Aqueous pigment dispersion

Abstract

To provide an aqueous pigment dispersion which is excellent in re-dispersibility of pigment particles, and is excellent in substrate adhesion of an ink coating film of an obtained printed material when used for printing on a low liquid absorptive printing substrate, and an aqueous ink using the aqueous pigment dispersion.SOLUTION: There are provided: an aqueous pigment dispersion in which a pigment is dispersed by a crosslinked polymer A, wherein the crosslinked polymer A contains a structure derived from a water-dispersible polymer A', and a structure derived from a polyfunctional epoxy crosslinking agent, and the water-dispersible polymer A' is a vinyl-based resin containing a structural unit derived from isobornyl (meth)acrylate (a-1); and an aqueous ink using the aqueous pigment dispersion.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In the sign graphics printing market, which prints on billboards and the like, synthetic resins are primarily used as printing substrates from the viewpoint of durability of printed matter for indoor and outdoor displays. In addition, inks using pigments as colorants are becoming mainstream from the viewpoint of weather resistance and water resistance of printed matter.

[0003] For example, Patent Document 1 discloses an aqueous pigment dispersion containing a pigment, water, a water-soluble organic solvent, and a polymer dispersant that disperses the pigment, the polymer dispersant comprising structural units (i) derived from at least one of (meth)acrylic acid and itaconic acid, and structural units (ii) derived from a (meth)acrylate derived from a biological material, the polymer having an acid value of 30 to 250 mgKOH / g, a content of structural units (ii) of 50 mass % or more, a number average molecular weight of 1,000 to 30,000, and a molecular weight distribution (weight average molecular weight / number average molecular weight) of 2.5 or less, and at least a portion of the carboxy groups of which have been neutralized with an alkali, for the purpose of providing an aqueous pigment dispersion that can be used to prepare an environmentally friendly aqueous inkjet ink that is capable of recording images in which the pigment is stably and highly finely dispersed and that exhibits excellent durability, gloss, color development, and adhesion to various printing substrates. The aqueous pigment dispersion also discloses an aqueous inkjet ink containing the aqueous pigment dispersion.

[0004] Furthermore, for example, Patent Document 2 discloses an inkjet ink for non-permeable substrates, which contains water, a resin-coated pigment in which at least a portion of the pigment is coated with a crosslinked resin, solvent A which is an alkanediol compound having a boiling point of 180°C to 200°C, and solvent B which is at least one of a monoalcohol compound having a boiling point of 70°C to 160°C and a glycol monoether compound having a boiling point of 70°C to 160°C, for the purpose of providing an inkjet ink for non-permeable substrates and an image recording method, which can record images on non-permeable substrates with excellent drying properties and excellent lamination strength with a substrate for lamination, and which also has excellent re-ejection properties after ejection has stopped. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-133936 [Patent Document 2] International Publication No. 2020 / 195360 Summary of the Invention [Problem to be solved by the invention]

[0006] A particular issue with using synthetic resin as a printing substrate is the need for improved substrate adhesion of the ink coating to the resulting printed matter, such as tape peel resistance. If the ink coating has insufficient tape peel resistance, the ink coating may peel off from the synthetic resin when an advertising sign or the like is displayed, which could result in a reduction in the aesthetic appeal of the printed matter or the display of inaccurate information. Therefore, when printing on synthetic resin as a printing substrate, there is a strong demand for improved substrate adhesion of the ink coating to the printed matter. In particular, when printing on synthetic resin using a water-based ink, the ink coating formed by the water-based ink must adhere sufficiently to the synthetic resin. Furthermore, when the ink dries and the content of the water-soluble organic solvent in the ink increases, the pigment particles aggregate and solidify, so the pigment particles must be redispersible.

[0007] However, the aqueous pigment dispersion of Patent Document 1 does not have excellent redispersibility of pigment particles, and when the aqueous pigment dispersion is used as a water-based ink to perform inkjet printing on a synthetic resin as a low-liquid-absorbent printing substrate, it has been found that the tape peel resistance of the ink coating film of the resulting printed matter is insufficient. Furthermore, in Patent Document 2, an aqueous dispersion of a crosslinked resin-coated pigment is used to prepare the ink, but the redispersibility of the aqueous dispersion of the crosslinked resin-coated pigment is insufficient. Furthermore, when the inkjet ink for non-permeable substrates of Patent Document 2 is used, it has been found that the tape peel resistance of the ink coating film of the resulting printed matter is an issue. An object of the present invention is to provide an aqueous pigment dispersion that exhibits excellent re-dispersibility of pigment particles and, when used for printing on a low-liquid-absorbent printing substrate, exhibits excellent substrate adhesion of the ink coating film of the resulting printed matter, and an aqueous ink that uses the aqueous pigment dispersion. [Means for solving the problem]

