JP6813241B2 - Water-based ink - Google Patents

Description

The present invention relates to water-based inks.

The inkjet recording method is a recording method in which ink droplets are directly ejected from a very fine nozzle onto a recording medium and adhered to obtain characters or images. This method is remarkably popular because it has many advantages that it is easy to make full color, it is inexpensive, plain paper can be used as a recording medium, and it does not contact the printed matter.
Recently, inks that use pigments as colorants have been widely used in order to impart weather resistance and water resistance to printed matter. Then, from the viewpoint of ejection stability and storage stability, in order to stably blend the pigment in the water-based ink, a technique such as encapsulating the pigment with a polymer using a polymer dispersant that modifies the surface of the pigment has been developed. ing.

Patent Document 1 describes water-soluble organic solvents such as 3-methyl-1,3-butanediol and glycerin, and fluorine-based surfactants for the purpose of improving image quality, ejection stability, clogging resistance, etc. with respect to plain paper. A recording ink containing an agent and an aqueous dispersion of water-insoluble vinyl polymer particles having an average particle size of 40 to 100 nm containing carbon black is disclosed.
Patent Document 2 describes a water-based ink containing pigment-containing water-insoluble polymer particles and 1,3-alkanediol for the purpose of improving fixability and ejection reliability, wherein the water-insoluble polymer contains a carboxy group. Water-based inks for inkjet recording having a monomer and a structural unit derived from a linear alkyl (meth) acrylate having 18 to 22 carbon atoms are disclosed. Further, in the example, it is disclosed that Emulgen 109P, which is a nonionic surfactant, is contained in the water-based ink, and that trimethylolpropane polyglycidyl ether is used to crosslink the water-insoluble polymer.
Further, Patent Document 3 discloses a pigment in which carbon black is encapsulated in a cross-linking dispersant obtained by cross-linking a polymer with polyglycerol polyglycidyl ether and an ink containing a liquid vehicle for the purpose of improving print quality on plain paper. ing. Further, in the example, it is disclosed that 1,2hexanediol is contained as a cross-linking agent and surfinol 465 is contained as a nonionic surfactant in the ink.

JP-A-2009-155460 Japanese Unexamined Patent Publication No. 2013-023546 Special Table 2012-527510

Pigment-based inks are excellent in weather resistance and water resistance, but when printed on plain paper, the pigment particles sink deeply into the paper fibers, so the print density is lower than that of dye inks that dye the entire paper fibers. .. In addition, although the dye is completely dissolved down to the molecular level, the pigment exists as solid particles, so that the storage stability is reduced under high temperature storage and the ejection head is capped when the inkjet printing is stopped. If left untreated, it causes blockage in the fine ejection nozzle, and there is a problem that the ink cannot be ejected normally when printing is restarted. It has been difficult to solve the above problems with the techniques of Patent Documents 1 to 3.
The present invention provides a water-based ink that is excellent in storage stability and ejection stability when printing is restarted after printing is paused (hereinafter, also referred to as "reprinting"), and can exhibit high print density on plain paper. That is the issue.

The present inventors have found that the above problems can be solved by using a specific polymer dispersant and a specific alkanediol as a water-soluble organic solvent.
That is, the present invention is a pigment, a polymer dispersant, a 1,2-alkanediol or a 1,3-alkane having 4 or more carbon atoms which may have a methyl group or an ethyl group at the 2-position, 3-position or 4-position. A water-based ink containing a diol, a nonionic surfactant, and water.
The polymer dispersant comprises cross-linking a water-insoluble polymer P having a carboxy group and an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound.
Provided is a water-based ink in which the acid value, the degree of neutralization, and the degree of cross-linking of the water-insoluble polymer P satisfy the following condition 1.
Condition 1: The value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of water-insoluble polymer P) 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 neutralizer / molar equivalent of carboxy group of water-insoluble polymer P", and the degree of cross-linking is "molar of epoxy group of water-insoluble polyfunctional epoxy compound". Equivalent number / molar equivalent number of carboxy groups of the water-insoluble polymer P "percentage (mol%).

According to the present invention, it is possible to provide a water-based ink which is excellent in storage stability and ejection stability at the time of reprinting and can exhibit a high printing density on plain paper.

[Water-based ink]
The water-based ink of the present invention is a pigment, a polymer dispersant, or 1,2-alkanediol having 4 or more carbon atoms or 1,3-alkanediol which may have a methyl group or an ethyl group at the 2-position, 3-position or 4-position. An aqueous ink containing an alkanediol, a nonionic surfactant, and water.
The polymer dispersant comprises cross-linking a water-insoluble polymer P having a carboxy group and an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound to obtain the acid value of the water-insoluble polymer P. A water-based ink in which the degree of neutralization and the degree of cross-linking satisfy the following condition 1.
Condition 1: The value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of water-insoluble polymer P) 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 term "water-based" means that water accounts for the largest proportion of the medium in which the pigment is dispersed.
Since the water-based ink of the present invention has excellent storage stability and a good printed matter can be obtained, it can be suitably used as a water-based ink for flexographic printing ink, gravure printing ink, or inkjet ink. Further, the water-based ink of the present invention is preferably used as a water-based ink for inkjet recording because it is excellent in ejection stability in the inkjet recording method.

The water-based ink of the present invention is excellent in storage stability and ejection stability during reprinting, and can exhibit high print density on plain paper. The reason is not clear, but it can be considered as follows.
The 1,2-alkanediol or 1,3-alkanediol which may have a methyl group or an ethyl group at the 2-position, 3-position or 4-position contained in the water-based ink of the present invention has alkyl two hydroxyl groups. It is a water-soluble organic solvent having a structure biased to one side of the chain, and is hydrophobic but highly polar. For this reason, in the vicinity of the ink ejection nozzle port, due to this hydrophobicity, the evaporation of water of the water-based ink is suppressed to reduce ejection defects such as clogging, and when printed on plain paper, the polarity is biased. It is considered that the water-based ink promotes the wetting and spreading of the water-based ink on the paper pulp, which makes it easier for the water-based ink to spread in the horizontal direction than the movement of the water-based ink trying to spread in the depth direction of the paper.
Further, the alkanediol swells the polymer particles and deteriorates the storage stability. In the present invention, the polymer dispersant cross-links the water-insoluble polymer P having a carboxy group with a water-insoluble polyfunctional epoxy compound. Therefore, it is considered that a sufficiently high storage stability can be ensured even with a water-based ink containing water-insoluble polymer P particles containing a pigment.

<Pigment>
The pigment used in the present invention is not particularly limited, and may be either an inorganic pigment or an organic pigment, and a rake pigment or a fluorescent pigment may also be used. In addition, if necessary, they can be used in combination with extender pigments.
Specific examples of the inorganic pigment include metal oxides such as carbon black, titanium oxide, alumina, iron oxide, red iron oxide, chromium oxide, and pearl luster pigments. Especially for black ink, carbon black is preferable. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.
These inorganic pigments may be those treated with a known hydrophobizing agent such as a titanium coupling agent, a silane coupling agent, or a higher fatty acid metal salt.

Specific examples of organic pigments include anthraquinone pigments, quinacridone pigments, indigo pigments, dioxazine pigments, perylene pigments, perinone pigments, isoindolinone pigments, isoindolin pigments, phthalocyanine pigments, and quinophthalone pigments. , One or more selected from condensed polycyclic pigments such as diketopyrrolopyrrole pigments, and azo pigments such as disazo pigments and condensed azo pigments. Among these, one or more selected from quinacridone pigments, azo pigments and phthalocyanine pigments are preferable from the viewpoint of color reproducibility of the obtained image.
The hue is not particularly limited, and any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, and green can be used.
Specific examples of preferable organic pigments include C.I. I. Pigment Yellow, C.I. I. Pigment Red, C.I. I. Pigment Orange, C.I. I. Pigment Violet, C.I. I. Pigment Blue and C.I. I. One or more product numbers selected from Pigment Green can be mentioned.

