Aqueous pigment dispersion

Abstract

To provide an aqueous pigment dispersion which is excellent in base material adhesion (resistance against tape peelability) of an ink coating film of printed matter obtained when being used for printing a resin film, and an intermittent discharge property, and aqueous ink containing the aqueous pigment dispersion.SOLUTION: There are provided [1] an aqueous pigment dispersion in which a pigment is dispersed with a crosslinked polymer A, wherein the crosslinked polymer A includes a structure derived from a water-dispersible polymer A' and a structure derived from a water-insoluble polyfunctional epoxy crosslinking agent, and the water-dispersible polymer A' is a vinyl-based resin including a structural unit derived from cycloalkyl (meth)acrylate (a-1), and [2] aqueous ink containing the aqueous pigment dispersion described in [1] and a water-soluble organic solvent.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based pigment dispersion and a water-based ink containing the water-based pigment dispersion. [Background technology]

[0002] A printing method using the inkjet recording method is a method in which ink droplets are ejected from a fine nozzle and directly adhered to a printing substrate to obtain a printed matter on which characters or images are recorded. This printing method has become extremely popular because it has many advantages, such as being easy to produce full color and being inexpensive, being able to use various printing substrates such as plain paper, label paper, and resin film as the printing substrate, and being non-contact with the substrate to be printed. In particular, from the viewpoint of weather resistance and water resistance of the printed matter, inks using pigments as colorants have become mainstream.

[0003] For example, Patent Document 1 discloses an aqueous pigment dispersion in which a pigment is dispersed in an aqueous medium with a polymer dispersant, the polymer dispersant being a water-insoluble polymer having carboxy groups, at least a portion of which is neutralized with an alkali metal hydroxide, and which has a crosslinked structure obtained by reacting a portion of the carboxy groups with a water-insoluble polyfunctional epoxy compound, and which satisfies specified conditions, with the objective of providing an aqueous pigment dispersion and an aqueous ink that have excellent storage stability capable of suppressing solidification of the pigment or polymer in ink ejection nozzles while maintaining water resistance, which is an advantage of using a pigment, and further have excellent ejection properties and fixation properties. Furthermore, Patent Document 2 discloses a copolymer for inkjet inks containing cyclohexyl methacrylate units and acrylic acid units in a specified ratio, as well as a pigment dispersion for inkjet inks containing the copolymer, for the purpose of providing, with good productivity, an inkjet ink capable of forming printed matter having excellent weather resistance, fixation properties (abrasion resistance), and the like. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-119845 A [Patent Document 2] International Publication No. 2012 / 118078 Summary of the Invention [Problem to be solved by the invention]

[0005] Meanwhile, in the industrial printing market, such as packaging printing for food products, resin films are mainly used as printing substrates from the viewpoint of durability. Unlike paper printing substrates, resin films are printing substrates whose surfaces are hydrophobic and non-absorbent, and therefore the problem is that the ink wettability to the resin film surface is insufficient. Therefore, in general, a hydrophobic organic solvent is sometimes blended into the ink in order to improve the ink wettability to the resin film. However, in the case of inks blended with such hydrophobic organic solvents, there is a problem that the dispersion stability of the pigment decreases when the ink is concentrated in the inkjet nozzle, and the ejectability, so-called intermittent ejectability, decreases when the ink is ejected again after a predetermined time has elapsed without ejecting the ink from the inkjet nozzle. In addition, a particular problem with using a resin film as a printing substrate is the substrate adhesion, particularly tape peel resistance, of the ink coating film of the resulting printed matter. If the tape peel resistance of the ink coating film of the printed matter is insufficient, the ink coating film is likely to peel off from the resin film, not only impairing the aesthetic appeal of the printed matter, but also causing the resin film and the laminate film to peel off when laminated. Therefore, there is a demand for improving the substrate adhesion (tape peel resistance) of the ink coating film of the printed matter obtained when printing on a resin film. However, it was found that when inks using the aqueous pigment dispersion described in Patent Document 1 or the copolymer described in Patent Document 2 were used for printing on hydrophobic, non-liquid-absorbing resin films, the ink coating film of the resulting printed matter had insufficient adhesion to the substrate (tape peel resistance). An object of the present invention is to provide an aqueous pigment dispersion which, when used for printing on a resin film, results in an ink coating film having excellent substrate adhesion (tape peel resistance) and excellent intermittent ejection properties, and to provide an aqueous ink containing the aqueous pigment dispersion. [Means for solving the problem]

[0006] The present inventors have found that the above-mentioned problems can be solved by providing an aqueous pigment dispersion in which a pigment is dispersed in a crosslinked polymer, the crosslinked polymer containing a structure derived from a water-dispersible polymer and a structure derived from a water-insoluble polyfunctional epoxy crosslinking agent, and the water-dispersible polymer being a vinyl resin containing a structural unit derived from a cycloalkyl (meth)acrylate. That is, the present invention provides the following [1] and [2]. [1] An aqueous pigment dispersion in which a pigment is dispersed in a crosslinked polymer A, the crosslinked polymer A comprises a structure derived from a water-dispersible polymer A' and a structure derived from a water-insoluble multifunctional epoxy crosslinking agent; The water-based pigment dispersion, wherein the water-dispersible polymer A' is a vinyl resin containing a structural unit derived from a cycloalkyl (meth)acrylate (a-1). [2] A water-based ink comprising the water-based pigment dispersion according to [1] above and a water-soluble organic solvent. Effect of the Invention

[0007] According to the present invention, it is possible to provide an aqueous pigment dispersion which, when used for printing on a resin film, gives an ink coating film of a printed matter having excellent substrate adhesion (tape peel resistance) and excellent intermittent ejection properties, and an aqueous ink containing the aqueous pigment dispersion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Water-based pigment dispersion] The aqueous pigment dispersion of the present invention is an aqueous pigment dispersion in which a pigment is dispersed in a crosslinked polymer A, the crosslinked polymer A containing a structure derived from a water-dispersible polymer A' and a structure derived from a water-insoluble polyfunctional epoxy crosslinking agent, and the water-dispersible polymer A' is a vinyl resin containing a structural unit derived from a cycloalkyl (meth)acrylate (a-1). In the present invention, the pigment is dispersed in the aqueous medium by the crosslinked polymer A. In the present invention, the term "aqueous-based" means that water accounts for the largest proportion by mass of the liquid components. As the water in the aqueous medium, deionized water, ion-exchanged water, or distilled water is preferably used. The aqueous medium may further contain an organic solvent, such as aliphatic alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, and 2-propanol, ketones having 3 to 8 carbon atoms, such as acetone and methyl ethyl ketone, and ethers, such as tetrahydrofuran, that dissolve in water. From the viewpoint of environmental friendliness, the water content in the aqueous medium is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and still more preferably 95% by mass or more.

[0009] In the present invention, the term "(meth)acrylate" refers to one or more species selected from the group consisting of acrylates and methacrylates. The term "water-insoluble" for the polyfunctional epoxy crosslinking agent means that when the crosslinking agent is dissolved in 100 g of ion-exchanged water at 25° C. until it is saturated, the amount of the crosslinking agent dissolved is preferably less than 50 g. The term "non-liquid absorbing" in the context of the printing substrate of the present invention means that the amount of water absorbed by the printing substrate when it is in contact with pure water for 100 ms is 1 g / m 2 This means that: The term "hydrophobic" in the context of the printing substrate according to the present invention means that the surface free energy (wetting tension) is 45 mN / m or less. The surface free energy (wetting tension) of the printing substrate is measured using a mixture for wetting tension testing (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) in accordance with the wetting tension testing method of JIS K6768. In the present invention, "adhesion to substrate" refers to the tape peel resistance of the ink coating film of the printed matter obtained when used for printing on a resin film, and may be simply referred to as "adhesion to substrate".

