JP2017119797A - Method for producing pigment water dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a pigment water dispersion having an excellent retention stability and capable of giving fine pigment particles having a small average particle diameter, and a method for producing a water-based ink using the pigment water dispersion.SOLUTION: [1] A production method of a pigment water dispersion has step (I) of obtaining a dispersion A by performing dispersion treatment of a pigment mixture comprising C.I. Pigment Yellow 74 as a pigment, a dispersion polymer, a water-soluble organic solvent and water, and step (II) of obtaining a pigment water dispersion by removing the water-soluble organic solvent from the dispersion A, wherein the dispersion polymer has an acidic group and an acid number of 150-260 mgKOH/g, and the neutralization degree of the acidic group of the dispersion polymer in step (I) is 50-90 mol%. [2] A production method of a water-based ink has a step of mixing the pigment water dispersion obtained by the production method according to the [1] and a water-soluble organic solvent.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a pigment aqueous dispersion, and a method for producing an aqueous ink using the pigment aqueous dispersion.

The ink jet recording method is a recording method in which characters and images are obtained by directly ejecting and adhering ink droplets from a very fine nozzle to a recording medium. This method is easy to make full-color and inexpensive, and can be used for plain paper as a recording medium. It has a widespread use because it has many advantages such as non-contact with the printed material. In recent years, it is not only for home use but also for office use and commercial use. It is expanding to. In these applications, pigment-based inks have become mainstream from the viewpoint of light resistance and water resistance of printed materials, and pigment aqueous dispersions having small pigment particle diameter and excellent color developability are desired.
Patent Document 1 discloses C.I. I. Pigment Yellow 74, an styrene acrylic resin having an acid value of 100 to 250, and an aqueous pigment dispersion for inkjet inks containing a basic compound, and using a styrene acrylic resin having a specific monomer composition is disclosed. An ink using the aqueous pigment dispersion that is excellent in dispersion stability and the like and has a good coloring power and can obtain a high-quality printed image is disclosed. In the embodiment, C.I. I. A method for producing an aqueous pigment dispersion using a paint shaker charged with Pigment Yellow 74, a resin solution containing styrene acrylic resin, diethylene glycol, purified water, and zirconia beads is described.
Patent Document 2 includes a step of mixing a colorant dispersion and a water-insoluble polymer emulsion containing an organic solvent, a step of dispersing the resulting mixture to obtain a dispersion in which a water-insoluble polymer is attached to the colorant, and A method for producing an aqueous dispersion for inkjet recording having a step of removing an organic solvent from the obtained dispersion is disclosed, and it is disclosed that a high printing density is expressed. Specifically, an aqueous solution of a water-soluble polymer containing methyl ethyl ketone is added to C.I. I. Pigment Yellow 74 is added, mixed with a disperser blade, dispersed using a media-type disperser, and then dispersed using a circulation system. After adding a polymer emulsion and dispersing using a high-pressure homogenizer, an aqueous dispersion that removes methyl ethyl ketone The manufacturing method is described.

JP 2006-77201 A JP 2010-144095 A

However, the technique described in Patent Document 1 is still insufficient to obtain an aqueous dispersion of pigment particles having a small particle size.
Patent Document 2 includes C.I., which includes a dispersion treatment in the presence of methyl ethyl ketone. I. Although a method for producing an aqueous dispersion of CI Pigment Yellow 74 is disclosed, other pigments such as C.I. I. Pigment blue, C.I. I. Pigment Red, C.I. I. Pigment black and the like, and C.I. I. It is not distinguished from Pigment Yellow 74. Furthermore, C.I. I. In the method for producing an aqueous pigment dispersion having a step of dispersing Pigment Yellow 74 in the presence of a water-soluble organic solvent such as methyl ethyl ketone, the aqueous dispersion of pigment particles having a smaller particle size than other pigments is stable. It became clear that it was not obtained. This is because C.I. I. Pigment Yellow 74 has higher solubility in water-soluble organic solvents than other pigments, and the polymer has poor adsorptivity to pigments. Therefore, the retention stability of pigment particles in the presence of water-soluble organic solvents is low. It is considered that the aggregation and coalescence of pigment particles occur to increase the average particle size.
In the present invention, “retention stability” refers to an intermediate step in the production of a pigment water dispersion, that is, a step of removing the water-soluble organic solvent after the step of dispersing the pigment in the presence of the water-soluble organic solvent, It means the stability of the dispersion containing the water-soluble organic solvent until the start of the process for obtaining the dispersion (hereinafter also referred to as “residence stability”). If the retention stability is inferior, aggregation and coalescence of the dispersion occur in the intermediate step, and the average particle size of the pigment water dispersion finally obtained tends to increase.
The present invention relates to C.I. I. In the method for producing an aqueous pigment dispersion having a step of dispersing Pigment Yellow 74 in the presence of a water-soluble organic solvent, the dispersion containing the water-soluble organic solvent has excellent retention stability and has a small average particle size ( For example, an object of the present invention is to provide a method for producing a pigment aqueous dispersion from which fine pigment particles are obtained (for example, an average particle size is 130 nm or less) and a method for producing an aqueous ink using the pigment aqueous dispersion.
In this specification, “print” is a concept including printing and printing for recording characters and images, and “printed material” is a concept including printed materials and printed materials on which characters and images are recorded. “Water-based” means that water accounts for the largest proportion in the medium contained in the ink.

The inventors have used C.I. I. It has been found that the above-described problems can be solved by dispersing a pigment mixture containing Pigment Yellow 74, a specific dispersion polymer, a water-soluble organic solvent and water under specific conditions.
That is, the present invention provides the following [1] and [2].
[1] A method for producing a pigment aqueous dispersion having the following steps (I) and (II):
Step (I): C.I. I. Step of obtaining dispersion A by dispersing pigment yellow 74, a dispersion polymer, a water-soluble organic solvent (b-1) and water. Step (II): Water-soluble organic solvent (b- 1) Step for removing pigment to obtain an aqueous pigment dispersion The dispersion polymer has an acidic group and the acid value is 150 mgKOH / g or more and 260 mgKOH / g or less, and neutralization of the acidic group of the dispersion polymer in step (I) The manufacturing method of the pigment water dispersion whose degree is 50 mol% or more and 90 mol% or less.
[2] A method for producing a water-based ink, comprising a step of mixing the pigment aqueous dispersion obtained by the production method according to [1] and a water-soluble organic solvent (b-2).

  INDUSTRIAL APPLICABILITY According to the present invention, a method for producing an aqueous pigment dispersion having excellent retention stability and a fine pigment particle having a small average particle diameter, and a method for producing an aqueous ink using the aqueous pigment dispersion Can be provided.

[Method for producing pigment aqueous dispersion]
The present invention is a method for producing an aqueous pigment dispersion having the following steps (I) and (II):
Step (I): C.I. I. Step of obtaining dispersion A by dispersing pigment yellow 74, a dispersion polymer, a water-soluble organic solvent (b-1) and water. Step (II): Water-soluble organic solvent (b- 1) Step for removing pigment to obtain an aqueous pigment dispersion The dispersion polymer has an acidic group and the acid value is 150 mgKOH / g or more and 260 mgKOH / g or less, and neutralization of the acidic group of the dispersion polymer in step (I) The degree is 50 mol% or more and 90 mol% or less.

The present invention has an excellent effect that an aqueous dispersion of fine pigment particles having excellent residence stability and a small average particle diameter can be obtained. Although the reason is not certain, C.I. I. When Pigment Yellow 74 is dispersed in the presence of a water-soluble organic solvent, the dispersion polymer used has an acidic group and the acid value is in a specific range, and the neutralization degree of the acidic group of the dispersed polymer is specified. By adjusting to the range, dispersion ability due to electrostatic repulsion of the dispersed polymer is controlled, aggregation and coalescence of pigment particles in the presence of the water-soluble organic solvent are suppressed, and the retention stability of the dispersion containing the water-soluble organic solvent is stabilized. Improves. As a result, it is considered that an aqueous dispersion of fine pigment particles having a small average particle diameter can be obtained.
Hereinafter, each component, each process, etc. which are used for this invention are demonstrated.

<Pigment>
The pigment used in the present invention is CI Pigment Yellow 74 (hereinafter also referred to as “PY74”). Examples of commercially available products include FY7141 (trade name of Sanyo Dye Co., Ltd.) and the like.
The average particle diameter of PY74, which is a pigment, is preferably 100 nm or more, more preferably 150 nm or more, still more preferably 200 nm or more, from the viewpoint of pigment productivity, and from the viewpoint of productivity of the pigment aqueous dispersion, Preferably it is 500 nm or less, More preferably, it is 400 nm or less, More preferably, it is 350 nm or less.
The average particle diameter of the pigment can be measured using a transmission electron microscope. Specifically, using a transmission electron microscope, 500 pigment primary particles are extracted by image analysis and the particle diameter is measured. The weight average particle diameter is calculated as the average. Moreover, when a pigment has a major axis and a minor axis, the major axis is used for calculation.

<Dispersed polymer>
The dispersion polymer used for this invention has an acidic group, and an acid value is 150 mgKOH / g or more and 260 mgKOH / g or less. Examples of the acidic group include a carboxy group, a sulfonic acid group, and a phosphoric acid group, and a carboxy group is preferable from the viewpoint of improving the retention stability.
In the present invention, the “dispersion polymer” means a polymer having an ability to disperse a pigment in water or an aqueous medium containing water as a main component at room temperature.