Specific examples of quinacridone pigments include C.I. I. Pigment Red (PR) 122, PR192, PR202, PR207, PR209, and C.I. I. Pigment Violet 19 and the like, and one or more selected from PR122 and PV19 are more preferable.
Specific examples of the azo pigment include C.I. I. Pigment Yellow (PY) 74, PY151, PY154, PY155, PY180, PY213 and the like, and one or more selected from PY74 and PY154 are more preferable.
Specific examples of the phthalocyanine pigment include C.I. I. Pigment Blue (PB) 15: 1, PB15: 2, PB15: 3, PB15: 4, PB15: 5, PB15: 6, PB16, Pigment Green (PG) 7, PG36, etc., PB15: 3, And one or more selected from PB15: 4 are more preferable.
The organic pigment includes a derivative of the organic pigment which is a raw material. The pigment derivative can be prepared by subjecting a functional group such as a hydroxyl group, a carboxy group, a carbamoyl group, a sulfo group, a sulfonamide group, and a phthalimidemethyl group to the surface of an organic pigment.
Examples of the extender pigment include silica, calcium carbonate, talc and the like.
The above pigments can be used alone or in combination of two or more.

In the present invention, the pigment is preferably present as water-insoluble polymer P particles containing the pigment (hereinafter, also referred to as “pigment-containing polymer particles”) in the water-based ink. Here, "containing a pigment" means a form in which a pigment is encapsulated in a polymer dispersant having a crosslinked structure obtained by reacting a water-insoluble polymer P having a carboxy group with a water-insoluble polyfunctional epoxy compound. A form in which a part of the pigment is encapsulated in the polymer dispersant and a part of the pigment is exposed from the polymer dispersant, or a form in which the polymer dispersant is attached to the surface of the pigment, and the like are included. Mixtures are also included. Among these, a form in which a pigment is encapsulated in a polymer dispersant having a crosslinked structure is preferable.

<Polymer dispersant>
The polymer dispersant used in the present invention is a water-insoluble polymer P having a carboxy group and an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less (hereinafter, also simply referred to as "water-insoluble polymer P"). It is crosslinked with a functional epoxy compound, and preferably at least a part of the carboxy group is neutralized with a neutralizing agent, preferably an alkali metal compound, and then the pigment is dispersed in a water-insoluble polyfunctional state. It is formed in an aqueous medium by cross-linking with an epoxy compound. In this case, the polymer dispersant is not isolated, but condition 1 is determined by the monomer composition of the water-insoluble polymer P, the type and amount of the neutralizing agent (alkali metal compound), and the type and amount of the water-insoluble polyfunctional epoxy compound. , The state of the polymer dispersant can be defined as satisfying the condition 1.
In the present invention, if an alkali metal compound is used as the neutralizing agent, the charge repulsive force developed after neutralization becomes large, and the occurrence of thickening and aggregation in the water-based ink is suppressed, which has been further requested in recent years. It is considered that the storage stability is improved enough to meet the high reliability.

(Water-insoluble polymer P)
The water-insoluble polymer P for preparing the polymer dispersant used in the present invention has a function as a pigment dispersant that exhibits a pigment dispersion action and a function as a fixing agent on a recording medium.
This water-insoluble polymer P is water-insoluble not only in an unneutralized state but also after a part of its carboxy group is neutralized. Here, the "water-insoluble polymer" means that when the water-insoluble polymer is dispersed in water, it does not become transparent. Even if the aqueous dispersion of the water-insoluble polymer looks transparent visually, it is judged to be water-insoluble if the Tyndall phenomenon is observed by observation with laser light or normal light.

The acid value of the water-insoluble polymer P is derived from the carboxy group, but is preferably 200 mgKOH / g or more, more preferably 220 mgKOH / g or more, and preferably 320 mgKOH / g or less, more preferably 300 mgKOH / g or less, and further. It is 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 pigment is ensured. It is also preferable from the viewpoint of the balance between the affinity between the polymer dispersant and the aqueous medium and the interaction between the polymer dispersant and the pigment.
The acid value of the water-insoluble polymer P 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 polymer dispersant obtained by cross-linking the water-insoluble polymer P with a water-insoluble polyfunctional epoxy compound in the water-based ink includes (i) a state of being adsorbed on a pigment and (ii) a pigment. There are pigment-encapsulated (capsule) states and (iii) forms 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 P used include one or more selected from polyester, polyurethane, and vinyl-based polymers. From the viewpoint of improving the storage stability of water-based pigment dispersions and water-based inks, vinyl compounds and vinylidene compounds are used. , And a vinyl polymer obtained by addition polymerization of one or more vinyl monomers selected from vinylidene compounds is preferable.

Examples of the water-insoluble polymer P include (a) a carboxy group-containing vinyl monomer (hereinafter, also referred to as “(a) component”) and (b) a hydrophobic vinyl monomer (hereinafter, also referred to as “(b) component”). A vinyl-based polymer obtained by copolymerizing a vinyl monomer mixture containing the mixture (hereinafter, also simply referred to as “monomer mixture”) is preferable. This vinyl-based polymer has a structural unit derived from the component (a) and a structural unit derived from the component (b). This vinyl-based polymer is further derived from a structural unit derived from (c) a macromonomer (hereinafter, also referred to as “component (c)”) and (d) a nonionic monomer (hereinafter, also referred to as “component (d)”). Can contain building blocks.

[(A) Carboxylic group-containing vinyl monomer]
(A) The carboxy group-containing vinyl monomer is used as a monomer component of the water-insoluble polymer P from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the water-based ink. As the carboxy group-containing vinyl monomer, a carboxylic acid monomer is used.
Examples of the carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinic acid, and one selected from acrylic acid and methacrylic acid. The above is preferable.

[(B) Hydrophobic vinyl monomer]
(B) The hydrophobic vinyl monomer is used as a monomer component of the water-insoluble polymer P from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the water-based ink. Examples of the hydrophobic vinyl monomer include an alkyl group having 1 to 22 carbon atoms, an alkyl (meth) acrylate having an aryl group having 6 to 22 carbon atoms, and an aromatic group-containing monomer.
The alkyl (meth) acrylic acid ester preferably has an alkyl group having 1 to 22 carbon atoms, preferably 6 to 18 carbon atoms, and is preferably, for example, methyl (meth) acrylate, ethyl (meth) acrylate, or 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 the like can be mentioned.
In addition, "(meth) acrylate" means one or more kinds selected from acrylate and methacrylate. "(Meta)" in the following is also synonymous.

As the aromatic group-containing monomer, a vinyl monomer having an aromatic group having 6 to 22 carbon atoms, which may have a substituent containing a heteroatom, is preferable, and a styrene-based monomer and an aromatic group-containing (meth) acrylate Is more preferable.
As the styrene-based monomer, styrene, α-methylstyrene, vinyltoluene, and divinylbenzene are preferable, and 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.
(B) As the hydrophobic monomer, two or more of the above-mentioned monomers may be used, or a styrene-based monomer and an aromatic group-containing (meth) acrylic acid ester may be used in combination.

[(C) Macromonomer]
(C) The macromonomer is a compound having a polymerizable functional group at one end and having a number average molecular weight of 500 or more and 100,000 or less, and is water-insoluble from the viewpoint of improving the dispersion stability of pigment-containing polymer particles in an aqueous ink. It can be used as a monomer component of polymer P. As the polymerizable functional group present at one end, an acryloyloxy group or a methacryloyloxy group is preferable, and a methacryloyloxy group is more preferable.
(C) The number average molecular weight of the macromonomer is preferably 1,000 or more and 10,000 or less. The number average molecular weight is measured by a gel permeation chromatography method using chloroform containing 1 mmol / L dodecyldimethylamine as a solvent, using polystyrene as a standard substance.
As the macromonomer, aromatic group-containing monomer-based macromonomers and silicone-based macromonomers are preferable, and aromatic group-containing monomer-based macromonomers are preferable from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the water-based ink. Is more preferable.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromonomer include the aromatic group-containing monomer described in (b) Hydrophobic Vinyl Monomer, and styrene and benzyl (meth) acrylate are preferable, and styrene. 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 silicone-based macromonomer include organopolysiloxane having a polymerizable functional group at one end.