[0010] According to the present invention, it is possible to provide an aqueous pigment dispersion which, when used for printing on a resin film, gives an ink coating film of a printed matter having excellent substrate adhesion (tape peel resistance) and excellent intermittent ejection properties, and an aqueous ink containing the aqueous pigment dispersion. The reason for this is not necessarily clear, but is thought to be as follows. In the present invention, the crosslinked polymer that disperses the pigment contains a structure derived from a water-dispersible polymer and a structure derived from a water-insoluble polyfunctional epoxy crosslinker, and the water-dispersible polymer is a vinyl resin containing a structural unit derived from a cycloalkyl (meth)acrylate. The cycloalkyl ester moiety of this cycloalkyl (meth)acrylate has a polarity value close to that of the polar functional group present on the surface of the resin film used as the printing substrate, which is considered to improve the wettability of the resin film when the water-based pigment dispersion of the present invention is used in a water-based ink. Furthermore, hydrogen bonds are formed between the polar functional group and the cycloalkyl ester moiety, and van der Waals interactions can be efficiently expressed between the hydrophobic moiety of the resin film and the cycloalkyl moiety of the cycloalkyl (meth)acrylate and the water-dispersible polymer main chain containing the structural unit derived from the cycloalkyl (meth)acrylate, which is considered to improve the substrate adhesion of the ink coating film to the resin film. In addition, since the crosslinked polymer that disperses the pigment has a crosslinked structure that includes a structure derived from the water-dispersible polymer and a structure derived from a water-insoluble polyfunctional epoxy crosslinking agent, the polymer is unlikely to swell even with an organic solvent blended in the ink, and the dispersion stability of the pigment can be improved. As a result, even if the ink is exposed to the atmosphere for a long period of time near the inkjet nozzle during a period during which the ink is not ejected from the inkjet nozzle, the moisture in the ink evaporates, and the ratio of the organic solvent in the ink increases, it is believed that aggregation of the pigment can be suppressed and intermittent ejection properties can be improved.

[0011] <Pigments> The pigment used in the present invention may be either an inorganic pigment or an organic pigment. Examples of inorganic pigments include carbon black and metal oxides, and carbon black is preferred for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, channel black, etc. Examples of white inks include titanium dioxide, zinc oxide, silica, alumina, magnesium oxide, and other metal oxides. Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. In the achromatic ink, achromatic pigments such as white, black, and gray can be used, while in the chromatic ink, chromatic pigments such as yellow, magenta, cyan, red, blue, orange, and green can be used. The above pigments can be used alone or in combination of two or more kinds.

[0012] <Crosslinked polymer A> The crosslinked polymer A contains a structure derived from the water-dispersible polymer A' and a structure derived from a water-insoluble multifunctional epoxy crosslinking agent, and the water-dispersible polymer A' is a vinyl resin containing a structural unit derived from a cycloalkyl (meth)acrylate (a-1). That is, the crosslinked polymer A is a polymer obtained by crosslinking the water-dispersible polymer A' with a water-insoluble multifunctional epoxy crosslinking agent. Here, the "water-dispersible" of the water-dispersible polymer A' means that when the polymer, which has been dried at 105°C for 2 hours and has reached a constant weight, is dissolved in 100 g of water at 25°C, the amount of dissolution is 10 g or less. The amount of dissolution of the water-dispersible polymer A' is preferably 5 g or less, more preferably 1 g or less. In the case where the water-dispersible polymer A' has an anionic group as described below and the anionic group is further neutralized with a neutralizing agent, the water-dispersible polymer A' is judged from the amount of dissolution measured under conditions in which the neutralizing agent is mixed at the same mass ratio of the water-dispersible polymer A' to the neutralizing agent in the aqueous pigment dispersion of the present invention.

[0013] (Water-dispersible polymer A') The water-dispersible polymer A' is a vinyl resin that contains a structural unit derived from a cycloalkyl (meth)acrylate (a-1) from the viewpoint of improving adhesion to a substrate. The water-dispersible polymer A' preferably has an anionic group from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property. The anionic group refers to an anionic group or a group that can be ionized to become an anionic group. Examples of the anionic group include a carboxy group (-COOM), a sulfonic acid group (-SO3M), and a phosphoric acid group (-OPO3M2). In the above chemical formula, M represents a hydrogen atom, an alkali metal, ammonium, or an organic ammonium. Among these, the water-dispersible polymer A' preferably has a carboxy group as the anionic group, from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property.

[0014] [Cycloalkyl (meth)acrylate (a-1)] The number of carbon atoms in the cycloalkyl group of the cycloalkyl (meth)acrylate (a-1) is, from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, as well as from the viewpoint of improving the adhesion to the substrate, preferably 4 or more, more preferably 5 or more, and is preferably 12 or less, more preferably 8 or less, and even more preferably 7 or less. The cycloalkyl (meth)acrylate (a-1) is, from the viewpoint of improving the dispersion stability of the pigment to improve intermittent ejection properties, and from the viewpoint of improving adhesion to the substrate, preferably at least one selected from the group consisting of cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and cycloheptyl (meth)acrylate, more preferably cyclohexyl (meth)acrylate, and even more preferably cyclohexyl acrylate.

[0015] [Carboxylic acid group-containing ionic monomer (a-2)] From the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, the water-dispersible polymer A' is preferably a vinyl resin further containing a structural unit derived from an ionic monomer (a-2) having a carboxy group. The ionic monomer (a-2) having a carboxy group is preferably one or more selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, more preferably one or more selected from the group consisting of acrylic acid and methacrylic acid, and even more preferably acrylic acid.

[0016] [Hydrophobic monomer (a-3)] From the viewpoints of improving the adsorption of the crosslinked polymer to the pigment and improving the dispersion stability of the pigment to improve intermittent ejection properties, the water-dispersible polymer A' is preferably a vinyl resin further containing a structural unit derived from one or more hydrophobic monomers (a-3) selected from the group consisting of alkyl (meth)acrylates and aromatic group-containing (meth)acrylates. Preferred examples of the hydrophobic monomer (a-3) include one or more selected from the group consisting of alkyl (meth)acrylates having an alkyl group with 1 to 22 carbon atoms, and aryl group-containing (meth)acrylates having an aryl group with 6 to 22 carbon atoms. Among these, as the hydrophobic monomer (a-3), from the viewpoints of lowering the glass transition temperature (Tg) of the crosslinked polymer A obtained by crosslinking the water-dispersible polymer A', thereby alleviating the stress when the ink coating film is peeled off from the printing substrate, and improving the adhesion to the substrate, preferred is a monomer having a glass transition temperature (Tg) of 30°C or less when made into a homopolymer, more preferred is a monomer having a glass transition temperature (Tg) of 20°C or less, and even more preferred is a monomer having a glass transition temperature (Tg) of 10°C or less. As the glass transition temperature (Tg) of the homopolymer of each monomer, for example, the value described in Polymer Handbook Third Edition (Wiley-Interscience 1989) can be used.

