JP7144231B2 - Aqueous pigment dispersion - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water-based pigment dispersion, a water-based ink containing the water-based pigment dispersion, an inkjet printing method using the water-based ink, and an ink set.

In the field of commercial printing and industrial printing such as label printing used for product packaging printing and advertisements, low water absorption printing media such as coated paper, PET (polyethylene terephthalate), PVC (polyvinyl chloride), PE (polyethylene), Non-absorbent printing media such as PP (polypropylene) and NY (nylon) are printed using inkjet recording methods, flexographic printing methods, and gravure printing methods to reduce environmental impact, save energy, and improve safety. From this point of view, it is required to use water-based ink.
In addition, from the viewpoint of weather resistance and water resistance of printed matter, water-based inks using pigments as colorants have become mainstream.

For example, in Patent Document 1, C.I. I. Pigment Red (hereinafter also referred to as "PR") 150, a colorant dispersion containing a quinacridone pigment and water, and an ink composition containing the colorant dispersion and a water-soluble organic solvent are described. . In Examples, inks using PR150 and PR122 as a quinacridone pigment are described.
Patent Document 2 describes a pigment composition exhibiting a clear and highly saturated hue, in which a quinacridone pigment and a monoazo pigment are obtained by adding a monoazo pigment during a dehydration condensation reaction to obtain a quinacridone pigment in the process of producing the pigment composition. Pigment compositions comprising pigments are described. In Examples, a red pigment composition using PR122 as a quinacridone pigment and PR269 as a monoazo pigment, and an inkjet ink prepared from the red pigment composition are described.
Patent Document 3 describes a magenta inkjet ink containing a quinacridone pigment and an azo pigment containing at least one azo compound represented by a specific formula. In Examples, magenta inks using PR282 as a quinacridone pigment and PR150 or PR269 as an azo pigment are described.

Patent Document 4 describes a magenta ink containing a magenta pigment mixture, wherein the magenta pigment mixture contains a quinacridone pigment represented by a specific general formula and an azo pigment represented by a specific general formula. is described. In Examples, magenta ink using PR282 as a quinacridone pigment and PR150 as an azo pigment, and C.I. I. A magenta ink using Pigment Violet (hereinafter also referred to as "PV") 19 and PR122 and PR150 as an azo pigment is described.
Patent Document 5 discloses a coloring composition containing a coloring agent, a binder resin and a polymerizable compound as a coloring composition for forming a colored cured film with high brightness, wherein the coloring agent contains PV19 and a red coloring agent. A composition is described. In Examples, colorant compositions using PV19 and PR149, PR166, PR177, PR208, PR214, PR242, PR254, or PR264 as a red colorant are described.
In Patent Document 6, a magenta water-based ink for inkjet recording capable of reproducing a magenta color with an appropriate color tone on a recording material and capable of drawing a hue with excellent hue clarity etc. is disclosed. A magenta water-based ink for inkjet recording is described which is a mixture of 2,9-dimethylquinacridone pigment and at least one other red pigment or a solid solution pigment thereof. In Examples, mixtures or solid solution pigments using PR122 and PR177, PR5, PR254, PR209, or PV19 as other pigments, and magenta water-based inks for inkjet recording using these are described.

WO2014/156569 JP 2016-74749 A U.S. Patent Application Publication No. 2017/0022383 U.S. Patent Application Publication No. 2017/0183523 JP 2016-147977 A JP-A-2001-2962

However, since the print media used in commercial printing and industrial printing have low or no water absorbency, and the water-based ink does not penetrate into the print media, the pigment particles contained in the water-based ink remain on the surface of the print media. However, at that time, as a result of aggregation of the pigment particles, irregularities are likely to occur on the printed surface. Therefore, conventional water-based inks are insufficient in fixability and print image quality when printed on a low-absorbent or non-absorbent print medium, and improvements in these aspects are desired.
The present invention provides a water-based pigment dispersion, a water-based ink containing the water-based pigment dispersion, and a water-based ink that can provide printed matter with excellent fixability and print quality even when printed on a low water-absorbing printing medium. An object of the present invention is to provide an inkjet printing method and an ink set.
In this specification, the term “low water absorption” is a concept including low water absorption and non-water absorption of water and/or ink, and low water absorption can be evaluated by the water absorption of pure water. . More specifically, it means that the water absorption amount of the print medium is 0 g/m ² or more and 10 g/m ² or less during a contact time of 100 msec between the print medium and pure water. The water absorption is measured by the method described in Examples.

The inventors of the present invention have found that by combining PR176 and a quinacridone pigment and dispersing these pigments with a polymer, it is possible to obtain a printed material with excellent fixability and print quality even when printed on a low water-absorbing printing medium. Found it.
That is, the present invention provides the following [1] to [4].
[1] An aqueous pigment dispersion in which a pigment A is dispersed in an aqueous medium with a polymer B,
The pigment A is C.I. I. An aqueous pigment dispersion containing Pigment Red 176 and a quinacridone pigment.
[2] A water-based ink containing the water-based pigment dispersion described in [1] above and a water-soluble organic solvent C.
[3] An inkjet printing method, wherein an image is formed on a low water-absorbent printing medium by an inkjet recording method using the water-based ink described in [2] above.
[4] An ink set containing at least magenta ink, yellow ink, and cyan ink,
An ink set, wherein the magenta ink is the water-based ink described in [2] above.
In the present invention, the term "aqueous" means that water accounts for the maximum proportion in the medium. In addition, "to form an image" is a concept that includes printing that forms characters and images, and "printed matter" is a concept that includes printed matter and printed matter on which characters and images are formed.

According to the present invention, a water-based pigment dispersion, a water-based ink containing the water-based pigment dispersion, and the water-based ink, which can provide a printed material with excellent fixability and print quality even when printed on a low water-absorbing printing medium. can provide an inkjet printing method and an ink set using

[Aqueous Pigment Dispersion]
The water-based pigment dispersion of the present invention (hereinafter also simply referred to as "pigment dispersion") is a water-based pigment dispersion in which a pigment A is dispersed in an aqueous medium with a polymer B, and the pigment A is a C.I. I. Contains Pigment Red 176 (PR176) and quinacridone pigments.
The pigment dispersion preferably contains particles obtained by dispersing each pigment contained in pigment A with polymer B in an aqueous medium. Here, the form of the particles is not particularly limited as long as at least each pigment contained in the pigment A and the polymer B form particles. Examples include a particle form in which the pigment is encapsulated in the polymer B, a particle form in which the pigment is uniformly dispersed in the polymer B, a particle form in which the pigment is exposed on the particle surface of the polymer B, and mixtures thereof. be
INDUSTRIAL APPLICABILITY The pigment dispersion of the present invention can be used as a water-based pigment dispersion for flexographic printing inks, gravure printing inks, or inkjet printing inks because printed matter having excellent fixability and print image quality can be obtained. . In particular, it is preferable to use it as a water-based pigment dispersion for inkjet printing ink.

By using the pigment dispersion of the present invention in a water-based ink, it is possible to obtain a printed material excellent in fixability and print quality even when printed on a low water-absorbing printing medium. Although the reason is not clear, it is considered as follows.
When an image is formed on a low water-absorbing print medium, the water-based ink does not penetrate into the print medium, and the pigment particles contained in the water-based ink remain on the surface of the print medium. At this time, the water is volatilized, the ink is concentrated, and the dispersion stability of the pigment is lowered. Therefore, in conventional water-based inks containing two or more pigments, heteroaggregation between different pigments tends to occur on the print medium. On the other hand, in the present invention, PR176, which is a naphthol-based monoazo pigment having a benzimidazolone skeleton, and pigment A containing quinacridone pigment are dispersed with polymer B in an aqueous medium. By having a benzimidazolone skeleton in PR176, the dispersion stability of the pigment is improved without impairing the inherent color development properties of the naphthol-based monoazo pigment. Since a smooth ink film can be formed, it is thought that fixability and print image quality are improved.

