JP2016204514A - Aqueous pigment dispersion and inkjet recording ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an aqueous pigment dispersion using a quinacridone pigment for providing an inkjet recording aqueous ink which can be applied to a printer carrying a high resolution inkjet head, has reduced coarse particles and is excellent in discharge stability.SOLUTION: There are provided: a method for producing an aqueous pigment dispersion obtained by dispersing a polymer (A) having a number average molecular weight of 1000-6000 which has an anionic group, has a solubility in water of 0.1 g/100 ml or less and forms fine particles in water when the neutralization rate of the anionic group by a basic compound is set at 100%, a water-soluble organic solvent, a red azo pigment and a basic compound in water, wherein the amount of water at the initial stage of dispersion is less than 15 mass% with respect to the red azo pigment; and an inkjet recording ink using the aqueous pigment dispersion obtained by the production method.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing an aqueous pigment dispersion using a red azo pigment.

Pigment compositions that use pigments as coloring materials make use of the excellent light resistance of pigments, whether it is indoors or outdoors, in the paint field for automobiles and building materials, offset inks, gravure inks, flexo inks, silk screen inks Are used in various applications such as the printing ink field or the water-based ink field for inkjet recording.
Among these, water-based ink using water as a main solvent has an excellent feature that the risk of fire and the like like solvent ink can be further reduced, and water-based ink is mainly used for ink jet recording. ing.

The pigment is insoluble in water and is used as an aqueous pigment dispersion dispersed in an aqueous medium. For this reason, a technique for stably dispersing a pigment in an aqueous medium has been conventionally studied.
For example, in the presence of an organic solvent such as a ketone solvent or an alcohol solvent, a synthetic resin having a specific acid value, a base, and a colorant are mixed well using a stirrer or a dispersion device to dissolve or disperse the colorant. And a method of dispersing small droplets of a self-water dispersible resin solution containing a colorant in an aqueous medium by mixing the colored resin solution and the aqueous medium, For example, refer to paragraph 0024 of Patent Document 1 and paragraph 0025 of Patent Document 2), a method of using a block polymer compound having a hydrophobic segment and a hydrophilic segment including a hydrophobic unit and a hydrophilic unit as a pigment dispersant (for example, Patent Reference 3), an AB block polymer, A is styrene, B is acrylic acid, A has a degree of polymerization of about 5 to about 50, and B has a degree of polymerization of about 70 to about 80. Is (An-Bm) method using a block polymer as a pigment dispersing agent are known (e.g., see Patent Document 4).

On the other hand, one of the problems of the aqueous pigment dispersion is to reduce coarse particles that are considered to occur during dispersion. Coarse particles are particles that have a very large particle size compared to the average particle size of the resulting aqueous pigment dispersion, such as undispersed pigments, broken or agglomerated pigments during dispersion, or pigments It is presumed that the polymer used as a dispersant is agglomerated.
Coarse particles can be generated in any pigment, and therefore, studies have been conducted for each color pigment. For example, in Patent Document 5, as a method for reducing the cohesiveness of a red azo pigment and realizing stable ink ejection without nozzle clogging over time, a method of setting the content of a compound having a specific structural formula in an ink to 400 ppm or less. It is disclosed.

Coarse particles obstruct the formation of a uniform coating film surface during coating or printing, while causing nozzle clogging in an inkjet head in a method of printing by ejecting ink from nozzles, such as aqueous ink for inkjet recording. In particular, along with the recent increase in resolution of ink jet printers, the density of ink jet head nozzles and the finer droplets, that is, the diameter of nozzles for ejecting ink and the higher integration have been advanced (for example, see Patent Document 6). ). As the nozzle diameter becomes smaller, the size of allowable foreign matter also becomes smaller, resulting in increased nozzle clogging. In other words, the ink that could be applied to a conventional inkjet printer is a newly developed high-resolution inkjet head. There arises a problem that the printer cannot be used.
The above-described method is an excellent method for producing a water-based ink for ink-jet recording, but there is still room for study to provide an ink corresponding to the recent miniaturization and high integration of the nozzle diameter.

Japanese Patent Laid-Open No. 08-183920 JP 2007-238949 A JP 2008-195769 A Japanese Patent Laid-Open No. 10-7955 JP 2012-184334 A JP2013-993A

  An object of the present invention is to provide an aqueous pigment dispersion using a red azo pigment that can be applied to a printer equipped with a high-resolution inkjet head and provides a water-based ink for inkjet recording with reduced coarse particles and excellent ejection stability. It is in providing the manufacturing method of.

  The present inventors have a polymer having a specific number average molecular weight, an anionic group, but very low solubility in water, and forming fine particles when the anionic group is neutralized by a basic compound at a rate of 100%. Is used as a pigment dispersant, and the amount of water at the initial stage of dispersion is less than a specific amount with respect to the red azo pigment.

  That is, the present invention has an anionic group, has a solubility in water of 0.1 g / 100 ml or less, and fine particles in water when the neutralization rate of the anionic group by a basic compound is 100%. A method for producing an aqueous pigment dispersion in which a polymer (A) having a number average molecular weight in the range of 1000 to 6000, a water-soluble organic solvent, a red azo pigment, and a basic compound is dispersed in water And the manufacturing method of the aqueous pigment dispersion whose water quantity of an initial stage of dispersion | distribution is less than 15 mass% with respect to the said red azo pigment is provided.

  The present invention also provides an ink for inkjet recording using the aqueous pigment dispersion obtained by the production method described above.

  According to the present invention, it is possible to obtain an aqueous pigment dispersion using a red azo pigment that provides a water-based ink for ink jet recording with reduced coarse particles and excellent discharge stability.

(Polymer (A))
The polymer (A) used in the present invention has a solubility in water of 0.1 g / 100 ml or less, and fine particles in water when the neutralization rate of the anionic group by the basic compound is 100%. It is a polymer having a number average molecular weight in the range of 1000 to 6000.

(Solubility in water)
In the present invention, the solubility of the polymer (A) in water is defined as follows. That is, 0.5 g of a polymer whose particle size is adjusted in the range of 250 μm to 90 μm using a sieve having openings of 250 μm and 90 μm is sealed in a bag processed with a 400 mesh wire net, immersed in 50 ml of water, and at a temperature of 25 ° C. For 24 hours. After soaking for 24 hours, drying was performed by performing drying for 2 hours in a dryer set at 110 ° C. with a 400-mesh wire mesh enclosing the polymer. The change in the weight of the 400 mesh wire mesh encapsulating the polymer before and after water immersion was measured, and the solubility was calculated according to the following equation.

(Fine particles)
Further, in the present invention, whether or not to form fine particles in water when the neutralization rate of the anionic group with the basic compound was set to 100% was determined as follows.
(1) The acid value of the polymer is previously measured by an acid value measuring method based on JIS test method K 0070-1992. Specifically, 0.5 g of a polymer is dissolved in a tetrahydrofuran (hereinafter sometimes referred to as THF) solvent, and titrated with a 0.1 M potassium hydroxide alcohol solution using phenolphthalein as an indicator to obtain an acid value.
(2) After adding 1 g of polymer to 50 ml of water, 0.1 mol / L potassium hydroxide aqueous solution that only neutralizes the obtained acid value is added to make 100% neutralization.
(3) 100% neutralized liquid was irradiated with ultrasonic waves in an ultrasonic cleaner (SND Ultrasonic Cleaner US-102, 38 kHz self-excited transmission) at a temperature of 25 ° C. for 2 hours. Leave for 24 hours at room temperature.
After standing for 24 hours, a sample solution obtained by sampling a liquid at a depth of 2 cm from the liquid surface was used as a dynamic light scattering particle size distribution measuring device (dynamic light scattering particle size measuring device “Microtrack” manufactured by Nikkiso Co., Ltd. Using a particle size distribution meter UPA-ST150 "), it is confirmed whether or not fine particles are present by determining whether or not light scattering information by fine particle formation can be obtained.

(Particle size of fine particles)
If the particle size of the fine particles obtained from the polymer (A) used in the present invention is too large, the polymer (A) may not be stable in water. Accordingly, the particle diameter of the polymer (A) is preferably not so large, preferably in the range of 5 to 1,000 nm, more preferably in the range of 7 to 700 nm, and most preferably in the range of 10 to 500 nm. In addition, the narrow particle size distribution tends to be more excellent in dispersibility, but this does not hinder the implementation when the particle size distribution is wide.
As for the particle size and particle size distribution, the dynamic light scattering type particle size distribution measuring device (dynamic light scattering type particle size measuring device “Microtrac particle size distribution meter UPA-ST150 manufactured by Nikkiso Co., Ltd. )).

(Neutralization rate of polymer (A))
The neutralization rate of the polymer (A) used in the present invention was determined by the following formula.

  The acid value of the polymer (A) was measured based on JIS test method K 0070-1992. Specifically, 0.5 g of a sample was dissolved in a THF solvent and titrated with a 0.1 M potassium hydroxide alcohol solution using phenolphthalein as an indicator.