[0017] Preferred examples of alkyl (meth)acrylates having an alkyl group having 1 to 22 carbon atoms include one or more selected from the group consisting of methyl acrylate (Tg: 8° C.), ethyl acrylate (Tg: −20° C.), propyl acrylate (Tg: 3° C.), isopropyl acrylate (Tg: −3° C.), butyl acrylate (Tg: −55° C.), isobutyl acrylate (Tg: −33° C.), hexyl acrylate (Tg: −57° C.), 2-ethylhexyl acrylate (Tg: −70° C.), octyl acrylate (Tg: −65° C.), dodecyl acrylate (Tg: −3° C.), and stearyl acrylate. Among these, from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, and from the viewpoint of improving the adhesion to the substrate, more preferably, one or more types selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, and isobutyl acrylate, and even more preferably, one or more types selected from the group consisting of methyl acrylate, butyl acrylate, and isobutyl acrylate. Preferred examples of the aryl group-containing (meth)acrylate having an aryl group having 6 to 22 carbon atoms include one or more selected from the group consisting of phenyl acrylate, benzyl acrylate (Tg: 6° C.), phenoxyethyl acrylate (Tg: −22° C.), and phenoxydiethylene glycol acrylate (Tg: −25° C.). Among these, benzyl acrylate is more preferred from the viewpoints of improving the dispersion stability of the pigment to improve intermittent ejection properties and improving adhesion to the substrate. The values ​​in parentheses above indicate the glass transition temperature (Tg) when each monomer is made into a homopolymer. The monomers contained in each of the above (a-1) to (a-3) can be used alone or in combination of two or more kinds.

[0018] As described above, from the viewpoints of improving the dispersion stability of the pigment and improving the intermittent ejection property, and from the viewpoints of improving the adhesion to the substrate, the water-dispersible polymer A' is preferably a vinyl resin containing a structural unit derived from a cycloalkyl(meth)acrylate (a-1), a structural unit derived from an ionic monomer (a-2) having one or more carboxy groups selected from the group consisting of acrylic acid and methacrylic acid, and a structural unit derived from one or more hydrophobic monomers (a-3) selected from the group consisting of alkyl(meth)acrylates and aromatic group-containing (meth)acrylates.

[0019] The water-dispersible polymer A' may contain structural units derived from monomers other than the monomers (a-1) to (a-3) described above, within the range that does not impair the effects of the present invention. Examples of the other monomers include ionic monomers, hydrophobic monomers, and nonionic monomers other than the monomers (a-1) to (a-3).

[0020] (Content of each structural unit in water-dispersible polymer A') From the viewpoint of improving adhesion to a substrate, the content of cycloalkyl (meth)acrylate (a-1) in the raw material monomer constituting the water-dispersible polymer A' or the content of structural units derived from cycloalkyl (meth)acrylate (a-1) in the water-dispersible polymer A' is preferably 10 mass % or more, more preferably 20 mass % or more, even more preferably 35 mass % or more, and is preferably 85 mass % or less, more preferably 80 mass % or less, even more preferably 75 mass % or less. The content of the ionic monomer (a-2) having a carboxy group in the raw material monomers constituting the water-dispersible polymer A' or the content of the structural units derived from the ionic monomer (a-2) having a carboxy group in the water-dispersible polymer A' is, from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, preferably 14 mass% or more, more preferably 18 mass% or more, even more preferably 23 mass% or more, and is preferably 36 mass% or less, more preferably 32 mass% or less, even more preferably 28 mass% or less. The content of the hydrophobic monomer (a-3) in the raw material monomers constituting the water-dispersible polymer A' or the content of the structural units derived from the hydrophobic monomer (a-3) in the water-dispersible polymer A' is, from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, as well as from the viewpoint of improving the adhesion to the substrate, preferably 2 mass% or more, more preferably 3 mass% or more, even more preferably 4 mass% or more, and is preferably 65 mass% or less, more preferably 50 mass% or less, even more preferably 35 mass% or less.

[0021] The mass ratio of the content of hydrophobic monomer (a-3) to the content of cycloalkyl (meth)acrylate (a-1) in the raw material monomers constituting the water-dispersible polymer A', or the mass ratio of the content of structural units derived from hydrophobic monomer (a-3) to the content of structural units derived from cycloalkyl (meth)acrylate (a-1) in the water-dispersible polymer A' [hydrophobic monomer (a-3) / cycloalkyl (meth)acrylate (a-1)] is preferably 0.03 or more, more preferably 0.04 or more, and even more preferably 0.05 or more, from the viewpoint of improving adhesion to the substrate, and from the same viewpoint as above, is preferably 1 or less, more preferably 0.95 or less, and even more preferably 0.90 or less.

[0022] (Preparation of Water-Dispersible Polymer A') The water-dispersible polymer may be a suitably synthesized product or a commercially available product. The water-dispersible polymer A' can be produced by copolymerizing raw material monomers including the monomers (a-1) to (a-3) by a known polymerization method, preferably a solution polymerization method. The solvent used in the solution polymerization method is not limited, but polar solvents such as aliphatic alcohols, ketones, ethers, and esters are preferred, and methanol, ethanol, acetone, methyl ethyl ketone, and the like are more preferred. In the polymerization, a polymerization initiator or a polymerization chain transfer agent can be used. Examples of the polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate; water-soluble azo polymerization initiators, etc. Examples of the polymerization chain transfer agent include mercaptans, etc. The polymerization temperature varies depending on the types of polymerization initiator, monomer, solvent, etc. used, but is preferably 30° C. or higher, more preferably 50° C. or higher, and is preferably 95° C. or lower, more preferably 80° C. or lower. The polymerization atmosphere is preferably a nitrogen gas or inert gas atmosphere.

[0023] (Physical Properties of Water-Dispersible Polymer A') From the viewpoint of adhesion to a substrate, the glass transition temperature (Tg) of the water-dispersible polymer A' is preferably 55° C. or lower, more preferably 45° C. or lower, even more preferably 35° C. or lower, and is preferably −30° C. or higher, more preferably −15° C. or higher, even more preferably 0° C. or higher. The glass transition temperature of the water-dispersible polymer A' is calculated by the method described in the examples. The acid value of the water-dispersible polymer A' is preferably 100 mgKOH / g or more, more preferably 140 mgKOH / g or more, and even more preferably 180 mgKOH / g or more, from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, and is preferably 300 mgKOH / g or less, more preferably 250 mgKOH / g or less, and even more preferably 220 mgKOH / g or less, from the viewpoint of improving the adhesion to the substrate. The weight average molecular weight of the water-dispersible polymer A' is preferably 5,000 or more, more preferably 8,000 or more, and even more preferably 10,000 or more, from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, and from the viewpoint of adhesion to the substrate, and is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. The acid value and weight average molecular weight of the water-dispersible polymer A' are measured by the method described in Examples. The acid value of the water-dispersible polymer A' can also be calculated from the mass ratio of the constituent monomers.

[0024] (Neutralizer) When the water-dispersible polymer A' has an anionic group, it is preferable that at least a part of the anionic group of the water-dispersible polymer is neutralized with a neutralizing agent, which is believed to increase the charge repulsive force of the anionic group after neutralization, suppress the aggregation of pigment particles in the water-based ink, improve the dispersion stability of the pigment, and improve the intermittent ejection property. In the case of neutralization, it is preferable to neutralize so that the pH is 7 or more and 11 or less. Examples of the neutralizing agent include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, and bases such as organic amines. Among these, preferred is one or more selected from the group consisting of sodium hydroxide, ammonia, and organic amines, and more preferred is an organic amine. Suitable examples of the organic amine used as the neutralizing agent include alkylamines, alkanolamines, aminoalkanediols, alkoxyamines, and heterocyclic amines. Among these, alkanolamines are more preferred. The alkanolamine is preferably one or more selected from the group consisting of N-methyldiethanolamine, N-ethyldiethanolamine, N,N-dimethylethanolamine, and N,N-diethylethanolamine, and more preferably N,N-dimethylethanolamine.