<Pigment A>
Pigment A is dispersed in an aqueous medium with polymer B, and C.I. I. Contains Pigment Red 176 (PR176) and quinacridone pigments.
PR176 is an azo pigment containing a benzimidazolone skeleton and a monoazonaphthol skeleton represented by the following formula (1).

Commercially available products of PR176 include Novoperm Carmine HF3C (trade name) manufactured by Clariant Chemicals Co., Ltd., and the like.
The quinacridone pigment is not particularly limited as long as it has a quinacridone skeleton, and from the viewpoint of fixability and print quality, it is preferably a compound represented by the following general formula (2).

In formula (2), R ¹ and R ² each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group.
Examples of the quinacridone pigment represented by formula (2) include unsubstituted quinacridone, 2,9-dimethylquinacridone, 2,9-dichloroquinacridone, 2,9-dimethoxyquinacridone, 3,10-dimethylquinacridone, 3, 10-dichloroquinacridone, 3,10-dimethoxyquinacridone, 4,11-dimethylquinacridone, 4,11-dichloroquinacridone, 4,11-dimethoxyquinacridone and the like. Any of α-type, β-type and γ-type unsubstituted quinacridone can be used. The quinacridone pigments may be used singly or in combination of two or more.

The quinacridone pigment is preferably a red pigment classified into magenta, red, and violet in terms of fixability and print quality. Specific examples include PR122, PR202, PR209, PR282, PV19, and the like. Among them, it is preferable that at least one pigment (a) selected from PR122, PR202, PR282 and PV19 is included.
The content of the pigment (a) in the quinacridone pigment is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and preferably 100% by mass or less, still more preferably is 100% by mass.

A solid solution pigment can also be suitably used as the quinacridone pigment. Examples of the solid solution pigment include unsubstituted quinacridone and quinacridone having a structure in which any two hydrogen atoms on the benzene ring of unsubstituted quinacridone are substituted with groups other than hydrogen atoms (hereinafter also referred to as "disubstituted quinacridone"). is preferred, and a combination of unsubstituted quinacridone and dimethyl-substituted quinacridone, and a combination of unsubstituted quinacridone and dichloro-substituted quinacridone are more preferred. Specific combinations include a combination of unsubstituted quinacridone (PV19) and 2,9-dimethylquinacridone (PR122), a combination of unsubstituted quinacridone (PV19) and 2,9-dichloroquinacridone (PR202), and the like. be done. Among them, a combination of unsubstituted quinacridone (PV19) and 2,9-dimethylquinacridone (PR122) is preferable from the viewpoint of improving fixability.
The mass ratio of unsubstituted quinacridone to disubstituted quinacridone [unsubstituted quinacridone/disubstituted quinacridone] in the solid solution pigment is preferably 5/95 or more, more preferably 10/90, and preferably 95/5 or less. , more preferably 90/10 or less.

Commercially available quinacridone pigments include DIC Corporation's "FASTOGEN SUPER MAGENTA" series, "QUINDO MAGENTA" series, "FASTOGEN SUPER RED" series, and "QUINDO VIOLET19 228-1119"; BASF's "Cinquasia Magenta" series. , and the "Cinquasia Violet" series.

The mass ratio of PR176 to the quinacridone pigment [PR176/quinacridone pigment] is preferably 3/97 or more, more preferably 5/95 or more, still more preferably 10/90 or more, still more preferably 20/80 or more, And it is preferably 80/20 or less, more preferably 70/30 or less, still more preferably 60/40 or less, still more preferably 50/50 or less, and even more preferably 40/60 or less.

Pigment A may further contain pigments other than PR176 and quinacridone pigments as long as they do not impair the effects of the present invention. Other pigments include, for example, PR5, PR48:3, PR57:1, PR146, PR150, PR177, PR185, PR254 and PR269.
The total content of PR176 and quinacridone pigments in Pigment A is preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, and even more preferably 90% by mass or more, and It is preferably 100% by mass or less, more preferably 100% by mass.

<Polymer B>
The polymer B should just have pigment dispersibility at least.
The presence form of the polymer B in the pigment dispersion is a form in which the polymer B is adsorbed to each pigment contained in the pigment A, and a pigment encapsulation (capsule) in which the polymer B contains each pigment contained in the pigment A. and a form in which the polymer B is not adsorbed to each pigment contained in the pigment A. From the viewpoint of the dispersion stability of the pigment, in the present invention, the form in which the polymer B contains each pigment contained in the pigment A, that is, the form of pigment-containing polymer particles is preferable, and the polymer B contains each pigment contained in the pigment A. A pigment encapsulating form in which the pigment is contained is more preferable.

From the viewpoint of the dispersion stability of the pigment, the polymer B preferably has acid groups, and more preferably at least part of the acid groups are neutralized with a neutralizing agent. It is believed that this increases the charge repulsion that develops after neutralization, and contributes to the suppression of heteroaggregation between different pigment particles when printing on a low water-absorbing printing medium.
Examples of the acid group include groups exhibiting acidity by dissociating to release hydrogen ions, such as a carboxy group (--COOM), a sulfonic acid group (--SO ₃ M), and a phosphoric acid group (--OPO ₃ M ₂ ). , or their dissociated ionic forms (-COO ^- , -SO ₃ ^- , -OPO ₃ ^2- , -OPO ₃ ^- M), and the like. In the above chemical formula, M represents a hydrogen atom, alkali metal, ammonium or organic ammonium. Among these, a carboxy group (--COOM) is preferable from the viewpoint of pigment dispersion stability, fixability, and print image quality.

The acid value of polymer B is preferably 50 mgKOH/g or more, more preferably 70 mgKOH/g or more, still more preferably 100 mgKOH/g or more, and preferably 300 mgKOH/g or less, more preferably 270 mgKOH/g or less, and further Preferably, it is 250 mgKOH/g or less. When the acid value is within the above range, the amount of acid groups and their neutralized acid groups is sufficient to ensure the dispersion stability of the pigment. It is also preferable from the viewpoint of the balance between the affinity between the polymer B and the aqueous medium and the interaction between the polymer B and the pigment.
The acid value of polymer B can be calculated from the mass ratio of the constituent monomers. It can also be obtained by a method of dissolving or swelling the polymer B in a suitable organic solvent (eg, MEK) and titrating.

The acid group contained in the polymer B molecule is preferably introduced into the polymer skeleton by the monomer (b-1) having an acid group. That is, the polymer B preferably contains structural units derived from the monomer (b-1) having an acid group. Examples of the polymer B include polyester-based resins, polyurethane-based resins, vinyl-based resins, and the like. Among them, vinyl resins are preferable, and a monomer (b-1) having an acid group (hereinafter also referred to as "(b-1) component") and a hydrophobic monomer (b-2) (hereinafter referred to as "(b-2 ) component”) (hereinafter also simply referred to as “raw material monomer”) is copolymerized. The vinyl resin contains a structural unit derived from component (b-1) and a structural unit derived from component (b-2). The vinyl resin further contains structural units derived from the macromonomer (b-3) (hereinafter also referred to as "component (b-3)") and/or nonionic monomers (b-4) (hereinafter referred to as "(b- 4) may contain structural units derived from (also referred to as "component").

[Monomer (b-1) having an acid group]
The acid group-containing monomer (b-1) is preferably used as a monomer component of the vinyl resin from the viewpoint of improving the dispersion stability of the pigment and improving the fixability and print image quality.
Examples of the acid group-containing monomer (b-1) include those having the aforementioned acid group. Among them, carboxylic acid monomers are preferred.
Examples of the carboxylic acid monomer include (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-methacryloyloxymethylsuccinic acid and the like, preferably (meth)acrylic acid. .
As used herein, "(meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid.

