JP6822637B2 - Aqueous pigment dispersion for inkjet recording - Google Patents

Description

The present invention relates to a water-based pigment dispersion for inkjet recording, a water-based ink for inkjet recording, and a method for producing the water-based ink.

An ink using a pigment is known as a water-based ink for inkjet recording. Inks using pigments can be expected to have excellent water resistance and light resistance, but there is a problem of clogging of the ejection nozzle due to aggregation and sedimentation of pigments. In order to solve this, a method of dispersing the pigment in an aqueous medium using a polymer dispersant has been performed, but it is difficult to stably disperse the pigment over a long period of time with the polymer dispersant alone, and the pigment is more long-term. A water-based pigment-dispersed inkjet recording ink having storage stability is desired.

In particular, in water-based pigment dispersions and water-based inks using a yellow pigment as a coloring material, there is a high demand for hue and transparency in terms of the width of the color gamut during full-color printing and the hue when mixed with other colors.
Since it is difficult for inorganic yellow pigments to meet these demands, it is a water-based ink that uses organic yellow pigments, and is used for inkjet recording that has little fluctuation in physical properties that affect ejection properties and can satisfy high print quality. The development of water-based inks is expected.

For example, Patent Document 1 contains a yellow azo pigment, a styrene resin, and an alkali metal hydroxide as a yellow aqueous pigment dispersion liquid suitable for an inkjet recording ink having excellent dispersion stability, and a styrene resin is used. Disperses water-based pigment dispersions for inkjet recording, which have a styrene-based monomer unit of 60% by mass or more and an unsaturated aliphatic carboxylic acid monomer unit of 10 to 40% by mass and have a specific weight average molecular weight.
Patent Document 2 describes a bisacetoacetalilide pigment as a yellow aqueous pigment dispersion liquid suitable for ink for inkjet recording, which can be dispersed in an extremely fine particle size, has excellent dispersion stability, and has little precipitation even with low viscosity. A pigment composition obtained by kneading a mixture containing a styrene-acrylic acid-based copolymer having a specific acid value, a basic compound, a wetting agent and a specific kneading aid is disclosed.

Japanese Unexamined Patent Publication No. 2005-60419 International Publication No. 2011/34043

However, in the technique of Patent Document 1, the particle size of the pigment particles is as large as 150 nm or more, and further atomization is required in order to obtain good print quality. Further, in the technique of Patent Document 2, a process of dropping high energy called kneading is indispensable.
As described above, in the water-based pigment dispersion liquid and the water-based ink for inkjet recording using the organic yellow pigment as a coloring material, a technique for satisfying the required performance by a simple method has not been established.
In the aqueous pigment dispersion for inkjet recording using Pigment Yellow 74 dispersed with a polymer dispersant, there are no problems with the particle size of the particles in the pigment dispersion, the inkjet ejection property, and the glossiness of the obtained image. Nevertheless, when other yellow azo pigments are used, even if they are dispersed with the same polymer dispersant, the particle size of the particles in the obtained pigment dispersion liquid becomes large, and the inkjet ejection property and the glossiness of the obtained image are improved. It was sometimes inferior.
According to the present invention, even if a yellow azo pigment is used, the particle size of the particles in the pigment dispersion is small, and the water-based pigment dispersion for inkjet recording, which has excellent storage stability, and the aqueous pigment dispersion are included in the ejection property. It is an object of the present invention to provide a water-based ink for inkjet recording capable of obtaining a recorded material having excellent and excellent gloss, and a method for producing the water-based ink.

The present inventors are an aqueous pigment dispersion containing a yellow azo pigment, an aromatic group-containing polymer, and an alkali metal hydroxide, wherein the aromatic group-containing polymer has a specific acid value. A water-based pigment dispersion for inkjet recording, which is crosslinked with a specific polyfunctional epoxy compound and whose acid value, neutralization degree, and crosslinkability of the water-insoluble polymer satisfy specific conditions, can solve the above problems. I found it.

That is, the present invention provides the following [1] to [3].
[1] An aqueous pigment dispersion for inkjet recording containing a yellow azo pigment (A), an aromatic group-containing polymer (B), and an alkali metal hydroxide (C).
The aromatic group-containing polymer (B) is formed by cross-linking the aromatic group-containing water-insoluble polymer (a) having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound (b).
An aqueous pigment dispersion for inkjet recording in which the acid value, the degree of neutralization, and the degree of cross-linking of the water-insoluble polymer (a) satisfy the following condition 1.
Condition 1: The value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of the water-insoluble polymer (a)) is −30 mgKOH / g or more and 130 mgKOH / g or less.
Here, the degree of neutralization is a percentage (mol%) of "molar equivalent of alkali metal hydroxide (C) / molar equivalent of carboxy group of water-insoluble polymer (a)", and the degree of cross-linking is "water-insoluble polyfunctionality". The molar equivalent of the epoxy group of the epoxy compound (b) / the molar equivalent of the carboxy group of the water-insoluble polymer (a) ”is a percentage (mol%).
[2] A water-based ink for inkjet recording containing the aqueous pigment dispersion for inkjet recording as the main component according to the above [1].

[3] A method for producing a water-based ink for inkjet recording, which comprises the following steps 1 to 4 and in which the aromatic group-containing water-insoluble polymer (a) in step 1 satisfies the following condition 1.
Step 1: A yellow azo pigment (A), an aromatic group-containing water-insoluble polymer (a) having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less, an alkali metal hydroxide (C), an organic solvent, and water. Step 2: Obtaining a pigment dispersion liquid by dispersing the contained mixture Step 2: Removing the organic solvent from the pigment dispersion obtained in Step 1 to obtain a pigment aqueous dispersion A Step 3: Obtaining in Step 2. The pigment aqueous dispersion A was crosslinked with a water-insoluble polyfunctional epoxy compound (b), and the crosslinked aromatic group-containing polymer (B) contained a yellow azo pigment (A). Step 4: Step 4: Mix the pigment aqueous dispersion B obtained in Step 3 with an organic solvent to obtain a water-based ink Condition 1: [(100-neutralization-crosslinking) / 100] × ( The value of the water-insoluble polymer (a) (acid value) is −30 mgKOH / g or more and 130 mgKOH / g or less.
Here, the degree of neutralization and the degree of cross-linking are as described above.

According to the present invention, even if a yellow azo pigment is used, a discharge containing an aqueous pigment dispersion for inkjet recording, which has a small particle size of particles in the pigment dispersion and excellent storage stability, and the aqueous pigment dispersion. It is possible to provide a water-based ink for inkjet recording capable of obtaining a recorded material having excellent properties and excellent gloss, and a method for producing the water-based ink.

[Aqueous pigment dispersion for inkjet recording]
The aqueous pigment dispersion for inkjet recording of the present invention is an aqueous pigment dispersion for inkjet recording containing a yellow azo pigment (A), an aromatic group-containing polymer (B), and an alkali metal hydroxide (C). hand,
The aromatic group-containing polymer (B) is formed by cross-linking the aromatic group-containing water-insoluble polymer (a) having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound (b).
An aqueous pigment dispersion for inkjet recording in which the acid value, the degree of neutralization, and the degree of cross-linking of the water-insoluble polymer (a) satisfy the following condition 1.
Condition 1: The value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of the water-insoluble polymer (a)) is −30 mgKOH / g or more and 130 mgKOH / g or less.
Here, the degree of neutralization and the degree of cross-linking are as described above.
The "recording" is a concept including printing and printing for recording characters and images, and the "recorded matter" is a concept including printed matter and printed matter on which characters and images are recorded.
Further, "water-based" means that water occupies the largest proportion in the medium for dispersing the pigment.

The aqueous pigment dispersion for inkjet recording of the present invention has a small particle size of particles in the pigment dispersion and is excellent in storage stability even when a yellow azo pigment is used, and is for inkjet recording containing the aqueous pigment dispersion. The water-based ink can give a recorded material having excellent ejection properties and excellent glossiness. The reason is not clear, but it can be considered as follows.
Since the aromatic group-containing polymer (B) used in the present invention is a polymer dispersant obtained by cross-linking the aromatic group-containing water-insoluble polymer (a) with the water-insoluble polyfunctional epoxy compound (b), the polymer is dispersed. Since the agent is adsorbed on the surface of the azo pigment by the aromatic group and the polymer dispersant is crosslinked, once the polymer dispersant is adsorbed on the yellow azo pigment (A), it is difficult to desorb and the dispersibility of the pigment particles becomes high. It is considered that this is improved, the particle size of the pigment particles is reduced, and the storage stability of the obtained aqueous pigment dispersion liquid and the aqueous ink using the same is improved. Further, since the water-insoluble polyfunctional epoxy compound (b) exists near the surface of the yellow azo pigment (A) and the cross-linking reaction proceeds to reduce the water solubility of the polymer dispersant, a water-soluble cross-linking agent is used. It is considered that the obtained aromatic group-containing polymer (B) is less likely to be desorbed from the pigment (C) than when it is used, and the storage stability is excellent even when an aqueous ink containing an ink vehicle such as an organic solvent is stored.
Further, at least a part of the insoluble polymer (a) having a relatively high acid value constituting the aromatic group-containing polymer (B) is neutralized with the alkali metal hydroxide (C) in a specific amount range. , Strong charge repulsion is obtained, and it is considered that the ejection property is excellent.
Further, it is considered that a recorded material having excellent glossiness can be obtained because the strong charge repulsion makes it difficult to aggregate on the paper surface.

