JP7152254B2 - Fine particle aqueous dispersion and inkjet ink composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fine particle aqueous dispersion and an inkjet ink composition.

In recent years, due to the growing awareness of the environment in the use of pigments, there has been a demand for the development of environmentally friendly pigments such as water-based pigments that do not use organic solvents as much as possible.
Conventionally, titanium oxide particles have been used as a white pigment even in water-based pigment inks.
Titanium oxide particles have excellent optical properties such as white opacity and chemical resistance. However, due to their high specific gravity, the pigment particles tend to settle out. becomes. For example, in order to prevent clogging of the ink head, it is necessary to continuously discharge ink that is not used for printing from the head, and to install a circulation device to reduce sedimentation in the device. .

To solve these problems, a method of adding a polymer dispersant in the process of dispersing titanium oxide particles for stabilization (Patent Document 1), and forming a titanium oxide coating layer on the surface of a resin having a lower specific gravity than titanium oxide. Therefore, a method of lowering the specific gravity (Patent Documents 2 and 3) has been proposed.
However, even if it is added in the process of dispersing titanium oxide with a polymer dispersant, long-term dispersion stability cannot be obtained, and by adding a large amount of dispersant, the ink viscosity increases and foaming occurs. There were problems such as
In addition, even if a titanium oxide coating layer is formed on the surface of the resin particles, the thickness of the coating layer is insufficient, and aggregation and coalescence of the particles occur during compounding, which deviates from the optimum particle size range. There was a problem that the white hiding property as was not sufficiently expressed.

JP-A-6-145570 JP 2006-274214 A JP 2017-141441 A

Accordingly, it is an object of the present invention to provide a fine particle aqueous dispersion that is superior in lower sedimentation properties than in the past and that can maintain a high whiteness-hiding property.

The present inventors arrived at the present invention as a result of conducting studies to achieve the above object.
That is, in the present invention, composite particles (C) in which resin particles (A) having a specific gravity of 1.0 or less and containing an acid-modified polyolefin (a) are coated with titanium oxide (B) are added to an aqueous medium (D). A fine particle aqueous dispersion (E) in which the composite particles (C) have a volume average particle diameter of 150 to 500 nm as determined by a dynamic light scattering method; and this fine particle aqueous dispersion is contained. It is an ink composition for inkjet to be used.

The inkjet ink composition containing the fine particle aqueous dispersion of the present invention exhibits an effect of being excellent in low sedimentation and capable of increasing white hiding power as compared with a conventional white pigment dispersion containing composite particles.

The fine particle aqueous dispersion of the present invention comprises composite particles (C) in which resin particles (A) having a specific gravity of 1.0 or less and containing acid-modified polyolefin (a) are coated with titanium oxide (B) in an aqueous medium ( D), and the volume average particle diameter of the composite particles (C) measured by a dynamic light scattering method is 150 to 500 nm.

The specific gravity of the resin particles (A) in the present invention is 1.0 or less, preferably 0.95 or less, more preferably 0.93 or less. If it exceeds 1.0, there may be problems with sedimentation.
The particle specific gravity of the resin particles (A) is the true specific gravity at 25° C. that can be measured by a Guerlussac type pycnometer method or the like. In this specification, the specific gravities of the composite particles (C) and aqueous medium (D) are also true specific gravities at 25°C.

The resin particles (A) in the present invention preferably have a specific gravity of 1.0 or less and an acid value of 1 to 13 mgKOH/g. .
Moreover, when the acid value is less than 1.0 mgKOH/g, the hydrophobicity becomes high and the particle size is not preferable, which is not preferable.
The acid value of the resin particles (A) can be measured by the method specified in JIS K0070 (1992 edition) by dissolving the dried resin pieces obtained by solid-liquid separation of the obtained resin particles (A) in an organic solvent.

The resin particles (A) of the present invention contain an acid-modified polyolefin (a).
The acid-modified polyolefin (a) of the present invention is a polyolefin having an acidic group selected from a carboxyl group, a sulfonyl group and a phosphonyl group in the molecule of the polyolefin. Among these acid-modified polyolefins (a), polyolefins having carboxyl groups in the molecule are preferred.

The content of the acid-modified polyolefin (a) in the resin particles (A) of the present invention is not particularly limited, but since the acid value of the resin particles (A) is preferably 1 to 13 mgKOH/g, it is preferably 30 to 100% by weight. , 50 to 100% by weight is more preferred.

The acid-modified polyolefin (a) in which the acidic group is a carboxyl group is a polyolefin having a carbon-carbon unsaturated double bond in the molecule to which no acidic group is added, an unsaturated carboxylic acid or an acid anhydride thereof, and a lower alkyl thereof. can be obtained by heating and mixing the esterified product of and causing an addition reaction.

The polyolefins before modification include (co)polymers of one or more olefins, and copolymers of olefins and monomers other than olefins, in which carbon-carbon saturated double bonds are present in the molecule. Those having
The above olefins include alkenes having 2 to 30 carbon atoms (hereinafter abbreviated as C) such as ethylene, propylene, 1- and 2-butene, and isobutene, and α-olefins having 5 to 30 carbon atoms (1-hexene, 1-decene, 1-dodecene, etc.), and other monomers include C4-30 unsaturated monomers having copolymerizability with olefins, such as vinyl acetate and styrene.

Acid-modified polyolefin (a) is a polyolefin in which one molecule of an acidic group is added to one or both ends, a polyolefin in which an acidic group is copolymerized at one or both ends, and a monomer having an acidic group. It is a homopolymerized polymer.

The carbon-carbon unsaturated double bonds are preferably present at the molecular ends of the polyolefin, and preferably 0.1 to 20 on average per 1,000 carbon atoms in the polyolefin. 0.2 to 10 is more preferred, and 0.3 to 3.0 is particularly preferred.
In order to add an acid to a polyolefin having less than 0.1 C═C bonds, a large amount of initiator must be used, and the water dispersibility tends to be poor for the reasons described below. If the number exceeds 20, the affinity with polypropylene is lowered, which is not preferable.

Specific methods for producing polyolefins containing at least one carbon-carbon unsaturated double bond include, for example, using a diene or the like as a monomer to leave an unsaturated group in the skeleton; A method of degrading a commercially available polyolefin by heating (thermal degradation method) can be mentioned.

The thermal degradation method includes (1) continuously or discontinuously thermally degrading a polyolefin in the absence of an organic peroxide at 300 to 450° C. for 0.5 to 10 hours under a stream of nitrogen; and (2) a method of continuously or discontinuously thermally degrading in the presence of an organic peroxide, usually at 180° C. to 300° C. for 0.01 to 10 hours. In both cases (1) and (2), continuous thermal degradation is preferable from an industrial point of view.

Specific examples of known commercially available polyolefins are (co)polymers containing ethylene units [e.g. high, medium and low density polyethylene, ethylene and C4-30 unsaturated monomers (1-butene, 2- propylene unit-containing (co)polymers [e.g., polypropylene, propylene and C4-30 unsaturated monomers (1-butene, 2-butene, 1- hexene, 1,4-hexadiene, etc.); ethylene/propylene copolymers; polybutene and the like.

