JP5156303B2 - Method for producing aqueous pigment dispersion - Google Patents

Description

  The present invention relates to a method for producing an aqueous pigment dispersion containing hydrophobic silica, an aqueous pigment dispersion obtained by the production method, and an aqueous ink for inkjet recording.

The ink jet recording method is a recording method in which characters and images are obtained by ejecting ink droplets directly from a very fine nozzle onto a recording member and attaching them. This method is easily spread at full color and inexpensive, and can be used for recording paper as a recording member, and has many advantages in that it is non-contact with the substrate, so that it is widely used.
Among them, from the viewpoint of weather resistance and water resistance of printed materials, those using pigment-based inks have become mainstream, and a technique of adding a hydrophilic inorganic oxide to improve the print density of a printed image. Are disclosed (Patent Document 1, Patent Document 2).

Japanese Patent Laid-Open No. 11-080628 JP-A-11-209671

On the other hand, there is a problem that aggregation of the pigment dispersion occurs when the hydrophobic silica is added to the pigment-based ink. Therefore, in order to uniformly disperse the pigment, a disperser that imparts high shearing force or a high-speed stirring mixer is used. Severe wear occurred in the part, and foreign matter could be mixed in the dispersion.
An object of the present invention is to provide an aqueous pigment dispersion production method, an aqueous pigment dispersion, and an aqueous ink for ink-jet recording, in which even when hydrophobic silica is blended, there is little mixing of impurities and excellent dispersibility and dispersion stability. It is to provide.

The present invention
(1) Step 1: A step of obtaining a dispersion (A) by dispersing a mixture containing a pigment, a water-insoluble polymer, a hydrophobic organic solvent and water,
Step 2: A step of obtaining a dispersion (B) by mixing a hydrophobic silica, a hydrophobic organic solvent and a hydrophilic organic solvent in an amount of 0.5 to 10 times by weight with respect to the amount of the hydrophobic silica, and a step 3: A step of obtaining a dispersion (C) by mixing the dispersion (A) and the dispersion (B),
A method for producing an aqueous pigment dispersion having
(2) an aqueous pigment dispersion obtained by the production method described in (1) above, and (3) an aqueous ink for inkjet recording containing the aqueous pigment dispersion described in (2) above,
About.

  According to the present invention, even when hydrophobic silica is blended, a water-based pigment dispersion and a water-based ink for ink-jet recording can be produced that are less contaminated with foreign matters and excellent in dispersibility and dispersion stability.

[Method for producing aqueous pigment dispersion]
The method for producing a water-based pigment dispersion of the present invention includes a step of obtaining a dispersion (A) by dispersing a mixture containing a pigment, a water-insoluble polymer, a hydrophobic organic solvent and water (step 1), hydrophobic silica, A step (Step 2) of obtaining a dispersion (B) by mixing a hydrophobic organic solvent and a hydrophilic organic solvent 0.5 to 10 times by weight with respect to the amount of the hydrophobic silica, and the dispersion (A ) And the dispersion (B) to obtain a dispersion (C) (step 3).

Process 1
Step 1 is a step of obtaining a dispersion (A) by dispersing a mixture containing a pigment, a water-insoluble polymer, a hydrophobic organic solvent, and water.
(Pigment)
The pigment according to the present invention has a bronze phenomenon in which reflected light is observed in a color different from the original color depending on the observation angle of the printed matter (for details on the bronze phenomenon, see “Color Science Handbook” (Tokyo University Press), page 777. Organic pigments are preferably used from the standpoint of reducing), and examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, Examples include perinone pigments, thioindigo pigments, anthoraquinone pigments, and quinophthalone pigments.
Specific examples of preferred organic pigments include C.I. I. Pigment yellow, C.I. I. Pigment Red, C.I. I. Pigment violet, C.I. I. Pigment blue, and C.I. I. One or more types of products selected from the group consisting of pigment green are listed.

  Among organic pigments, a cyan pigment is preferably used and a phthalocyanine pigment is more preferable from the viewpoint of a large effect of reducing the bronze phenomenon. Examples of the phthalocyanine pigments include metal-free phthalocyanine pigments; metal phthalocyanine pigments such as copper, aluminum, nickel, cobalt, iron, titanium, and tin, and unsubstituted or halogen-substituted phthalocyanine pigments such as chlorine and bromine. . More specifically, a copper phthalocyanine pigment is preferable, and C.I. I. One or more selected from the group consisting of CI Pigment Blue 15, 15: 1, 15: 2, 15: 3, 15: 4, 16 and 60 are preferred. Among these, from the viewpoint of durability against light, heat and solvent, C.I. I. Pigment Blue 15: 3 and 15: 4 are particularly preferable. The pigment used in step 1 does not include silica containing hydrophobic silica.

(Water-insoluble polymer)
Examples of the water-insoluble polymer in Step 1 include a water-insoluble vinyl polymer, a water-insoluble ester polymer, and a water-insoluble urethane polymer. Among these, a water-insoluble vinyl polymer is preferable from the viewpoint of the stability of the aqueous dispersion. In the present invention, the water-insoluble polymer means that when it is dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C., the dissolved amount is 10 g or less, preferably 5 g or less, more preferably 1 g or less. A polymer. When the water-insoluble polymer has a salt-forming group, the above-mentioned dissolution amount refers to the dissolution amount when the salt-forming group of the water-insoluble polymer is neutralized 100% with acetic acid or sodium hydroxide, depending on the type.

The water-insoluble polymer preferably contains a structural unit derived from the salt-forming group-containing monomer (a), a structural unit derived from the hydrophobic monomer (b) and / or a structural unit derived from the macromer (c).
Examples of such a water-insoluble polymer include a salt-forming group-containing monomer (a) (hereinafter also referred to as “(a) component”), a hydrophobic monomer (b) (hereinafter also referred to as “(b) component”). And / or a water-insoluble vinyl polymer obtained by copolymerizing a monomer mixture (hereinafter also referred to as “monomer mixture”) containing macromer (c) (hereinafter also referred to as “component (c)”) is preferable.
Further, the water-insoluble polymer is preferably a water-insoluble graft polymer containing a structural unit derived from the macromer (c) from the viewpoint of developing a sufficient printing density.

