JP2006299253A - Pigment dispersion, and composition for coated paper, containing the pigment dispersion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composition for coated paper, providing the coated paper having excellent white paper gloss, whiteness, opacity and smoothness, and also having excellent gloss of print and dry pick strength, and having good fluidity; and to provide a pigment dispersion having excellent sedimentation resistance. <P>SOLUTION: The pigment dispersion contains (A) hollow polymer particles having 0.3-3.0 μm average particle diameter, and (B) solid polymer particles containing a conjugated diene monomer unit and having 0.06-1.5 μm particle diameters. Preferably, the dispersion is regulated so that the ratio of the hollow polymer particles (A) to the solid polymer particles may be (20/80)-(80/20). Further, the composition preferably contains (C) solid polymer particles having the content of the conjugated diene monomer unit regulated so as to be ≥20 wt.% and also having ≥200 mPa s viscosity measured by a Brookfield type viscometer, and ≤0.13 μm average particle diameter. The composition for the coated paper contains the pigment dispersion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pigment dispersion and a coated paper composition containing the pigment dispersion. More specifically, the present invention is excellent in white paper gloss, whiteness, opacity and smoothness, printing gloss and dry pick. The present invention relates to a coated paper composition having good fluidity that gives coated paper having excellent strength, and a pigment dispersion having excellent sedimentation resistance.

  In recent years, as printing applications such as publications such as books and magazines and commercial advertisements such as flyers, brochures, and posters have rapidly expanded, their printing methods have become diversified, and coated papers are used accordingly. More and more quality has been required. That is, in order to be suitable for single color printing and multicolor printing in a wide range of applications, coated paper is required to have excellent white paper gloss, whiteness, opacity and smoothness, and excellent print gloss and dry pick strength. It has been.

  Conventionally, a coated paper composition containing hollow polymer particles has been used as a method for producing a coated paper for printing having high white paper gloss, whiteness, opacity and smoothness. However, since the hollow polymer particles contain water inside the particles in the dispersion, increasing the solid concentration decreases the water concentration outside the particles and lowers the fluidity. It was known that the hollow polymer particles would settle if left alone.

  For example, Patent Document 1 discloses a first particle group having a particle diameter of 0.3 to 5.0 μm and a second particle having a smaller particle diameter of 0.05 to 0.3 μm. A particle composition for coated paper comprising a particle group is proposed, the first particle group is a hollow polymer particle, and the second particle group has a particle diameter D ′ that is D with respect to the particle diameter D of the first particle group. '<D / 2 is disclosed. However, such particles have improved flowability, but have a problem in that the balance between white paper gloss, printing gloss, whiteness and opacity and dry pick strength is poor.

  Patent Document 2 discloses a composition for coated paper containing a pigment containing 50 to 100 parts by weight of calcium carbonate and a polymer dispersion having a solid content of 1 to 25 parts by weight. Includes a specific amount of an emulsion polymer (a) having an average particle size of 0.15 to 3 μm and an emulsion polymer (b) having an average particle size of 0.04 to 0.6 μm, and at least (a) is a hollow polymer particle. There is disclosed a paper coating composition wherein the emulsion polymer of (a) or (b) is prepared in the presence of the other emulsion polymer. However, such a polymer dispersion is complicated to manufacture, and the coated paper composition has a poor balance between white paper gloss, print gloss, whiteness and opacity, and dry pick strength, and also has settling resistance. It was insufficient.

Japanese Patent No. 3217417 JP 2001-323223 A

  In view of the above circumstances, an object of the present invention is a coated paper with good fluidity that gives a coated paper excellent in white paper gloss, whiteness, opacity and smoothness, and excellent in print gloss and dry pick strength. Another object of the present invention is to provide a pigment dispersion having excellent composition resistance and sedimentation resistance.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have a specific amount of hollow polymer particles (A) having a specific particle size and a specific amount of conjugated diene monomer units. The pigment dispersion containing the dense polymer particles (B) has excellent sedimentation resistance, and the coated paper composition comprising the pigment dispersion has high fluidity, white paper gloss, whiteness, The present inventors have found that a coated paper excellent in transparency and smoothness and excellent in printing gloss and dry pick strength is obtained, and based on this knowledge, the present invention has been completed.

Thus, according to the present invention, the following inventions 1 to 4 are provided.
1. Hollow polymer particles (A) having an average particle size of 0.3 to 3.0 μm and dense particles having an average particle size of 0.06 to 1.5 μm and a content of conjugated diene monomer units of 5 to 20% by weight A pigment dispersion containing actual polymer particles (B).
2. 2. The pigment dispersion according to 1 above, wherein the weight ratio of the solid content of each of the hollow polymer particles (A) and the dense polymer particles (B) is 20/80 to 80/20.
3. When the content of the conjugated diene monomer unit is more than 20% by weight and the solid content concentration is 50% by weight, the viscosity measured by a B-type viscometer is 200 mPa · s or more and the average particle size is 0.13 μm or less. 3. The pigment dispersion according to the above 1 or 2, further comprising polymer particles (C).
4). The composition for coated paper formed by containing the pigment dispersion liquid as described in any one of said 1-3.

  According to the present invention, a coated paper composition having good fluidity, which gives a coated paper excellent in white paper gloss, whiteness, opacity and smoothness, and excellent in print gloss and dry pick strength, and precipitation resistance A pigment dispersion having excellent properties is provided.

  The pigment dispersion of the present invention comprises a hollow polymer particle (A) having an average particle size of 0.3 to 3.0 μm (hereinafter sometimes abbreviated as hollow particle (A)), a conjugated diene monomer. It contains dense polymer particles (B) having an average particle size of 0.06 to 1.5 μm and having a unit content of 5 to 20% by weight.

