JP6947369B2 - Manufacturing method of aqueous pigment dispersion - Google Patents

Description

The present invention relates to a method for producing an aqueous pigment dispersion and an ink jet recording ink containing the aqueous pigment dispersion.

The inkjet recording method is a recording method in which ink droplets are directly ejected from a fine nozzle and adhered to a printing medium to obtain a printed matter on which characters and images are recorded. This method has the advantages of easy and inexpensive full-color printing and non-contact with the printed matter. Therefore, this method is not limited to consumer printing for general consumers, and in recent years, it has been used for analog printing such as offset printing and gravure printing. It is beginning to be applied to the commercial printing and industrial printing fields that have been practiced.
The advantage of developing inkjet printing in the fields of commercial printing and industrial printing is that it does not require a printing plate unlike analog printing, so it can handle small quantities and on-demand printing such as variable printing. From the viewpoint of reducing the burden on the environment and the weather resistance and water resistance of printed matter, water-based inks that use pigments as colorants have become mainstream.

For example, Patent Document 1 describes a pigment, an aqueous medium, a hydrophobic monomer, and hydrophilicity for the purpose of providing a pigment dispersion, an ink composition, or the like having excellent glossiness and storage stability of the ink composition. It contains at least a copolymer resin with a monomer, a urethane resin, and a cross-linking agent, and the effective solid content weight ratio of the amount of the cross-linking agent added (amount of cross-linking agent / (copolymerized resin of hydrophobic monomer and hydrophilic monomer) And a pigment dispersion liquid in which the total amount of the urethane resin)) is in a specific range, an ink composition containing the pigment dispersion liquid, and the like are disclosed.
Patent Document 2 describes a specific hydrophobic structural unit (a) and a hydrophilic structural unit for the purpose of providing a water-based ink for inkjet recording that has excellent dispersion stability and can achieve both ejection stability and abrasion resistance. A water-based ink for inkjet recording containing a resin (A) having (b), a pigment (B) dispersed by the resin (A), a resin emulsion (C), and an aqueous liquid medium (D) is disclosed. There is.

Japanese Unexamined Patent Publication No. 2005-48016 JP-A-2009-191133

With the development of the packaging industry, the use of on-demand flexible packaging materials is advancing in commercial printing and inkjet printing in the industrial printing field. A resin film is mainly used as the flexible packaging material, and since it is used as various packaging materials, the printed matter is required to have excellent bending resistance. However, when printing on a resin film with conventional ink, it was found that the bending resistance of the printed matter was not sufficient.
As a method for improving the bending resistance, there is a method of increasing the amount of polymer in the ink. When a large amount of polymer is used when dispersing the pigment in order to increase the amount of the polymer in the ink, the bending resistance is improved, but the viscosity at the time of dispersing the pigment is excessively increased. Further, it has been found that when a large amount of polymer emulsion is mixed at the time of ink preparation in order to increase the amount of polymer in the ink, the viscosity immediately after ink preparation and at the time of ink concentration increases, and the ejection reliability of inkjet printing deteriorates.
An object of the present invention is to provide a method for producing an aqueous pigment dispersion having excellent ejection reliability and bending resistance of a printed matter by using it for an aqueous ink, and an ink for inkjet recording containing the aqueous pigment dispersion. do.

The present inventors have a step of heat-treating a mixture of a pigment aqueous dispersion, a polymer emulsion, and a cross-linking agent at a specific temperature, and specify the mass ratio of the pigment (pigment / total polymer amount) to the total amount of the polymer. It was found that the above-mentioned problems can be solved by setting the range. That is, the present invention relates to the following [1] and [2].
[1] A method for producing an aqueous pigment dispersion (I) containing a pigment and a polymer.
It has a step of heat-treating a mixture of the aqueous pigment dispersion (A), the emulsion of the polymer (B), and the cross-linking agent (C) at 45 ° C. or higher and 100 ° C. or lower.
A method for producing an aqueous pigment dispersion (I), wherein the mass ratio (pigment / total polymer amount) of the pigment to the total amount of the polymer is 0.48 or more and 2.15 or less.
[2] An ink jet recording ink containing an aqueous pigment dispersion (I) and a water-soluble organic compound (II) obtained by the production method according to the above [1].

According to the present invention, it is possible to provide a method for producing an aqueous pigment dispersion having excellent ejection reliability and bending resistance of printed matter by using it for an aqueous ink, and an inkjet recording ink containing the aqueous pigment dispersion. can.

[Manufacturing method of aqueous pigment dispersion (I)]
The present invention is a method for producing an aqueous pigment dispersion (I) containing a pigment and a polymer, wherein a mixture of the aqueous pigment dispersion (A), the emulsion of the polymer (B), and the cross-linking agent (C) is prepared. It has a step of heat treatment at 45 ° C. or higher and 100 ° C. or lower (hereinafter, also referred to as “heat treatment step”), and the mass ratio of the pigment (pigment / total polymer amount) to the total amount of the polymer is 0.48 or more and 2.15. The following is a method for producing an aqueous pigment dispersion (I).
In the present invention, the term "water-based" means that water occupies the maximum proportion of the medium in which the pigment is dispersed. The polymer (B) emulsion used in the present invention is an aqueous dispersion of pigment-free polymer (B) particles.
Since the aqueous pigment dispersion (I) obtained by the production method of the present invention can obtain a printed matter having excellent bending resistance, it can be used as an aqueous pigment dispersion for flexographic printing inks, gravure printing inks, or inkjet inks. Since it can be preferably used and has excellent ejection reliability in inkjet printing, it is particularly preferable to use it as an aqueous pigment dispersion for inkjet ink.

By using the production method of the present invention for water-based inks, it is possible to produce an water-based pigment dispersion having excellent ejection reliability and bending resistance of printed matter. The reason is not clear, but it can be considered as follows.
In the present invention, a mixture of a pigment aqueous dispersion, a polymer emulsion, and a cross-linking agent is heat-treated at a specific temperature to cross-link the polymer, whereby the pigment aqueous dispersion and the polymer emulsion are composited, and a cross-linked structure is further formed. Is introduced. As a result, it is considered that the number of particles becomes small while a large amount of polymer is present in the system, and as a result, the increase in viscosity is suppressed. Further, since the low viscosity can be maintained, it is considered that the nozzles in inkjet printing are less likely to be clogged and the ejection reliability is improved. Further, since the obtained aqueous pigment dispersion contains a large amount of polymer, it is presumed that the adhesion of the ink to the flexible resin film is improved and the bending resistance is improved.

<Aqueous pigment dispersion (A)>
The pigment aqueous dispersion (A) used in the present invention is formed by dispersing the pigment in an aqueous medium.
The pigment may be either an inorganic pigment or an organic pigment, and a lake pigment or a fluorescent pigment can also be used. In addition, if necessary, they can be used in combination with extender pigments.
Specific examples of the inorganic pigment include carbon black, titanium oxide, iron oxide, red iron oxide, metal oxides such as chromium oxide, and pearl luster pigments. Especially for black ink, carbon black is preferable. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, and isoind. Examples thereof include polycyclic pigments such as linone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and slen pigments.
The hue is not particularly limited, and any achromatic pigment such as white, black, or gray; or any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, or green can be used.
Examples of the extender pigment include silica, calcium carbonate, talc and the like.
The pigment can be used alone or in combination of two or more.

The pigment aqueous dispersion (A) used in the present invention is an aqueous dispersion of a self-dispersing pigment or an aqueous dispersion in which the pigment is dispersed with a polymer dispersant (a) from the viewpoint of discharge reliability and bending resistance. It is preferably a body, and more preferably an aqueous dispersion in which the pigment is dispersed with the polymer dispersant (a).

(Aqueous dispersion of self-dispersing pigment)
In the present invention, the self-dispersing pigment refers to one or more of hydrophilic functional groups (anionic hydrophilic groups such as carboxy group and sulfonic acid group, or cationic hydrophilic groups such as quaternary ammonium group) directly or carbon. It means a pigment that can be dispersed in an aqueous medium without using a surfactant or a polymer dispersant by binding to the surface of the pigment via another atomic group such as an alcandiyl group having a number of 1 or more and 12 or less. In order to make the pigment a self-dispersing pigment, for example, the required amount of hydrophilic functional groups may be chemically bonded to the pigment surface by a conventional method. As the hydrophilic functional group, an anionic group is preferable, and a carboxy group is more preferable.
Commercially available self-dispersing pigments include CAB-O-JET 200, 300, 352K, 250A, 260M, 270Y, 450A, 465M, 470Y, and 480V manufactured by Cabot Japan Co., Ltd. ( BONJET BLACK CW-1 manufactured by Orient Chemical Industries Co., Ltd., CW-2 (trade name) manufactured by Orient Chemical Industries Co., Ltd., Aqua-Black 162 manufactured by Tokai Carbon Co., Ltd., SENSIJET manufactured by SENSIENT INDUSTRIAL COLORS, etc. BLACK SDP100, SDP1000, SDP2000 (above, trade name) and the like can be mentioned.

(Aqueous dispersion in which the pigment is dispersed with the polymer dispersant (a))
When an aqueous dispersion in which a pigment is dispersed with a polymer dispersant (a) is used as the pigment aqueous dispersion (A), the present form of the polymer dispersant (a) in the pigment aqueous dispersion (A) is a pigment. There are a state in which the polymer dispersant (a) is adsorbed, a pigment inclusion (capsule) state in which the pigment is contained in the polymer dispersant (a), and a form in which the polymer dispersant (a) is not adsorbed on the pigment. .. From the viewpoint of the dispersion stability of the pigment, in the present invention, the form in which the polymer dispersant (a) contains the pigment, that is, the form of the polymer particles containing the pigment (hereinafter, also referred to as “pigment-containing polymer particles”) is preferable. It is more preferable that the pigment is contained in the polymer dispersant (a).

The polymer dispersant (a) used in the present invention is preferably one or more selected from (meth) acrylic resin, polyester resin and polyurethane resin from the viewpoint of discharge reliability and bending resistance, and more preferably. One or more selected from (meth) acrylic resin and polyester resin.