  The dispersion polymer is preferably a vinyl polymer obtained by addition polymerization of a vinyl monomer, and more preferably an acidic group-containing monomer (a-1) (from the viewpoint of improving residence stability and ink printing density. Hereinafter, a vinyl polymer containing a structural unit derived from “monomer (a-1)” and a structural unit derived from a hydrophobic monomer (a-2) (hereinafter also referred to as “monomer (a-2)”). It is a copolymer. The copolymer is obtained by copolymerizing the monomer (a-1) and a monomer mixture containing the monomer (a-2) (hereinafter also referred to as “monomer mixture”).

[Acid group-containing monomer (a-1)]
The monomer (a-1) is used from the viewpoint of improving the residence stability.
Examples of the monomer (a-1) include a carboxylic acid monomer, a sulfonic acid monomer, and a phosphoric acid monomer.
Examples of the carboxylic acid monomer include (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid.
Examples of the sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate.
Examples of phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloyloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxyethyl phosphate, and the like. It is done.
Among these, from the viewpoint of improving retention stability, it is preferably at least one selected from carboxylic acid monomers and sulfonic acid monomers, more preferably carboxylic acid monomers, and still more preferably (meth) acrylic acid and maleic acid. It is 1 or more types chosen from an acid, More preferably, it is (meth) acrylic acid, More preferably, it is acrylic acid.
In the present specification, “(meth) acrylic acid” means one or more selected from acrylic acid and methacrylic acid, and “(meth) acrylate” means one or more selected from acrylate and methacrylate. Means. In the following, “(meth) acrylic acid” and “(meth) acrylate” are also synonymous.

[Hydrophobic monomer (a-2)]
The monomer (a-2) is used from the viewpoint of increasing the affinity of the dispersion polymer for the pigment, and examples thereof include alkyl (meth) acrylate, alkyl (meth) acrylamide, and aromatic ring-containing monomers.
As alkyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, amyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) Acrylate, dodecyl (meth) acrylate, cetyl (meth) acrylate, stearyl (meth) acrylate, behenyl (meth) acrylate, isopropyl (meth) acrylate, isobutyl (meth) acrylate, tertiary butyl (meth) acrylate, isoamyl (meth) Acrylate, isooctyl (meth) acrylate, isodecyl (meth) acrylate, isododecyl (meth) acrylate, isocetyl (meth) acrylate, isostearyl (meth ) Acrylate, Isobeheniru (meth) having an alkyl group having 3 to 30 carbon atoms in the acrylate (meth) acrylic acid ester.
Examples of the alkyl (meth) acrylamide include dimethyl (meth) acrylamide, diethyl (meth) acrylamide, dibutyl (meth) acrylamide, t-butyl (meth) acrylamide, octyl (meth) acrylamide, dodecyl (meth) acrylamide and the like. Examples include (meth) acrylamide having an alkyl group of 22 or less.
Examples of aromatic ring-containing monomers include styrene monomers such as styrene, α-methylstyrene, 2-methylstyrene, and vinyl toluene; aryl esters of (meth) acrylic acid such as benzyl (meth) acrylate and phenoxyethyl (meth) acrylate; Aromatic group-containing vinyl monomers having 6 to 22 carbon atoms such as ethyl vinyl benzene, 4-vinyl biphenyl, 1,1-diphenyl ethylene, vinyl naphthalene, chlorostyrene and the like can be mentioned.
Among these, Preferably it is an aromatic ring containing monomer, More preferably, it is a styrene-type monomer, More preferably, it is 1 or more types chosen from styrene and alpha-methyl styrene, More preferably, styrene and alpha-methyl styrene It is combined use with.
In the present specification, “(meth) acrylamide” means one or more selected from acrylamide and methacrylamide. In the following, “(meth) acrylamide” is also synonymous.

[Monomer (a-3)]
The dispersion polymer may further have a macromer-derived structural unit as the monomer (a-3) (hereinafter also referred to as “monomer (a-3)”) from the viewpoint of improving the residence stability. As the monomer (a-3), a styrene macromer, an aromatic group-containing (meth) acrylate macromer, and a silicone macromer can be used.
Examples of commercially available styrenic macromers include AS-6 (S), AN-6 (S), HS-6 (S) (trade name of Toa Gosei Co., Ltd.), and the like.
Examples of the aromatic group-containing (meth) acrylate-based macromer include a homopolymer of an aromatic group-containing (meth) acrylate or a copolymer thereof with another monomer. The aromatic group-containing (meth) acrylate is an arylalkyl group having 7 to 12 carbon atoms which may have a substituent containing a hetero atom or an (meth) acrylate having an aryl group, such as benzyl (meth) acrylate. ) Acrylate, phenoxyethyl (meth) acrylate, and the like.
The macromer may be a silicone macromer, and examples of the silicone macromer include organopolysiloxane having a polymerizable functional group at one end.

[Nonionic monomer (a-4)]
The dispersion polymer may further have a structural unit derived from the nonionic monomer (a-4) (hereinafter also referred to as “monomer (a-4)”) from the viewpoint of improving the residence stability.
As a monomer (a-4), 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polyethyleneglycol (n = 2-30, n shows the average addition mole number of an oxyalkylene group. Same) (meth) acrylate, polypropylene glycol (n = 2 to 30) (meth) acrylate, poly (ethylene glycol (n = 1-15) / propylene glycol (n = 1-15)) (meth) acrylate, methoxypolyethylene Glycol (n = 1-30) (meth) acrylate, methoxypolytetramethylene glycol (n = 1-30) (meth) acrylate, ethoxypolyethylene glycol (n = 1-30) (meth) acrylate, octoxypolyethylene glycol ( n = 1-30) (meth) acryl , Polyethylene glycol (n = 1-30) (meth) acrylate 2-ethylhexyl ether, (iso) propoxypolyethylene glycol (n = 1-30) (meth) acrylate, butoxypolyethylene glycol (n = 1-30) ( (Meth) acrylate, methoxypolypropylene glycol (n = 1-30) (meth) acrylate, methoxy (ethylene glycol / propylene glycol copolymer) (n = 1-30, ethylene glycol therein: 1-29) (meth) acrylate , Phenoxypolyethylene glycol (n = 1-15) / polypropylene glycol (n = 1-15) / methacrylate and the like.
Examples of commercially available monomers (a-4) include NK Ester M-40G, 90G, and 230G from Shin-Nakamura Chemical Co., Ltd., Bremer PE-90, 200, 350, and PME-100 from NOF Corporation. 200, 400, 1000, PP-500, 800, 1000, AP-150, 400, 550, 800, 50PEP-300, 50POEP-800B, 43PAPE-600B, and the like.
The monomers (a-1) to (a-4) can be used alone or in combination of two or more.

The dispersion polymer preferably has a structural unit derived from the monomer (a-1) and a structural unit derived from the monomer (a-2), and if necessary, a structural unit derived from the monomer (a-3) and the monomer (a -4) It has a derived structural unit.
The content of the structural unit derived from the monomer (a-1) in all the structural units of the dispersion polymer is preferably 20% by mass or more, more preferably 25% by mass or more, and still more preferably, from the viewpoint of improving the retention stability. From the same viewpoint as described above, it is preferably 40% by mass or less, more preferably 35% by mass or less, and further preferably 32% by mass or less.
The content of the structural unit derived from the monomer (a-2) in all the structural units of the dispersion polymer is preferably 60% by mass or more, more preferably 65% by mass or more, from the viewpoint of increasing the affinity of the dispersion polymer to the pigment. More preferably, it is 68% by mass or more, and from the same viewpoint as described above, it is preferably 80% by mass or less, more preferably 75% by mass or less, and further preferably 70% by mass or less.
The dispersion polymer may have a structural unit other than the structural unit derived from the monomer (a-1) and the structural unit derived from the monomer (a-2) as long as the effects of the present invention are not impaired. The total content of the structural unit derived from -1) and the structural unit derived from the monomer (a-2) is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 90% by mass or more. More preferably, it is preferably composed of only the structural unit derived from the monomer (a-1) and the structural unit derived from the monomer (a-2).

(Manufacture of dispersion polymer)
The dispersion polymer is produced by copolymerizing monomers (a-1) and (a-2) and, if necessary, a monomer mixture containing monomers (a-3) and (a-4) by a known polymerization method. From the viewpoint of controlling the molecular weight, the solution polymerization method is preferable.
The content of the monomer mixture containing the monomer (a-1) and the monomer (a-2) (content as an unneutralized amount; the same applies hereinafter) in the dispersion polymer production is the monomer ( It is the same as the content of the structural unit derived from a-1) and the monomer (a-2).
Although there is no restriction | limiting in the solvent used by the solution polymerization method, from the viewpoint of using as it is, without removing a solvent when manufacturing the pigment mixture mentioned later, using the water-soluble organic solvent (b-1) used by process (I). Is preferred, ketones having 3 to 8 carbon atoms are more preferred, and methyl ethyl ethone is more preferred.
Any polymerization initiator can be used as long as it is used for usual solution polymerization, but preferably an azo compound, more preferably 2,2′-azobis (2,4-dimethylvaleronitrile).
The chain transfer agent is preferably a mercaptan, more preferably 2-mercaptoethanol.