<Hollow polymer particles (A)>
The hollow particles (A) used in the present invention are polymer particles having an average particle size of 0.3 to 3.0 μm and obtained by polymerizing an organic monomer and having voids therein. The hollow particles (A) have a specific gravity smaller than that of inorganic pigments, non-hollow polymer particles, that is, solid polymer particles, so that the coating properties of the coating paper composition are improved, and the bulky coated paper with high opacity is high. It is effective to get. Further, since the hollow particles (A) are easily deformable, the surface of the coated paper is smoothed with a small pressure, so that high white paper gloss can be easily obtained.

The average particle size of the hollow particles (A) needs to be 0.3 to 3.0 μm, preferably 0.3 to 1.5 μm, more preferably 0.4 to 1.3 μm, and particularly preferably 0. .5 to 1.1 μm. The average particle diameter of the hollow particles (A) can be measured by observation using a transmission electron microscope.
If the average particle diameter of the hollow particles (A) is too small, the whiteness, white paper gloss, opacity, smoothness and print gloss of the coated paper tend to be reduced. The fluidity of the composition tends to decrease.

  The porosity of the hollow particles (A) is preferably 10 to 75%, more preferably 20 to 65%, and particularly preferably 25 to 60%.

  The composition of the polymer constituting the hollow particles (A) is not limited, but a polymer having a glass transition temperature (Tg) of 25 ° C. or higher is preferable. The preferred polymer composition of the hollow particles (A) contains a monomer unit of an aromatic vinyl compound and an ethylenically unsaturated carboxylic acid ester monomer unit as essential repeating units, and is copolymerized with these as necessary. It contains other possible monomer units.

  Examples of the aromatic vinyl compound include styrene, methyl styrene, vinyl toluene, chlorostyrene, and hydroxymethyl styrene. Styrene and α-methyl styrene are preferable, and styrene is particularly preferable.

  Examples of ethylenically unsaturated carboxylic acid ester monomers 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, dibutyl maleate, dibutyl fumarate, diethyl maleate, methoxymethyl (meth) acrylate, ethoxyethyl (meth) acrylate , Methoxyethoxyethyl (meth) acrylate, cyanomethyl (meth) acrylate, 2-cyanoethyl (meth) acrylate, hydroxyethyl (meth) acrylate, glycidyl (meth) acrylate, and the like. Of these, methyl methacrylate is preferred.

  Examples of other copolymerizable monomers used as necessary include ethylenically unsaturated nitrile monomers, ethylenically unsaturated carboxylic acid monomers, ethylenically unsaturated carboxylic acid amide monomers, Examples thereof include at least one selected from a conjugated diene monomer, a crosslinkable monomer, a vinyl acetate monomer, and the like.

  Examples of the ethylenically unsaturated nitrile monomer include (meth) acrylonitrile, fumaronitrile, α-chloroacrylonitrile, α-cyanoethylacrylonitrile, acrylonitrile, and acrylonitrile is particularly preferable.

Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; and ethylenically unsaturated monomers such as fumaric acid, maleic acid, itaconic acid, and butenetricarboxylic acid. Examples thereof include polycarboxylic acids; partially esterified products of ethylenically unsaturated polyvalent carboxylic acids such as monoethyl maleate and monomethyl itaconate.
Examples of the ethylenically unsaturated carboxylic acid amide monomer include (meth) acrylamide, N-methylol (meth) acrylamide, N, N-dimethylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide and the like. .

  Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene and chloroprene. Can be mentioned.

  Examples of the crosslinkable monomer include divinyl monomers such as divinylbenzene, ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane trimethacrylate, and allyl methacrylate. In particular, divinylbenzene, ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate are preferred. Examples of the alkyl (meth) acrylamide monomer include acrylamide, methacrylamide, N-methylolacrylamide, N, N-dimethylacrylamide, N, N-dimethylaminopropyl (meth) acrylamide and the like.

The method for producing the hollow particles (A) is not limited as long as hollow polymer particles having an average particle diameter of 0.3 to 3.0 μm are obtained. For example, JP-A 64-1704 and JP-A 5- The following methods (1) to (7) are exemplified, including the methods described in Japanese Patent Application Laid-Open No. 279409, Japanese Patent Application Laid-Open No. 6-248812, Japanese Patent Application Laid-Open No. 10-11018, and Japanese Patent Application Laid-Open No. 10-182761. The
(1) A method of foaming the foaming agent of a latex containing a foaming agent in polymer particles, and (2) gasifying the volatile material of a latex in which a volatile material such as butane is encapsulated in the polymer particles. A method of expanding, (3) a method in which polymer particles are melted and a gas jet such as air is blown into the polymer particles to enclose bubbles, and (4) an alkali-swelling substance is contained inside the polymer particles. , A method of infiltrating an alkaline liquid into the particles to expand the alkali-swellable substance, (5) a method of emulsion polymerization of styrene in the presence of seed particles of polymethyl methacrylate, and (6) a polymerizable monomer component in water. A method of carrying out polymerization by finely dispersing an oil-in-water emulsion and (7) a polymerizable monomer including a crosslinkable monomer and a hydrophilic monomer from a monomer different from the monomer composition How to aqueous polymerization in the presence microparticles engaged heterologous polymer.
Among these, the method (4) (see Japanese Patent Laid-Open No. 10-182761) is preferable.
The method for setting the average particle size of the hollow polymer particles within the range specified in the present invention is not particularly limited, and a conventionally known method can be adopted in emulsion polymerization. For example, the type and amount of an emulsifier used in emulsion polymerization are appropriately selected. A method is mentioned.

<Dense polymer particles (B)>
The dense polymer particles (B) (hereinafter sometimes abbreviated as dense particles (B)) used in the pigment dispersion of the present invention have a conjugated diene monomer unit content of 5 to 20 wt. % Is essential, preferably 6 to 18% by weight, more preferably 7 to 16% by weight. When the amount of the conjugated diene monomer unit is too small, the printed paper has poor print gloss and dry pick strength, while when too large, the coated paper has poor white gloss, whiteness and opacity.