[(Meta) acrylic resin]
The (meth) acrylic resin preferably contains a structural unit derived from a hydrophilic monomer from the viewpoint of improving the dispersion stability of the pigment and improving the discharge reliability and bending resistance. Examples of the hydrophilic monomer include a monomer having an ionic functional group and a non-ionic hydrophilic monomer having no ionic functional group, and a monomer having an ionic functional group is preferable.
In the present invention, "hydrophilic" means that when the monomer is dissolved in 100 g of ion-exchanged water at 25 ° C. until it is saturated, the amount of the monomer dissolved is 10 g or more. The dissolved amount of the hydrophilic monomer is preferably 50 g or more. The term "hydrophilic" in the case of a monomer having an ionic functional group means that the amount of the dissolved ionic functional group in a neutralized state is within the above range.

Examples of the monomer having an ionic functional group include a monomer having a cationic group and a monomer having an anionic group, and an anion is used from the viewpoint of improving the dispersion stability of the pigment and improving the discharge reliability and bending resistance. Monomers having a sex group are preferred. As the anionic group, a carboxy group (-COOM ¹ ), a sulfonic acid group (-SO ₃ M ¹ ), a phosphoric acid group (-OPO ₃ M ¹ ₂ ) and the like are dissociated and hydrogen ions are released. group showing acidity, or their dissociated ionic form _{^{(-COO -, -SO 3 -,}} -OPO 3 2-, -OPO 3 - M 1) , and the like. In the above chemical formula, M ¹ represents a hydrogen atom, an alkali metal, ammonium or an organic ammonium.
Examples of the monomer having a carboxy group include (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-methacryloyloxymethylsuccinic acid and the like.
Examples of the monomer having a sulfonic acid group include styrene sulfonic acid, 2-acrylamide-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate and the like.
Examples of the monomer having a phosphoric acid group include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate and the like.
Among these, a monomer having a carboxy group is preferable, and at least selected from (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid and 2-methacryloyloxymethylsuccinic acid. It is one kind, and more preferably (meth) acrylic acid.
In the present specification, "(meth) acrylic acid" means at least one selected from acrylic acid and methacrylic acid, and "(meth) acrylate" is at least one selected from acrylate and methacrylate.

As the nonionic hydrophilic monomer, 2-hydroxyethyl (meth) acrylate and 3-hydroxypropyl (meth) acrylate are preferable from the viewpoint of improving the dispersion stability of the pigment and improving the ejection reliability and bending resistance. Hydroxyalkyl (meth) acrylates such as, polyethylene glycol (n = 2 to 30, n indicates the average number of moles of oxyethylene groups added; hereinafter, n indicates the average number of moles of oxyalkylene groups added) (meth). ) Polyalkylene glycol (meth) acrylate such as acrylate; alkoxypolyalkylene glycol (meth) acrylate such as methoxypolyethylene glycol (n = 1-30) (meth) acrylate; phenoxy (ethylene glycol / propylene glycol copolymerization) (n = 1 to 30, ethylene glycol among them: n = 1-29) At least one selected from (meth) acrylate, more preferably alkoxypolyalkylene glycol (meth) acrylate, still more preferably methoxypolyethylene glycol (meth). It is an acrylate.

Specific examples of commercially available nonionic hydrophilic monomers include NK ester M-40G, 90G, 230G, etc. (these are trade names of Shin Nakamura Chemical Industry Co., Ltd.), Blemmer PE-90, and the same. Examples thereof include 200, 350, etc., Blemmer PME-100, 200, 400, etc., Blemmer 50 PEP-300, Blemmer 50 POEP-800B, etc. (these are trade names of NOF CORPORATION).

The (meth) acrylic resin used in the present invention is a hydrophobic monomer in addition to a constituent unit derived from a hydrophilic monomer from the viewpoint of improving the dispersion stability of the pigment and improving the discharge reliability and bending resistance. It preferably contains the building blocks of origin.
In the present invention, "hydrophobicity" means that when the monomer is dissolved in 100 g of ion-exchanged water at 25 ° C. until it is saturated, the amount of the monomer dissolved is less than 10 g. The amount of the hydrophobic monomer dissolved is preferably 5 g or less, more preferably 1 g or less, from the viewpoint of adsorptivity to the pigment.

The hydrophobic monomer is preferably at least one selected from (meth) acrylates having a hydrocarbon group derived from an aliphatic alcohol and an aromatic group-containing monomer.
The (meth) acrylate having a hydrocarbon group derived from an aliphatic alcohol preferably has a hydrocarbon group derived from an aliphatic alcohol having 1 or more and 22 or less carbon atoms. For example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, (Meta) acrylate having a linear alkyl group such as stearyl (meth) acrylate; isopropyl (meth) acrylate, isobutyl (meth) acrylate, tertiary butyl (meth) acrylate, isopentyl (meth) acrylate, isooctyl (meth) acrylate, (Meta) acrylate having a branched chain alkyl group such as isodecyl (meth) acrylate, isododecyl (meth) acrylate, isostearyl (meth) acrylate, 2-ethylhexyl (meth) acrylate; alicyclic alkyl such as cyclohexyl (meth) acrylate Examples thereof include (meth) acrylate having a group. Among these, those having an alkyl group having 1 or more and 10 or less carbon atoms are more preferable, and those having an alkyl group having 1 or more and 8 or less carbon atoms are more preferable.

The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group having 6 to 22 carbon atoms which may have a substituent containing a hetero atom, and more preferably a styrene-based monomer and an aromatic group-containing monomer. One or more selected from (meth) acrylates. The molecular weight of the aromatic group-containing monomer is preferably less than 500.
Examples of the styrene-based monomer include styrene, α-methylstyrene, 2-methylstyrene and the like, and examples of the aromatic group-containing (meth) acrylate include benzyl (meth) acrylate and phenoxyethyl (meth) acrylate. Among these, one or more selected from styrene, α-methylstyrene and benzyl (meth) acrylate are preferable.

The (meth) acrylic resin used in the present invention may contain a structural unit derived from a macromonomer as a hydrophobic monomer. The macromonomer is a compound having a polymerizable functional group at one end and having a number average molecular weight of 500 or more and 100,000 or less, and is used as a monomer component of a (meth) acrylic resin from the viewpoint of pigment dispersion stability. As the polymerizable functional group present at one end, an acryloyloxy group or a methacryloyloxy group is preferable, and a methacryloyloxy group is more preferable.
The number average molecular weight of the macromonomer is preferably 1,000 or more and 10,000 or less. The number average molecular weight is measured by gel permeation chromatography using chloroform containing 1 mmol / L dodecyldimethylamine as a solvent, using polystyrene as a standard substance.
As the macromonomer, from the viewpoint of dispersion stability of the pigment, an aromatic group-containing monomer-based macromonomer and a silicone-based macromonomer are preferable, and an aromatic group-containing monomer-based macromonomer is more preferable.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer include the aromatic group-containing monomer described in the above-mentioned hydrophobic monomer, and styrene and benzyl (meth) acrylate are preferable, and styrene is more preferable. ..
Specific examples of commercially available styrene-based macromonomers include AS-6 (S), AN-6 (S), HS-6 (S) (trade name of Toagosei Co., Ltd.) and the like.
Examples of the silicone-based macromonomer include organopolysiloxane having a polymerizable functional group at one end.

(Content of each component or constituent unit in monomer mixture or (meth) acrylic resin)
Content of hydrophilic monomer and hydrophobic monomer in the monomer mixture during production of (meth) acrylic resin (content as unneutralized amount; the same applies hereinafter) or derived from hydrophilic monomer in (meth) acrylic resin The contents of the constituent unit and the constituent unit derived from the hydrophobic monomer are as follows from the viewpoint of improving the dispersion stability of the pigment.
The content of the hydrophilic monomer component is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 25% by mass or more, and preferably 75% by mass or less, more preferably 60% by mass or less. , More preferably 50% by mass or less.
The content of the hydrophobic monomer component is preferably 25% by mass or more, more preferably 40% by mass or more, further preferably 50% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less. , More preferably 75% by mass or less.

The mass ratio of [hydrophilic monomer component / hydrophobic monomer component] is preferably 0.1 or more, more preferably 0.15 or more, still more preferably 0.25 or more, and preferably 3 or less, more preferably. Is 2 or less, more preferably 1 or less.

The (meth) acrylic resin preferably has an acid group from the viewpoint of discharge reliability and bending resistance, and more preferably at least a part of the acid group is neutralized with a neutralizing agent. As a result, the charge repulsive force generated after neutralization is increased, aggregation of pigment particles in the water-based pigment dispersion or water-based ink can be suppressed, thickening can be suppressed, and ejection reliability is considered to be improved. Further, a part of the (meth) acrylic resin is crosslinked with the cross-linking agent (C) to form a crosslinked structure, so that the (meth) acrylic resin is more strongly pigmented together with the polymer (B) contained as an emulsion. Adsorbed or immobilized on the surface. Therefore, the number of particles is small while a large amount of polymer is present in the system, and the obtained aqueous pigment dispersion maintains a low viscosity and contains a large amount of polymer, so that the resin film has flexibility as a printing medium. It is considered that the adhesion to the film is improved, and as a result, the ejection reliability and the bending resistance are improved. Examples of the acid group include the above-mentioned anionic group. ^{Among these, a carboxy group (-COOM 1} ) is preferable from the viewpoint of discharge reliability and bending resistance.