Among these, polypropylene, polyethylene, poly-1-butene, propylene-ethylene copolymer, propylene-1-butene copolymer, ethylene-1-butene copolymer, propylene-ethylene-1-butene copolymer, Propylene-ethylene-1-alkene (C=5-20) copolymer, ethylene-propylene-1,4-hexadiene copolymer, ethylene-propylene-dicyclopentadiene copolymer, ethylene-propylene-ethylidene norbornene copolymer Combination and the like are preferred.

Examples of organic peroxides include monofunctional (having one peroxide group in the molecule) (benzoyl peroxide, di-t-butyl peroxide, lauroyl peroxide, dicumyl peroxide, etc.) and polyfunctional (intramolecular having two or more peroxide groups in) [2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, di-t-butylperoxyhexahydroterephthalate, diallyl peroxydicarbonate, etc. ] and the like.
Among these, those having a 1-minute half-life temperature of 170° C. or higher are preferred from the viewpoint of decomposability at the thermal degradation temperature, and particularly preferred are di(2-t-butylperoxyisopropyl)benzene, di -t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy) Hexyne-3).

Examples of unsaturated carboxylic acids to be reacted with polyolefins containing carbon-carbon unsaturated double bonds include unsaturated monocarboxylic acids such as aliphatic (C3-30, such as acrylic acid, methacrylic acid, α-ethyl acrylic acid, crotonic acid, isocrotonic acid) and cycloaliphatic (C6-24, such as cyclohexanecarboxylic acid)]; unsaturated aliphatic dicarboxylic acids (maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, etc.); unsaturated cycloaliphatic Containing dicarboxylic acid (cyclohexenedicarboxylic acid, cycloheptenedicarboxylic acid, bicycloheptenedicarboxylic acid, methyltetrahydrophthalic acid, etc.); (C5-24, eg aconitic acid)] and the like.
Among these, unsaturated aliphatic dicarboxylic acids are preferable, and maleic acid and fumaric acid are more preferable.

In addition to unsaturated carboxylic acids, derivatives of unsaturated carboxylic acids can also be used as compounds to be reacted with polyolefins containing carbon-carbon unsaturated double bonds.
Derivatives of unsaturated dicarboxylic acids to be reacted with polyolefins containing carbon-carbon unsaturated double bonds include the acid anhydrides of unsaturated carboxylic acids [anhydrides of the unsaturated polycarboxylic acids mentioned above, such as maleic anhydride, acid, itaconic anhydride, citraconic anhydride, cyclohexenedicarboxylic anhydride, aconitic anhydride)], lower alkyl esters, amides, and imides. The unsaturated carboxylic acid or unsaturated carboxylic acid derivative may be used alone or in combination of two.
Of these, acid anhydrides of maleic acid and fumaric acid are preferred.

In order to synthesize the acid-modified polyolefin (a) of the present invention, at least one carbon-carbon unsaturated double bond is formed under nitrogen aeration with no more than 0.3% by weight or no radical initiator. It is most preferable to heat and mix the contained polyolefin and unsaturated dicarboxylic acid. Since the unsaturated carboxylic acid may vaporize at this time, it is preferable to flow hot water at a temperature at which the unsaturated carboxylic acid melts in the reflux pipe to reflux the unsaturated dicarboxylic acid.

The temperature at which the polyolefin and the unsaturated carboxylic acid are mixed is not particularly limited as long as it is equal to or higher than the melting point of the polyolefin. If the temperature is less than 160°C, the addition reaction rate of the unsaturated carboxylic acid is slow, and long-time heating is required. gets worse.
The time for mixing the polyolefin and the unsaturated carboxylic acid is not particularly limited, but it is industrially preferable to keep it within 30 hours.

Since the unreacted and remaining acid is easily vaporized, it can be easily removed under reduced pressure under heating. Since the presence of residual acid deteriorates the water resistance, it is preferable to remove the residual acid by heating the acid-modified polyolefin prepared by the above method above the melting point and reducing the pressure.

The acid-modified polyolefin (a) in which the acidic group is a sulfonyl group can be obtained in the same manner as in the above acid-modified polyolefin except that the unsaturated carboxylic acid and its derivatives are replaced with unsaturated sulfonic acid and its derivatives.

Unsaturated sulfonic acids to be reacted with polyolefins containing carbon-carbon unsaturated double bonds, and their derivatives such as C2-20 aliphatic unsaturated sulfonic acids (vinylsulfonic acid, etc.), C6-20 aromatic unsaturations Sulfonic acid (styrenesulfonic acid, etc.), sulfonic acid group-containing (meth)acrylates [sulfoalkyl (C2-20) (meth)acrylates [2-(meth)acryloyloxyethane, -propane and -butanesulfonic acid, 3-( meth)acryloyloxypropanesulfonic acid, 4-(meth)acryloyloxybutanesulfonic acid, 2-(meth)acryloyloxy-2,2-dimethylethanesulfonic acid, p-(meth)acryloyloxymethylbenzenesulfonic acid, etc.], Sulfonic acid group-containing (meth)acrylamides [2-(meth)acryloylaminoethanesulfonic acid, 2- and 3-(meth)acryloylaminopropanesulfonic acid, 2- and 4-(meth)acryloylaminobutanesulfonic acid, 2- (Meth)acryloylamino-2,2-dimethylethanesulfonic acid, p-(meth)acryloylaminomethylbenzenesulfonic acid, etc.], alkyl (C1-20) (meth)allylsulfosuccinate ester [methyl(meth)allylsulfosuccinate ester, etc.], (meth)acryloylpolyoxyalkylene (alkylene group is C1-6) sulfate ester, (meth)acryloylpolyoxyethylene (polymerization degree 2-50) sulfate ester, and the like.

The acid-modified polyolefin (a) in which the acidic group is a phosphonyl group can be obtained in the same manner as in the above acid-modified polyolefin except that the unsaturated carboxylic acid and its derivatives are replaced with unsaturated phosphonic acid and its derivatives.

Unsaturated phosphonic acids to be reacted with polyolefins containing carbon-carbon unsaturated double bonds, and derivatives thereof such as C2-20 aliphatically unsaturated phosphonic acids (vinylphosphonic acid, etc.), C6-20 aromatic unsaturations Phosphonic acid (styrene phosphonic acid, etc.), phosphoric acid group-containing (meth) acrylate [phosphoalkyl (C2-20) (meth) acrylate [2-(meth) acryloyloxyethane, -propane and -butanesulfonic acid, 3-( meth)acryloyloxypropanephosphonic acid, 4-(meth)acryloyloxybutanephosphonic acid, 2-(meth)acryloyloxy-2,2-dimethylethanephosphonic acid, p-(meth)acryloyloxymethylbenzenephosphonic acid, etc.] , phosphate group-containing (meth)acrylamide [2-(meth)acryloylaminoethanephosphonic acid, 2- and 3-(meth)acryloylaminopropanephosphonic acid, 2- and 4-(meth)acryloylaminobutanephosphonic acid, 2 -(meth)acryloylamino-2,2-dimethylethanephosphonic acid, p-(meth)acryloylaminomethylbenzenephosphonic acid, etc.], alkyl (C1-20) (meth)allyl phosphosuccinate [methyl (meth)allyl phosphosuccinic acid ester, etc.], (meth)acryloylpolyoxyalkylene (the alkylene group is C1-6) phosphate, (meth)acryloylpolyoxyethylene (polymerization degree 2-50) phosphate, and the like.