  The dense particles (B) are 100% by weight of a monomer mixture composed of 5 to 20% by weight of a conjugated diene monomer and 80 to 95% by weight of another monomer copolymerizable with the conjugated diene monomer. The part is preferably obtained by emulsion polymerization.

Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene and chloroprene. These may be used alone or in combination of two or more. Of these, 1,3-butadiene is preferable.
The amount of the conjugated diene monomer used is 5 to 20% by weight of the total monomer mixture, preferably 6 to 18% by weight, and more preferably 7 to 16% by weight. If the amount of the conjugated diene monomer is too small, the printed paper may be inferior in printed gloss and dry pick strength, while if too large, the coated paper may be inferior in white paper gloss, whiteness and opacity.

  Examples of other monomers copolymerizable with the conjugated diene monomer include aromatic vinyl monomers, ethylenically unsaturated carboxylic acid ester monomers, ethylenically unsaturated nitrile monomers, and ethylenic monomers. Examples include unsaturated carboxylic acid monomers, ethylenically unsaturated carboxylic acid amide monomers, crosslinkable monomers, and ethylenically unsaturated acid monomers other than ethylenically unsaturated carboxylic acid monomers.

  As said other monomer, the same monomer as what was mentioned by the hollow particle (A) can be illustrated.

  Among them, styrene is preferable as the aromatic vinyl monomer, and (meth) acrylonitrile is preferable as the ethylenically unsaturated nitrile monomer, and the ethylenically unsaturated carboxylic acid ester is a single monomer. Among them, methyl methacrylate is preferable as the body, and (meth) acrylamide is preferable as the ethylenically unsaturated carboxylic acid amide monomer.

Of these ethylenically unsaturated carboxylic acid monomers, itaconic acid, acrylic acid and methacrylic acid are preferred as the ethylenically unsaturated carboxylic acid monomer.
The amount of the ethylenically unsaturated carboxylic acid monomer used is preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight, based on the total monomers. If this amount is too small, there is a problem that a large amount of coarse aggregates are generated during emulsion polymerization. Conversely, the viscosity of the pigment dispersion containing the solid particles (B) becomes too high, making it difficult to handle. Or the glossiness of the blank paper may decrease.

  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 acrylamide-2-hydroxypropanesulfonic acid; (meth) acrylic acid-3-chloro-2-propyl phosphate, (meth) acrylic acid-2-phosphoric acid And phosphoric acid group-containing monomers such as ethyl, 3-allyloxy-2-hydroxypropane phosphate, and the like.

  Other monomers copolymerizable with these conjugated diene monomers can be used alone or in combination of two or more. Of these other monomers, aromatic vinyl monomers, ethylenically unsaturated nitrile monomers, ethylenically unsaturated carboxylic acid ester monomers, and ethylenically unsaturated carboxylic acid amide monomers are preferably used. Is done.

  The amount of other monomers used is 80 to 95% by weight of the total monomer mixture, preferably 82 to 94% by weight, more preferably 84 to 93% by weight. If the amount used is too small, the coated paper has poor white paper gloss and whiteness, and conversely if too large, the dry pick strength of the coated paper may be inferior.

  The particle diameter of the dense particles (B) used in the present invention must be 0.06 to 1.5 μm, preferably 0.08 to 1.3 μm, more preferably 0.1 to 1.1 μm. It is. If the particle size is too small or too large, the balance between the white paper gloss and the printed gloss of the coated paper and the dry pick strength decreases.

  The method for emulsion polymerization of the monomer mixture is not particularly limited as long as dense particles (B) having a particle size of 0.06 to 1.5 μm are obtained, and a conventionally known method is adopted in emulsion polymerization. it can. For example, it is desired to use seed particles at the time of emulsion polymerization, or to select appropriately the types and amounts of monomers, emulsifiers, dispersants, inorganic salts and polymerization initiators used, polymerization temperature, polymerization concentration, etc. The value can be controlled.

  The solid particles (B) used in the present invention preferably have an insoluble content of tetrahydrofuran of 40% by weight or more, more preferably 50 to 95% by weight. When this amount is too small, the opacity and blocking resistance of the coated paper tend to be lowered. On the other hand, if the amount of insoluble tetrahydrofuran is too much, the print gloss tends to decrease or the dry pick strength tends to decrease.

  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.

  In the emulsion polymerization, polymerization auxiliary materials such as a molecular weight adjusting agent, a chelating agent, an oxygen scavenger, and a pH adjusting agent that are usually used can be used.

Although it does not specifically limit as a kind of emulsifier, Anionic emulsifier, a nonionic emulsifier, an amphoteric surfactant etc. are mentioned. Of these, anionic emulsifiers are preferred.
The use amount of the emulsifier is usually 0.05 to 5 parts by weight, preferably 0.05 to 2 parts by weight with respect to 100 parts by weight of the total amount of the monomer mixture used for the polymerization.

Although it does not specifically limit as a polymerization initiator, For example, an inorganic peroxide, an organic peroxide, an azo compound etc. are mentioned. Of these, inorganic peroxides can be preferably used. These can be used alone or in combination of two or more. The peroxide initiator 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 0.1-5 weight part normally with respect to 100 weight part of monomer mixture whole quantity used for superposition | polymerization, Preferably it is 0.3-2 weight part.

For the purpose of adjusting the tetrahydrofuran-insoluble matter of the dense particles (B), it is preferable to use a molecular weight modifier.
Examples of the molecular weight modifier include α-methylstyrene dimer, mercaptans, halogenated hydrocarbons, sulfur-containing compounds and the like. These may be used alone or in combination of two or more. Among these molecular weight regulators, it is preferable to use mercaptans and α-methylstyrene dimer in combination, and t-dodecyl mercaptan is preferably used as the mercaptans.
The usage-amount of a molecular weight modifier is 0.5-5 weight part normally per 100 weight part of monomer mixture whole quantity used for superposition | polymerization, Preferably it is 1-4 weight part.