Although preferable polymerization conditions vary depending on the type of polymerization initiator and the like, the polymerization temperature is preferably 50 ° C or higher, more preferably 60 ° C or higher, still more preferably 70 ° C or higher, and preferably 90 ° C or lower, more Preferably it is 85 degrees C or less. The polymerization time is preferably 1 hour or longer, more preferably 4 hours or longer, still more preferably 6 hours or longer, and preferably 20 hours or shorter, more preferably 15 hours or shorter, still more preferably 10 hours or shorter. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, unreacted monomers and the like can be removed from the reaction solution by reprecipitation, membrane separation, chromatographic methods, extraction methods and the like.

The dispersion polymer is preferably an acrylic resin, more preferably a structural unit derived from the monomer (a-1) and a structural unit derived from the monomer (a-2). ) Derived structural unit and monomer (a-4) -derived acrylic resin, more preferably acidic group-containing monomer (a-1) derived structural unit and hydrophobic monomer (a-2) derived An acrylic resin having the following structural unit.
The acrylic resin is preferably an acrylic resin having a structural unit derived from a carboxylic acid monomer and a structural unit derived from one or more selected from alkyl (meth) acrylate, alkyl (meth) acrylamide and an aromatic ring-containing monomer. More preferably an acrylic resin having a structural unit derived from a carboxylic acid monomer and a structural unit derived from at least one selected from alkyl (meth) acrylates and aromatic ring-containing monomers, more preferably derived from a carboxylic acid monomer And an acrylic resin having a structural unit derived from an aromatic ring-containing monomer. Further, from the viewpoint of controlling the residence stability, a ternary polymer is more preferable among acrylic resins.

Specific examples include, for example, styrene / (meth) acrylic acid copolymer, (meth) acrylic acid ester / (meth) acrylic acid copolymer, styrene / methylstyrene / acrylic acid copolymer, styrene / α-methyl. (Meth) acrylic copolymers such as styrene / acrylic acid copolymer, styrene / (meth) acrylic acid ester / (meth) acrylic acid copolymer; styrene / maleic acid copolymer, styrene / methylstyrene / Maleic acid copolymers, maleic acid copolymers such as styrene / (meth) acrylic acid ester / maleic acid copolymer; styrene / (meth) acrylic acid ester / styrene sulfonic acid copolymer, styrene / (meth) Examples thereof include sulfonic acid copolymers such as acrylic acid ester / allyl sulfonic acid copolymers. These may be used alone or in appropriate combination of two or more.
The (meth) acrylic acid ester constituting the acrylic resin is preferably a (meth) acrylic acid alkyl ester having a lower alkyl group, more preferably a (meth) acrylic having a lower alkyl group having 1 to 4 carbon atoms. Acid alkyl ester.
Among these, from the viewpoint of improving retention stability and obtaining fine pigment particles, a (meth) acrylic acid copolymer is preferable, and a styrene / α-methylstyrene / acrylic acid copolymer is more preferable. is there.

The acid value of the dispersion polymer is 150 mgKOH / g or more, preferably 160 mgKOH / g or more, more preferably 180 mgKOH / g or more, and further preferably 200 mgKOH / g, from the viewpoint of improving the retention stability and obtaining fine pigment particles. g, more preferably 210 mgKOH / g or more, still more preferably 220 mgKOH / g or more, and from the same viewpoint as above, it is 260 mgKOH / g or less, preferably 250 mgKOH / g or less, more preferably 240 mgKOH. / G or less.
In the present invention, the acid value can be calculated from the constituent units of the dispersed polymer. Alternatively, it can also be determined by a method in which the dispersion polymer is dissolved in an appropriate solvent (for example, methyl ethyl ketone) and titrated.

The weight average molecular weight in terms of polystyrene of the dispersed polymer is preferably 3,000 or more, more preferably 5,000 or more, still more preferably 10,000 or more, from the viewpoint of improving the residence stability, and the same as described above. From the above viewpoint, it is preferably 100,000 or less, more preferably 50,000 or less, still more preferably 30,000 or less, and still more preferably 20,000 or less.
In addition, the measurement of a weight average molecular weight can be performed by the method as described in an Example.

<Water-soluble organic solvent (b-1)>
As the water-soluble organic solvent (b-1), a solvent which is arbitrarily mixed with water may be used. From the viewpoint of improving the wettability of the pigment to water and improving the retention stability, the water-soluble organic solvent ( The solubility of b-1) in 100 g of water at 20 ° C. is preferably 5 g or more, more preferably 10 g or more, still more preferably 15 g or more, and preferably 50 g or less, more preferably 40 g or less.
Examples of the water-soluble organic solvent (b-1) include alcohol solvents and ketone solvents, with ketone solvents being preferred. Specifically, it preferably contains one or more selected from methanol, ethanol, 1-butanol, 2-butanol, acetone and methyl ethyl ketone, more preferably one or more selected from acetone and methyl ethyl ketone, more preferably methyl ethyl ketone. preferable. These can be used alone or in admixture of two or more.
When methyl ethyl ketone is contained as the water-soluble organic solvent (b-1), the content of methyl ethyl ketone is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably in the water-soluble organic solvent (b-1). 90% by mass or more, and preferably 100% by mass or less.

<Water>
The pigment mixture according to the present invention contains water from the viewpoint of improving the residence stability and sufficiently miniaturizing the pigment.

(Manufacture of pigment aqueous dispersion)
The production method of the present invention includes the following steps (I) and (II). Thereby, even if it is the dispersion containing a water-soluble organic solvent, the retention stability of this dispersion improves, and the pigment water dispersion from which a fine pigment particle is obtained can be manufactured efficiently.
Step (I): Step of obtaining dispersion A by dispersing a pigment mixture containing PY74, a dispersion polymer, a water-soluble organic solvent (b-1) and water as a pigment Step (II): Water-soluble organic from dispersion A Removing the solvent (b-1) to obtain a pigment aqueous dispersion

(Process (I-1))
In the present invention, the order of adding the pigment, dispersion polymer, water-soluble organic solvent (b-1) and water when obtaining the pigment mixture to be used is not particularly limited, but from the viewpoint of enhancing the dispersibility of the pigment, the step ( It is preferable to have the following process (I-1) before I).
Step (I-1): To the dispersion polymer solution obtained by dissolving the dispersion polymer in the water-soluble organic solvent (b-1), water and, if necessary, the water-soluble organic solvent (b-1) are further added. Step of obtaining a pigment mixture by adding a pigment after obtaining an emulsion In step (I-1), the solvent is an aqueous solvent, which enhances the dispersibility of the pigment, wettability of the pigment, and adsorption of the dispersed polymer to the pigment From the viewpoint of promoting the properties, it is preferable to add a water-soluble organic solvent (b-1). Examples of the water-soluble organic solvent (b-1) include those described above.
In the step (I-1), from the viewpoint of the productivity of the pigment aqueous dispersion, the dispersion polymer solution is prepared by using a water-soluble organic solvent in the polymerization reaction when the dispersion polymer is produced. It is preferable to use it as a dispersion polymer solution as it is without removing.
There is no particular limitation on the mixing method, and any method that allows uniform mixing may be used.

[Step (I)]
Step (I) is a step of obtaining dispersion A by dispersing a pigment mixture containing PY74, a dispersion polymer, a water-soluble organic solvent (b-1) and water as pigments.
The degree of neutralization of the acidic group of the dispersion polymer in the step (I) is 50 mol% or more, preferably 60 mol% or more, more preferably 70 mol% or more, from the viewpoint of improving the residence stability, and From the same viewpoint, it is 90 mol% or less, preferably 80 mol% or less.
Here, the neutralization degree of the acidic group is a value calculated by the following formula (1).
Degree of neutralization = {[weight of neutralizer (g) / equivalent of neutralizer] / [acid value of dispersion polymer (mgKOH / g) × weight of dispersion polymer (g) / (56 × 1000)]} × 100 (1)

The degree of neutralization is preferably adjusted by neutralizing the acidic group of the dispersion polymer with a neutralizing agent in step (I). In the case where the step (I-1) is included, from the viewpoint of the productivity of the pigment aqueous dispersion, a neutralizing agent is further added to the dispersion polymer solution in the step (I-1) to neutralize the dispersion polymer. It is preferable.
Examples of the neutralizing agent include ammonia; organic amines such as ethylamine, diethylamine, trimethylamine, triethylamine, and triethanolamine; bases such as alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide. It is done. From the viewpoint of improving the residence stability, an alkali metal hydroxide is preferable, and sodium hydroxide is more preferable.
These neutralizing agents can be used alone or in admixture of two or more.
The neutralizing agent is preferably used as an aqueous neutralizing agent solution. The concentration of the neutralizing agent aqueous solution is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 40% by mass from the viewpoint of sufficiently promoting neutralization. Hereinafter, it is more preferably 30% by mass or less, and still more preferably 20% by mass or less.

  In the step (I), the content of the water-soluble organic solvent (b-1) is preferably 5.0% by mass or more in the pigment mixture from the viewpoint of improving the residence stability and obtaining fine pigment particles. Preferably, it is 10% by mass or more, more preferably 13% by mass or more, and from the same viewpoint as described above, it is preferably 30% by mass or less, more preferably 20% by mass or less, still more preferably 18% by mass or less. .