The component (a) is used from the viewpoint of enhancing the dispersion stability of the resulting dispersion, and examples thereof include a cationic monomer and an anionic monomer. As the cationic monomer, N, N-dimethylaminoethyl (meth) acrylate and N- (N ′, N′-dimethylaminopropyl) (meth) acrylamide are preferable.
The anionic monomer is preferably an unsaturated carboxylic acid monomer, more preferably acrylic acid or methacrylic acid, from the viewpoints of dispersion stability, dischargeability, and the like. The said (a) component can be used individually or in combination of 2 or more types, respectively.

  The hydrophobic monomer of the component (b) is used from the viewpoints of water resistance, scratch resistance, print density improvement, and the like, and examples thereof include alkyl (meth) acrylate, alkyl (meth) acrylamide, and aromatic ring-containing monomers.

The component (c) is used from the viewpoint of stably dispersing pigments and silica particles with a water-insoluble polymer, and has a number average molecular weight of 500 to 100,000, preferably 1,000 to 10,000, and is not present at one end. Examples include macromers that are monomers having a polymerizable functional group such as a saturated group.
The number average molecular weight of the component (c) can be measured by gel permeation chromatography using polystyrene as a standard substance and tetrahydrofuran containing 50 mmol / L acetic acid as a solvent.
As the macromer of component (c), a styrenic macromer having a polymerizable functional group at one end is preferable from the viewpoint of high affinity with the pigment and improving storage stability.
In the present invention, the macromers may be used alone or in combination of two or more.

  When the polymer used in the present invention is a water-insoluble graft polymer, the weight ratio of [main chain / side chain] is 1/1 to 20/1 from the viewpoint of improving scratch resistance and storage stability. It is preferably 3/2 to 15/1, more preferably 2/1 to 10/1. It is calculated that the polymerizable functional group is contained in the side chain.

In the present invention, the monomer mixture containing the components (a), (b), and (c) further contains a hydroxyl group-containing monomer (d) (hereinafter sometimes referred to as “component (d)”). Is preferred.
The component (d) increases the dispersion stability of the aqueous dispersion. As the component (d), 2-hydroxyethyl (meth) acrylate, polyethylene glycol monomethacrylate, and polypropylene glycol methacrylate are preferable.

The monomer mixture may further contain a monomer (e) represented by the following formula (1) (hereinafter sometimes referred to as “component (e)”).
^{_{CH 2 = C (R 1)}} COO (R 2 O) pR 3 (1)
(In the formula, R ¹ represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, R ² represents a divalent hydrocarbon group having 1 to 30 carbon atoms which may have a hetero atom, R ³ Represents a monovalent hydrocarbon group having 1 to 30 carbon atoms which may have a hetero atom, but p represents the average number of added moles, and is 1 to 60, preferably 1 to 30.)
The component (e) exhibits excellent effects such as improving the ejection stability of the water-based ink and suppressing the occurrence of twisting even when continuous printing is performed.

As the component (e), methoxypolyethylene glycol (p = 1 to 30) (meth) acrylate is preferable.
Specific examples of commercially available (d) and (e) components include: Shin-Nakamura Chemical Co., Ltd., polyfunctional acrylate monomer (NK ester) M-40G, 90G, 230G; Mer series, PE-90, 200, 350, PME-100, 200, 400, 1000, PP-1000, PP-500, PP-800, AP-150, AP-400, AP-550, AP-800, 50PEP -300,50POEP-800B etc. are mentioned.
The component (d) and the component (e) can be used alone or in combination of two or more.

The contents of the components (a) to (e) in the monomer mixture are preferably as follows.
The content of component (a) is preferably 3 to 30% by weight, more preferably 4 to 20% by weight, from the viewpoint of dispersion stability of the resulting dispersion.
The content of the component (b) is preferably 10 to 70% by weight, more preferably 15 to 60% by weight, from the viewpoint of water resistance, scratch resistance, and print density.
The content of the component (c) is preferably 1 to 25% by weight, more preferably 5 to 20% by weight, from the viewpoint of stably dispersing pigments and silica particles with a water-insoluble polymer.
The weight ratio ((a) / [(b) + (c)]) of the content of the component (a) and the total content of the components (b) and (c) is the long-term storage of the resulting water-based ink. From the viewpoints of stability, dischargeability and the like, it is preferably 0.01 to 1, more preferably 0.02 to 0.67, and still more preferably 0.03 to 0.50.

The content of the component (d) is preferably 5 to 40% by weight, more preferably 7 to 30% by weight from the viewpoints of dischargeability and print density.
The content of the component (e) is preferably 5 to 50% by weight, more preferably 10 to 40% by weight, from the viewpoints of dischargeability and dispersion stability.
The total content of the component (a) and the component (d) is preferably 6 to 60% by weight, more preferably 10 to 50% by weight from the viewpoints of stability in water and printing density.
The total content of the component (a) and the component (e) is preferably 6 to 75% by weight, more preferably 13 to 50% by weight from the viewpoints of dispersion stability in water, dischargeability, and the like.
The total content of the component (a), the component (d), and the component (e) is preferably 6 to 60% by weight, more preferably 7 to 7% from the viewpoints of dispersion stability in water, print density, and dischargeability. 50% by weight.
The content of the components derived from the components (a) to (e) in the water-insoluble polymer is the same as the content of the components.