(Manufacturing of (meth) acrylic resin)
The (meth) acrylic resin is produced by copolymerizing the monomer mixture by a known polymerization method such as a massive polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. Among these polymerization methods, the solution polymerization method is preferable.
The solvent used in the solution polymerization method is not particularly limited, but a polar organic solvent is preferable. When the polar organic solvent is miscible with water, it can be mixed with water and used. Examples of the polar organic solvent include aliphatic alcohols having 1 to 3 carbon atoms, ketones having 3 to 5 carbon atoms, ethers, and esters such as ethyl acetate. Among these, methanol, ethanol, acetone, methyl ethyl ketone (MEK), or a mixed solvent of one or more of these and water is preferable, and methyl ethyl ketone or a mixed solvent of it and water is preferable.
At the time of polymerization, a polymerization initiator or a polymerization chain transfer agent can be used.
Examples of the polymerization initiator include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), t-butylperoxyoctate, benzoyl peroxide and the like. A known radical polymerization initiator such as the organic peroxide of Azobisisobutyria can be used. The amount of the radical polymerization initiator is preferably 0.001 mol or more and 5 mol or less, and more preferably 0.01 mol or more and 2 mol or less, per 1 mol of the monomer mixture.
Examples of the polymerization chain transfer agent include carboxy group-containing mercaptans such as mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, and mercaptosuccinic acid; butanethiol, octanethiol, decanethiol, dodecanethiol, hexadecanethiol, and octadecanethiol. Alkyl mercaptones such as 2-mercaptoethanol, hydroxy group-containing mercaptans such as 3-mercapto-1,2-propanediol; known chain transfer agents such as thiuram disulfides can be used.
Further, the mode of chaining the polymerization monomers is not limited, and any polymerization mode such as random, block, and graft may be used.

Preferred polymerization conditions vary depending on the type of polymerization initiator, monomer, solvent and the like used, but usually the polymerization temperature is preferably 30 ° C. or higher, more preferably 50 ° C. or higher, and preferably 95 ° C. or lower. More preferably, it is 80 ° C. or lower. The polymerization time is preferably 1 hour or more, more preferably 2 hours or more, and preferably 20 hours or less, more preferably 10 hours or less. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, the produced polymer can be isolated from the reaction solution by a known method such as reprecipitation and solvent distillation. Further, the obtained polymer can be purified by removing unreacted monomers and the like by reprecipitation, membrane separation, chromatographic method, extraction method and the like.

The acid value of the (meth) acrylic resin used in the present invention is preferably 50 mgKOH / g or more, more preferably 70 mgKOH / g or more, still more preferably 100 mgKOH / g or more, from the viewpoint of discharge reliability and bending resistance. It is even more preferably 130 mgKOH / g or more, and preferably 300 mgKOH / g or less, more preferably 270 mgKOH / g or less, still more preferably 250 mgKOH / g or less. When the acid value is in the above range, the amount of the acid group and its neutralized acid group is sufficient, and the dispersion stability of the pigment is ensured. It is also preferable from the viewpoint of the balance between the affinity between the polymer dispersant (a) and the aqueous medium and the interaction between the polymer dispersant (a) and the pigment.
The acid value of the (meth) acrylic resin can be calculated from the mass ratio of the constituent monomers. It can also be obtained by a method of dissolving or swelling a (meth) acrylic resin in a suitable organic solvent (for example, MEK) and titrating it.

From the viewpoint of bending resistance, the number average molecular weight of the (meth) acrylic resin is preferably 300 or more, more preferably 500 or more, still more preferably 1,000 or more, still more preferably 3,000 or more, and From the viewpoint of dispersion stability of the pigment, it is preferably 10,000 or less, more preferably 7,000 or less, and further preferably 5,000 or less. When the number average molecular weight of the (meth) acrylic resin is within the above range, the adsorptive power to the pigment is sufficient and dispersion stability can be exhibited. The number average molecular weight can be measured by the method described in Examples.

[Polyester resin]
The polyester resin used in the present invention contains a structural unit derived from an alcohol component and a structural unit derived from a carboxylic acid component, and can be obtained by polycondensing the alcohol component and the carboxylic acid component.

(Alcohol component)
The alcohol component, which is the raw material monomer of the polyester resin, preferably contains an aromatic diol from the viewpoint of improving the dispersion stability of the pigment and improving the discharge reliability and bending resistance. As the aromatic diol, an alkylene oxide adduct of bisphenol A is preferable. The alkylene oxide adduct of bisphenol A means the entire structure in which an oxyalkylene group is added to 2,2-bis (4-hydroxyphenyl) propane.
The alkylene oxide adduct of bisphenol A is preferably a compound represented by the following general formula (I).

In the general formula (I), both OR ¹ and R ² O are oxyalkylene groups, preferably oxyalkylene groups having 1 or more and 4 or less carbon atoms independently, and more preferably oxyethylene groups or oxypropylene. It is a group.
x and y correspond to the number of moles of alkylene oxide added. Further, from the viewpoint of reactivity with the carboxylic acid component, the average value of the sum of x and y is preferably 2 or more, and preferably 7 or less, more preferably 5 or less, still more preferably 3 or less. ..
Further, x OR ¹ and y R ² O may be the same or different from each other, but they are the same from the viewpoint of improving the adhesion to the printing medium and improving the bending resistance. It is preferable to have. The alkylene oxide adduct of bisphenol A may be used alone or in combination of two or more. The alkylene oxide adduct of bisphenol A is preferably a propylene oxide adduct of bisphenol A and an ethylene oxide adduct of bisphenol A, and more preferably a propylene oxide adduct of bisphenol A.
The content of the alkylene oxide adduct of bisphenol A in the alcohol component is preferably 50 mol% or more, more preferably 60 mol, from the viewpoint of improving the dispersion stability of the pigment and improving the discharge reliability and bending resistance. % Or more, more preferably 70 mol% or more, and the upper limit thereof is preferably 100 mol% or less.

The alcohol component, which is the raw material monomer of the polyester resin, may contain the following other alcohol components in addition to the alkylene oxide adduct of bisphenol A. For example, ethylene glycol, propylene glycol (1,2-propanediol), glycerin, pentaerythritol, trimethylolpropane, hydrogenated bisphenol A, sorbitol, or their alkylene (2 to 4 carbon atoms) oxide adduct (average addition). The number of moles is 1 or more and 16 or less). The other alcohol components may be used alone or in combination of two or more.

(Carboxylic acid component)
The carboxylic acid component which is a raw material monomer of the polyester resin includes carboxylic acids, anhydrides of those acids, and alkyl (carbon atoms 1 to 3) esters thereof.
As the carboxylic acid component, an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, an alicyclic dicarboxylic acid and a polyvalent carboxylic acid having a trivalent or higher valence are preferable, from the viewpoint of discharge reliability and bending resistance, and reactivity with an alcohol component. From the viewpoint of the above, aromatic dicarboxylic acids and aliphatic dicarboxylic acids are more preferable, and aliphatic dicarboxylic acids are even more preferable.
As the aromatic dicarboxylic acid, phthalic acid, isophthalic acid, and terephthalic acid are preferable, and terephthalic acid is more preferable.
Examples of the aliphatic dicarboxylic acid include unsaturated aliphatic dicarboxylic acid and saturated aliphatic dicarboxylic acid, and as the unsaturated aliphatic dicarboxylic acid, fumaric acid and maleic acid are preferable, and fumaric acid is more preferable. As the saturated aliphatic dicarboxylic acid, adipic acid and succinic acid are preferable.
The alicyclic dicarboxylic acid is preferably cyclohexanedicarboxylic acid, decalindicarboxylic acid, or tetrahydrophthalic acid, and the trivalent or higher polyvalent carboxylic acid is preferably trimellitic acid or pyromellitic acid.
Among these, an aliphatic dicarboxylic acid is preferable, an unsaturated aliphatic dicarboxylic acid is more preferable, and fumaric acid is more preferable.
The carboxylic acid component can be used alone or in combination of two or more.

(Manufacturing of polyester resin)
The polyester resin can be obtained by polycondensing the alcohol component and the carboxylic acid component in an appropriate combination. For example, it can be produced by polycondensing the alcohol component and the carboxylic acid component in an inert gas atmosphere at a temperature of 150 ° C. or higher and 250 ° C. or lower, if necessary, using an esterification catalyst. ..
Examples of the esterification catalyst include a tin catalyst, a titanium catalyst, an antimony trioxide, zinc acetate, a metal compound such as germanium dioxide, and the like. A tin catalyst is preferable from the viewpoint of the reaction efficiency of the esterification reaction in the synthesis of polyester. As the tin catalyst, dibutyltin oxide, tin (II) di (2-ethylhexane), salts thereof and the like are preferably used, and tin (2-ethylhexane) acid (II) is more preferably used. If necessary, an esterification co-catalyst such as 3,4,5-trihydroxybenzoic acid (gallic acid) may be further used.
Further, a radical polymerization inhibitor such as 4-t-butylcatechol or hydroquinone may be used in combination.

The polyester resin preferably has an acid group from the viewpoint of discharge reliability and bending resistance. As a result, it is considered that the same effect as when the above-mentioned (meth) acrylic resin has an acid group can be obtained. The acid value of the polyester resin is preferably 5 mgKOH / g or more, more preferably 15 mgKOH / g or more, and preferably 40 mgKOH / g or less, more preferably 30 mgKOH / g, from the viewpoint of discharge reliability and bending resistance. It is g or less, more preferably 25 mgKOH / g or less.
The number average molecular weight (Mn) of the polyester resin is preferably 1,000 or more, more preferably 2,000 or more, still more preferably 3,000 or more, and the dispersion stability of the pigment, from the viewpoint of bending resistance. From the viewpoint of the above, it is preferably 10,000 or less, more preferably 7,000 or less, and further preferably 5,000 or less.
The acid value and the number average molecular weight (Mn) can all be obtained as desired by appropriately adjusting the type of monomer used, the compounding ratio, the temperature of polycondensation, and the reaction time.

[Production of aqueous pigment dispersion (A)]
When the polymer dispersant (a) is used, as a method for producing the pigment aqueous dispersion (A), the pigment is mechanically dispersed with the polymer dispersant (a) from the viewpoint of discharge reliability and bending resistance. preferable.