[(D) Nonionic monomer]
For the water-insoluble polymer P, (d) a nonionic monomer can be further used as a monomer component from the viewpoint of improving the dispersion stability of the pigment-containing polymer particles in the water-based ink.
(D) As the nonionic monomer, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polypropylene glycol (n = 2 to 30, n indicates the average number of moles of oxyalkylene group added. Same) Polyalkylene glycol (meth) acrylate such as (meth) acrylate, polyethylene glycol (n = 2-30) (meth) acrylate, alkoxypolyalkylene glycol such as methoxypolyethylene glycol (n = 1-30) (meth) acrylate Examples thereof include (meth) acrylate, phenoxy (ethylene glycol / propylene glycol copolymerization) (n = 1 to 30, ethylene glycol: n = 1 to 29) (meth) acrylate and the like. 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.

Specific examples of the commercially available component (d) include Shin Nakamura Chemical Industry Co., Ltd.'s NK Ester M-20G, 40G, 90G, 230G, etc., NOF Corporation's Blemmer PE-90, and the same. 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 so on.
The above components (a) to (d) can be used alone or in combination of two or more.
As described above, the water-insoluble polymer P having a carboxy group used in the present invention includes a structural unit derived from one or more (a) carboxy group-containing vinyl monomers selected from acrylic acid and methacrylic acid, and an acrylate monomer and a methacrylate monomer. A vinyl polymer containing a structural unit derived from one or more (b) hydrophobic vinyl monomers selected from the aromatic group-containing monomers is preferable. Further, it may be a vinyl polymer further containing (c) a structural unit derived from a macromonomer and (d) a structural unit derived from a nonionic monomer.

(Content of each component or structural unit in the monomer mixture or polymer)
The content of (a) a carboxy group-containing vinyl monomer and (b) a hydrophobic vinyl monomer in a monomer mixture during the production of the water-insoluble polymer P (content as an unneutralized amount; the same applies hereinafter), that is, the water-insoluble polymer P. The contents of the constituent units derived from each component in the composition are as follows from the viewpoints of storage stability, ejection stability at the time of reprinting, and print density.
The content of the component (a) is preferably 20% by mass or more, more preferably 25% by mass or more, further preferably 28% by mass or more, and preferably 75% by mass or less, more preferably 60% by mass or less. , More preferably 55% by mass or less, still more preferably 50% by mass or less.
The content of the component (b) is preferably 15% by mass or more, more preferably 20% by mass or more, further preferably 25% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less. , More preferably 70% by mass or less.
When the component (c) is contained, the content of the component (c) is preferably 3% by mass or more, more preferably 5% by mass or more, still more preferably 8% by mass or more, and preferably 30% by mass or more. Below, it is more preferably 25% by mass or less, still more preferably 20% by mass or less.
When the component (d) is contained, the content of the component (d) is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 40% by mass or more. Below, it is more preferably 35% by mass or less, still more preferably 30% by mass or less.

The mass ratio of [component (a) / component (b)] 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 1.2 or less.
When the component (c) is contained, the mass ratio of [(a) component / [(b) component + (c) component]] is preferably 0.1 or more, more preferably 0.3 or more, and further. It is preferably 0.5 or more, preferably 2.0 or less, more preferably 1.7 or less, still more preferably 1.5 or less.

(Manufacture of water-insoluble polymer P)
The water-insoluble polymer P 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 and 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.

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 solvent used in the polymerization reaction is not removed, and the contained organic solvent is used as the organic solvent used in step I described later, so that it is water-insoluble as it is. It is preferably used as a polymer solution.
The solid content concentration of the water-insoluble polymer solution is preferably 30% by mass or more, more preferably 40% by mass or more, and preferably 70% by mass from the viewpoint of improving the productivity of the aqueous dispersion of the pigment-containing polymer particles. % Or less, more preferably 65% by mass or less.

The number average molecular weight of the water-insoluble polymer P used in the present invention is preferably 2,000 or more, more preferably 5,000 or more, and preferably 5,000 or more, from the viewpoint of adsorption power to the pigment and expression of dispersion stability. It is 20,000 or less, more preferably 18,000 or less. The weight average molecular weight is preferably 6,000 or more, more preferably 8,000 or more, and preferably 80,000 or less, more preferably 40,000 or less.
The number average molecular weight can be measured by the method described in Examples.

[Manufacture of pigment-containing polymer particles]
The water-insoluble polymer P particles containing a pigment (pigment-containing polymer particles) can be efficiently produced as an aqueous dispersion by a method having the following steps 1 to 3.
Step 1: A mixture containing a water-insoluble polymer P having a carboxy group, an organic solvent, an alkali metal compound as a neutralizing agent, a pigment, and water (hereinafter, also referred to as "pigment mixture") is dispersed and treated to carry out a pigment-containing polymer. Step 2: Step 2: A step of removing the organic solvent from the dispersion obtained in Step 1 to obtain an aqueous dispersion of pigment-containing polymer particles (hereinafter, also referred to as "pigment aqueous dispersion"). Step 3: The pigment aqueous dispersion obtained in Step 2 is crosslinked with a water-insoluble polyfunctional epoxy compound to obtain an aqueous pigment dispersion containing the crosslinked water-insoluble polymer P particles.

(Step 1)
In step 1, a mixture containing a water-insoluble polymer P having a carboxy group, an organic solvent, an alkali metal compound as a neutralizing agent, a pigment, and water (pigment mixture) is dispersed to obtain a dispersion of pigment-containing polymer particles. This is the process of obtaining.
The mixing order in step 1 is not particularly limited, but first, the water-insoluble polymer P is dissolved in an organic solvent, and then the alkali metal compound, water, pigment as a neutralizing agent, and if necessary, a surfactant and the like are used in that order. In addition, a method of adding and mixing with the obtained organic solvent solution to obtain an oil-in-water dispersion is preferable.
The organic solvent used is not limited, but aliphatic alcohols having 1 to 3 carbon atoms, ketones, ethers, esters and the like are preferable, and the wettability to pigments, the solubility of water-insoluble polymers, and the solubility of water-insoluble polymers P are preferable. From the viewpoint of improving the adsorptivity to the pigment, a ketone having 4 or more and 8 or less carbon atoms is more preferable, acetone, methyl ethyl ketone and methyl isobutyl ketone are more preferable, and methyl ethyl ketone is even more preferable.
When the water-insoluble polymer P is synthesized by the solution polymerization method, the solvent used in the polymerization may be used as it is.