The water-insoluble polymer is produced by copolymerizing the monomer mixture by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. In the case of the solution polymerization method, effects such as high printing density and high bleed resistance can be preferably obtained.
As the solvent used in the solution polymerization method, a polar organic solvent having a high affinity for the water-insoluble polymer is preferable, and the solubility in water at 20 ° C. is preferably 50% by weight or less, and more preferably 5% by weight or more. As the polar organic solvent, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, butoxyethanol, or a mixed solvent of one or more of these with water is preferable.

In the polymerization, azo compounds such as 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), tert-butyl peroxyoctoate, dibenzoyl oxide, etc. Known polymerization initiators such as organic peroxides can be used. The amount of the polymerization initiator is preferably 0.001 to 5 mol, more preferably 0.01 to 2 mol, per mol of the monomer mixture.
In the polymerization, a known polymerization chain transfer agent such as mercaptans such as octyl mercaptan and 2-mercaptoethanol, and thiuram disulfide can be further added.
The polymerization conditions of the monomer mixture vary depending on the type of polymerization initiator, monomer, and solvent used, but the polymerization temperature is usually 30 to 100 ° C., preferably 50 to 80 ° C., and the polymerization time is 1 to 20 hours. is there. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, the produced polymer can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation.

The weight average molecular weight of the obtained water-insoluble polymer is preferably from 5,000 to 500,000, more preferably from 10,000 to 400,000, from the viewpoint of pigment dispersion stability, water resistance, dischargeability, and the like. ~ 300,000 is particularly preferred.
The weight average molecular weight of the polymer is measured using polystyrene as a standard substance by gel chromatography using dimethylformamide in which 60 mmol / L phosphoric acid and 50 mmol / L lithium bromide are dissolved as a solvent. .
The solid content of the water-insoluble polymer solution is preferably 3 to 30% by weight, more preferably 5 to 20% by weight, and most preferably 10 to 15% by weight.

  When the water-insoluble polymer has a salt-forming group derived from the salt-forming group-containing monomer (a), it is neutralized with a neutralizing agent. As the neutralizing agent, an acid or a base can be used depending on the kind of the salt-forming group in the polymer. For example, hydrochloric acid, acetic acid, propionic acid, phosphoric acid, sulfuric acid, lactic acid, succinic acid, glycolic acid, Examples include acids such as gluconic acid and glyceric acid, bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, trimethylamine, triethanolamine, and tributylamine. .

The degree of neutralization of the salt-forming group is preferably 10 to 200%, more preferably 20 to 150%, and particularly preferably 50 to 150%. Here, the degree of neutralization can be determined by the following formula when the salt-forming group is an anionic group.
{[Weight of neutralizing agent (g) / equivalent of neutralizing agent] / [acid value of polymer (KOH mg / g) × polymer weight (g) / (56 × 1000)]} × 100
On the other hand, when the salt-forming group is a cationic group, it can be obtained by the following formula.
[[Weight of neutralizing agent (g) / equivalent of neutralizing agent] / [amine value of polymer (HCL mg / g) × weight of polymer (g) / (36.5 × 1000)]] × 100
The acid value and amine value can be calculated from the structural unit of the polymer, but can also be determined by a method of titrating by dissolving the polymer in an appropriate solvent (for example, methyl ethyl ketone).

(Hydrophobic organic solvent)
The hydrophobic organic solvent used in Step 1 is preferably an organic solvent having a solubility parameter (SP value) of less than 22 (MJ / m ³ ) ^0.5 from the viewpoint of wetness of the pigment surface and affinity with the water-insoluble polymer. From the viewpoint of the stability of the dispersion due to the adsorption of the water-insoluble polymer to the surface, an organic solvent of 18 (MJ / m ³ ) ^0.5 or more is preferable. Preferred examples of such an organic solvent include ketone solvents and ether solvents, and those having a solubility in water at 20 ° C. of 50% by weight or less and 10% by weight or more are more preferable.
As the ketone solvent, acetone (SP value: 20.1 (MJ / m ³ ) ^0.5 ), methyl ethyl ketone (SP value: 19.0 (MJ / m ³ ) ^0.5 ), diethyl ketone (SP value: 18.2 ( MJ / m ³ ) ^0.5 ), methyl isobutyl ketone (SP value: 19.4 (MJ / m ³ ) ^0.5 ) and the like. Examples of ether solvents include dibutyl ether (SP value: (MJ / m ³ ) ^0.5 ), tetrahydrofuran (SP value: 18.8 (MJ / m ³ ) ^0.5 ), dioxane (SP value: 20.7 (MJ)). / m ³ ) ^0.5 ) and the like. Among these solvents, acetone and methyl ethyl ketone are preferable from the above viewpoint, and methyl ethyl ketone is more preferable. These solvents can be used alone or in combination of two or more.

(Dispersion (A))
Regarding the blending amount of the pigment, water-insoluble polymer, hydrophobic organic solvent and water in the dispersion (A) in step 1, wetting of the pigment surface by the hydrophobic organic solvent, the amount of adsorption of the water-insoluble polymer to the pigment and the pigment From the viewpoint of the stability of the dispersion, the pigment is preferably 5 to 50% by weight, the water-insoluble polymer is preferably 2 to 40% by weight, and more preferably 2 to 20% by weight. 5 to 30% by weight, and the hydrophobic organic solvent is preferably 10 to 70% by weight, more preferably 10 to 50% by weight.

  The method for dispersing the mixture in Step 1 is not particularly limited as long as it can be atomized so that water-insoluble polymer particles having a desired average particle diameter can be obtained. As the disperser, for example, a kneader such as a roll mill, a kneader or an extruder, a disperser such as a sand mill or a bead mill, a high pressure homogenizer such as a chamber type can be used. Among these, from the viewpoint of uniformly dispersing the pigment, a method of wet pulverization with a disperser using a dispersion medium is preferable. Furthermore, it is also preferable to adopt a method of dispersing by a high-pressure homogenizer after wet pulverization if necessary.