[0008] 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 A, wherein the crosslinked polymer A contains a structure derived from a water-dispersible polymer A' and a structure derived from a polyfunctional epoxy crosslinking agent, and the water-dispersible polymer A' is a vinyl resin containing a structural unit derived from isobornyl (meth)acrylate (a-1). 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 contains a structure derived from the water-dispersible polymer A' and a structure derived from the 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 isobornyl (meth)acrylate (a-1). [2] A water-based ink containing the water-based pigment dispersion according to [1] above and a water-soluble organic solvent. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an aqueous pigment dispersion and an aqueous ink using the aqueous pigment dispersion, which have excellent re-dispersibility of pigment particles and, when used for printing on a low-liquid-absorbent printing substrate, provide an ink coating film of the resulting printed matter with excellent substrate adhesion. DETAILED DESCRIPTION OF THE INVENTION

[0010] [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 contains a structure derived from the water-dispersible polymer A' and a structure derived from the multifunctional epoxy crosslinking agent; The water-based pigment dispersion is one in which the water-dispersible polymer A' is a vinyl resin containing a structural unit derived from isobornyl (meth)acrylate (a-1).

[0011] In the present invention, the adhesion between the low-liquid-absorbent printing substrate and the ink coating film in a printed matter obtained when an aqueous ink containing an aqueous pigment dispersion is used to print on the low-liquid-absorbent printing substrate is referred to as “substrate adhesion.” Substrate adhesion can be regarded as the peel durability of the ink coating film from the low-liquid-absorbent printing substrate, and this can be evaluated as “tape peel resistance” using, for example, adhesive tape or the like, by the method described in the Examples.

[0012] In the present invention, the term "aqueous system" means that water accounts for the largest proportion by mass of the medium. In the present invention, the term "water-soluble organic solvent" refers to an organic solvent that dissolves in 100 mL of water at 25°C in an amount of 5 mL or more. In this specification, the term "low liquid absorption" in the context of a low liquid absorption printing substrate is a concept that encompasses both low liquid absorption and non-liquid absorption, and refers to a printing substrate with a water absorption of 0 g / m when the printing substrate is in contact with pure water for 100 ms. 2 More than 10g / m 2The water absorption amount can be measured as the amount transferred in pure water for a contact time of 100 ms under conditions of 23°C and 50% relative humidity using an automatic scanning absorption meter (for example, "KM500win" manufactured by Kumagai Riki Kogyo Co., Ltd.). Furthermore, "printing" is a concept that includes printing and printed letters on which characters and images are recorded, and "printed matter" is a concept that includes printed matter and printed letters on which characters and images are recorded.

[0013] The aqueous pigment dispersion according to the present invention is prepared by dispersing a pigment in a crosslinked polymer A. More specifically, particles are formed by the crosslinked polymer A and the pigment, and the particles are dispersed in an aqueous medium. The form in which the pigment is dispersed in the crosslinked polymer A is preferably particles of the crosslinked polymer A containing the pigment (hereinafter also referred to as "pigment-containing crosslinked polymer particles"). Here, the form of the pigment-containing crosslinked polymer particles is not particularly limited, as long as the particles are formed from at least the pigment and the crosslinked polymer A. Examples include a particle form in which the pigment is encapsulated in the crosslinked polymer A, a particle form in which the pigment is uniformly dispersed in the crosslinked polymer A, a particle form in which the pigment is exposed on the particle surface of the crosslinked polymer A, and a form in which the crosslinked polymer A is adsorbed to the pigment, and mixtures of these are also included.