  Although the usage-amount of the water used for emulsion polymerization is not specifically limited, It is 70-300 weight part normally per 100 weight part of monomer mixture whole quantity used for superposition | polymerization, Preferably it is 85-150 weight part.

The polymerization temperature is usually in the range of 0 to 100 ° C, preferably 50 to 95 ° C.
After the polymerization is started, the polymerization reaction is stopped at a predetermined polymerization conversion rate by cooling the polymerization system or adding a polymerization terminator. 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, the unreacted monomer is removed if desired to obtain an aqueous dispersion containing dense particles (B).

  The glass transition temperature of the dense particles (B) is greatly influenced by the type of monomer used, but 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 that is excellent in balance between white paper gloss and dry pick strength can be obtained.

  The weight ratio of the solid contents of the hollow particles (A) and the dense particles (B) contained in the pigment dispersion of the present invention is preferably 20/80 to 80/20, and preferably 30/70 to 70 /. More preferably, it is 30. Here, the said ratio is a weight ratio of solid content which does not contain water. When this ratio is in the above range, a coated paper excellent in balance between white paper gloss, whiteness, opacity, smoothness, printing gloss, and dry pick strength can be obtained, and the flow of the composition for coated paper can be obtained. As well as the settling resistance of the pigment dispersion.

  The pigment dispersion of the present invention 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 as necessary. . There are no particular limitations on the type and amount used.

<Dense polymer particles (C)>
The pigment dispersion of the present invention has an average particle content of more than 20% by weight of the conjugated diene monomer unit, and a viscosity measured by a B-type viscometer is 200 mPa · s or more at a solid content concentration of 50% by weight. It is preferable to further contain solid polymer particles (C) (hereinafter sometimes abbreviated as solid particles (C)) of a total of 0.13 μm or less.

  The dense particles (C) used in the present invention must have a conjugated diene monomer unit content of more than 20% by weight, preferably 25 to 55% by weight, more preferably 30 to 50% by weight. . If the amount of the conjugated diene monomer unit is too small, the dry pick strength of the coated paper may be inferior.

  Dense particles (C) consist of a conjugated diene monomer in an amount of more than 20% by weight and other monomers copolymerizable with the conjugated diene monomer in an amount of 80% by weight or less. It is preferable to obtain by emulsion polymerization of 100 parts by weight of the body mixture.

  Examples of the conjugated diene monomer include the same conjugated diene monomers as mentioned in the dense particles (B), and these can be used alone or in combination of two or more. Of these, 1,3-butadiene is preferable.

  The amount of the conjugated diene monomer used is preferably more than 20% by weight of the total monomer mixture, more preferably 25 to 55% by weight, and particularly preferably 30 to 50% by weight. If the amount of the conjugated diene monomer is too small, the dry pick strength of the coated paper may be inferior.

  The other monomer copolymerizable with the conjugated diene monomer is the same monomer as the other monomer copolymerizable with the conjugated diene monomer used in the dense particles (B). Is mentioned. Moreover, the monomer used preferably also includes the same monomer as the solid particles (B).

The solid particles (C) used in the present invention have a viscosity measured by a B-type viscometer at a solid content of 50% by weight of 200 mPa · s or more, preferably in the range of 200 to 600 mPa · s, 250 More preferably, it is in the range of ˜500 mPa · s. Here, the pH value of the dispersion of dense particles (C) at the time of viscosity measurement is 8.5.
When this viscosity is in the above range, the pigment dispersion has excellent sedimentation resistance, the coated paper composition has good fluidity, and the resulting coated paper has excellent dry pick strength.

The method for adjusting the B-type viscosity of the dense particles (C) at pH 8.5 and a solid content concentration of 50% by weight to the above range includes the types and amounts of monomers and surfactants used for polymerization, and polymerization. Adjusting the solid content concentration at the time.
As a kind of monomer, the method of adjusting the usage-amount of a highly hydrophilic monomer is mentioned, Especially, the method of adjusting the kind and quantity of an ethylenically unsaturated carboxylic acid monomer is mentioned.
The amount of the ethylenically unsaturated acid monomer is preferably 1 to 15% by weight, more preferably 2 to 13% by weight, and particularly preferably 3 to 10% by weight.

The average particle diameter of the dense particles (C) used in the present invention is 0.13 μm or less, preferably 0.05 to 0.12 μm, and more preferably 0.08 to 0.1 μm.
The method for adjusting the particle diameter to the above range is not particularly limited, and can be controlled to a desired value by a conventionally known method similar to the method for adjusting the particle diameter of the dense particles (B).

  As the method for producing the dense particles (C), the same emulsion polymerization method as that for the dense particles (B) can be employed.

<Pigment dispersion>
When the pigment dispersion of the present invention further contains dense polymer particles (C), the content of the hollow particles (A), the dense particles (B), and (C) is a specific solid content ratio. Preferably there is. The content of the hollow particles (A) in the pigment dispersion is preferably 20 to 78% by weight, more preferably 20 to 75% by weight, and particularly preferably 20 to 70% by weight. The content of the dense particles (B) is preferably 20 to 78% by weight, more preferably 20 to 75% by weight, and particularly preferably 20 to 70% by weight. The content of the dense particles (C) is preferably 2 to 35% by weight, more preferably 5 to 30% by weight, and particularly preferably 10 to 25% by weight.

  The mixing method and mixing order of the hollow particles (A), the dense particles (B) and the dense particles (C) of the pigment dispersion of the present invention are not particularly limited as long as the particles can be mixed uniformly. The pH of the pigment dispersion of the present invention is not limited as long as it does not impair the fluidity and sedimentation resistance, and is preferably 7 to 10, more preferably 8 to 9. The solid content concentration of the pigment dispersion is also not particularly limited, but is preferably 20 to 50% by weight, more preferably 30 to 45% by weight.