(Polymer (A) number average molecular weight)
The number average molecular weight of the polymer (A) used in the present invention is 1000 to 6000. Since the resin of the present invention has a low solubility in water of 0.1 g / 100 ml or less as described above, a resin having a very high molecular weight can be precipitated when dispersed in water even in a state neutralized with a basic compound. There is sex. In addition, the permeability to the pigment aggregates is weakened, and the disintegration property of the pigment aggregates tends to be lowered, making it difficult to disperse the pigments easily.
On the other hand, when the number average molecular weight is less than 1000, the stability of the obtained aqueous pigment dispersion may be lowered.
From this viewpoint, the polymer (A) used in the present application preferably has a lower molecular weight. Among them, the number average molecular weight is more preferably 1300 to 5000, and most preferably 1500 to 4500.
In the present invention, the number average molecular weight is a value in terms of polystyrene measured by GPC (gel permeation chromatography), specifically a value measured under the following conditions.

(Measurement method of number average molecular weight (Mn))
It measured by the gel permeation chromatography (GPC) method on the following conditions.

Measuring device: High-speed GPC device (“HLC-8220GPC” manufactured by Tosoh Corporation)
Column: The following columns manufactured by Tosoh Corporation were connected in series.
"TSKgel G5000" (7.8 mm ID x 30 cm) x 1 "TSKgel G4000" (7.8 mm ID x 30 cm) x 1 "TSKgel G3000" (7.8 mm ID x 30 cm) x 1 “TSKgel G2000” (7.8 mm ID × 30 cm) × 1 detector: RI (differential refractometer)
Column temperature: 40 ° C
Eluent: Tetrahydrofuran (THF)
Flow rate: 1.0 mL / min Injection amount: 100 μL (THF solution with a sample concentration of 0.4 mass%)
Standard sample: A calibration curve was prepared using the following standard polystyrene.

(Standard polystyrene)
"TSKgel standard polystyrene A-500" manufactured by Tosoh Corporation
"TSKgel standard polystyrene A-1000" manufactured by Tosoh Corporation
"TSKgel standard polystyrene A-2500" manufactured by Tosoh Corporation
"TSKgel standard polystyrene A-5000" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-1" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-2" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-4" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-10" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-20" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-40" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-80" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-128" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-288" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-550" manufactured by Tosoh Corporation

(surface tension)
Some of the aqueous resin dispersions containing the polymer (A) used in the present invention have a surface tension of nearly 70 dyn / cm and a surface tension close to water. The higher the surface tension of the pigment dispersant, the higher the surface tension of the resulting pigment dispersion can be expected to be maintained. On the other hand, when a polymer that dissolves in water and has high solubility in water and does not form fine particles when the neutralization rate of the anionic group with a basic compound is 100%, the surface of the aqueous solution of the polymer is used. Tension tends to be very low. In the present invention, the surface tension of the aqueous resin dispersion obtained from the polymer (A) is preferably 30 dyn / cm or more, and more preferably the surface tension of the polymer (A) is 40 dyn / cm or more. The surface tension was measured for a resin solution that was neutralized 100% by adding 0.1 g / L aqueous potassium hydroxide solution that neutralized 100% of the obtained acid value after adding 1 g of the polymer (A). Value.

The polymer (A) is a polymer that is insoluble or hardly soluble in water that is the main medium of the pigment dispersion as described above, and forms fine particles in a state where it is neutralized 100%. The polymer is not particularly limited as long as it is a polymer having a hydrophobic group in one molecule in addition to an anionic group which is a hydrophilic group.
Examples of such a polymer include a block polymer having a polymer block having a hydrophobic group and a polymer block having an anionic group. In addition, even if it is a block polymer, the polymer which does not form microparticles | fine-particles when the solubility in water exceeds 0.1g / 100ml, or the neutralization rate by the basic compound of the said anionic group is 100% is the present invention. The effect of cannot be obtained.

  When the number of the hydrophobic group and the anionic group is too large, the solubility in water exceeds 0.1 g / 100 ml, or the neutralization rate of the anionic group by the basic compound is 100. %, The possibility of not forming fine particles increases. From this viewpoint, the number of anionic groups is preferably not so high. In the polymer, the number of anionic groups and the solubility in water are not necessarily specified by the acid value or the number of anionic groups at the time of polymer design. For example, the polymers having the same acid value However, those having a low molecular weight tend to have high solubility in water, and those having a high molecular weight tend to have low solubility in water. From this, in the present invention, the polymer (A) is specified by the solubility in water.

The polymer (A) may be a homopolymer, but is preferably a copolymer, and may be a random polymer, a block polymer, or an alternating polymer, but is particularly a block polymer. Is preferred. The polymer may be a branched polymer, but is preferably a linear polymer.
In addition, the polymer (A) is preferably a vinyl polymer from the viewpoint of design freedom, and methods for producing a vinyl polymer having a desired molecular weight and solubility characteristics in the present invention include living radical polymerization and living cationic polymerization. It is preferable to produce by using “living polymerization” such as living anionic polymerization.
Among them, the polymer (A) is preferably a vinyl polymer produced using a (meth) acrylate monomer as one of the raw materials, and as a method for producing such a vinyl polymer, living radical polymerization and living anion polymerization are possible. Further, living anionic polymerization is preferable from the viewpoint of more precisely designing the molecular weight of the block polymer and each segment.

(The polymer (A) produced by living anionic polymerization)
Specifically, the polymer (A) produced by living anionic polymerization is a polymer represented by the general formula (1).

（１）

(1)

In formula (1), A ¹ represents an organolithium initiator residue, A ² represents a polymer block of a monomer having an aromatic ring or a heterocyclic ring, A ³ represents a polymer block containing an anionic group, and n is 1 represents an integer of 1 to 5, and B represents an aromatic group or an alkyl group.

In the general formula (1), A ¹ represents an organic lithium initiator residues. Specific examples of the organic lithium initiator include methyl lithium, ethyl lithium, propyl lithium, butyl lithium (n-butyl lithium, sec-butyl lithium, iso-butyl lithium, tert-butyl lithium, etc.), pentyl lithium, hexyl lithium, Alkyllithium such as methoxymethyllithium and ethoxymethyllithium; phenylalkylenelithium such as benzyllithium, α-methylstyryllithium, 1,1-diphenyl-3-methylpentyllithium, 1,1-diphenylhexyllithium and phenylethyllithium Alkenyl lithium such as vinyl lithium, allyl lithium, propenyl lithium, butenyl lithium; ethynyl lithium, butynyl lithium, pentynyl lithium, hexynyl lithium, etc. Alkylithium such as phenyllithium and naphthyllithium; Heterocyclic lithium such as 2-thienyllithium, 4-pyridyllithium and 2-quinolyllithium; Alkyl such as tri (n-butyl) magnesiumlithium and trimethylmagnesiumlithium Examples include lithium magnesium complex.
In the organic lithium initiator, the bond between the organic group and lithium is cleaved to generate an active terminal on the organic group side, and polymerization is started therefrom. Therefore, an organic group derived from organolithium is bonded to the polymer terminal obtained. In the present invention, an organic group derived from organolithium bonded to the polymer terminal is referred to as an organolithium initiator residue. For example, in the case of a polymer using methyl lithium as an initiator, the organic lithium initiator acid group is a methyl group, and in the case of a polymer using butyl lithium as an initiator, the organic lithium initiator acid group is a butyl group.

In the general formula (1), A ² represents a polymer block having a hydrophobic group. A ² is preferably a group that is highly adsorbed to the pigment when it comes into contact with the pigment in addition to the purpose of balancing an appropriate balance of solubility as described above. From this viewpoint, A ² is an aromatic ring or A polymer block of a monomer having a heterocyclic ring is preferable.
Specifically, the polymer block of a monomer having an aromatic ring or a heterocycle refers to homopolymerization or copolymerization of a monomer having an aromatic ring such as a styrene monomer or a monomer having a heterocycle such as a vinylpyridine monomer. It is a polymer block of the homopolymer or copolymer obtained in this way.
Examples of the monomer having an aromatic ring include styrene, p-tert-butyldimethylsiloxystyrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, p-tert-butoxystyrene, m-tert-butoxystyrene, Styrene monomers such as p-tert- (1-ethoxymethyl) styrene, m-chlorostyrene, p-chlorostyrene, p-fluorostyrene, α-methylstyrene, p-methyl-α-methylstyrene, and vinylnaphthalene And vinyl anthracene.
Examples of the monomer having a heterocyclic ring include vinylpyridine monomers such as 2-vinylpyridine and 4-vinylpyridine.
These monomers can be used alone or in admixture of two or more.