[0025] From the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, the amount of the neutralizer used is preferably 10 mol % or more, more preferably 15 mol % or more, even more preferably 20 mol % or more, and is preferably 60 mol % or less, more preferably 50 mol % or less, even more preferably 40 mol % or less. The equivalent amount of the neutralizing agent used can be calculated by the following formula (1). Equivalent amount of neutralizing agent used (mol%) = ((weight of neutralizing agent added (g) / equivalent amount of neutralizing agent) / ((acid value of water-dispersible polymer A' before neutralization (mg KOH / g) x weight of water-dispersible polymer A' before neutralization (g)) / (56 x 1000)) x 100 (1)

[0026] (Crosslinking agent) The crosslinked polymer A contains a structure derived from the water-dispersible polymer A' and a structure derived from a water-insoluble multifunctional epoxy crosslinking agent (hereinafter also referred to as "crosslinking agent" or "multifunctional epoxy crosslinking agent"). The "water-insoluble" of the crosslinking agent is as described above. From the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection properties, the crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule, more preferably a polyfunctional epoxy compound having two or more glycidyl ether groups in the molecule, and even more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 or more and 8 or less carbon atoms. From the viewpoint of efficient crosslinking reaction in an aqueous medium, the molecular weight of the crosslinking agent is preferably 120 or more, more preferably 150 or more, and preferably 2,000 or less, more preferably 1,500 or less, and even more preferably 500 or less. The epoxy equivalent (g / eq.) of the crosslinking agent is preferably 90 or more, more preferably 100 or more, and is preferably 300 or less, more preferably 200 or less. From the viewpoint of efficient crosslinking reaction in an aqueous medium, the water solubility of the crosslinking agent is preferably less than 50% by mass, more preferably 40% by mass or less, and even more preferably 35% by mass or less. Here, the water solubility refers to the solubility (mass%) when 10 parts by mass of the crosslinking agent is dissolved in 90 parts by mass of water at 25°C. LogP is the common logarithm of the partition coefficient P (1-octanol / water) of the crosslinker between 1-octanol and water ow (hereinafter referred to as “logP ow From the viewpoint of improving the dispersion stability of the pigment in the ink containing a hydrophobic water-soluble organic solvent and thereby improving the intermittent ejection properties, the ratio of the pigment dispersion stability to the intermittent ejection properties is preferably -1.5 or more, more preferably -1.0 or more, even more preferably -0.5 or more, and is preferably 2.0 or less, more preferably 1.5 or less, even more preferably 1.0 or less. logP ow is measured and calculated by the following method in accordance with the flask shaking method described in JIS Z7260-107. [Measurement of partition coefficient P (1-octanol / water)] 10 g of ion-exchanged water and 10 g of 1-octanol are placed in a 50 mL separatory funnel and equilibrated by shaking at 25°C. 1 g of crosslinker is added and after thorough shaking, the 1-octanol phase and the water phase are separated by centrifugation. The amount of crosslinker dissolved in each phase is quantified by gas chromatography, and the common logarithm of the partition coefficient P between the two phases is called logP. ow Let us assume that.

[0027] Preferred examples of the crosslinking agent include one or more polyglycidyl ethers selected from the group consisting of trimethylolpropane polyglycidyl ether, 1,6-hexanediol diglycidyl ether, and 1,4-cyclohexanedimethanol diglycidyl ether.

[0028] From the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, the crosslinking rate of the crosslinked polymer A, expressed as the ratio of the molar equivalent number of epoxy groups of the crosslinking agent to the molar equivalent number of carboxy groups of the water-dispersible polymer A', is preferably 15 mol % or more, more preferably 20 mol % or more, even more preferably 25 mol % or more, still more preferably 30 mol % or more, still more preferably 35 mol % or more, and from the same viewpoint as above, it is preferably 85 mol % or less, more preferably 75 mol % or less, still more preferably 70 mol % or less, still more preferably 65 mol % or less.

[0029] From the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, the acid value of the crosslinked polymer A is preferably 25 mgKOH / g or more, more preferably 35 mgKOH / g or more, even more preferably 55 mgKOH / g or more, and is preferably 170 mgKOH / g or less, more preferably 130 mgKOH / g or less, even more preferably 120 mgKOH / g or less. The acid value of the crosslinked polymer A is measured by the method described in the Examples. The acid value of the crosslinked polymer A can be calculated by the following formula (2). Acid value of crosslinked polymer A (mg KOH / g) = [Acid value of water-dispersible polymer A' (mg KOH / g)] × [100 - crosslinking rate (mol%)] / 100 (2)

[0030] In the present invention, the form in which the pigment is dispersed in the crosslinked polymer A is preferably in the form of crosslinked polymer particles containing the pigment (hereinafter also referred to as "pigment-containing crosslinked polymer particles"), from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection properties even when water evaporates and becomes concentrated in an inkjet nozzle when used in an ink. The morphology of the pigment-containing crosslinked polymer particles in the present invention includes a morphology in which a particle of crosslinked polymer A encompasses the pigment, a morphology in which a part of the pigment is exposed on the surface of a particle consisting of a particle of crosslinked polymer A and the pigment, a morphology in which a particle of crosslinked polymer A is adsorbed to a part of the pigment, and a mixture of these morphologies. Among these, the morphology in which a particle of crosslinked polymer A encompasses the pigment, i.e., the morphology in which a particle of crosslinked polymer A encompasses the pigment, is preferred.

[0031] (Production of Water-Based Pigment Dispersion) The water-based pigment dispersion of the present invention can be efficiently produced by a method including the following steps 1 to 3. Step 1: A step of dispersing a pigment mixture containing a pigment, a water-dispersible polymer A', an organic solvent, and water to obtain a pigment dispersion. Step 2: A step of removing the organic solvent from the pigment dispersion liquid obtained in step 1 to obtain an aqueous pigment dispersion in which the pigment is dispersed in the water-dispersible polymer A' (hereinafter, also referred to as "aqueous pigment dispersion (i)"). Step 3: A step of adding a water-insoluble multifunctional epoxy crosslinking agent to the aqueous pigment dispersion (i) obtained in step 2, and crosslinking the water-dispersible polymer A' with the multifunctional epoxy crosslinking agent to obtain an aqueous pigment dispersion.

[0032] (Process 1) The pigment mixture in step 1 is preferably obtained by a method in which a pigment, water, and, if necessary, a neutralizing agent, a surfactant, etc. are added to an organic solvent solution of the water-dispersible polymer A' obtained by dissolving the water-dispersible polymer A' in an organic solvent, and then mixed. Although there is no limitation on the organic solvent used in step 1, ketones, ethers, esters, aliphatic alcohols having 1 to 3 carbon atoms, etc. are preferred, and from the viewpoint of improving the wettability to the pigment and the adsorption of the water-dispersible polymer to the pigment, ketones having 4 to 8 carbon atoms are more preferred, methyl ethyl ketone, methyl isobutyl ketone are even more preferred, and methyl ethyl ketone is even more preferred. When the water-dispersible polymer A' is synthesized by a solution polymerization method, the solvent used in the polymerization may be used as it is. The water-dispersible polymer A' may be one which has been neutralized in advance with a neutralizing agent.

[0033] In the dispersion treatment in step 1, the pigment can be atomized to a desired particle size only by main dispersion using shear stress. However, from the viewpoint of obtaining a uniform aqueous pigment dispersion, it is preferable to pre-disperse the pigment mixture and then further perform main dispersion. As a dispersing machine used for preliminary dispersion, a commonly used mixing and stirring device such as an anchor blade or a dispersing blade can be used. Examples of means for applying shear stress used in the present dispersion include kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersers such as paint shakers and bead mills. Among these, from the viewpoint of reducing the particle size of the pigment, it is preferable to use one or more types selected from the group consisting of high-pressure homogenizers and bead mills. When the dispersion process is carried out using a high-pressure homogenizer, the pigment can be controlled to have a desired particle size by controlling the number of passes at a dispersion pressure of 20 MPa or more, and the average particle size of the pigment (pigment-containing crosslinked polymer particles) dispersed in crosslinked polymer A in the final aqueous pigment dispersion can also be adjusted.