The melting point of the acid-modified polyolefin (a) as a raw material for the resin particles (A) in the present invention is in the range of 60 to 100°C, preferably 70 to 90°C, more preferably 75 to 85°C, from the viewpoint of water dispersibility. is.
If it is less than 60°C, the heat resistance of the image may be problematic, and if it exceeds 100°C, it is difficult to form particles of the resin containing the acid-modified polyolefin.

<Measurement of melting point>
A sample (5 mg) was collected and placed in an aluminum pan, and DSC (differential scanning calorimetry) [DSC20, SSC/580 manufactured by Seiko Instruments Inc.] was performed at a temperature increase rate of 10 ° C. per minute to detect an endothermic peak due to crystal melting. was obtained.

The weight average molecular weight of the acid-modified polyolefin is preferably 5,000 or more and 200,000 or less. If it is 200,000 or less, the water dispersibility is good. From the viewpoint of water dispersibility, it is more preferably 10,000 or more and 150,000 or less.
The weight average molecular weight and number average molecular weight of the present invention are measured by gel permeation chromatography (GPC).

Measurement conditions for the weight average molecular weight (Mw) and number average molecular weight (Mn) by gel permeation chromatography (GPC) in the present invention are as follows.
Apparatus: high-temperature gel permeation chromatograph [“Alliance GPC V2000”, manufactured by Waters Co., Ltd.]
Solvent: ortho-dichlorobenzene
Reference material: Polystyrene Sample concentration: 3 mg/ml
Column stationary phase: Two PLgel 10 μm MIXED-B [manufactured by Polymer Laboratories] connected in series Column temperature: 135°C

If the resin particles (A) in the present invention have a specific gravity of (A) of 1.0 or less and contain at least the acid-modified polyolefin (a), a resin other than the acid-modified polyolefin (a) is used in combination. It doesn't matter.
Light specific gravity resins that can be used in combination include alkenes of 2 to 30, such as ethylene, propylene, 1- and 2-butene, and isobutene, and α-olefins of C5 to 30 (1-hexene, 1-decene, 1-dodecene, etc.), non-acid-modified polyolefins obtained by (co)polymerizing olefin monomers such as; copolymers; polymers having cationic functional groups; and polymers having oxyethylene groups.

Examples of the polymer having a cationic functional group include (co)polymers of nitrogen-containing monomers having a cationic functional group and an ethylenically unsaturated group. Specific examples of the monomer include aminoethyl ( meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, t-butylaminoethyl methacrylate, N-aminoethyl (meth)acrylamide, (meth)allylamine, morpholinoethyl (meth)acrylate, 4-vinyl pyridine, 2-vinylpyridine, crotylamine, N,N-dimethylaminostyrene, methyl-α-acetaminoacrylate, vinylimidazole, N-vinylpyrrole, N-vinylthiopyrrolidone, N-arylphenylenediamine, aminocarbazole, aminothiazole , aminoindole, aminopyrrole, aminoimidazole, aminomercaptothiazole and salts thereof.

Polymers having an oxyethylene group include (co)polymers of monomers having an ethylenically unsaturated group. Specific examples of such monomers include vinyl monomers having a polyalkylene glycol chain [polyethylene glycol (molecular weight 300) mono(meth)acrylate, polypropylene glycol (molecular weight 500) monoacrylate, methyl alcohol ethylene oxide 10 mol adduct (meth)acrylate, lauryl alcohol ethylene oxide 30 mol adduct (meth)acrylate, etc.].

Polyolefins that are not acid-modified are preferable as resins other than (a) that are used in combination.

The resin particles (A) containing the acid-modified polyolefin (a) in the present invention can be prepared by dispersing in water a neutralized product obtained by neutralizing the acid group portion of the acid-modified polyolefin (a) with an amine.
Therefore, the amine is not limited as long as it can neutralize the acid groups of the acid-modified polyolefin (a), but it must be an amine that is difficult to volatilize in the process of preparing the composite particles (C).
Alkali metal compounds such as sodium hydroxide and potassium hydroxide can also neutralize the acid groups, but when these are used, the acid groups become metal salts, which is not preferable from the viewpoint of titanium oxide (B) coverage.

Amines used in the present invention for this purpose include tertiary amines such as dimethylaminoethanol, secondary amines such as diethanolamine and morpholine, and primary amines such as aniline and aliphatic amines. Two or more amines may be used in combination.
Among these, tertiary amines are preferred. Amines having a boiling point of 70° C. or higher and 200° C. or lower are preferred.
Specific examples include dimethylaminoethanol, diethylaminoethanol, and triethylamine.

The weight ratio of the amine to the weight of the acid-modified polyolefin (a) is preferably acid-modified polyolefin:amine = 100:0.1 to 5.0 from the viewpoint of dispersion stability and water resistance, and 100:0.3. ~4.0 is more preferred, and 100:0.6 to 3.0 is even more preferred.

The method for producing the aqueous dispersion of the resin particles (A) containing the acid-modified polyolefin (a) is not particularly limited, but examples thereof include the following methods.
(1) Phase inversion emulsification: A resin containing acid-modified polyolefin (a), an amine, and, if necessary, an additive such as an emulsifier are dissolved in a solvent other than water (e.g., tetrahydrofuran, xylene, toluene, etc.), and then stirred. , By adding water little by little from the outside under heating to prepare a mixture of a resin containing the acid-modified polyolefin (a), an amine, an additive, water, and a solvent other than water, and then removing the solvent other than water. A method for producing resin particles (A).
(2) Forced emulsification: Resin containing acid-modified polyolefin (a), amine, additives such as emulsifiers if necessary, and water are all put into a pressurized reaction vessel, and the resin containing acid-modified polyolefin (a) dissolves. A production method for obtaining resin particles (A) by stirring at a temperature equal to or higher than the temperature.
Among the above, (1) phase inversion emulsification is preferable from the viewpoint of reducing the particle size.

Emulsifiers are compounds having a hydrophobic group and a hydrophilic group, and specific examples include anionic surfactants such as fatty acid salts and nonionic surfactants such as alkylene oxide adducts of higher alcohols.

The volume-average particle size of the resin particles (A) of the present invention as determined by a dynamic light scattering method is preferably 70 to 500 nm, more preferably 100 to 400 nm, from the viewpoint of white hiding properties.
If it is 100 nm or more, visible light can be efficiently reflected, and if it is 500 nm or less, sedimentation can be suppressed.
The volume average particle diameter of the resin particles (A) is the 50% volume average particle diameter measured by wet particle size distribution measurement by dynamic light scattering (DLS) method and calculated by Marquadt method analysis. For example, a measuring instrument such as "ELS-Z2" manufactured by Otsuka Electronics can be used.