<Coated paper composition>
The composition for coated paper of the present invention comprises a pigment dispersion liquid containing the hollow particles (A) and the dense particles (B), and the pigment dispersion liquid is further dense particles. It is preferable that it comprises (C).
In the coated paper composition of the present invention, the pigment dispersion preferably contains a binder, and more preferably contains an inorganic pigment.

  The coated paper composition of the present invention contains 3 to 50 parts by weight of the pigment dispersion of the present invention in solid content with respect to 100 parts by weight of the inorganic pigment, and further has a glass transition temperature of −50 to + 30 ° C. as a binder. It is preferable that 3 to 20 parts by weight of the copolymer latex is blended as a solid content.

  As the binder used in the composition of the present invention, the same binder as that contained in the coated paper composition for coating on paper can be used, for example, styrene-butadiene copolymer, methyl methacrylate-butadiene. Conjugated diene copolymer latex such as copolymer; Acrylic copolymer latex; α-olefin copolymer latex such as ethylene-vinyl acetate copolymer; Modification of these copolymers modified with acid monomer A copolymer latex such as a copolymer latex is preferred. In addition, synthetic resin adhesives such as polyvinyl alcohol; starches such as starch, cationized starch, esterified starch, and oxidized starch; proteins such as casein, soy protein, and synthetic protein; cellulose derivatives such as carboxymethylcellulose and methylcellulose; Water-soluble adhesives can also be used. In this invention, these binders can be used individually by 1 type or in combination of 2 or more types. Of these, styrene-butadiene-acid monomer-modified copolymer latex is preferred.

  The method for producing the copolymer latex as a binder is not limited, and examples of the method for producing a styrene-butadiene-acid monomer modified copolymer latex include JP-A Nos. 2004-27034 and 2002-53602. Are preferably exemplified.

  When the copolymer latex is used as the binder, the weight average particle diameter of the latex particles measured with a laser diffraction / scattering particle size distribution analyzer is preferably 30 to 200 nm, more preferably 50 to 150 nm. If the particle size is too small, the coated paper tends to be inferior in white paper gloss, whiteness and opacity, and conversely if it is too large, the dry pick strength tends to be inferior.

  The glass transition temperature of the copolymer constituting the copolymer latex of the binder is preferably −50 ° C. to + 30 ° C., more preferably −40 to + 25 ° C. If the glass transition temperature is too low, the coated paper tends to be inferior in blocking resistance. Conversely, if it is too high, the dry pick strength tends to be inferior.

  The amount of the binder used is preferably 2 to 16 parts by weight, more preferably 4 to 13 parts by weight in terms of solid content with respect to 100 parts by weight of the inorganic pigment. If this amount is too small, the coated paper tends to be inferior in dry pick strength, and conversely if it is too much, it tends to be inferior in blocking resistance and ink setting.

  The coated paper composition of the present invention is an aqueous dispersion. Usually, the above-mentioned pigment dispersion or binder dispersion medium is used as it is, and distilled water, deionized water, etc. are added as necessary.

  The inorganic pigment used in the composition of the present invention contains 0 to 50% by weight of one or more of calcium carbonate, clay, barium sulfate, talc, titanium oxide, satin white, aluminum hydroxide, silica, mica and the like. May be.

  The solid content concentration of the coated paper composition is preferably 40 to 75% by weight, more preferably 50 to 70% by weight. If the solid content concentration of the composition for coated paper is too low, the dry pick strength of the resulting coated paper tends to decrease, and further, the drying load increases and may reduce the productivity of the coated paper. . On the other hand, if it is too high, the fluidity of the composition for coated paper may be lowered and the productivity of the coated paper may be impaired.

  In the coated paper composition of the present invention, if necessary, a pH adjuster, a dispersant, a water resistance agent, an antifoaming agent, a dye, a lubricant, a thickener, a water retention agent, an antioxidant, an antiseptic, Arbitrary compounding agents such as an antibacterial agent, a conductive treatment agent, an ultraviolet absorber, and a water repellent can be appropriately blended.

  The method for preparing the coated paper composition of the present invention is not limited. For example, the inorganic pigment is sufficiently dispersed in water in a container equipped with a stirrer, and then the pigment dispersion or binder dispersion of the present invention is used. A method of mixing a compounding agent is employed.

A coated paper can be obtained by coating the base paper with the composition for coated paper of the present invention to form a surface coating layer. The surface coating layer may be a single layer that is in direct contact with the base paper, or may be the uppermost layer on another undercoat layer.
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, the basic weight of a base paper is not specifically limited, Usually, it is 40-220 g / m < ² >.

In the present invention, an ordinary coating method may be used for forming the coating layer, for example, blade coater, roll transfer coater, air knife coater, bar coater, rod blade coater, short dwell coater, curtain coater, bill blade. It can be coated on the base paper using a conventionally known coating means such as a coater or a die coater. Among these, it is preferable to use a coating method suitable for high-speed coating such as a blade coater, an air knife coater, a curtain coater, or a bill blade coater. Coated amount per one surface coated paper for composition in terms of solid content in the range of preferably 3 to 30 g / ^{m 2,} more preferably in 5 to 25 g / ^{m 2.}

In the production of coated paper, the coated layer is formed and then dried. The drying temperature and drying time vary depending on the coating speed and the like, but are usually 80 to 180 ° C. and about 0.03 to 10 seconds.
The coated paper obtained by the above method can be finished with a calendering treatment as necessary, so that the gloss of the white paper can be further increased. An apparatus for performing the calendar process is not particularly limited, and the calendar process is performed by various calendar apparatuses such as a super calendar, a gloss calendar, and a soft calendar. The conditions for the calendar are not particularly limited, and are usually 30 to 200 ° C. and a linear pressure of 50 to 200 kg / cm ² .

  The coated paper of the present invention is excellent in whiteness, opacity, white paper gloss, smoothness, printing gloss, and dry pick strength, so it can be used for publications such as books and magazines, and commercial advertisements such as flyers, brochures, and posters. It is suitable for.