[0034] (Process 2) The organic solvent can be removed by a known method in step 2. It is preferable that the organic solvent in the obtained water-based pigment dispersion (i) has been substantially removed, but it may remain in an amount of, for example, 0.1% by mass or less, as long as the object of the present invention is not impaired. In addition, for the purpose of removing coarse particles and the like, it is preferable that the aqueous pigment dispersion from which the organic solvent has been removed is further centrifuged, and then the liquid phase portion is recovered and filtered through a filter or the like, and the portion that has passed through the filter or the like is obtained as the aqueous pigment dispersion (i). In the aqueous pigment dispersion (i) obtained in step 2, the form in which the pigment is dispersed in the water-dispersible polymer A' is preferably in the form of polymer particles containing the pigment (hereinafter also referred to as "pigment-containing polymer particles"), from the viewpoint of improving intermittent ejection properties. The form of the pigment-containing polymer particles in step 2 includes a form in which a particle of the water-dispersible polymer A' encapsulates the pigment, a form in which a part of the pigment is exposed on the surface of a particle consisting of a particle of the water-dispersible polymer A' and the pigment, a form in which the particle of the water-dispersible polymer A' is adsorbed to a part of the pigment, and a mixture of these forms. Among these, the form in which a particle of the water-dispersible polymer A' encapsulates the pigment, i.e., the form of particles of the water-dispersible polymer A' encapsulating the pigment, is preferred.

[0035] (Step 3) Step 3 is a step of adding a polyfunctional epoxy crosslinking agent to the water-based pigment dispersion (i) obtained in step 2, and crosslinking the water-dispersible polymer A' with the polyfunctional epoxy crosslinking agent to obtain a water-based pigment dispersion. In the present invention, when the pigment dispersed in the crosslinked polymer A is in the form of pigment-containing crosslinked polymer particles, a crosslinked structure can be formed in the surface layer of the pigment-containing polymer particles formed in step 2 to form pigment-containing crosslinked polymer particles. This allows the polymer (i.e., crosslinked polymer A) obtained by crosslinking the water-dispersible polymer A' with the polyfunctional epoxy crosslinking agent to be firmly adsorbed or fixed on the pigment surface, suppressing aggregation of the pigment, and as a result, it is believed that the dispersion stability of the pigment in the resulting ink can be improved, thereby improving intermittent ejection properties. The temperature of the crosslinking treatment in step 3 is preferably 40° C. or more, more preferably 50° C. or more, and is preferably 90° C. or less, more preferably 85° C. or less, from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property.

[0036] The non-volatile component concentration (solids concentration) of the aqueous pigment dispersion of the present invention is, from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, and from the viewpoint of improving the adhesion to the substrate, preferably 10% by mass or more, more preferably 15% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less. The solids concentration is measured by the method described in the Examples.

[0037] (Content and properties of each component of water-based pigment dispersion) The content of the pigment in the aqueous pigment dispersion of the present invention is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 9% by mass or more from the viewpoint of print density, and is preferably 35% by mass or less, more preferably 30% by mass or less, from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property.

[0038] The mass ratio of the crosslinked polymer A to the pigment in the aqueous pigment dispersion of the present invention [crosslinked polymer A / pigment] is, from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, and from the viewpoint of improving the adhesion to the substrate, preferably 0.15 or more, more preferably 0.25 or more, and is preferably 1.8 or less, more preferably 1.5 or less.

[0039] In the present invention, when the pigment dispersed in the crosslinked polymer A is in the form of pigment-containing crosslinked polymer particles, the average particle size of the pigment-containing crosslinked polymer particles in the aqueous pigment dispersion of the present invention is, from the viewpoint of improving the dispersion stability of the pigment and improving the intermittent ejection property, and from the viewpoint of improving the adhesion to the substrate, preferably 50 nm or more, more preferably 70 nm or more, even more preferably 80 nm or more, still more preferably 90 nm or more, and is preferably 400 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less, and still more preferably 150 nm or less. The average particle size of the pigment-containing crosslinked polymer particles in the water-based pigment dispersion of the present invention is measured by the method described in the Examples.

[0040] The aqueous pigment dispersion of the present invention can be suitably used by being blended in aqueous inks for various printing applications such as inkjet printing, flexographic printing, gravure printing, etc. Among these, from the viewpoints of the intermittent ejection properties of the ink and the adhesion to the substrate, it is preferable to use the aqueous ink for inkjet printing.

[0041] [Water-based ink] The water-based ink of the present invention (hereinafter also referred to as "the ink of the present invention" or "ink") preferably contains the water-based pigment dispersion and a water-soluble organic solvent, from the viewpoints of the intermittent ejection properties of the ink and the adhesion to the substrate.

[0042] <Water-soluble organic solvent> The water-soluble organic solvent is an organic solvent that can be mixed with water in any ratio. The water-soluble organic solvents can be used alone or in combination of two or more. Examples of the water-soluble organic solvent include glycol ethers, polyhydric alcohols, nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, alkanolamines, etc. Among these, from the viewpoints of the intermittent ejection properties of the ink and the adhesion to the substrate, one or more types selected from the group consisting of glycol ethers and polyhydric alcohols are preferred.

[0043] Examples of glycol ethers include (poly)alkylene glycol monoalkyl ethers such as monoalkylene glycol monoalkyl ethers, dialkylene glycol monoalkyl ethers, and trialkylene glycol monoalkyl ethers; and (poly)alkylene glycol dialkyl ethers such as monoalkylene glycol dialkyl ethers and dialkylene glycol dialkyl ethers. The alkylene oxide group of the glycol ether may be at least one selected from the group consisting of an ethylene oxide group and a propylene oxide group, with an ethylene oxide group being more preferred. The glycol ether preferably has at least one hydrocarbon group having 2 to 8 carbon atoms.

[0044] From the viewpoint of wettability to the resin film and drying property, the glycol ether is preferably at least one selected from the group consisting of (poly)alkylene glycol monoalkyl ethers and (poly)alkylene glycol dialkyl ethers, and more preferably a (poly)alkylene glycol monoalkyl ether. The (poly)alkylene glycol monoalkyl ether is preferably at least one selected from the group consisting of ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monoisobutyl ether, and diethylene glycol mono-n-butyl ether, and more preferably at least one selected from the group consisting of diethylene glycol monoisobutyl ether and diethylene glycol mono-n-butyl ether.

[0045] As the polyhydric alcohol, from the viewpoint of wettability to the resin film and drying property, one or more selected from the group consisting of alkanediols having 2 to 6 carbon atoms, such as propylene glycol (1,2-propanediol) and 1,2-hexanediol; diethylene glycol; and glycerin are preferred, and propylene glycol is more preferred.

[0046] The ink of the present invention may contain various additives commonly used in water-based inks, such as fixing resins, surfactants, humectants, wetting agents, viscosity adjusters, defoamers, preservatives, antifungal agents and rust inhibitors.

[0047] The surfactant is preferably a nonionic surfactant, and more preferably at least one selected from the group consisting of acetylene glycol surfactants and silicone surfactants. Examples of acetylene glycol surfactants that can be used from the viewpoints of wettability to resin films and defoaming properties include acetylene diols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-ol, and 2,4-dimethyl-5-hexyne-3-ol, as well as ethylene oxide adducts of these acetylene diols. Commercially available examples of acetylene glycol surfactants include the "Surfynol" series and the "Olfine" series manufactured by Nissin Chemical Industry Co., Ltd. As the silicone surfactant, polyether-modified silicone is preferred. Examples of commercially available silicone surfactants include the KF series (KF-353, KF-355A, KF-642, KF-6011, etc.) manufactured by Shin-Etsu Chemical Co., Ltd., the Silface SAG series manufactured by Nissin Chemical Industry Co., Ltd., and the BYK series manufactured by BYK Japan K.K.

