JP2009144029A - Aqueous dispersion containing hollow polymer particles and method for producing the same - Google Patents

Abstract

The present invention provides an aqueous dispersion that provides a coated paper excellent in white paper gloss, whiteness, opacity, dry pick strength and printing gloss.
SOLUTION: A step in which 20 to 50% by mass of an acid group-containing monomer and 80 to 50% by mass of another monomer are copolymerized to form a core polymer particle (A); A step in which 99% to 90% by mass of other monomers and 99 to 90% by mass of the monomer are copolymerized in the presence of (A) to form a shell layer (B) surrounding (A), 0.2 to 2.5% by mass of acrylic acid And 99.8-97.5% by weight of other monomers are copolymerized in the presence of (B) surrounding (A) to form a shell layer (C) surrounding (B), and Hollow polymer particles in which a base is added to an aqueous dispersion containing polymer particles having at least a three-layer structure of (A), (B), and (C), and the pH is adjusted to 7 or more. A method for producing an aqueous dispersion comprising An aqueous dispersion containing hollow polymer particles comprising the above production method.
[Selection figure] None

Description

  The present invention relates to an aqueous dispersion that provides a coated paper having excellent white paper gloss, whiteness, opacity, dry pick strength and printing gloss, and a method for producing the same.

  In recent years, printing methods for printed materials such as publications such as books and magazines; commercial advertisements such as flyers, brochures, and posters have been diversified. From the viewpoint of adaptability to single color printing and multicolor printing in a wide range of applications, it is required to improve the white paper gloss, whiteness, opacity, dry pick strength and print gloss of the coated paper.

  Conventionally, coated paper compositions containing hollow polymer particles have been used in the manufacture of coated paper. A monomer mixture (a) comprising 20 to 60% by weight of an acid group-containing monomer and 80 to 40% by weight of another monomer copolymerizable therewith is copolymerized in the presence of a specific surfactant. Monomer mixture (b) comprising the core polymer (A) thus formed, 0 to 15% by weight of the acid group-containing monomer and 100 to 85% by weight of other monomers copolymerizable therewith Void formed by neutralization of acidic groups contained in the core polymer (A), which has an outer layer polymer (B) surrounding the core polymer (A), An aqueous dispersion containing hollow polymer particles having a particle size has been studied (for example, see Patent Document 1). The hollow polymer particles settled during long-term storage of the aqueous dispersion.

On the other hand, (a) a hydrophilic core polymer formed from 5 to 100% by weight of hydrophilic monoethylenically unsaturated monomer and 0 to 95% by weight of nonionic monoethylenically unsaturated monomer, and (b) 90 to 99% A hydrophobic shell polymer formed from 9 wt% nonionic monoethylenically unsaturated monomer and 0.1 to 10 wt% acid functional monoethylenically unsaturated monomer, the shell polymer comprising the core polymer Aqueous dispersions containing fully encapsulated multistaged polymer particles have been investigated (see, for example, Patent Document 2). The gloss of the white paper coated with the aqueous dispersion was not sufficiently high. Furthermore, improvement of the printing gloss of the coated paper has been studied, but no effective solution has been found.
JP 2005-206752 A JP-A-8-81506

  The problem to be solved by the present invention is to provide an aqueous dispersion that provides a coated paper with excellent white paper gloss, whiteness, opacity, dry pick strength and printing gloss. Another problem to be solved by the present invention is to provide a method for producing the aqueous dispersion.

  In the present invention, (1) a monomer mixture (a) comprising 20 to 50% by mass of an acid group-containing monomer and 80 to 50% by mass of a monomer copolymerizable therewith is copolymerized to form a core polymer. A step of forming particles (A), (2) a monomer mixture (b) comprising 1 to 10% by weight of an acid group-containing monomer and 99 to 90% by weight of a monomer copolymerizable therewith, A step of copolymerization in the presence of the core polymer particle (A) to form a shell layer (B) substantially surrounding the core polymer particle (A); (3) acrylic acid monomer 0 The monomer mixture (c) comprising 2 to 2.5% by mass and 99.8 to 97.5% by mass of a monomer copolymerizable therewith is substantially surrounded by the shell layer (B). A shell layer (C) that is copolymerized in the presence of the core polymer particles (A) and substantially surrounds the shell layer (B) is formed. (4) a base is added to an aqueous dispersion containing polymer particles having a three-layer structure of at least the core polymer particles (A), the shell layer (B) and the shell layer (C), This is a method for producing an aqueous dispersion containing hollow polymer particles, wherein the step of adjusting the pH of the aqueous dispersion to 7 or more is performed.