As a method of mechanically dispersing the pigment with the polymer dispersant (a), a method of dispersing the pigment mixture containing the pigment, the polymer dispersant (a), and the aqueous medium is preferable, and the following steps 1-1 and 1-2 are preferable. The method having is more preferable.
Step 1-1: A step of dispersing a pigment mixture containing a pigment, a polymer dispersant (a), an organic solvent, and water to obtain a dispersion. Step 1-2: Organic from the dispersion obtained in Step 1-1. Step of removing solvent to obtain pigment aqueous dispersion (A)

(Step 1-1)
In the pigment mixture in step 1-1, the polymer dispersant (a) is dissolved in an organic solvent, and then the pigment, water, and if necessary, a neutralizing agent, a surfactant, etc. are added to the obtained organic solvent solution. Method (i) of additionally mixing to obtain an oil-in-water type dispersion liquid; a pigment and water are added to an emulsion solution obtained by adding an organic solvent to the emulsion of the polymer dispersant (a) to obtain an oil-in-water type dispersion liquid. It is preferably obtained by the method (ii) of obtaining. In the method (i), the order in which the polymer dispersant (a) is added to the organic solvent solution is not limited, but it is preferable to add water, a neutralizer, and a pigment in this order.

The organic solvent used in step 1-1 is not limited, but ketones, ethers, esters, aliphatic alcohols having 1 to 3 carbon atoms and the like are preferable, and the wettability to the pigment and the polymer dispersant (a) are used. From the viewpoint of improving the solubility and the adsorptivity of the polymer dispersant (a) to the pigment, a ketone having 4 or more and 8 or less carbon atoms is more preferable, a methyl ethyl ketone and a methyl isobutyl ketone are more preferable, and a methyl ethyl ketone is even more preferable. When a (meth) acrylic resin or polyester resin is synthesized as the polymer dispersant (a) by a solution polymerization method, the solvent used in the polymerization may be used as it is.
The mass ratio of the organic solvent to the polymer dispersant (a) in the pigment mixture [organic solvent / polymer dispersant (a)] is preferably from the viewpoint of wettability to the pigment and solubility of the polymer dispersant (a). It is 0.3 or more, more preferably 0.7 or more, still more preferably 0.9 or more, and preferably 2 or less, more preferably from the viewpoint of improving the adsorptivity of the polymer dispersant (a) to the pigment. Is 1.5 or less, more preferably 1.3 or less.

When the polymer dispersant (a) has an acid group, at least a part of the acid group is preferably neutralized with a neutralizing agent from the viewpoint of discharge reliability and bending resistance. When neutralizing, it is preferable to neutralize so that the pH is 7 or more and 11 or less.
Examples of the neutralizing agent include bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, and various amines, and sodium hydroxide is preferable. Further, the polymer dispersant (a) may be neutralized in advance.
The equivalent amount of the neutralizing agent used is preferably 10 mol% or more, more preferably 30 mol% or more, and preferably 80 mol% or less, more preferably 70 mol, from the viewpoint of discharge reliability and bending resistance. % Or less, more preferably 60 mol% or less.
Here, the equivalent amount of the neutralizing agent used can be calculated by the following formula.
Equivalent to use of neutralizer (mol%) = [{Mass of neutralizer added (g) / Equivalent of neutralizer} / [{Acid value of polymer dispersant (a) (mgKOH / g) x Polymer dispersant (A) mass (g)} / (56 x 1,000)]] x 100

The emulsion of the polymer dispersant (a) used in the method (ii) may contain a dispersant such as a surfactant, if necessary. As the emulsion, an appropriately synthesized one may be used, or a commercially available product may be used.
Examples of commercially available (meth) acrylic resin emulsions include acrylics such as "John Krill 390", "John Krill 7100", "John Krill 734", and "John Krill 538" (all manufactured by BASF Japan Ltd.). Examples thereof include resins and dispersions of vinyl chloride-acrylic resins such as "Viniblanc 701" (manufactured by Nisshin Chemical Industry Co., Ltd.).
Examples of commercially available polyester resin emulsions include "New Track 2010" (manufactured by Kao Corporation), "Elitel KA series", and "Elitel KT series" (manufactured by Unitika Ltd.).

(Manufacture of (meth) acrylic resin emulsion)
When a (meth) acrylic resin is used as the polymer dispersant (a), the (meth) acrylic resin emulsion heats a mixture containing the (meth) acrylic resin, water and, if necessary, a neutralizing agent. A method of stirring while stirring and then lowering the temperature; a mixture containing a (meth) acrylic resin, an organic solvent, a neutralizing agent, and water is dispersed to obtain a dispersion liquid, and then the organic solvent is removed from the dispersion liquid. It can be manufactured by a method such as Above all, from the viewpoint of workability, a method of stirring a mixture containing a (meth) acrylic resin, water, and a neutralizing agent if necessary while heating the mixture, and then lowering the temperature is preferable.
The temperature at which the mixture is stirred is preferably 60 ° C. or higher, more preferably 70 ° C. or higher, further preferably 80 ° C. or higher, and preferably 100 ° C. or lower, more preferably 95 ° C. or lower. The stirring time is preferably 0.5 hours or more, more preferably 0.8 hours or more, and preferably 30 hours or less, more preferably 10 hours or less, still more preferably 5 hours or less.

Examples of the neutralizing agent used for producing the (meth) acrylic resin emulsion include the base used in the above-mentioned method (i), and sodium hydroxide is preferable. The equivalent amount (mol%) of the neutralizing agent used is preferably 10 mol% or more, more preferably 20 mol% or more, and further, from the viewpoint of dispersion stability of the (meth) acrylic resin emulsion and dispersion stability of the pigment. It is preferably 30 mol% or more, and from the same viewpoint as described above, it is preferably 90 mol% or less, more preferably 80 mol% or less, still more preferably 70 mol% or less. The equivalent amount of the neutralizing agent used can be determined by the same method as described above.

(Manufacturing of polyester resin emulsion)
Examples of the polyester resin emulsion include a method of adding a polyester resin to an aqueous medium and performing a dispersion treatment by a disperser or the like, a method of gradually adding an aqueous medium to the polyester resin and emulsifying the phase inversion. Above all, the method by phase inversion emulsification is preferable from the viewpoint of discharge stability and bending resistance. Examples of the phase inversion emulsification method include the methods described in JP-A-2016-222896. First, the polyester resin is dissolved in an organic solvent, then an aqueous medium is added to this solution to invert the phase, and then the phase is inverted. A method of removing the organic solvent is preferable.

In the dispersion treatment in step 1-1, the pigment particles can be atomized to a desired particle size only by the main dispersion due to shear stress, but the pigment mixture is pre-dispersed from the viewpoint of obtaining a uniform pigment aqueous dispersion. After that, it is preferable to further disperse the particles.
As the disperser used for the pre-dispersion, a commonly used mixing and stirring device such as an anchor blade and a disperser blade can be used.

Examples of the means for applying the shear stress used for this dispersion include a kneader such as a roll mill and a kneader, a high-pressure homogenizer such as a microfluidizer, and a media type disperser such as a paint shaker and a bead mill. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment.
When the dispersion treatment is performed using a high-pressure homogenizer, the pigment can be controlled to have a desired particle size by controlling the treatment pressure and the number of passes, and the cumulant average particle size of the pigment aqueous dispersion (A) described later can be controlled. Can also be adjusted.
From the viewpoint of productivity and economy, the treatment pressure is preferably 60 MPa or more, more preferably 100 MPa or more, further preferably 150 MPa or more, and preferably 300 MPa or less, more preferably 250 MPa or less.
The number of passes is preferably 3 or more, more preferably 7 or more from the viewpoint of reducing the particle size of the pigment, and preferably 30 or less, more preferably 20 or less from the viewpoint of dispersion stability of the pigment. Is.

(Step 1-2)
Step 1-2 is a step of removing the organic solvent from the dispersion obtained in Step 1-1 to obtain the pigment aqueous dispersion (A). The removal of the organic solvent can be carried out by a known method. It is preferable that the organic solvent in the obtained aqueous pigment dispersion (A) is substantially removed, but it may remain as long as the object of the present invention is not impaired. The amount of the residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.
Further, for the purpose of removing coarse particles and the like, the aqueous dispersion from which the organic solvent has been removed is further centrifuged, the liquid layer portion is filtered with a filter or the like, and the aqueous dispersion passing through the filter or the like is filtered. It is preferably obtained as the aqueous pigment dispersion (A).

The non-volatile component concentration (solid content concentration) of the aqueous pigment dispersion (A) is preferably 10% by mass or more from the viewpoint of improving the dispersion stability of the aqueous pigment dispersion and facilitating the production of the aqueous pigment dispersion. , More preferably 15% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less. The solid content concentration of the aqueous pigment dispersion (A) is measured by the method described in Examples.
From the viewpoint of dispersion stability, the content of the pigment in the aqueous pigment dispersion (A) is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably. Is 40% by mass or less, more preferably 30% by mass or less, still more preferably 25% by mass or less.
When the pigment aqueous dispersion (A) is an aqueous dispersion in which the pigment is dispersed with the polymer dispersant (a), the mass ratio of the pigment to the polymer dispersant (a) in the pigment aqueous dispersion (A) [pigment] / Polymer dispersant (a)] is preferably 50/50 or more, more preferably 60/40 or more, still more preferably 70/30 or more, and preferably 95/5 or less, more preferably 90/10. Hereinafter, it is more preferably 85/15 or less.
The average particle size of the cumulant of the aqueous pigment dispersion (A) is preferably 40 nm or more, more preferably 50 nm or more, still more preferably 60 nm or more, still more preferably 70 nm or more, from the viewpoint of discharge reliability and bending resistance. It is more preferably 80 nm or more, and preferably 200 nm or less, more preferably 150 nm or less, still more preferably 130 nm or less, still more preferably 110 nm or less, still more preferably 100 nm or less. The average particle size can be measured by the method described in Examples.