Titanium oxide (B) in the present invention includes, but is not limited to, titanium dioxide formed by using the following conventionally known reactions.
Specifically, the method for coating the resin particles (A) with titanium oxide (B) includes:
(1) Titanium alkoxide and water are dissolved in a liquid phase in the presence of the resin particles (A), and a sol-gel reaction is carried out, whereby the microparticles produced by the sol-gel reaction are adsorbed on the particle surfaces to form a layer of titanium oxide. (B),
(2) In the presence of the resin particles (A), a metal salt is subjected to a reductive deposition reaction by heating in a liquid phase, and the deposited nanoparticles are adsorbed on the particle surface to form a layer of titanium oxide (B),
(3) Titanium oxide (B) formed by forming a layer by adsorbing finely divided titanium oxide (B) onto the particle surface in the presence of the resin particles (A) in a liquid phase or in a gas phase. .
Among these, the method (1) or (3) is preferable from the viewpoint of the mechanical strength of the formed coating layer.
Specifically, in an organic solvent solution of titanium alkoxide in which the resin particles (A) are dispersed, the titanium alkoxide is subjected to a sol-gel reaction to form titanium oxide (B) on the surface of the resin particles (A) to coat the surface. can be done.

When titanium oxide (B) is coated by a sol-gel reaction, a solution of resin particles (A) or a dispersion of resin particles (A) dispersed in an organic solvent is added with a titanium alkoxide, a solvent and, if necessary, a dispersant. The resin particles (A) can be coated with the titanium oxide (B) by addition to form a solution and a sol-gel reaction.

As the organic solvent, conventionally used organic solvents can be used without limitation. Moreover, 1 type may be used and 2 or more types may be used together.
As the organic solvent, water is dissolved at a concentration of 0.1% by weight or more from the viewpoint of the dispersibility of the resin particles (A) and the composite particles in the process of forming the coating layer and the homogeneity of the formation of the titanium oxide (B) coating layer. and more preferably dimethylformamide, ethylene glycol, nitromethane, N-methylpyrrolidone, methanol, ethanol, isopropanol, 1-butanol, 2-methoxyethanol, bis(2-methoxyethyl) ether, methanol, At least one selected from the group consisting of ethanol, 2-butanol, isobutanol and diethylene glycol dimethyl ether, particularly preferably at least selected from the group consisting of ethylene glycol, methanol, ethanol, isopropanol, 1-butanol and 2-methoxyethanol It is one type.

Titanium alkoxides include those in which four alkoxides (RO ⁻ : R represents a hydrocarbon group) are bonded to tetravalent titanium. From the viewpoint of reactivity and productivity, the alkoxide is preferably an alkoxide having a hydrocarbon group of 1 to 8 carbon atoms, more preferably an alkoxide having a hydrocarbon group of 1 to 4 carbon atoms.
The hydrocarbon group is preferably an aliphatic hydrocarbon group, more preferably a branched or linear aliphatic hydrocarbon group.
Specific examples of alkoxides having a hydrocarbon group of 1 to 8 carbon atoms include n-butoxide, t-butoxide, ethoxide, 2-ethylhexaoxide, isobutoxide, isopropoxide, methoxide, n-propoxide and the like. be done.
One type of titanium alkoxide may be used, or two or more types may be used in combination. Moreover, in titanium alkoxides, all alkoxides may be the same or different.
From the viewpoint of reactivity and versatility, the titanium alkoxide is preferably at least one selected from the group consisting of titanium tetraisopropoxide, titanium tetrabutoxide and titanium tetraethoxide, more preferably titanium tetraisopropoxide and/or titanium alkoxide. Or titanium tetrabutoxide.

Examples of the dispersant include polymeric dispersion stabilizers, and specific examples include polyvinylpyrrolidone, polyvinyl alcohol, carboxymethylcellulose, polyoxyalkylene glycol, and polycarboxylic acid (salt) (polyacrylic acid (salt) ) etc.).
Among these, at least one selected from the group consisting of polyvinylpyrrolidone, polyvinyl alcohol and polyoxyalkylene glycol is preferable from the viewpoint of dispersion stability and zeta potential of the resin particles (A).

Furthermore, as a dispersant, it is preferable to use a nonionic surfactant and/or a cationic surfactant in combination from the viewpoint of controlling the wettability of the resin particles (A).
Examples of nonionic surfactants include the following.
Ether interfaces such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, polyoxyethylene alkyl ether, and polyoxyarylalkyl alkyl ether active agent;
Polyoxyethylene oleic acid, polyoxyethylene oleate, polyoxyethylene distearate, sorbitan laurate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene monooleate, polyoxyethylene stearate Ester-based surfactants such as;
2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyn-3-ol acetylene glycol-based surfactants such as
Examples of cationic surfactants include the following, and quaternary ammonium salt-type cationic surfactants, amine salt-type cationic surfactants, and the like can be used.
Examples of quaternary ammonium salt cationic surfactants include tetraalkylammonium cations such as lauryltrimethylammonium chloride and didecyldimethylammonium chloride (each alkyl group preferably has 1 to 18 carbon atoms); lauryldimethylbenzylammonium chloride ( ammonium cations having a benzyl group and an alkyl group (having preferably 1 to 18 carbon atoms) such as benzalkonium chloride); pyridinium cations such as cetylpyridinium chloride and oleylpyridinium chloride; is preferably a quaternary ammonium salt composed of an ammonium cation having 1 to 18). Anions constituting these quaternary ammonium salts include hydroxide ions, halogen ions (e.g., fluorine ions, chloride ions, bromide ions, iodine ions), nitrate ions, nitrite ions, methosulfate ions, and 1 carbon atom. ∼8 carboxyl anions (eg, anions derived from formic acid, acetic acid, propionic acid, 2-ethylhexanoic acid, lactic acid, malic acid, gluconic acid, etc.) and the like can be used.
Amine salt-type cationic surfactants include primary amine salts such as laurylamine chloride, stearylamine bromide, and cetylamine methosulfate; laurylmethylamine chloride, stearylethylamine bromide, dilaurylamine methosulfate, laurylpropylamine acetate, and the like. secondary amine salts of; tertiary amine salts such as lauryldiethylamine chloride and laurylethylmethylamine bromide;
Among these, nonionic surfactants are preferred from the viewpoints of the wettability of the resin particles (A) in organic solvents, the solubility of the active agent in organic solvents, and the zeta potential of the resin particles (A).

The solvent is appropriately selected according to the solubility of the titanium alkoxide, and examples thereof include water and organic solvents.

In the reaction solution, the weight ratio of the titanium alkoxide and the resin particles (A) (titanium alkoxide/resin particles (A)) is appropriately selected depending on the target thickness of the titanium oxide (B) coating. And from the viewpoint of spreadability, it is preferably 0.01 to 5, more preferably 0.01 to 1.
In the reaction solution, the content of the resin particles (A) is 0.1 to 50% by weight based on the weight of the solution, from the viewpoint of the ratio of the volume average particle size to the number average particle size of the composite particles and the productivity. is preferred, and more preferably 0.3 to 25% by weight.
In the reaction solution, the content of the titanium alkoxide is preferably 0.1 to 30% by weight, more preferably 0.2 to 15% by weight, based on the weight of the solution, from the viewpoint of the particle specific gravity of the composite particles and the white hiding property. % by weight.
In the reaction solution, the content of the dispersant is preferably 0 to 15% by weight, more preferably 1 to 10% by weight, based on the weight of the reaction solution, from the viewpoint of the average circularity of the composite particles.