  Furthermore, the present invention is an aqueous dispersion containing hollow polymer particles produced by the above production method.

  The aqueous dispersion of the present invention provides a coated paper with excellent white paper gloss, whiteness, opacity, dry pick strength and printing gloss. Furthermore, the method for producing an aqueous dispersion of the present invention provides an aqueous dispersion that gives the coated paper.

The hollow polymer particles contained in the aqueous dispersion of the present invention have at least a three-layer structure of core polymer particles (A), shell layer (B), and shell layer (C).
The core polymer particles (A) are formed by copolymerization of a monomer mixture (a) comprising 20 to 50% by mass of an acid group-containing monomer and 80 to 50% by mass of a monomer copolymerizable therewith. The

  The acidic group-containing monomer is a monomer having an acidic functional group. Specific examples of the acidic group-containing monomer include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, and cinnamic acid; ethylenically unsaturated monomers such as itaconic acid, fumaric acid, maleic acid, and butenetricarboxylic acid. Saturated polyvalent carboxylic acids; partially esterified products of ethylenically unsaturated polyvalent carboxylic acids such as monobutyl fumarate and monobutyl maleate; sulfonic acid group-containing monomers such as styrenesulfonic acid; One or two or more acidic group-containing monomers are used.

  When an acidic group-containing monomer having excessively high hydrophilicity is used, acidic groups are likely to be localized outside the core layer (A), and the surrounding of the core polymer particles (A) by the shell layer (B) Further, it becomes difficult to form voids in the polymer particles. A preferred acidic group-containing monomer is an ethylenically unsaturated monocarboxylic acid, and a more preferred acidic group-containing monomer is methacrylic acid.

  Specific examples of the monomer copolymerizable with the acidic group-containing monomer include aromatic vinyl monomers such as styrene, α-methylstyrene, p-methylstyrene, and halogenated styrene; acrylonitrile, methacrylonitrile, and the like. Ethylenically unsaturated nitrile monomer; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, glycidyl (meth) acrylate, 2-hydroxy Ethylenically unsaturated carboxylic acid ester monomers such as ethyl (meth) acrylate; ethylenically unsaturated carboxylic acid amides such as (meth) acrylamide, N-methylol (meth) acrylamide and N-butoxymethyl (meth) acrylamide Body: butadiene, isoprene, etc. Role diene monomer, vinyl carboxylic acids such as vinyl acetate ester monomers, halogenated vinyl monomers such as vinyl chloride; a and the like; vinyl pyridine; halogenated vinylidene monomers such as vinylidene chloride. One or more monomers are used. Preferred monomers are ethylenically unsaturated carboxylic acid ester monomers, and more preferred monomers are methyl (meth) acrylate and butyl (meth) acrylate.

  A preferable core layer (A) is formed from a monomer mixture composed of 35 to 77% by mass of methyl methacrylate, 3 to 15% by mass of butyl acrylate, and 20 to 50% by mass of methacrylic acid. A more preferable core layer (A) is formed from a monomer mixture composed of 42 to 71% by mass of methyl methacrylate, 4 to 13% by mass of butyl acrylate, and 25 to 45% by mass of methacrylic acid. A more preferable core layer (A) is formed from a monomer mixture composed of 50 to 65% by mass of methyl methacrylate, 5 to 10% by mass of butyl acrylate, and 30 to 40% by mass of methacrylic acid.

  Crosslinkable monomers such as divinylbenzene, diallyl phthalate, allyl (meth) acrylate, and ethylene glycol di (meth) acrylate can be used during the copolymerization of the monomer mixture (a). However, when a large amount of the crosslinkable monomer is used, it becomes difficult to form voids inside the core layer, and therefore the amount needs to be kept within a range in which stable void formation can be maintained.

  The copolymerization of the monomer mixture (a) is usually performed in an aqueous medium. Usually, water is used as an aqueous medium, and a water-soluble organic solvent such as methanol and ethanol can be used in combination as long as the dispersion stability of the polymer particles during production is not impaired. The usage-amount of an aqueous medium is 100-1000 mass parts normally with respect to 100 mass parts of monomer mixtures (a), Preferably it is 200-600 mass parts. If the amount of aqueous medium used is too small, the amount of aggregates generated during polymerization tends to increase, and if the amount of aqueous medium used is too large, the productivity of hollow polymer particles tends to be poor.