<Polymer (B) emulsion>
The polymer (B) emulsion used in the present invention is an aqueous dispersion of pigment-free polymer (B) particles. Examples of the polymer (B) include condensation polymers such as polyurethane and polyester; (meth) acrylic resin, styrene resin, styrene- (meth) acrylic resin, butadiene resin, styrene-butadiene resin, vinyl chloride resin. , Vinyl-based polymers such as vinyl acetate-based resin and acrylic silicone-based resin.
As the emulsion of the polymer (B), an emulsion synthesized as appropriate may be used, or a commercially available product may be used. When the polymer (B) is a (meth) acrylic resin or polyester resin, the above-mentioned (meth) acrylic resin emulsion or polyester resin emulsion may be used.
Commercially available products of the polymer (B) emulsion include, for example, "NeoCryl A-1127" (manufactured by DSM Coating Resins, anionic self-crosslinked water-based acrylic resin), "John Krill 390", "John Krill 7100", and "John". Acrylic resins such as "Krill 7600", "John Krill 537J", "John Krill PDX-7164", "John Krill 538J", "John Krill 780" (manufactured by BASF Japan Co., Ltd.), "WBR-2018""WBR-2000U" (Manufactured by Taisei Fine Chemical Co., Ltd.), styrene-butadiene resin such as "SR-100" and "SR102" (manufactured by Nippon A & L Co., Ltd.), and "Viniblanc 700" and "Viniblanc 701" (Japan) Disperses such as vinyl chloride resins (manufactured by Shinkagaku Kogyo Co., Ltd.), "New Track 2010" (manufactured by Kao Co., Ltd.), "Elitel KA series", "Elitel KT series" (manufactured by Unitika Co., Ltd.) Can be mentioned.
The cumulant average particle size of the emulsion of the polymer (B) is preferably 20 nm or more, more preferably 30 nm or more, still more preferably 40 nm or more, from the viewpoint of reducing coarse particles and improving discharge reliability and bending resistance. It is more preferably 50 nm or more, and preferably 150 nm or less, more preferably 120 nm or less, still more preferably 110 nm or less. The average particle size is measured by the method described in Examples.

<Crosslinking agent (C)>
The cross-linking agent (C) used in the present invention has a water content (mass ratio) of the cross-linking agent (C) from the viewpoint of efficiently performing a cross-linking reaction in an aqueous medium, and from the viewpoint of discharge reliability and bending resistance. It is preferably 50% or less, more preferably 40% or less, still more preferably 35% or less. Here, the water content% (mass ratio) means the dissolution rate (%) when 10 parts by mass of the cross-linking agent (C) is dissolved in 90 parts by mass of water at room temperature of 25 ° C.

The cross-linking agent (C) is preferably a compound having two or more epoxy groups in the molecule, more preferably a compound having a glycidyl ether group, and further preferably a polyhydric alcohol having a hydrocarbon group having 3 or more and 8 or less carbon atoms. Polyglycidyl ether compound.
The molecular weight of the cross-linking agent (C) is preferably 120 or more, more preferably 150 or more, still more preferably 200 or more, and preferably 2000 or less from the viewpoint of reaction easiness, discharge reliability and bending resistance. , More preferably 1500 or less, still more preferably 1000 or less.
The epoxy equivalent of the cross-linking agent (C) is preferably 90 or more, more preferably 100 or more, still more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, still more preferably 150 or less.
The number of epoxy groups in the cross-linking agent (C) is 2 or more per molecule, and preferably 6 or less per molecule, from the viewpoint of efficiently cross-linking and improving discharge reliability and bending resistance. From the viewpoint of availability, it is more preferably 4 or less.

Specific examples of the cross-linking agent (C) include polypropylene glycol diglycidyl ether (water content 31%), glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether (water content 27%), and sorbitol polyglycidyl. Ether, pentaerythritol polyglycidyl ether (water content 0%), resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, hydrogenated bisphenol A type diglycidyl ether and other polyglycidyl ethers, etc. Can be mentioned. Among these, one or more selected from trimethylolpropane polyglycidyl ether and pentaerythritol polyglycidyl ether are preferable.

(Heat treatment process)
The mixture according to the present invention is obtained by mixing an aqueous pigment dispersion (A), an emulsion of a polymer (B), and a cross-linking agent (C). The mixing method of each component is not particularly limited, but it is preferable to mix using a stirring device having a stirring unit. Examples of the stirring unit include a stirring blade having one or more stirring blades on the shaft, a single-screw or two-screw or more screw, a stirrer containing a magnetically rotatable metal, and the like.

The content of each component in the mixture is as follows from the viewpoint of discharge reliability and bending resistance.
The content of the pigment in the mixture is preferably 3% by mass or more, more preferably 5% by mass or more, further preferably 7% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass. It is as follows.
The content of the aqueous pigment dispersion (A) in the mixture is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 7% by mass or more, and preferably 50% by mass or more as a solid content. It is mass% or less, more preferably 40 mass% or less, still more preferably 30 mass% or less.
The content of the emulsion of the polymer (B) in the mixture is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 7% by mass or more, and preferably 30% by mass as a solid content. % Or less, more preferably 20% by mass or less.
The amount of the cross-linking agent (C) used is preferably 10% or more, as a cross-linking ratio represented by the ratio of the molar equivalents of the cross-linking functional groups of the cross-linking agent (C) to the molar equivalents of the acid groups of the polymer. It is preferably 20% or more, more preferably 30% or more, and preferably 60% or less, more preferably 50% or less.
The mixture may contain an organic solvent, but from the viewpoint of discharge reliability and bending resistance, the content of the organic solvent in the mixture is preferably 10% by mass or less, more preferably 7% by mass or less. It is more preferably 5% by mass or less, still more preferably 3% by mass or less, and even more preferably less than 1% by mass.

In the present invention, when an aqueous dispersion in which the pigment is dispersed with the polymer dispersant (a) is used as the pigment aqueous dispersion (A), the polymer dispersant (a) and the polymer (B) may be the same. Although they may be different, they are preferably the same from the viewpoint of discharge reliability and bending resistance, and the polymer dispersant (a) and the polymer (B) are both (meth) acrylic resins or polyesters. It is more preferably a resin.

In the present invention, the heat treatment is performed in the range of 45 ° C. or higher and 100 or lower. As a result, the emulsion of the aqueous pigment dispersion (A) and the polymer (B) is composited, and an aqueous pigment dispersion (I) in which a crosslinked structure is further introduced into the polymer is obtained.
The temperature of the heat treatment is preferably 50 ° C. or higher, more preferably 60 ° C. or higher, still more preferably 70 ° C. or higher, still more preferably 80 ° C. or higher, from the viewpoint of promoting the crosslinking reaction and improving discharge reliability and bending resistance. ° C. and above, and preferably 95 ° C. and below.
The heat treatment time is preferably 0.5 hours or more, more preferably 1 hour or more, further preferably 1.5 hours or more, and preferably 12 hours or less, from the viewpoint of completion of the crosslinking reaction and economic efficiency. It is more preferably 10 hours or less, still more preferably 8 hours or less, still more preferably 5 hours or less, still more preferably 3 hours or less.

The aqueous pigment dispersion (I) obtained by the production method of the present invention may contain 1% by mass or more and 10% by mass or less of glycerin, triethylene glycol or the like as a moisturizer to prevent drying, or may contain antifungal agents. Additives such as agents may be included. The additive may be blended in the pigment aqueous dispersion (A) or may be blended after the heat treatment.

The mass ratio of the pigment (pigment / total polymer amount) to the total amount of the polymer in the aqueous pigment dispersion (I) according to the present invention is 0.48 or more, preferably 0.48 or more, from the viewpoint of discharge reliability and bending resistance. 0.5 or more, more preferably 0.6 or more, still more preferably 0.7 or more, even more preferably 0.8 or more, and 2.15 or less, preferably 2.0 or less, more preferably. Is 1.5 or less, more preferably 1.3 or less, still more preferably 1.1 or less, still more preferably 1.0 or less, still more preferably 0.95 or less.
In the present invention, the total amount of the polymer means the total amount of the polymer contained in the aqueous pigment dispersion (I). In the heat treatment, the cross-linking agent (C) is included in the total amount of the polymer because it forms a part of the polymer skeleton in the aqueous pigment dispersion (I) by the cross-linking reaction. For example, when an aqueous dispersion in which the pigment is dispersed with the polymer dispersant (a) is used as the pigment aqueous dispersion (A), the total amount of the polymer is crosslinked with the polymer dispersant (a) and the polymer (B). It is the total amount of the agent (C). When an aqueous dispersion of a self-dispersing pigment is used as the aqueous pigment dispersion (A), the total amount of the polymer is the total amount of the polymer (B) and the cross-linking agent (C).

The non-volatile component concentration (solid content concentration) of the aqueous pigment dispersion (I) is preferably 10% by mass or more, more preferably from the viewpoint of improving the dispersion stability of the dispersion and facilitating the preparation of the aqueous ink. Is 15% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less. The solid content concentration is measured by the method described in Examples.
The average cumulant particle size of the aqueous pigment dispersion (I) is preferably 50 nm or more, more preferably 60 nm or more, still more preferably 70 nm or more, from the viewpoint of reducing coarse particles and improving discharge reliability and bending resistance. Yes, and it is preferably 200 nm or less, more preferably 160 nm or less, still more preferably 140 nm or less, still more preferably 120 nm or less. The average particle size is measured by the method described in Examples.
Further, the cumulant average particle size of the water-based ink is the same as that of the water-based pigment dispersion (I), and the preferred aspect of the average particle size is the same as the preferred aspect of the cumulant average particle size of the water-based pigment dispersion (I). Is.

In the present invention, the cumulant average particle size ratio of the aqueous pigment dispersion (I) to the aqueous pigment dispersion (A) [aqueous pigment dispersion (I) / pigment aqueous dispersion (A)] has discharge reliability and bending resistance. From the viewpoint of sex, it is preferably 0.8 or more, more preferably 0.9 or more, still more preferably 0.95 or more, and preferably 1.5 or less, more preferably 1.4 or less, still more preferably. It is 1.3 or less, more preferably 1.2 or less, and even more preferably 1.1 or less.