The composite particles (C) in the present invention include resin particles (A) having a titanium oxide (B) layer formed thereon by the method described above.

The aqueous medium (D) in the present invention is water alone or a mixed solvent of water and a water-soluble organic solvent that is miscible with water.

The water-soluble organic solvent is not particularly limited and can be appropriately selected depending on the purpose.
For example, monoalcohols, polyhydric alcohols, ketones, esters, amines, thiols, and pyrrolidone-based solvents that are compatible with water can be used.

A polyhydric alcohol is preferable as the water-soluble organic solvent.
Such polyhydric alcohol is not particularly limited and can be appropriately selected depending on the purpose. Examples include propylene glycol, 1,2,3-butanetriol, 1,2,4-butanetriol, glycerin, diglycerin, triethylene glycol, tetraethylene glycol, diethylene glycol and 1,3-butanediol.

The volume-average particle size of the composite particles (C) of the present invention as measured by a dynamic light scattering method is 150 to 500 nm, preferably 100 to 400 nm, from the viewpoint of white hiding property.
If it is 150 nm or more, visible light can be efficiently reflected, and if it is 500 nm or less, sedimentation can be suppressed.
The volume average particle size of the composite particles (C) is the 50% volume average particle size measured by wet particle size distribution measurement by dynamic light scattering (DLS) method and calculated by Marquadt method analysis. For example, a measuring instrument such as "ELS-Z2" manufactured by Otsuka Electronics can be used.

The specific gravity of the composite particles (C) of the present invention is preferably 0.9 to 1.4, more preferably 1.0 to 1.15. Outside this range, there may be problems with sedimentation. The particle specific gravity of the composite particles is the true specific gravity at 25° C. that can be measured by a Guerlussac type pycnometer method or the like.

Selection of resin particles (A) to be used, volume ratio of titanium oxide (B) to resin particles (A) when coating resin particles (A) with titanium oxide (B), crystals of titanium oxide (B) to be coated It can be adjusted according to the structure. Specifically, the resin particles (A) having a small specific gravity are used, and the volume ratio of the titanium oxide (B) to the resin particles (A) when the resin particles (A) are coated with the titanium oxide (B) is determined by white masking. The particle specific gravity of the composite particles can be reduced by making the crystal structure of the titanium oxide (B) to be coated amorphous.

The absolute value _Δd of the difference between the specific gravity dC of the composite particles (C) of the present invention and the specific gravity dD of the aqueous medium ( _D ) is preferably 0.3 or less, more preferably 0.2 or less. Outside this range, there may be problems with sedimentation.
The specific gravity of the composite particles (C) can be adjusted by the specific gravity, particle size, volume ratio of the titanium oxide (B), and crystal structure of the resin particles (A) selected as described above.
The specific gravity of the aqueous medium (D) can be adjusted by adjusting the mixing ratio of the water-miscible water-soluble organic solvent and water.

The absolute value Δn of the difference between the refractive index n _A of the resin particles (A) of the present invention and the refractive index n _B of the titanium oxide (B) is preferably 0.6 or more, and if it is less than 0.6, the internal reflection efficiency From this point of view, the white hiding property may become a problem.

The refractive indices of the resin particles (A) and titanium oxide (B) were measured at a wavelength of 589 nm and a measurement temperature of 25° C. using an Abbe refractometer (“DR-M4” manufactured by Atago Co., Ltd.).

The white pigment dispersion of the invention contains the fine particle aqueous dispersion (E) of the invention.
The fine particle aqueous dispersion (E) of the present invention is obtained by dispersing the composite particles obtained by the above method for producing composite particles (C) in water alone or in a mixed solvent of water and a water-soluble organic solvent that is miscible with water. can be obtained.

Since the composite particles (C) of the present invention themselves are white, the fine particle aqueous dispersion (E) can be used as a white pigment dispersion even if only the composite particles (C) are used as a pigment component. It may be contained in combination.

The white pigment used in combination for this purpose is not particularly limited, but for example, generally commercially available inorganic white pigments, organic white pigments, or hollow particles can be used.
Examples of inorganic white pigments include, but are not limited to, titanium oxide, calcium carbonate, barium sulfate, finely divided silicic acid, silicas, calcium silicate, alumina, zinc oxide, cerium oxide, talc, and clay.

The organic white pigment is not particularly limited, and examples thereof include organic compound salts disclosed in JP-A-11-129613 and alkylenebismelamine derivatives disclosed in JP-A-11-140365 and JP-A-2001-234093. be done.

Examples of hollow particles include, but are not limited to, thermoplastic particles substantially made of organic polymers as disclosed in US Pat. No. 4,089,800.

An inkjet ink composition having low sedimentation and excellent white-hiding property can be obtained by using the obtained white pigment fine particle aqueous dispersion.

Other appropriately selected components can be added to the fine particle aqueous dispersion for white pigment or the inkjet ink of the present invention, if necessary. Examples thereof include dispersants, penetrants, pH adjusters, water-dispersible resins, antiseptic and antifungal agents, chelating reagents, rust inhibitors, antioxidants, ultraviolet absorbers, oxygen absorbers, light stabilizers, and the like. mentioned.

<Water-soluble organic solvent>
When the ink medium is water, it may contain a water-soluble organic solvent for the purpose of preventing drying of the ink and improving the dispersion stability of the pigment. There are no particular restrictions on the water-soluble organic solvent, and it can be appropriately selected according to the purpose.

A polyhydric alcohol is preferable as the water-soluble organic solvent. Such a polyhydric alcohol is not particularly limited and can be appropriately selected depending on the purpose. Examples of the water-soluble organic solvent A include propylene glycol, 1,2,3-butanetriol, 1,2,4 -butanetriol, glycerin, diglycerin, triethylene glycol, tetraethylene glycol, diethylene glycol, 1,3-butanediol and the like.

In addition to the above water-soluble organic solvents, the ink may contain other water-soluble organic solvents or solid wetting agents in place of some of these water-soluble organic solvents or in addition to these water-soluble organic solvents, if necessary. agents can be used in combination.
Examples of the water-soluble organic solvent or solid wetting agent include polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, and propylene carbonate. , ethylene carbonate, and other water-soluble organic solvents.

Examples of the polyhydric alcohol include dipropylene glycol, 1,5-pentanediol, 3-methyl-1,3-butanediol, propylene glycol, 2-methyl-2,4-pentanediol, ethylene glycol, and tripropylene. Glycol, hexylene glycol, polyethylene glycol, polypropylene glycol, 1,6-hexanediol, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane and the like.
Examples of the polyhydric alcohol alkyl ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, ethylene glycol mono-2-ethylhexyl ether and propylene glycol monoethyl ether.
The content of the water-soluble organic solvent in the ink is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 1 to 50% by weight.

The inkjet ink composition using the composite particles or composite particle dispersion of the present invention can be used for offset printing ink, letterpress printing ink, gravure printing ink, silk printing ink, inkjet recording ink, color filter, and the like. can be used for

EXAMPLES The present invention will be further described below with reference to Examples and Comparative Examples, but the present invention is not limited to these. Hereinafter, unless otherwise specified, % means % by weight, and part means part by weight.