(Neutralization)
At least a portion of the carboxy group of the water-insoluble polymer P is neutralized with a neutralizing agent, preferably an alkali metal compound. The pH of the obtained water-based pigment dispersion and water-based ink is preferably 5.5 or more, more preferably 6 or more from the viewpoint of handleability such as reducing skin irritation, and from the viewpoint of suppressing corrosion of members. 13 or less is preferable, 12 or less is more preferable, and 11 or less is further preferable.
Alkali metal compounds that are neutralizers are compounds that generate alkali metal ions in water-based media such as water and water-based inks, and are, for example, alkali metals such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide. Hydroxides, alkali metal salts of silicic acids such as sodium orthosilicate, sodium metasilicate, sodium sesquisilicate, alkali metal salts of phosphoric acid such as trisodium phosphate, carbonic acid such as disodium carbonate, sodium hydrogencarbonate, dipotassium carbonate, etc. Examples thereof include alkali metal salts of boric acid and alkali metal salts of boric acid such as sodium borate. Two or more kinds of alkali metal compounds may be combined. As the alkali metal compound, alkali metal hydroxide is preferable, and sodium hydroxide and potassium hydroxide are more preferable. Moreover, the water-insoluble polymer P may be neutralized in advance.
The neutralizing agent is preferably used as an aqueous neutralizing agent from the viewpoint of sufficiently and uniformly promoting neutralization. From the above viewpoint, the concentration of the neutralizing agent 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, preferably 25% by mass or less. More preferred.
The degree of neutralization of the carboxy group of the water-insoluble polymer P is preferably 15 mol% or more, more preferably 20 mol% or more, from the viewpoints of storage stability of the obtained water-based ink, ejection stability during reprinting, and print density. It is more preferably 25 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less, still more preferably 60 mol% or less, still more preferably 50 mol% or less.
Here, the degree of neutralization is a percentage (mol%) obtained by dividing the molar equivalent number of the neutralizing agent (alkali metal compound) by the molar equivalent number of the carboxy group of the water-insoluble polymer P, that is, "neutralizing agent (alkali metal compound)". ) Mole equivalent number / molar equivalent number of carboxy groups of the water-insoluble polymer P ”is a percentage (mol%). In the present invention, the degree of neutralization is calculated from the molar equivalent number of the alkali metal compound, and therefore exceeds 100 mol% when the alkali metal compound is used in excess.

Further, in step 1, a volatile basic compound may be used in combination with the alkali metal compound. Examples of the volatile basic compound include ammonia, trimethylamine, triethylamine and the like, but 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 is used, it is 10 mol% or more, preferably 20 mol% or more, more preferably 25 mol% or more, still more preferably 30 mol. % Or more, and 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. Only the amount of the alkali metal compound used is used for calculating the degree of neutralization, and the amount of the volatile basic compound used is not used for calculating the degree of neutralization of the present invention.

(Content of each component in pigment mixture)
The content of each component in the pigment mixture is as follows from the viewpoints of storage stability of the obtained water-based ink, ejection stability at the time of reprinting, and printing density.
The content of the pigment in the pigment mixture in step 1 is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 12.5% by mass or more, and preferably 35% by mass or less. It is preferably 30% by mass or less, more preferably 20% by mass or less.
The content of the water-insoluble polymer P 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 8. It is 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 4% by mass or more, more preferably 5% by mass or more, further preferably 6% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass. % Or less, more preferably 15% 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, further preferably 50% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass. Hereinafter, it is more preferably 80% by mass or less.

The mass ratio of the pigment to the water-insoluble polymer P in the pigment mixture [pigment / water-insoluble polymer P] is preferably 0.5 or more, more preferably 1.0, from the viewpoint of the viscosity and storage stability of the obtained water-based ink. As mentioned above, it is more preferably 2.0 or more, and preferably 6.0 or less, more preferably 5.0 or less, still more preferably 4.5 or less.

(Dispersion treatment of pigment mixture)
In step 1, the pigment mixture is dispersed to obtain a dispersion of pigment-containing polymer particles. There is no particular limitation on the dispersion method for obtaining the dispersion. 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 pre-dispersion, is preferably 0 ° C. or higher, 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, 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 dispersion obtained in Step 1 to obtain an aqueous dispersion of pigment-containing polymer particles (pigment aqueous dispersion).
In step 2, an aqueous dispersion of pigment-containing polymer particles (pigment aqueous dispersion) can be obtained by removing the organic solvent from the dispersion obtained in step 1 by a known method. It is preferable that the organic solvent in the obtained aqueous pigment dispersion 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.
If necessary, the dispersion can be heat-stirred before distilling off the organic solvent.
The obtained pigment aqueous dispersion 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 and the water-insoluble polymer P. However, as described above, the particle form in which the pigment is contained in the water-insoluble polymer P. Is preferable.

The non-volatile component concentration (solid content concentration) of the obtained pigment aqueous dispersion 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 aqueous ink. It is preferably 15% by mass or more, preferably 30% by mass or less, and more preferably 25% by mass or less.
The solid content concentration of the aqueous pigment dispersion is measured by the method described in Examples.
The average particle size of the pigment-containing polymer particles in the pigment aqueous dispersion is preferably 50 nm or more, more preferably 60 nm or more, still more preferably 70 nm or more, from the viewpoint of reducing coarse particles and improving the ejection stability of the water-based ink. It is preferably 200 nm or less, more preferably 160 nm or less, and further preferably 120 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 pigment-containing polymer particles in the water-based ink is the same as the average particle size in the pigment aqueous dispersion, and the preferred average particle size is the preferred embodiment of the average particle size in the pigment aqueous dispersion. Is the same as.

(Step 3)
Step 3 is a step of cross-linking the pigment aqueous dispersion obtained in Step 2 with a water-insoluble polyfunctional epoxy compound to obtain an aqueous pigment dispersion containing the crosslinked water-insoluble polymer P particles.
In step 3, from the viewpoint of further improving the storage stability and redispersibility of the obtained aqueous pigment dispersion and water-based ink at high temperatures, the pigment aqueous dispersion obtained in step 2 is a water-insoluble polyfunctional epoxy described later. Crosslinking is performed with a compound (crosslinking agent) to obtain an aqueous pigment dispersion containing the crosslinked water-insoluble polymer P. In this step, a part of the carboxy group of the water-insoluble polymer P 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 polymer dispersant according to the present invention is obtained by cross-linking the water-insoluble polymer P and the water-insoluble polyfunctional epoxy compound on the pigment surface, and is contained in the pigment-containing polymer particles in the pigment aqueous dispersion. Is a water-insoluble polymer P crosslinked with a water-insoluble polyfunctional epoxy compound.
In this way, the aqueous pigment dispersion of the present invention becomes an aqueous pigment dispersion in which the pigment is dispersed in an aqueous medium with the polymer dispersant according to the present invention.

<Water-insoluble polyfunctional epoxy compound>
The water-insoluble polyfunctional epoxy compound (crosslinking agent) used in the present invention is dissolved in 100 g of water at 20 ° C. from the viewpoint of efficiently cross-linking with the carboxy group of the water-insoluble polymer P in a medium mainly composed of water. In addition, the dissolved amount is preferably 55 g or less, more preferably 44 g or less, still more preferably 39 g or less.
Further, the water-insoluble polyfunctional epoxy compound has a water content of preferably 50% by mass or less, more preferably 50% by mass or less, from the viewpoint of further improving the storage stability and redispersibility of the obtained water-based pigment dispersion and water-based ink at high temperatures. Is 40% by mass or less, more preferably 35% by mass or less.
Here, the water content (mass%) means the dissolution rate (mass%) 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.

The water-insoluble polyfunctional epoxy compound is preferably a compound having two or more epoxy groups in the molecule, more preferably a compound having a glycidyl ether group, and further preferably a polyvalent compound having a hydrocarbon group having 3 or more and 8 or less carbon atoms. It is a glycidyl ether compound of alcohol.
The molecular weight of the water-insoluble polyfunctional epoxy compound is preferably 120 or more, more preferably 150 or more, still more preferably 200 or more, and from the viewpoint of ease of reaction and storage stability of the obtained crosslinked polymer. It is preferably 2000 or less, more preferably 1500 or less, and even more preferably 1000 or less.
The number of epoxy groups in the water-insoluble polyfunctional epoxy compound is 2 or more, preferably 3 or more per molecule, from the viewpoint of efficiently cross-linking with the carboxy group to improve the storage stability of the pigment-containing polymer particles. It is preferably 6 or less per molecule. 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 is preferably 100 or more, more preferably 110 or more, further preferably 120 or more, and preferably 300 or less, more preferably 270 or less. More preferably, it is 250 or less.