[0048] The water-based ink of the present invention can be efficiently produced by mixing the water-based pigment dispersion and the water-soluble organic solvent, and, if necessary, water, a surfactant, a fixing resin, and other additives, etc. There are no particular limitations on the method of mixing them.

[0049] (Content and properties of each component of water-based ink) From the viewpoint of print density, the content of the pigment in the ink of the present invention is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 4% by mass or more, and from the viewpoint of improving the dispersion stability of the pigment and thereby improving the intermittent ejection properties, the content of the pigment in the ink of the present invention is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less.

[0050] The mass ratio of the content of crosslinked polymer A to the content of pigment in the ink of the present invention [crosslinked polymer A / pigment] is, from the viewpoint of improving the dispersion stability of the pigment and thereby improving intermittent ejection properties, and from the viewpoint of improving adhesion to the substrate, preferably 0.15 or more, more preferably 0.25 or more, and is preferably 1.8 or less, more preferably 1.5 or less.

[0051] In the present invention, when the pigment dispersed in the crosslinked polymer A is in the form of pigment-containing crosslinked polymer particles, the content of the pigment-containing crosslinked polymer particles in the ink of the present invention is preferably 3% by mass or more, more preferably 4% by mass or more, even more preferably 5% by mass or more, and preferably 20% by mass or less, more preferably 18% by mass or less, even more preferably 16% by mass or less.

[0052] The water content in the ink of the present invention is preferably 35% by mass or more, more preferably 45% by mass or more, even more preferably 55% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less.

[0053] From the viewpoint of improving adhesion to the substrate, the content of the water-soluble organic solvent in the ink of the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less.

[0054] When the ink of the present invention contains a surfactant, the content of the surfactant in the ink is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less.

[0055] In the ink of the present invention, when the pigment dispersed in the crosslinked polymer A is in the form of pigment-containing crosslinked polymer particles, the average particle size of the pigment-containing crosslinked polymer particles in the ink of the present invention is, from the viewpoint of improving the dispersion stability of the pigment and thereby improving the intermittent ejection property, and from the viewpoint of improving adhesion to the substrate, preferably 50 nm or more, more preferably 70 nm or more, even more preferably 80 nm or more, still more preferably 90 nm or more, and is preferably 400 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less, and still more preferably 150 nm or less. The average particle size of the pigment-containing crosslinked polymer particles in the ink of the present invention is measured by the method described in the Examples.

[0056] The viscosity of the ink of the present invention at 32°C is, from the viewpoint of improving the dispersion stability of the pigment and thereby improving the intermittent ejection property, and from the viewpoint of improving the adhesion to the substrate, preferably 2 mPa·s or more, more preferably 3 mPa·s or more, even more preferably 4 mPa·s or more, and is preferably 20 mPa·s or less, more preferably 15 mPa·s or less, even more preferably 12 mPa·s or less. The viscosity of the ink of the present invention at 32° C. is measured using an E-type viscometer according to the method described in the examples.

[0057] The ink of the present invention can be used as a variety of printing inks, such as for inkjet printing, gravure printing, and flexographic printing. From the viewpoint of improving intermittent ejection properties and improving adhesion to a substrate, it is preferable to use the ink of the present invention as a water-based ink for inkjet printing. When the ink of the present invention is used as a water-based ink for inkjet printing, the water-based ink can be loaded into a known inkjet printing device and ejected as ink droplets onto a printing substrate such as a resin film to print an image, etc. As the method for ejecting ink droplets, any of a piezoelectric method, a thermal method, and an electrostatic method can be adopted.

[0058] From the viewpoint of adhesion to the substrate, the printing substrate used in printing with the ink of the present invention is preferably a resin film. That is, the water-based ink of the present invention is preferably used in printing using a resin film as the printing substrate. Examples of the resin film include transparent synthetic resin films, such as polyester films such as polyethylene terephthalate films; vinyl chloride films; polyolefin films such as polypropylene films and polyethylene films; and polyamide films such as nylon films. These resin films may be stretched films such as biaxially stretched films and uniaxially stretched films, or non-stretched films. In addition, these resin films are preferably surface-treated, such as corona discharge treatment, in order to impart polar functional groups to the resin film surface, improve the wettability of the water-based ink to the resin film, and form hydrogen bonds between the polar functional groups and the cycloalkyl ester moieties to improve adhesion to the substrate. Among these, one or more selected from the group consisting of polyester film and stretched polypropylene film are preferred, and one or more selected from the group consisting of corona discharge treated polyethylene terephthalate (PET) film and corona discharge treated biaxially oriented polypropylene (OPP) film are more preferred. EXAMPLES

[0059] In the following Production Examples, Examples and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring and calculating each physical property are as follows.

[0060] (1) Measurement of weight average molecular weight of water-dispersible polymer A' The measurement was performed by gel permeation chromatography under the following conditions. GPC equipment: Tosoh Corporation "HLC-8320GPC" Columns: Tosoh Corporation's "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolum Super AW-H" Eluent: N,N-dimethylformamide with phosphoric acid and lithium bromide dissolved at concentrations of 60mmol / L and 50mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kit with known molecular weight [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500)] (manufactured by Tosoh Corporation) Measurement sample: 0.1 g of water-dispersible polymer A' was mixed with 10 mL of the eluent in a glass vial, stirred with a magnetic stirrer at 25°C for 10 hours, and filtered with a syringe filter "DISMIC-13HP" (PTFE, 0.2 μm, Advantec Co., Ltd.) for use.

[0061] (2) Measurement of acid value of water-dispersible polymer A' and crosslinked polymer A Using an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), in the case of water-dispersible polymer A', the water-dispersible polymer A' was dissolved in a titration solvent consisting of a mixture of toluene and acetone (2:1), and in the case of crosslinked polymer A, the aqueous pigment dispersion was dispersed in the titration solvent and titrated with a 0.1N potassium hydroxide / ethanol solution by potentiometric titration, with the inflection point on the titration curve being the end point. The acid value (mgKOH / g) was calculated from the titration amount of the potassium hydroxide solution up to the end point.

[0062] (3) Calculation of the glass transition temperature of water-dispersible polymer A' The glass transition temperature of the water-dispersible polymer A', which is a copolymer, can be calculated from the mass ratio of each monomer constituting the water-dispersible polymer A' and the glass transition temperature of the homopolymer when each monomer is made into a homopolymer according to the following Fox equation. 1 / Tg=(W1 / Tg1)+(W2 / Tg2)+···+(W m / Tg m ) W1+W2+...W m =1 In the Fox formula, Tg is the glass transition temperature of the water-dispersible polymer A', and Tg1, Tg2, . . . , Tg m is the glass transition temperature of the homopolymer when each monomer is made into a homopolymer. The unit of temperature is K. Also, W1, W2, ..., W m represents the mass ratio of each monomer in the water-dispersible polymer A'. As the glass transition temperature of a homopolymer of each monomer in the Fox formula, for example, the value described in Polymer Handbook Third Edition (Wiley-Interscience 1989) can be used.

[0063] (4) Measurement of solids concentration 10.0 g of sodium sulfate, which had been kept constant in a desiccator, was weighed out into a 30 mL polypropylene container (φ=40 mm, height=30 mm), and about 1.0 g of the sample was added and mixed, then accurately weighed, and the mixture was kept at 105°C for 2 hours to remove volatile matter, and then left in the desiccator for 15 minutes, after which the mass was measured. The mass of the sample after removing the volatile matter was taken as the solid content, and divided by the mass of the sample added to obtain the solid content concentration (%).