The non-volatile component ratio in the pigment mixture is preferably 3.0% by mass or more, more preferably 5.0% by mass or more, and further preferably 10% by mass from the viewpoint of improving retention stability and obtaining fine pigment particles. From the same viewpoint as described above, it is preferably 25% by mass or less, more preferably 20% by mass or less, still more preferably 18% by mass or less, still more preferably 15% by mass or less, and still more preferably 13%. It is below mass%.
In this invention, a non-volatile component is a dispersion polymer, a pigment, the neutralizing agent added as needed, and surfactant. The “nonvolatile component” in the following is also synonymous.
The “nonvolatile component ratio” in the pigment mixture is a value calculated by the following formula (2).
Nonvolatile component ratio (mass%) = [(total mass of nonvolatile components) / (mass of pigment mixture)] × 100 (2)

  The pigment ratio in the non-volatile component [pigment / (total amount of non-volatile components)] is preferably 35% by mass or more, more preferably 40% by mass or more, from the viewpoint of improving retention stability and obtaining fine pigment particles. More preferably, it is 45% by mass or more, and from the same viewpoint as described above, it is preferably 70% by mass or less, more preferably 65% by mass or less, and further preferably 60% by mass or less.

  The mass ratio of the pigment to the dispersion polymer in the non-volatile component [pigment / dispersion polymer] is preferably 30/70 or more, more preferably 40/60 or more, and still more preferably 50/50, from the viewpoint of improving the printing density of the ink. From the viewpoint of improving the retention stability, it is preferably 90/10 or less, more preferably 80/20 or less, still more preferably 70/30 or less, and even more preferably 60/40 or less.

(Preliminary distributed processing)
The dispersion treatment in the step (I) may be carried out by a single dispersion. However, from the viewpoint of obtaining a uniform dispersion, it is preferable that the pigment mixture is predispersed and then further dispersed.
The disperser used for the preliminary dispersion is preferably a commonly used mixing and stirring device such as an anchor blade or a disper blade, and specific examples include Ultra Disper, Desperm (Iwata Tekko Co., Ltd., trade name), Milder ( Ebara Manufacturing Co., Ltd., Taiheiyo Kiko Co., Ltd., trade names), TK homomixers, TK pipeline mixers, TK homojetters, TK homomic line flows, fill mixes (above, Primix Corporation, trade names), etc. Is preferred.
The temperature of the preliminary dispersion is preferably 10 ° C. or higher, more preferably 15 ° C. or higher, further preferably 18 ° C. or higher, and preferably 35 ° C. from the viewpoint of reducing the viscosity of the dispersion containing the water-soluble organic solvent. Hereinafter, it is more preferably 30 ° C. or lower, and further preferably 27 ° C. or lower.
The preliminary dispersion time is preferably 10 minutes or more, more preferably 30 minutes or more from the viewpoint of sufficiently miniaturizing the pigment, and preferably 10 hours or less from the viewpoint of the productivity of the pigment aqueous dispersion. More preferably, it is 5 hours or less, More preferably, it is 3 hours or less.
After the preliminary dispersion treatment, before performing this dispersion treatment, water may be added as necessary to adjust the nonvolatile component ratio. The non-volatile component ratio of the pre-dispersion after the pre-dispersion treatment is preferably 10% by mass or more, more preferably 12% by mass or more, still more preferably 15% by mass or more, and preferably 40% by mass or less, more preferably Is 35% by mass or less, more preferably 30% by mass or less.

(This distributed processing)
Examples of means for applying a shear stress used for the dispersion include a kneader such as a roll mill, a kneader, and an extruder; a high pressure homogenizer represented by a high pressure homogenizer (Izumi Food Machinery Co., Ltd., trade name); a microfluidizer ( Chamber type high-pressure homogenizers such as Microfluidics, trade name), Nanomizer (Yoshida Kikai Kogyo Co., Ltd., trade name), Optimizer, Starburst (Sugino Machine Co., trade name); Media-type dispersion such as paint shaker and bead mill Machine. Commercially available media-type dispersers include Ultra Apex Mill (trade name, manufactured by Kotobuki Industries Co., Ltd.), Picomill (trade name, manufactured by Iwata Iron Works Co., Ltd.), Dino Mill (trade name, manufactured by Shinmaru Enterprises Co., Ltd.), etc. Is mentioned. A plurality of these devices can be combined.

The dispersion treatment in step (I) preferably includes a high-pressure dispersion treatment from the viewpoint of sufficiently miniaturizing the pigment. Specifically, after the pigment mixture is predispersed, it is preferable to obtain a dispersion A by performing high-pressure dispersion treatment as the main dispersion treatment. More preferably, dispersion A is obtained by high-pressure dispersion treatment.
Here, “high pressure dispersion” means dispersion at a dispersion pressure of 20 MPa or more. From the viewpoint of uniformly dispersing the pigment, the dispersion pressure is preferably 50 MPa or more, more preferably 100 MPa or more, and still more preferably. From the viewpoint of the operability of the dispersion treatment, it is preferably 250 MPa or less, more preferably 200 MPa or less.
The number of passes of the high-pressure dispersion treatment is preferably 3 passes or more, more preferably 5 passes or more, still more preferably 10 passes or more from the viewpoint of uniformly dispersing the pigment, and preferably from the viewpoint of the efficiency of the dispersion treatment. Is 20 paths or less, more preferably 18 paths or less. As the operation method, either a circulation method or a continuous method can be adopted, but the continuous method is preferable from the viewpoint of suppressing the occurrence of distribution depending on the number of passes.
The temperature during the high-pressure dispersion treatment is not particularly limited, but is preferably 5 ° C or higher and 80 ° C or lower.
The high-pressure disperser used is preferably a high-pressure homogenizer from the viewpoint of the time required for dispersion treatment and production cost, and examples thereof include the homovalve type high-pressure homogenizer and the chamber type high-pressure homogenizer.

  The average particle diameter of the pigment particles dispersed with the dispersion polymer in the dispersion A obtained from the step (I) is preferably 40 nm or more, more preferably 50 nm or more, and still more preferably 60 nm or more, from the viewpoint of improving the retention stability. And preferably 200 nm or less, more preferably 150 nm or less, still more preferably 130 nm or less. The average particle diameter can be measured by the method described in Examples described later.

[Process (II)]
Step (II) is a step of removing the water-soluble organic solvent (b-1) from the dispersion A to obtain a pigment water dispersion.
In step (II), the pigment aqueous dispersion according to the present invention is obtained by removing the water-soluble organic solvent (b-1) from the dispersion A obtained in step (I) by a known method to form an aqueous system. Can be obtained.
Examples of the method for removing the water-soluble organic solvent (b-1) include a method of distilling off the water-soluble organic solvent under heating or reduced pressure, filtration, and the like. From the viewpoint of productivity of the pigment aqueous dispersion, A method of distilling off the water-soluble organic solvent under heating and reduced pressure is preferred.
The heating temperature depends on the type of the water-soluble organic solvent (b-1), but from the viewpoint of the productivity of the pigment water dispersion, it is preferably 35 ° C. or higher, more preferably 45 ° C. or higher, more preferably 45 ° C. or lower under reduced pressure. From the viewpoint of suppressing thermal decomposition and the like, it is preferably 85 ° C. or lower, more preferably 75 ° C. or lower, and further preferably 65 ° C. or lower. The pressure at this time is preferably 0.005 MPa or more, more preferably 0.01 MPa or more, and preferably 0.5 MPa or less, more preferably 0.2 MPa or less, and further preferably 0.1 MPa or less.
The removal of the water-soluble organic solvent (b-1) is preferably 1 hour or more, more preferably 2 hours or more, still more preferably 5 hours or more, and preferably 24 hours or less, more preferably, under the above conditions. It is carried out by holding for 12 hours or less, more preferably 10 hours or less.
The water-soluble organic solvent (b-1) in the obtained pigment aqueous dispersion is preferably substantially removed, but may remain as long as the object of the present invention is not impaired. The amount of the remaining water-soluble organic solvent (b-1) in the pigment aqueous dispersion is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.

  Moreover, after removing the water-soluble organic solvent (b-1), water may be added as necessary to adjust the solid content concentration. The solid content concentration of the obtained pigment aqueous dispersion is preferably 10% by mass or more, more preferably 12% by mass or more, still more preferably 15% by mass or more, and preferably 40% by mass or less, more preferably It is 35 mass% or less, More preferably, it is 30 mass% or less.

[Process (III)]
The present invention preferably further includes the following step (III) after step (II) from the viewpoint of improving the print density of the ink.
Step (III): Step of crosslinking the dispersion polymer with a crosslinking agent Examples of the crosslinking agent used in the step (III) include the following (i) to (iii).
(I) Examples of the compound having two or more epoxy groups in the molecule include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin triglycidyl ether, glycerol polyglycidyl ether, polyglycerol poly Examples include polyglycidyl ethers such as glycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, and hydrogenated bisphenol A type diglycidyl ether.
(Ii) Examples of the compound having two or more oxazoline groups in the molecule include bisoxazolines such as 2,2′-bis (2-oxazoline), 1,3-phenylenebisoxazoline, and 1,3-benzobisoxazoline. And compounds having a terminal oxazoline group obtained by reacting the compound with a polybasic carboxylic acid.
(Iii) Examples of the compound having two or more isocyanate groups in the molecule include organic polyisocyanates and isocyanate group-terminated prepolymers. Examples of the organic polyisocyanates include hexamethylene diisocyanate and 2,2,4- Examples include aliphatic diisocyanates such as trimethylhexamethylene diisocyanate; aromatic diisocyanates such as tolylene-2,4-diisocyanate and phenylene diisocyanate; alicyclic diisocyanates; aromatic triisocyanates;
Among these, Preferably (i) It is a compound which has 2 or more epoxy groups in a molecule | numerator, More preferably, it is 1 or more types chosen from ethylene glycol diglycidyl ether and a trimethylol propane polyglycidyl ether, More preferably, it is a trimethylol. Propane polyglycidyl ether.