[Hydrophobic monomer (b-2)]
The hydrophobic monomer (b-2) is a monomer component of the vinyl resin from the viewpoint of improving the adsorption of the polymer to the pigment, improving the dispersion stability of the pigment, and improving the fixability and print image quality. It is preferably used as
As used herein, the term "hydrophobic" means that the amount dissolved in 100 g of deionized water at 25° C. until the monomer is saturated is less than 10 g. The dissolved amount of the hydrophobic monomer (b-2) is preferably 5 g or less, more preferably 1 g or less, from the viewpoint of the adsorption of the polymer to the pigment.
The hydrophobic monomer (b-2) is preferably at least one selected from (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols and aromatic group-containing monomers.
As used herein, "(meth)acrylate" is at least one selected from acrylate and methacrylate.

The (meth)acrylate having a hydrocarbon group derived from an aliphatic alcohol preferably has a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 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, (meth)acrylates 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, (meth)acrylates 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 group-containing (meth)acrylates, and the like. Among them, those having an alkyl group having 1 to 10 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, more preferably a styrene-based monomer and an aromatic It is at least one selected from group-containing (meth)acrylates. The molecular weight of the aromatic group-containing monomer is preferably less than 500.
The styrenic monomer is preferably at least one selected from styrene, α-methylstyrene, 2-methylstyrene, vinyltoluene, and divinylbenzene, more preferably at least one selected from styrene and α-methylstyrene. is.
Further, the aromatic group-containing (meth)acrylate is preferably at least one selected from phenyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate, more preferably benzyl (meth)acrylate. is.

[Macromonomer (b-3)]
The macromonomer (b-3) 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. can be used as The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, more preferably a methacryloyloxy group.
The number average molecular weight of the macromonomer (b-3) 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 of dodecyldimethylamine as a solvent, using polystyrene as a standard substance.
From the viewpoint of dispersion stability of the pigment, the macromonomer (b-3) is preferably an aromatic group-containing monomer-based macromonomer or a silicone-based macromonomer, more preferably an aromatic group-containing monomer-based macromonomer.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer include the aromatic group-containing monomers described in the hydrophobic monomer (b-2), preferably styrene and benzyl (meth)acrylate, and styrene is more preferred.
Specific examples of commercially available styrenic macromonomers include AS-6(S), AN-6(S), HS-6(S) (trade name of Toagosei Co., Ltd.) and the like.
Examples of silicone-based macromonomers include organopolysiloxanes having a polymerizable functional group at one end.

[Nonionic monomer (b-4)]
The nonionic monomer (b-4) can be used as a monomer component of the vinyl resin from the viewpoint of dispersion stability of the pigment.
The nonionic monomer (b-4) includes hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate; polypropylene glycol (n = 2 to 30, n is oxypropylene Shows the average number of added moles of the group.N below indicates the average number of added moles of the oxyalkylene group.) Polyalkylene glycols such as (meth)acrylate, polyethylene glycol (n = 2 to 30) (meth)acrylate ( meth) acrylate; alkoxypolyalkylene glycol (meth) acrylate such as methoxypolyethylene glycol (n = 1 to 30) (meth) acrylate; phenoxy (ethylene glycol/propylene glycol copolymerization) (n = 1 to 30, ethylene Glycol: n=1 to 29) (meth)acrylate and the like. Among them, polypropylene glycol (n=2 to 30) (meth)acrylates, alkoxypolyalkylene glycol (meth)acrylates, and phenoxy (ethylene glycol/propylene glycol copolymer) (meth)acrylates are preferred.
Specific examples of commercially available nonionic monomers (b-4) include NK Ester M-20G, 40G, 90G, 230G, etc. of Shin-Nakamura Chemical Co., Ltd., Brenmer PE of NOF Corporation. -90, 200, 350, etc., PME-100, 200, 400, etc., PP-500, 800, 1000, etc., AP-150, 400, 550, etc., 50PEP-300, 50POEP-800B , 43PAPE-600B and the like.

Each of the components (b-1) to (b-4) can be used alone or in combination of two or more.
As described above, the polymer B according to the present invention has a structural unit derived from a monomer (b-1) having one or more acid groups selected from acrylic acid and methacrylic acid, and a hydrocarbon group derived from an aliphatic alcohol. It is preferably a vinyl-based resin containing structural units derived from one or more hydrophobic monomers (b-2) selected from (meth)acrylates and aromatic group-containing monomers, and further macromonomers (b-3). It may be a vinyl resin containing structural units derived from the nonionic monomer (b-4).

(Content of each component or structural unit in raw material monomer or vinyl resin)
The content of components (b-1) and (b-2) in raw material monomers (content as an unneutralized amount; the same shall apply hereinafter) or (b- The content of structural units derived from components 1) and (b-2) is as follows from the viewpoint of the dispersion stability of the pigment.
The content of component (b-1) is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 20% by mass or more, and preferably 70% by mass or less, more preferably 60% by mass. % or less, more preferably 50 mass % or less.
The content of component (b-2) is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass. % or less, more preferably 80 mass % or less.
The mass ratio of component (b-1) to component (b-2) [(b-1) component/(b-2) component] is preferably 0.05 or more, more preferably 0.1 or more, and further It is preferably 0.2 or more, still more preferably 0.3 or more, and preferably 2.3 or less, more preferably 2 or less, even more preferably 1 or less, and even more preferably 0.5 or less.

(Manufacture of vinyl resin)
Vinyl-based resins are produced by copolymerizing raw material monomers by known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these polymerization methods, the solution polymerization method is preferred.
Solvents used in the solution polymerization method are not particularly limited, but polar organic solvents are preferred. If the polar organic solvent has water miscibility, it can be used by mixing with water. Examples of polar organic solvents 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, or a mixed solvent of one or more of these with water is preferable, and methyl ethyl ketone or a mixed solvent of it and water is preferable.
A polymerization initiator and a polymerization chain transfer agent can be used in the polymerization.
Examples of polymerization initiators include azo compounds such as 2,2'-azobisisobutyronitrile and 2,2'-azobis(2,4-dimethylvaleronitrile), tert-butyl peroxyoctoate, benzoyl peroxide, and the like. A known radical polymerization initiator such as an organic peroxide of can be used. The amount of the radical polymerization initiator is preferably 0.001 mol or more and 5 mol or less, more preferably 0.01 mol or more and 2 mol or less per 1 mol of raw material monomer.
As the polymerization chain transfer agent, known chain transfer agents such as mercaptans such as octylmercaptan and 2-mercaptoethanol, and thiuram disulfides can be used.
Moreover, there is no restriction on the chain mode of the polymerization monomers, and any polymerization mode such as random, block, or graft may be used.

Preferred polymerization conditions vary depending on the type of polymerization initiator, monomer, solvent, etc. used, but usually the polymerization temperature is preferably 30° C. or higher, more preferably 50° C. or higher, and preferably 95° C. or lower. It is more preferably 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 polymer produced can be isolated from the reaction solution by known methods such as reprecipitation and solvent distillation. The obtained polymer can be purified by removing unreacted monomers and the like by reprecipitation, membrane separation, chromatography, extraction, or the like.

The number average molecular weight of polymer B used in the present invention is preferably 2,000 or more, more preferably 5,000 or more, still more preferably 7,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, more preferably 30,000 or less, still more preferably 20,000 or less. If the number average molecular weight of the polymer B is within the above range, the adsorptive power to the pigment is sufficient and dispersion stability can be exhibited.
The number average molecular weight is measured by the method described in Examples.

(Production of water-based pigment dispersion)
The water-based pigment dispersion (pigment dispersion) of the present invention is obtained by dispersing each pigment contained in pigment A by type with polymer B, and then mixing the obtained water-based dispersion P of each pigment with each other Method 1, It can be produced by Method 2 or the like in which Pigment A is dispersed with Polymer B. Among them, method 1 is preferable from the viewpoint of the dispersion stability of the pigment.
Method 1 will be described below with each pigment contained in pigment A as “pigment n”.