The material of the dispersion medium is preferably ceramic beads such as titania (TiO ₂ ), zirconia (ZrO ₂ ), zircon (ZrSiO ₄ ) alumina (Al ₂ O ₃ ), particularly titania (TiO ₂ ), from the viewpoint of hardness and the like. Zirconia (ZrO ₂ ) is preferred.
The particle diameter of the dispersion medium is usually 30 to 500 μm, preferably 30 to 400 μm, from the viewpoint of uniformly dispersing the pigment.
The weight ratio of the dispersion medium / dispersion liquid (including all dispersions such as pigment, water-insoluble polymer, water, and organic solvent) in the wet pulverization dispersion is usually 10/1 to 4 / from the viewpoint of uniformly dispersing the pigment. 6, preferably 10/1 to 5/5.

The peripheral speed of the disperser that uses the dispersion medium refers to the speed of the outer periphery of the stirring blade when it has a stirring blade. In the present invention, it is preferably 3 to 30 m / sec, more preferably 5 to 25 m / sec. It is. When there is no stirring blade, it is the rotational speed of the container, and in the present invention, it is preferably a speed of 0.1 to 1 m / sec. The dispersion time is preferably 3 minutes to 15 hours, more preferably 5 minutes to 10 hours, from the viewpoint of uniformly dispersing the pigment. From the same point, the temperature during dispersion is preferably 0 to 60 ° C, more preferably 5 to 30 ° C.
The average particle size of the dispersed particles of the dispersion (A) obtained in Step 1 is 30 from the viewpoint of the stability of the water-based ink obtained through the post-process or prevention of clogging when printing using the water-based ink. It is preferable that it is -200 nm, and it is more preferable that it is 60-120 nm.

From the viewpoint of the stability of the dispersion (C) obtained in Step 3, the dispersion (A) in Step 1 may contain a hydrophilic organic solvent similar to the hydrophilic organic solvent used in Step 2 described later. preferable.
The blending amount of the hydrophilic organic solvent in the step 1 is preferably 0 to 50% by weight with respect to the dispersion (A) from the viewpoint of the stability of the dispersion (C) obtained in the step 3. More preferably, it is -35 weight%.
The order of blending the pigment, water-insoluble polymer, hydrophobic organic solvent and water in step 1 is not particularly limited, but from the viewpoint of pigment wetting and uniform dispersion of the pigment, the hydrophobic organic solvent, the water-insoluble polymer, It is preferable to add in the order of water and pigment, or in the order of water-insoluble polymer, hydrophobic organic solvent, water and pigment.

Process 2
Step 2 is a step of mixing the hydrophobic silica, the hydrophobic organic solvent, and the hydrophilic organic solvent in an amount of 0.5 to 10 times by weight with respect to the amount of the hydrophobic silica to obtain a dispersion (B).
(Hydrophobic silica)
In the present invention, the hydrophobic silica refers to one in which 1 g of the silica is stably dispersed in 10 g of methyl ethyl ketone at 25 ° C. for 1 week, and the dispersion stability can be judged visually.
Hydrophobic silica can be used as silica particles, and the average particle size is preferably 3 nm or more, 100 nm or less, more preferably 50 nm or less, more preferably 30 nm, from the viewpoint of reducing the bronze phenomenon. Or less, more preferably 20 nm or less. From these viewpoints, 3 to 100 nm is preferable, 3 to 50 nm is more preferable, 3 to 30 nm is more preferable, and 3 to 20 nm is still more preferable.

For the measurement of the average particle diameter of the hydrophobic silica, 100 particles are measured using a scanning electron microscope, and the number average particle diameter calculated from image analysis is used. In addition, when there exists a long diameter and a short diameter, it calculates using a long diameter.
The blending amount of the hydrophobic silica is preferably 1/10 to 5/1 in terms of weight ratio to the pigment (hydrophobic silica / pigment), more preferably 1/5 to 5%, from the viewpoint of reducing bronzing reduction. 3/1.

(Hydrophobic organic solvent)
As the hydrophobic organic solvent in Step 2, any of those used in Step 1 can be used in the same manner. From the viewpoint of dispersion stability, the hydrophobic silica is usually marketed by being dispersed in a hydrophobic organic solvent. The blending amount of the hydrophobic organic solvent is preferably 80 to 400 parts by weight and more preferably 100 to 250 parts by weight with respect to 100 parts by weight of the hydrophobic silica.

(Hydrophilic organic solvent)
From the viewpoint of the stability of the dispersion (C) obtained in Step 3, the hydrophilic organic solvent in Step 2 is preferably an organic solvent having a solubility parameter (SP value) of 22 (MJ / m ³ ) ^0.5 or more. For example, isopropyl alcohol (SP value 22.8 (MJ / m ³ ) ^0.5 ), ethanol (SP value 26.2 (MJ / m ³ ) ^0.5 ) and the like are preferable, and ethanol is more preferable.
From the viewpoint of dispersion stability of the aqueous pigment dispersion, the blending amount of the hydrophilic organic solvent in Step 2 with respect to the hydrophobic silica is 0.5 times or more by weight and 1.5 times or more. Preferably, it is 3 times or more. Further, from the viewpoint of production cost, the blending amount is 10 times or less, preferably 8 times or less, and more preferably 7 times or less.

  As described above, in Step 1, it is preferable to contain the same hydrophilic organic solvent as in Step 2, but from the viewpoint of dispersion stability of the aqueous pigment dispersion, the hydrophilic organic solvent used in Step 1 and Step 2 is used. The total blending amount is 0.5 times or more by weight with respect to hydrophobic silica, preferably 1.5 times or more, and more preferably 3 times or more. Further, from the viewpoint of production cost, the total blending amount is 10 times or less, preferably 8 times or less, and more preferably 7 times or less.