  The present invention will be described more specifically with reference to the following examples. In the following, “parts” and “%” are based on weight unless otherwise specified. The test and evaluation of each characteristic were performed as follows.

(Average particle size)
Using a transmission electron microscope, the maximum particle size of each of 200 hollow particles or solid particles was measured, and they were arithmetically averaged to determine the weight average particle size.

(B type viscosity)
The obtained solid particles were adjusted to a solid content concentration of 50% and pH 8.5 using ion-exchanged water and 10% aqueous sodium hydroxide solution to prepare a sample for viscosity measurement. A B-type viscometer (Tokyo Keiki Co., Ltd.) The viscosity of the dispersion of dense particles is measured.

(Settling resistance)
Place 100 ml of pigment dispersion in a 100 ml graduated cylinder and let stand for 30 days. Next, 1.5 ml of the pigment dispersion is sampled from a position 3 mm from the upper end surface of the pigment dispersion using an injector, and the solid content concentration in the upper part is measured. The absolute value of the difference between the solid content concentration in the upper part after standing and the solid content concentration of the entire pigment dispersion is evaluated according to the following criteria. The smaller this difference, the better the settling resistance.
Less than 0.1: ◎
Less than 0.4%: ○
Less than 1.0%: △
1% or more: ×

(Fluidity of coated paper composition)
The high shear viscosity, which is the viscosity under high shear of the coated paper composition having a solid content concentration of 62%, was measured at a rotational speed of 8800 rpm using a high shear rotational viscometer (PM-9000HV: Bob F, manufactured by SMT Corporation). The smaller this value, the better the fluidity.

(White paper gloss)
With respect to the coated paper, the reflectance (%) of light on the surface of the coated paper was measured using a gloss meter (GM-26D, manufactured by Murakami Color Co., Ltd.) under the conditions of an incident angle of 75 degrees and a reflection angle of 75 degrees. The larger the value, the better the gloss of white paper.

(Whiteness)
ISO whiteness was measured (unit:%) using a spectral color whiteness meter (PF10: manufactured by Nippon Denshoku Industries Co., Ltd.) according to the method defined in JIS P8148-1993. The higher the value, the better the whiteness.

(Opacity)
It was measured using a spectral color whiteness meter (PF10: manufactured by Nippon Denshoku Industries Co., Ltd.) according to the method defined in JIS P8138-1976 (unit:%). The larger the value, the better the opacity.

(Smoothness)
Measurement was performed using a universal surface shape measuring instrument (SE-3C: manufactured by Kosaka Laboratory Ltd.) (unit: μm) by the method defined in JIS B 0601. The smaller the value, the better the smoothness.

(Print gloss)
Using RI testers in which process inks of three colors of indigo, red and yellow (manufactured by Toyo Ink Co., Ltd., TK Mark V) were attached to different rubber rolls, they were printed on coated paper at 20 ° C. and 65% R.D. H. After being allowed to stand in a constant temperature and humidity chamber for 24 hours, the glossiness was measured using a gloss meter (GM-26D: manufactured by Murakami Color Research Laboratory) at an incident angle of 60 degrees. The higher the value, the better the print gloss.

(Dry pick strength)
Printing ink (tack value 20) 0.4 cm ³ was adhered to a rubber roll of an RI tester (manufactured by Akashi Seisakusho), and then overprinted four times on the coated paper using this RI tester. The five-point method was evaluated by observing the state of peeling (picking) of the paper and taking the case where there was no peeling as 5 points. The higher the score, the higher the dry pick strength.

(Hollow polymer particles: A)
(Production Example 1)
In a pressure vessel equipped with a stirrer, 50 parts of methyl methacrylate (MMA), 10 parts of butyl acrylate (BA), 40 parts of methacrylic acid (MAA), polyoxyethylene alkyl ether sodium sulfate (alkyl group) as surfactant 1 C ₁₂ H ₃₅ , ethylene oxide addition number 18) 0.9 part, sodium tripolyphosphate 0.15 part and ion-exchanged water 80 part are stirred to give an emulsion of monomer mixture (a) for core polymer formation Was prepared.
To a pressure resistant reactor equipped with a stirrer, 40 parts of ion-exchanged water and 0.28 part of seed latex (methyl methacrylate polymer particles having a volume average particle diameter of 82 nm) were added, and the temperature was raised to 85 ° C.
Next, 1.63 parts of a 3% aqueous solution of potassium persulfate was added, and 7% of the above emulsion was continuously added to the reactor over 3 hours, followed by further reaction for 1 hour.
Thereafter, 250 parts of ion-exchanged water and 18.6 parts of a 3% aqueous solution of potassium persulfate were added, and the remaining emulsion was continuously fed to the reactor over 3 hours while maintaining the reaction temperature at 85 ° C. Added to. After completing the continuous addition of the monomer emulsion, the reaction was continued for another 2 hours to obtain a core polymer that was an alkali swellable substance. The polymerization conversion rate was 99%.

In a pressure vessel equipped with a stirrer, MMA 7.8 parts, BA 1.6 parts, MAA 0.6 parts, t-dodecyl mercaptan (TDM) 0.03 parts, surfactant 1 0.02 parts and ion-exchanged water 16 Part was added, stirred and mixed to prepare an emulsion of the monomer mixture (b). Separately, 79.44 parts of styrene (ST), 0.56 parts of MAA, 0.4 parts of surfactant 1 and 130 parts of ion-exchanged water were stirred and mixed to prepare an emulsion of the monomer mixture (c). .
An aqueous dispersion containing 130 parts of ion exchange water and 7 parts of the above core polymer was added to a pressure resistant reactor equipped with a stirrer, and the temperature was raised to 85 ° C.
Then, 10 parts of a 4% aqueous potassium persulfate solution was added and the above emulsion of monomer mixture (b) was continuously added to the reactor over 20 minutes. Thereafter, the emulsion of the monomer mixture (c) was continuously added to the reactor over 120 minutes.
Immediately after completing the continuous addition of the emulsion of the monomer mixture (c), 25 parts of 5% aqueous ammonia was added to raise the reaction temperature to 90 ° C. Base treatment was performed for 1 hour to swell the core polymer, and water was absorbed therein to form water-containing voids. Then, 10 parts of a 4% potassium persulfate aqueous solution was added, and the reaction was continued for another 2 hours. The polymerization conversion rate was 99%.
The polymerization system was cooled to room temperature to obtain an aqueous dispersion containing hollow polymer particles A1.
The resulting hollow polymer particles (A1) had a weight average particle diameter of 1.0 μm, a porosity of 50%, and the solid content concentration of the aqueous dispersion of the hollow polymer particles (A1) was 26.5%.