In the general formula (1), A ³ represents a polymer block containing an anionic group. A ³ is another object to provide a described above moderate solubility, there is a purpose of imparting dispersion stability in water when a pigment dispersion.
Examples of the anionic group in the polymer block A ³ include a carboxyl group, a sulfonic acid group, and a phosphoric acid group. Among them, a carboxyl group is preferable because of its preparation and availability of monomer varieties. Two carboxyl groups may be acid anhydride groups obtained by dehydration condensation within a molecule or between molecules.

Method for introducing anionic groups of the A ³ is not particularly limited, for example, the case the anionic group is a carboxyl group, (meth) homopolymer obtained by copolymerizing a homopolymer or other monomers acrylic acid or It may be a polymer block (PB1) of a copolymer, or a homopolymer obtained by homopolymerizing or copolymerizing with other monomers a (meth) acrylate having a protective group that can be regenerated into an anionic group by deprotection. The polymer or copolymer may be a polymer block (PB2) in which a part or all of the protective group reproducible to the anionic group is regenerated to the anionic group.
In addition, (meth) acrylic acid used in the polymer block A ³ represents a generic name of acrylic acid and methacrylic acid, and (meth) acrylate represents a generic name of acrylate and methacrylate.

  Specific examples of (meth) acrylic acid and (meth) acrylate include (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, iso-propyl (meth) acrylate, and (meth) acrylic acid. Allyl, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, n-amyl (meth) acrylate, (meth) Iso-amyl acrylate, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-lauryl (meth) acrylate, n-tridecyl (meth) acrylate , (Meth) acrylic acid n-stearyl, (meth) acrylic acid phenyl, (meth) acrylic acid benzyl, (meth) acrylic acid Chlorhexyl, 4-tert-butylcyclohexyl (meth) acrylate, isobornyl (meth) acrylate, tricyclodecanyl (meth) acrylate, dicyclopentadienyl (meth) acrylate, adamantyl (meth) acrylate, ( Glycidyl acrylate, tetrahydrofurfuryl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylamino (meth) acrylate Ethyl, trifluoroethyl (meth) acrylate, tetrafluoropropyl (meth) acrylate, pentafluoropropyl (meth) acrylate, octafluoropentyl (meth) acrylate, pentadecafluorooctyl (meth) acrylate, (meth Acrylic acid hep Heptadecafluorodecyl, N, N-dimethyl (meth) acrylamide, (meth) acryloyl morpholine, (meth) acrylonitrile,

Polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, polyethylene glycol-polypropylene glycol (meth) acrylate, polyethylene glycol-polybutylene glycol (meth) acrylate, polypropylene glycol-polybutylene glycol (meth) acrylate, methoxypolyethylene glycol ( (Meth) acrylate, ethoxypolyethyleneglycol (meth) acrylate, butoxypolyethyleneglycol (meth) acrylate, octoxypolyethyleneglycol (meth) acrylate, lauroxypolyethyleneglycol (meth) acrylate, stearoxypolyethyleneglycol (meth) acrylate, phenoxypolyethyleneglycol (Meta) acryle DOO, methoxy polypropylene glycol (meth) acrylate, octoxypolyethylene glycol - containing polyalkylene oxide groups such as polypropylene glycol (meth) acrylate (meth) acrylate and the like. These monomers can be used alone or in admixture of two or more.

In the living anion polymerization method, when the monomer to be used is a monomer having a group having an active proton such as an anionic group, the active end of the living anion polymerization polymer immediately reacts with the group having an active proton and deactivates. A polymer cannot be obtained. In living anionic polymerization, it is difficult to polymerize a monomer having a group having an active proton as it is. Therefore, a group having an active proton is obtained by polymerizing the group having an active proton in a protected state and then deprotecting the protecting group. Is preferably reproduced.
For this reason, in the polymer block A ^3, it is preferable to use a monomer containing a (meth) acrylate having a renewable protecting group an anionic group by deprotection. By using the monomer, the above-described inhibition of polymerization can be prevented during polymerization. An anionic group protected by a protecting group can be regenerated into an anionic group by deprotection after obtaining a block polymer.

  For example, when the anionic group is a carboxyl group, the carboxyl group can be regenerated by esterifying the carboxyl group and deprotecting it by hydrolysis or the like as a subsequent step. In this case, the protecting group that can be converted into a carboxyl group is preferably a group having an ester bond, such as a primary alkoxycarbonyl group such as a methoxycarbonyl group, an ethoxycarbonyl group, an n-propoxycarbonyl group, or an n-butoxycarbonyl group. Secondary alkoxycarbonyl groups such as isopropoxycarbonyl group and sec-butoxycarbonyl group; tertiary alkoxycarbonyl groups such as t-butoxycarbonyl group; phenylalkoxycarbonyl groups such as benzyloxycarbonyl group; ethoxyethylcarbonyl group and the like; And the like.

  When the anionic group is a carboxyl group, usable monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, sec -Butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate (lauryl (meth) ) Acrylate), tridecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate (stearyl (meth) Acrylate), nonadecyl (meth) acrylate, icosanyl (meth) acrylate and other alkyl (meth) acrylates; benzyl (meth) acrylate and other phenylalkylene (meth) acrylates; ethoxyethyl (meth) acrylate and other alkoxyalkyl (meth) acrylates Etc. These (meth) acrylates (c1) can be used alone or in combination of two or more. Of these (meth) acrylates (c1), t-butyl (meth) acrylate and benzyl (meth) acrylate are preferred because the conversion reaction to a carboxyl group is easy. In view of industrial availability, t-butyl (meth) acrylate is more preferable.

In general formula (1), B represents an aromatic group or an alkyl group having 1 to 10 carbon atoms. N represents an integer of 1 to 5.
In the living anionic polymerization method, when a (meth) acrylate monomer is directly polymerized to the active end of a highly nucleophilic styrenic polymer, it may not be polymerized due to nucleophilic attack on the carbonyl carbon. For this reason, when superposing | polymerizing a (meth) acrylate monomer to said A < ¹ > -A < ² >, after using a reaction modifier and adjusting nucleophilicity, superposing | polymerizing a (meth) acrylate monomer is performed. B in the general formula (1) is a group derived from the reaction modifier. Specific examples of the reaction modifier include diphenylethylene, α-methylstyrene, p-methyl-α-methylstyrene, and the like.

(Living anion polymerization using microreactor)
The living anion polymerization method can be carried out by a batch system as used in conventional free radical polymerization by adjusting the reaction conditions, and can also include a method of continuous polymerization using a microreactor. Since the microreactor has a good mixing property between the polymerization initiator and the monomer, the reaction starts at the same time, the temperature is uniform and the polymerization rate can be made uniform, and therefore the molecular weight distribution of the produced polymer can be narrowed. At the same time, since the growth terminal is stable, it becomes easy to produce a block copolymer in which both components of the block are not mixed. Moreover, since the controllability of the reaction temperature is good, it is easy to suppress side reactions.

A general method of living anionic polymerization using a microreactor will be described with reference to FIG. 1 which is a schematic diagram of a microreactor.
A T-shaped micromixer M1 having a flow path capable of mixing a plurality of liquids from the tube reactors P1 and P2 (7 and 8 in FIG. 1), respectively, with the first monomer and the polymerization initiator for initiating the polymerization is shown. 1), the first monomer is subjected to living anion polymerization in the T-shaped micromixer M1 to form a first polymer (step 1).

Next, the obtained first polymer is moved to the T-shaped micromixer M2 (2 in FIG. 1), and the growth terminal of the obtained polymer is moved into the tube reactor P3 (FIG. 1) in the mixer M2. The reaction is adjusted by trapping with the reaction modifier introduced from the middle 9) (step 2).
At this time, the number of n in the general formula (1) can be controlled by the type and amount of the reaction modifier.

Next, the first polymer subjected to reaction control in the T-shaped micromixer M2 is moved to the T-shaped micromixer M3 (3 in FIG. 1), and the tube reactor P4 is moved in the mixer M3. The introduced second monomer and the first polymer subjected to the reaction control are continuously subjected to living anion polymerization (step 3).
Then, the block copolymer is produced by quenching the reaction with a compound having an active proton such as methanol.

When the polymer (A) represented by the general formula (1) of the present invention is produced by the microreactor, a monomer having an aromatic ring or a heterocyclic ring is used as the first monomer, and an organic compound is used as the initiator. by reacting the lithium initiator, an organic group at one terminal of the polymer block (the polymer block a ² monomers are organolithium initiator residues of the a ¹ having an aromatic ring or a heterocyclic ring of the a ² Get bound).
Next, after adjusting the reactivity of the growth terminal using a reaction modifier, a polymer block containing (meth) acrylate having a reproducible protecting group on the anionic group is reacted as the second monomer. Get.
Thereafter, by reproducing the anionic group by deprotection reaction such as hydrolysis, polymer blocks containing the A ³ i.e. anionic groups are obtained.