[0064] (5) Measurement of the average particle size of pigment-containing crosslinked polymer particles in an aqueous pigment dispersion or aqueous ink Cumulant analysis was performed using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), and the obtained cumulant average particle diameter was used to measure the average particle diameter of the water-based pigment dispersion or water-based ink. The measurement sample had a particle concentration of 5 × 10 -3 The dispersion was diluted with water to a concentration of 1.0% (solid content equivalent). The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 cumulative measurements. The refractive index of water (1.333) was entered as the refractive index of the dispersion solvent.

[0065] (6) Measurement of viscosity of water-based pigment dispersions and water-based inks Using an E-type viscometer "TV-25" (manufactured by Toki Sangyo Co., Ltd., using a standard cone rotor 1°34' x R24, rotation speed 50 rpm), measurements were taken at 20°C for water-based pigment dispersions and at 32°C for water-based inks.

[0066] (Preparation of Water-Dispersible Polymer A') Manufacturing Example 1 As an initial charge, 1.28 parts of cyclohexyl acrylate, 1.32 parts of acrylic acid, 2.50 parts of butyl acrylate, 3.76 parts of methyl ethyl ketone (hereinafter, referred to as "MEK"), and 0.42 parts of water were charged into a reaction vessel equipped with a stirrer, a reflux condenser, and a dropping tank, and the temperature of the reaction vessel was maintained at 77°C and stirred for 10 minutes. Next, a mixture of 11.49 parts of cyclohexyl acrylate, 11.95 parts of acrylic acid, 22.52 parts of butyl acrylate, 39.13 parts of MEK, 4.35 parts of water, 0.56 parts of 4,4'-azobis(4-cyanovaleric acid) as a polymerization initiator, and 0.72 parts of 3-mercaptopropionic acid as a chain transfer agent was continuously added to the reaction vessel over 5 hours. After the addition was completed, the polymerization reaction was carried out for 1 hour, and then the polymerization reaction was terminated by cooling to room temperature to obtain a solution of water-dispersible polymer A'1 (solid concentration 55%). 20.54 parts of the obtained solution of water-dispersible polymer A'1 was diluted with 11.74 parts of MEK so that the solid content concentration was 35%. Next, 1.08 parts of N,N-dimethylethanolamine (hereinafter referred to as "DMAE") was added so that the neutralization degree of the carboxyl group of water-dispersible polymer A'1 was 30 mol%, and the mixture was stirred at 25°C. Then, 69.14 parts of water was added over 1 hour. After the addition was completed, MEK was distilled off with an evaporator to obtain an aqueous dispersion of water-dispersible polymer A'1 (DMAE neutralized) (polymer solid content concentration 25%). The physical properties of water-dispersible polymer A'1 are shown in Table 1.

[0067] Production Examples 2 to 10 and Comparative Production Example 1 In Production Example 1, the raw material monomer composition constituting the water-dispersible polymer A' was changed to the conditions shown in Table 1, and the amount of neutralizing agent was changed as necessary so that the neutralization degree of the water-dispersible polymer A' was 30 mol %, and the same procedure as in Production Example 1 was used to obtain aqueous dispersions (all of which had a polymer solids concentration of 25%) of water-dispersible polymers A'2 to A'10 and A'C1 (all of which were neutralized with DMAE). The physical properties of the water-dispersible polymers A'2 to A'10 and A'C1 are shown in Table 1.

[0068] [Table 1]

[0069] (Production of Water-Based Pigment Dispersion) Example 1-1 (Process 1) To 72.59 parts of an aqueous dispersion (polymer solids concentration 25%) of water-dispersible polymer A'1 (neutralized with DMAE), 5.64 parts of MEK and 3.15 parts of ion-exchanged water were added, and 18.62 parts of a cyan pigment (manufactured by DIC Corporation, trade name: Fastogen Blue CA5380 Pigment Blue15:3) was further added to obtain a pigment mixture. The resulting pigment mixture was mixed for 1 hour at 7000 rpm and 20°C using a disperser blade, and then further dispersed for 10 passes at a pressure of 180 MPa using a Microfluidizer (high-pressure homogenizer, product name: M-140K, manufactured by Microfluidics) to obtain a pigment dispersion. (Process 2) From the obtained pigment dispersion, MEK was removed under reduced pressure at 60°C, and then some of the water was removed and centrifuged. The liquid phase portion was then filtered through a membrane filter (manufactured by Sartorius, product name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining an aqueous pigment dispersion (i-1) (total concentration of pigment and water-dispersible polymer A': 22%) in which pigment-containing polymer particles are dispersed in an aqueous medium. (Step 3) 88.20 parts of the obtained water-based pigment dispersion (i-1) (total concentration of pigment and water-dispersible polymer A': 22%) was placed in a screw-capped glass bottle, and trimethylolpropane polyglycidyl ether (Denacol EX-321LT, manufactured by Nagase ChemteX Corporation, epoxy value: 139 g / eq., water solubility: 27%, logP ow 2.88 parts of EX321LT (2.88 parts of toluene, -0.39) (hereinafter referred to as "EX321LT") and ion-exchanged water were added to make a total of 100 parts, the mixture was sealed, and heated at 80°C for 5 hours while stirring with a stirrer. The temperature was then lowered to room temperature, and the mixture was filtered through a membrane filter (manufactured by Sartorius, product name: Minisart Syringe Filter, pore size: 5 µm, material: cellulose acetate) to remove coarse particles, thereby obtaining an aqueous pigment dispersion D1 (total concentration of pigment and crosslinked polymer A: 22%) in which pigment-containing crosslinked polymer particles are dispersed in an aqueous medium.

[0070] Examples 1-2 to 1-16 and Comparative Example 1-1 Water-based pigment dispersions D2 to D16 and DC1 were obtained in the same manner as in Example 1-1, except that the conditions in Example 1-1 were changed to those shown in Table 2.

[0071] Examples 1-17 In Examples 1-3, trimethylolpropane polyglycidyl ether (EX321LT) was used as a multifunctional epoxy crosslinking agent, and 1,6-hexanediol diglycidyl ether (Denacol EX-212L, manufactured by Nagase ChemteX Corporation, epoxy value: 135 g / eq., water solubility: 0%, logP ow A water-based pigment dispersion D17 was obtained in the same manner as in Example 1-3, except that the viscosity was changed to 100% by mass % (EX212L: 0.95) (hereinafter referred to as "EX212L").

[0072] Examples 1-18 In Examples 1-3, trimethylolpropane polyglycidyl ether (EX321LT) was used as a multifunctional epoxy crosslinking agent, and 1,4-cyclohexanedimethanol diglycidyl ether (Denacol EX-216L, manufactured by Nagase ChemteX Corporation, epoxy value 150 g / eq., water solubility 0%, logP owA water-based pigment dispersion D18 was obtained in the same manner as in Example 1-3, except that the viscosity index was changed to 1.0:0.79 (hereinafter referred to as "EX216L").

[0073] Examples 1-19 A water-based pigment dispersion D19 was obtained in the same manner as in Example 1-3, except that the cyan pigment in Example 1-3 was changed to carbon black (manufactured by Cabot Corporation, product name: MONARCH717).

[0074] (Preparation of Water-Based Ink) Example 2-1 To obtain the ink composition (total 100 parts) shown in Table 2, 12 parts of the aqueous pigment dispersion D1 (pigment and crosslinked polymer A in total), 22 parts of propylene glycol, 4 parts of diethylene glycol monoisobutyl ether, 1 part of an acetylene glycol surfactant (manufactured by Nissin Chemical Industry Co., Ltd., product name: Surfynol 104-PG50 (propylene glycol solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, active content 50%), and 61 parts of ion-exchanged water were added and stirred, and filtered with a membrane filter (manufactured by Sartorius, product name: Minisart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to obtain aqueous ink 1. The average particle size and viscosity of aqueous ink 1 are shown in Table 2.