Specific examples of the water-insoluble polyfunctional epoxy compound include polypropylene glycol diglycidyl ether, glycerin polyglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, and pentaerythritol polyglycidyl. Examples thereof include polyglycidyl ethers such as ethers, resorcinol diglycidyl ethers, neopentyl glycol diglycidyl ethers, and hydrogenated bisphenol A type diglycidyl ethers.
Among these, one or more selected from polypropylene glycol diglycidyl ether (water content 31%), trimethylolpropane polyglycidyl ether (water content 27%), and pentaerythritol polyglycidyl ether (water content less than 20%) are selected. preferable.

(Crosslink reaction)
In the present invention, a part of the carboxy group of the water-insoluble polymer P is neutralized with an alkali metal compound, the pigment is dispersed, and then a part of the carboxy group of the water-insoluble polymer P is a water-insoluble polyfunctional epoxy compound. It is preferable to form an aqueous pigment dispersion in which a crosslinked structure is formed by reacting with and the pigment is dispersed in an aqueous medium with a polymer dispersant obtained in the system. At that time, from the viewpoints of storage stability of the obtained water-based ink, ejection stability at the time of reprinting, and print density, the neutralizing agent (alkali metal compound) and the neutralizing agent (alkali metal compound) and the amount satisfying the following condition 1, preferably further condition 2. A water-insoluble polyfunctional epoxy compound is used.

[Condition 1]
Condition 1 is that the value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of water-insoluble polymer P) is −30 mgKOH / g or more and 130 mgKOH / g or less.
Here, the degree of neutralization is a percentage (mol%) of "molar equivalent number of neutralizing agent (alkali metal compound) / molar equivalent number of carboxy group of water-insoluble polymer P", and the degree of cross-linking is "water-insoluble polyfunctional epoxy compound". The molar equivalent number of the epoxy group of the water-insoluble polymer P / the molar equivalent number of the carboxy group of the water-insoluble polymer P ”is a percentage (mol%).
The acid value of the water-insoluble polymer P 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.
Condition 1 indicates the amount of unneutralized carboxy groups of the polymer dispersant in the water-based ink required to enhance ejection stability and storage stability, and the acid value, neutralization degree, and cross-linking of the water-insoluble polymer P. Determined by degree. In other words, Condition 1 represents the acid value of the water-insoluble polymer P after neutralization and cross-linking.
If the value of Condition 1 is -30 mgKOH / g or more and 130 mgKOH / g or less, the amount of charge on the pigment surface is sufficient when a pigment dispersion is prepared using the polymer, and the polymer dispersant is also water-insoluble. It becomes sufficient, and high discharge stability and storage stability can be exhibited.
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 140 mgKOH / g or less, more preferably 130 mgKOH / g or less. , More preferably 120 mgKOH / g or less.

[Condition 2]
Condition 2 is that the value of [(crosslinking degree) / 100] × (acid value of water-insoluble polymer P) is 30 mgKOH / g or more and 180 mgKOH / g or less.
Condition 2 indicates the degree of cross-linking required to enhance storage stability. In other words, Condition 2 represents the acid value of the water-insoluble polymer P reduced by cross-linking. In the water-based ink, in order to improve the storage stability of the pigment particles, it is preferable to satisfy the condition of the degree of cross-linking in addition to the above-mentioned conditions.
When the value of Condition 2 is 30 mgKOH / g or more, the water insolubility of the polymer dispersant can be sufficiently enhanced, the adsorption to the pigment becomes strong, and the storage stability can be enhanced. On the other hand, when the value of Condition 2 is 180 mgKOH / g or less, the hydrophobicity of the polymer dispersant is sufficient and can be strongly adsorbed on the pigment, and the amount of carboxy anion present in the water-based ink is also sufficient to cause aggregation. It can be suppressed.
The value of condition 2 is preferably 40 mgKOH / g or more, more preferably 50 mgKOH / g or more, still more preferably 80 mgKOH / g or more, and preferably 170 mgKOH / g or less, more preferably 150 mgKOH / g or less, still more preferable. Is 120 mgKOH / g or less.
Since it is difficult to actually measure the amount of the water-insoluble polyfunctional epoxy compound that reacts with the carboxy group of the water-insoluble polymer P, the number of moles of the epoxy group of the water-insoluble polyfunctional epoxy compound used. Is converted into the acid value per 1 g of the water-insoluble polymer P used to disperse the pigment.

The temperature of the cross-linking reaction 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. from the viewpoint of completion of the reaction and economic efficiency. The above, and preferably 95 ° C. or lower, more preferably 90 ° C. or lower.
From the same viewpoint as above, the reaction time is preferably 0.5 hours or more, more preferably 1 hour or more, still more preferably 1.5 hours or more, still more preferably 3.0 hours or more. Then, 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 water-insoluble polymer P 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 70 mol% or less. , More preferably 60 mol% or less. The degree of cross-linking is an apparent degree of cross-linking calculated from the acid value of the polymer and the equivalent of the epoxy group of the cross-linking agent. That is, the degree of cross-linking is a percentage (mol%) of "molar equivalent number of epoxy groups of water-insoluble polyfunctional epoxy compound / molar equivalent number of carboxy groups of water-insoluble polymer P".

The pH of the obtained pigment dispersion is preferably 8.0 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 pH of the pigment dispersion is preferably 8.5 or more, and the upper limit thereof is not particularly limited. However, when the pH exceeds 11, the pH of the ink using the pigment dispersion becomes too high, and the ink is used. It is not preferable because it adversely affects the members of the printer or printing machine. Therefore, the pH of the pigment dispersion is more preferably 10.5 or less.
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. Specifically, it is measured by the method described in Examples.

[Water-based ink]
The water-based ink of the present invention is a pigment, a polymer dispersant, a 1,2-alkanediol having 4 or more carbon atoms or 1,3-alkanediol which may have a methyl group or an ethyl group at the 2-position, 3-position or 4-position. Contains alkanediol, nonionic surfactant, and water.

<1,2-Alkanediol or 1,3-Alkanediol having 4 or more carbon atoms which may have a methyl group or an ethyl group at the 2-position, 3-position or 4-position>
A 1,2-alkanediol or a 1,3-alkanediol having 4 or more carbon atoms which may have a methyl group or an ethyl group at the 2-position, 3-position or 4-position used in the present invention (hereinafter, simply "alkane"). The diol) is preferably a water-soluble one that is soluble in 1000 g of water at 25 ° C. in an amount of 3 g or more, and is a 1,2-alkanediol having no methyl group or ethyl group at the 2-position, 3-position or 4-position. Alternatively, 1,3-alkanediol having a methyl group or an ethyl group at any of the 2-position, 3-position and 4-position is more preferable.
Specific examples thereof include 1,2-butanediol, 1,2-hexanediol, 1,2-octanediol, 2-methyl-1,3-butanediol, 2-ethyl-1,3-hexanediol, and 3 -Methyl-1,3-butanediol, 3-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol and the like can be mentioned. Among these, 1,2-alkanediol or 1,3-alkanediol having 5 or more carbon atoms is preferable, and 1,2-hexanediol and 3-methyl-1,3-butanediol are more preferable.
Further, an organic solvent other than the alkanediol can be used in combination. Examples of such an organic solvent include propylene glycol, glycerin, diethylene glycol, triethylene glycol, tetraethylene glycol, alkyl ethers thereof, 2-pyrrolidone and the like.