<Yellow azo pigment (A)>
The yellow azo pigment (A) used in the present invention (hereinafter, also referred to as "pigment (A)") has an azo structure (N = N) in the molecule and a hydrazone structure (= N-) which is a tautomer thereof. It is a general term for yellow pigments containing either or both of NH-).
Examples of the yellow azo pigment (A) include (a) an azo lake pigment and (b) an insoluble azo pigment.
Examples of (a) azolake pigments include acetoacetic acid allylide pigments, and more specifically, C.I. I. Pigment Yellow 133, 168, 169 and the like.
Examples of the (b) insoluble azo pigments include (i) acetoacetic acid allylide-based monoazo pigments, (ii) acetoacetic acid allylide-based disazo pigments, (iii) pyrazolone pigments, (iv) condensed disazo pigments, and (v) metal complexes. Pigments and the like can be mentioned.
(I) Examples of the acetoacetic acid allylide-based monoazo pigment include Hanseatic pigments and benzimidazolone-based pigments. Specifically, as the Hanseatic pigment, C.I. I. Pigment Yellow 1,2,3,5,6,49,63,65,73,74,75,87,90,97,98,106,111,114,116,121,124,126,127,130 , 136, 152, 165, 167, 170, 174, 176, 188 and the like, and examples of the benzimidazolone pigment include C.I. I. Pigment Yellow 120, 151,154,156,175,180,181,194 and the like.
(Ii) Examples of the acetoacetic acid allylide-based disazo pigment include C.I. I. Pigment Yellow 12, 13, 14, 17, 55, 81, 83, 113, 171, 172, 214 and the like.
(Iii) Examples of pyrazolone pigments include C.I. I. Pigment Yellow 10, 60 and the like.
(Iv) Examples of condensed disuazo pigments include C.I. I. Pigment Yellow 93, 94, 95, 128, 155, 166 and the like.
(V) Metal complex pigments include C.I. I. Pigment Yellow 117, 129, 150, 153 and the like.

The above-mentioned yellow azo pigment can be used alone or as a mixture of two or more kinds or a solid solution. The pigment may be a powdery, granular or lumpy dry pigment, or may be a wet cake or a slurry.
Among the above yellow azo pigments, from the viewpoint of fully exerting the effects of the present invention, (b) insoluble azo pigments are preferable, (i) acetoacetic acid allylide monoazo pigments, and (iv) condensation One or more selected from disazo pigments and (v) metal complex pigments, more preferably C.I. I. Pigment Yellow 128, C.I. I. Pigment Yellow 155, C.I. I. Pigment Yellow 150, and C.I. I. One or more selected from Pigment Yellow 180. Among these, from the viewpoint of glossiness of the recorded material, C.I. I. Pigment Yellow 128, C.I. I. Pigment Yellow 150, and C.I. I. One or more selected from Pigment Yellow 155 is preferable. Among these, from the viewpoint of ink ejection property, C.I. I. Pigment Yellow 150, C.I. I. Pigment Yellow 155, and C.I. I. One or more selected from Pigment Yellow 180 is preferable. Further, from the viewpoints of storage stability, glossiness of recorded matter, and ejection property of water-based ink, C.I. I. Pigment Yellow 150 and C.I. I. One or more selected from Pigment Yellow 155 is more preferable, and C.I. I. Pigment Yellow 150 is even more preferred.
Further, as long as the object of the present invention is not impaired, a yellow pigment known or commonly used for inkjet recording can be used, if necessary.

In the present invention, the pigment (A) is a pigment dispersed in an aqueous pigment dispersion and an aqueous ink with an aromatic group-containing polymer (B), or an aromatic group-containing polymer (B) containing a pigment, that is, It is contained in the form of pigment-containing aromatic group-containing polymer (B) particles.
The pigment (A) contains an aromatic group containing the pigment (A) from the viewpoint of suppressing solidification of the pigment or polymer in the ink ejection nozzle and further improving storage stability and glossiness while maintaining water resistance. It is preferably contained as polymer (B) particles (hereinafter, also simply referred to as “pigment-containing polymer particles”).
In this preferred embodiment, the aqueous pigment dispersion and the aqueous ink contain pigment-containing polymer particles, an organic solvent and water.

<Aromatic group-containing polymer (B)>
The aqueous pigment dispersion for inkjet recording of the present invention contains an aromatic group-containing polymer (B) as a polymer dispersant.
The aromatic group-containing polymer (B) is a water-insoluble polymer (a) having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less (hereinafter, also simply referred to as “water-insoluble polymer (a)”). It is crosslinked with an insoluble polyfunctional epoxy compound (b).
The water-insoluble polymer (a) constituting the aromatic group-containing polymer (B) has a carboxy group, and at least a part of the carboxy group is neutralized with an alkali metal hydroxide (C), and further, water. It is crosslinked with the insoluble polyfunctional epoxy compound (b). The acid value, the degree of neutralization, and the degree of cross-linking of the water-insoluble polymer (a) satisfy the above condition 1.

The aromatic group-containing polymer (B) used in the present invention is preferably a yellow azo pigment (preferably in a state where at least a part of the carboxy group of the water-insoluble polymer (a) is neutralized with an alkali metal hydroxide (C). A) is dispersed in an aqueous medium and then crosslinked with a water-insoluble polyfunctional epoxy compound (b) to be formed in the aqueous medium. In this way, the aromatic group-containing polymer (B) is not isolated, but the monomer composition, molecular weight, type and amount of alkali metal hydroxide (C) used, and the water-insoluble polyfunctional epoxy compound (b) of the water-insoluble polymer (a). Condition 1 is determined from the type and amount used in), and the state of the water-insoluble polymer (a) can be defined as satisfying the condition 1.
In the present invention, by using the alkali metal hydroxide (C) as the neutralizing agent for the carboxy group of the water-insoluble polymer (a), the charge repulsive force developed after the neutralization is increased, and the aqueous pigment dispersion or the aqueous pigment dispersion or the like. It is considered that the thickening and the occurrence of aggregation when the water-based ink is stored for a long period of time are suppressed, and the storage stability is improved.

(Aromatic group-containing water-insoluble polymer (a))
The water-insoluble polymer (a) has a function as a pigment dispersant that exhibits a dispersing action of the yellow azo pigment (A) and a function as a fixing agent on a recording medium.
The water-insoluble polymer (a) is water-insoluble not only in an unneutralized state but also after a part of its carboxy group is neutralized. In the present invention, when the Tyndall phenomenon is observed in the aqueous dispersion of the unneutralized or neutralized water-insoluble polymer (a) by observation with laser light or normal light, or averaged under the following measurement conditions. When the particle size is observed, it is judged to be "water insoluble" if any of the cases is satisfied.
Measurement conditions: Cumulant analysis is performed using the laser particle analysis system "ELSZ-1000" (manufactured by Otsuka Electronics Co., Ltd.). The measurement conditions are a temperature of 25 ° C., an angle between the incident light and the detector of 165 °, and the number of integrations is 32 times, and the refractive index of water (1.333) is input as the refractive index of the dispersion solvent. Dilute with water so that the measured concentration is 0.18% by mass (converted to solid content concentration).

The amount of the carboxy group of the water-insoluble polymer (a) can be expressed by the acid value. Its acid value is 200 mgKOH / g or more, preferably 220 mgKOH / g or more, and 320 mgKOH / g or less, preferably 300 mgKOH / g or less, more preferably 270 mgKOH / g or less. When the acid value is in the above range, the amount of the carboxy group and its neutralized carboxy group is sufficient, and the dispersion stability of the yellow azo pigment (A) is ensured. It is also preferable from the viewpoint of the balance between the affinity between the aromatic group-containing polymer (B) and the aqueous medium and the interaction between the aromatic group-containing polymer (B) and the yellow azo pigment (A).
The acid value of the water-insoluble polymer (a) can be calculated from the mass ratio of the constituent monomers. It can also be determined by a method of dissolving or swelling the polymer in a suitable organic solvent (for example, MEK) and titrating it.

The present form of the aromatic group-containing polymer (B) obtained by cross-linking the water-insoluble polymer (a) with the water-insoluble polyfunctional epoxy compound (b) in the water-based pigment dispersion liquid and the water-based ink is (i) pigment. There are two types: (ii) a pigment-containing (capsule) state containing a pigment, and (iii) a form in which the pigment is not adsorbed. From the viewpoint of the dispersion stability of the pigment, the state of (i) or (ii) is preferable in the present invention, and (ii) the pigment-encapsulating state containing the pigment is more preferable.

Examples of the water-insoluble polymer (a) include (i) an aromatic group-containing monomer (hereinafter, also referred to as “(i) component”) and (ii) a carboxy group-containing vinyl monomer (hereinafter, also referred to as “(ii) component”). A polymer obtained by copolymerizing an aromatic group-containing monomer mixture containing () and (hereinafter, also simply referred to as “monomer mixture”) is preferable. This polymer has (i) component-derived structural units and (ii) component-derived structural units.