The aqueous pigment dispersion (I) of the present invention is an aqueous dispersion in which the pigment aqueous dispersion (A) is dispersed with a polymer dispersant (a) from the viewpoint of discharge reliability and bending resistance, and is a polymer. It is more preferable that both the dispersant (a) and the polymer (B) have an acid group, and a part of the acid group is crosslinked with the cross-linking agent (C). As a result, a part of the acid groups of the polymer dispersant (a) and the polymer (B) is crosslinked with the cross-linking agent (C), and the polymer dispersant (a) between the chains, the polymer (B) between the chains, and the polymer dispersant ( It is considered that a crosslinked structure is formed between the a) chain and the polymer (B) chain via the crosslinking agent (C). Therefore, the number of particles is small while a large amount of polymer is present in the system, and the obtained aqueous pigment dispersion maintains a low viscosity and contains a large amount of polymer, so that the resin film has flexibility as a printing medium. It is considered that the adhesion to the film is improved, and as a result, the ejection reliability and the bending resistance are improved.

[Water-based ink]
The water-based pigment dispersion (I) obtained by the production method of the present invention is preferably used for water-based ink (hereinafter, also referred to as "water-based ink" or "ink"). As a result, the ejection reliability and bending resistance of the water-based ink can be improved. The water-based pigment dispersion (I) can be used as it is as a water-based ink, but from the viewpoint of improving the storage stability of the water-based ink, the water-based ink includes the water-based pigment dispersion (I) and the water-soluble organic solvent (I). II) is preferably contained.

<Water-soluble organic solvent (II)>
The water-soluble organic solvent (II) may be a liquid or a solid at room temperature (25 ° C.). The water-soluble organic solvent (II) refers to an organic solvent having a dissolution amount of 10 ml or more when the organic solvent is dissolved in 100 ml of water at 25 ° C.
The water-soluble organic solvent (II) preferably contains at least one organic solvent having a boiling point of 90 ° C. or higher. The weighted average value of the boiling points of the water-soluble organic solvent (II) is preferably 150 ° C. or higher, more preferably 180 ° C. or higher, and preferably 240 ° C. or lower, more preferably 220 ° C. or lower, still more preferably 200 ° C. or higher. It is as follows.
Examples of the water-soluble organic solvent (II) include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers are preferable, and ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, trimethylolpropane and diethylene glycol diethyl ether are selected. One or more is more preferable, and propylene glycol is further preferable.

The ink of the present invention can be obtained by mixing an aqueous pigment dispersion (I) and a water-soluble organic solvent (II), and if necessary, a moisturizing agent, a wetting agent, and a penetrating agent usually used for an aqueous ink. Various additives such as agents, surfactants, viscosity modifiers, defoamers, preservatives, antifungal agents, and rust preventives can be added, and further filtration treatment with a filter or the like can be performed.
The content of each component of the water-based ink and the physical characteristics of the ink are as follows.

(Pigment content)
From the viewpoint of print density, the content of the pigment in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, and the ink viscosity at the time of solvent volatilization. From the viewpoint of lowering the pressure and improving the discharge reliability, it is preferably 15% by mass or less, more preferably 10% by mass or less, and further preferably 7% by mass or less.
(Total content of pigment and polymer dispersant)
The total content of the pigment and the polymer in the water-based ink is preferably 2% by mass or more, more preferably 2.5% by mass or more, still more preferably 3% by mass or more, still more preferably 3% by mass or more, from the viewpoint of bending resistance. From the viewpoint of 3.5% by mass or more, lowering the ink viscosity at the time of solvent volatilization, and improving ejection reliability, it is preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass. % Or less, more preferably 15% by mass or less, still more preferably 12% by mass or less.
(Content of water-soluble organic solvent (II))
The content of the water-soluble organic solvent (II) in the water-based ink is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 7% by mass or more, and from the viewpoint of ejection reliability. From the viewpoint of bending resistance, it is preferably 50% by mass or less, more preferably 45% by mass or less, and further preferably 40% by mass or less.
(Water content)
The content of water in the water-based ink is preferably 30% by mass or more, more preferably 40% by mass or more, further preferably 50% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass. It is as follows.

The mass ratio of the pigment in the total solid content of the water-based ink [pigment / (total solid content of the water-based ink)] is preferably 0.25 or more, more preferably 0.3, from the viewpoint of ejection stability and bending resistance. The above is more preferably 0.35 or more, still more preferably 0.4 or more, and preferably 0.75 or less, more preferably 0.7 or less, still more preferably 0.6 or less.

(Physical characteristics of water-based ink)
The viscosity of the water-based ink at 32 ° C. is preferably 2 mPa · s or more, more preferably 3 mPa · s or more, still more preferably 5 mPa · s or more, and preferably 12 mPa · s or more from the viewpoint of improving the storage stability of the ink. -S or less, more preferably 9 mPa · s or less, still more preferably 7 mPa · s or less.
The viscosity of the water-based ink can be measured using an E-type viscometer.
The pH of the water-based ink is preferably 7.0 or more, more preferably 7.2 or more, still more preferably 7.5 or more, from the viewpoint of improving the storage stability of the ink. Further, from the viewpoint of member resistance and skin irritation, the pH is preferably 11 or less, more preferably 10 or less, still more preferably 9.5 or less.
The pH of the water-based ink can be measured by a conventional method.

The water-based ink can be suitably used for flexographic printing ink, gravure printing ink, or inkjet ink, and is particularly preferably used for inkjet ink. It can be loaded into a known inkjet recording device and ejected as ink droplets onto a printing medium to record an image or the like.
The inkjet recording apparatus includes a thermal type and a piezo type, but it is more preferable to use it as a piezo type water-based ink for inkjet recording.
Examples of the printing medium that can be used include high water absorption plain paper, low water absorption coated paper, and non-water absorption resin film. Examples of the coated paper include general-purpose glossy paper and multicolor foam gloss paper. The resin film is preferably at least one selected from a polyester film, a polyvinyl chloride film, a polypropylene film, and a polyethylene film. As the resin film, a corona-treated base material may be used.
Commonly available resin films include, for example, Lumirer T60 (manufactured by Toray Co., Ltd., polyester), PVC80BP (manufactured by Lintec Co., Ltd., vinyl chloride), DGS-210WH (manufactured by Roland DG Co., Ltd., vinyl chloride), and transparent. PVC RE-137 (Mimaki Engineering Co., Ltd., vinyl chloride), Kinus KEE70CA (Lintech Co., Ltd., polyethylene), YUPO SG90 PAT1 (Lintech Co., Ltd., polypropylene), FOR, FOA (all manufactured by Futamura Chemical Co., Ltd., Polypropylene), Bonnir RX (manufactured by Kojin Film & Chemicals Co., Ltd., nylon), emblem ONBC (manufactured by Unitika Co., Ltd., nylon) and the like.

In the following synthetic examples, preparation examples, examples and comparative examples, "%" is "mass%" unless otherwise specified.

(1) Measurement of number average molecular weight of polymer Gel chromatography method using a solution prepared by dissolving phosphoric acid and lithium bromide in N, N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively, as an eluent. [GPC device (HLC-8320GPC) manufactured by Tosoh Corporation, column (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel SuperAW-H) manufactured by Tosoh Corporation, flow velocity: 0.5 mL / min], the molecular weight is known as a standard substance. Monodisperse polystyrene kit [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A) -500), manufactured by Tosoh Corporation].
For the measurement sample, 0.1 g of resin was mixed with 10 mL of the eluent in a glass vial, stirred at 25 ° C. for 10 hours with a magnetic stirrer, and a syringe filter (DISMIC-13HP PTFE 0.2 μm, manufactured by Advantech Co., Ltd.). The one filtered with was used.

(2) Measurement of average cumulant particle size of polymer emulsion, pigment aqueous dispersion (A) and aqueous pigment dispersion (I) Cumulant analysis using laser particle analysis system "ELSZ-2000ZS" (manufactured by Otsuka Electronics Co., Ltd.) The cumulant average particle size was measured. The measurement conditions were a temperature of 25 ° C., an angle of 90 ° between the incident light and the detector, and 100 times of integration, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measured concentration was 5 × 10 ^-3 % (converted to solid content concentration).

(3) Measurement of solid content concentration of polymer emulsion, pigment aqueous dispersion (A) and aqueous pigment dispersion (I) Sulfate homogenized in a desiccator in a 30 ml polypropylene container (φ = 40 mm, height = 30 mm). Weigh 10.0 g of sodium, add about 1.0 g of sample to it, mix, weigh accurately, maintain at 105 ° C for 2 hours to remove volatiles, and further room temperature (25 ° C). ) Was left in the desiccator for another 15 minutes, and then the mass was measured. The mass of the sample after removing the volatile matter was taken as the solid content and divided by the mass of the added sample to obtain the solid content concentration.

<Synthesis of (meth) acrylic resin>
Synthesis Example 1-1
Acrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., reagent) 30 g, styrene (manufactured by Wako Pure Chemical Industries, Ltd., reagent) 65 g, α-methylstyrene (manufactured by Wako Pure Chemical Industries, Ltd., reagent) in a 500 mL polyethylene beaker, 5 g of reagent), 100 g of methyl ethyl ketone (hereinafter, also referred to as "MEK"), azo radical polymerization initiator (manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65, 2,2'-azobis (2,4-dimethyl) Valeronitrile)) 1.2 g and 2-mercaptopropionic acid (polymerization chain transfer agent) 0.5 g were added and mixed well to prepare a monomer mixture. 10% of this monomer mixture was placed in a 500 mL three-necked round-bottom flask equipped with a thermometer, a reflux device and a dropping funnel and mixed well with a magnetic stirrer to sufficiently replace nitrogen gas.
On the other hand, the remaining 90% of the monomer mixture was placed in the dropping funnel. Under a nitrogen atmosphere, the temperature of the monomer mixture in the reaction vessel was raised to 65 ° C. while stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 65 ° C. from the end of the dropping, the temperature was raised to 75 ° C., and after reaching 75 ° C., the mixture was stirred for 2 hours to complete the reaction. Then, the solvent and the residual monomer were removed by drying under reduced pressure to obtain a (meth) acrylic resin (PA-1) (acid value: 217 mgKOH / g, number average molecular weight: 3,900).
The yield was determined by dividing the mass of the obtained resin by the total mass of the charged monomer, the polymerization chain transfer agent, and the azo radical polymerization initiator, and multiplying by 100.