[Method 1]
Method 1 is preferably carried out by a method including steps 1-1 to 1-3 below.
Step 1-1: A step of dispersing a pigment mixture (i) containing a polymer B, an organic solvent, a pigment n, and water (hereinafter also referred to as “pigment mixture (i)”) to obtain a dispersion liquid p. 1-2: An aqueous dispersion P of polymer particles containing pigment n (hereinafter also referred to as “pigment (n)-containing polymer particles”) is obtained by removing the organic solvent from the dispersion p obtained in step 1-1. Step 1-3: A step of mixing the aqueous dispersion P obtained in Step 1-2 with each other to obtain a pigment dispersion

(Step 1-1)
Step 1-1 is a step of dispersing a pigment mixture (i) containing a polymer B, an organic solvent, a pigment n, and water to obtain a dispersion liquid p.
In step 1-1, polymer B is first dissolved in an organic solvent, then pigment n, water, and if necessary a neutralizing agent, a surfactant, etc. are added to the obtained organic solvent solution and mixed. , to obtain an oil-in-water dispersion p. The order of addition to the organic solvent solution of polymer B is not limited, but it is preferable to add water, the neutralizer, and the pigment in this order.
The organic solvent for dissolving polymer B is not limited, but aliphatic alcohols having 1 to 3 carbon atoms, ketones having 3 to 8 carbon atoms, ethers, esters, etc. are preferable, and wettability to pigments, polymer From the viewpoint of improving the solubility of B and the adsorptivity of polymer B to pigments, ketones having 4 to 8 carbon atoms are more preferred, methyl ethyl ketone and methyl isobutyl ketone are more preferred, and methyl ethyl ketone is even more preferred. When the polymer B is synthesized by a solution polymerization method, the solvent used in the polymerization may be used as it is.

(neutralization)
Some of the acid groups of polymer B are preferably neutralized with a neutralizing agent from the viewpoint of pigment dispersion stability, fixability, and print image quality. When neutralizing, it is preferable to neutralize so that the pH becomes 7 or more and 11 or less.
Examples of neutralizing agents include alkali metal hydroxides and ammonia. Alkali metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide and cesium hydroxide. The neutralizing agent is preferably an alkali metal hydroxide, more preferably sodium hydroxide or potassium hydroxide, from the viewpoints of pigment dispersion stability, fixability, and print image quality. Moreover, the polymer B may be neutralized in advance.
The neutralizing agent is preferably used as an aqueous neutralizing agent solution from the viewpoint of promoting neutralization sufficiently and uniformly. From the same viewpoint as above, the concentration of the neutralizing agent aqueous solution is preferably 3% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 50% by mass or less. Preferably, it is 25% by mass or less.
The use equivalent of the neutralizing agent is preferably 10 mol % or more, more preferably 30 mol % or more, and preferably 80 mol % or less, from the viewpoint of pigment dispersion stability, fixability, and print image quality. It is more preferably 70 mol % or less, still more preferably 60 mol % or less.
Here, the use equivalent of the neutralizing agent can be determined by the following formula. When the use equivalent of the neutralizing agent is 100 mol % or less, it is synonymous with the degree of neutralization. When the use equivalent of the neutralizing agent exceeds 100 mol%, it means that the neutralizing agent is excessive with respect to the acid groups of the polymer B, and the degree of neutralization of the polymer B at this time is 100 mol%. I reckon.
Equivalent weight of neutralizing agent used (% by mole)=[{additional weight of neutralizing agent (g)/equivalent weight of neutralizing agent}/[{acid value of polymer B (mgKOH/g)×mass of polymer B (g) }/(56×1,000)]]×100

(Content of each component in pigment mixture (i))
The content of each component in the pigment mixture (i) is as follows from the viewpoint of the dispersion stability of the pigment, fixability and print image quality.
The content of pigment n in pigment mixture (i) is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 30% by mass or less, more preferably is 25% by mass or less, more preferably 20% by mass or less.
The content of the polymer B in the pigment mixture (i) is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, and preferably 45% by mass or less, more preferably is 30% by mass or less, more preferably 10% by mass or less.
The content of the organic solvent in the pigment mixture (i) is preferably 3% by mass or more, more preferably 7% by mass or more, still more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably is 25% by mass or less, more preferably 20% by mass or less.
The water content in the pigment mixture (i) is preferably 40% by mass or more, more preferably 45% by mass or more, still more preferably 50% by mass or more, and preferably 80% by mass or less, more preferably It is 75% by mass or less.

The mass ratio of pigment n to the total amount of pigment n and polymer B in the pigment mixture (i) [pigment n/(pigment n + polymer B)] is determined from the viewpoint of dispersion stability, fixability, and print image quality of the pigment. , preferably 0.1 or more, more preferably 0.4 or more, still more preferably 0.7 or more, and preferably 0.95 or less, more preferably 0.9 or less, still more preferably 0.85 or less is.

There is no particular limitation on the method of mixing the pigment mixture (i), and generally used mixing and stirring devices such as anchor blades and disper blades can be used. Among them, a high-speed stirring mixer is preferable.
The mixing temperature is preferably 0° C. or higher, and preferably 40° C. or lower, more preferably 30° C. or lower, and even more preferably 25° C. or lower.
The mixing time is preferably 0.5 hours or longer, and preferably 30 hours or shorter, more preferably 10 hours or shorter, even more preferably 5 hours or shorter, and even more preferably 3 hours or shorter.

Examples of means for applying shear stress to the pigment mixture (i) include kneaders such as roll mills and kneaders, high-pressure homogenizers such as Microfluidizer (manufactured by Microfluidic), media-type dispersers such as paint shakers and bead mills. . A plurality of these devices can also be combined. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment.
When 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.
The treatment pressure is preferably 60 MPa or higher, more preferably 100 MPa or higher, still more preferably 150 MPa or higher, and preferably 300 MPa or lower, more preferably 250 MPa or lower, from the viewpoint of productivity and economy.
The number of passes is preferably 3 or more, more preferably 7 or more, and is preferably 30 or less, more preferably 20 or less.

(Step 1-2)
In step 1-2, the organic solvent is removed from the dispersion p obtained in step 1-1 by a known method to obtain an aqueous dispersion P of pigment (n)-containing polymer particles (hereinafter, “dispersion P”). ) is obtained. Through step 1-2, at least a polymer particle dispersion PI containing PR176 and a polymer particle dispersion PII containing a quinacridone pigment are obtained. When pigment A further contains pigments other than PR176 and quinacridone pigments, a dispersion PIII of polymer particles containing further pigments is also obtained.
The organic solvent in the obtained dispersion liquid P is preferably substantially removed, but may remain as long as the object of the present invention is not impaired. The amount of residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less.

The non-volatile component concentration (solid content concentration) of the dispersion liquid P is preferably 10% by mass or more, more preferably 15% by mass or more, from the viewpoint of improving the dispersion stability of the pigment and facilitating the preparation of the water-based ink. Yes, and preferably 30% by mass or less, more preferably 25% by mass or less. The solid content concentration of the dispersion liquid P is measured by the method described in Examples.
The mass ratio of pigment n to the total solid content of dispersion P [pigment n/(total solid content of dispersion P)] is preferably 0.1 from the viewpoint of dispersion stability, fixability, and print image quality of the pigment. Above, it is more preferably 0.4 or more, still more preferably 0.7 or more, and is preferably 0.95 or less, more preferably 0.9 or less, and still more preferably 0.85 or less.
The average particle diameter of the pigment (n)-containing polymer particles in the dispersion liquid P is from the viewpoint of reducing coarse particles and improving the fixability and print image quality, and when used as a water-based pigment dispersion for inkjet printing, the water-based ink From the viewpoint of improving ejection stability, the thickness is preferably 50 nm or more, more preferably 60 nm or more, still more preferably 70 nm or more, and preferably 200 nm or less, more preferably 160 nm or less, still more preferably 150 nm or less.
The average particle diameter of the pigment (n)-containing polymer particles in the dispersion liquid P is measured by the method described in Examples.

(Step 1-3)
Step 1-3 is a step of mixing the dispersions P obtained in step 1-2 with each other to obtain a pigment dispersion. The mixing method in step 1-3 is not particularly limited, and at least the PR176-containing polymer particle dispersion PI and the quinacridone pigment-containing polymer particle dispersion PII are mixed together.
In addition, the pigment dispersion 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 moisturizing agent to prevent drying, and may contain additives such as antifungal agents. You may The additive may be added when the pigment is dispersed, or may be added after the pigment is dispersed.