[(I) Aromatic group-containing monomer]
(I) The aromatic group-containing monomer is used as a monomer component of the water-insoluble polymer (a) from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the aqueous pigment dispersion liquid and the aqueous ink.
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 a styrene-based monomer and an aromatic group-containing (meth) acrylate are more preferable. preferable.
Examples of styrene-based monomers include alkyl styrenes such as styrene, α-methyl styrene, β-methyl styrene, 2,4-dimethyl styrene, α-ethyl styrene, α-butyl styrene and α-hexyl styrene, 4-fluorostyrene and 3-. Examples thereof include halogenated styrene such as chlorostyrene and 3-bromostyrene, 3-nitrostyrene, 4-methoxystyrene, vinyltoluene, divinylbenzene and the like. Of these, styrene and α-methylstyrene are more preferable.
Further, as the aromatic group-containing (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate and the like are preferable, and benzyl (meth) acrylate is more preferable.
As the aromatic group-containing monomer, two or more of the above-mentioned monomers may be used, or a styrene-based monomer and an aromatic group-containing (meth) acrylate may be used in combination.

[(Ii) Carboxylic acid-containing vinyl monomer]
(Ii) The carboxy group-containing vinyl monomer is used as a monomer component of the water-insoluble polymer (a) from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the aqueous pigment dispersion liquid and the aqueous ink.
A carboxylic acid monomer is used as the carboxy group-containing vinyl monomer, and the carboxylic acid monomer includes acrylic acid, methaconic acid, α-ethylacrylic acid, crotonic acid, α-methylcrotonic acid, α-ethylcrotonic acid, and isocrotonic acid. , Itaconic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, glutaconic acid, 2-methacryloyloxymethyl succinic acid and the like. Among these, one or more selected from acrylic acid and methacrylic acid are preferable.

[(Iii) Other monomers]
In addition to (i) aromatic group-containing monomer and (ii) carboxy group-containing vinyl monomer, the water-insoluble polymer (a) includes alkyl (meth) acrylate, macromonomer, and nonionic monomer from the viewpoint of improving dispersion stability. A known monomer such as the above can be used as a monomer component.

The alkyl (meth) acrylate preferably has an alkyl group having 1 to 22 carbon atoms, preferably 6 to 18 carbon atoms, and examples thereof include methyl (meth) acrylate, ethyl (meth) acrylate, and propyl (meth) acrylate. Butyl (meth) acrylate, amyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, Isopropyl (meth) acrylate, isobutyl (meth) acrylate, tertiary butyl (meth) acrylate, isoamyl (meth) acrylate, isooctyl (meth) acrylate, isodecyl (meth) acrylate, isododecyl (meth) acrylate, isostearyl (meth) acrylate And so on.
In addition, "(meth) acrylate" means one or more kinds selected from acrylate and methacrylate. "(Meta)" in the following is also synonymous.

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 the polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, preferably methacryloyl. Oxy groups are more preferred.
Examples of the macromonomer include an aromatic group-containing monomer-based macromonomer and a silicone-based macromonomer, and an aromatic group-containing monomer-based macromonomer is preferable.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer include the above-mentioned aromatic group-containing monomer, and a styrene-based monomer is more preferable.
Specific examples of the styrene-based macromonomer include AS-6 (S), AN-6 (S), HS-6 (S) (trade name of Toagosei Co., Ltd.) and the like.

Examples of the nonionic monomer include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and polypropylene glycol (n = 2 to 30, n indicates the average number of moles of oxyalkylene group added; the same applies hereinafter) (. Polyalkylene glycol (meth) acrylate such as meta) acrylate and polyethylene glycol (n = 2 to 30) (meth) acrylate, alkoxy polyalkylene glycol (meth) such as methoxypolyethylene glycol (n = 1 to 30) (meth) acrylate Examples thereof include acrylate and phenoxy (ethylene glycol / propylene glycol copolymerization) (n = 1 to 30, ethylene glycol: n = 1 to 29) (meth) acrylate. Among these, polypropylene glycol (n = 2 to 30) (meth) acrylate and phenoxy (ethylene glycol / propylene glycol copolymer) (meth) acrylate are preferable, and polypropylene glycol (n = 2 to 30) (meth) acrylate is preferable. More preferred.
Commercially available nonionic monomers include Shin Nakamura Chemical Industry Co., Ltd.'s NK Ester M-20G, 40G, 90G, 230G, etc., and NOF Corporation's Blemmer PE-90, 200, 350, etc. Etc., PME-100, 200, 400, etc., PP-500, 800, 1000, etc., AP-150, 400, 550, etc., 50PEP-300, 50POEP-800B, 43PAPE-600B, etc. ..
The above-mentioned monomer components can be used alone or in combination of two or more.

(Content of each component or structural unit in the monomer mixture or polymer)
Water-insoluble polymer (a) Content of (i) aromatic group-containing monomer and (ii) carboxy group-containing vinyl monomer in the monomer mixture during production (content as unneutralized amount; the same shall apply hereinafter), that is, water. The content of the constituent units derived from the components (i) and (ii) in the insoluble polymer (a) determines the affinity of the water-insoluble polymer (a) for the yellow azo pigment (A) of the water-insoluble polymer (a). It is as follows from the viewpoint of improving and improving the storage stability of the aqueous pigment dispersion liquid and the aqueous ink, and from the viewpoint of maintaining water resistance, plain paper recording characteristics, and image recording density.
(I) The content of the aromatic group-containing monomer is preferably 50% by mass or more, more preferably 55% by mass or more, further preferably 60% by mass or more, and preferably 90% by mass or less, more preferably 90% by mass or less. It is 80% by mass or less, more preferably 75% by mass or less.
(Ii) The content of the carboxy group-containing vinyl monomer is preferably more than 10% by mass, more preferably more than 20% by mass, still more preferably more than 25% by mass, and preferably less than 50% by mass, more preferably. It is less than 45% by mass, more preferably less than 40% by mass.

The mass ratio of [(ii) component / (i) component] is preferably 0.3 or more, more preferably 0.35 or more, still more preferably 0.40 or more, and preferably 2.0 or less. It is more preferably 1.5 or less, still more preferably 1.0 or less.

(Manufacture of water-insoluble polymer (a))
The water-insoluble polymer (a) 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. Of 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, 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 the above can be used. The amount of the radical polymerization initiator is preferably 0.001 to 5 mol, more preferably 0.01 to 2 mol, per 1 mol of the monomer mixture.
As the polymerization chain transfer agent, known chain transfer agents such as octyl mercaptan, mercaptans such as 2-mercaptoethanol, and 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, but random and graft are preferable, and random is more preferable.

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 than 80 ° C. 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.
In the present invention, any known method can be used as a method for dispersing the pigment using the polymer dispersant, but it is preferable to use an aqueous dispersion of pigment-containing polymer particles described later. From the viewpoint of improving the productivity of the aqueous dispersion of the pigment-containing polymer particles, the organic solvent contained therein is used as it is as an organic solvent used in step 1 described later without removing the solvent used in the polymerization reaction. It is preferably used as a polymer (a) solution.
The solid content concentration of the water-insoluble polymer (a) solution is preferably 30% by mass or more, more preferably 40% by mass or more, and preferably 40% by mass or more, from the viewpoint of improving the productivity of the aqueous dispersion of the pigment-containing polymer particles. Is 70% by mass or less, more preferably 65% by mass or less.

The number average molecular weight of the water-insoluble polymer (a) used in the present invention is preferably 3,000 or more, more preferably 5,000 or more, still more preferably 7,000 or more, and preferably 20,000 or less. , More preferably 18,000 or less, still more preferably 16,000 or less. When the number average molecular weight of the polymer is in the above range, the adsorptive power to the pigment is sufficient and storage stability can be exhibited.
The number average molecular weight can be measured by the method described in Examples.

[Manufacture of pigment-containing polymer particles]
The aromatic group-containing polymer (B) particles (pigment-containing polymer particles) containing the yellow azo pigment (A) can be efficiently produced as an aqueous dispersion by a method having the following steps 1 to 3. ..
Step 1: A yellow azo pigment (A), an aromatic group-containing water-insoluble polymer (a) having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less, an alkali metal hydroxide (C), an organic solvent, and water. Step 2: Obtaining a pigment dispersion by dispersing the contained mixture (hereinafter, also referred to as "pigment mixture") Step 2: Remove the organic solvent from the pigment dispersion obtained in Step 1 to remove the organic solvent to obtain the pigment aqueous dispersion A. Step 3: The pigment aqueous dispersion A obtained in Step 2 is crosslinked with a water-insoluble polyfunctional epoxy compound (b), and the crosslinked aromatic group-containing polymer (B) is subjected to a yellow azo pigment (B). Step of obtaining pigment aqueous dispersion B containing A)

(Step 1)
Step 1 includes a yellow azo pigment (A), an aromatic group-containing water-insoluble polymer (a) having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less, an alkali metal hydroxide (C), an organic solvent, and water. This is a step of obtaining a pigment dispersion liquid by dispersing the mixture containing the above.
The method for producing the water-insoluble polymer (a) is as described above.
In step 1, it is preferable that the water-insoluble polymer (A) is first dissolved in an organic solvent and neutralized with an alkali metal hydroxide (C).
The organic solvent for dissolving the water-insoluble polymer (a) is not limited, but a volatile organic solvent having a boiling point of 150 ° C. or lower at atmospheric pressure is preferable, and for example, an aliphatic alcohol having 1 to 3 carbon atoms, acetone, methyl ethyl ketone, etc. Examples thereof include ketones such as diethyl ketone and methyl isobutyl ketone, ethers such as ethyl ether, isopropyl ether and tetrahydrofuran, and esters. Among these, ketones having 4 or more and 8 or less carbon atoms are more preferable from the viewpoint of improving the wettability to the pigment, the solubility of the water-insoluble polymer (a), and the adsorptivity of the water-insoluble polymer (a) to the pigment. Preferably, methyl ethyl ketone and methyl isobutyl ketone are more preferable, and methyl ethyl ketone is even more preferable.
When the water-insoluble polymer (a) is produced by the solution polymerization method, the solvent used in the polymerization may be used as it is.