[0014] The aqueous pigment dispersion according to the present invention has excellent redispersibility of pigment particles, and when used for printing on a low-liquid-absorbent printing substrate, the ink coating film of the resulting printed matter has excellent substrate adhesion (tape peel resistance). The reason for this is unclear, but is thought to be as follows. The aqueous pigment dispersion of the present invention comprises pigment-containing crosslinked polymer particles dispersed in an aqueous medium, and the crosslinked polymer A constituting the pigment-containing crosslinked polymer particles contains a structural unit derived from isobornyl (meth)acrylate, which has an isobornyl structure within the molecule. The isobornyl structural portion of this isobornyl (meth)acrylate-derived structural unit is highly hydrophobic, providing high affinity for the hydrophobic surface of synthetic resins used as low-liquid-absorbent printing substrates, thereby improving substrate adhesion. Furthermore, the isobornyl group has a compact structure relative to its carbon number, and does not undergo π-π stacking like a benzene ring, resulting in low cohesive force between polymer molecules. This results in more pronounced adhesion of the ink coating to low-liquid-absorbent printing substrates. Because the pigment is dispersed and coated with crosslinked polymer A containing an isobornyl structure, which has high substrate adhesion, it is believed that adhesion is further improved by fusion between the pigment particles and the substrate, and between pigment particles themselves, via the crosslinked polymer A. Furthermore, in addition to the structural units derived from isobornyl (meth)acrylate having an isobornyl structure, the crosslinked polymer A also contains a crosslinked structure derived from a polyfunctional epoxy crosslinker within the molecule. Therefore, even when the ink dries and the content of the water-soluble organic solvent in the ink increases, swelling of the polymer is suppressed, making it less likely for the polymer to detach from the pigment. As a result, it is believed that aggregation and coagulation of pigment particles can be suppressed, resulting in high redispersibility of the pigment particles. When the aqueous pigment dispersion of the present invention is used as an aqueous ink for inkjet printing, the aqueous ink has excellent ejection stability.

[0015] <Pigments> The pigment used in the present invention may be either an inorganic pigment or an organic pigment, and lake pigments and fluorescent pigments may also be used. If necessary, these pigments may also be used in combination with extender pigments. Specific examples of inorganic pigments include carbon black, metal oxides such as titanium oxide, iron oxide, red iron oxide, and chromium oxide, and pearlescent pigments. Carbon black is particularly preferred for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne 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, blue, red, orange, and green can be used. Specific examples of preferred organic pigments include one or more product numbers selected from CI Pigment Yellow, CI Pigment Red, CI Pigment Orange, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green. Examples of extender pigments include silica, calcium carbonate, and talc. The above pigments can be used alone or in combination of two or more.

[0016] <Crosslinked polymer A> The crosslinked polymer A according to the present invention contains a structure derived from the water-dispersible polymer A' and a structure derived from the polyfunctional epoxy crosslinker. Furthermore, the water-dispersible polymer A' is a vinyl resin containing a structural unit derived from isobornyl (meth)acrylate (a-1). The crosslinked polymer A functions as a pigment dispersant that exhibits a pigment dispersing effect and as a fixing agent for the printing substrate. The crosslinked polymer A may be used alone or in combination of two or more.

[0017] (Water-dispersible polymer A') The water-dispersible polymer A' is a vinyl resin containing a structural unit derived from isobornyl (meth)acrylate (a-1). Hereinafter, the isobornyl (meth)acrylate (a-1) may be simply referred to as "monomer (a-1)." In the present invention, the term "water-dispersible polymer" refers to a polymer that can be dispersed in water or an aqueous medium at room temperature (25°C). The water-dispersible polymer A' may be any of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer.

[0018] From the viewpoints of further improving the redispersibility of pigment particles and further improving the adhesion to a substrate, the isobornyl (meth)acrylate (a-1) is preferably isobornyl acrylate (a-1a). That is, the water-dispersible polymer A' is preferably a vinyl resin containing a structural unit derived from isobornyl acrylate (a-1a).

[0019] The water-dispersible polymer A' preferably further contains a structural unit derived from an ionic monomer (a-2) having one or more carboxy groups selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid. When the water-dispersible polymer A' contains a structural unit derived from the ionic monomer (a-2), the redispersibility of the pigment particles can be further improved. The ionic monomer (a-2) is preferably acrylic acid or itaconic acid, more preferably acrylic acid, from the viewpoint of further improving the redispersibility of the pigment particles and further improving the adhesion to the substrate.

[0020] From the viewpoint of further improving adhesion to a substrate, the water-dispersible polymer A' preferably contains a structural unit derived from a hydrophobic monomer (a-3) in addition to the structural unit derived from isobornyl (meth)acrylate and the structural unit derived from the ionic monomer (a-2). Here, the term "hydrophobic" in the context of a hydrophobic monomer means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturated, the amount of dissolution is less than 10 g.

[0021] Examples of the hydrophobic monomer (a-3) include (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms; aromatic group-containing monomers such as styrene-based monomers and aromatic group-containing (meth)acrylates; and styrene-based macromonomers. The molecular weight of the aromatic group-containing monomer, preferably the styrene-based monomer, is preferably less than 500. The styrene-based macromonomer is a compound having a polymerizable functional group at one end and a number-average molecular weight of 500 to 100,000. Among these, the hydrophobic monomer (a-3) is preferably at least one selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms and aromatic group-containing monomers, more preferably at least one selected from the group consisting of (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms and aromatic group-containing (meth)acrylates, and even more preferably (meth)acrylates having a hydrocarbon group derived from an aliphatic alcohol having 1 to 22 carbon atoms.