[Method 2]
Method 2 is a method of dispersing the pigment A with the polymer B, and is preferably carried out by a method including the following steps 2-1 and 2-2.
Step 2-1: A step of dispersing a pigment mixture (ii) containing a polymer B, an organic solvent, a pigment A, and water (hereinafter also referred to as “pigment mixture (ii)”) to obtain a dispersion liquid d. 2-2: A step of removing the organic solvent from the dispersion d obtained in step 2-1 to obtain an aqueous pigment dispersion of polymer particles containing pigment A (pigment (A)-containing polymer particles) step 2- 1 can be dispersed by the same method except that the pigment A is used in place of the pigment n in the above step 1-1. Also, the removal of the organic solvent and the like in step 2-2 are the same as those in step 1-2 described above.

Preferred aspects of the solid content concentration of the pigment dispersion are the same as those of the dispersion P.
The mass ratio of the pigment A to the total solid content of the pigment dispersion [pigment A/(total solid content of the pigment dispersion)] is preferably 0.1 from the viewpoint of the dispersion stability of the pigment, fixability, and print image quality. Above, it is more preferably 0.4 or more, still more preferably 0.7 or more, and is preferably 0.95 or less, more preferably 0.9 or less, and still more preferably 0.85 or less.
The average particle diameter of the pigment (A)-containing polymer particles in the pigment dispersion is from the viewpoint of reducing coarse particles and improving fixability and print image quality, and when used as a water-based pigment dispersion for inkjet printing, the water-based ink From the viewpoint of improving ejection stability, the thickness is preferably 50 nm or more, more preferably 60 nm or more, still more preferably 70 nm or more, and preferably 200 nm or less, more preferably 160 nm or less, still more preferably 150 nm or less.
The average particle size of the pigment (A)-containing polymer particles in the pigment dispersion is measured by the same method as the method for measuring the average particle size of the pigment (n)-containing polymer particles described in Examples.
Moreover, the average particle diameter of the pigment (A)-containing polymer particles in the water-based ink described later is preferably the same as the average particle diameter in the pigment dispersion. The preferable average particle size of the pigment (A)-containing polymer particles in the water-based ink is the same as the preferable average particle size in the pigment dispersion.

[Water-based ink]
The pigment dispersion of the present invention is preferably used for water-based ink (hereinafter also referred to as "water-based ink" or "ink"). As a result, even when printing is performed on a low water-absorbing printing medium, it is possible to obtain a printed matter excellent in fixability and print image quality. The water-based ink preferably contains a pigment dispersion and a water-soluble organic solvent C (hereinafter also referred to as "organic solvent C") from the viewpoint of improving fixability and print image quality. "Water-soluble" in the water-soluble organic solvent C means a property of being miscible with water at any ratio.

(Water-soluble organic solvent C)
The boiling point of the organic solvent C is preferably 150° C. or higher, more preferably 180° C. or higher, and preferably 240° C. or lower, more preferably 230° C. or lower. When two or more organic solvents are used together as the organic solvent C, the boiling point of the organic solvent C is a weighted average value weighted by the content (% by mass) of each organic solvent.
Examples of the organic solvent C include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among them, one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers are preferable. Also, a polyhydric alcohol and a polyhydric alcohol alkyl ether may be used in combination.
When polyhydric alcohols are used, a plurality of alcohols included in the concept of polyhydric alcohols can be mixed and used. Similarly, when polyhydric alcohol alkyl ether is used, it is also possible to mix and use a plurality of substances included in the concept of polyhydric alcohol alkyl ether.

Examples of the polyhydric alcohol include ethylene glycol (boiling point 197° C.), propylene glycol (boiling point 188° C.), dipropylene glycol (boiling point 232° C.), polypropylene glycol, 1,3-propanediol (boiling point 210° C.), 2-methyl -1,3-propanediol (boiling point 214°C), 1,2-butanediol (boiling point 192°C), 1,3-butanediol (boiling point 208°C), 1,4-butanediol (boiling point 230°C), 2 , 3-butanediol (boiling point 180°C), 3-methyl-1,3-butanediol (boiling point 203°C), 1,5-pentanediol (boiling point 242°C), 2-methyl-2,4-pentanediol ( boiling point 196°C), 1,2-hexanediol (boiling point 223°C), 1,2,6-hexanetriol (boiling point 178°C), 1,2,4-butanetriol (boiling point 190°C), 1,2,3 -butanetriol (boiling point 175°C), petriol (boiling point 216°C), and the like. In addition, diethylene glycol (boiling point 244°C), polyethylene glycol, 1,6-hexanediol (boiling point 250°C), triethylene glycol (boiling point 285°C), tripropylene glycol (boiling point 273°C), glycerin (boiling point 290°C), etc. can also be used. When a compound having a boiling point of over 240°C is used, it is preferably used in combination with a compound having a boiling point of less than 240°C.

Examples of the polyhydric alcohol alkyl ethers include alkylene glycol monoalkyl ethers, dialkylene glycol monoalkyl ethers, and trialkylene glycol monoalkyl ethers. Specifically, ethylene glycol monoethyl ether (boiling point 135 ° C.), ethylene glycol monobutyl ether (boiling point 171 ° C.), diethylene glycol monomethyl ether (boiling point 194 ° C.), diethylene glycol monoethyl ether (boiling point 202 ° C.), diethylene glycol monobutyl ether (boiling point 230°C), triethylene glycol monomethyl ether (boiling point 122°C), triethylene glycol monobutyl ether (boiling point 278°C), triethylene glycol monoisobutyl ether (boiling point 160°C), tetraethylene glycol monomethyl ether (boiling point 158°C), propylene Glycol monoethyl ether (boiling point 133°C), dipropylene glycol monomethyl ether (boiling point 190°C), dipropylene glycol monobutyl ether (boiling point 227°C), tripropylene glycol monomethyl ether (boiling point 243°C), tripropylene glycol monobutyl ether (boiling point 276°C) and the like. When a compound having a boiling point of over 240°C is used, it is preferably used in combination with a compound having a boiling point of less than 240°C.

From the viewpoint of fixability and print quality, the organic solvent C more preferably contains a polyhydric alcohol, and more preferably contains an alkanediol having 3 or more and 6 or less carbon atoms.
The content of the polyhydric alcohol in the organic solvent C is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, and preferably 90% by mass or less, more preferably It is 85% by mass or less, more preferably 80% by mass or less.

From the viewpoint of fixability and print quality, the water-based ink may further contain an aqueous dispersion of polymer particles containing no pigment. Aqueous dispersions of polymer particles that do not contain pigments can function as fixing aids.
Polymers constituting the pigment-free polymer particles include condensation resins such as polyurethane resins and polyester resins; acrylic resins, styrene resins, styrene-acrylic resins, butadiene resins, styrene-butadiene resins, and vinyl chloride. vinyl-based resins such as vinyl-based resins, vinyl acetate-based resins, and acrylic silicone-based resins. The pigment-free aqueous dispersion of polymer particles may be appropriately synthesized or commercially available.

Water-based ink is prepared by adding preferably organic solvent C to the above-mentioned pigment dispersion, and if necessary, moisturizing agent, wetting agent, penetrating agent, surfactant, viscosity modifier, and antifoaming agent which are usually used for water-based ink. , an antiseptic, an antifungal agent, an antirust agent, etc. are added, and filtration treatment is performed using a filter or the like. Further, when the pigment dispersion is obtained by Method 1, the water-based ink may be obtained by blending the water-based dispersion liquid P of each pigment n contained in the pigment A.
The content of each component of the water-based ink and the physical properties of the ink are as follows.

(Content of pigment A)
The content of Pigment A in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, and still more preferably 3% by mass or more, from the viewpoint of printing density. It is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 7% by mass or less, from the viewpoint of improving fixability and print image quality.
The preferred range of the mass ratio [PR176/quinacridone pigment] between PR176 and the quinacridone pigment in the water-based ink is the same as the preferred range of the above-described water-based pigment dispersion.