(Dispersion (B))
The blending amount of the hydrophobic silica, the hydrophobic organic solvent and the hydrophilic organic solvent in the dispersion (B) in Step 2 is the stability of the silica, the hydrophobic organic solvent and the hydrophilic organic solvent, and the stability of the aqueous pigment dispersion. From the viewpoint of properties, the hydrophobic silica is preferably 6 to 30% by weight, and more preferably 8 to 20% by weight. The hydrophobic organic solvent is preferably 6 to 60% by weight, more preferably 9 to 50% by weight, and the hydrophilic organic solvent is preferably 20 to 85% by weight, preferably 33 to 63% by weight. % Is more preferable.

As the blending order of the hydrophobic silica, the hydrophobic organic solvent and the hydrophilic organic solvent in Step 2, from the viewpoint of dispersibility of the hydrophobic silica, the hydrophobic silica and the hydrophobic organic solvent are mixed, and then the hydrophilic organic solvent is added. It is preferable to add.
The mixing means and mixing conditions are not particularly limited as long as they are general methods, and may be any mixing method that can uniformly mix and disperse the above components, such as anchor blades, turbine blades, and paddle blades. So-called high-speed agitation and mixing devices such as dispersers such as dispersers, sand mills and bead mills, high-pressure homogenizers such as a chamber type, or high shear dispersion devices are not necessarily required. From the viewpoint of prevention, it is preferable not to use the high-speed stirring and mixing device and the high shear dispersion device.
Although there is no restriction | limiting in particular also about mixing temperature and mixing time, From a viewpoint of the dispersion stability of hydrophobic silica, 0-60 degreeC is preferable and 5-35 degreeC is more preferable. The mixing time is preferably 30 seconds to 5 hours, more preferably 1 minute to 1 hour.

Process 3
Step 3 is a step in which the dispersion (A) obtained in Step 1 and the dispersion (B) obtained in Step 2 are mixed to obtain a dispersion (C).
The blending ratio of the dispersion (A) and the dispersion (B) is not particularly limited as long as it is an amount that satisfies the relationship between the components described above. For example, the dispersion (C) obtained in step 3 From the viewpoint of the stability of the dispersion, the dispersion (A) / dispersion (B) weight ratio is preferably 0.5 to 10, and more preferably 1.5 to 4.
Although there is no restriction | limiting in particular in the mixing order of a dispersion (A) and a dispersion (B), From a viewpoint of operativity, it is preferable to add a dispersion (B) to a dispersion (A) and to mix.

  The mixing means and mixing conditions are not particularly limited as long as they are general methods, and may be any mixing method that can uniformly mix each dispersion, such as anchor blades, turbine blades, and paddle blades. Dispersers such as dispersers, sand mills and bead mills, so-called high-speed stirring and mixing devices such as high pressure homogenizers such as chamber type, or high shear dispersion devices are not always necessary, and prevent foreign matter contamination due to mixer wear. From the viewpoint, it is preferable not to use the high-speed stirring and mixing device and the high shear dispersion device. Although there is no restriction | limiting in particular also about mixing temperature and mixing time, From a viewpoint of the dispersion stability of hydrophobic silica, 0-60 degreeC is preferable and 5-35 degreeC is more preferable. The mixing time is preferably 30 seconds to 5 hours, and more preferably 1 minute to 1 hour.

In the present invention, an aqueous pigment dispersion of water-insoluble polymer particles having a desired average particle diameter is obtained by removing the hydrophobic organic solvent and the hydrophilic organic solvent from the dispersion (C) obtained in Step 3 to obtain an aqueous system. Can be obtained. The organic solvent contained in the dispersion (C) can be removed by a known method such as vacuum distillation.
In the obtained water-based pigment dispersion, the organic solvent is substantially removed, and the amount of the organic solvent is preferably 0.1% by weight or less, more preferably 0.01% by weight or less. Moreover, it is preferable to remove coarse particles by centrifuging or filtering the obtained aqueous dispersion.

[Water-based pigment dispersion]
The aqueous pigment dispersion of the present invention is obtained by the above-described production method, and the average particle size of the dispersion is preferably 30 to 200 nm, more preferably 50 from the viewpoint of prevention of clogging of the nozzles of the printer and printing density. It is -130 nm, More preferably, it is 60-120 nm.
In the present invention, the difference between the average particle size and the average particle size of the dispersed particles of the dispersion (A) in Step 1 is preferably 30 nm or less, more preferably 10 nm or less, and more preferably 5 nm or less. More preferably.

In the present invention, the average particle size of the aqueous pigment dispersion and dispersion (A) can be measured under the following conditions using a laser particle analysis system ELS-8000 (cumulant analysis) manufactured by Otsuka Electronics Co., Ltd. it can.
Temperature: 25 ° C
Angle between incident light and detector: 90 °
Number of integration: 100 times Refractive index of dispersion solvent: Refractive index of water (1.333)
Reference material: Uniform Microparticles (average particle size 204 nm) manufactured by Seradyn

The content of each component in the aqueous pigment dispersion of the present invention is as follows.
The content of the hydrophobic silica is preferably 0.1 to 10% by weight, more preferably 0.3 to 8% by weight, and still more preferably 0.5 to 5% by weight, from the viewpoint of reducing the bronze phenomenon.
The content of the pigment is preferably 1 to 10% by weight, more preferably 2 to 10% by weight, still more preferably 3 to 10% by weight, and further preferably 4 to 8% by weight from the viewpoint of increasing the printing density.
The content of the water-insoluble polymer is preferably 0.5 to 10% by weight, more preferably 1 to 8% by weight, and still more preferably 1 to 5% by weight, from the viewpoint of dispersion stability of silica and pigment.
The content ratio of silica and pigment (silica / pigment) is 1/10 to 5/1 by weight, preferably 1/5 to 3/1, more preferably 1/4, from the viewpoint of reducing the bronze phenomenon. ~ 2/1.