[0022] From the viewpoint of further improving the adhesion to the substrate, the hydrophobic monomer (a-3) is preferably one having a glass transition temperature (Tg) of 10° C. or less when made into a homopolymer. From the viewpoint of further improving the adhesion to the substrate, such hydrophobic monomer (a-3) is preferably an alkyl acrylate having an alkyl group having 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms. Specific examples thereof 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), isopentyl acrylate (Tg: -45°C), hexyl acrylate (Tg: -57°C), octyl acrylate (Tg: -65°C), and 2-ethylhexyl acrylate (Tg: -70°C).

[0023] Among these, from the viewpoint of further improving adhesion to the substrate, the hydrophobic monomer (a-3) is more preferably one or more selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, and isobutyl acrylate, even more preferably one or more selected from the group consisting of butyl acrylate and isobutyl acrylate, and even more preferably butyl acrylate. The values ​​in parentheses above indicate the glass transition temperature (Tg) of the homopolymer of each monomer. The glass transition temperature (Tg) of the homopolymer of each monomer can be, for example, the value described in Polymer Handbook Third Edition (Wiley-Interscience 1989).

[0024] 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 such other monomers include nonionic monomers. Here, the nonionic monomer is a monomer that has a high affinity with water or a water-soluble organic solvent, and is, for example, a monomer that contains a hydroxy group or a polyalkylene glycol chain. Examples of nonionic monomers include polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate; and alkoxypolyalkylene glycol mono(meth)acrylates such as methoxypolyethylene glycol mono(meth)acrylate and octoxypolyethylene glycol mono(meth)acrylate.

[0025] The content of structural units derived from isobornyl (meth)acrylate (a-1) in all structural units of the water-dispersible polymer A' is preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 27% by mass or more, and still more preferably 30% by mass or more, from the viewpoints of further improving the redispersibility of the pigment particles and further improving the adhesion to the substrate, and from the same viewpoints, is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, still more preferably 60% by mass or less, still more preferably 50% by mass or less, and still more preferably 40% by mass or less.

[0026] The content of the structural units derived from the ionic monomer (a-2) in all structural units of the water-dispersible polymer A' is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 13% by mass or more, and still more preferably 18% by mass or more, from the viewpoint of further improving the redispersibility of the pigment particles, and is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 32% by mass or less, from the viewpoint of further improving the adhesion to the substrate.

[0027] The content of structural units derived from hydrophobic monomer (a-3) in all structural units of water-dispersible polymer A' is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, still more preferably 20% by mass or more, and still more preferably 30% by mass or more, from the viewpoint of further improving adhesion to substrates, and is preferably 50% by mass or less, more preferably 45% by mass or less, from the viewpoint of further improving redispersibility of pigment particles. The water-dispersible polymer A' can be obtained, for example, by addition polymerization of raw material monomers including isobornyl (meth)acrylate (a-1), an ionic monomer (a-2), a hydrophobic monomer (a-3), or, if necessary, a nonionic monomer, using a known method.

[0028] The acid value of the water-dispersible polymer A' is preferably 60 mgKOH / g or more, more preferably 90 mgKOH / g or more, even more preferably 100 mgKOH / g or more, still more preferably 150 mgKOH / g or more, and still more preferably 170 mgKOH / g or more, from the viewpoint of further improving the redispersibility of the pigment particles, and is preferably 300 mgKOH / g or less, more preferably 280 mgKOH / g or less, and even more preferably 260 mgKOH / g or less, from the viewpoint of further improving the adhesion to the substrate. The acid value of the water-dispersible polymer A' can be determined by the method described in the examples, but can also be calculated from the mass ratio of the constituent monomers.

[0029] The glass transition temperature Tg of the water-dispersible polymer A' is preferably 100°C or lower, more preferably 60°C or lower, even more preferably 30°C or lower, still more preferably 20°C or lower, and even more preferably 15°C or lower, from the viewpoint of further improving the adhesion to the substrate, and is preferably -20°C or higher, more preferably -10°C or higher, even more preferably 0°C or higher, and even more preferably 5°C or higher, from the viewpoint of further improving the redispersibility of the pigment particles. The glass transition temperature of the water-dispersible polymer A' is calculated by the method described in the examples.

[0030] The weight-average molecular weight of the water-dispersible polymer A' is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 13,000 or more from the viewpoint of further improving the adhesion to the substrate, and from the same viewpoint, is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. The weight-average molecular weight of the water-dispersible polymer A' can be measured by the method described in the examples.