A method for regenerating an ester bond of a protective group that can be regenerated to the anionic group to an anionic group by a deprotection reaction such as hydrolysis will be described in detail.
The hydrolysis reaction of the ester bond proceeds under acidic conditions or basic conditions, but the conditions are slightly different depending on the group having an ester bond. For example, when the group having an ester bond is a primary alkoxycarbonyl group such as a methoxycarbonyl group or a secondary alkoxycarbonyl group such as an isopropoxycarbonyl group, a carboxyl group is obtained by hydrolysis under basic conditions. be able to. In this case, examples of the basic compound to be subjected to basic conditions include metal hydroxides such as sodium hydroxide and potassium hydroxide.

  Further, when the group having an ester bond is a tertiary alkoxycarbonyl group such as a t-butoxycarbonyl group, a carboxyl group can be obtained by hydrolysis under acidic conditions. In this case, examples of acidic compounds to be used under acidic conditions include mineral acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; Breasted acids such as trifluoroacetic acid; Lewis acids such as trimethylsilyl triflate. The reaction conditions for hydrolysis under acidic conditions of the t-butoxycarbonyl group are disclosed in, for example, “The Chemical Society of Japan, 5th edition, Experimental Chemistry Course 16 Synthesis of Organic Compounds IV”.

Furthermore, as a method for converting a t-butoxycarbonyl group into a carboxyl group, a method using a cation exchange resin in place of the above-mentioned acid may be mentioned. Examples of the cation exchange resin, e.g., a carboxyl group (-COOH) in the side chain of the polymer chain, resins having a sulfo group (-SO 3 _H) acid groups and the like. Among these, a strong cation exchange resin having a sulfo group on the side chain of the resin is preferable because the reaction can proceed rapidly. Examples of commercially available cation exchange resins that can be used in the present invention include strongly acidic cation exchange resin “Amberlite” manufactured by Organo Corporation. Since the amount of the cation exchange resin used can be effectively hydrolyzed, the range of 5 to 200 parts by mass is preferable with respect to 100 parts by mass of the polymer represented by the general formula (1), and 10 to 100 parts by mass. The range of is more preferable.

  Further, when the group having an ester bond is a phenylalkoxycarbonyl group such as a benzyloxycarbonyl group, it can be converted to a carboxyl group by performing a hydrogenation reduction reaction. At this time, as the reaction conditions, the phenylalkoxycarbonyl group can be quantitatively regenerated into a carboxyl group by performing the reaction using hydrogen gas as a reducing agent at room temperature in the presence of a palladium catalyst such as palladium acetate.

As described above, since the reaction conditions during the conversion of the type of group to the carboxyl group are different with, for example, t- butyl as a raw material of A ³ (meth) acrylate and n- butyl (meth) acrylate with an ester bond The polymer obtained by copolymerization has a t-butoxycarbonyl group and an n-butoxycarbonyl group. Here, since the n-butoxycarbonyl group does not hydrolyze under acidic conditions where the t-butoxycarbonyl group is hydrolyzed, only the t-butoxycarbonyl group can be selectively hydrolyzed and deprotected to the carboxyl group. It becomes. Therefore, it is possible to the acid value of the adjustment of the hydrophilic block (A ³⁾ by appropriately selecting a monomer containing a (meth) acrylate having a renewable protecting group an anionic group which is a raw material monomer of A ^3.

Further, in the polymer (A) represented by the general formula (1), the polymer block (A ² ) and the polymer block (A ³ ) are more clearly separated, and the resulting aqueous pigment dispersion is more stable. Is advantageous in terms of sex. The molar ratio A ² : A ³ between the polymer block (A ² ) and the polymer block (A ³ ) is preferably in the range of 100: 10 to 100: 500. If the ratio of A ³ is less than 10 per 100 of the A ^2, it tends to be inferior in ejection stability at the time of dispersion stability and inkjet discharge of the pigment. On the other hand if the ratio of A ³ is more than 500 per 100 of A ^2, too high hydrophilicity of the polymer, the recording medium is apt to penetrate into the the case of paper or the like, coloring property decreases. In particular, the ratio is preferably A ² : A ³ = 100: 10 to 100: 450.

In the polymer (A) represented by the general formula (1), the number of monomers having an aromatic ring or a heterocyclic ring constituting the polymer block (A ² ) is preferably in the range of 5 to 40, and in the range of 6 to 30. Is more preferable, and the range of 7 to 25 is most preferable. The number of anionic groups constituting the polymer block (A ³ ) is preferably in the range of 3-20, more preferably in the range of 4-17, and most preferably in the range of 5-15.
Configure ^{A 3,} and the number of moles having an aromatic ring or a heterocyclic ring constituting the polymer block ^{(A 2),} the ^{(A 3):} molar ratio ^A 2 of the polymer block ^{(A 2)} and polymer blocks ^{(A 3)} 100: 7.5-100: 400 is preferable when it represents with the molar ratio of the number of moles of the anionic group to do.

  The acid value of the polymer (A) represented by the general formula (1) is preferably 40 to 400 mgKOH / g, more preferably 40 to 300 mgKOH / g, and most preferably 40 to 190 mgKOH / g. When the acid value is less than 40 mgKOH / g, there is a possibility that the dispersion stability of the pigment and the ejection stability at the time of inkjet ejection are not sufficient. On the other hand, when the acid value exceeds 400 mgKOH / g, the hydrophilicity of the polymer increases, and the color developability decreases because it easily penetrates into the recording medium. If the acid value exceeds 190 mgKOH / g, the water resistance of the resulting ink may be affected depending on the case.

  In addition, the acid value of the polymer in this invention was made into the acid value by the acid value measuring method similar to the measuring method of the fine particle of the said polymer (A).

(Neutralizer, basic compound)
In the aqueous pigment dispersion obtained by the production method of the present invention, the anionic group of the polymer (A) is preferably neutralized.
As the basic compound for neutralizing the anionic group of the polymer (A), any known and conventional compounds can be used, for example, inorganic basic compounds such as alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. Substances and organic basic compounds such as ammonia, triethylamine and alkanolamine can be used.
In the present invention, the neutralization amount of the polymer (A) present in the aqueous pigment dispersion need not be 100% neutralized with respect to the acid value of the polymer. Specifically, the neutralization rate of the polymer (A) is preferably 20% to 200%, more preferably 80% to 150%.

(Pigment)
As the pigment type of the red azo pigment used in the present invention, any known ones can be used, and among them, a naphthol azo pigment is preferable. For example, C.I. I. Pigment Red 31, 32, 146, 147, 150, 184, 187, 188, 210, 238, 245, 247, 266, 268, 269, and a mixture or solid solution of at least two pigments selected from these pigments Can be mentioned. The form of the pigment may be a dry pigment in the form of powder, granule or block, or a wet cake or slurry.
Among these, from the viewpoint of hue and lightness, C.I. I. Pigment Red 150, 170, 187, 266, 268, and 269 are preferable.

(Water-soluble organic solvent)
The water-soluble organic solvent used in the present invention is added for the purpose of accelerating the familiarity between the red azo pigment and the polymer (A) after wetting the surface of the red azo pigment in Step 1. In addition, when the obtained aqueous pigment dispersion is used as a raw material for ink jet recording ink, it has a high boiling point of 100 ° C. or higher so that it does not affect the ink specification and is preferably applied as an ink drying inhibitor. Water-soluble organic solvents are preferred, polyhydric alcohols having high boiling point, low volatility and high surface tension are preferred, and glycols such as diethylene glycol and triethylene glycol are particularly preferred. In general, glycols are often contained in ink compositions, and there is no problem even if they remain in the final product.

  Preferred water-soluble organic solvents include, for example, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol; butanediol, pentanediol, hexanediol, and diols of the same family Diols such as propylene glycol laurate; diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl Ether, di Glycol ethers such as cellosolve including propylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether; sulfolane; lactones such as γ-butyrolactone; N -Lactams such as-(2-hydroxyethyl) pyrrolidone, 2-hydroxypyrrolidone and N-methylpyrrolidone; glycerin, ethylene oxide adducts of glycerin, alkylene oxide adducts of glycerin such as propylene oxide adducts of glycerin, etc. Examples include various other solvents known as organic solvents. These water-soluble organic solvents can be used alone or in combination.

(water)
Water used in the present invention is a pigment dispersion medium finally obtained. As the water, pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water can be used. Moreover, water may be used independently and the mixed solvent which consists of water and a water-soluble solvent may be sufficient. Examples of the water-soluble solvent include ketones such as acetone, methyl ethyl ketone, methyl butyl ketone, and methyl isobutyl ketone; methanol, ethanol, 2-propanol, 2-methyl-1-propanol, 1-butanol, 2-methoxyethanol, Alcohols such as tetrahydrofuran; ethers such as tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane; dimethylformamide, N-methylpyrrolidone, and the polyhydric alcohols described above as preferred water-soluble organic solvents. These water-soluble organic solvents can be used alone or in combination.