The amount of the crosslinking agent used is preferably 10 mol% or more, more preferably in the crosslinking rate (mol%) of the crosslinked dispersion polymer (hereinafter also referred to as “crosslinked polymer”) calculated by the following formula (3). 20 mol% or more, more preferably 30 mol% or more, and preferably 90 mol% or less, more preferably 70 mol% or less, still more preferably 50 mol% or less, and even more preferably 40 mol% or less. .
The crosslinking ratio is calculated from the amount of the crosslinking agent used and the number of moles of the reactive group, the amount of the dispersion polymer used and the number of moles of the reactive group of the polymer capable of reacting with the reactive group of the crosslinking agent according to the following formula (3). Is the value to be
Crosslinking rate (mol%) = [number of moles of reactive group of crosslinking agent / number of moles of reactive group capable of reacting with crosslinking agent of dispersion polymer] × 100 (3)
In the above formula (3), “the number of moles of the reactive group of the crosslinking agent” is obtained by multiplying the number of moles of the crosslinking agent used by the number of reactive groups in one molecule of the crosslinking agent.
As conditions for the crosslinking reaction, the reaction temperature is preferably 40 ° C. or higher, more preferably 60 ° C. or higher, and preferably 95 ° C. or lower, more preferably 90 ° C. or lower. The reaction time is preferably 0.5 hours or more, more preferably 1 hour or more, and preferably 7 hours or less, more preferably 5 hours or less.
The cross-linking agent may be added in any one of steps (I) to (III) or in a plurality of steps, but it is preferably added after step (II).

(Filtering process)
The present invention preferably includes a step of filtering with a filter after step (II) or step (III) from the viewpoint of removing coarse particles. Since the aqueous pigment dispersion obtained in the present invention contains fine pigment particles and is excellent in filterability, the filtration process can be advanced efficiently. The aperture of the filter used for filtration is preferably 20 μm or less, more preferably 10 μm or less from the viewpoint of removing coarse particles, and preferably 1 μm or more from the viewpoint of shortening the time for filtration.
The solid content concentration of the obtained pigment aqueous dispersion is preferably 10% by mass or more, more preferably 15% by mass or more, and still more preferably 18% by mass or more, from the viewpoint of facilitating preparation of the pigment water dispersion. And, it is preferably 40% by mass or less, more preferably 30% by mass or less, and still more preferably 25% by mass or less.

<Composition of pigment aqueous dispersion>
The content of the pigment is preferably 3.0% by mass or more, more preferably 5.0% by mass in the pigment aqueous dispersion from the viewpoint of obtaining fine pigment particles and from the viewpoint of improving the printing density of the ink. % Or more, more preferably 7.0% by mass or more, and from the same viewpoint as described above, preferably 20% by mass or less, more preferably 17% by mass or less, and further preferably 15% by mass or less. .

  The content of the dispersion polymer or the crosslinked dispersion polymer (hereinafter also referred to as “(crosslinked) dispersion polymer”) is preferably 3.0% by mass or more in the pigment aqueous dispersion from the viewpoint of obtaining fine pigment particles. More preferably, it is 5.0 mass% or more, More preferably, it is 7.0 mass% or more, From the same viewpoint as the above, Preferably it is 20 mass% or less, More preferably, it is 15 mass% or less, More preferably, it is 10 It is below mass%.

  From the viewpoint of obtaining fine pigment particles, the water content is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass or more in the pigment water dispersion. From the same viewpoint, it is preferably 90% by mass or less, more preferably 85% by mass or less.

The mass ratio of the pigment to the (crosslinked) dispersion polymer in the pigment aqueous dispersion [pigment / (crosslinked) dispersed polymer] is preferably 30 / from the viewpoint of obtaining fine pigment particles and improving the printing density of the ink. 70 or more, more preferably 40/60 or more, still more preferably 50/50 or more, and preferably 90/10 or less, more preferably 80/20 or less, still more preferably 70/30 or less, still more preferably 60/40 or less.
The average particle diameter of the pigment particles dispersed with the (crosslinked) dispersion polymer in the pigment water dispersion is preferably 40 nm or more, more preferably 50 nm or more, still more preferably 60 nm or more, from the viewpoint of improving the printing density of the ink. More preferably, it is 80 nm or more, Preferably it is 200 nm or less, More preferably, it is 150 nm or less, More preferably, it is 130 nm or less.
The average particle diameter of the pigment particles in the pigment aqueous dispersion can be measured by the method described in Examples similar to the average particle diameter in the dispersion A.

From the viewpoint of obtaining fine pigment particles, the viscosity of the pigment aqueous dispersion at 35 ° C. is preferably 2.0 mPa · s or more, more preferably 3.0 mPa · s or more, and further preferably 3.5 mPa · s or more. From the same viewpoint as described above, it is preferably 12 mPa · s or less, more preferably 9.0 mPa · s or less, still more preferably 7.0 mPa · s or less, still more preferably 5.5 mPa · s or less, and even more. Preferably, it is 4.5 mPa · s or less.
The viscosity at 35 ° C. can be measured using an E-type viscometer “TV-25” (manufactured by Toki Sangyo Co., Ltd., using a standard cone rotor 1 ° 34 ′ × R24, rotating at 50 rpm).
The pH of the pigment aqueous dispersion at 25 ° C. is preferably 5.5 or higher, more preferably 6.0 or higher, still more preferably 6.5 or higher, from the viewpoint of member resistance and skin irritation. From the same viewpoint, it is preferably 11.0 or less, more preferably 10.0 or less, still more preferably 9.5 or less, and still more preferably 9.0 or less.
The pH at 25 ° C. can be measured using a desktop pH meter “F-71” (manufactured by Horiba, Ltd.) using a pH electrode “6337-10D” (manufactured by Horiba, Ltd.).

  The pigment aqueous dispersion obtained by the production method of the present invention comprises a solvent, a surfactant, a wetting agent, a penetrating agent, a dispersing agent, a viscosity modifier, an antifoaming agent, an antifungal agent, and a rust preventing agent that are usually used in aqueous inks. In addition, various additives such as preservatives and ultraviolet absorbers can be added and used as water-based inks for flexographic printing, gravure printing, or ink-jet recording, preferably as water-based inks for ink-jet recording.

[Method for producing water-based ink]
The present invention includes a water-based ink comprising a step of mixing a pigment aqueous dispersion obtained by the above-described production method, a water-soluble organic solvent (b-2), and, if necessary, water, a surfactant, and various additives. (Hereinafter, also simply referred to as “ink”).
The ink according to the present invention further includes various additives such as commonly used wetting agents, penetrating agents, dispersants, viscosity modifiers, antifoaming agents, antifungal agents, rustproofing agents, preservatives, and UV absorbers. can do.
The components in the ink according to the present invention and the composition and physical properties of the water-based ink are as follows.

<Water-soluble organic solvent (b-2)>
Examples of the water-soluble organic solvent (b-2) include polyhydric alcohols, polyhydric alcohol alkyl ethers, and nitrogen-containing heterocyclic compounds.
Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, glycerin and the like.
Examples of the polyhydric alcohol alkyl ether include diethylene glycol monoalkyl ether, triethylene glycol monoalkyl ether, dipropylene glycol monoalkyl ether and the like.
Examples of the nitrogen-containing heterocyclic compound include N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethylimidazolidinone and the like.
Among these, a polyhydric alcohol is preferable, more preferably one or more selected from diethylene glycol, propylene glycol and glycerin, and still more preferably one or more selected from propylene glycol and glycerin.
These can be used alone or in combination of two or more.

<Surfactant>
The ink according to the present invention preferably further contains a surfactant from the viewpoint of storage stability.
As the surfactant, a nonionic surfactant is preferable from the viewpoint of the storage stability of the ink. For example, (1) a saturated or unsaturated, linear or branched higher alcohol having 8 to 22 carbon atoms, Polyoxyalkylene alkyl ether, alkenyl ether, alkynyl ether or aryl ether obtained by adding ethylene oxide, propylene oxide or butylene oxide to a polyhydric alcohol or aromatic alcohol, (2) saturated or unsaturated having 8 to 22 carbon atoms An ester of a higher alcohol having a linear or branched hydrocarbon group and a polyvalent fatty acid, (3) a polyoxy having a linear or branched alkyl group or an alkenyl group having 8 to 20 carbon atoms Alkylene aliphatic amines, (4) higher fatty acids having 8 to 22 carbon atoms and polyhydric alcohols Ester compounds or ethylene oxide, a compound obtained by adding propylene oxide or butylene oxide, and the like.

  Among the nonionic surfactants, acetylene glycol surfactants are preferable, and specific examples thereof include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl. -4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 3, 1 or more types chosen from 5-dimethyl- 1-hexyn-3-ol and these ethylene oxide adducts are mentioned, More preferably, 2,4,7,9-tetramethyl-5-decyne-4,7- One or more selected from diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, and these ethylene oxide adducts; Preferably, at least one selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol and ethylene oxide adducts thereof.

  Examples of commercially available nonionic surfactants include “Surfinol 104PG-50 (propylene glycol solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, manufactured by Air Products, 50% effective) "," Surfinol 465 (2,4,7,9-tetramethyl-5-decyne-4,7-diol addition product of ethylene oxide (hereinafter also referred to as "EO"), EO average addition mole) Number: 10) "," Surfinol 485 (same EO adduct, EO average added moles: 30) "," Orphine E1010 (same EO adduct, EO average added moles: 10) ", Kawaken Fine Chemical Co., Ltd. “Acetylenol E81 (EO average added mole number: 8.1)”, “Acetylenol E100 (EO average added mole number: 10)”, “Acetylenol” 200 (EO average addition mole number: 20), "" Emulgen 120 (polyoxyethylene lauryl ether) manufactured by Kao Corporation ", and the like.