The copolymerization method of the monomer mixture (a) is usually an emulsion polymerization method. The polymerization method may be any of batch, semi-continuous and continuous methods. The polymerization pressure, polymerization temperature, and polymerization time are not particularly limited, and known conditions are employed.
Various additives generally used in the emulsion polymerization reaction, such as a surfactant, a polymerization initiator, a chain transfer agent, a chelating agent, an electrolyte, and an oxygen scavenger, can be used as a secondary material for polymerization.

As the surfactant used in the copolymerization of the monomer mixture (a), generally known surfactants can be used in combination. Specifically, rosinates such as potassium rosinate and sodium rosinate; fatty acid salts such as potassium oleate, potassium laurate, sodium laurate, sodium stearate and potassium stearate; aliphatic alcohols such as sodium lauryl sulfate Anionic surfactants such as sodium dodecylbenzenesulfonate; alkyl ether sulfates such as sodium polyoxyethylene alkyl ether sulfate; alkyl esters of polyethylene glycol, alkyl ethers or alkylphenyls Hydrophilic synthesis such as nonionic surfactants such as ether, polyacrylic acid, polymethacrylic acid, polyvinyl sulfonic acid, polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol Molecular substance; like dispersion stabilizer and the like; carboxymethyl hydrophilic semi-synthetic polymeric substances such as methylcellulose; gelatin, natural hydrophilic polymeric substance, such as a water soluble starch.
These surfactants are used alone or in combination of two or more.
Of these, alkyl ether sulfates such as sodium polyoxyethylene alkyl ether sulfate are preferred because of good polymerization stability.
The usage-amount of surfactant is 0.1-5 mass% with respect to the whole quantity of the said monomer mixture (a), Preferably it is 0.5-3 mass%. If this amount is too small, aggregates are likely to be formed, and conversely if too large, the porosity of the hollow polymer particles will be low.

  The copolymerization of the monomer mixture (a) is desirably performed in the presence of seeds. Use of a seed facilitates control of the diameter of the polymer particles produced. The composition of the seed is not particularly limited. The polymerization conversion rate of the monomer mixture (a) in the polymerization reaction is usually 90% by mass or more, preferably 97% by mass or more. The composition of the produced copolymer is almost the same as that of the monomer mixture (a).

  The method for adding the surfactant is not particularly limited. The surfactant is added to the reactor in batches, in portions or continuously. A surfactant is preferably added continuously to the reaction system in that the amount of aggregates produced during production is reduced. The monomer mixture (a) and the surfactant may be mixed and added to the reaction system, or may be added separately to the reaction system. Preferably, an emulsion obtained by mixing the monomer mixture (a), the surfactant and the aqueous medium is added to the reaction system.

The monomer mixture (a) is preferably copolymerized in the presence of a small amount of inorganic salt. When the surfactant and the inorganic salt are used in combination, the formation of aggregates is suppressed, and an aqueous dispersion containing hollow polymer particles having a narrow particle size distribution is obtained.
The inorganic salt is not particularly limited. Specific examples of inorganic salts include sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium nitrate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, sodium phosphate, sodium tripolyphosphate, and other alkali metal salts; calcium chloride, barium sulfate Alkaline earth metal salts such as aluminum sulfate and aluminum chloride. Of these, alkali metal salts are preferable, and sodium tripolyphosphate is more preferable.

  The usage-amount of an inorganic salt is 0.01-1 mass% with respect to the whole quantity of a monomer mixture (a), Preferably it is 0.05-0.5 mass%. If the amount used is too small, it is difficult to achieve the effect, while if it is too large, the generation of aggregates tends to be promoted. The method for adding the inorganic salt is not particularly limited. The inorganic salt is added to the reaction system all at once, in portions or continuously.

  The distribution in the radial direction of the acidic group-containing monomer units of the core polymer particles (A) is not particularly limited. Copolymerization can be performed while the composition of the monomer mixture (a) is sequentially changed and added to the polymerization reaction system. When a radial distribution of the content of acidic group-containing monomer units occurs in the core polymer particles (A) by such a polymerization method, the least part of the acidic group-containing monomer units is the part. The acid group-containing monomer unit is contained in an amount of 10% by mass or more, preferably 15% by mass or more, based on the total monomer units forming the. When this ratio is less than 10% by mass, small particles may be generated in the voids of the hollow polymer particles, and the porosity may be lowered.