  The content ratio of the pigment and silica to the water-insoluble polymer [water-insoluble polymer / (pigment + silica)] is 5/95 to 90/10 in weight ratio from the viewpoint of enhancing the printing density, scratch resistance and dispersion stability. More preferably, it is 10 / 90-75 / 25, More preferably, it is 20 / 80-50 / 50. The water content in the aqueous pigment dispersion of the present invention is preferably 30 to 90% by weight, more preferably 40 to 80% by weight.

The surface tension (20 ° C.) of the aqueous pigment dispersion of the present invention is preferably 30 to 65 mN / m, and more preferably 35 to 60 mN / m.
The viscosity (20 ° C.) of 20% by weight (solid content) of the aqueous pigment dispersion of the present invention is preferably 1 to 12 mPa · s, more preferably 1 to 9 mPa · s in order to obtain a preferable viscosity when used as an aqueous ink. More preferably, 2 to 6 mPa · s is more preferable, and 2 to 5 mPa · s is still more preferable.

[Water-based ink for inkjet recording]
The water-based ink of the present invention may use the above-mentioned water-based pigment dispersion as it is, but the water-based pigment dispersion generally includes a wetting agent, a penetrating agent, a dispersant, a viscosity modifier, an antifoaming agent, An antifungal agent, an antirust agent, etc. may be added.
The water content in the water-based ink of the present invention is preferably 30 to 95% by weight, more preferably 40 to 90% by weight.
The surface tension (20 ° C.) of the aqueous ink of the present invention is preferably 23 to 50 mN / m, more preferably 23 to 45 mN / m, more preferably 23 to 40 mN / m, and still more preferably 23 to 30 mN / m. m. The viscosity (20 ° C.) of the water-based ink of the present invention is preferably 2 to 12 mPa · s, more preferably 2.5 to 10 mPa · s, and preferably 2.5 to 6 mPa · s in order to maintain good ejection properties. Further preferred.

In the following production examples, examples and comparative examples, “parts” and “%” are “parts by weight” and “% by weight” unless otherwise specified.
Production Example 1
In a reaction vessel, 8.2 parts of methyl ethyl ketone, 0.03 part of a polymerization chain transfer agent (2-mercaptoethanol) and 10% of 200 parts of the monomer mixture shown in Table 1 were mixed and mixed with nitrogen gas. This was carried out sufficiently to obtain a mixed solution.
Meanwhile, the remaining 90% of the monomer mixture shown in Table 1 was charged into the dropping funnel, and 0.28 part of a polymerization chain transfer agent (2-mercaptoethanol), 73.6 parts of methyl ethyl ketone and 2,2′-azobis (2,4 -Dimethylvaleronitrile) 1.8 parts was mixed and nitrogen gas substitution was performed sufficiently to obtain a mixed solution.
Under a nitrogen atmosphere, the temperature of the mixed solution in the reaction vessel was increased to 75 ° C. while stirring, and the mixed solution in the dropping funnel was dropped over 5 hours. After 2 hours at 75 ° C. from the end of dropping, a solution in which 1.6 parts of 2,2′-azobis (2,4-dimethylvaleronitrile) was dissolved in 21.8 parts of methyl ethyl ketone was added, and further at 75 ° C. for 2 hours, The polymer solution was obtained by aging at 80 ° C. for 2 hours.
The amount of the polymer obtained dissolved in water (25 ° C.) was 0.10 g with respect to 100 g.

Production Example 2
The amount of polymerization chain transfer agent (2-mercaptoethanol) charged into the reaction vessel in Production Example 1 from 0.03 part to 0.05 part, and the amount of polymerization chain transfer agent (2-mercaptoethanol) charged into the dropping funnel Was changed from 0.28 part to 0.41 part, and the same operation as in Production Example 1 was performed except that the monomer mixture was changed to the composition shown in Table 1.
The weight average molecular weight of the obtained polymer was measured by gel chromatography using 60 mmol / L phosphoric acid and 50 mmol / L lithium bromide-containing dimethylformamide as a solvent using polystyrene as a standard substance. The results are shown in Table 1.
The amount of the polymer obtained dissolved in water (25 ° C.) was 0.15 g with respect to 100 g of water.

The details of the compounds shown in Table 1 are as follows.
Polyethylene glycol monomethacrylate (ethylene oxide average addition mole number: 9): Shin-Nakamura Chemical Co., Ltd., trade name: NK ester M-90G
Polypropylene glycol monomethacrylate (propylene oxide average added mole number: 12): manufactured by NOF Corporation, trade name: Blemmer PP-800
Styrene macromer: manufactured by Toa Gosei Co., Ltd., trade name: AS-6S, number average molecular weight: 6000, polymerizable functional group: methacryloyloxy group

Example 1
(Process 1)
45 g of the polymer obtained by drying the polymer solution obtained in Production Example 1 under reduced pressure was dissolved in 117 g of methyl ethyl ketone, and 7.9 g of a neutralizing agent (5N aqueous sodium hydroxide solution) and 458 g of ion-exchanged water were added thereto to form a salt. After neutralizing the group, copper phthalocyanine pigment (CI Pigment Blue 15: 4 [P.B. 15: 4], manufactured by Toyo Ink Co., Ltd., trade name: LIONOGEN BLUE BGJ) was added as a cyan pigment, The mixture was mixed with a disper blade at a temperature of 20 ° C. for 1 hour. Next, the obtained mixture was subjected to a dispersion treatment at 20 ° C. using a bead mill (Koto Kogyo Co., Ltd., trade name Ultra Apex Mill). As the dispersion medium, 0.05 mmφ zirconia beads were used, and dispersion treatment was performed for 1 hour under the conditions of a bead filling rate of 80% and a stirring blade peripheral speed of 12 m / s. Further, a high pressure homogenizer (trade name: Microfluidizer, manufactured by Microfluidics, Inc.) was subjected to high pressure dispersion of 5 passes at 180 MPa to obtain a dispersion (A) having an average particle diameter of 71 nm.