(Composition of water-based ink)
The content of the pigment in the water-based ink is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, still more preferably 3.0% by mass or more, from the viewpoint of printing density, and the dispersion. From the viewpoint of stability, it is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, and still more preferably 8.0% by mass or less.

The content of the dispersion polymer in the water-based ink is preferably 0.10% by mass or more, more preferably 0.15% by mass or more, and further preferably 0.20% by mass or more, from the viewpoint of dispersion stability. From the viewpoint of printing density, it is preferably 5.0% by mass or less, more preferably 3.5% by mass or less, and further preferably 3.0% by mass or less.
It is.

  The content of the water-soluble organic solvent (b-2) in the water-based ink is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and further preferably 3.0% by mass from the viewpoint of printing density. From the viewpoint of dispersion stability, it is preferably 35% by mass or less, more preferably 30% by mass or less, still more preferably 25% by mass or less, still more preferably 10% by mass or less, and still more preferably. It is 5.0 mass% or less.

  The content of the surfactant in the water-based ink is preferably 0.10% by mass or more, more preferably 0.20% by mass or more, and further preferably 0.30% by mass or more from the viewpoint of storage stability. From the same viewpoint as described above, it is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and further preferably 2.5% by mass or less.

  The content of water in the water-based ink is preferably 40% by mass or more, more preferably 50% by mass or more from the viewpoint of dispersion stability, and preferably 95% by mass or less from the viewpoint of print density. Preferably it is 90 mass% or less, More preferably, it is 88 mass% or less.

(Physical properties of water-based ink)
The viscosity of the water-based ink at 35 ° C. is preferably 1.0 mPa · s or more, more preferably 1.5 mPa · s or more, further preferably 2.0 mPa · s or more, from the viewpoint of printing density, and dispersion stability. From the viewpoint of property, it is preferably 10 mPa · s or less, more preferably 7.0 mPa · s or less, and still more preferably 4.0 mPa · s or less.
The viscosity at 35 ° C. can be measured using an E-type viscometer “TV-25” (manufactured by Toki Sangyo Co., Ltd., using a standard cone rotor 1 ° 34 ′ × R24, rotating at 50 rpm).
The pH of the water-based ink at 25 ° C. is preferably 5.5 or more, more preferably 6.0 or more, still more preferably 6.5 or more, from the viewpoint of member resistance and skin irritation, and the same as described above. From the viewpoint, it is preferably 11.0 or less, more preferably 10.0 or less, still more preferably 9.5 or less, and still more preferably 9.0 or less.
The pH at 25 ° C. can be measured using a desktop pH meter “F-71” (manufactured by Horiba, Ltd.) using a pH electrode “6337-10D” (manufactured by Horiba, Ltd.).

The average particle diameter of the pigment particles dispersed with the (crosslinked) dispersion polymer in the water-based ink is preferably such that the particles do not swell or shrink, and do not aggregate between the particles, and are the same as the average particle diameter in the pigment aqueous dispersion. It is more preferable that The preferable average particle diameter of the pigment particles dispersed with the (crosslinked) dispersion polymer in the water-based ink is the same as the preferable average particle diameter of the pigment aqueous dispersion described above.
The average particle diameter of the pigment particles dispersed with the (crosslinked) dispersion polymer in the water-based ink can be measured by the method described in Examples similar to the average particle diameter in the dispersion A.

In the following Examples and Comparative Examples, “parts” and “%” are “parts by mass” and “mass%” unless otherwise specified.
The weight average molecular weight of the dispersion polymer used in the examples and comparative examples, the solid content concentration of the pigment water dispersion, the average particle size of the dispersion A, the evaluation of the residence stability, and the evaluation of the printing density were evaluated by the following methods. went.

(1) Weight average molecular weight of dispersed polymer Gel permeation chromatography using a solution prepared by dissolving phosphoric acid and lithium bromide in N, N-dimethylformamide so as to have concentrations of 60 mmol / L and 50 mmol / L, respectively. [Tosoh Co., Ltd. GPC apparatus (HLC-8120GPC), Tosoh Co., Ltd. column (TSK-GEL, α-M × 2), flow rate: 1 mL / min], monodisperse polystyrene having a known molecular weight as a standard substance And measured.

(2) Solid content concentration of pigment aqueous dispersion In a 30 ml polypropylene container (φ = 40 mm, height = 30 mm), 10.0 g of sodium sulfate constant in a desiccator is weighed, and about 1.0 g of a sample is put therein. After adding and mixing, the sample was accurately weighed and maintained at 105 ° C. for 2 hours to remove volatile matter, and further left in a desiccator for 15 minutes to measure the mass. The mass of the sample after removal of the volatile matter was taken as the solid content and divided by the mass of the added sample to obtain the solid content concentration.

(3) Measurement of average particle diameter The average particle diameter of the dispersion A obtained in the step (I) was measured using a laser particle analysis system “ELS-8000” (cumulant analysis) manufactured by Otsuka Electronics Co., Ltd. The measurement conditions were a temperature of 25 ° C., an angle between incident light and a detector of 90 °, and the number of integrations of 100. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measurement concentration was 5 × 10 ⁻³ % (in terms of solid content concentration), and evaluation was performed according to the following criteria. The results are shown in Tables 1-4.
A: Average particle size is 130 nm or less B: Average particle size is more than 130 nm

(4) Evaluation of retention stability of dispersion A 8 g of dispersion A obtained in step (I) was filled in a 10 ml screw tube, sealed, and kept standing at 25 ° C. for 1 day. The average particle size before and after holding was measured by the method (3) above, and the retention stability of Dispersion A was evaluated according to the following criteria. The results are shown in Tables 1-4.
(Evaluation criteria)
A: Increase in average particle diameter is less than 6 nm B: Increase in average particle diameter is 6 nm or more and less than 15 nm C: Increase in average particle diameter is 15 nm or more, or gelation occurs after holding.

(5) Print density evaluation of printed matter Water-based ink obtained in Examples and Comparative Examples using a printer manufactured by Seiko Epson Corporation (model number: EM-930C, piezo method) is used as a general-purpose coated paper OK top coat (Oji Paper Co., Ltd.) (Solid, 216 mm wide x 279 mm long) (printing condition = paper type: plain paper, mode setting: fine, printing speed: 6 sheets / min), heated at 90 ° C for 2 minutes, and left at 25 ° C for 24 hours The printing density was measured with a Macbeth densitometer (product of Gretag Macbeth Co., product number: Spectroeye) at the center and four corners of the printed material (5.1 cm × 8.0 cm), and the average value was determined. The higher the numerical value, the better the print density. The results are shown in Table 3.

(Preparation of dispersion polymer)
Preparation Example 1
62 g of acrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., reagent), 129 g of styrene (manufactured by Wako Pure Chemical Industries, Ltd.), and 9 g of α-methylstyrene (manufactured by Wako Pure Chemical Industries, Ltd., reagent) are mixed to prepare a monomer mixture. Prepared.
Separately, 20 g of methyl ethyl ketone (hereinafter also referred to as “MEK”), 0.3 g of a polymerization chain transfer agent (2-mercaptoethanol), and 10% of the monomer mixture are mixed in a reaction vessel, and then replaced with nitrogen gas. Well done.
Next, in the dropping funnel, the remaining 90% of the monomer mixture, 0.27 g of the polymerization chain transfer agent, 60 g of MEK, and an azo radical polymerization initiator (trade name: V-65, 2 manufactured by Wako Pure Chemical Industries, Ltd.) , 2′-azobis (2,4-dimethylvaleronitrile)) 2.2 g, and the temperature of the monomer mixture in the reaction vessel is increased to 65 ° C. with stirring in a nitrogen atmosphere. Was added dropwise over 3 hours. After 2 hours at 65 ° C. from the end of dropping, a solution prepared by dissolving 0.3 g of the polymerization initiator in 5 g of MEK was added, and the mixture was further aged at 65 ° C. for 2 hours and 70 ° C. for 2 hours. By adding 220 g of MEK, a dispersion polymer solution (a) having a carboxy group as an acidic group (weight average molecular weight of the dispersion polymer: 16,000, acid value of 240 mg KOH / g, dispersion polymer concentration of 40%) was obtained.

Preparation Example 2
A monomer mixture was prepared by mixing 54 g of acrylic acid (made by Wako Pure Chemical Industries, Ltd., reagent), 137 g of styrene (made by Wako Pure Chemical Industries, Ltd.), and 9 g of α-methylstyrene (made by Wako Pure Chemical Industries, Ltd., reagent). Prepared.
Separately, 20 g of MEK, 0.3 g of a polymerization chain transfer agent (2-mercaptoethanol), and 10% of the monomer mixture were mixed in the reaction vessel, and nitrogen gas substitution was sufficiently performed.
Subsequently, the remaining 90% of the monomer mixture, 0.27 g of the polymerization chain transfer agent, 60 g of MEK, and 2.2 g of azo radical polymerization initiator (V-65) are put into a dropping funnel. In the same manner as in Example 1, a dispersion polymer solution (b) having a carboxy group as an acidic group (weight average molecular weight of the dispersion polymer: 14,000, acid value of 213 mgKOH / g, dispersion polymer concentration of 40%) was obtained.