<Nonionic surfactant>
The nonionic surfactant is used as a surface tension adjusting agent from the viewpoint of improving image quality and ejection stability.
Examples of the nonionic surfactant include (1) saturated or unsaturated linear or branched higher alcohols, polyhydric alcohols, or aromatic alcohols having 8 to 22 carbon atoms, ethylene oxide, and propylene oxide. Alternatively, a polyoxyalkylene alkyl ether to which butylene oxide is added, an alkenyl ether, an alkynyl ether or an aryl ether, (2) a higher grade having a saturated or unsaturated, linear or branched hydrocarbon group having 8 to 22 carbon atoms. Ester of alcohol and polyhydric fatty acid, (3) Polyoxyalkylene aliphatic amine having an alkyl group or alkenyl group of linear or branched chain having 8 or more and 20 or less carbon atoms, (4) 8 or more and 22 or less carbon atoms. Higher fatty acids and compounds of polyhydric alcohol ester compounds or compounds to which ethylene oxide, propylene oxide or butylene oxide are added, (5) silicone-based surfactants such as polysiloxane oxyethylene adducts, (6) perfluoroalkyl carboxylic acids. Examples thereof include fluorine-based surfactants such as salts, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers.
Among these, one or more selected from polyoxyalkylene alkyl ether-based surfactants such as polyoxyethylene alkyl ether, acetylene glycol-based surfactants, and fluorine-based surfactants are preferable, and from the viewpoint of discharge stability. Therefore, one or more selected from acetylene glycol-based surfactants and fluorine-based surfactants is more preferable, and acetylene glycol-based surfactants are even more preferable.

Preferable examples of the acetylene glycol-based surfactant are 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octin-3,6-diol, 2 , 5-Dimethyl-3-hexyne-2,5-diol, 2,5,8,11-tetramethyl-6-dodecin-5,8-diol, 3,5-dimethyl-1-hexin-3-ol, And one or more selected from these ethylene oxide adducts, more preferably 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octin-. One or more selected from 3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, and ethylene oxide adducts thereof, more preferably 2,4,7,9-tetra. One or more selected from methyl-5-decine-4,7-diol and its ethylene oxide adduct.

Commercially available nonionic surfactants include, for example, "Surfinol 104PG-50 (2,4,7,9-tetramethyl-5-decine-4) manufactured by Nissin Chemical Industry Co., Ltd. and Air Products & Chemicals. , 7-diol propylene glycol solution, effective content 50%) ”,“ Surfinol 465 (2,4,7,9-tetramethyl-5-decine-4,7-diol ethylene oxide (hereinafter also referred to as “EO”) "Adductant, EO average number of moles added: 10)", "Surfactant 485 (same EO adduct, average number of EO moles: 30)", "Orfin E1010 (same EO adduct, average number of EO moles: 30)" 10) ”,“ Acetyrenol (ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decine-4,7-diol) E81 (EO average number of moles added: 8.1) manufactured by Kawaken Fine Chemicals Co., Ltd. ) ”,“ Acetyleneol E100 (EO average adduct number: 10) ”,“ Acetylenol E200 (EO average adduct number: 20) ”,“ Emargen 120 (polyoxyethylene lauryl ether) ”manufactured by Kao Co., Ltd., Dupont Examples thereof include a fluorine-based surfactant "Zonil FS300" manufactured by Zoneil FS300.

The content of each component of the water-based ink of the present invention and the physical characteristics of the ink are as follows.
(Pigment content)
The content of the pigment in the water-based ink is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, still more preferably 2.5% by mass or more, from the viewpoint of improving the printing density of the water-based ink. is there. Further, from the viewpoint of lowering the ink viscosity at the time of solvent volatilization and improving the storage stability, it is preferably 15.0% by mass or less, more preferably 10.0% by mass or less, and further preferably 7.0% by mass or less. ..
(Total content of pigment and water-insoluble polymer P)
The total content of the pigment and the water-insoluble polymer P 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, still 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 8.0% by mass or less. Is.
(Alkanediol content)
The content of the alcan diol is preferably 2% by mass or more, more preferably 5% by mass or more, still more preferably 5% by mass or more in the water-based ink from the viewpoint of improving the ejection stability of the water-based ink and improving the printing density on plain paper. Is 7% by mass or more, and preferably 15% by mass or less, more preferably 14% by mass or less, still more preferably 13% by mass or less.

(Water content)
As the water used for the water-based ink of the present invention, pure water such as ion-exchanged water and distilled water and ultrapure water are preferable. The water content is preferably 45% by mass or more, more preferably 50% by mass or more, still more preferably 55% by mass in the water-based ink from the viewpoint of reducing the amount of the organic solvent used and improving the ejection stability. % Or more, and preferably 85% by mass or less, more preferably 80% by mass or less, still more preferably 75% by mass or less.

(Water-based 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, still more preferably 5.0 mPa · s, from the viewpoint of further improving the storage stability of the ink. It is s or more, 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.

[Manufacturing of water-based ink]
In the water-based ink of the present invention, after producing an aqueous dispersion of water-insoluble polymer P particles (pigment-containing polymer particles) containing a pigment by the above steps 1 to 3, the alcandiol and the nonionic surfactant are added thereto. , And water can be added.
In addition, if necessary, various types of moisturizers, wetting agents, penetrants, dispersants, surfactants, viscosity modifiers, defoamers, preservatives, fungicides, rust preventives, etc., which are usually used for water-based inks. Additives can be added, and further filtration treatment with a filter or the like can be performed.
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 P N, N-dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd., for high performance liquid chromatography) and phosphoric acid (manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent) And lithium bromide (manufactured by Tokyo Kasei Kogyo Co., Ltd., reagent) dissolved at a concentration of 60 mmol / L and 50 mmol / L, respectively, as an eluent, and a gel chromatography method [GPC apparatus manufactured by Toso Co., Ltd. (HLC-) 8120 GPC), a column manufactured by Toso Co., Ltd. (TSK-GEL, α-M × 2), flow velocity: 1 mL / min], and a monodisperse polystyrene having a known molecular weight was used as a standard substance.

(2) Measurement of average particle size of 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 dispersion In a 30 ml polypropylene container (φ = 40 mm, height = 30 mm), 10.0 g of sodium sulfate homogenized in a desiccator was weighed, and about 1.0 g of a sample was placed therein. Was added, mixed, weighed accurately, maintained at 105 ° C. for 2 hours to remove volatiles, and left in a desiccator for an additional 15 minutes to measure 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 epoxy compound 90 parts by mass of ion-exchanged water and 10 parts by mass of cross-linking agent were added to a glass tube (25 mmφ × 250 mmh) at room temperature 25 ° C., and the glass tube was adjusted to a constant temperature of 25 ° C. It was allowed to stand in the tank for 1 hour. 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 water-insoluble polymer P>
Preparation Example 1
Methacrylate (manufactured by Wako Pure Chemical Industries, Ltd., reagent) 73.5 parts, benzyl acrylate (manufactured by Wako Pure Chemical Industries, Ltd., reagent) 66.5 parts, styrene macromer (manufactured by Toa Synthetic Co., Ltd., trade name: AS- 6S, number average molecular weight: 6000, solid content concentration 50%) 40 parts (20 parts as solid content), polypropylene glycol monomethacrylate (manufactured by Nichiyu Co., Ltd., trade name: Blemmer PP-800, average number of moles of propylene oxide added 13) , Terminal: hydroxyl group) 40 parts were mixed to prepare a monomer mixed solution. In the reaction vessel, 20 parts of methyl ethyl ketone (MEK), 0.3 part of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the monomer mixed solution were put and mixed, and nitrogen gas substitution was sufficiently performed.
On the other hand, in the dropping funnel, the remaining 90% of the monomer mixed solution, 0.27 parts of the polymerization chain transfer agent, 60 parts of MEK, and an azo radical polymerization initiator (manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65). , 2,2'-azobis (2,4-dimethylvaleronitrile)) 2.2 parts of the mixed solution was added, and the temperature was raised to 65 ° C. while stirring the monomer mixed solution in the reaction vessel under a nitrogen atmosphere. The mixed solution in the dropping funnel was dropped 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, and then the solid content concentration. MEK was added so that the concentration was 40.8% to obtain a water-insoluble polymer solution (i) having a carboxy group (number average molecular weight of polymer: 12000, acid value 240 mgKOH / g). The results are shown in Table 1.