Production Example 1 [Production of acid-modified polyolefin (a-1)]
A reaction vessel is charged with 100 parts of a polyolefin having propylene and 1-butene as structural units [trade name "Tafmer XM5070", manufactured by Mitsui Chemicals, Inc.], and heated with a mantle heater while passing nitrogen through the gas phase. The mixture was melted and thermally degraded at 330° C. for 80 minutes while stirring to obtain polyolefin (F-1). Polyolefin (F-1) had Mw of 66,000 and the number of double bonds in the molecular terminal and/or the molecular chain per 1,000 carbon atoms was 1.1.
1,000 parts of the obtained polyolefin (F-1) and 1 part of IRGANOX 1010 [manufactured by BASF Japan Co., Ltd.] were added to a reactor equipped with a nitrogen vent and a reflux tube through which hot water at 80° C. was flowed. , the inside of the kiln was replaced with nitrogen. The temperature was raised to 160° C. while stirring under a nitrogen stream. 46.2 parts of maleic anhydride was charged, and the temperature was raised to 200° C. with a slight flow of nitrogen. After stirring at 200° C. for 15 hours, vacuum topping was performed for 5 hours to remove unreacted maleic anhydride. After cooling to 160° C., it was taken out from the reactor to obtain an acid-modified polyolefin (a-1). The acid value of the obtained (a-1) was 4.

Production Example 2 [Production of acid-modified polyolefin (a-2)]
A reaction vessel was charged with 100 parts of polyolefin (A0-3) (trade name “VESTOPLAST750”, manufactured by Evonik) having ethylene, propylene and 1-butene as constituent units, and a mantle heater was added while passing nitrogen through the gas phase. and thermally degraded at 350° C. for 50 minutes while stirring to obtain polyolefin (F-2). The polyolefin (F-2) had an Mw of 10,000 and a molecular terminal and/or double bond number in the molecular chain per 1,000 carbon atoms of 10.3.
1,000 parts of the obtained polyolefin (F-2) and 1 part of IRGANOX 1010 [manufactured by BASF Japan Co., Ltd.] were added to a reactor equipped with a nitrogen vent and a reflux tube through which hot water at 80 ° C. was flowed. , the inside of the kiln was replaced with nitrogen. The temperature was raised to 160° C. while stirring under a nitrogen stream. 144.3 parts of maleic anhydride was charged, and the temperature was raised to 200° C. with a slight flow of nitrogen. After stirring at 200° C. for 15 hours, vacuum topping was performed for 5 hours to remove unreacted maleic anhydride. After cooling to 160° C., it was taken out from the reactor to obtain an acid-modified polyolefin (a-2). The acid value of the obtained (a-2) was 12.

Production Example 3 [Production of resin particles (A-1)]
12.5 parts of acid-modified polyolefin (a-1), 12.5 parts of polyolefin (F-1), dimethylaminoethanol [Tokyo Chemical Industry Co., Ltd. 0.5 part of tetrahydrofuran and 60 parts of tetrahydrofuran were added, and the temperature was adjusted to 60° C. with stirring to dissolve them uniformly. 74.5 parts of water was added little by little over 5 hours to effect phase inversion emulsification.
After cooling to room temperature, tetrahydrofuran was removed under reduced pressure, and water was added to adjust the solid content to 30.0%, thereby obtaining a resin particle dispersion (A-1). The obtained (A-1) had a specific gravity of 0.90, an acid value of 3.2, a melting point of 82° C., a refractive index of 1.48, and a particle diameter of 325 nm.

Production Example 4 [Production of resin particles (A-2)]
25.0 parts of acid-modified polyolefin (a-2), 0.9 parts of dimethylaminoethanol [manufactured by Tokyo Chemical Industry Co., Ltd.], Emalmin 50 [Sanyo 2.5 parts of Kasei Kogyo Co., Ltd.] and 60 parts of tetrahydrofuran were charged, and the temperature was adjusted to 60° C. with stirring to uniformly dissolve them. 74.5 parts of water was added little by little over 5 hours to effect phase inversion emulsification.
After cooling to room temperature, tetrahydrofuran was removed under reduced pressure, and water was added to adjust the solid content to 30.0% to obtain a resin particle dispersion (A-2). The obtained (A-2) had a specific gravity of 0.90, an acid value of 2.4, a melting point of 78° C., a refractive index of 1.48, and a particle diameter of 212 nm.

Production Example 5 [Production of resin particles (A-3)]
20.0 parts of acid-modified polyolefin (a-1) and 5.0 parts of acid-modified polyolefin (a-2) are added to a reaction vessel equipped with a stirring device, a heating/cooling device and a thermometer, and dimethylaminoethanol [Tokyo Chemical Industry Co., Ltd. Co., Ltd.] 0.4 parts, Emalmin 50 [manufactured by Sanyo Chemical Industries, Ltd.] 2.5 parts, and tetrahydrofuran 60 parts were charged, and the temperature was adjusted to 60° C. with stirring to uniformly dissolve them. 74.5 parts of water was added little by little over 5 hours to effect phase inversion emulsification.
After cooling to room temperature, tetrahydrofuran was removed under reduced pressure, and water was added to adjust the solid content to 30.0% to obtain a resin particle dispersion (A-3). The obtained (A-3) had a specific gravity of 0.90, an acid value of 1.2, a melting point of 80° C., a refractive index of 1.48, and a particle diameter of 275 nm.

Production Example 6 [Production of resin particles (A-4)]
12.5 parts of acid-modified polyolefin (a-2), 12.5 parts of polyolefin (F-2), dimethylaminoethanol [Tokyo Chemical Industry Co., Ltd. 0.4 parts of Emalmin 50 (manufactured by Sanyo Chemical Industries, Ltd.), 2.5 parts of tetrahydrofuran, and 60 parts of tetrahydrofuran were charged, and the temperature was adjusted to 60° C. with stirring to uniformly dissolve them. 74.5 parts of water was added little by little over 5 hours to effect phase inversion emulsification.
After cooling to room temperature, tetrahydrofuran was removed under reduced pressure, and water was added so that the solid content was 30.0% to obtain a resin particle dispersion (A-4). The obtained (A-4) had a specific gravity of 0.90, an acid value of 1.2, a melting point of 78° C., a refractive index of 1.48, and a particle diameter of 305 nm.

Comparative Production Example 1 [Production of resin particles (A'-1)]
In a reaction vessel equipped with a stirring rod and a thermometer, 0.1 part of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (manufactured by Wako Pure Chemical; V-50) as a polymerization initiator, styrene 14.8 parts of deionized water, 84.9 parts of ion-exchanged water, and 0.3 parts of sodium alkyldiphenyl ether disulfonate aqueous solution (manufactured by Sanyo Chemical Industries; Eleminol MON-7) were charged, sealed, and the air inside was replaced with nitrogen. , a reaction was carried out at 80° C. for 2 hours, and then a polymerization reaction was further carried out at 90° C. for 1.5 hours to obtain a dispersion of resin particles (A′-1). The obtained (A'-1) had a specific gravity of 1.05, an acid value of 0, no melting point detected, a refractive index of 1.59, and a particle diameter of 270 nm.