<Alkali metal hydroxide (C)>
At least a part of the carboxy group of the water-insoluble polymer (a) is neutralized with the alkali metal hydroxide (C) from the viewpoint of water resistance, storage stability and the like of the obtained water-based pigment dispersion and water-based ink. It is preferable to neutralize the pH at this time so that it is 7 or more and 11 or less.
Examples of the alkali metal hydroxide (C) include lithium hydroxide, sodium hydroxide, potassium hydroxide and cesium hydroxide, but sodium hydroxide and potassium hydroxide are preferable. Moreover, the water-insoluble polymer may be neutralized in advance.
Neutralizers such as organic amines and organophosphorus compounds are not preferable from the viewpoint of safety because they have a peculiar odor and toxicity, and they need to be used in large amounts in order to improve storage stability. There are adverse effects such as the viscosity of the ink becoming too high.
The alkali metal hydroxide (C) is preferably used as an aqueous solution from the viewpoint of sufficiently and uniformly promoting neutralization. From the above viewpoint, the concentration of the aqueous solution is preferably 3% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more, and preferably 50% by mass or less, more preferably 25% by mass or less. ..
The amount of the alkali metal hydroxide (C) added may be 0.2 to 1.0 times the amount required to neutralize all the carboxyl groups of the water-insoluble polymer (a). preferable.

The degree of neutralization of the carboxy group of the water-insoluble polymer (a) is preferably 20 mol% or more, more preferably 25 mol% or more, from the viewpoint of water resistance and storage stability of the obtained water-based pigment dispersion and water-based ink. It is more preferably 30 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less, still more preferably 60 mol% or less.
Here, the degree of neutralization is a value obtained by dividing the molar equivalent of the alkali metal hydroxide (C) by the molar equivalent of the carboxy group of the water-insoluble polymer (a), that is, "of the alkali metal hydroxide (C). It is a percentage (mol%) of "molar equivalent number / molar equivalent number of carboxy group of water-insoluble polymer (a)". In the present invention, the degree of neutralization is calculated from the molar equivalent number of the alkali metal hydroxide (C), so that it exceeds 100 mol% when the alkali metal hydroxide (C) is used in excess.

In step 1, in addition to the alkali metal hydroxide (C), a volatile basic compound can also be used in combination. In the present invention, the volatile basic compound means an organic amine having a boiling point of 100 ° C. or lower at atmospheric pressure, and specific examples of the volatile basic compound include ammonia, trimethylamine, triethylamine and the like. Among these, ammonia is preferable from the viewpoint of high volatility.
The amount of the volatile basic compound used is not particularly limited, but if it is not used at all, or if it is used, it is 10 mol% or more, preferably 20 mol% or more, more preferably 25 mol% or more, still more preferably 30. It is mol% or more, preferably 100 mol% or less, more preferably 90 mol% or less, still more preferably 80 mol% or less, still more preferably 75 mol% or less.
In the calculation of the degree of neutralization of the present invention, only the amount of the alkali metal hydroxide (C) used is included, and the amount of the volatile basic compound used is not used.

(Content of each component in pigment mixture)
The content of each component in the pigment mixture in step 1 is as follows from the viewpoint of water resistance, storage stability, and productivity of the obtained aqueous pigment dispersion.
The content of the pigment (A) in the pigment mixture in the step 2 is preferably 2% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, and preferably 35% by mass or less. It is more preferably 30% by mass or less, still more preferably 20% by mass or less.
The content of the water-insoluble polymer (a) in the pigment mixture is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, still more preferably 3.0% by mass or more, and preferably. It is 8.0% by mass or less, more preferably 7.0% by mass or less, still more preferably 6.0% by mass or less.
The content of the organic solvent in the pigment mixture is preferably 5% by mass or more, more preferably 7% by mass or more, further preferably 10% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass. % Or less, more preferably 25% by mass or less.
The content of water in the pigment mixture is preferably 40% by mass or more, more preferably 45% by mass or more, still more preferably 50% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or more. Hereinafter, it is more preferably 75% by mass or less.
The mass ratio of the pigment (A) to the water-insoluble polymer (a) in the pigment mixture [pigment (A) / water-insoluble polymer (a)] is preferably 0.5 or more, more preferably 1.5 or more, still more preferable. Is 2.0 or more, and is preferably 4.0 or less, more preferably 3.8 or less, and even more preferably 3.5 or less.

(Dispersion treatment of pigment mixture)
In step 1, there is no particular limitation on the dispersion method for obtaining the pigment dispersion liquid. Although it is possible to atomize the average particle size of the pigment particles to a desired particle size only by the main dispersion, preferably, after the pigment mixture is pre-dispersed, the main dispersion is further applied by applying shear stress to perform the main dispersion of the pigment particles. It is preferable to control the average particle size of the above to a desired particle size.
The temperature in step 1, particularly the temperature in the pre-dispersion, is preferably 0 ° C. or higher, and preferably 40 ° C. or lower, more preferably 30 ° C. or lower, still more preferably 25 ° C. or lower, and the dispersion 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.
When the pigment mixture is pre-dispersed, a commonly used mixing and stirring device such as an anchor blade and a discharge blade can be used, and a high-speed stirring and mixing device is particularly preferable.

Examples of means for applying the shear stress of this dispersion include a kneader such as a roll mill and a kneader, a high-pressure homogenizer such as a microfluidic (manufactured by Microfluidic), and a media type disperser such as a paint shaker and a bead mill. Examples of commercially available media-type dispersers include Ultra Apex Mill (manufactured by Kotobuki Kogyo Co., Ltd.) and Pico Mill (manufactured by Asada Iron Works Co., Ltd.). A plurality of these devices can 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 the main dispersion is performed using a high-pressure homogenizer, the pigment can be controlled to have a desired particle size by controlling the processing pressure and the number of passes.
From the viewpoint of productivity and economy, the treatment pressure is preferably 60 MPa or more, more preferably 100 MPa or more, further preferably 130 MPa or more, and preferably 200 MPa or less, more preferably 180 MPa or less.
The number of passes is preferably 3 or more, more preferably 10 or more, and preferably 30 or less, more preferably 25 or less.

(Step 2)
Step 2 is a step of removing the organic solvent from the pigment dispersion liquid obtained in step 1 to obtain a pigment aqueous dispersion liquid 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, if necessary, the pigment dispersion liquid can be heat-stirred before distilling off the organic solvent.
The obtained pigment aqueous dispersion A is one in which pigment-containing polymer particles are dispersed in a medium containing water as a main medium. Here, the form of the pigment-containing polymer particles is not particularly limited, and at least the particles may be formed by the pigment (A) and the water-insoluble polymer (a), but as described above, the water-insoluble polymer (a) may be used. It is preferably in the form of particles containing the pigment (A).

The non-volatile component concentration (solid content concentration) of the obtained pigment aqueous dispersion A is preferably 10% by mass or more from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and facilitating the preparation of the water-based ink. It is more preferably 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less.
The solid content concentration of the pigment aqueous dispersion A is measured by the method described in Examples.
The average particle size of the pigment-containing polymer particles in the pigment aqueous dispersion A is preferably 50 nm or more, more preferably 60 nm or more, still more preferably 70 nm, from the viewpoint of reducing coarse particles and improving the ejection stability of the water-based ink. The above, and preferably 180 nm or less, more preferably 160 nm or less, still more preferably 140 nm or less.
The average particle size of the pigment-containing polymer particles is measured by the method described in Examples.

(Step 3)
In step 3, the pigment aqueous dispersion A obtained in step 2 is crosslinked with a water-insoluble polyfunctional epoxy compound (b), and the crosslinked aromatic group-containing polymer (B) is coated with a yellow azo pigment (A). This is a step of obtaining the pigment aqueous dispersion B containing the above.
In this step, a part of the carboxy group of the water-insoluble polymer (a) constituting the pigment-containing polymer particles is crosslinked to form a crosslinked structure on the surface layer portion of the pigment-containing polymer particles. That is, the aromatic group-containing polymer (B) according to the present invention is prepared from the water-insoluble polymer (a) and the water-insoluble polyfunctional epoxy compound (b) on the pigment surface.

<Water-insoluble polyfunctional epoxy compound (b)>
The water-insoluble polyfunctional epoxy compound (b) used in the present invention was dissolved in 100 g of water at 20 ° C. from the viewpoint of efficiently reacting with the carboxy group of the water-insoluble polymer (a) in a water-based medium. Occasionally, the dissolved amount is preferably 50 g or less, more preferably 40 g or less, still more preferably 35 g or less.
The water-insoluble polyfunctional epoxy compound has a water content (mass ratio) of preferably 50% or less, more preferably 40, from the viewpoint of water resistance, storage stability, and ejection property of the obtained water-based pigment dispersion and water-based ink. % Or less, more preferably 35% or less. Here, the water content% (mass ratio) means the dissolution rate (%) when 10 parts by mass of the epoxy compound is dissolved in 90 parts by mass of water at room temperature of 25 ° C., and more specifically, in Examples. Measured by the method described.