  The volume average particle diameter of the core layer (A) is preferably 100 to 600 nm, more preferably 250 to 500 nm. If the particle size is too small, it tends to be difficult to produce hollow polymer particles having a high porosity and a large particle size. Conversely, if the particle size is too large, the core polymer formed by the shell layer (B). It tends to be difficult to coat the particles (A) and to form voids in the core polymer particles (A).

  The shell layer (B) substantially surrounds the core polymer particle (A). A monomer mixture (b) comprising 1 to 10% by mass of an acid group-containing monomer and 99 to 90% by mass of a monomer copolymerizable therewith is co-polymerized in the presence of the core polymer particle (A). By polymerization, a shell layer (B) that substantially surrounds the core polymer particles (A) is formed.

The acidic group-containing monomer contained in the monomer mixture (b) is the same as the acidic group-containing monomer contained in the monomer mixture (a). A preferred acidic group-containing monomer contained in the monomer mixture (b) is an ethylenically unsaturated monocarboxylic acid, and more preferred acidic group-containing monomers are acrylic acid and methacrylic acid.
The monomer copolymerizable with the acidic group-containing monomer contained in the monomer mixture (b) is a monomer copolymerizable with the acidic group-containing monomer contained in the monomer mixture (a). It is the same.

  A preferred shell layer (B) is formed from a monomer mixture consisting of 68 to 89% by weight of methyl methacrylate, 10 to 22% by weight of butyl acrylate, and 1 to 10% by weight of methacrylic acid and / or acrylic acid. (B) is formed from a monomer mixture consisting of 71 to 85% by weight of methyl methacrylate, 12 to 20% by weight of butyl acrylate, 3 to 9% by weight of methacrylic acid and / or acrylic acid, and more preferable shell layer (B). Is formed from a monomer mixture consisting of 74 to 81% by weight of methyl methacrylate, 14 to 18% by weight of butyl acrylate, and 5 to 8% by weight of methacrylic acid and / or acrylic acid.

  The copolymerization of the monomer mixture (b) is 0.1 to 2% by mass, more preferably 0.1 to 1.5% by mass, particularly preferably 0.1 to 1.5% by mass, based on the total amount of the monomer mixture (b). Preferably it is carried out in the presence of 0.2 to 1% by mass. If the amount of the chain transfer agent is too small, the void ratio of the resulting hollow polymer particles tends to be low. Conversely, if the amount of the chain transfer agent is excessive, the amount of aggregates generated during polymerization tends to increase. In addition, there is a tendency for the porosity to be low.

  A known chain transfer agent used in general emulsion polymerization is used. Specific examples of the chain transfer agent include mercaptans such as octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-hexadecyl mercaptan, n-tetradecyl mercaptan, t-tetradecyl mercaptan; dimethylxanthogen disulfide, diethylxanthogen disulfide Xanthogen disulfides such as diisopropylxanthogen disulfide; thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide and tetrabutylthiuram disulfide; halogenated hydrocarbons such as carbon tetrachloride and carbon tetrabromide; diphenylethylene, pentaphenyl Hydrocarbons such as ethane and α-methylstyrene dimer; acrolein, methacrolein, allyl alcohol, 2-ethane Hexyl thioglycolate, terpinolene, alpha-terpinene, .gamma.-terpinene, is dipentene. One or more chain transfer agents are used. Preferred chain transfer agents are mercaptans and α-methylstyrene dimers, more preferred chain transfer agents are mercaptans, and a particularly preferred chain transfer agent is t-dodecyl mercaptan.

  The shell layer (C) substantially surrounds the shell layer (B). A monomer mixture (c) comprising 0.2 to 2.5% by mass of an acrylic acid monomer and 99.8 to 97.5% by mass of a monomer copolymerizable therewith is the shell layer (B). Is copolymerized in the presence of the core layer (A) substantially surrounded by (1) to form a shell layer (C) substantially surrounding the shell layer (B).

  The monomer copolymerizable with acrylic acid contained in the monomer mixture (c) is the same as the monomer copolymerizable with the acidic group-containing monomer contained in the monomer mixture (a). . Preferred monomers are aromatic vinyl monomers and ethylenically unsaturated monocarboxylic acid ester monomers, and more preferred monomers are styrene. When a monomer other than the aromatic vinyl monomer is used in combination, preferably 90% by mass or more of the aromatic vinyl monomer is used with respect to the total amount of monomers contained in the monomer mixture (c). Is done.