(Production Example 2)
In Production Example 1, the amount of seed latex used was changed to 4.5 parts instead of 0.28 parts, and in the same manner as Production Example 1, the average particle size was 0.5 μm and the porosity was 50%. Hollow polymer particles (A2) were obtained.

(Dense polymer particles: B)
(Production Example 3)
In a pressure-resistant reaction vessel equipped with a stirrer, a monomer (d) consisting of 40 parts of styrene, 55 parts of butadiene, 3 parts of itaconic acid, 2 parts of methacrylic acid, 0.15 part of t-dodecyl mercaptan, dodecylbenzenesulfonic acid After charging 4 parts of soda, 0.3 part of potassium persulfate and 150 parts of ion-exchanged water, the mixture was heated to 60 ° C. with stirring and polymerized while maintaining 60 ° C. Next, when the polymerization conversion rate exceeded 70%, the mixture was heated to 70 ° C., and the polymerization was continued while maintaining 70 ° C. After 12 hours from the heating to 60 ° C., the mixture was cooled to room temperature to obtain a polymer. The polymerization conversion rate of the polymer was 96% or more.
Next, 50 parts of ion-exchanged water, 15 parts of the polymer, 0.1 part of sodium dodecylbenzenesulfonate, and 0.51 part of potassium persulfate were charged in a pressure-resistant reaction vessel equipped with another apparatus and heated to 80 ° C. did. Next, while maintaining the inside of the reaction vessel at 80 ° C., a monomer (e) composed of 75 parts of styrene, 5 parts of butadiene, 14 parts of methyl methacrylate and 6 parts of methacrylic acid, and sodium dodecylbenzenesulfonate. An emulsion composed of 16 parts and 50 parts of ion-exchanged water was continuously added to the reaction vessel over 4 hours. After completion of the addition of the emulsion, the mixture was further polymerized for 4 hours and cooled to room temperature to obtain an aqueous dispersion of dense polymer particles (B1). The polymerization conversion rate in the polymerization of the monomer (e) was 96% or more. The content of tetrahydrofuran insoluble in the dense polymer particles (B1) was 65%.

(Production Example 4)
Dense polymer particles (B2) were produced in the same manner as in Production Example 3 except that the monomer composition in Production Example 3 was changed as shown in Table 1.

(Production Example 5)
A dense polymer particle (B3) was produced in the same manner as in Production Example 4 except that the monomer composition in Production Example 3 was changed as shown in Table 1.

(Dense polymer particles: C)
(Production Example 6)
In a pressure vessel equipped with a stirring device, 27 parts of ion exchange water, 0.2 part of sodium dodecylbenzenesulfonate, 33 parts of styrene, 10 parts of methyl methacrylate, 15 parts of acrylonitrile, 39 parts of 1,3-butadiene, acrylic acid 2 parts, 0.7 part of t-dodecyl mercaptan (hereinafter abbreviated as “TDM”) and 1 part of α-methylstyrene dimer (hereinafter abbreviated as “MSD”) are added. The monomer mixture (f) was prepared by stirring.
In a pressure-resistant reactor equipped with a stirrer, 95 parts of ion-exchanged water, 0.1 part of sodium ethylenediaminetetraacetate, 1.2 parts of sodium dodecylbenzenesulfonate, 1 part of itaconic acid, and 0.4 part of potassium persulfate And heated to 65 ° C. with stirring.
While maintaining the polymerization temperature at 65 ° C., the monomer mixture (f) was continuously added to the reaction vessel over 270 minutes. After completing the addition of the monomer mixture (f), the polymerization temperature was raised to 80 ° C., and the reaction was continued until the polymerization conversion reached 96%. Thereafter, the polymerization reaction was stopped by cooling to room temperature.

  After adding sodium hydroxide aqueous solution to the obtained polymer dispersion liquid and adjusting to pH 8.5, the unreacted monomer was removed by steam distillation. Next, the solid content concentration was adjusted to 50% and pH 8.5 to obtain dense polymer particles (C1). The viscosity of the dense particles (C1) measured by a B-type viscometer at a pH of 8.5 and a solid concentration of 50% was 300 mPa · s, and the average particle size was 0.09 μm.

(Production Example 7)
In Production Example 4, solid polymer particles (D1) having an average particle diameter of 0.2 μm were obtained in the same manner as in Production Example 4 except that the butadiene having a monomer composition was changed to styrene.

Example 1
The hollow particles (A1) produced in Production Example 1 and the dense particles (B1) produced in Production Example 3 are mixed so that the solid content ratio is 50/50, and a pigment dispersion having a solid content concentration of 35%. I was obtained. The resulting pigment dispersion was measured for sedimentation resistance, and the results are shown in Table 2.
To 100 parts of an inorganic pigment composed of 60 parts of kaolin clay (Astra Coat: Imeris Minerals Japan) and 40 parts of calcium carbonate (FMT90: manufactured by Pimatech), calcium stearate (Nopcoat C-104HS: San Nopco) as a lubricant 0.5 parts, phosphoric esterified starch (MS-4600: manufactured by Nippon Shokuhin Kako Co., Ltd.) 2 parts, carboxy-modified styrene-butadiene copolymer latex (Nipol LX407F: manufactured by Nippon Zeon Co., Ltd.) 9 parts, pigment The dispersion I was added with 8 parts of solid content and ion-exchanged water, mixed and stirred to obtain a coated paper composition I having a solid content concentration of 62%.
Next, the resulting coated paper composition to basis weight 65 g / m ² on a base paper, and coated on both sides with one side 10 g / m ^2, to obtain a coated paper and dried at 120 ° C.. The fluidity of the coated paper composition, the white gloss, whiteness, opacity, smoothness, printing gloss and dry pick strength of the coated paper were tested and evaluated. The results are listed in Table 2.