As the water-insoluble polyfunctional epoxy compound (b), a compound having 2 or more epoxy groups in the molecule, preferably a glycidyl ether group is preferable, and a polyhydric alcohol glycidyl ether having a hydrocarbon group having 3 or more and 8 or less carbon atoms is preferable. Compounds are more preferred.
The molecular weight of the water-insoluble polyfunctional epoxy compound (b) is preferably 120 or more, more preferably 150 or more, still more preferably 200 or more, from the viewpoint of ease of reaction and storage stability of the obtained crosslinked polymer. And, preferably 1500 or less, more preferably 1000 or less, still more preferably 800 or less.
The number of epoxy groups in the water-insoluble polyfunctional epoxy compound (b) is preferably 2 to 6 per molecule from the viewpoint of efficiently reacting with the carboxy group to improve the storage stability of the pigment-containing polymer particles. 3 to 6 are more preferable. Further, those having 5 or more epoxy groups in one molecule are poorly available on the market, and therefore, those having 3 or 4 epoxy groups in one molecule are more preferable from the viewpoint of achieving both reactivity and economy.
From the same viewpoint as above, the epoxy equivalent of the water-insoluble polyfunctional epoxy compound (b) is preferably 100 or more, more preferably 110 or more, still more preferably 120 or more, and preferably 300 or less, more preferably 300 or less. It is 270 or less, more preferably 250 or less.

Specific examples of the water-insoluble polyfunctional epoxy compound (b) include polypropylene glycol diglycidyl ether (water content 31%), glycerin polyglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and trimethylolpropane polyglycidyl ether (trimethylol propane polyglycidyl ether). Water solubility 27%), sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, hydrogenated bisphenol A type diglycidyl ether and other polyglycidyl ethers. Among these, one or two selected from trimethylolpropane polyglycidyl ether (water content 27%) and pentaerythritol polyglycidyl ether (water insoluble) are preferable.

(Crosslink reaction)
In the present invention, a part of the carboxy group of the water-insoluble polymer (a) is neutralized with an alkali metal hydroxide (C) to disperse the pigment (A) to obtain a pigment aqueous dispersion A, and then further. A part of the carboxy group of the water-insoluble polymer (a) is reacted with the water-insoluble polyfunctional epoxy compound (b) to form a crosslinked structure, and the aromatic group-containing polymer (B) obtained in the system is used. An aqueous pigment dispersion liquid B in which the pigment (A) is dispersed in an aqueous medium is used. At that time, from the viewpoint of improving the storage stability and ejection property of the obtained aqueous pigment dispersion and the aqueous ink, the alkali metal hydroxide (C) and the water-insoluble polyfunctional epoxy compound (in an amount satisfying the following condition 1) ( b) is used.

[Condition 1]
Condition 1 is that the value of [(100-neutralization degree-crosslinking degree) / 100] × [acid value of water-insoluble polymer (A)] is −30 mgKOH / g or more and 130 mgKOH / g or less.
Here, the degree of neutralization is a percentage (mol%) of "molar equivalent of alkali metal hydroxide (C) / molar equivalent of carboxy group of water-insoluble polymer (a)", and the degree of cross-linking is "water-insoluble polyfunctionality". The molar equivalent of the epoxy group of the epoxy compound (b) / the molar equivalent of the carboxy group of the water-insoluble polymer (a) ”is a percentage (mol%).
Condition 1 indicates the amount of unneutralized carboxy groups of the polymer dispersant in the pigment aqueous dispersion required to improve storage stability and discharge, and the acid value and neutralization of the water-insoluble polymer (a). It is determined by the degree and degree of cross-linking. In other words, condition 1 represents the acid value of the water-insoluble polymer (a) after neutralization and cross-linking.
When the value of Condition 1 exceeds -30 mgKOH / g and 130 mgKOH / g or less, the amount of charge on the pigment surface is sufficient when the pigment aqueous dispersion is prepared using the polymer, and the polymer dispersant It is sufficiently water-insoluble and can exhibit high discharge stability and storage stability.
The value of condition 1 is preferably -20 mgKOH / g or more, more preferably -10 mgKOH / g or more, still more preferably -5 mgKOH / g or more, and preferably 120 mgKOH / g or less, more preferably 110 mgKOH / g or less. , More preferably 100 mgKOH / g or less.

The cross-linking reaction between the carboxy group of the water-insoluble polymer (a) and the water-insoluble polyfunctional epoxy compound (b) is preferably carried out after the pigment (A) is dispersed in the water-insoluble polymer (a).
From the same viewpoint as above, the reaction temperature is preferably 40 ° C. or higher, more preferably 50 ° C. or higher, still more preferably 55 ° C. or higher, still more preferably 60 ° C. or higher, still more preferably 65 ° C. or higher. The temperature is preferably 95 ° C. or lower, more preferably 90 ° C. or lower.
Further, the reaction time is preferably 0.5 hours or more, more preferably 1 hour or more, further preferably 1.5 hours or more, still more preferably 3.0 hours or more, from the viewpoint of completion of the reaction and economic efficiency. And it is preferably 12 hours or less, more preferably 10 hours or less, still more preferably 8.0 hours or less, still more preferably 6 hours or less.
The degree of cross-linking of the crosslinked water-insoluble polymer (a) is preferably 5 mol% or more, more preferably 10 mol% or more, further preferably 15 mol% or more, and preferably 80 mol% or less, more preferably. Is 70 mol% or less, more preferably 60 mol% or less. The degree of cross-linking is an apparent degree of cross-linking calculated as a percentage (mol%) of "molar equivalent number of epoxy groups of water-insoluble polyfunctional epoxy compound (b) / molar equivalent number of carboxy groups of water-insoluble polymer (a)". is there.

The average particle size of the pigment-containing polymer particles in the pigment aqueous dispersion B is preferably 50 nm or more, more preferably 60 nm or more, still more preferably 70 nm, from the viewpoint of reducing coarse particles and improving the ejection stability of the water-based ink. The above, and preferably 180 nm or less, more preferably 160 nm or less, still more preferably 140 nm or less.
The average particle size of the pigment-containing polymer particles is measured by the method described in Examples.
Further, the average particle size of the water-based ink of the present invention is substantially the same as the average particle size of the pigment aqueous dispersion B.
The pH of the aqueous pigment dispersion B is preferably 8.0 or higher, more preferably 8.5 or higher. When the pH is 8.0 or more, the dissociation of the anionic group is promoted, and the charge amount of the pigment dispersion is sufficient, which can enhance the storage stability of the pigment dispersion. The upper limit of pH is not particularly limited, but the pH of the aqueous pigment dispersion B is preferably 11 or less, more preferably 10.5 or less, in order to avoid adversely affecting the members of the printer or printing machine.
The pH measuring method is not particularly limited, but a pH measuring method using a glass electrode is defined in JIS Z8802, and this method is preferable from the viewpoint of simplicity and accuracy.

The mass ratio of the pigment (A) to the aromatic group-containing polymer (B) (pigment (A) / aromatic group-containing polymer (B)) is from the viewpoint of improving the storage stability of the aqueous pigment dispersion and the aqueous ink, and From the viewpoint of maintaining water resistance, plain paper recording characteristics, and image recording density, it is preferably 1.0 or more, more preferably 1.5 or more, still more preferably 1.8 or more, and preferably 3.5 or less. , More preferably 3.0 or less, still more preferably 2.8 or less.
Additives such as a wetting agent and an antifungal agent can be added to the obtained aqueous pigment dispersion B to prevent drying.

[Manufacturing method of water-based ink]
The method for producing a water-based ink of the present invention has the following steps 1 to 4, and the aromatic group-containing water-insoluble polymer (a) in step 1 satisfies the following condition 1.
Step 1: A yellow azo pigment (A), an aromatic group-containing water-insoluble polymer (a) having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less, an alkali metal hydroxide (C), an organic solvent, and water. Step 2: Obtaining a pigment dispersion liquid by dispersing the contained mixture Step 2: Removing the organic solvent from the pigment dispersion obtained in Step 1 to obtain a pigment aqueous dispersion A Step 3: Obtaining in Step 2. The pigment aqueous dispersion A was crosslinked with a water-insoluble polyfunctional epoxy compound (b), and the crosslinked aromatic group-containing polymer (B) contained a yellow azo pigment (A). Step 4: Step 4: Mix the pigment aqueous dispersion B obtained in Step 3 with an organic solvent to obtain a water-based ink Condition 1: [(100-neutralization-crosslinking) / 100] × ( The value of the water-insoluble polymer (a) (acid value) is −30 mgKOH / g or more and 130 mgKOH / g or less.
Here, the degree of neutralization and the degree of cross-linking are as described above.

The details of steps 1 to 3 are as described in steps 1 to 3 in the above-mentioned [Production of Pigment-Containing Polymer Particles].
Step 4 is a step of mixing the aqueous pigment dispersion B obtained in Step 3 with an organic solvent to obtain an aqueous ink, but the mixing method is not particularly limited.
The organic solvent in step 4 is used from the viewpoint of further improving the storage stability of the water-based ink. The organic solvent used here preferably contains one kind or two or more kinds of organic solvents having a boiling point of 90 ° C. or higher, and an organic solvent having a weighted average value of boiling points of 250 ° C. or lower is preferable. The weighted average value of the boiling points of the organic solvent 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 lower.
Specific examples of the organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds and the like. Among these, one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers are preferable, and one or more selected from ethylene glycol, propylene glycol, diethylene glycol, and triethylene glycol are more preferable, and triethylene glycol and propylene glycol are more preferable. One or more selected from the above is more preferable.