  A preferable shell layer (C) is formed from a monomer mixture composed of 0.3 to 2.2% by mass of acrylic acid and 97.8 to 99.7% by mass of styrene, and a more preferable shell layer (C) is an acrylic layer. It is formed from a monomer mixture composed of 0.4 to 1.8% by mass of acid and 98.2 to 99.6% by mass of styrene, and a more preferable shell layer (C) is 0.6 to 1.5% by mass of acrylic acid. % And 98.5 to 99.4% by weight of styrene.

  The mass ratio (parts by mass) of the monomer mixture (a), monomer mixture (b) and monomer mixture (c) is preferably 1-25 / 2 to 25 / 40-65, more preferably. Is from 3 to 20/3 to 20/44 to 60, more preferably from 5 to 15/5 to 15/48 to 55. When the proportion of the monomer mixture (a) is too small, hollow polymer particles having a high porosity tend to be difficult to obtain. Conversely, when the proportion of the monomer mixture (a) is too large, the base treatment is performed. However, the amount of aggregates tends to increase.

  The shell layer (B) and the shell layer (C) are usually formed by emulsion polymerization. As the polymerization method, any of batch method, semi-continuous method, and continuous method is adopted. The polymerization pressure, polymerization temperature, and polymerization time are not particularly limited, and known conditions are employed.

  The polymerization auxiliary material exemplified in the formation of the core polymer particles (A) is used. The type of the surfactant is not particularly limited and is used. An aqueous medium can be additionally added. The additional amount of the aqueous medium is usually in the range where the solid content concentration of the polymer particles having at least a three-layer structure is 10 to 50% by mass, preferably 20 to 40% by mass.

  A base is added to an aqueous dispersion containing polymer particles having at least a three-layer structure of a core polymer particle (A), a shell layer (B), and a shell layer (C), and the pH of the aqueous dispersion is 7 Thus, hollow polymer particles having at least one void formed by neutralizing at least part of the acidic groups contained in the core polymer particle (A) are obtained. The voids are filled with an aqueous medium that forms an aqueous dispersion.

  The base is a volatile base and / or a nonvolatile base. Specific examples of the volatile base are ammonia, ammonium hydroxide, morpholine, trimethylamine, and triethylamine. Specific examples of the non-volatile base include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide; sodium carbonate, potassium bicarbonate Alkali metal (bi) carbonates such as; ammonium (bi) carbonates such as ammonium carbonate and ammonium bicarbonate. Preferred bases are volatile bases, and more preferred bases are ammonia and ammonium hydroxide.

  The amount of the base used is an amount that neutralizes at least some of the acidic groups of the core polymer particles (A) so that the pH of the aqueous dispersion is 7 or more. The base is preferably added in the form of an aqueous solution from the viewpoint of suppressing the generation of aggregates at the time of addition, and the concentration is preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass. Furthermore, from the above viewpoint, an anionic surfactant and / or a nonionic surfactant can be added before the base is added.

  In order for the acidic groups inside the polymer particles to be neutralized by adding the base to the aqueous dispersion, it is necessary to allow time for the bases to diffuse into the polymer particles. Thus, desirably, stirring is performed over time after the addition of the base. A preferable base treatment temperature is equal to or higher than a temperature at which the polymer particles are sufficiently softened. The base treatment time after the base addition is usually 5 to 120 minutes, preferably 10 to 90 minutes.

  The base can be added in the presence of an organic solvent according to the method disclosed in JP-A-3-26724. The polymer particles are softened by using an organic solvent, and the diffusion of the base is promoted. Specific examples of the organic solvent are aromatic hydrocarbons, halogenated hydrocarbons, alcohols, ethers, ketones, and saturated carboxylic acid esters. The organic solvent is usually used in the range of 0.1 to 1000 parts by mass with respect to 100 parts by mass of the polymer particles. The used organic solvent is evaporated and removed after the base treatment.

  Instead of the organic solvent, a polymerizable monomer can be used. The polymerizable monomer may contain a monomer containing an acidic group and is usually used in the range of 1 to 20 parts by mass, preferably 2 to 10 parts by mass with respect to 100 parts by mass of the polymer particles. The The polymerizable monomer can be newly added. The base treatment can be performed in a state where the polymerizable monomer is added excessively at the time of forming the shell layer (B) and the shell layer (C) and the polymerization reaction is stopped by adding a polymerization inhibitor or a reducing agent. . Excess polymerizable monomer is polymerized by adding a polymerization initiator after the base treatment.