(Method for producing aqueous pigment dispersion)
In the present invention, the aqueous pigment dispersion refers to an aqueous pigment dispersion in which a pigment before being converted into an ink is dispersed at a high concentration in water as a dispersion medium.
The pigment concentration of the aqueous pigment dispersion is usually adjusted to be 10 to 50% by mass. When using this to make ink, depending on the desired ink application and physical properties, water or additives are added as appropriate, and the pigment concentration is simply diluted to 0.1 to 20% by mass. Ink can be obtained.

  The method for producing an aqueous pigment dispersion of the present invention is a method for producing an aqueous pigment dispersion in which the polymer (A), a water-soluble organic solvent, a red azo pigment, and a basic compound are dispersed. It is characterized in that the initial amount of water is less than 15% by mass with respect to the pigment.

Specifically, the following methods can be mentioned.
(Method 1) The polymer (A), the water-soluble organic solvent, and the red azo pigment are kneaded, the solid content ratio is 40% by mass or more, and the amount of water is less than 15% by mass with respect to the red azo pigment. A method for producing an aqueous pigment dispersion, comprising the step 1 of obtaining a kneaded dispersion and the step 2 of mixing the basic compound and the water in the kneaded dispersion in this order.

(Method 2) The polymer (A), the water-soluble organic solvent, the basic compound, and the red azo pigment are kneaded, and the solid content ratio is 40% by mass or more and the amount of water is 15 with respect to the red azo pigment. A method for producing an aqueous pigment dispersion, comprising the step 1 of obtaining a kneaded dispersion of less than mass% and the step 2 of mixing the water with the kneaded dispersion in this order.

In (Method 1), the amount of water in the initial stage of dispersion, that is, in Step 1, is less than 15% by mass with respect to the red azo pigment, and the timing of neutralizing with the polymer (A) is not performed in Step 1, but in Step 2. It is the feature to carry out in.
In Step 1, the polymer (A) is not neutralized and the amount of water charged is less than 15% by mass with respect to the red azo pigment. The adsorptivity to the red azo pigment is improved, and the stability of the obtained aqueous pigment dispersion can be enhanced.

The red azo pigment used in the present application is very hydrophobic. In order to effectively adsorb the polymer (A) used as a dispersant to such a highly hydrophobic pigment, the hydrophobicity of the polymer (A) during dispersion is increased and the hydrophobic interaction is maximized. I think that it is preferable. The amount of water in step 1 is less than 15% by mass with respect to the red azo pigment, and dispersion is performed in the absence of a basic compound that is a neutralizing agent for the polymer (A), thereby allowing the polymer (A) to be dispersed. It is considered that the repulsion of the polymer (A) to the red azo pigment is improved because charge repulsion due to the highly polar ionic group generated in the polymer can be minimized.
Thus, a good aqueous pigment dispersion can be obtained by performing Step 2 of adding the basic compound and water to the dispersion of the red azo pigment and the polymer (A) firmly adsorbed to the pigment. .

  In particular, when the polymer represented by the general formula (1) is used as the polymer (A), the polymer represented by the general formula (1) has a block type structure in which a hydrophobic group and a hydrophilic group are separated. Since the hydrophilic portion is densified unlike the random structure, when one hydrophilic group is neutralized and hydrated, the adjacent hydrophilic group is easily neutralized. In this way, since the neutralization reaction of the acid groups proceeds sequentially, the affinity to water is increased. For example, a random copolymer in which hydrophobic groups and hydrophilic groups known as pigment dispersants are randomly arranged. Thus, there is no fear of precipitation or precipitation which is a concern when using the above, and a good aqueous pigment dispersion can be obtained.

On the other hand, the (Method 2) is characterized in that the amount of water in Step 1 is less than 15% by mass with respect to the red azo pigment, and the timing of neutralization with the polymer (A) is also performed in Step 1.
The polymer (A) has a water solubility of 0.1 g / 100 ml or less and is hardly soluble in water when not neutralized. However, in some cases, the polymer (A) is hardly compatible with the water-soluble organic solvent to be used and may be difficult to disperse. . Neutralization facilitates compatibility with a water-soluble organic solvent, that is, facilitates dispersion, but there is a concern that the hydrophilicity becomes high. As described above, since the red azo pigment used in the present application is very hydrophobic, it is preferable to suppress the hydrophilicity of the polymer (A) as much as possible. From this point, the amount of water in the initial stage of dispersion is the red azo pigment. When the content is less than 15% by mass, the adsorptivity of the polymer (A) to the red azo pigment can be improved, and the stability of the resulting aqueous pigment dispersion can be improved. The amount of water at the initial stage of dispersion is preferably less than 12% by mass.

  In the initial stage of dispersion (hereinafter referred to as step 1) in the production method of the present invention, specifically, the polymer (A), the water-soluble organic solvent, and the red azo pigment are kneaded and dispersed in a high solid content ratio. The process to do. In the initial stage of dispersion, the red azo pigment is agglomerated, and the mass is gradually refined as it blends with the polymer (A) while being wetted with a water-soluble organic solvent. This step is preferably a kneading and dispersing method suitable for dispersing a mixture having a higher solid content ratio. Examples of the apparatus suitable for the kneading and dispersing method include a roll mill, a Henschel mixer, a pressure kneader, an intensive mixer, a Banbury mixer, and a planetary mixer. The solid content ratio at this time is preferably 40% by mass or more.

  In order to give a strong shearing force, which is a merit of the kneading dispersion method, to the mixture, it is preferable to knead the mixture at a high solid content ratio, and a higher shearing force can be applied to the mixture. The solid content ratio is more preferably 50% by mass or more.

In order to increase the pigment concentration of the obtained aqueous pigment dispersion, it is preferable to increase the amount of the red azo pigment in the mixture as much as possible. For example, it is preferable to set it as 35 mass% or more with respect to the said mixture whole quantity, and it is still more preferable that it is 40 mass% or more.
Further, the content ratio of the pigment and the polymer (A) is not particularly limited, but for example, the polymer (A) is preferably blended in an amount of 5 to 200 parts by weight, more preferably 5 parts per 100 parts by weight of the pigment. -100 mass parts.

  The water-soluble organic solvent is usually blended in an amount of 10 to 50% by mass, preferably 20 to 40% by mass, in the charged mixture. The amount added is about 1/2 to 10 times the amount of polymer (A), and preferably about 1 to 5 times the amount of polymer (A). If the amount of the water-soluble organic solvent is less than ½ of the amount of the polymer (A), the resin cannot be dissolved, partially dissolved, or swollen, and the dispersion stability of the red azo pigment may be lowered. On the other hand, if it exceeds 10 times, the viscosity of the mixture for kneading is lowered and sufficient kneading cannot be performed, so that the dispersibility of the red azo pigment is lowered and there is a risk of causing image quality deterioration such as ejection failure in the ink composition. .

  Moreover, it is preferable to mix | blend 20-200 mass parts with respect to 100 mass parts of pigments with respect to a red azo pigment, and, more preferably, it is 30-200 mass parts with respect to a red azo pigment. If it is less than 20 parts by mass, the surface of the red azo pigment may not be sufficiently wet at the initial stage of kneading.

As the basic compound used as the neutralizing agent in the step 1 and the step 2, a 100% pure product may be added, but it is preferable to use an aqueous solution because there is a risk of heat generation. In addition, when using aqueous solution, the water in this aqueous solution shall be counted in the amount of water of the dispersion | distribution initial stage of this application.
The basic compound is preferably used so that the neutralization rate of the polymer (A) is 20% to 200%, and more preferably 50% to 150%. The neutralization rate at this time is calculated by the following formula as described above.

In the step 2 of diluting the kneaded product obtained in the step 1 with water, adding water at a time and mixing it may sometimes fail to obtain a uniform aqueous pigment dispersion. It is preferable to add and mix in portions. Usually, it is dispersed using a disperser.
As the disperser used in the step 2, a known one can be used. For example, in the case of using a medium, a paint shaker, a ball mill, an attritor, a basket mill, a sand mill, a sand grinder, a dyno mill, a disper mat, an SC mill, Examples include spike mills and agitator mills. Examples of media that do not use media include ultrasonic homogenizers, nanomizers, resolvers, dispersers, and high-speed impeller dispersers. The concentration may be adjusted with a water-soluble solvent as necessary after dispersion.
Depending on the type of the disperser used, before carrying out water dispersion with the disperser, if necessary, a water-soluble organic solvent is further added to the dispersion, mixed and diluted, and then processed with the disperser. It is preferable to adjust the viscosity to be suitable for the above (hereinafter, the viscosity-adjusted product may be referred to as a viscosity-adjusted product). For example, when a sand mill is used, it is preferable to perform dispersion by driving the sand mill after diluting to a solid content concentration of 10 to 40 mass% and adjusting the viscosity to several tens to several hundred centipoise.
Moreover, after performing the water dispersion of the process 2, you may insert a centrifugation and a filtration process as needed.