(Process 2)
Hydrophobic silica containing 70% methyl ethyl ketone (manufactured by Nissan Chemical Industries, Ltd .; trade name MEK-ST, average particle size 10 to 20 nm) 167 g (50 g as hydrophobic silica) and ethanol (SP value 26 as hydrophilic organic solvent) ^0.2 (MJ / m ³ ) ^0.5 ) was mixed and mixed with a paddle blade at 20 ° C. for 20 minutes to obtain a dispersion (B).
(Process 3)
100 parts of the dispersion (A) obtained in the step 1 and 56 parts of the dispersion (B) obtained in the step 2 are mixed, and mixed at 20 ° C. for 20 minutes using a paddle blade. )

After removing methyl ethyl ketone and a part of water from the obtained dispersion (C) under reduced pressure at 60 ° C., a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.) was used. By filtering with an attached needleless syringe with a volume of 25 mL (manufactured by Terumo Corp.) and removing coarse particles, an aqueous pigment dispersion 1 having a solid content concentration of 20% by weight and an average particle size of 71 nm was obtained.
To 40 parts of this aqueous pigment dispersion, 10 parts of glycerin, 7 parts of triethylene glycol monobutyl ether, 1 part of Surfynol 465 (manufactured by Nissin Chemical Industry Co., Ltd.), 0.3 part of Proxel XL2 (manufactured by Avicia Co., Ltd.) And 41.7 parts of ion-exchanged water were mixed, and the obtained mixture was mixed with a 1.2 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.) without a 25 mL needle. Aqueous ink 1 was obtained by filtering with a syringe and removing coarse particles.

Example 2
An aqueous pigment was prepared in the same manner as in Example 1 except that ethanol was 150 g in Step 2 of Example 1 and that in Step 3 Dispersion (B) was 43 parts with respect to 100 parts of Dispersion (A). Dispersion 2 and aqueous ink 2 were obtained.

Example 3
In Step 1 of Example 1, 5 parts of isopropyl alcohol (IPA) (SP value 22.8 (MJ / m ³ ) ^0.5 ) was further added to 73 parts of the resulting dispersion and mixed for 20 minutes with a paddle blade. A water-based pigment dispersion 3 was prepared in the same manner as in Example 1 except that 200 g of ethanol was used in step 2 and 46 parts of dispersion (B) was added to 100 parts of dispersion (A) in step 3. And water-based ink 3 was obtained.

Example 4
167 g of hydrophobic silica (manufactured by Nissan Chemical Industries, Ltd .; trade name MIBK-ST) containing 70% of methyl isobutyl ketone in step 2 of Example 3 (50 g as hydrophobic silica, average particle size of 10 to 20 nm) The aqueous pigment dispersion 4 and the aqueous ink 4 were obtained in the same manner as in Example 3 except that the aqueous pigment dispersion 4 and the aqueous ink 4 were changed.

Example 5
An aqueous pigment dispersion 5 and an aqueous ink 5 were obtained in the same manner as in Example 3, except that isopropyl alcohol was changed to ethanol in Step 1 of Example 3.

Example 6
The polymer obtained in Production Example 1 in Step 1 of Example 1 was changed to the polymer obtained in Production Example 2, and isopropyl alcohol (IPA) (SP value 22. 8 (MJ / m ³ ) ^0.5 ) 12.5 parts was added and mixed with a paddle blade for 20 minutes. In step 2, the amount of ethanol was 125 g, and in step 3, dispersion (B) was dispersed (A ) A water-based pigment dispersion 6 and a water-based ink 6 were obtained in the same manner as in Example 1 except that the amount was 34 parts with respect to 100 parts.

Example 7
30 parts of isopropyl alcohol (IPA) (SP value 22.8 (MJ / m ³ ) ^0.5 ) was further added to 73 parts of the dispersion obtained in Step 1 of Example 1, and mixed for 20 minutes with a paddle blade. A water-based pigment dispersion was prepared in the same manner as in Example 1 except that the amount of ethanol was 100 g in Step 2 and that the dispersion (B) was 25 parts with respect to 100 parts of the dispersion (A) in Step 3. 7 and water-based ink 7 were obtained.

Example 8
20 parts of isopropyl alcohol (IPA) (SP value 22.8 (MJ / m ³ ) ^0.5 ) was further added to 73 parts of the dispersion obtained in Step 1 of Example 1, and mixed for 20 minutes with a paddle blade. An aqueous pigment dispersion was prepared by performing the same operation as in Example 1 except that the amount of ethanol was 200 g in Step 2 and that the dispersion (B) was 39 parts with respect to 100 parts of the dispersion (A) in Step 3. 8 and water-based ink 8 were obtained.

Example 9
10 parts of isopropyl alcohol (IPA) (SP value 22.8 (MJ / m ³ ) ^0.5 ) was further added to 73 parts of the dispersion obtained in Step 1 of Example 1, and mixed for 20 minutes with a paddle blade. An aqueous pigment dispersion was prepared in the same manner as in Example 1 except that the amount of ethanol was 300 g in Step 2 and that the dispersion (B) was 56 parts with respect to 100 parts of the dispersion (A) in Step 3. 9 and water-based ink 9 were obtained.

Example 10
A dispersion (C) was obtained in the same manner as in Example 1 except that ethanol was changed to 50 g in Step 2 of Example 1.