(Total content of pigment A and polymer B)
The total content of pigment A and polymer B in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, and still more preferably 4% by mass or more, from the viewpoint of fixability and print quality. The content is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

(Content of water-soluble organic solvent C)
The content of the organic solvent C in the water-based ink is preferably 10% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass or more, from the viewpoint of fixability and print quality. It is 48% by mass or less, more preferably 45% by mass or less, and even more preferably 43% by mass or less.

(water content)
The water content in the water-based ink is preferably 40% by mass or more, more preferably 45% by mass or more, still more preferably 50% by mass or more, and preferably 80% by mass, from the viewpoint of fixability and print quality. % or less, more preferably 70 mass % or less, and still more preferably 60 mass % or less.

(mass ratio [pigment A/(total solid content of water-based ink)])
The mass ratio of pigment A to the total solid content of water-based ink [pigment A/(total solid content of water-based ink)] is preferably 0.1 or more, more preferably 0.4 or more, from the viewpoint of fixability and print quality. , more preferably 0.6 or more, and preferably 0.95 or less, more preferably 0.9 or less, and still more preferably 0.85 or less.

(Physical properties 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, from the viewpoint of fixability and print quality. Below, more preferably 9 mPa·s or less, still more preferably 7 mPa·s or less. The viscosity of water-based ink can be measured using an E-type viscometer.
The pH of the water-based ink at 20° C. is preferably 7.0 or higher, more preferably 7.2 or higher, and even more preferably 7.5 or higher, from the viewpoint of the dispersion stability of the pigment. Also, from the viewpoint of member resistance and skin irritation, the pH is preferably 11 or less, more preferably 10 or less, and even more preferably 9.5 or less. The pH of water-based ink at 20° C. can be measured by the method described in Examples.

[Inkjet printing method]
Water-based inks can be suitably used as flexographic printing inks, gravure printing inks, or inkjet printing inks, and are particularly preferably used as inkjet printing inks. As a printing method using water-based ink, a method of loading water-based ink into a known inkjet recording apparatus and forming an image on a printing medium by an inkjet recording method is preferable. There are thermal type and piezo type ink jet recording devices, and the piezo type is preferable from the viewpoint of fixability and print quality.

(print media)
Usable print media include plain paper, coated paper, and resin film. Examples of coated paper include general-purpose glossy paper, multicolor foam gloss paper, and the like. The resin film is preferably at least one selected from polyester film, polyvinyl chloride film, polypropylene film and polyethylene film. A corona-treated substrate may be used for the resin film.
Examples of commonly available resin films include Lumirror T60 (manufactured by Toray Industries, Inc., polyester), PVC80BP (manufactured by Lintec Corporation, vinyl chloride), DGS-210WH (manufactured by Roland DG Co., Ltd., vinyl chloride), and transparent. PVC RE-137 (manufactured by Mimaki Engineering Co., Ltd., vinyl chloride), Cainus KEE70CA (manufactured by Lintec Corporation, polyethylene), YUPO SG90 PAT1 (manufactured by Lintec Corporation, polypropylene), FOR, FOA (both manufactured by Futamura Chemical Co., Ltd., Polypropylene), Bonyl RX (manufactured by Kohjin Film & Chemicals Co., Ltd., nylon), Emblem ONBC (manufactured by Unitika Ltd., nylon), and the like.

The print medium is preferably a low water absorption print medium from the viewpoint of fixability and print quality.
The water absorption amount of the low-absorbent printing medium at a contact time of 100 ms with pure water is preferably 1 g/m ² or more, more preferably 2 g/m ² or more, from the viewpoint of fixability and print image quality. is 8 g/m ² or less, more preferably 6 g/m ² or less. The water absorption can be measured by the method described in Examples using an automatic scanning liquid absorber.

The inkjet printing method preferably includes a step of discharging ink droplets onto a printing medium for printing by an inkjet recording method, and then drying the ink droplets that have landed on the printing medium.
In the drying step, the surface temperature of the print medium is preferably 25° C. or higher, more preferably 30° C. or higher, and still more preferably 50° C. or higher, from the viewpoint of improving print image quality, and suppresses deformation of the print medium due to heat. and energy reduction, the temperature is preferably 100° C. or lower, more preferably 85° C. or lower, and even more preferably 70° C. or lower.

[Ink set]
The water-based ink is preferably used for the magenta ink of an ink set comprising two or more inks including at least magenta ink. As a result, it is possible to obtain a printed material having excellent fixability and print image quality. When the water-based ink is used as magenta ink, the hue of pigment A is magenta.
The print may be multi-color. As a method for obtaining a multicolor print, there is a method of forming an image by superimposing two or more different hue ink dots on a printing medium, and two or more different hue ink dots are deposited in parallel. and a method of forming an image by pressing the ink.
The ink set may be any of a 2-color ink set, a 3-color ink set, a 4-color ink set, a 5-color ink set, a 6-color ink set, and a 7-color ink set or more, but it is a subtractive color mixture of three primary colors. Magenta ink, yellow ink, and cyan ink are included, and the magenta ink is preferably the water-based ink. A secondary color image can be formed by combining the magenta ink with at least one selected from yellow ink and cyan ink. For example, a combination of magenta ink and yellow ink can form a red secondary color image. A combination of magenta and cyan inks can form a blue secondary color image. It is also possible to form a black image with composite black in which magenta ink, yellow ink, and cyan ink are superimposed.

The yellow ink and cyan ink used in the ink set are not particularly limited as long as they use known pigments. As the pigment Y used in the yellow ink, for example, C.I. I. Pigment Yellow (hereinafter also referred to as "PY") 74, PY150, PY151, PY155 and the like. Pigment C used for cyan ink includes, for example, C.I. I. Pigment Blue (hereinafter also referred to as “PB”) 15:3, PB 15:4 and the like. These pigments are preferably dispersed in a water-based medium with a polymer B similar to the pigment A.

In the ink set, when obtaining red prints, for example, the mass ratio [pigment A/pigment Y] of pigment A and pigment Y contained in magenta ink and yellow ink is preferably 10 from the viewpoint of fixability and print quality. /90 or more, more preferably 25/75 or more, still more preferably 40/60 or more, and preferably 90/10 or less, more preferably 75/25 or less, still more preferably 60/40 or less.
In the ink set, when obtaining blue prints, for example, the mass ratio [pigment A/pigment C] of pigment A and pigment C contained in magenta ink and cyan ink is preferably 10 from the viewpoint of fixability and print quality. /90 or more, more preferably 30/70 or more, still more preferably 50/50 or more, and preferably 90/10 or less, more preferably 80/20 or less, still more preferably 70/30 or less.

In the following Preparation Examples, Production Examples, Examples and Comparative Examples, "parts" and "%" are "mass parts" and "mass%" unless otherwise specified.

(1) Measurement of number average molecular weight N, N-dimethylformamide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., for high-performance liquid chromatography), phosphoric acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., reagent special grade) and lithium bromide (manufactured by Tokyo Kasei Kogyo Co., Ltd., reagent) was dissolved to a concentration of 60 mmol / L and 50 mmol / L, respectively, as an eluent, gel permeation chromatography [Tosoh Corporation GPC device (HLC-8120GPC) , column manufactured by Tosoh Corporation (TSK-GEL, α-M×2), flow rate: 1 mL/min] using monodisperse polystyrene with a known molecular weight as a standard substance.

(2) Measurement of Average Particle Diameter of Pigment (n)-Containing Polymer Particles Measurement was performed by performing cumulant analysis using a laser particle analysis system "ELSZ-1000" (manufactured by Otsuka Electronics Co., Ltd.). A dispersion diluted with water was used so that the concentration of the particles to be measured was 5×10 ^-3 % (converted to solid concentration). The measurement conditions were a temperature of 25° C., an angle between the incident light and the detector of 165°, and 100 integration times, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The resulting cumulant average particle size was used as the average particle size of the pigment (n)-containing polymer particles contained in the dispersion P.