In the method for producing a water-based ink of the present invention, if necessary, a wetting agent, a penetrant, a surfactant, a moisturizing agent, a dispersant, a viscosity adjusting agent, a pH adjusting agent, and a defoaming agent usually used for the water-based ink. , Preservatives, fungicides, rust preventives, antioxidants and other various additives can be added, and further filtration treatment with a filter or the like can be performed.

(Wetting agent)
The wetting agent is added for the purpose of preventing the ink from drying. For example, polyalkylene glycols such as polyethylene glycol and polypropylene glycol, trihydric or higher alcohols such as glycerin, trimethylolpropane, and pentaerythritol, and glycerin ethylene glycol. Polyhydric alcohol alkyl ethers such as monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, polyhydric alcohol aryl ethers, including Examples thereof include nitrogen heterocyclic compounds, amides, amines and sulfur-containing compounds.
The content of the wetting agent is not particularly limited, but it can be used in an aqueous ink in an amount of 1 to 50% by mass, preferably 2 to 30% by mass, and more preferably 3 to 30% by mass.

(Penetrating agent)
The penetrant is added for the purpose of improving the permeability to the recording medium and adjusting the dot diameter on the recording medium. For example, lower alcohols such as ethanol and isopropyl alcohol, and alkyl alcohols such as ethylene glycol hexyl ether and diethylene glycol butyl ether. Examples thereof include ethylene oxide adducts of the above and propylene oxide adducts of alkyl alcohols such as propylene glycol propyl ether.
The content of the penetrant is not particularly limited, but can be used in an aqueous ink in an amount of 0.01 to 10% by mass, preferably 0.1 to 8% by mass.
The above-mentioned wetting agent and penetrant can be used alone or in combination of two or more.

(Surfactant)
Surfactants are added to adjust ink characteristics such as surface tension, and examples thereof include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Anionic surfactants and nonionic surfactants are preferable.
Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, higher fatty acid ester sulfate, higher fatty acid ester sulfonate, and higher alcohol ether. Examples thereof include sulfate ester salts and sulfonates, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates and the like.
Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, and glycerin fatty acid ester. , Polyoxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, fatty acid alkylolamide, alkylalkanolamide, acetylene glycol, oxyethylene adduct of acetylene glycol, Examples thereof include polyethylene glycol polypropylene glycol block copolymer.
As other surfactants, silicone-based surfactants such as polysiloxane oxyethylene adducts, fluorine-based surfactants, and the like can also be used.
These surfactants can be used alone or in admixture of two or more.
The content of the surfactant is not particularly limited, but it is used in an aqueous ink in an amount of 0.001 to 3% by mass, preferably 0.01 to 2% by mass, and more preferably 0.1 to 1.0% by mass. Can be done.

The content and physical characteristics of each component of the water-based ink obtained by the production method of the present invention are as follows.
(Content of yellow azo pigment (A))
The content of the pigment (A) in the water-based ink is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, still more preferably 2.5% by mass, from the viewpoint of improving the printing density of the water-based ink. % Or more. Further, from the viewpoint of lowering the ink viscosity at the time of solvent volatilization and further improving the storage stability at high temperature, it is preferably 15.0% by mass or less, more preferably 10.0% by mass or less, still more preferably 7.0% by mass. % Or less.
(Total content of yellow azo pigment (A) and water-insoluble polymer (a))
The total content of the pigment (A) and the water-insoluble polymer (a) in the water-based ink is preferably 2.0% by mass or more, more preferably 2.5% by mass or more, still more preferably 3.0% by mass or more. , More preferably 3.5% by mass or more, and preferably 17.0% by mass or less, more preferably 12.0% by mass or less, still more preferably 10.0% by mass or less, still more preferably 8. It is 0.0% by mass or less, more preferably 6.0% by mass or less.

(Aqueous ink physical characteristics)
The viscosity of the water-based ink at 32 ° C. is preferably 2.0 mPa · s or more, more preferably 3.0 mPa · s or more, and further preferably 5.0 mPa · s, from the viewpoint of improving the storage stability of the ink. It is s or more, and preferably 12 mPa · s or less, more preferably 9.0 mPa · s or less, and further preferably 7.0 mPa · s or less.
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 further improving the storage stability of the ink. From the viewpoint of member resistance and skin irritation, the pH is preferably 11.0 or less, more preferably 10.0 or less, and further preferably 9.5 or less.

The water-based ink of the present invention can be loaded into a known inkjet recording device and ejected as ink droplets onto a recording medium to record an image or the like.
Examples of the inkjet recording device include a continuous injection type (charge control type, spray type, etc.), an on-demand type (piezo method, thermal method, electrostatic suction method, etc.), and are used as a piezo type water-based ink for inkjet recording. Is more preferable.
Examples of the recording medium that can be used include high water absorption plain paper, low water absorption coated paper and film. Examples of the coated paper include general-purpose glossy paper and multicolor foam gloss paper, and examples of the film include polyester film, polyvinyl chloride film, polypropylene film, polyethylene film and the like.

In the following preparation examples, production examples, examples and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified.

(1) Measurement of number average molecular weight of water-insoluble polymer N, N-dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd., for high performance liquid chromatography), phosphoric acid (manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent) and Gel chromatography method using a solution prepared by dissolving lithium bromide (manufactured by Tokyo Kasei Kogyo Co., Ltd., reagent) so as to have concentrations of 60 mmol / L and 50 mmol / L, respectively [GPC apparatus manufactured by Toso Co., Ltd. (HLC-8120 GPC) ), Tosoh Co., Ltd. column (TSK-GEL, α-M × 2), flow velocity: 1 mL / min], using monodisperse polystyrene with a known molecular weight as a standard substance.

(2) Measurement of average particle size of water-insoluble polymer particles and pigment-containing polymer particles Cumulant analysis was performed using a laser particle analysis system "ELSZ-1000" (manufactured by Otsuka Electronics Co., Ltd.). The measurement conditions were a temperature of 25 ° C., an angle between the incident light and the detector of 165 °, and the number of integrations was 100 times, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. It was diluted with water so that the measured concentration was 5 × 10-3% by mass (converted to solid content concentration).

(3) Measurement of solid content concentration of pigment aqueous dispersion Weigh 10.0 g of sodium sulfate homogenized in a desiccator into a 30 ml polypropylene container (φ = 40 mm, height = 30 mm), and sample about 1. After adding 0 g and mixing, the mixture was accurately weighed, maintained at 105 ° C. for 2 hours to remove volatiles, and left in a desiccator for another 15 minutes to measure the mass. 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.

(4) Measurement of water content of polyfunctional epoxy compound 90 parts by mass of ion-exchanged water and 10 parts by mass of cross-linking agent are added to a glass tube (25 mmφ × 250 mmh) at room temperature of 25 ° C., and the glass tube is adjusted to a water temperature of 25 ° C. It was allowed to stand for 1 hour in a constant temperature bath. Then, the glass tube was vigorously shaken for 1 minute and then allowed to stand again in a constant temperature bath for 10 minutes. Then, the undissolved material was weighed and the water content (mass%) was calculated.

<Preparation of polymer dispersant>
Preparation Example 1 (Preparation of aromatic group-containing water-insoluble polymer a1)
Mix 150 parts of styrene (reagent manufactured by Wako Pure Chemical Industries, Ltd.), 9 parts of α-methylstyrene (reagent manufactured by Wako Pure Chemical Industries, Ltd.), and 38 parts of acrylic acid (reagent manufactured by Wako Pure Chemical Industries, Ltd.). A monomer mixture was prepared. In the reaction vessel, 20 parts of MEK, 0.3 part of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the monomer mixture were placed and mixed, and nitrogen gas replacement was sufficiently performed.
On the other hand, the remaining 90% of the monomer mixed solution, 0.27 parts of the polymerization chain transfer agent, 60 parts of MEK and 2.2 parts of the azo radical polymerization initiator (V-65) are put into the dropping funnel, and nitrogen is added. In an 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 have passed at 65 ° C. from the end of the dropping, a solution prepared by dissolving 0.3 part of the polymerization initiator in 5 parts of MEK is added, and the mixture is further aged at 65 ° C. for 2 hours and 70 ° C. for 2 hours to be insoluble in water containing an aromatic group. A polymer solution of polymer a1 (number average molecular weight: 11000) was obtained.

Preparation Examples 2 to 5 (Preparation of aromatic group-containing water-insoluble polymers a2 to a5)
In Preparation Example 1, polymer solutions a2 to a5 were obtained in the same manner as in Preparation Example 1 except that the mixing amounts of styrene, α-methylstyrene, benzyl methacrylate, acrylic acid, and methacrylic acid were changed as shown in Table 1. It was. The results are shown in Table 1.

