mixture (B) comprising 30 to 84.5% by weight (provided that the total amount of the monomer mixture (A) and the monomer mixture (B) is 100 parts by weight) An organic pigment obtained by emulsion copolymerization. The content ratio of the conjugated diene monomer (a1) in the monomer mixture (A) is larger than the content ratio of the conjugated diene monomer (a2) in the monomer mixture (B). 1. The organic pigment according to 1. A composition for paper coating containing the organic pigment according to claim 1. A blend of 3 to 20 parts by weight (in terms of solid content) of a copolymer latex having a glass transition temperature of -50 to + 25 ° C is added to 100 parts by weight of the pigment containing 3 to 50 parts by weight of the organic pigment according to claim 1. A composition for paper coating. The composition for paper coating according to claim 4, wherein the copolymer latex has a volume average particle diameter of 30 to 120 nm. The composition for paper coating according to claim 4, wherein the weight ratio of the organic pigment to the copolymer latex is 20/80 to 90/10 in terms of solid content. Coated paper obtained by coating the base paper with the paper coating composition according to any one of claims 3 to 6.