(Example 2)
A pigment dispersion II was obtained in the same manner as in Example 1 except that the hollow polymer particles (A2) were used instead of the hollow polymer particles (A1) used in Example 1, and various physical properties were measured and evaluated. did. The results are shown in Table 2.

(Example 3)
A pigment dispersion III was obtained in the same manner as in Example 1 except that the dense polymer particles (B2) were used instead of the dense polymer particles (B1) used in Example 1, and various physical properties were measured. ,evaluated. The results are shown in Table 2.

Example 4
The solid content ratio of the hollow polymer particles (A1), the dense polymer particles (B1), and the dense polymer particles (C1) is mixed so as to be 50/25/25, and the solid content concentration A 35% pigment dispersion IV was obtained. The resulting pigment dispersion IV was measured for sedimentation resistance, and the results are shown in Table 2.
Various physical properties were measured and evaluated in the same manner as in Example 1 except that Pigment Dispersion Liquid IV was used instead of Pigment Dispersion Liquid I used in Example 1. The results are shown in Table 2.

(Example 5)
A pigment dispersion V was obtained in the same manner as in Example 4 except that the hollow polymer particles (A2) were used instead of the hollow polymer particles (A1) used in Example 4, and various physical properties were measured and evaluated. did. The results are shown in Table 2.

(Comparative Example 1)
By using the hollow polymer particles (A1) produced in Production Example 1 alone, a comparative pigment dispersion I containing no dense polymer particles was obtained. Various physical properties were measured and evaluated in the same manner as in Example 1 except that Comparative Pigment Dispersion I was used instead of Pigment Dispersion I used in Example 1. The results are shown in Table 2.

(Comparative Example 2)
The solid polymer particles (B1) and the solid polymer particles (C1) were mixed so that the solid content ratio was 50/50 to obtain a comparative pigment dispersion II having a solid content concentration of 50%. The resulting comparative pigment dispersion II was measured for sedimentation resistance, and the results are shown in Table 2.
Further, various physical properties were measured and evaluated in the same manner as in Example 1 except that Comparative Pigment Dispersion Liquid II was used instead of Pigment Dispersion Liquid I used in Example 1. The results are shown in Table 2.

(Comparative Example 3)
The hollow polymer particles (A1) and the solid polymer particles (D1) were mixed so that the ratio of the solid content was 50/50 to obtain a comparative pigment dispersion III having a solid content concentration of 35%. The resulting comparative pigment dispersion III was measured for sedimentation resistance, and the results are shown in Table 2.
Further, various physical properties were measured and evaluated in the same manner as in Example 1 except that Comparative Pigment Dispersion Liquid III was used instead of Pigment Dispersion Liquid I used in Example 1. The results are shown in Table 2.

(Comparative Example 4)
The hollow polymer particles (A1) and the dense polymer particles (B3) were mixed so that the ratio of the solid content was 50/50 to obtain a comparative pigment dispersion IV having a solid content concentration of 35%. The precipitation resistance of the obtained comparative pigment dispersion IV was measured, and the results are shown in Table 2.
Further, various physical properties were measured and evaluated in the same manner as in Example 1 except that Comparative Pigment Dispersion Liquid IV was used instead of Pigment Dispersion Liquid I used in Example 1. The results are shown in Table 2.

Table 2 shows the following.
The comparative pigment dispersion I containing no dense polymer particles (B) is poor in sedimentation resistance, the fluidity of the coated paper composition is low, and the dry pick strength is also poor (Comparative Example 1).
The comparative pigment dispersion II containing no hollow polymer particles (A) is excellent in sedimentation resistance and fluidity of the coated paper composition, but the white paper gloss, whiteness, opacity and printing of the resulting coated paper. It is inferior in gloss (Comparative Example 2).
If the comparative pigment dispersion III containing dense polymer particles not containing the conjugated diene polymer is used instead of the dense polymer particles containing a specific amount of the conjugated diene monomer unit, the dry pick strength decreases. (Comparative Example 3).
When the dense polymer particles (B3) having a conjugated diene monomer unit content larger than the range specified in the present invention are used, blank paper gloss, whiteness and opacity are inferior. (Comparative Example 4).
On the other hand, the pigment dispersions I to V defined in the present application comprising the hollow polymer particles (A) and the dense polymer particles (B) are excellent in sedimentation resistance, and the fluidity of the composition for coated paper is high. The coated paper obtained by using this is excellent in white paper gloss, whiteness, opacity and smoothness, and in print gloss and dry pick strength (Examples 1 to 5).

Claims (4)

Hollow polymer particles (A) having an average particle size of 0.3 to 3.0 μm and dense particles having an average particle size of 0.06 to 1.5 μm and a content of conjugated diene monomer units of 5 to 20% by weight A pigment dispersion containing actual polymer particles (B). The pigment dispersion according to claim 1, wherein the weight ratio of the solid content of each of the hollow polymer particles (A) and the dense polymer particles (B) is 20/80 to 80/20. When the content of the conjugated diene monomer unit is more than 20% by weight and the solid content concentration is 50% by weight, the viscosity measured by a B-type viscometer is 200 mPa · s or more and the average particle size is 0.13 μm or less. The pigment dispersion according to claim 1 or 2, further comprising polymer particles (C). A coated paper composition comprising the pigment dispersion according to any one of claims 1 to 3.