Synthesis Examples 1-2 and 1-3
(Meta) acrylic resins (PA-2) and (PA-3) were obtained in the same manner as in Synthesis Example 1-1 except that the preparation was changed according to Table 1. Table 1 shows the yields, acid values and number average molecular weights of the (meth) acrylic resins (PA-2) and (PA-3).

<Synthesis of polyester resin>
Synthesis Example 2-1
BPA-PO, fumaric acid, di (2-ethylhexanoic acid) tin (II) (esterification catalyst), 4-t-butylcatechol (radical polymerization inhibitor) shown in Table 2, thermometer, stainless steel stirring rod The temperature was raised to 210 ° C. over 10 hours in a mantle heater in a nitrogen atmosphere in a 10 L four-necked flask equipped with a flow-down condenser and a nitrogen introduction tube. Then, after reacting at 210 ° C. for 1 hour, the reaction was carried out at 40 kPa until the acid value shown in Table 2 was reached, and the reaction was carried out with a polyester resin (PES-1) (acid value: 20 mgKOH / g, number average molecular weight: 3,700). Got

<Preparation of polymer emulsions (EM-1) to (EM-3)>
Preparation Example 1
50 g of the (meth) acrylic resin (PA-1) obtained in Synthesis Example 1-1 is mixed with 50 g of ion-exchanged water, and sodium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.) is further added to add a neutralizing agent. The (meth) acrylic resin (PA-1) was neutralized so that the equivalent used was 60 mol%. Then, the polymer was dispersed in water by sealing and heating to 90 ° C. using a warm bath, stirring for 3 hours while maintaining the temperature at 90 ° C., and then cooling to room temperature. Next, the concentration was adjusted with ion-exchanged water to obtain a polymer emulsion (EM-1) (cumulant average particle size 62 nm, solid content concentration 50%).

Preparation Example 2
A polymer emulsion (EM-2) was obtained in the same manner as in Preparation Example 1 except that the preparation was changed according to Table 3.

Preparation Example 3
50 g of polyester resin (PES-1) and 50 g of MEK were put into a 3 L container equipped with a stirrer, a reflux condenser, a dropping funnel, a thermometer and a nitrogen introduction tube, and the mixture was stirred at 30 ° C. for 2 hours to make a polyester resin (PES). -1) was dissolved. To the obtained solution, a 5% by mass aqueous sodium hydroxide solution was added so that the equivalent amount of the neutralizing agent used was 60 mol%, and the mixture was stirred for 30 minutes.
While maintaining the temperature at 30 ° C., while stirring at a stirring speed of 280 r / min (stirring peripheral speed 88 m / min), 100 g of ion-exchanged water was added over 100 minutes for phase inversion emulsification. Then, the temperature was raised to 73 ° C., and MEK and water were distilled off under reduced pressure. When the solid content concentration reached 50%, the depressurization was stopped and the mixture was cooled to room temperature. Next, the concentration was adjusted with ion-exchanged water to obtain a polymer emulsion (EM-3) (cumulant average particle size 104 nm, solid content concentration 50%).

Example 1
<Manufacturing of water-based pigment dispersion (I-1)>
(Step 1-1)
To a 3 L polyethylene beaker, 25 g of the (meth) acrylic resin (PA-1) obtained in Synthesis Example 1-1 and 25 g of MEK were added and dissolved in a magnetic stirrer at room temperature. Sodium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd., reagent) was added to 50 g of this solution as a neutralizing agent, and neutralized so that the equivalent amount of the neutralizing agent used was 60%. To the obtained (meth) acrylic resin (PA-1) solution, 100 g of ion-exchanged water and 100 g of cyan pigment (CI Pigment Blue 15: 3, manufactured by DIC Co., Ltd., trade name TGR-SD) were added. The resulting pigment mixture is pre-dispersed using a disper (manufactured by Asada Iron Works Co., Ltd., trade name "Ultra Disper") at 20 ° C. under the condition that a disper blade having a diameter of 40 mm is rotated at 6,000 rpm for 3 hours. bottom. Next, a 15-pass dispersion treatment was performed with a microfluidics (manufactured by Microfluidics, trade name) at a pressure of 150 MPa to obtain a dispersion liquid.
(Step 1-2)
420 g of ion-exchanged water was added to the dispersion obtained in step 1-1, and after stirring, MEK was removed at 60 ° C. under reduced pressure, and a part of water was further removed. The obtained dispersion liquid is put into a 500 ml angle rotor, centrifuged at 3,660 rpm for 20 minutes using a high-speed cooling centrifuge "himac CR22G" (manufactured by Hitachi Koki Co., Ltd., set temperature 20 ° C.), and then the liquid layer. The portion was filtered through a 5 μm membrane filter (manufactured by Sartorius, trade name “Minisalt”), and the pigment aqueous dispersion (A-1) having a solid content concentration of 25% (pigment content 20%, polymer content 5%). ) Was obtained.
(Heat treatment process)
100 g (20 g of pigment, 5 g of polymer) of the aqueous pigment dispersion (A-1) obtained in step 1-2 is placed in a glass bottle with a screw cap, and 30 g (EM-1) of the polymer emulsion (EM-1) is used as an emulsion of the polymer (B). Solid content 15 g), trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name "Denacol EX-321LT", epoxy equivalent 129) as a cross-linking agent (C) was added so as to have a cross-linking rate of 40%, and a mixture was added. Obtained.
The glass bottle containing the mixture was sealed and heated at 90 ° C. for 1.5 hours with stirring with a magnetic stirrer (crosslinking rate 40%). Then, the temperature was lowered to room temperature (25 ° C.), filtered through a needleless syringe (manufactured by Terumo Corporation) having a capacity of 25 mL and equipped with the above-mentioned 5 μm filter, and ion-exchanged water was added to adjust the solid content concentration to 30%. An aqueous pigment dispersion (I-1) was obtained.

<Manufacturing of water-based ink 1>
34.7 g of the obtained water-based pigment dispersion (I-1), 35 g of propylene glycol, and Surfinol 104PG-50 (trade name, manufactured by Air Products and Chemicals Co., Ltd.) so that the pigment concentration with respect to the entire water-based ink is 5%. , 1 g of propylene glycol solution of acetylene glycol-based nonionic surfactant, effective content 50%), and 29.3 g of ion-exchanged water are mixed and stirred at room temperature for 15 minutes using a magnetic stirrer to add 100 g of ink 1. Obtained.

Examples 2-4 and 14
In the production of the aqueous pigment dispersion of Example 1, the same procedure as in Example 1 was carried out except that the amounts of the polymer dispersant (a), the emulsion of the polymer (B) and the cross-linking agent were changed as shown in Table 4. Aqueous pigment dispersions (I-2) to (I-4) and (I-14) and inks 2-4 and 14 were obtained. The solid content concentrations of the aqueous pigment dispersions (I-2) to (I-4) and (I-14) were 30%.

Example 5
<Manufacturing of water-based pigment dispersion (I-5)>
(Step 1-1)
To a 3 L polyethylene beaker, 50 g (25 g in solid content) of the polymer emulsion (EM-1) obtained in Preparation Example 1 and 25 g of MEK were added. Obtained by adding 100 g of ion-exchanged water and 100 g of cyan pigment (CI Pigment Blue 15: 3, manufactured by DIC Co., Ltd., trade name "TGR-SD") to the obtained polymer emulsion (EM-1) solution. The pigment mixture was pre-dispersed using a disper (manufactured by Asada Iron Works Co., Ltd., trade name "Ultra Disper") at 20 ° C. under the condition of rotating a disper blade having a diameter of 40 mm at 6,000 rpm for 3 hours. Next, a 15-pass dispersion treatment was performed with a microfluidics (manufactured by Microfluidics, trade name) at a pressure of 150 MPa to obtain a dispersion liquid.
(Step 1-2)
After adding 370 g of ion-exchanged water to the dispersion obtained in step 1-1 and stirring, MEK was removed at 60 ° C. under reduced pressure, and a part of water was further removed. The obtained dispersion liquid is put into a 500 ml angle rotor, centrifuged at 3,660 rpm for 20 minutes using a high-speed cooling centrifuge "himac CR22G" (manufactured by Hitachi Koki Co., Ltd., set temperature 20 ° C.), and then the liquid layer. The portion was filtered through a 5 μm membrane filter (manufactured by Sartorius, trade name “Minisalt”), and a pigment aqueous dispersion (A-5) having a solid content concentration of 25% (pigment content 20%, polymer content 5%). ) Was obtained.
(Heat treatment process)
In the heat treatment step of Example 1, the same procedure was carried out except that the pigment aqueous dispersion (A-1) was changed to the pigment aqueous dispersion (A-5), and the aqueous pigment dispersion (I-5) (solid content concentration:: 30%) was obtained.
<Manufacturing of water-based ink 5>
In the production of the water-based ink 1 of Example 1, the same procedure was carried out except that the water-based pigment dispersion (I-1) was changed to the water-based pigment dispersion (I-5) to obtain ink 5.

Examples 6-8, 13 and 15
In Example 5, the same procedure as in Example 5 was carried out except that the amounts of the polymer dispersant (a), the emulsion of the polymer (B) and the cross-linking agent were changed as shown in Table 4, and the aqueous pigment dispersion (I-) was carried out. 6)-(I-8), (I-13), (I-15) and inks 6-8, 13, 15 were obtained. The solid content concentrations of the aqueous pigment dispersions (I-6) to (I-8), (I-13) and (I-15) were 30%.