(3) Measurement of Solid Content Concentration 10.0 g of sodium sulfate that has been made constant in a desiccator is weighed into a 30 ml polypropylene container (φ = 40 mm, height = 30 mm), and about 1.0 g of a sample is added thereto. , After mixing, accurately weighed, maintained in an environment of 105 ° C., -0.08 MPa (gauge pressure) for 2 hours to remove volatile matter, and further left in a desiccator for 15 minutes. was measured. The mass of the sample after removing the volatile matter was defined as the solid content, and the mass of the added sample was divided to obtain the solid content concentration.

(4) Measurement of pH Using a desktop pH meter "F-71" (manufactured by Horiba, Ltd.) using a pH electrode "6337-10D" (manufactured by Horiba, Ltd.), pH was measured at 20°C. .

(5) Water absorption amount of the print medium at a contact time of 100 msec between the print medium and pure water Using an automatic scanning liquid absorption meter "KM500win" (manufactured by Kumagai Riki Kogyo Co., Ltd.), conditions of 23 ° C. and 50% relative humidity Below, the amount of transfer at a pure water contact time of 100 msec was measured and taken as the water absorption amount at 100 msec. Measurement conditions are shown below.
"Spiral Method"
Contact Time (seconds): 0.010 to 1.0
Pitch (mm): 7
Length Per Sampling (degree): 86.29
Start Radius (mm): 20
End Radius (mm): 60
Min Contact Time (ms): 10
Max Cintact Time (ms): 1,000
Sampling Pattern (1 to 50): 50
Number of Sampling Points (>0): 19
"Square Head"
Slit Span (mm): 1
Slit Width (mm): 5

<Preparation of polymer B>
Preparation example 1
Raw material monomer 1 was prepared by mixing 61.5 parts of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., reagent) and 138.5 parts of benzyl acrylate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., reagent). In a reaction vessel, 30 parts of methyl ethyl ketone (hereinafter also referred to as "MEK"), 0.3 parts of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the raw material monomer 1 are added and mixed, and the nitrogen gas is sufficiently replaced. went to
On the other hand, in the dropping funnel, the remainder of the raw material monomer 1, 0.27 parts of the polymerization chain transfer agent, 60 parts of MEK, and an azo radical polymerization initiator (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., trade name: V-65, 2 ,2′-azobis(2,4-dimethylvaleronitrile)) 2.2 parts mixed solution is added, and under a nitrogen atmosphere, the raw material monomer 1 in the reaction vessel is heated to 65° C. while stirring, and the temperature is increased to 65° C. in a dropping funnel. was added dropwise over 3 hours. After 2 hours at 65 ° C. from the end of dropping, a solution of 0.3 parts of the polymerization initiator dissolved in 5 parts of MEK was added, and further aged at 65 ° C. for 2 hours and at 70 ° C. for 2 hours. A solution of B1) (number average molecular weight: 14,000, acid value: 240 mgKOH/g) was obtained.

Preparation example 2
A polymer (B2) solution was obtained in the same manner as in Preparation Example 1, except that the proportions of raw material monomers of acrylic acid and benzyl acrylate were changed as shown in Table 1. Table 1 shows the results.

<Production of dispersion liquid P>
Production example 1
25 parts of polymer (B1) obtained by drying the solution of polymer (B1) obtained in Preparation Example 1 under reduced pressure was mixed with 78.6 parts of MEK, and further 5N sodium hydroxide aqueous solution (concentration 16.9%, Fuji Film Wako Pure Chemical Co., Ltd., for volumetric titration) was added and neutralized so that the ratio of the number of moles of sodium hydroxide to the number of moles of carboxy groups in the polymer (B1) was 50% (medium concentration of 50 mol%). Furthermore, 400 parts of ion-exchanged water is added, 100 parts of pigment (C.I. Pigment Red 176, manufactured by Clariant Chemicals Co., Ltd., trade name: Novoperm Carmine HF3C) is added, and Disper (manufactured by Asada Iron Works Co., Ltd., commercial product) is added. A pigment mixture (i-1) was obtained by stirring for 60 minutes at 20° C. under the conditions of rotating the disper blade at 7,000 rpm.
The resulting pigment mixture (i-1) was subjected to 10 passes of dispersion treatment with a Microfluidizer (manufactured by Microfluidics, trade name) at a pressure of 200 MPa. After adding 250 parts of ion-exchanged water to the resulting dispersion p1 and stirring, the MEK was completely removed at 60° C. under reduced pressure, a part of the water was further removed, and a 5 μm filter (acetylcellulose membrane, outer Diameter: 2.5 cm, manufactured by Fuji Film Co., Ltd.) was filtered with a 25 mL needleless syringe (manufactured by Terumo Corporation) to remove coarse particles, thereby obtaining a dispersion PI- with a solid content concentration of 20%. got 1. The dispersion PI-1 was measured for the pH and the average particle size of the pigment (PR176)-containing polymer particles. Table 2 shows the results.

Production example 2
Except that in Production Example 1, instead of the solution of polymer (B1) obtained in Preparation Example 1, the solution of polymer (B2) obtained in Preparation Example 2 was dried under reduced pressure to obtain polymer (B2). obtained a dispersion PI-2 in the same manner as in Production Example 1. Dispersion PI-2 was measured for pH and average particle size of pigment (PR176)-containing polymer particles. Table 2 shows the results.

Production Examples 3-7 and Comparative Production Examples 1-3
Dispersions PII-1 to PII-3, PY-1, PC-1, and PI'-1 to PI'- were prepared in the same manner as in Production Example 1 except that the pigments shown in Table 2 were used in Production Example 1. got 3. The pH of these dispersions and the average particle size of the pigment (n)-containing polymer particles were measured. Table 2 shows the results.

Details of each pigment in Table 2 are as follows.
PR176: Novoperm Carmine HF3C (manufactured by Clariant Chemicals Co., Ltd.)
PR122/PV19: Inkjet Magenta E-02 (manufactured by Clariant Chemicals Co., Ltd., solid solution of PR122/PV19)
PR282: Cinquasia Magenta L 4400 (manufactured by BASF)
PV19/PR202: Cinquasia Magenta D 4500 J (manufactured by BASF, solid solution of PV19/PR202)
PY74: Fast Yellow 7423 (manufactured by Sanyo Pigment Co., Ltd.)
PB15: 3: FASTOGEN BLUE TGR-SD (manufactured by DIC Corporation)
PR150: FUJI FAST CARMIME 522-1D (manufactured by Fuji Pigment Co., Ltd.)
PR146: FUJI FAST CARMIME 550 (manufactured by Fuji Pigment Co., Ltd.)
PR269: Toner Magenta F8B (manufactured by Clariant Chemicals Co., Ltd.)

<Production of water-based pigment dispersion>
Example 1-1
Dispersion PI-1 obtained above (solid content concentration 20%) 3.1 parts (pigment 0.5 parts) and dispersion liquid PII-1 (solid content concentration 20%) 28.1 parts (pigment 4.1 parts) 5 parts) were mixed to obtain a pigment dispersion I-1.

Examples 1-2 to 1-3, 1-5 to 1-7, Comparative Examples 1-1 to 1-5 , Reference Example 1-4
Pigment Dispersions I-2 to I-7 and IC-1 to IC-5 were prepared in the same manner as in Example 1-1, except that the composition of Example 1-1 was as shown in Table 3. Obtained.

<Water-based ink and its evaluation>
Example 2-1
(manufacture of ink)
Pigment Dispersion I-1 obtained in Example 1-1, 30 parts of 1,3-propanediol (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), triethylene glycol monobutyl ether (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd. ) and 0.5 part of an acetylenic surfactant Surfynol 440 (manufactured by Evonik Industries) were added, and ion-exchanged water was added to weigh the total amount to 100 parts. Stir with a magnetic stirrer to mix well, filter with a 25 mL needleless syringe fitted with a 1.2 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Corporation) to remove the ink. Obtained.