  The formation of the core polymer particles (A), the formation of the shell layer (B), the formation of the shell layer (C) and the base treatment may be carried out stepwise in the same reactor. The product of the previous stage may be transferred to another reactor, and the next stage process may be performed in the reactor.

  The polymerization reaction of the aqueous dispersion containing the hollow polymer particles is stopped by cooling the polymerization system, adding a polymerization inhibitor or the like. Thereafter, if desired, unreacted monomers are removed, the pH and solid content concentration of the aqueous dispersion are adjusted, and an aqueous dispersion containing the hollow polymer particles of the present invention is obtained.

  The number average particle diameter of the hollow polymer particles in the aqueous dispersion of the present invention is preferably 0.6 to 1.5 μm, more preferably 0.8 to 1.4 μm, still more preferably 0.9 to 1.3 μm. It is. The number average particle diameter is a value obtained by simply averaging the maximum particle diameter of each of the 200 hollow polymer particles measured by a transmission electron microscope.

  The porosity of the hollow polymer particles is preferably 40 to 65%, more preferably 44 to 60%, and still more preferably 48 to 55%. The porosity is a value obtained by simply averaging the porosity obtained by calculation from the numerical values of the maximum particle diameter and the maximum diameter of each of the 200 hollow polymer particles measured by a transmission electron microscope.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples.
The physical properties of the aqueous dispersion and the hollow polymer particles were measured as follows.

(1) Number average particle diameter of hollow polymer particles The number average particle diameter of the hollow polymer particles was determined by simply averaging the maximum particle diameter of each of the 200 hollow polymer particles by a transmission electron microscope.

(2) Porosity of hollow polymer particles The maximum particle diameter and the maximum void diameter of each of the 200 hollow polymer particles were measured by a transmission electron microscope H-7500 (manufactured by Hitachi, Ltd.) and calculated by the following equation. The value obtained by simply averaging the void ratio was the void ratio of the hollow polymer particles.

(3) Sedimentation resistance of aqueous dispersion 100 ml of the aqueous dispersion was placed in a 100 ml graduated cylinder and allowed to stand for 30 days. Subsequently, the hollow polymer particles settled in the graduated cylinder were separated by decantation, and the amount of sedimentation of the hollow polymer particles was measured. The settling resistance of the aqueous dispersion was evaluated according to the following criteria.
No sediment: ○
The sedimentation amount of the hollow polymer particles is less than 3 ml: Δ
Settling amount of hollow polymer particles is 3 ml or more: x

(4) Type B Viscosity of Aqueous Dispersion Ion exchange water and 10% by mass aqueous sodium hydroxide solution were added to the aqueous dispersion to prepare a viscosity measurement sample having a solid content concentration of 26% by mass and pH 8.5. Next, the viscosity of the viscosity measurement sample was measured with a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.).

(5) White paper gloss (75 °)
Phosphoric esterified starch (MS-4600 manufactured by Nippon Food Processing Co., Ltd.) 2.5 parts by mass and 9 parts by mass of carboxy-modified styrene-butadiene copolymer latex (Nipol LX407F manufactured by Nippon Zeon Co., Ltd.) are kaolin clay ( It was added to 100 parts by mass of inorganic pigment consisting of 45 parts by mass of Engelhard Ultra White-90, 20 parts by mass of KCS (Imeris KCS 20 parts by mass) and 35 parts by mass of calcium carbonate (FMT 90 by Fematec), and then hollow. An aqueous dispersion containing 8 parts by mass of polymer particles and ion-exchanged water were mixed into the resulting mixture and stirred to obtain a coated paper composition having a solid content concentration of 61% by mass. Thereafter, the coated paper for composition, the base paper both surfaces of a basis weight of 65 g / m ^2, is applied in an amount of one-sided 13 g / m ^2, dried at 130 ° C., coated paper was obtained.
The light reflectance of the coated paper surface was measured with a gloss meter (GM-26D, manufactured by Murakami Color Research Laboratory Co., Ltd.) under conditions of an incident angle of 75 degrees and a reflection angle of 75 degrees. The larger the value, the better the glossiness of blank paper.

(6) Whiteness The ISO whiteness of the coated paper was measured with 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 number, the better the whiteness.