(Manufacture of pigment aqueous dispersion)
Example 1
(1) Step (I-1): Step of obtaining a pigment mixture To 333 g of the dispersion polymer solution (a) obtained in Preparation Example 1, 1000 g of ion-exchanged water, 81 g of 5N sodium hydroxide aqueous solution, and 120 g of methyl ethyl ketone were added to obtain an emulsion. Got.
To this emulsion, 200 g of yellow pigment PY74 (CI Pigment Yellow 74, Sanyo Color Co., Ltd., trade name: FY7414) was added to obtain a pigment mixture.
(2) Step (I): Dispersion treatment step The pigment mixture obtained in step (I-1) is subjected to a preliminary dispersion treatment at 20 ° C. for 1 hour using a disper blade, and a preliminary dispersion (the above formula (2) ) To obtain a non-volatile component ratio of 20%). After adding 105 g of methyl ethyl ketone and 1051 g of ion-exchanged water to the obtained preliminary dispersion, using a high-pressure homogenizer (trade name: Microfluidizer, manufactured by Microfluidics), a 15-pass continuous system at a pressure of 150 MPa. This dispersion treatment was performed to obtain Dispersion A1.
(3) Step (II): Organic solvent removal step From the dispersion A1 obtained in Step (I), methyl ethyl ketone is removed at 60 ° C. using a hot water heating medium under reduced pressure, and a part of water is further removed. And filtering with a 25 mL needleless syringe (Terumo Corporation) equipped with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Corporation) to remove coarse particles, A pigment aqueous dispersion having a solid content concentration of 25% was obtained.
It took about 30 minutes from the end of step (I) to the start of step (II).
(4) Step (III): Crosslinking step To 300 g of the pigment aqueous dispersion obtained in Step (II), 5.4 g of Denacol EX-321L (trimethylolpropane polyglycidyl ether) and 70 g of ion-exchanged water are added. Stir at 90 ° C. for 90 minutes. After cooling to room temperature, it is filtered with a 25 mL needleless syringe (Terumo Corporation) equipped with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Corporation) to remove coarse particles. As a result, a pigment aqueous dispersion 1 having a solid content concentration of 20% was obtained.

Example 2
In Step (I-1) of Example 1, the dispersion polymer solution (a) is replaced with the dispersion polymer solution (b) obtained in Preparation Example 2, 996 g of ion-exchanged water, 96 g of 5N sodium hydroxide aqueous solution, and The same procedure as in Example 1 was conducted except that methyl ethyl ketone was changed to 123 g and methyl ethyl ketone was changed to 106 g and ion-exchanged water to 1059 g in Step (I). Got. The crosslinking rate was 34 mol%.

Example 3
In the step (I-1) of Example 1, 992 g of ion-exchanged water was changed to 108 g of 5N sodium hydroxide aqueous solution and 125 g of methyl ethyl ketone, and in step (I), 107 g of methyl ethyl ketone and 1065 g of ion-exchanged water were used. The pigment water dispersion 3 having a solid content concentration of 20% was obtained in the same manner as in Example 1 except for changing to The crosslinking rate was 36 mol%.

Example 4
In step (I-1) of Example 1, ion exchange water was changed to 988 g, 5N sodium hydroxide aqueous solution 121 g, and methyl ethyl ketone to 127 g. In step (I), 107 g of methyl ethyl ketone and 1072 g of ion exchange water were used. The pigment water dispersion 4 having a solid content concentration of 20% was obtained in the same manner as in Example 1 except that it was changed to.

Example 5
In step (I-1) of Example 1, 500 g of the dispersed polymer solution (a), 1180 g of ion-exchanged water, 162 g of 5N sodium hydroxide aqueous solution, and 94 g of methyl ethyl ketone were changed to 94 g. In step (I), methyl ethyl ketone was changed. The pigment water dispersion 5 having a solid content concentration of 20% was obtained in the same manner as in Example 1, except that 130 g was changed to 1295 g.

Example 6
In step (I-1) of Example 1, 333 g of the dispersed polymer solution (a) was replaced with 500 g of the dispersed polymer solution (b), ion-exchanged water was changed to 1197 g, and 5N sodium hydroxide aqueous solution was changed to 108 g. In I), except that methyl ethyl ketone was changed to 127 g and ion-exchanged water was changed to 1267 g, the same operation as in Example 1 was performed to obtain a pigment water dispersion 6 having a solid content concentration of 20%.

Example 7
The same operations as in Example 2 were performed up to step (II), and pigment aqueous dispersion 7 having a solid content concentration of 25% was obtained without performing step (III).

Example 8
The same operations as in Example 3 were performed up to step (II), and pigment aqueous dispersion 8 having a solid content concentration of 25% was obtained without performing step (III).

Comparative Example 1
In the step (I-1) of Example 1, the dispersion polymer solution (a) is replaced with the dispersion polymer solution (b), the ion exchange water is changed to 1014 g, the 5N sodium hydroxide aqueous solution is 36 g, and the methyl ethyl ketone is 113 g. In step (I), except that methyl ethyl ketone was changed to 131 g and ion-exchanged water was changed to 435 g, the same operation as in Example 1 was carried out to obtain a pigment water dispersion C1 having a solid content concentration of 20%.

Comparative Example 2
(1) Step (I-1) ′: Step of obtaining a pigment mixture 133 g of polymer obtained by drying the dispersion polymer solution (b) under reduced pressure, 988 g of ion-exchanged water, and 36 g of 5N aqueous sodium hydroxide solution were mixed at 90 ° C. The mixture was stirred for 10 hours to obtain an emulsion. To this emulsion, 200 g of yellow pigment PY74 (CI Pigment Yellow 74, manufactured by Sanyo Color Co., Ltd., trade name: FY7414) was added to obtain a pigment mixture containing no water-soluble organic solvent.
(2) Step (I) ′: Dispersion treatment step The pigment mixture obtained in step (I-1) ′ was subjected to a preliminary dispersion treatment at 20 ° C. for 1 hour using a disper blade, and a preliminary dispersion (the above formula The nonvolatile component ratio calculated by (2) was 25%). The obtained preliminary dispersion was subjected to a main dispersion treatment in a 15-pass continuous system at a pressure of 150 MPa using a high-pressure homogenizer (trade name: Microfluidizer, manufactured by Microfluidics) to obtain dispersion AC2.
(3) Step (III) ′: Crosslinking Step To 300 g of dispersion AC2 obtained in Step (I) ′, 5.4 g of Denacol EX-321L and 70 g of ion-exchanged water were added and stirred at 90 ° C. for 90 minutes. . After cooling to room temperature, it is filtered with a 25 mL needleless syringe (Terumo Corporation) equipped with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Corporation) to remove coarse particles. As a result, a pigment aqueous dispersion C2 having a solid content concentration of 20% was obtained.

Comparative Example 3
(1) Step (I-1) ′: Step of obtaining a pigment mixture 133 g of a polymer obtained by drying the dispersion polymer solution (b) under reduced pressure, 976 g of ion-exchanged water, and 72 g of 5N aqueous sodium hydroxide solution were mixed at 90 ° C. The mixture was stirred for 10 hours to obtain an emulsion. To this emulsion, 200 g of yellow pigment PY74 (CI Pigment Yellow 74, Sanyo Color Co., Ltd., trade name: FY7414) was added to obtain a pigment mixture containing no water-soluble organic solvent.
(2) Step (I) ′: Dispersion treatment step The pigment mixture obtained in step (I-1) ′ was subjected to a preliminary dispersion treatment at 20 ° C. for 1 hour using a disper blade, and a preliminary dispersion (the above formula The nonvolatile component ratio calculated by (2) was 25%). After adding 1497 g of ion-exchanged water to the obtained pre-dispersion, this dispersion treatment is performed by a 15-pass continuous system at a pressure of 150 MPa using a high-pressure homogenizer (trade name: Microfluidizer, manufactured by Microfluidics). Dispersion AC3 was obtained.
(3) Step (III) ′: Crosslinking Step To 300 g of the dispersion AC3 obtained in Step (I) ′, 5.4 g of Denacol EX-321L and 70 g of ion-exchanged water were added and stirred at 90 ° C. for 90 minutes. . After cooling to room temperature, it is filtered with a 25 mL needleless syringe (Terumo Corporation) equipped with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Corporation) to remove coarse particles. As a result, a pigment aqueous dispersion C3 having a solid content concentration of 20% was obtained.

Comparative Example 4
In the step (I-1) of Example 1, the dispersion polymer solution (a) is replaced with the dispersion polymer solution (b), the ion exchange water is changed to 1014 g, the 5N sodium hydroxide aqueous solution is 36 g, and the methyl ethyl ketone is 113 g. In step (I), except that methyl ethyl ketone was changed to 74 g and ion-exchanged water was changed to 492 g, the same operation as in Example 1 was carried out to obtain a pigment water dispersion C4 having a solid content concentration of 20%.

Comparative Example 5
In step (I-1) of Example 1, the dispersion polymer solution (a) was replaced with the dispersion polymer solution (b), ion exchange water was changed to 1010 g, 5N sodium hydroxide aqueous solution 48 g, and methyl ethyl ketone 115 g, In step (I), except that methyl ethyl ketone was changed to 74 g and ion-exchanged water was changed to 495 g, an operation was performed in the same manner as in Example 1 to obtain a pigment water dispersion C5 having a solid content concentration of 20%.