Comparative Example 1
45 g of the polymer obtained by drying the polymer solution obtained in Production Example 1 under reduced pressure was dissolved in 117 g of methyl ethyl ketone, and 7.9 g of a neutralizing agent (5N aqueous sodium hydroxide solution) and 458 g of ion-exchanged water were added thereto to form a salt. The group was neutralized and copper phthalocyanine pigment (CI Pigment Blue 15: 4 [P.B. 15: 4], manufactured by Toyo Ink Co., Ltd., trade name: LIONOGEN BLUE BGJ) as a cyan pigment and methyl ethyl ketone 70 % -Containing hydrophobic silica (manufactured by Nissan Chemical Industries, Ltd .; trade name MEK-ST) 167 g (50 g as hydrophobic silica) was added and mixed with a disper blade at a temperature of 20 ° C. for 1 hour. Next, the obtained mixture was subjected to a dispersion treatment using a bead mill (Koto Kogyo Co., Ltd., trade name Ultra Apex Mill). 0.05 mmφ zirconia beads were used as a dispersion medium, and dispersion treatment was performed at 20 ° C. for 1 hour under the conditions of a bead filling rate of 80% and a stirring blade peripheral speed of 12 m / s. Further, a high pressure homogenizer (trade name: Microfluidizer, manufactured by Microfluidics, Inc.) was subjected to high pressure dispersion of 5 passes at 180 MPa to obtain a dispersion.
The obtained dispersion was subjected to removal of methyl ethyl ketone and a part of water under reduced pressure at 60 ° C., and then attached with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.) By filtering with a 25 mL needleless syringe (manufactured by Terumo Corp.) and removing coarse particles, an aqueous pigment dispersion 10 and an aqueous ink 10 having a solid content concentration of 20% by weight and an average particle diameter of 69 nm were obtained.

Comparative Example 2
In Step 2 of Example 1, ethanol was not added and 167 g of hydrophobic silica containing 70% methyl ethyl ketone (manufactured by Nissan Chemical Industries, Ltd .; trade name MEK-ST) (50 g as hydrophobic silica) was directly dispersed (B The dispersion (C) was obtained by carrying out the same operations as in Example 1 except that.

Comparative Example 3
In Step 2 of Example 1, a dispersion (C) was obtained in the same manner as in Example 1, except that 250 g of toluene (SP value 18.2 (MJ / m ³ ) ^0.5 ) was used instead of ethanol.

Comparative Example 4
In Step 2 of Example 1, a dispersion (C) was obtained in the same manner as in Example 1, except that 250 g of methyl ethyl ketone (SP value 19.0 (MJ / m ³ ) ^0.5 ) was used instead of ethanol.

The cohesiveness of each of the dispersions (C) obtained in Examples 1 to 10 and Comparative Examples 2 to 4 was evaluated as follows. The results are shown in Table 2-1 and Table 2-2.
Aggregate amount (%)
The dispersion (C) obtained in step 3 is filtered through a 200-mesh sieve, the solid content remaining on the mesh and the weight of the solid content that has passed through the mesh are measured, and the ratio [(residual on the mesh Solid content weight / solid content weight that passed through the mesh) × 100] [%] was calculated as the aggregate amount.
Particle size change (nm)
Increase amount of average particle size of dispersion (C) obtained in step 3 with respect to average particle size of dispersion (A) obtained in step 1 (average particle size of dispersion (C) −dispersion (A ) (Average particle size) (nm) was defined as the amount of change in particle size.

Next, the aqueous pigment dispersions obtained in each of Examples 1 to 10 and Comparative Example 1 were evaluated as follows.
Viscosity (mPa · s)
The viscosity of the aqueous pigment dispersion was measured with an E-type viscometer [manufactured by Toki Sangyo Co., Ltd., model number: RE80 type].
Zirconia content (mg / kg)
The content of zirconia as an inorganic component considered to be derived from the disperser (bead mill) was quantified by ICP emission analysis (inductively coupled plasma emission analysis) and calculated as the amount per 1 kg of the dispersion.

From Table 2-1, it can be seen that the dispersions (C) of Examples 1 to 10 have few coarse particles after mixing, and the rate of increase in particle size is also slight. Moreover, the viscosity of the obtained water-based pigment dispersion is low, and the zirconia component considered to be derived from the dispersion equipment was not detected, indicating that a good water-based pigment dispersion was obtained.
On the other hand, from Table 2-2, it was found that the aqueous pigment dispersion obtained in Comparative Example 1 contained a large amount of a zirconia component that was considered to be derived from the dispersion equipment, although the viscosity was low. Further, in the dispersions (C) of Comparative Examples 2 to 4, a large amount of aggregates were generated, the organic solvent could not be removed, and an aqueous pigment dispersion could not be obtained.

Claims (6)

Step 1: A step of obtaining a dispersion (A) by dispersing a mixture containing a pigment, a water-insoluble polymer, a hydrophobic organic solvent and water,
Step 2: A step of obtaining a dispersion (B) by mixing a hydrophobic silica, a hydrophobic organic solvent and a hydrophilic organic solvent in an amount of 0.5 to 10 times by weight with respect to the amount of the hydrophobic silica, and a step 3: A step of obtaining a dispersion (C) by mixing the dispersion (A) and the dispersion (B),
The water-insoluble polymer is a polymer having a dissolution amount of 10 g or less when the water-insoluble polymer is dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C., The hydrophobic silica is one in which 1 g of the silica is stably dispersed in 10 g of methyl ethyl ketone at 25 ° C. for 1 week, and the solubility parameter of the hydrophobic organic solvent in the steps 1 and 2 is less than 22 (MJ / m ³ ) ^0.5 And the solubility parameter of the hydrophilic organic solvent in Step 2 is 22 (MJ / m ³ ) ^0.5 or more . The method for producing an aqueous pigment dispersion according to claim 1 , wherein the dispersion (A) contains a hydrophilic organic solvent, and the solubility parameter of the hydrophilic organic solvent is 22 (MJ / m ³ ) ^0.5 or more .   The method for producing an aqueous pigment dispersion according to claim 1 or 2, wherein the dispersion treatment in step 1 is performed with a disperser using a dispersion medium.   The method for producing an aqueous pigment dispersion according to any one of claims 1 to 3, wherein the pigment is a cyan pigment. The water-based pigment dispersion obtained by the manufacturing method in any one of Claims 1-4 . An aqueous ink for ink-jet recording containing the aqueous pigment dispersion according to claim 5 .