Comparative Production Example 2 [Production of resin particles (A'-2)]
In a reaction vessel equipped with a stirring rod and a thermometer, 0.1 part of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (Wako Pure Chemical Industries; V-50) as a polymerization initiator, methacrylic 12.6 parts of methyl acid, 2.2 parts of divinylbenzene, 84.9 parts of ion-exchanged water, and 0.3 parts of sodium alkyldiphenyl ether disulfonate aqueous solution (manufactured by Sanyo Chemical Industries; Eleminol MON-7) were charged and sealed. After the air inside was replaced with nitrogen, the reaction was carried out at 80° C. for 2 hours, and then the polymerization reaction was further carried out at 90° C. for 1.5 hours to obtain a resin particle (A′-2) dispersion. The obtained (A′-2) had a specific gravity of 1.18, an acid value of 0, a melting point of 160° C., a refractive index of 1.49, and a particle diameter of 270 nm.

Comparative Production Example 3 [Production of resin particles (A'-3)]
50 parts of styrene-butadiene rubber latex JSR SBLTX0573 grade [manufactured by JSR Corporation] is charged into a glass container, 30 parts of water is added and stirred so that the solid content becomes 30.0%, and the resin particle dispersion (A '-3) obtained. The obtained (A'-3) had a specific gravity of 0.97, an acid value of 0, no melting point detected, a refractive index of 1.55, and a particle diameter of 225 nm.

Comparative Production Example 4 [Production of resin particles (A'-4)]
12.5 parts of acid-modified polyolefin (a-1), 12.5 parts of polyolefin (F-1), dimethylaminoethanol [Tokyo Chemical Industry Co., Ltd. 0.5 parts of Emalmin 50 (manufactured by Sanyo Chemical Industries, Ltd.), 2.5 parts of tetrahydrofuran, and 60 parts of tetrahydrofuran were charged, and the temperature was adjusted to 50° C. with stirring to uniformly dissolve them.
Then, 74.5 parts of water was added, and stirring was continued for 1 hour at 50° C. to effect forced phase inversion emulsification.
After cooling to room temperature, tetrahydrofuran was removed under reduced pressure, and water was added to adjust the solid content to 30.0% to obtain a resin particle dispersion (A'-4). The obtained (A′-4) had a specific gravity of 0.90, an acid value of 3.2, a melting point of 82° C., a refractive index of 1.48, and a particle diameter of 575 nm.

Table 1 shows the results of physical property measurements of the resin particles in Production Examples 3-6 and Comparative Production Examples 1-4.

Example 1 [fine particle aqueous dispersion (E-1)]
In a reaction vessel equipped with a stirring rod and a thermometer, 40.30 parts of the obtained resin particle (A-1) dispersion, polyoxyethylene alkyl (12-14) ether (manufactured by Sanyo Chemical Industries; Sannonic SS- 120) 0.24 parts, 873.57 parts of ethanol, 76.93 parts of polyvinylpyrrolidone (manufactured by Nippon Shokubai Co., Ltd.; polyvinylpyrrolidone K-85N), 8.96 parts of titanium tetrabutoxide, charged, biomixer (( After dispersing and mixing for 3 minutes at 6000 rpm using Bio Mixer BM-2) manufactured by Nippon Seiki Seisakusho Co., Ltd., a sol-gel reaction is performed at 70 ° C. for 1.5 hours, and then the composite particle (C-1) dispersion is subjected to ion exchange. Composite particles (C-1) were obtained by washing with water, solid-liquid separation, and drying.
10 parts of the resulting composite particles (C-1), 38 parts of ion-exchanged water (D-1), 1 part of Sunspearl PS-2 (manufactured by Sanyo Chemical Industries) as a dispersant and Newpol PE-108 (Sanyo Kasei Kogyo Co., Ltd.) was blended and dispersed and mixed for 3 minutes at 6000 rpm using a bio mixer (manufactured by Nippon Seiki Seisakusho Co., Ltd.; Bio Mixer BM-2) to prepare a fine particle aqueous dispersion (E-1). .
The composite particles (C-1) of the resulting dispersion had a specific gravity of 1.10, a difference in refractive index between the resin particles (A-1) and the titanium oxide layer of 0.72, and a volume average particle diameter determined by a dynamic light scattering method. was 350 nm, and the absolute value Δd of the difference in specific gravity between the composite particles (C-1) and the ion-exchanged water (D-1) as an aqueous medium was 0.10.

Example 2 [fine particle aqueous dispersion (E-2)]
In Example 1, the same operation as in Example 1 was performed except that resin particles (A-1) were changed to resin particles (A-2) to obtain fine particle aqueous dispersion (E-2) of the present invention. .
The composite particles (C-2) of the obtained dispersion had a specific gravity of 1.10, a refractive index difference of 0.72 between the resin particles (A-2) and the titanium oxide layer, a particle diameter of 230 nm, and an absolute value of the specific gravity difference. Δd was 0.10.

Example 3 [fine particle aqueous dispersion (E-3)]
A fine particle aqueous dispersion (E-3) of the present invention was obtained in the same manner as in Example 1, except that the resin particles (A-1) in Example 1 were changed to resin particles (A-3). .
The composite particles (C-3) of the resulting dispersion had a specific gravity of 1.10, a refractive index difference of 0.72 between the resin particles (A-3) and the titanium oxide layer, a particle diameter of 300 nm, and an absolute value of the specific gravity difference. Δd was 0.10.

Example 4 [fine particle aqueous dispersion (E-4)]
In a reaction vessel equipped with a stirring rod and a thermometer, 40.30 parts of the obtained resin particle (A-4) dispersion, polyoxyethylene alkyl (12-14) ether (manufactured by Sanyo Chemical Industries; Sannonic SS- 120) 0.24 parts, 873.57 parts of ethanol, 76.93 parts of polyvinylpyrrolidone (manufactured by Nippon Shokubai Co., Ltd.; polyvinylpyrrolidone K-85N), 8.96 parts of titanium tetrabutoxide, charged, biomixer (( After dispersing and mixing for 3 minutes at 6000 rpm using Bio Mixer BM-2) manufactured by Nippon Seiki Seisakusho Co., Ltd., a sol-gel reaction is performed at 70 ° C. for 1.5 hours, and then the composite particle (C-4) dispersion is subjected to ion exchange. Composite particles (C-4) were obtained by washing with water, solid-liquid separation, and drying.
10 parts of the resulting composite particles (C-4), an aqueous medium of 35 parts of ion-exchanged water (D-1) and 3 parts of glycerin (D-2), and Sunspearl PS-2 (Sanyo Chemical Industries, Ltd.) as a dispersant. ) and 1 part of Newpol PE-108 (manufactured by Sanyo Chemical Industries), and dispersed and mixed for 3 minutes at 6000 rpm using a bio mixer (manufactured by Nippon Seiki Seisakusho Co., Ltd.; Bio Mixer BM-2). , to prepare a fine particle aqueous dispersion (E-4).
The composite particles (C-4) of the obtained dispersion had a specific gravity of 1.10, a refractive index difference of 0.72 between the resin particles (A-4) and the titanium oxide layer, a particle diameter of 330 nm, and composite particles (C-4). The absolute value Δd of the difference between the specific gravity of 4) and the specific gravity of the mixed aqueous medium of (D-1) and (D-2) was 0.05.