(7) Opacity The opacity of the coated paper was measured with a spectral color whiteness meter (PF10 manufactured by Nippon Denshoku Industries Co., Ltd.) according to the method defined in JIS P8138-1976. The higher the number, the better the opacity.

(8) Dry pick strength 0.4 cm ^{3 of} printing ink (tack value 20) was adhered to a rubber roll of an RI tester (manufactured by Akashi Seisakusho Co., Ltd.). Thereafter, four overprints were performed on the coated paper by the RI tester. Next, the state of peeling (picking) of the paper surface was observed. The case where there was no peeling was set to 5 points, and the dry pick strength was evaluated. The higher the score, the higher the dry pick strength.

(9) Printing gloss (heavy color 60 °)
After preparing an RI tester (manufactured by Akashi Seisakusho Co., Ltd.) in which process inks of three colors of indigo, red, and yellow (TK Mark V manufactured by Toyo Ink Manufacturing Co., Ltd.) were attached to different rubber rolls, respectively Printing was performed on the coated paper by the RI tester. After that, the solid coated paper is left in a constant temperature and humidity chamber at 20 ° C. and 65% RH for 24 hours, and the printed gloss of the coated paper is gloss meter (GM manufactured by Murakami Color Research Laboratory Co., Ltd.). -26D), measured under conditions of an incident angle of 60 degrees. The higher the value, the better the print gloss.

Example 1
Formation of core polymer particles (A) 60 parts by mass of methyl methacrylate (MMA), 5 parts by mass of butyl acrylate (BA), 35 parts by mass of methacrylic acid (MAA) 0.9 parts by mass of sodium polyoxyethylene alkyl ether sulfate 0.15 parts by mass of sodium tripolyphosphate and 85 parts by mass of ion-exchanged water are added to a pressure vessel equipped with a stirrer and then stirred to give an emulsion of the monomer mixture (a) for forming the core polymer particles (A) Was prepared.

To a reaction vessel equipped with a stirrer, 800 parts by mass of ion-exchanged water, 100 parts by mass of MMA, 5 parts by mass of sodium dodecylbenzenesulfonate, and 5 parts by mass of potassium persulfate were added and then stirred. The reaction vessel was heated to 80 ° C. and reacted to obtain a seed latex having a volume average particle size of 82 nm.
40 parts by mass of ion-exchanged water and 0.28 parts by mass of the seed latex (as solid content) were added to a pressure-resistant vessel equipped with a stirrer, and then heated to 85 ° C. 1.63 parts by weight of a 3% by weight aqueous potassium persulfate solution is added to the aqueous seed latex dispersion, after which 7% by weight of the emulsion of the monomer mixture (a) is added to the reaction system over 3 hours. The reaction was continued for 1 hour. Thereafter, 250 parts by mass of ion-exchanged water and 18.6 parts by mass of a 3% by mass aqueous potassium persulfate solution were added to the reaction system, and the emulsion of the monomer mixture (a) was maintained while maintaining the reaction temperature at 85 ° C. Was continuously added to the reaction system over 3 hours, and the reaction was further conducted for 2 hours. The reaction system was cooled to room temperature, and an aqueous dispersion containing the core polymer particles (A) was obtained. The polymerization conversion rate was 99% or more. The volume average particle diameter of the core polymer particles (A) measured by a dynamic light scattering particle measuring device N4 (manufactured by Coulter Inc.) was 420 nm.

Formation of shell layer (B) and shell layer (C) MMA 7.8 parts by mass, BA 1.6 parts by mass, MAA 0.6 parts by mass, t-dodecyl mercaptan (TDM) 0.03 parts by mass, polyoxyethylene alkyl ether sulfate 0.02 parts by mass of sodium and 16 parts by mass of ion-exchanged water were added to a pressure vessel equipped with a stirrer and then stirred to prepare an emulsion of the monomer mixture (b) for forming the shell layer (B). .

  On the other hand, 89.37 parts by mass of styrene (ST), 0.63 parts by mass of acrylic acid (AA), 0.4 parts by mass of polyoxyethylene alkyl ether sodium sulfate and 130 parts by mass of ion-exchanged water were added to the pressure vessel with a stirrer. It was added and then stirred to prepare an emulsion of the monomer mixture (c) for forming the shell layer (C).