Comparative Example 6
In step (I-1) of Example 1, the dispersion polymer solution (a) was replaced with the dispersion polymer solution (b), 1011 g of ion-exchanged water was changed to 48 g of 5N sodium hydroxide aqueous solution, and 115 g of methyl ethyl ketone were changed. A pigment water dispersion C6 having a solid content concentration of 20% was obtained in the same manner as in Example 1 except that 103 g of methyl ethyl ketone and 1035 g of ion-exchanged water were changed in step (I).

Comparative Example 7
In the step (I-1) of Example 1, 1009 g of ion exchange water was changed to 54 g of 5N aqueous sodium hydroxide solution and 116 g of methyl ethyl ketone. In step (I), 104 g of methyl ethyl ketone and 1038 g of ion exchange water were used. The pigment water dispersion C7 having a solid content concentration of 20% was obtained in the same manner as in Example 1 except that the pigment water dispersion C7 was changed to.

Comparative Example 8
In step (I-1) of Example 1, 984 g of ion exchange water was changed to 135 g of 5N sodium hydroxide aqueous solution and 129 g of methyl ethyl ketone. In step (I), 108 g of methyl ethyl ketone and 1079 g of ion exchange water were used. The pigment water dispersion C8 having a solid content concentration of 20% was obtained in the same manner as in Example 1 except for changing to

Reference example 1
(1) Step (I-1) ": Step of obtaining a pigment mixture A polymer 133g obtained by drying the dispersion polymer solution (a) under reduced pressure, 946 g of ion-exchanged water, 40 g of 5N sodium hydroxide aqueous solution, and 97 g of methyl ethyl ketone are mixed. The mixture was stirred for 10 hours at 90 ° C. to obtain an emulsion, and 200 g of pigment PBk7 (CI Pigment Black 7, manufactured by Cabot Specialty Chemicals, Inc., trade name: Monarch 717) was added to the emulsion. In addition, a pigment mixture was obtained.
(2) Step (I) ": Dispersion treatment step The pigment mixture obtained in Step (I-1)" is subjected to a preliminary dispersion treatment at 20 ° C for 1 hour using a disper blade, and a preliminary dispersion (the above formula The non-volatile component ratio calculated by (2) was 24%). The obtained preliminary dispersion was subjected to a main dispersion treatment in a 15-pass continuous system at a pressure of 150 MPa using a high-pressure homogenizer (trade name: Microfluidizer, manufactured by Microfluidics) to obtain dispersion AR1.
(3) Step (II) ": Organic solvent removal step 472 g of ion-exchanged water is added to the dispersion AR1 obtained in Step (I)", and methyl ethyl ketone is removed at 60 ° C using a hot water heating medium under reduced pressure. Further, a part of the water was removed and filtered with a 25 mL needleless syringe (Terumo Corporation) attached with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Film Co., Ltd.) By removing the coarse particles, a pigment aqueous dispersion having a solid content concentration of 25% was obtained.
(4) Step (III) ": Crosslinking Step To 300 g of the pigment water dispersion obtained in Step (II)", 5.4 g of Denacol EX-321L and 70 g of ion-exchanged water are added and stirred at 90 ° C for 90 minutes. did. After cooling to room temperature, it is filtered with a 25 mL needleless syringe (Terumo Corporation) equipped with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Corporation) to remove coarse particles. As a result, a pigment aqueous dispersion R1 having a solid content concentration of 20% was obtained.

Reference example 2
(1) Step (I-1) ": Step of obtaining a pigment mixture 133 g of polymer obtained by drying the dispersion polymer solution (b) under reduced pressure, 517 g of ion-exchanged water, and 48 g of 5N aqueous sodium hydroxide solution were mixed at 90 ° C. After stirring for 10 hours, an emulsion was obtained, and 200 g of pigment PR122 (CI Pigment Red 122, Dainichi Seika Kogyo Co., Ltd., trade name: CFR6111T) was added to the emulsion to obtain a pigment mixture.
(2) Step (I) ": Dispersion treatment step The pigment mixture obtained in Step (I-1)" is subjected to a preliminary dispersion treatment at 20 ° C for 1 hour using a disper blade, and a preliminary dispersion (the above formula The non-volatile component ratio calculated by (2) was 38%). After adding 467 g of ion-exchanged water to the obtained preliminary dispersion, this dispersion treatment was performed by a 15-pass continuous system at a pressure of 150 MPa using a high-pressure homogenizer (trade name: Microfluidizer, manufactured by Microfluidics). Dispersion AR2 was obtained.
(3) Step (III) ": Crosslinking Step To 300 g of the dispersion AR2 obtained in Step (I)", 5.4 g of Denacol EX-321L and 70 g of ion-exchanged water were added and stirred at 90 ° C for 90 minutes. . After cooling to room temperature, it is filtered with a 25 mL needleless syringe (Terumo Corporation) equipped with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Corporation) to remove coarse particles. As a result, a pigment aqueous dispersion R2 having a solid content concentration of 20% was obtained.

Reference example 3
In step (I-1) of Example 1, the pigment was replaced with PB15: 3 (CI Pigment Blue 15: 3, DIC Corporation, trade name: TGR-SD), and ion-exchanged water was 1106 g, 5N. The same procedure as in Example 1 was carried out except that the amount of sodium hydroxide aqueous solution was changed to 54 g, and methyl ethyl ketone was changed to 0 g and ion-exchanged water was changed to 302 g in step (I). Dispersion R3 was obtained.

(Manufacture of water-based ink)
Each pigment aqueous dispersion obtained in Examples 2-3 and 6-7, glycerin and propylene glycol as the water-soluble organic solvent (b-2), Surfynol 465 as the surfactant, manufactured by Air Products, 2 , 4,7,9-tetramethyl-5-decyne-4,7-diol (EO average addition mole number: 10)] was mixed, and water was further added to obtain a pigment mixture.
The obtained pigment mixed solution was similarly filtered with the 5 μm filter and the needleless syringe to remove coarse particles, whereby the pigment content was 5%, the dispersion polymer content was 3%, and the water-soluble organic solvent ( Each water-based ink in which the total content of b-2) is 4.5% (glycerin 1.5%, propylene glycol 3%), the surfactant content is 0.5%, and the water content is 87%. 20 g was obtained.

In addition, each component shown in the table is as follows.
(Pigment)
PY74: C.I. I. Pigment Yellow 74
PBk7: C.I. I. Pigment Black 7
PR122: C.I. I. Pigment Red 122
PB15: 3: C.I. I. Pigment Blue 15: 3
(Water-soluble organic solvent (b-1))
MEK: Methyl ethyl ketone

As shown in Table 1, Examples 1 to 4 in which the neutralization degree of the acidic group of the dispersed polymer using a water-soluble organic solvent was 60 to 90% were compared with Comparative Examples 1 to 8, The average particle size was small, and the dispersion stability of the dispersion A containing a water-soluble organic solvent was good.
As shown in Table 2, a dispersion containing a water-soluble organic solvent having a small average particle diameter even in Examples 5 and 6 having a low pigment ratio [pigment / (total amount of non-volatile components)] in the non-volatile component. The residence stability of A was good.
As shown in Table 3, Examples 2 and 3 having a crosslinking step had better printing density than Examples 7 and 8 having no crosslinking step.
As shown in Table 4, in Reference Example 2 using a pigment other than PY74, the average particle size was small and the retention stability was good without using a water-soluble organic solvent. In Reference Examples 1 and 3, the dispersion polymer has a neutralization degree of 30 to 40%, and even when a water-soluble organic solvent is used, the average particle size is small, and the retention stability of the dispersion A containing the water-soluble organic solvent is stable. The property was good.
Since the average particle diameter of the dispersion A containing the water-soluble organic solvent of Examples 1 to 8 is small and fine, the pigment water dispersion obtained from the dispersion A also has a small average particle diameter and is fine.

  Since the production method of the present invention has excellent retention stability and fine pigment particles can be obtained, it is suitable as a method for producing a pigment water dispersion and a method for producing a water-based ink using the pigment water dispersion. It is.

Claims (6)

A method for producing an aqueous pigment dispersion having the following steps (I) and (II):
Step (I): C.I. I. Step of obtaining dispersion A by dispersing pigment yellow 74, a dispersion polymer, a water-soluble organic solvent (b-1) and water. Step (II): Water-soluble organic solvent (b- 1) Step for removing pigment to obtain an aqueous pigment dispersion The dispersion polymer has an acidic group and the acid value is 150 mgKOH / g or more and 260 mgKOH / g or less, and neutralization of the acidic group of the dispersion polymer in step (I) The manufacturing method of the pigment water dispersion whose degree is 50 mol% or more and 90 mol% or less.   The method for producing a pigment water dispersion according to claim 1, wherein the dispersion treatment in step (I) includes a high-pressure dispersion treatment.   The manufacturing method of the pigment water dispersion of Claim 1 or 2 whose dispersion polymer is acrylic resin.   The manufacturing method of the pigment water dispersion in any one of Claims 1-3 in which a water-soluble organic solvent (b-1) contains methyl ethyl ketone. Furthermore, the manufacturing method of the pigment water dispersion in any one of Claims 1-4 which has the following process (III) after process (II).
Step (III): Step of cross-linking the dispersion polymer using a cross-linking agent   A method for producing a water-based ink, comprising a step of mixing an aqueous pigment dispersion obtained by the production method according to claim 1 and a water-soluble organic solvent (b-2).