Preparation Example 2
Acrylic acid (reagent manufactured by Wako Pure Chemical Industries, Ltd.) 38.5 parts, styrene (reagent manufactured by Wako Pure Chemical Industries, Ltd.) 152.5 parts, α-methylstyrene (reagent manufactured by Wako Pure Chemical Industries, Ltd.) 9 The parts were mixed to prepare a monomer mixture. 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) were put into the dropping funnel. After that, a water-insoluble polymer solution (ii) having a carboxy group having a solid content concentration of 40.8% was obtained in the same manner as in Preparation Example 1. The results are shown in Table 1.

Preparation Examples 3, 4
In Preparation Example 2, water-insoluble polymer solutions (iii) and (iv) having a carboxy group were obtained in the same manner as in Preparation Example 2 except that the amounts of acrylic acid and styrene were set to the amounts shown in Table 1. The results are shown in Table 1.

<Manufacturing of aqueous pigment dispersion of pigment-containing polymer particles>
Production Example 1 (Production of water-based pigment dispersion A1)
(1) Step 1
157.6 g of the water-insoluble polymer solution (i) (solid content concentration 40.8%) obtained in Preparation Example 1 was mixed with 60.7 g of methyl ethyl ketone (MEK) and charged into a 2 L volume disper at 1400 rpm. While stirring under the conditions, 446.9 g of ion-exchanged water and 51.3 g of a 5N sodium hydroxide aqueous solution (neutralization degree with sodium hydroxide 32%) were added, and the mixture was stirred at 1400 rpm for 15 minutes while cooling in a water bath at 0 ° C. .. Next, 256 g of a cyan pigment (CI Pigment Blue 15: 3, copper phthalocyanine, manufactured by DIC Corporation, trade name: TGR-SD) was added, and the mixture was stirred at 7000 rpm for 3 hours. Further, 1044 g of ion-exchanged water was added, and the obtained pigment mixture was subjected to 20-pass dispersion treatment at a pressure of 150 MPa using a microfluidizer "M-110EH-30XP" (manufactured by Microfluidics) to disperse the dispersion (solid content concentration). 21.0% by mass) was obtained.
(2) Step 2
1000 g of the dispersion obtained in step 1 was placed in a 2 L eggplant flask, 400 g of ion-exchanged water was added (solid content concentration 15.0% by mass), and a rotary distillation apparatus (manufactured by Tokyo Rika Kikai Co., Ltd., product name: rotary evaporator) was added. Using N-1000S), the organic solvent was removed by holding at a pressure of 0.09 MPa for 3 hours in a warm bath adjusted to 32 ° C. at a rotation speed of 50 rpm. Further, the warm bath was adjusted to 62 ° C., the pressure was lowered to 0.07 MPa, and the mixture was concentrated to a solid content concentration of 25.0% by mass.
The obtained concentrate was put into a 500 ml angle rotor, centrifuged at 7000 rpm for 20 minutes using a high-speed cooling centrifuge (manufactured by Hitachi Koki Co., Ltd., product name: himacCR22G, set temperature 20 ° C.), and then the liquid layer portion. Was filtered through a 5 μm membrane filter (manufactured by Sartorius, trade name: Minisart) to obtain a pigment aqueous dispersion a1.
(3) Step 3
54.6 g of ion-exchanged water was added to 400 g of the pigment aqueous dispersion a1 obtained in step 2, and further, Proxel LVS (manufactured by Arch Chemicals Japan Co., Ltd., antifungal agent, effective content 20%) 0.89 g, degree of cross-linking. Add 4.8 g of a water-insoluble polyfunctional epoxy compound (trimethylolpropane polyglycidyl ether, manufactured by Nagase ChemteX Corporation, trade name: Denacol EX321, water content 27%, epoxy equivalent 140) so as to be 40 mol%. , 70 ° C. for 2 hours. After cooling to 25 ° C., the mixture is filtered through the 5 μm filter, ion-exchanged water is further added so that the solid content concentration becomes 22.0% by mass, and an aqueous pigment dispersion of pigment-containing polymer particles (crosslinking degree 40 mol%) is added. I got A1.

Production Example 2 (Production of water-based pigment dispersion A2)
(1) Step 1
Except for using the polymer solution (ii) obtained in Preparation Example 2 (solid content concentration 40.8%) to make 32.1 g of a 5N sodium hydroxide aqueous solution (neutralization degree with sodium hydroxide 32%). A dispersion (solid content concentration 21.0% by mass) was obtained in the same manner as in Step 1 of Production Example 1.
(2) Step 2
The pigment aqueous dispersion a2 was obtained in the same manner as in Step 2 of Production Example 1.
(3) Step 3
Pigment-containing polymer particles in the same manner as in Step 3 of Production Example 1 except that 3.0 g of the water-insoluble polyfunctional epoxy compound (Denacol EX321) was added using the pigment aqueous dispersion a2 obtained in Step 2. An aqueous pigment dispersion A2 having a degree of cross-linking of 40 mol% was obtained.

Production Example 3 (Production of water-based pigment dispersion A3)
(1) Step 1
Using the polymer solution (iii) (solid content concentration 40.8%) obtained in Preparation Example 3, a dispersion (solid content concentration 21.0% by mass) was obtained in the same manner as in Step 1 of Production Example 1. It was.
(2) Step 2
The pigment aqueous dispersion a3 was obtained in the same manner as in Step 2 of Production Example 1.
(3) Step 3
Pigment-containing polymer particles in the same manner as in Step 3 of Production Example 1 except that 4.8 g of the water-insoluble polyfunctional epoxy compound (Denacol EX321) was added using the pigment aqueous dispersion a3 obtained in Step 2. Water-based pigment dispersion A3 was obtained.

Production Examples 4 to 11 (Production of water-based pigment dispersions A4 to A11)
In Production Example 3, the pigment-containing polymer particles were prepared in the same manner as in Production Example 3 except that the amount of the 5N sodium hydroxide aqueous solution in Step 1 and the amount of the water-insoluble polyfunctional epoxy compound in Step 3 were as shown in Table 2. A4 to A11 aqueous pigment dispersions were obtained.

Production Example 12 (Production of water-based pigment dispersion A12)
In Production Example 3, steps 1 and 2 were carried out in the same manner as steps 1 and 2 of Production Example 3.
In step 3, the pigment dispersion a3 obtained in step 2 was used to obtain a water-soluble polyfunctional epoxy compound (polyglycerol polyglycidyl ether, manufactured by Nagase ChemteX Corporation, trade name: Denacol EX521, epoxy equivalent 183). An aqueous pigment dispersion A12 of pigment-containing polymer particles was obtained in the same manner as in Step 3 of Production Example 1 except that 3 g was added.

Production Example 13 (Production of water-based pigment dispersion A13)
(1) Step 1
Except that the polymer solution (iv) (solid content concentration 40.8%) obtained in Preparation Example 4 was used to make 79.1 g of a 5N sodium hydroxide aqueous solution (neutralization degree with sodium hydroxide 32%). A dispersion (solid content concentration 21.0% by mass) was obtained in the same manner as in Step 1 of Production Example 1.
(2) Step 2
The pigment aqueous dispersion a9 was obtained in the same manner as in Step 2 of Production Example 1.
(3) Step 3
Pigment-containing polymer particles in the same manner as in Step 3 of Production Example 1 except that 7.4 g of the water-insoluble polyfunctional epoxy compound (Denacol EX321) was added using the pigment aqueous dispersion a9 obtained in Step 2. An aqueous pigment dispersion A13 having a degree of cross-linking of 40 mol% was obtained.