(Preparation of printed matter by inkjet printing method)
The ink obtained above is filled into the head of a piezo inkjet printer (manufactured by Seiko Epson Corporation, model number: EM-930C), coated paper (manufactured by Oji Paper Co., Ltd., product name: OK Topcoat +, contact time Water absorption in 100 msec: 4.9 g/m ² ), and a solid image was printed (printing conditions = paper type: plain paper, mode setting: fine). After drying for 10 minutes in a drier at 60° C., the printed material was prepared by allowing it to stand still for one day in an environmental room with a room temperature of 25° C. and a relative humidity of 50%.

Examples 2-2 to 2-3, 2-5 to 2-9, Comparative Examples 2-1 to 2-5 , Reference Example 2-4
In Example 2-1, except that the composition shown in Table 4 was used, the same operation as in Example 2-1 was performed to obtain each ink and each printed matter.

[Evaluation of fixability]
Plain paper (manufactured by XEROX, trade name: XEROX 4200) was attached to the bottom surface (1 inch×1 inch) of a weight made of stainless steel weighing 460 g with double-sided tape.
Next, a weight with plain paper attached is placed on the printed surface of the printed material obtained by the above method so that the printed surface and the plain paper attached to the bottom surface of the weight are in contact with each other. It was rubbed back and forth 10 times in a width of 4 inches. Thereafter, the optical density of the plain paper attached to the bottom surface of the weight was measured at any five locations using a spectrophotometer (manufactured by Gretag Macbeth, model number: SpectroEye) (measurement conditions = observation light source: D65, observation field : 2 times, density standard: DIN), and the average value was obtained. The lower the average optical density, the better the fixability. If the average value of the optical density is 0.05 or less, sufficient fixability can be obtained and it can be put to practical use.

[Evaluation of chroma (C ^* )]
A spectrophotometer (manufactured by Gretag Macbeth, model number: SpectroEye) was set to measurement mode L ^* a ^* b ^* for the printed matter obtained by the above method (measurement conditions = observation light source: D65, observation field: 2 degrees ), the a ^* value and b ^* value were measured at five arbitrary points, and the average value was obtained. From the average value, the saturation was obtained by the following formula.
Saturation is a measure of the degree of vividness of a color, expressed as the distance from an achromatic color of equal brightness. Here, chroma is represented by the L ^* a ^* b ^* color system (where L ^* is lightness, a ^* is chromaticity in the red-green direction, and b ^* is yellow-blue direction), as shown by the following formula. ), and is expressed by the distance from the center (position where both a ^* b ^* are 0: achromatic color). The higher the saturation value, the better the print quality.
Saturation (C ^* ) = [(a ^* ) ² + (b ^* ) ² ] ^1/2

From Table 4, it can be seen that the inks of Examples give prints with excellent fixability and print quality. On the other hand, since the inks of the comparative examples did not use PR176 and quinacridone pigment in combination, they were inferior to the inks of the examples in either fixability or print quality, or both of them. I understand.

<Ink set and its evaluation>
Example 3-1, Comparative Examples 3-1 to 3-2
(Preparation of ink set)
In Example 2-1, an ink set was obtained by combining the yellow ink, cyan ink, and magenta ink obtained by performing the same operation as in Example 2-1, except that the composition shown in Table 5 was used.

(Preparation of ink set printed matter)
The ink set obtained by the above method was filled in the head of a piezo inkjet printer (manufactured by Seiko Epson Corporation, model number: EM-930C). A color chart image was printed on coated paper (manufactured by Oji Paper Co., Ltd., product name: OK Topcoat+, water absorption at 100 msec contact time: 4.9 g/m ² ) (printing conditions = paper type: plain paper, mode setting: fine). After drying for 10 minutes in a drier at 60° C., it was allowed to stand still for one day in an environment room with a room temperature of 25° C. and a relative humidity of 50% to prepare an ink set printed matter.

[Evaluation of Secondary Color Fixability]
The fixability of the red printed surface (secondary colors of magenta and yellow) and the blue printed surface (secondary colors of magenta and cyan) of the ink set printed matter obtained by the above method was evaluated according to the following evaluation criteria.
Plain paper (manufactured by XEROX, trade name: XEROX 4200) was attached to the bottom surface (1 inch×1 inch) of a weight made of stainless steel weighing 460 g with double-sided tape. Next, a weight with plain paper attached is placed on the printed surface of the secondary color print obtained by the above method so that the printed surface and the plain paper attached to the bottom surface of the weight are in contact with each other, and a solid image is obtained. The image was rubbed back and forth 10 times in a width of 4 inches. The fixability of the secondary color after rubbing was visually evaluated according to the following evaluation criteria.
(Evaluation criteria)
A: The printed surface is not peeled off and the periphery of the printed surface is not stained.
B: The printed surface was slightly peeled, and the periphery of the printed surface was slightly soiled.
C: The printed surface is peeled off, and the area around the printed surface is stained.

[Evaluation of print quality of ink set printed matter]
For the hue of the ink set printed matter obtained by the above method, L ^* a ^* b ^* is measured using a spectrophotometer (manufactured by Gretag Macbeth, model number: SpectroEye), and is defined by Japan Color 2007 for sheet-fed printing. The print image quality was evaluated according to the following evaluation criteria.
(Evaluation criteria)
A: Color reproduction area equivalent to Japan color.
B: The color reproduction area is slightly less than Japan color.
C: The color reproduction area is less than Japan color.

From Table 5, it can be seen that the ink set of Example 3-1 yields prints with excellent secondary color fixability and print image quality. On the other hand, it can be seen that Comparative Example 3-1, in which only the quinacridone pigment was used as the magenta ink pigment, is inferior to Example 3-1 in both the fixability of the secondary color and the print image quality. Also, in Comparative Example 3-2 using only PR176 as a magenta ink pigment, the fixability of the secondary color was equivalent to that of Example 3-1, but the print image quality was inferior to that of Example 3-1. I understand.

The water-based pigment dispersion of the present invention can be suitably used as a water-based pigment dispersion for flexographic printing ink, gravure printing ink, or inkjet printing ink, since printed matter having excellent fixability and print quality can be obtained.

Claims (8)

An aqueous pigment dispersion in which a pigment A is dispersed in an aqueous medium with a polymer B,
The pigment A is C.I. I. Contains Pigment Red 176 and quinacridone pigments ,
C. I. Pigment Red 176 and the quinacridone pigment mass ratio [C.I. I. Pigment Red 176/quinacridone pigment] is 10/90 or more and 50/50 or less,
An aqueous pigment dispersion , wherein the polymer B contains a structural unit derived from a monomer (b-1) having an acid group, and the acid value of the polymer B is 50 mgKOH/g or more and 300 mgKOH/g or less . 2. The quinacridone pigment of claim 1 , wherein the quinacridone pigment is a solid solution pigment, and the solid solution pigment is a combination of unsubstituted quinacridone and 2,9-dimethylquinacridone or a combination of unsubstituted quinacridone and 2,9-dichloroquinacridone . Water-based pigment dispersion. Polymer B is a vinyl resin containing a structural unit derived from the monomer (b-1) having an acid group and a structural unit derived from the hydrophobic monomer (b-2), the aqueous system according to claim 1 or 2 Pigment Dispersion. The water-based pigment dispersion according to any one of claims 1 to 3, wherein the number average molecular weight of polymer B is 5,000 or more and 20,000 or less . A water-based ink containing the water-based pigment dispersion according to any one of claims 1 to 4 and a water-soluble organic solvent C. 6. The water-based ink according to claim 5, wherein the water-soluble organic solvent C contains an alkanediol having 3 or more and 6 or less carbon atoms. An inkjet printing method, wherein an image is formed on a low water-absorbing printing medium by an inkjet recording method using the water-based ink according to claim 5 or 6. An ink set containing at least magenta ink, yellow ink, and cyan ink,
An ink set, wherein the magenta ink is the water-based ink according to claim 5 or 6.