In the present application, an aqueous pigment dispersion using water as a medium is formed by phase inversion emulsification or a similar mechanism in Step 2 described above.
By passing through step (1) and step (2) in this order in this order, an aqueous pigment dispersion with reduced coarse particles can be obtained.
In addition, it is presumed that the aqueous pigment dispersion obtained in this manner is stabilized by inclusion or partial adsorption of the pigment in the red azo pigment.

(Water-based ink for inkjet recording)
The aqueous pigment dispersion obtained in the present invention is diluted to a desired concentration, and is used in the paint field for automobiles and building materials, in the printing ink field such as offset ink, gravure ink, flexo ink, silk screen ink, or for inkjet recording. It can be used for various applications such as the water-based ink field. Especially, since coarse particles are reduced, it can be particularly preferably used as a water-based ink for ink jet recording.
When the aqueous pigment dispersion of the present invention is applied to an aqueous ink for inkjet recording, water, a binder resin, and the like are further added to obtain desired physical properties, and a wetting agent (drying inhibitor), a penetrating agent as necessary. Or by adding other additives.
After the ink adjustment, a centrifugal separation or filtration process may be added.

(Wetting agent)
The wetting agent is added for the purpose of preventing the ink from drying. The content of the wetting agent in the ink for the purpose of preventing drying is preferably 3 to 50% by mass.
The wetting agent used in the present invention is not particularly limited, but a wetting agent that is miscible with water and can prevent clogging of the head of an inkjet printer is preferable. For example: glycerin, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol having a molecular weight of 2000 or less, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propylene glycol, isopropylene glycol, isobutylene glycol, 1,4-butane Diol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, mesoerythritol, pentaerythritol, sulfolane; lactones such as γ-butyrolactone; N- (2-hydroxyethyl) pyrrolidone, etc. Lactams; and glycerin and its derivatives. Among them, the inclusion of propylene glycol and 1,3-butanediol is safe and has excellent effects in ink drying properties and ejection performance.

(Penetration agent)
The penetrant is added for the purpose of improving the permeability to a recording medium and adjusting the dot diameter on the recording medium.
Examples of the penetrant include lower alcohols such as ethanol and isopropyl alcohol, ethylene oxide adducts of alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether, and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether.
The penetrant content in the ink is preferably 0.01 to 10% by mass.

(Surfactant)
The surfactant is added to adjust ink properties such as surface tension. The surfactant that can be added for this purpose is not particularly limited, and examples include various anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Of these, anionic surfactants and nonionic surfactants are preferred.

  Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate of higher fatty acid ester, sulfonate of higher fatty acid ester, higher alcohol ether. Sulfate salts and sulfonates of the above, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, etc. Specific examples include dodecylbenzene sulfonate, isopropyl naphthalene sulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenyl sulfonate, dibutylphenylphenol disulfate. , And the like salts.

  Nonionic surfactants include, for example, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester , Polyoxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, fatty acid alkylolamide, alkyl alkanolamide, acetylene glycol, oxyethylene adduct of acetylene glycol, Polyethylene glycol polypropylene glycol block copolymer, etc. Among them, polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid Preference is given to alkylolamide, acetylene glycol, oxyethylene adducts of acetylene glycol and polyethylene glycol polypropylene glycol block copolymers. Among these, those having an HLB in the range of 7 to 20 are preferable because of excellent dissolution stability.

  Other surfactants include silicone surfactants such as polysiloxane oxyethylene adducts; fluorine surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers. Biosurfactants such as spicrispolic acid, rhamnolipid, lysolecithin and the like can also be used.

  These surfactants can be used alone or in combination of two or more. When the surfactant is added, the addition amount is preferably in the range of 0.001 to 2% by mass, more preferably 0.001 to 1.5% by mass, and more preferably 0.01 to 1.5% by mass with respect to the total mass of the ink. More preferably, it is in the range of 1% by mass. When the addition amount of the surfactant is less than 0.001% by mass, the effect of adding the surfactant tends to be not obtained, and when it exceeds 2% by mass, problems such as blurring of the image are likely to occur. .

Moreover, antiseptic | preservative, a viscosity modifier, a pH adjuster, a chelating agent, a plasticizer, antioxidant, an ultraviolet absorber etc. can be added as needed.
In addition, the water-soluble organic solvent used in the step 1 includes one that functions as a wetting agent or a penetrating agent, for example. When the water-soluble organic solvent having such a function is used in the step 1, it is preferable to add while adjusting the amount.

  The amount of pigment in the water-based ink for inkjet recording is preferably 0.1 to 20% by mass in order to obtain a sufficient image density and to ensure dispersion stability of the pigment in the ink.

(recoding media)
The recording medium of the water-based ink for inkjet recording is not particularly limited, and is an absorbent recording medium such as copy paper (PPC paper) generally used in a copying machine, a recording medium having an ink absorbing layer, There may be a non-water-absorbing recording medium that does not have absorptivity, a hard-absorbing recording medium that has a low water-absorbing property, and the like. The water-based ink for ink-jet recording of the present invention is also characterized by good color developability particularly when recording on a recording medium having an absorption layer, a non-water-absorbing recording medium, or a hardly-absorbing recording medium.

  Examples of the absorbent recording medium include plain paper, fabric, cardboard, wood, and the like. Further, examples of the recording medium having an absorption layer include inkjet dedicated paper, and specific examples thereof include, for example, Pictrico Pro Photo Paper from Pictorico Co., Ltd.

  Examples of non-water-absorbing recording media that do not have ink absorbency include those used for food packaging materials and the like, and known plastic films can be used. Specific examples include polyester films such as polyethylene terephthalate and polyethylene naphthalate, polyolefin films such as polyethylene and polypropylene, polyamide films such as nylon, polystyrene films, polyvinyl alcohol films, polyvinyl chloride films, polycarbonate films, polyacrylonitrile films, A polylactic acid film etc. are mentioned. In particular, a polyester film, a polyolefin film, and a polyamide film are preferable, and polyethylene terephthalate, polypropylene, and nylon are more preferable. Moreover, the above-mentioned film coated with polyvinylidene chloride or the like for imparting a barrier property may be used, and if necessary, a film in which a deposited layer of a metal oxide such as aluminum or a metal oxide such as silica or alumina is used in combination. May be.

The plastic film may be an unstretched film, but may be stretched in a uniaxial or biaxial direction. Further, the surface of the film may be untreated, but those subjected to various treatments for improving adhesive properties such as corona discharge treatment, ozone treatment, low temperature plasma treatment, flame treatment, glow discharge treatment and the like are preferable.
The film thickness of the plastic film is appropriately changed according to the use. For example, in the case of a flexible packaging application, the film thickness is 10 μm to 100 μm as having flexibility, durability, and curl resistance. Preferably there is. More preferably, it is 10 micrometers-30 micrometers. Specific examples thereof include Pyrene (registered trademark) manufactured by Toyobo Co., Ltd.

  Art paper such as printing paper, coated paper, lightweight coated paper, finely coated paper, and the like can be used as a recording medium having low ink water absorption and poor absorbability. These hardly absorbent recording media are those in which a coating layer is provided by applying a coating material on the surface of high-quality paper, neutral paper, etc. that are generally not surface-treated mainly composed of cellulose. Oji Paper Co., Ltd. “OK Everlight Coat” manufactured by Nippon Paper Industries Co., Ltd., “Aurora S” manufactured by Nippon Paper Industries Co., Ltd., “OK Coat L” manufactured by Oji Paper Co., Ltd., and “Aurora L” manufactured by Nippon Paper Industries Co., Ltd. , Etc. Lightweight coated paper (A3), Oji Paper Co., Ltd. “OK Top Coat +” and Nippon Paper Industries Co., Ltd. “Aurora Coat” coated paper (A2, B2), Oji Paper Co., Ltd. Art paper (A1) such as “OK Kanfuji +” manufactured by Mitsubishi and “Tokuhishi Art” manufactured by Mitsubishi Paper Industries Co., Ltd., and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by a following example, unless the summary is exceeded. In the following examples, “parts” and “%” are based on mass unless otherwise specified.

(Synthesis example of polymer (A))
(Synthesis Example 1)
Living anion polymerization is performed by introducing n-butyllithium (BuLi) as a polymerization initiator and styrene (St) as a first monomer from the tube reactors P1 and P2 in FIG. 1 into the T-shaped micromixer M1 in FIG. To form a polymer.
Next, the obtained polymer is moved to the T-shaped micromixer M2 in FIG. 1 through the tube reactor R1 in FIG. 1, and the growth regulator of the polymer is introduced into the reaction regulator (3) introduced from the tube reactor P3 in FIG. Trapped with 1,1-diphenylethylene (DPE).
Next, methacrylic acid tert-butyl ester (t-BMA) as a second monomer was introduced into the T-shaped micromixer M3 from the tube reactor P4 shown in FIG. 1, and moved through the tube reactor R2 in FIG. Then, a continuous living anion polymerization reaction was performed. Thereafter, the reaction was quenched with methanol to produce a block copolymer (PA-1).