Example 1 (Manufacturing of water-based ink 1)
26.0 parts of the aqueous pigment dispersion A1 obtained in Production Example 1, 10.0 parts of 1,2-hexanediol (reagent manufactured by Wako Pure Chemical Industries, Ltd.) and triethylene glycol (Wako Pure Chemical Industries, Ltd.) 5.0 parts of reagent), 7.0 parts of glycerin (manufactured by Kao Co., Ltd.), Surfinol 104PG-50 (manufactured by Nissin Chemical Industries, Ltd., acetylene-based nonionic surfactant, 2, 4, 7, 9 0.5 part of a solution of propylene glycol (50%) of −tetramethyl-5-decine-4,7-diol) and 51.0 parts of ion-exchanged water were mixed, and the obtained mixed solution was a 1.2 μm membrane. A water-based ink 1 was obtained by filtering with a filter (manufactured by Sartorius, trade name: Minisart).

Examples 2-28, Comparative Examples 1-14 (Manufacturing of water-based inks 2-42)
Water-based pigment dispersions A2 to A13, an organic solvent, a surfactant, and ion-exchanged water were mixed according to the formulation shown in Tables 3 and 4, and water-based inks 2-42 were obtained in the same manner as in Example 1.

The water-soluble organic solvents used in Tables 3 and 4 are all reagents manufactured by Wako Pure Chemical Industries, Ltd.
In Tables 3 and 4, "3-M-1,3-BD" is 3-methyl-1,3-butanediol, and "2,2,4-TM-1,3-PD" is 2,2. , 4-Trimethyl-1,3-pentanediol, and "3-E-1,3-HD" is 3-ethyl-1,3-hexanediol.
The details of the surfactant used are as follows.
Surfinol 104PG-50: manufactured by Nissin Chemical Industry Co., Ltd., propylene glycol solution of 2,4,7,9-tetramethyl-5-decine-4,7-diol, effective content 50%
-Acetyleneol E100: Kawaken Fine Chemicals Co., Ltd., 2,4,7,9-tetramethyl-5-decine-4,7-diol ethylene oxide approximately 10 mol adduct-Zonil FS300: DuPont, fluorine-based surfactant , 40% solution ・ Emargen 120: Polyoxyethylene lauryl ether manufactured by Kao Corporation

<Evaluation of water-based inks 1-42>
Using the water-based inks 1-42 obtained in Examples and Comparative Examples, storage stability, ejection stability at the time of reprinting, and print density were evaluated by the following methods. The results are shown in Tables 3 and 4.

(1) Storage stability Water-based ink is filled in a closed glass container, and the viscosity of the ink after storage at 80 ° C. for 30 days is measured at 20 ° C. using an E-type viscometer (RE80L manufactured by Toki Sangyo Co., Ltd.). Then, the viscosity change rate was calculated from the following formula. If there is no change, it will be 100%, and the closer the value of the viscosity change rate is to 100%, the better the storage stability.
Viscosity change rate (%) = ([Viscosity after storage] / [Viscosity before storage]) x 100
(Evaluation criteria)
A: Viscosity change rate within 100 ± 5% A-: Viscosity change rate within 100 ± 10% B: Viscosity change rate within 100 ± 15% C: Viscosity change rate within 100 ± 20% D: Viscosity change rate If the evaluation result is A or A-> 100 ± 20%, the storage stability is sufficient.

(2) Discharge stability After filling the ink cartridge of a commercially available inkjet printer (manufactured by Ricoh Co., Ltd., IPSIO SG 2010L, piezo method) with water-based ink, leave it for 30 minutes without capping the head, and then start printing again. The state of ink ejection was confirmed, the number of missing nozzles among all 96 nozzles was counted, and the ejection stability was evaluated according to the following evaluation criteria.
(Evaluation criteria)
A: No chipping.
A-: The number of missing nozzles is 2/48 or less of all nozzles, and it recovers if maintenance is performed.
B: The number of missing nozzles is more than 2/48 in all nozzles and less than 5/48, but it can be recovered by maintenance.
C: There are more missing nozzles than 5/48 of all nozzles, but they can be recovered by maintenance.
D: Nozzle chipping is not fixed even after maintenance.
If the evaluation result is A, A- or B, there is no practical problem in discharge stability.

(3) Print density A solid image is printed on plain paper "CopyPlus" (manufactured by Hammermill) using a commercially available inkjet printer (manufactured by Ricoh Co., Ltd., IPSIO SG 2010L, piezo method), left for one day, and then optical. The print density at any 10 locations was measured using a densitometer SpectroEye (manufactured by Gretag Macbeth), and the average value was calculated.
(Evaluation criteria)
A: 1.10 or more.
A-: 1.05 or more and less than 1.10 B: 1.00 or more and less than 1.05 C: 0.95 or more and less than 1.00 D: less than 0.95 If the evaluation result is A or A-, the print density is There is no problem in practical use.

From Tables 3 and 4, the water-based inks 1 to 28 of Examples 1 to 28 of the present invention have long-term storage stability and ejection stability during inkjet recording as compared with the water-based inks 29 to 42 of Comparative Examples 1 to 14. It can be seen that the properties are excellent and a high print density can be obtained when printing on plain paper.

Claims (6)

A water-based ink containing pigments, polymer dispersants , alkanediols, nonionic surfactants, and water.
The alkanediol has no methyl group or ethyl group at the 2-position, 3-position or 4-position, and is a 1,2-alkanediol having 4 or more carbon atoms, or a methyl group at any of the 2-position, 3-position and 4-position. Alternatively, it is a 1,3-alkanediol having an ethyl group and having 4 or more carbon atoms, and the content of the alkanediol is 3.0% by mass or more and 15% by mass or less in the aqueous ink.
The polymer dispersant comprises cross-linking a water-insoluble polymer P having a carboxy group and an acid value of 200 mgKOH / g or more and 320 mgKOH / g or less with a water-insoluble polyfunctional epoxy compound.
The water-insoluble polyfunctional epoxy compound is a polyhydric alcohol glycidyl ether compound having 2 or more and 6 or less epoxy groups in the molecule and having a hydrocarbon group having 3 or more and 8 or less carbon atoms.
A water-based ink in which the acid value, the degree of neutralization, and the degree of cross-linking of the water-insoluble polymer P satisfy the following condition 1.
Condition 1: The value of [(100-neutralization degree-crosslinking degree) / 100] × (acid value of water-insoluble polymer P) 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 neutralizer / molar equivalent of carboxy group of water-insoluble polymer P", and the degree of cross-linking is "molar of epoxy group of water-insoluble polyfunctional epoxy compound". Equivalent number / molar equivalent number of carboxy groups of the water-insoluble polymer P "percentage (mol%). The water-based ink according to claim 1, further satisfying the following condition 2.
Condition 2: The value of [(crosslinking degree) / 100] × (acid value of water-insoluble polymer P) is 30 mgKOH / g or more and 180 mgKOH / g or less. The water-based ink according to claim 1 or 2 , wherein the water-insoluble polyfunctional epoxy compound is at least one selected from polypropylene glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, and pentaerythritol polyglycidyl ether. The water-based ink according to any one of claims 1 to 3 , wherein the nonionic surfactant is at least one selected from an alkyl ether-based surfactant, an acetylene glycol-based surfactant, and a fluorine-based surfactant. .. The acetylene glycol-based surfactants are 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 2,5-dimethyl. The aqueous ink according to any one of claims 1 to 4, which is one or more selected from -3-hexyne-2,5-diol and ethylene oxide adducts thereof. The water-based ink according to any one of claims 1 to 5, wherein the mass ratio of the pigment to the water-insoluble polymer P [pigment / water-insoluble polymer P] is 0.5 or more and 6.0 or less.