[0075] Examples 2-2 to 2-19 and Comparative Example 2-1 Water-based inks 2 to 19 and C1 were obtained in the same manner as in Example 2-1, except that the water-based pigment dispersion in Example 2-1 was changed to one shown in Table 2. The average particle size and viscosity of each water-based ink are shown in Table 2.

[0076] Using the water-based inks 1 to 19 and C1 obtained in the above examples and comparative examples, the adhesion to substrates (tape peel resistance) and intermittent ejection properties were evaluated by the methods described below. The results are shown in Table 2.

[0077] <Evaluation of adhesion to substrate (tape peel resistance)> A printing evaluation device (Seiko Epson Corporation, inkjet printer, PX105, piezoelectric type) was used, and an A4-sized film heater (Kawai Electric Works, Ltd.) was attached to the print media outlet so that the area where the ink was injected could be heated to 50°C. The printing substrates used were a corona discharge-treated PET film (manufactured by Futamura Chemical Co., Ltd., product number: FE2001, film thickness: 20 μm) and a corona discharge-treated OPP film (manufactured by Futamura Chemical Co., Ltd., product number: FOR-AQ, film thickness: 20 μm) cut to A4 size. In an environment of 25±1°C temperature and 30±5% relative humidity, the cartridge of the printing evaluation device was filled with each of the water-based inks of the Examples and Comparative Examples, a solid image of 50 mm x 50 mm was printed with 100% ink duty, and then the print was obtained by drying for 3 minutes on a film heater set to heat at 50°C. A 50 mm long, 15 mm wide tape "Nistack No. 4" (registered trademark) (manufactured by Nichiban Co., Ltd.) was attached to the printed surface of the obtained print, leaving a margin of 1 cm, and a T-type peel test was performed using a Tensilon universal material testing machine (manufactured by A & D Co., Ltd., product name: RTC-1150A) to measure the peel strength (N / 15 mm), which is an index of substrate adhesion (tape peel resistance), and the substrate adhesion (tape peel resistance) was evaluated according to the following evaluation criteria. In the following evaluation criteria, A indicates excellent adhesion to the substrate, and E indicates poor adhesion to the substrate. (Evaluation Criteria) A:2.5N / 15mm or more B: 2.0N / 15mm or more, less than 2.5N / 15mm C: 1.5N / 15mm or more, less than 2.0N / 15mm D: 1.0N / 15mm or more, less than 1.5N / 15mm E: Less than 1.0N / 15mm

[0078] <Evaluation of intermittent ejection of water-based ink> Using the printing evaluation device, 10 solid images of 20 mm x 20 mm were printed with 100% ink duty, and then left for 5 minutes without printing. After that, one solid image of 20 mm x 20 mm was printed to obtain a solid print, and the ratio of the ejection area of ​​the solid print immediately after leaving for 5 minutes (i.e., the solid print obtained by the command to print one sheet immediately after leaving) to the ejection area of ​​the solid print immediately before leaving for 5 minutes (i.e., the 10th print of the solid print obtained by the command to print 10 sheets) was calculated (ejection recovery rate (%) according to the following formula) to evaluate intermittent ejection properties. In this evaluation, no electricity was applied to the film heater. Discharge recovery rate (%) = [(discharge area of ​​solid print immediately after leaving for 5 minutes) / (solid print immediately before leaving for 5 minutes)] × 100 An evaluation result of A indicates excellent intermittent dischargeability, and a result of D indicates poor intermittent dischargeability. (Evaluation Criteria) A: Discharge recovery rate is 90% or more B: Discharge recovery rate is 87.5% or more but less than 90% C: Discharge recovery rate is 85% or more but less than 87.5% D: Discharge recovery rate is less than 85%

[0079] [Table 2]

[0080] From Table 2, it can be seen that the water-based ink using the water-based pigment dispersion of the Example can produce printed matter with excellent substrate adhesion (tape peel resistance) and excellent intermittent ejection properties compared to the water-based ink using the water-based pigment dispersion of the Comparative Example. [Industrial Applicability]

[0081] According to the aqueous pigment dispersion of the present invention, an aqueous ink having excellent intermittent ejection properties can be provided, and when used for printing on a resin film, a printed matter having excellent adhesion of the ink coating to the substrate (tape peel resistance) can be obtained.

Claims

1. An aqueous pigment dispersion in which a pigment is dispersed in a crosslinked polymer A, the crosslinked polymer A comprises a structure derived from the water-dispersible polymer A′ and a structure derived from a water-insoluble multifunctional epoxy crosslinking agent; The water-based pigment dispersion, wherein the water-dispersible polymer A' is a vinyl resin containing a structural unit derived from a cycloalkyl(meth)acrylate (a-1).

2. 2. The aqueous pigment dispersion according to claim 1, wherein the water-dispersible polymer A' is a vinyl resin containing structural units derived from a cycloalkyl(meth)acrylate (a-1), structural units derived from one or more ionic monomers (a-2) having a carboxy group selected from the group consisting of acrylic acid and methacrylic acid, and structural units derived from one or more hydrophobic monomers (a-3) selected from the group consisting of alkyl(meth)acrylates and aromatic group-containing (meth)acrylates.

3. The water-based pigment dispersion according to claim 1 , wherein the crosslinked polymer A has an acid value of 25 mgKOH / g or more and 170 mgKOH / g or less.

4. 2. The aqueous pigment dispersion according to claim 1, wherein the polyfunctional epoxy crosslinking agent is a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms.

5. 3. The water-based pigment dispersion according to claim 2, wherein the crosslinking rate of the crosslinked polymer A is 15 mol % or more and 85 mol % or less, in terms of the ratio of the molar equivalent number of epoxy groups of the polyfunctional epoxy crosslinking agent to the molar equivalent number of carboxy groups of the water-dispersible polymer A'.

6. A water-based ink comprising the water-based pigment dispersion according to any one of claims 1 to 5 and a water-soluble organic solvent.

7. The water-based ink according to claim 6, which is used in printing on a resin film as a printing substrate.

8. The water-based ink of claim 6 for ink-jet printing.

9. A pigment-containing crosslinked polymer particle, comprising: the crosslinked polymer comprises a structure derived from the water-dispersible polymer A′ and a structure derived from the water-insoluble multifunctional epoxy crosslinker; The pigment-containing crosslinked polymer particles are such that the water-dispersible polymer A' is a vinyl resin containing a structural unit derived from a cycloalkyl(meth)acrylate (a-1).

10. A method for producing polymer particles containing the pigment described in claim 9, comprising the following steps 1 to 3. Step 1: A step of dispersing a pigment mixture containing a pigment, a water-dispersible polymer A′, an organic solvent, and water to obtain a pigment dispersion. Step 2: A step of removing the organic solvent from the pigment dispersion liquid obtained in Step 1 to obtain an aqueous pigment dispersion (i) in which the pigment is dispersed in the water-dispersible polymer A'. Step 3: A step of adding a water-insoluble polyfunctional epoxy crosslinking agent to the water-based pigment dispersion (i) obtained in Step 2, and crosslinking the water-dispersible polymer A′ with the polyfunctional epoxy crosslinking agent to obtain a water-based pigment dispersion.

11. A water-based ink containing crosslinked polymer particles containing the pigment described in claim 9 and a water-soluble organic solvent.

12. A water-based ink as described in claim 11, used for printing using a resin film as the printing substrate.

13. The water-based ink of claim 11, for use in inkjet printing.