Example 9
<Manufacturing of water-based pigment dispersion (I-9)>
As a pigment aqueous dispersion (A-9), 100 g of a self-dispersing pigment "BONJET BLACK CW-1" (manufactured by Orient Chemical Industries Co., Ltd., trade name, solid content 20%) is taken in a glass bottle with a screw cap and polymer (B). ), 30 g of the polymer emulsion (EM-1) (15 g as the resin solid content), and trimethylolpropane polyglycidyl ether (EX-321LT) as the cross-linking agent (C) so as to have a cross-linking rate of 40%, and add the mixture. Got
The glass bottle containing the mixture was sealed and heated at 90 ° C. for 1.5 hours with stirring with a magnetic stirrer (crosslinking rate 40%). After that, the same procedure as in Example 1 was carried out to obtain an aqueous pigment dispersion (I-9) (solid content concentration: 30%).
<Manufacturing of water-based ink 9>
In the production of the water-based ink 1 of Example 1, the water-based pigment dispersion (I-1) was changed to the water-based pigment dispersion (I-9), and the same procedure as in Example 1 was carried out to obtain ink 9.

Example 10
In the production of the aqueous pigment dispersion of Example 1, the polymer dispersant (a) in step 1-1 was changed to a (meth) acrylic resin (PA-3), and a heat treatment step was further performed without adding a neutralizing agent. In the same manner as in Example 1 except that the solid content concentration was adjusted to 30% by concentrating under reduced pressure, an aqueous pigment dispersion (I-10) (solid content concentration: 30%) and ink 10 were obtained. ..

Example 11
In step 1-1 of Example 1, the same procedure as in Example 1 was carried out except that the treatment conditions using a microfluidics (manufactured by Microfluidics, trade name) were changed to 30 passes at a pressure of 150 MPa. I-11) (solid content concentration: 30%) and ink 11 were obtained.

Example 12
In step 1-1 of Example 1, the same procedure as in Example 1 was carried out except that the added MEK was changed to 35 g, and the aqueous pigment dispersion (I-12) (solid content concentration: 30%) and ink 12 were added. Obtained.

Examples 16 and 17
In the steps (1-1) and (1-2) of Example 1, the blending amounts of the pigment and the polymer dispersant (a) in the mixture in the heat treatment step were changed so as to be the amounts shown in Table 4. Other than that, the same procedure was carried out to obtain pigment aqueous dispersions (A-16) and (A-17) having a solid content concentration of 25%.
Then, in the heat treatment step of Example 1, the amounts of the pigment aqueous dispersions (A-16) and (A-17) used were changed to 200 g for Example 16 and 64 g for Example 17, and the cross-linking agents shown in Table 4 were changed. The amount of the aqueous pigment dispersion (I-16) and (I-16) and ( I-17) and inks 16 and 17 were obtained.

Comparative Example 1
As shown in Table 4, the same procedure as in Example 1 was carried out except that the polymer (B) emulsion was not added and the solid content concentration was adjusted to 30% by further concentrating under reduced pressure in the heat treatment step to disperse the aqueous pigment. Body (IC1) (solid content concentration: 30%) and ink C1 were obtained.

Comparative Example 2
As shown in Table 4, the same procedure as in Example 1 was carried out except that the cross-linking agent (C) was not added, to obtain an aqueous pigment dispersion (IC2) (solid content concentration: 30%) and ink C2.

Comparative Example 3
As shown in Table 4, the same procedure as in Example 1 was carried out except that the heat treatment temperature of the mixture was set to 40 ° C. to obtain an aqueous pigment dispersion (IC3) (solid content concentration: 30%) and ink C3.

Comparative Examples 4 and 5
In the steps (1-1) and (1-2) of Example 1, the blending amounts of the pigment and the polymer dispersant (a) in the mixture in the heat treatment step were changed so as to be the amounts shown in Table 4. Other than that, the same procedure was carried out to obtain pigment aqueous dispersions (A-C4) and (A-C5) having a solid content concentration of 25%.
Then, in the heat treatment step of Example 1, the amounts of the pigment aqueous dispersions (A-C4) and (A-C5) used were changed to 216 g in Comparative Example 4 and 60 g in Comparative Example 5, and the cross-linking agents shown in Table 4 were changed. The compounding amount of (C) was changed, and Comparative Example 4 was concentrated under reduced pressure to adjust the solid content concentration to 30%, and the same procedure as in Example 1 was carried out. (IC5) and inks C4 and C5 were obtained.

<Evaluation of water-based ink>
Using the obtained water-based ink, printing was performed by the following method, and the printed matter was evaluated. The results are shown in Table 5.
(1) Evaluation of bending resistance Inkjet equipped with an inkjet head (KJ4B-QA06NTB-STDV, Piezo type, number of nozzles 2656) in an environment with a temperature of 25 ± 1 ° C and a relative humidity of 30 ± 5%. The print evaluation device (manufactured by Tritech Co., Ltd.) was filled with water-based ink.
Set head voltage 26V, frequency 20kHz, discharge liquid appropriate amount 18pl, head temperature 32 ° C, resolution 600dpi, number of flushing before discharge 200, negative pressure 4.0kPa, and the direction in which the longitudinal direction and transport direction of the print medium are the same. The print medium was fixed to the transport table under reduced pressure. A print command was transferred to the print evaluation device, and a 100% duty image was printed.
A polyester film (manufactured by Toray Industries, Inc., Lumirror T60, thickness 75 um, water absorption 2.3 g / m ² ) is used as the printing medium, and after printing is completed, it is heated and dried at 60 ° C. for 10 minutes on a hot plate for evaluation. I got a printed matter.
The obtained evaluation printed matter is ^{bent inward at 50 g / cm 2} for 30 seconds, reopened, and the damaged image is wiped off with a soft cloth. It was used as an index. The smaller the maximum value of the width of the image defect, the better the bending resistance of the printed matter.

(2) Evaluation of ejection reliability qualification The same inkjet printing evaluation device as in (1) above is used to print a print check pattern that can determine whether or not ejection has been performed from all nozzles by leaving the nozzle surface unprotected for 30 minutes after printing. The number of nozzle chips (nozzles that did not eject normally) when printing on the medium was counted, and the ejection reliability was evaluated. The smaller the number of missing nozzles, the better the ejection reliability.

なお、表４に示す各成分の量は熱処理工程の混合物中の含有量である。また、表４中の自己分散型顔料、ポリマー分散剤（ａ）及びポリマー（Ｂ）のエマルションの量は、固形分量である。

The amount of each component shown in Table 4 is the content in the mixture of the heat treatment steps. The amount of the self-dispersing pigment, the polymer dispersant (a) and the polymer (B) emulsion in Table 4 is the amount of solid content.

From Table 5, it can be seen that Examples 1 to 17 are superior in both ejection reliability and bending resistance of the printed matter as compared with Comparative Examples 1 to 5.
In Comparative Example 1, since the emulsion of the polymer (B) is not used, the discharge reliability and the bending resistance are inferior.
In Comparative Example 2, since the cross-linking agent (C) is not used, the discharge reliability and the bending resistance are inferior.
In Comparative Example 3, since the heat treatment temperature is less than 45 ° C., the crosslinked structure is not sufficiently introduced into the polymer, and the discharge reliability and bending resistance are inferior.
In Comparative Example 4, since the mass ratio (total amount of pigment / polymer) is more than 2.15, it has ejection reliability but is inferior in bending resistance.
In Comparative Example 5, since the mass ratio (total amount of pigment / polymer) is less than 0.48, it has bending resistance but is inferior in discharge reliability.

According to the present invention, it is possible to provide a method for producing an aqueous pigment dispersion having excellent ejection reliability and bending resistance of printed matter by using it for an aqueous ink, and an inkjet recording ink containing the aqueous pigment dispersion. can.

Claims (9)

A method for producing an aqueous pigment dispersion (I) containing a pigment and a polymer.
It has a step of heat-treating a mixture of the aqueous pigment dispersion (A), the emulsion of the polymer (B), and the cross-linking agent (C) at 45 ° C. or higher and 100 ° C. or lower.
And pigment weight ratio of the total amount of the polymer (pigment / total polymer) of Ri der 0.48 or 2.15 or less
The pigment aqueous dispersion (A) is an aqueous dispersion in which the pigment is dispersed with the polymer dispersant (a).
The polymer dispersant (a) and the polymer (B) are both (meth) acrylic resins or all are polyester resins.
A method for producing an aqueous pigment dispersion (I), wherein the total amount of the polymer is the total amount of the polymer dispersant (a), the polymer (B), and the cross-linking agent (C). The method for producing an aqueous pigment dispersion (I) according to claim 1, wherein the mixture further contains 10% by mass or less of an organic solvent. The cumulant average particle size ratio of the aqueous pigment dispersion (I) to the aqueous pigment dispersion (A) [aqueous pigment dispersion (I) / pigment aqueous dispersion (A)] is 0.9 or more and 1.2 or less. , The method for producing an aqueous pigment dispersion (I) according to claim 1 or 2. The method for producing an aqueous pigment dispersion (I) according to any one of claims 1 to 3 , wherein the aqueous pigment dispersion (A) mechanically disperses the pigment with the polymer dispersant (a). The method for producing an aqueous pigment dispersion (I) according to any one of claims 1 to 4, wherein the (meth) acrylic resin contains a structural unit derived from a hydrophilic monomer and a structural unit derived from a hydrophobic monomer. The method for producing an aqueous pigment dispersion (I) according to claim 5, wherein the content of the constituent unit derived from the hydrophilic monomer in the (meth) acrylic resin is 10% by mass or more and 75% by mass or less. The method for producing an aqueous pigment dispersion (I) according to any one of claims 1 to 6, wherein the polyester resin contains a structural unit derived from an alcohol component and a structural unit derived from a carboxylic acid component. The method for producing an aqueous pigment dispersion (I) according to any one of claims 1 to 7, wherein the cross-linking agent (C) is a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 or more and 8 or less carbon atoms. .. Mixing the water-based pigment dispersion obtained by the production method according to any one of claims. 1 to 8 (I) and water-soluble organic solvent (II), the production method of the ink-jet recording ink.