Comparative Example 1 [fine particle aqueous dispersion (E'-1)]
In Example 1, the same operation as in Example 1 was performed except that the resin particles (A-1) were changed to resin particles (A'-1), and fine particle aqueous dispersion (E'-1) of the present invention was obtained. Obtained.
The composite particles (C′-1) of the resulting dispersion had a specific gravity of 1.30, a refractive index difference of 0.61 between the resin particles (A′-1) and the titanium oxide layer, a particle diameter of 300 nm, and the composite particles ( The absolute value Δd of the difference in specific gravity between C) and ion-exchanged water (D-1) was 0.30.

Comparative Example 2 [fine particle aqueous dispersion (E'-2)]
In Example 1, the same operation as in Example 1 was performed except that the resin particles (A-1) were changed to the resin particles (A'-2), and the fine particle aqueous dispersion (E'-2) of the present invention was obtained. Obtained.
The composite particles (C′-2) of the obtained dispersion had a specific gravity of 1.30, a refractive index difference of 0.71 between the resin particles (A′-2) and the titanium oxide layer, a particle diameter of 300 nm, and a specific gravity difference of The absolute value Δd was 0.40.

Comparative Example 3 [fine particle aqueous dispersion (E'-3)]
In Example 1, the same operation as in Example 1 was performed except that the resin particles (A-1) were changed to the resin particles (A'-3), and the fine particle aqueous dispersion (E'-3) of the present invention was obtained. Obtained.
The composite particles (C′-3) of the obtained dispersion had a specific gravity of 1.20, a refractive index difference of 0.65 between the resin particles (A′-3) and the titanium oxide layer, a particle diameter of 250 nm, and a specific gravity difference of The absolute value Δd was 0.20.

Comparative Example 4 [fine particle aqueous dispersion (E'-4)]
In Example 1, the same operation as in Example 1 was performed except that the resin particles (A-1) were changed to the resin particles (A'-3), and the fine particle aqueous dispersion (E'-3) of the present invention was prepared. Obtained.
The composite particles (C′-3) of the resulting dispersion had a specific gravity of 1.10, a refractive index difference of 0.72 between the resin particles (A′-3) and the titanium oxide layer, a particle diameter of 600 nm, and a specific gravity difference of The absolute value Δd was 0.10.

[Production of ink composition (F)]
50 parts of an ink vehicle was prepared by blending 18 parts of glycerin, 12 parts of triethylene glycol, 6 parts of triethylene glycol monobutyl ether, and 14 parts of urethane emulsion (manufactured by Sanyo Chemical Industries; Ucoat UWS-145).
50 parts of this ink vehicle were added to the fine particle dispersions (E-1) to (E-4) of the present invention prepared in Examples 1 to 4, and the comparative fine particle dispersions prepared in Comparative Examples 1 to 4 ( E'-1) to (E'-4) are blended with 50 parts by weight each to form ink compositions (F-1) to (F-4) and (F'-1) to (F'-4) was prepared, and the sedimentation and white hiding properties were evaluated by the following methods. Table 2 shows the results.

<Evaluation of sedimentation>
Evaluation of sedimentation property was performed by the method shown below.
8 ml of the sample was placed in a 10 ml sealed glass container and allowed to stand at room temperature for two weeks.
◎: The supernatant layer is 2 mm or less, and there is no sediment on the bottom of the container. The supernatant layer is 4 mm or more, and there is sediment on the bottom of the container.

<Evaluation of white hiding property>
Evaluation of white hiding property was performed by the method shown below.
The sample was coated on coated paper printed in solid black so that the thickness of the coating film after drying was 10 μm, and the coating film formed by drying was observed to confirm the white hiding property.
The white hiding property was evaluated by measuring the L value using a spectrophotometer (X-Rite938; manufactured by X-Rite).
◎; L value is 75 or more ○; L value is 70 or more and less than 75 △; L value is 60 or more and less than 70 ×; L value is less than 60

As shown in Table 2, the fine particle dispersions (E-1) to (E-4) of Examples 1 to 4 of the present invention have a small specific gravity difference from the medium of 0.1, so the ink composition (F -1) to (F-4) are excellent in sedimentation. In addition, since the particle size is 230 to 350 nm, the particle size is the most suitable for reflecting visible light from the viewpoint of Mie scattering, and is excellent in white hiding property.
On the other hand, the fine particle dispersion liquid (E'-1) of Comparative Example 1 and the fine particle dispersion liquid (E'-2) of Comparative Example 2, in which the specific gravity of the resin particles exceeds 1.0, are inferior in settling property compared to the examples. .
In addition, although the resin particles of Comparative Example 3 have a specific gravity of 1.0 or less, the ink composition (F'-3) having a specific gravity difference of 0.2 from the medium is inferior in sedimentation property to that of Examples. .
Further, the fine particle dispersion (E'-4) of Comparative Example 4 having a particle diameter of 600 nm is inferior to the Examples in settling property and white hiding property.

Since the fine particle aqueous dispersion of the present invention has a high white hiding property, it can be used as a white pigment, an additive for paints, a powder coating, an additive for cosmetics, a material for slush molding, and an additive for paper coating. In addition, since the fine particle aqueous dispersion of the present invention has a high reflectance and a small particle size, it is useful as an opaque touch panel member such as a touch panel bezel or a backlight member such as a reflector used in a display. be.
Among these, it is useful as a white pigment because of its low sedimentation property and excellent white hiding property, and can be used as a white pigment for inkjet and a white pigment for paint, and is suitable as an inkjet ink.

Claims (8)

Fine particle aqueous system comprising composite particles (C) in which resin particles (A) having a specific gravity of 1.0 or less and containing an acid-modified polyolefin (a) are coated with titanium oxide (B), dispersed in an aqueous medium (D) A fine particle aqueous dispersion (E), which is a dispersion and has a volume average particle diameter of 150 to 500 nm as measured by the dynamic light scattering method of the composite particles (C). 2. The fine particle aqueous dispersion according to claim 1, wherein the resin particles (A) have an acid value of 1 to 13 mgKOH/g. 3. The fine particle aqueous dispersion according to claim 1, wherein the composite particles (C) have a specific gravity of 0.9 to 1.4. The fine particle aqueous dispersion according to any one of claims 1 to 3, wherein the absolute value Δd of the difference between the specific gravity d _C of the composite particles (C) and the specific gravity d _D of the aqueous medium (D) is 0.3 or less. The fine particle aqueous dispersion according to any one of claims 1 to 4, wherein the resin particles (A) have a melting point of 60 to 100°C. The fine particle aqueous dispersion according to any one of claims 1 to 5, wherein the absolute value Δn of the difference between the refractive index n _A of the resin particles (A) and the refractive index n _B of the titanium oxide (B) is 0.6 or more. body. The fine particle aqueous dispersion according to any one of claims 1 to 6, which is for use as a white pigment.
An inkjet ink composition containing the fine particle aqueous dispersion (E) according to claim 7 .