  At this time, the reaction temperature was set to 24 ° C. by burying the entire microreactor in a thermostat. The monomer and reaction modifier introduced into the microreactor are dissolved in tetrahydrofuran (THF), and BuLi is a commercially available 2.6M hexane solution diluted with hexane. Depending on the dilution concentration and introduction rate, the block copolymer ( The molar ratio of PA-1) was adjusted as follows.

Mol ratio polymerization initiator of block copolymer (PA-1) / first monomer / reaction modifier / second monomer = 1.0 / 13.5 / 1.0 / 7.5

  The resulting block copolymer (PA-1) was treated with a cation exchange resin to hydrolyze the t-butoxycarbonyl group of the t-BMA block and regenerate it to a carboxyl group. The reaction solution was distilled off under reduced pressure, and the resulting solid was pulverized to obtain a powder of polymer (P-1) as polymer (A).

  The number average molecular weight, acid value, solubility in water, presence / absence of fine particles at a neutralization rate of 100% / average particle diameter (nm), and surface tension (mN / m) of the obtained polymer (A) are described below. Shown in the table.

(Synthesis Examples 2 to 6)
Polymers (P-2), (P-6), (P-7), (P-9), and (P-12) are prepared in the same manner as in Synthesis Example 1 by adjusting the monomer type and the amount introduced. Manufactured.

(Synthesis Example 7)
BuLi as a polymerization initiator and St as a first monomer were introduced into the T-shaped micromixer M1 in FIG. 1 from the tube reactors P1 and P2 in FIG. 1, and a living anion polymerization was performed to form a polymer.
Next, the obtained polymer is moved to the T-shaped micromixer M2 in FIG. 1 through the tube reactor R1 in FIG. 1, and the growth regulator of the polymer is introduced into the reaction regulator (3) introduced from the tube reactor P3 in FIG. Trapped with α-methylstyrene (α-MeSt)).
Next, t-BMA as a second monomer is introduced into the T-shaped micromixer M3 from the tube reactor P4 shown in FIG. 1, and the polymer moved through the tube reactor R2 in FIG. Reaction was performed. Thereafter, the reaction was quenched with methanol to produce a block copolymer (PA-13).

  At this time, the reaction temperature was set to 24 ° C. by burying the entire microreactor in a thermostat. The monomer and reaction modifier introduced into the microreactor are dissolved in THF, and BuLi is a commercially available 2.6M hexane solution diluted with hexane. Depending on the dilution concentration and introduction rate, the block copolymer (PA-13 ) Was adjusted as follows.

Mol ratio polymerization initiator of block copolymer (PA-13) / first monomer / reaction modifier / second monomer = 1.0 / 12.0 / 1.3 / 8.1

  The obtained block copolymer (PA-13) was hydrolyzed by treating with a cation exchange resin, the reaction solution was distilled off under reduced pressure, the resulting solid was pulverized, and the polymer (P- The powder of 13) was obtained.

(Synthesis Example 8)
In the same manner as in Synthesis Example 7, the polymer (P-14) was produced by adjusting the kind of monomer and the amount introduced.

(Comparative Synthesis Example 1 Synthesis Example of Comparative Example Polymer (PH-1))
(Method for adjusting random polymer)
100 parts of methyl ethyl ketone was charged into a reaction vessel having a stirring device, a dropping device, and a reflux device, and the inside of the reaction vessel was purged with nitrogen while stirring. After maintaining the inside of the reaction vessel in a nitrogen atmosphere and heating to reflux of methyl ethyl ketone, St 74 parts, 11 parts acrylic acid, 15 parts methacrylic acid and a polymerization initiator (Wako Pure Chemical Industries / “V- 75 ") 8 parts of the mixture was added dropwise over 2 hours. The temperature of the reaction system was kept at 80 ° C. during the dropping.
After completion of the dropwise addition, the reaction was continued for another 25 hours at the same temperature. In the middle of the reaction, a polymerization initiator was appropriately added while confirming the consumption status of the raw materials. After completion of the reaction, methyl ethyl ketone was distilled off under reduced pressure, and the resulting solid was pulverized to obtain a polymer (PH-1) powder.
The number average molecular weight of the polymer (PH-1) was 5255, the weight average molecular weight was 9000, and the acid value was 185 mgKOH / g.

(Measurement method of physical properties of polymer)
The physical property value of each obtained polymer (A) was measured as follows.

(Measurement method of number average molecular weight (Mn) and weight average molecular weight (Mw))
It measured by the gel permeation chromatography (GPC) method on the following conditions.

Measuring device: High-speed GPC device (“HLC-8220GPC” manufactured by Tosoh Corporation)
Column: The following columns manufactured by Tosoh Corporation were connected in series.
"TSKgel G5000" (7.8 mm ID x 30 cm) x 1 "TSKgel G4000" (7.8 mm ID x 30 cm) x 1 "TSKgel G3000" (7.8 mm ID x 30 cm) x 1 “TSKgel G2000” (7.8 mm ID × 30 cm) × 1 detector: RI (differential refractometer)
Column temperature: 40 ° C
Eluent: Tetrahydrofuran (THF)
Flow rate: 1.0 mL / min Injection amount: 100 μL (THF solution with a sample concentration of 0.4 mass%)
Standard sample: A calibration curve was prepared using the following standard polystyrene.

(Standard polystyrene)
"TSKgel standard polystyrene A-500" manufactured by Tosoh Corporation
"TSKgel standard polystyrene A-1000" manufactured by Tosoh Corporation
"TSKgel standard polystyrene A-2500" manufactured by Tosoh Corporation
"TSKgel standard polystyrene A-5000" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-1" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-2" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-4" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-10" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-20" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-40" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-80" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-128" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-288" manufactured by Tosoh Corporation
"TSKgel standard polystyrene F-550" manufactured by Tosoh Corporation

(Measurement method of acid value)
It measured based on JIS test method K0070-1992. It was determined by dissolving 0.5 g of a sample in a THF solvent and titrating with 0.1 M potassium hydroxide alcohol solution using phenolphthalein as an indicator.

(Measurement method of water solubility)
A polymer having a particle size of 250 μm to 90 μm using a sieve having an opening of 250 μm and a mesh size of 90 μm is sealed in a bag processed with a 400 mesh wire net, immersed in 50 ml of water, and 24 ° C. at a temperature of 25 ° C. Stir gently for a period of time. After soaking for 24 hours, drying was performed by performing drying for 2 hours in a dryer set at 110 ° C. with a 400-mesh wire mesh enclosing the polymer. The change in the weight of the 400 mesh wire mesh encapsulating the polymer before and after water immersion was measured, and the solubility was calculated according to the following equation.

(Judgment method of fine particle formation in water and measurement method of average particle size (nm)))
(1) The acid value of the polymer is determined according to the acid value measurement method.
(2) After adding 1 g of polymer to 50 ml of water, 0.1 mol / L potassium hydroxide aqueous solution that only neutralizes the acid value of the polymer obtained in (1) above is added to 100% neutralization. And
(3) 100% neutralized liquid is dispersed by irradiating with ultrasonic waves in an ultrasonic cleaner (SND Ultrasonic Cleaner US-102, 38 kHz self-excited transmission) at a temperature of 25 ° C. for 2 hours. And let stand at room temperature for 24 hours.
After leaving for 24 hours, sample liquid sampled at a depth of 2 centimeters from the liquid surface was measured using a dynamic light scattering particle size measuring device “Microtrac particle size distribution analyzer UPA-ST150” manufactured by Nikkiso Co., Ltd. It was confirmed whether or not fine particles were present by determining whether light scattering information due to formation could be obtained.
At the same time, the average particle size was measured.

(Measurement method of surface tension)
A sample solution similar to the sample solution obtained by the method for determining the formation of fine particles in water was measured using a Wilhelmi surface tension meter.

  The raw materials, reaction conditions, and physical properties of the polymers obtained in the synthesis examples and comparative synthesis examples are shown in the table.

In Tables 1 to 3,
BuLi represents normal butyl lithium;
St represents styrene,
DPE represents 1,1-diphenylethylene,
αMeSt represents α-methylstyrene,
tBMA represents methacrylic acid tert-butyl ester;
nBMA represents methacrylic acid n-butyl ester.

(Example Production method of aqueous pigment dispersion)
An aqueous pigment dispersion was obtained by any one of the following production examples. In addition, the usage-amount of the raw material to be used was described in the table | surface mentioned later.