  An aqueous dispersion containing 130 parts by mass of ion-exchanged water and the core polymer particles (A) is added to a pressure vessel with a stirrer in such an amount that the mass of the core polymer particles (A) becomes 10 parts by mass, and then The temperature was raised to 85 ° C. 10 parts by mass of a 4% by mass aqueous potassium persulfate solution was added to the reaction system, and the emulsion of the monomer mixture (b) was continuously added to the reaction system over 20 minutes. Thereafter, an emulsion of the monomer mixture (c) was continuously added to the reaction system over 2 hours.

Base treatment 25 parts by mass of 5% by mass aqueous ammonia was added to the reaction system, and the base treatment was carried out at 90 ° C. for 1 hour. The pH of the reaction solution was 7 or more over 1 hour. Thereafter, 10 parts by mass of a 4% by mass aqueous potassium persulfate solution was added to the reaction system, and the reaction was further carried out for 2 hours. The reaction system was cooled to room temperature, and an aqueous dispersion containing hollow polymer particles was obtained. The polymerization conversion rate was 99% or more. The results are shown in Table 1.

Examples 2 and 3, Comparative Examples 1-3
The same operation as in Example 1 was performed except that the compositions of the monomer mixtures (a) to (c) were changed as shown in Table 1. The results are shown in Table 1.

  The aqueous dispersions of Examples 1 to 3 had high sedimentation resistance, and the viscosity of these aqueous dispersions as a coated paper composition was appropriate. Furthermore, these aqueous dispersions gave coated papers with excellent white paper gloss, whiteness, opacity, dry pick strength and printing gloss.

The aqueous dispersion of Comparative Example 1 in which the monomer mixture (c) containing methacrylic acid instead of acrylic acid was used had low sedimentation resistance. Furthermore, the white paper gloss and printing gloss of the coated paper obtained by using the aqueous dispersion were low.
The precipitation resistance of the aqueous dispersion of Comparative Example 2 in which the monomer mixture (c) containing more than 2.5% by mass of acrylic acid was used was not so high. Furthermore, the white paper gloss and printing gloss of the coated paper obtained by using the aqueous dispersion were low.
The viscosity of the aqueous dispersion of Comparative Example 3 in which the monomer mixture (b) containing an acidic group-containing monomer exceeding 10% by mass was used was too high to prepare a coated paper composition. .

Comparative Example 4
The same operation as in Example 2 was performed except that a monomer mixture (c) consisting of ST99.9 parts by mass and AA0.1 parts by mass was used. The polymer particles contained in the obtained aqueous dispersion were solid, and an aqueous dispersion containing hollow polymer particles was not obtained.

  The aqueous dispersion of hollow polymer particles of the present invention is a coating of paper, ink, fiber, leather, etc .; organic pigment, light scattering agent or light scattering aid in applications such as paint, absorbent filler for inkjet paper, papermaking process Light weight by air, such as high-concealment pigment for correction ink or correction ribbon, microcapsule material, intermediate material of toner used for electrophotography, resin, cement, concrete, etc. It can be used for applications that utilize crystallization, applications that are added to semiconductor sealing materials, etc., and that utilize the low dielectric properties of air. The aqueous dispersion of hollow polymer particles of the present invention is suitable for a paper coating composition and not only improves the opacity of the coated paper, but also enables the production of high gloss coated paper.

Claims (2)

(1) A monomer mixture (a) composed of 20 to 50% by mass of an acid group-containing monomer and 80 to 50% by mass of a monomer copolymerizable therewith is copolymerized to form a core polymer particle (A) A process of forming
(2) A monomer mixture (b) comprising 1 to 10% by mass of an acid group-containing monomer and 99 to 90% by mass of a monomer copolymerizable therewith is the presence of the core polymer particle (A). A step of forming a shell layer (B) which is copolymerized under and substantially surrounds the core polymer particles (A),
(3) A monomer mixture (c) comprising 0.2 to 2.5% by mass of an acrylic acid monomer and 99.8 to 97.5% by mass of a monomer copolymerizable therewith is the shell layer. A step of copolymerizing in the presence of the core polymer particles (A) substantially surrounded by (B) to form a shell layer (C) substantially surrounding the shell layer (B);
(4) A base is added to the aqueous dispersion containing at least the polymer particles having a three-layer structure of the core polymer particles (A), the shell layer (B), and the shell layer (C), and the aqueous dispersion The step of adjusting the pH to 7 or higher,
A process for producing an aqueous dispersion containing hollow polymer particles. An aqueous dispersion containing hollow polymer particles produced by the production method according to claim 1.