<Manufacturing of pigment aqueous dispersion A>
Production Example 1 (Production of pigment aqueous dispersion A1)
25 parts of the water-insoluble polymer a2 obtained by drying the polymer solution obtained in Preparation Example 2 under reduced pressure was mixed with 78.6 parts of MEK, and further, a 5N sodium hydroxide aqueous solution (sodium hydroxide solid content 16.9%, 8.1 parts (manufactured by Wako Pure Chemical Industries, 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 of the polymer was 32% (neutralization degree 32). %). Further, 400 parts of ion-exchanged water was added, and 75 parts of yellow azo pigment IRGAPHOR Yellow 8GCF (manufactured by Ciba Specialty Chemicals Co., Ltd .: CI Pigment Yellow 128) was added therein, and Disper (manufactured by Asada Iron Works Co., Ltd., Ultra Disper) was added. : Trade name) was used to stir for 60 minutes under the condition that the disper blade was rotated at 7000 rpm at 20 ° C.
The obtained mixture was subjected to 10-pass dispersion treatment with a microfluidics (manufactured by Microfluidics, trade name) at a pressure of 200 MPa. 250 parts of ion-exchanged water was added to the obtained dispersion, and after stirring, MEK was completely removed at 60 ° C. under reduced pressure, and a part of water was further removed to remove a 5 μm filter (acetyl cellulose film, outer diameter). : A pigment aqueous dispersion A1 with a solid content concentration of 20% by filtering with a needleless syringe (manufactured by Terumo Co., Ltd.) with a capacity of 25 mL and equipped with 2.5 cm (manufactured by Fujifilm Co., Ltd.) to remove coarse particles. Got The results are shown in Table 2.

Production Examples 2 to 4 (Production of pigment aqueous dispersions A2 to A4)
In Production Example 1, pigment aqueous dispersions A2 to A4 having a solid content concentration of 20% were obtained in the same manner as in Production Example 1 except that the yellow azo pigment was changed to that shown in Table 2. The results are shown in Table 2.

Production Example 5 (Production of pigment aqueous dispersion A5)
In Production Example 1, the yellow azo pigment was changed to that shown in Table 2, and instead of 8.1 parts of the 5N sodium hydroxide aqueous solution, a 5N potassium hydroxide aqueous solution (potassium hydroxide solid content 21.9%, Wako Pure Chemical Industries, Ltd.) A pigment aqueous dispersion A5 having a solid content concentration of 20% was obtained in the same manner as in Production Example 1 except that the volume was 8.8 parts (manufactured by Co., Ltd., for volumetric titration). The results are shown in Table 2.

Production Examples 6 to 7 (Production of pigment aqueous dispersions A6 to A7)
In Production Example 3, the water-insoluble polymer a3 obtained in Preparation Example 3 or the water-insoluble polymer a4 obtained in Preparation Example 4 was used instead of the water-insoluble polymer a2 obtained in Preparation Example 2. In the same manner as in Production Example 3, the aqueous pigment dispersions A6 to A7 having a solid content concentration of 20% were obtained. The results are shown in Table 2.

Production Examples 8 to 11 (Production of pigment aqueous dispersions A8 to A11)
The water-insoluble polymer a1 obtained by drying the polymer solution obtained in Preparation Example 1 under reduced pressure was dried under reduced pressure, and 25 parts of the obtained polymer was mixed with 78.6 parts of MEK, and further, a 5N aqueous sodium hydroxide solution (hydroxide) was added. Add 5.1 parts of sodium solid content (16.9%, manufactured by Wako Pure Chemical Industries, Ltd., for volumetric titration) to 32% the ratio of the number of moles of sodium hydroxide to the number of moles of carboxy groups of the water-insoluble polymer a1. It was neutralized so as to be (neutralization degree 32%). Then, using the yellow azo pigments shown in Table 2, pigment aqueous dispersions A8 to A11 having a solid content concentration of 20% were obtained in the same manner as in Production Example 1. The results are shown in Table 2.

Production Examples 12 to 13 (Production of pigment aqueous dispersions A12 to A13)
In Production Example 3, pigment aqueous dispersions A12 to A13 were obtained in the same manner as in Production Example 3 except that the amount of the 5N aqueous sodium hydroxide solution was as shown in Table 2. The results are shown in Table 2.

Production Example 14 (Production of pigment aqueous dispersion A14)
The water-insoluble polymer a5 obtained by drying the polymer solution obtained in Preparation Example 5 under reduced pressure was dried under reduced pressure, and 25 parts of the obtained polymer was mixed with 78.6 parts of MEK, and further, a 5N aqueous sodium hydroxide solution (hydroxide) was added. Add 9.8 parts of sodium solid content (16.9%, manufactured by Wako Pure Chemical Industries, Ltd., for volumetric titration) to 25% the ratio of the number of moles of sodium hydroxide to the number of moles of carboxy groups of the water-insoluble polymer a5. It was neutralized so as to be (neutralization degree 25%). Then, using the yellow azo pigment shown in Table 2, a pigment aqueous dispersion A14 having a solid content concentration of 20% was obtained in the same manner as in Production Example 1. The results are shown in Table 2.

Production Example 15 (Production of pigment aqueous dispersion A15)
The water-insoluble polymer a1 obtained by drying the polymer solution obtained in Preparation Example 1 under reduced pressure was dried under reduced pressure, and 25 parts of the obtained polymer was mixed with 78.6 parts of MEK, and further, a 5N aqueous sodium hydroxide solution (hydroxide) was added. Add 5.1 parts of sodium solid content (16.9%, manufactured by Wako Pure Chemical Industries, Ltd., for volumetric titration) to 32% the ratio of the number of moles of sodium hydroxide to the number of moles of carboxy groups of the water-insoluble polymer a1. It was neutralized so as to be (neutralization degree 32%). Then, as a yellow azo pigment, C.I. I. Pigment Yellow 74 was used to obtain a pigment aqueous dispersion A15 having a solid content concentration of 20% in the same manner as in Production Example 1. The results are shown in Table 2.

The details of the yellow azo pigment in Table 1 are as follows.
-PY128: IRGAPHOR Yellow 8GCF (manufactured by Ciba Specialty Chemicals Co., Ltd .: CI Pigment Yellow 128)
・ PY150: Hostaperm Yellow HN4G (Clariant Japan Co., Ltd .: CI Pigment Yellow 150)
・ PY155: InkJet Yellow 4GV P2532 (Clariant Japan Co., Ltd .: CI Pigment Yellow 155)
・ PY180: PV Fast Yellow HG (Clariant Japan Co., Ltd .: CI Pigment Yellow 180)
・ PY74: Toner Yellow 5GXT (Clariant AG: CI Pigment Yellow 74)

<Manufacturing of pigment aqueous dispersion B>
Example 1
100 parts (solid content 20%) of the pigment aqueous dispersion A1 obtained in Production Example 1 is placed in a glass bottle with a screw cap, and trimethylolpropane polyglycidyl ether (trimethylolpropane polyglycidyl ether) as a cross-linking agent having three epoxy groups in one molecule ( Made by Nagase ChemteX Corporation, Denacol EX-321, molecular weight 302, epoxy equivalent 140, water content 27%) 0.96 parts (crosslinking degree 40%) was added and sealed, and the mixture was stirred with a stirrer at 70 ° C. for 5 hours. It was heated. After 5 hours, the temperature is lowered to room temperature, and the mixture is filtered with a needleless syringe (manufactured by Terumo Corporation) having a capacity of 25 mL and equipped with a 5 μm filter (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Co., Ltd.). , Pigment aqueous dispersion B1 was obtained.

Examples 2-5, 7-8
In Example 1, instead of the pigment aqueous dispersion A1, the pigment aqueous dispersions A2 to A7 shown in Table 3 were used, and under the conditions shown in Table 3, the pigment aqueous dispersion B2 to 2 in the same manner as in Example 1. 5, B7-8 were obtained.

Example 6
100 parts (solid content 20%) of the pigment aqueous dispersion A3 obtained in Production Example 3 is taken in a glass bottle with a screw cap, and 1.9 parts (crosslinking degree 80%) of the Denacol EX-321 is added and sealed. , Heated at 70 ° C. for 5 hours with stirring with a stirrer. Then, the pigment aqueous dispersion B6 was obtained in the same manner as in Example 1.

Comparative Example 1
Take 100 parts (solid content 20%) of the pigment aqueous dispersion A8 obtained in Production Example 8 into a glass bottle with a screw cap, add 0.60 part (crosslinkability 40%) of the Denacol EX-321, and seal the stopper. , Heated at 70 ° C. for 5 hours with stirring with a stirrer. Then, the pigment aqueous dispersion B9 was obtained in the same manner as in Example 1.

Comparative Examples 2-6, 8
In Comparative Example 1, the pigment water dispersions A9 to 14 were used instead of the pigment water dispersion A8, and the amount of the Denacol EX-321 added was as shown in Table 3, except that the same was applied to Comparative Example 1. , Pigment aqueous dispersions B10-14 and B16 were obtained.

Comparative Example 7
100 parts (solid content 20%) of the pigment aqueous dispersion A3 obtained in Production Example 3 is placed in a glass bottle with a screw cap, and polyglycerin polyglycidyl ether is used as a water-soluble cross-linking agent having two epoxy groups in one molecule. (Made by Nagase ChemteX Corporation, Denacol EX-521, Epoxy Equivalent 183) 1.3 parts (crosslinkability 40%) was added and sealed, and the mixture was heated at 70 ° C. for 5 hours while stirring with a stirrer. Then, the pigment aqueous dispersion B15 was obtained in the same manner as in Example 1.

Reference example 1
Using the pigment aqueous dispersion A15 obtained in Production Example 15, the pigment aqueous dispersion B17 was obtained in the same manner as in Comparative Example 1.