(Manufacturing method A)
The composition of Example 1 will be described as an example.
150 parts (45 parts as P-1) of a polymer (P-1) solution prepared by adding and stirring triethylene glycol to a pulverized resin to prepare a 30% triethylene glycol solution, and 120 parts of triethylene glycol as a water-soluble organic solvent And 19.19 parts of a 34% aqueous potassium hydroxide solution to a neutralization rate of 100% is added to neutralize the polymer (P-1). As an initial stage of dispersion (step 1), a 1.0 L intensive mixer (Nippon Eirich Co., Ltd.) was charged with 150 parts of the neutralized polymer (P-1) and Pigment Red 269 as a pigment, and the rotor peripheral speed was 2.94 m / s. The kneading was performed for 60 minutes at a pan peripheral speed of 1 m / s. Subsequently, as Step 2, 5600.81 parts of ion-exchanged water was gradually added to the kneaded product in the intensive mixer container while stirring was continued to obtain an aqueous pigment dispersion having a pigment concentration of 15.0%.
Similarly, aqueous pigment dispersions of Examples 2 to 8 and Example 11 were obtained.

(Manufacturing method B)
The composition of Example 9 will be described as an example.
150 parts (45 parts as P-13) of a polymer (P-13) solution in which triethylene glycol is added to the pulverized resin and stirred to form a 30% triethylene glycol solution, and 120 parts of triethylene glycol as a water-soluble organic solvent Were mixed. Into a 1.0 L intensive mixer (Nippon Eirich Co., Ltd.) 150 parts of the above polymer (P-13) and Pigment Red 269 as a pigment were charged, and in Step 1, the rotor peripheral speed was 2.94 m / s and the pan peripheral speed was 1 m / s And kneading for 60 minutes. Subsequently, in Step 2, 19.19 parts of a 34% aqueous potassium hydroxide solution was added to a neutralization rate while continuing stirring to the kneaded material in the intensive mixer vessel, and 5600.81 parts of ion exchange water was gradually added. In addition, an aqueous pigment dispersion having a pigment concentration of 15.0% was obtained.
Similarly, aqueous pigment dispersions of Examples 10 and 12 were obtained.

(Manufacturing method C)
The composition of Comparative Example 1 will be described as an example.
150 parts of a polymer (PH-1) solution prepared as a 30% triethylene glycol solution (45 parts as PH-1) and 120 parts of triethylene glycol as a water-soluble solvent were mixed, and a 34% aqueous potassium hydroxide solution was added in 100%. 24.49 parts are added to neutralize the polymer (PH-1) so that the sum is obtained. As an initial stage of dispersion, 150 parts of Pigment Red 269 as a neutralized polymer (PH-1) and a pigment were charged into a 1.0 L intensive mixer (Nippon Eirich Co., Ltd.), and rotor peripheral speed was 2.94 m / s as Step 1. The kneading was performed at a pan peripheral speed of 1 m / s for 60 minutes. Subsequently, as step 2, 555.51 parts of ion-exchanged water was gradually added to the kneaded product in the intensive mixer vessel while stirring, and an aqueous pigment dispersion having a pigment concentration of 15.0% was obtained.

(Manufacturing method D)
The composition of Comparative Example 2 will be described as an example.
150 parts of a polymer (P-1) solution prepared as a 30% triethylene glycol solution (45 parts as P-1) and 120 parts of triethylene glycol as a water-soluble solvent were mixed, and a 34% aqueous potassium hydroxide solution was added in 100%. Add 19.19 parts to neutralize polymer (P-1). As an initial stage of dispersion, a 1.0 L intensive mixer (Nippon Eirich Co., Ltd.) was charged with 150 parts of Pigment Red 269 and 15 parts of water as the pigment (PH-1) and pigment as the pigment. Kneading was performed for 60 minutes at 94 m / s and a peripheral speed of 1 m / s. Subsequently, as step 2, 545.81 parts of ion-exchanged water was gradually added to the kneaded product in the intensive mixer container while stirring was continued to obtain an aqueous pigment dispersion having a pigment concentration of 15.0%.

(Evaluation method)
The obtained aqueous pigment dispersion was evaluated by measuring the following items.

<Volume average particle diameter>
The prepared aqueous pigment dispersion was diluted 5000 times and measured with Microtrac UPA-150 (manufactured by Nikkiso Co., Ltd.). The measured value was an average value measured three times.
Judgment criteria
○: Volume average particle size is less than 150 nm
Δ: Volume average particle diameter of 150 nm to less than 160 nm
X: Volume average particle diameter is 160 nm or more

<Number of coarse particles>
The prepared aqueous pigment dispersion was diluted 250 times and measured with Accusizer 780APS (manufactured by International Business). The number of coarse particles was converted to the number of particles per ml of the aqueous pigment dispersion before dilution. The unit of (× 10 ⁸ particles / ml) is used for the number of particles in the table.
Judgment criteria
○: Number of coarse particles of 0.5 um or more, less than 5 × 10 ⁸ particles / ml
Δ: Number of coarse particles of 0.5 μm or more 5 to 10 × 10 ⁸ particles / ml
×: Number of coarse particles of 0.5 um or more 10 × 10 ⁸ particles / ml or more

<Dischargeability / Color development>
In order to measure the ejection characteristics of the inkjet and the print density of the printed matter, the following aqueous ink for inkjet recording for evaluation was prepared using the prepared aqueous pigment dispersion.
The aqueous pigment dispersion was adjusted in accordance with the pigment concentration of the prepared aqueous pigment dispersion in the following formulation of 100 parts in total so that the final pigment concentration was 5% by mass.
About 5 parts of aqueous pigment dispersion (as pigment content)
Triethylene glycol monobutyl ether 8 parts 2-pyrrolidone 8 parts Glycerin 3 parts Surfinol 440 (manufactured by Air Products Japan) 0.5 part Pure water remaining

Each produced water-based ink for inkjet recording was tested using the inkjet printer (EM-930C by EPSON). A nozzle check pattern was printed after filling the cartridge with ink. In addition, after printing with 100% print density setting in the range of 340 cm ^{2 on} one sheet of A4 paper on Pictorico Pro Photo Paper (Pictorico Co., Ltd.) and OK Top Coat + (Oji Paper Co., Ltd.) The nozzle check test pattern was printed again, the state of the nozzle before and after the test was compared, and whether or not nozzle chipping increased was checked, and the ejection performance was evaluated.
Judgment criteria
○: No. of nozzles missing
Δ: Nozzle chipping increase Less than 10%
X: Nozzle chip increase 10% or more

In the table, abbreviations are as follows.
KOH: Potassium hydroxide aqueous solution TEG: Triethylene glycol water: Ion exchange water

As a result, each of Examples 1 to 12 using the polymer (A) represented by the general formula (1) has a small volume average particle size, a small number of coarse particles, and an excellent discharge property. Dispersions and inks were obtained.
On the other hand, Comparative Example 1 was an example using a random polymer, but the volume average particle size was large, the number of coarse particles was large, and the dischargeability was poor. Comparative Example 2 was an example in which the amount of water relative to the pigment was 15% by mass or more at the initial stage of dispersion, but the volume average particle diameter and the number of coarse particles were large, and the dischargeability was poor.

It is a schematic diagram of the microreactor used by this invention.

1: T-shaped micromixer M1
2: T-shaped micromixer M2
3: T-shaped micromixer M3
4: Tube reactor R1
5: Tube reactor R2
6: Tube reactor R3
7: Tube reactor P1 for pre-cooling
8: Tube reactor P2 for pre-cooling
9: Tube reactor P3 for pre-cooling
10: Tube reactor P4 for pre-cooling

Claims (5)

A number having an anionic group, having a solubility in water of 0.1 g / 100 ml or less, and forming fine particles in water when the neutralization rate of the anionic group by a basic compound is 100%. A method for producing an aqueous pigment dispersion in which a polymer (A) having an average molecular weight in the range of 1000 to 6000, a water-soluble organic solvent, a red azo pigment, and a basic compound are dispersed in water. A method for producing an aqueous pigment dispersion, wherein an initial amount of water is less than 15% by mass based on the red azo pigment. A kneaded dispersion in which the polymer (A), the water-soluble organic solvent, and the red azo pigment are kneaded and the solid content ratio is 40% by mass or more and the amount of water is less than 15% by mass with respect to the red azo pigment. Obtaining step 1, and
The method for producing an aqueous pigment dispersion according to claim 1, wherein Step 2 of mixing the basic compound and the water with the kneaded dispersion is performed in this order. The polymer (A), the water-soluble organic solvent, the basic compound, and the red azo pigment are kneaded and the solid content ratio is 40% by mass or more and the amount of water is less than 15% by mass with respect to the red azo pigment. Step 1 for obtaining a kneaded dispersion;
The method for producing an aqueous pigment dispersion according to claim 1, wherein Step 2 of mixing the water with the kneaded dispersion is performed in this order. The method for producing an aqueous pigment dispersion according to any one of claims 1 to 3, wherein the polymer (A) is a polymer represented by the general formula (1).

(1)
(In Formula (1), A ¹ represents an organolithium initiator residue, A ² represents a polymer block of a monomer having an aromatic ring or a heterocyclic ring, A ³ represents a polymer block containing an anionic group, and n Represents an integer of 1 to 5, and B represents an aromatic group or an alkyl group.) An ink for inkjet recording using the aqueous pigment dispersion obtained by the production method according to claim 1.

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