<Preparation and evaluation test of water-based ink>
(Preparation of water-based ink)
Using each pigment aqueous dispersion B obtained in Examples and Comparative Examples, the pigment concentration was 5%, glycerin (manufactured by Kao Co., Ltd., wetting agent) 5%, and triethylene glycol (Wako Pure Chemical Industries, Ltd.) with respect to the entire water-based ink. 7% organic solvent (manufactured by the company), 0.5% acetylenol E100 (manufactured by Kawaken Fine Chemicals Co., Ltd., nonionic surfactant), add ion-exchanged water, weigh to 100% total amount, and magnetic. Stir with a stirrer to mix well, and filter with a needleless syringe with a capacity of 25 mL equipped with a 1.2 μm filter (acetylcellulose film, outer diameter: 2.5 cm, manufactured by Fujifilm Co., Ltd.) to obtain water-based ink. It was.
Using the obtained water-based ink, the following tests 1 to 3 were performed and evaluated. The results are shown in Table 3.

Test 1 (evaluation of storage stability)
Each water-based ink is sealed in a screw tube manufactured by Maruemu Corporation and allowed to stand in a thermostatic chamber set at 20 ° C. and 60 ° C. for 1 week, and then the average particle size is measured and the average particle size is measured from the following formula. The rate of increase was calculated.
Average particle size increase rate (%) = [(Average particle size of ink after storage-average particle size of aqueous dispersion used for ink preparation) / average particle size of aqueous dispersion used for ink preparation] × 100
The smaller the particle size increase rate, the more the aggregation is suppressed and the better the storage stability.
(Evaluation criteria)
⊚: Average particle size increase rate 0 to 5% or less ○: Average particle size increase rate more than 5% to 7% or less Δ: Average particle size increase rate more than 7% to 10% or less ×: Average particle size increase rate more than 10%

Test 2 (Evaluation of dischargeability)
An inkjet printer (manufactured by Seiko Epson Corporation, model number: EM-930C, piezo method) is loaded with the water-based ink obtained above, and 100 sheets of plain paper 4200 manufactured by XEROX are printed on 100 sheets (fine mode). The number of white lines (corresponding to the number of nozzles not ejected) was measured by observing the printed matter on the first sheet. Next, after performing the nozzle cleaning operation, 100 sheets of solid printing are performed on the entire surface, the 100th sheet (200th sheet in total) is observed again, and the number of white lines generated is measured per nozzle width. , Dischargeability was evaluated according to the following criteria.
(Evaluation criteria)
⊚: No white line was generated on the 100th printed matter and the 200th printed matter.
◯: No white line on the 100th printed matter and 2 or less white lines on the 200th printed matter.
Δ: Three or more white lines are generated on the 100th or 200th printed matter.
If it is evaluated as ⊚ and 〇, it can be practically used as a normal water-based ink for inkjet recording.

Test 3 (gloss evaluation)
Using the print pattern and print mode used in Test 1 (Ejectability Evaluation), print on coated paper (Oji Paper Co., Ltd., OK Top Coat) instead of plain paper, and handy gloss meter (Nippon Denshoku Industries Co., Ltd.) The 60 ° glossiness was measured with PG-II) manufactured by Nippon Denshoku Industries Co., Ltd.
(Evaluation criteria)
◎: Gloss 40 or more
◯: Glossiness less than 40 to 20 or more Δ: Glossiness less than 20 60 ° The higher the glossiness, the better the glossiness, and the printed matter looks clear, which is preferable.
If the evaluation is ⊚ and 〇, it is suitable for water-based ink for inkjet recording.

From Table 3, the water-based ink of the example has a relatively small average particle size as compared with the water-based ink of the comparative example, and a recorded material having excellent storage stability, ejection property, and glossiness can be obtained. You can see that you can.
Further, comparing Reference Example 1 and Comparative Examples 1 to 4 using a polymer dispersant composed of an aromatic group-containing water-insoluble polymer having an acid value of 150 mgKOH / g, Pigment Yellow 74 was used as the yellow azo pigment. Reference Example 1 shows Pigment Yellow 128, Pigment Yellow 150, Pigment Yellow 155 and Pigment Yellow, although there are no problems with storage stability, inkjet ejection property, and glossiness of the image of the recorded material obtained. It can be seen that in Comparative Examples 1 to 4 using 180, the inkjet ejection property and the glossiness of the obtained image are inferior. However, even with these pigments, in the water-based inks of Examples 1 to 8 using the aromatic group-containing water-insoluble polymer having an acid value in the range of 200 to 320 mgKOH / g, Pigment Yellow 74 was used as a reference. It can be seen that the storage stability, ejection property, and glossiness are equal to or higher than those of the water-based ink of Example 1.

Claims (9)

An aqueous pigment dispersion for inkjet recording containing a yellow azo pigment (A), an aromatic group-containing polymer (B), and an alkali metal hydroxide (C).
The aromatic group-containing polymer (B) is formed by cross-linking the aromatic group-containing water-insoluble polymer (a) having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound (b).
The aromatic group-containing water-insoluble polymer (a) has a structural unit derived from an aromatic group-containing monomer of 50% by mass or more and 90% by mass or less and a structural unit derived from a carboxy group-containing vinyl monomer.
The water-insoluble polyfunctional epoxy compound (b) is a polyhydric alcohol glycidyl ether compound having 2 to 6 epoxy groups in the molecule and having a hydrocarbon group having 3 or more and 8 or less carbon atoms.
The acid value of the aromatic group-containing water-insoluble polymer (a) and the neutralization degree and the degree of crosslinking, the inkjet recording aqueous pigment dispersion satisfying the following conditions 1.
Condition 1: The value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of the water-insoluble polymer (a)) is −30 mgKOH / g or more and 130 mgKOH / g or less.
Here, the degree of neutralization is a percentage (mol%) of "molar equivalent of alkali metal hydroxide (C) / molar equivalent of carboxy group of water-insoluble polymer (a)", and the degree of cross-linking is "water-insoluble polyfunctionality". The molar equivalent of the epoxy group of the epoxy compound (b) / the molar equivalent of the carboxy group of the water-insoluble polymer (a) ”is a percentage (mol%). The aqueous pigment dispersion for inkjet recording according to claim 1 , wherein the water-insoluble polymer (a) containing an aromatic group has a number average molecular weight of 3,000 to 20,000. The aromatic group-containing water-insoluble polymer (a) is derived from one or more constituent units selected from styrene, α-methylstyrene, and benzyl (meth) acrylate, and one or more selected from acrylic acid and methacrylic acid. The aqueous pigment dispersion for inkjet recording according to claim 1 or 2, which has a structural unit. The water-insoluble polyfunctional epoxy compound (b) is polypropylene glycol diglycidyl ether, glycerin polyglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether. The aqueous pigment dispersion for inkjet recording according to any one of claims 1 to 3, which is one or more selected from resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, and hydrogenated bisphenol A type diglycidyl ether. The yellow azo pigment (A) is C.I. I. Pigment Yellow 128, C.I. I. Pigment Yellow 150, C.I. I. Pigment Yellow 155, and C.I. I. The aqueous pigment dispersion for inkjet recording according to any one of claims 1 to 4 , which is one or more selected from the group consisting of Pigment Yellow 180. A water-based ink for inkjet recording, which comprises the aqueous pigment dispersion for inkjet recording according to any one of claims 1 to 5 as a main component. A method for producing a water-based ink for inkjet recording, which comprises the following steps 1 to 4 and in which the aromatic group-containing water-insoluble polymer (a) in step 1 satisfies the following condition 1.
Step 1: A yellow azo pigment (A), an aromatic group-containing water-insoluble polymer (a) having an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less, an alkali metal hydroxide (C), an organic solvent, and water. Step 2: Obtaining a pigment dispersion liquid by dispersing the contained mixture Step 2: Removing the organic solvent from the pigment dispersion obtained in Step 1 to obtain a pigment aqueous dispersion A Step 3: Obtaining in Step 2. The pigment aqueous dispersion A was crosslinked with a water-insoluble polyfunctional epoxy compound (b), and the crosslinked aromatic group-containing polymer (B) contained a yellow azo pigment (A). Step 4: Step 4: Mix the pigment aqueous dispersion B obtained in Step 3 with an organic solvent to obtain a water-based ink Condition 1: [(100-neutralization-crosslinking) / 100] × ( The value of the water-insoluble polymer (a) (acid value) is −30 mgKOH / g or more and 130 mgKOH / g or less.
Here, the aromatic group-containing water-insoluble polymer (a) has a structural unit derived from an aromatic group-containing monomer of 50% by mass or more and 90% by mass or less and a structural unit derived from a carboxy group-containing vinyl monomer.
The water-insoluble polyfunctional epoxy compound (b) is a polyhydric alcohol glycidyl ether compound having 2 to 6 epoxy groups in the molecule and having a hydrocarbon group having 3 or more and 8 or less carbon atoms.
The degree of neutralization is a percentage (mol%) of "molar equivalent of alkali metal hydroxide (C) / molar equivalent of carboxy group of water-insoluble polymer (a)", and the degree of cross-linking is "water-insoluble polyfunctional epoxy compound (water-insoluble polyfunctional epoxy compound). The molar equivalent number of the epoxy group of b) / the molar equivalent number of the carboxy group of the aromatic group-containing water-insoluble polymer (a) ”is a percentage (mol%). The method for producing a water-based ink for inkjet recording according to claim 7 , wherein the aromatic group-containing water-insoluble polymer (a) has a number average molecular weight of 3,000 to 20,000. The yellow azo pigment (A) is C.I. I. Pigment Yellow 128, C.I. I. Pigment Yellow 150, C.I. I. Pigment Yellow 155, and C.I. I. The method for producing a water-based ink for inkjet recording according to claim 7 or 8 , which is one or more selected from Pigment Yellow 180.