[0031] At least a portion of the carboxyl groups of the water-dispersible polymer A' may be neutralized with a neutralizing agent to further improve the redispersibility of the pigment particles. The neutralizing agent is preferably at least one selected from the group consisting of alkali metal hydroxides, organic amines, and ammonia, more preferably at least one selected from the group consisting of alkali metal hydroxides and organic amines, and even more preferably an organic amine. Examples of the alkali metal hydroxide include sodium hydroxide and potassium hydroxide. Examples of organic amines include alkanolamines, alkylamines, aminoalkanediols, alkoxyamines, and heterocyclic amines. Among these, one or more selected from the group consisting of alkanolamines and alkylamines are preferred, and alkanolamines are more preferred. Preferred examples of the alkanolamine include water-miscible alkanolamines having 2 to 8 carbon atoms, such as monoethanolamine, monoisopropanolamine, monoisobutanolamine, N-methylethanolamine, N,N-dimethylethanolamine, N-methyldiethanolamine, and triethanolamine. From the viewpoint of further improving the redispersibility of pigment particles, the degree of neutralization of the carboxyl groups in the water-dispersible polymer A' is preferably 15 mol % or more, more preferably 20 mol % or more, and even more preferably 25 mol % or more, and from the same viewpoint, it is preferably 100 mol % or less, more preferably 70 mol % or less, and even more preferably 50 mol % or less.

[0032] Here, the degree of neutralization can be calculated by the following formula, where the equivalent amount of neutralizing agent used is the amount of carboxyl groups in the water-dispersible polymer A'. When the equivalent amount of neutralizing agent used is 100 mol % or less, this is synonymous with the degree of neutralization. When the equivalent amount of neutralizing agent used exceeds 100 mol %, this means that the neutralizing agent is in excess of the carboxyl groups in the water-dispersible polymer A', and the degree of neutralization of the water-dispersible polymer A' in this case is considered to be 100 mol %. Equivalent amount of neutralizing agent used (mol %)=[(mass of neutralizing agent added (g) / equivalent amount of neutralizing agent) / [(acid value of water-dispersible polymer A' (mg KOH / g) × mass of water-dispersible polymer A' (g)) / (56.1 × 1000)]] × 100

[0033] (Multifunctional epoxy crosslinker) The crosslinked polymer A according to the present invention contains a structure derived from the polyfunctional epoxy crosslinking agent in addition to a structure derived from the water-dispersible polymer A'. In other words, it is believed that the crosslinked polymer A according to the present invention has a structure crosslinked by a polyfunctional epoxy crosslinking agent, and that the water-dispersible polymer A' has a three-dimensional structure due to components derived from the polyfunctional epoxy crosslinking agent. Because the crosslinked polymer A has such a crosslinked structure, when the aqueous pigment dispersion is applied to an aqueous ink, even if the water in the aqueous ink evaporates and the proportion of the water-soluble organic solvent in the aqueous ink increases, the crosslinked polymer A is less likely to swell and is less likely to detach from the pigment particles, resulting in excellent redispersibility of the pigment particles. The term "water-insoluble" in the context of a polyfunctional epoxy crosslinking agent means that when the crosslinking agent is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the amount of dissolution is less than 50 g. The amount of dissolution is preferably 40 g or less, more preferably 35 g or less.

[0034] From the viewpoint of further improving the redispersibility of pigment particles, the polyfunctional epoxy crosslinking agent is preferably a polyfunctional epoxy compound having two or more epoxy groups in the molecule, more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having from 3 to 8 carbon atoms, even more preferably one or more compounds selected from the group consisting of trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether, and from the viewpoint of further improving the adhesion to substrates, is preferably one or more compounds selected from the group consisting of trimethylolpropane polyglycidyl ether, 1,6-hexanediol diglycidyl ether, and 1,4-cyclohexanedimethanol diglycidyl ether, even more preferably trimethylolpropane polyglycidyl ether.

[0035] The epoxy group equivalent weight of the polyfunctional epoxy crosslinking agent is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, still more preferably 120 or more, still more preferably 130 or more, and is preferably 300 or less, more preferably 200 or less, even more preferably 160 or less.

[0036] The crosslinking rate of the crosslinked polymer A according to the present invention can be calculated as 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'. The crosslinking rate of the crosslinked polymer A according to the present invention is preferably 15 mol % or more, more preferably 20 mol % or more, even more preferably 30 mol % or more, and still more preferably 35 mol % or more, from the viewpoint of further improving the redispersibility of the pigment particles, and is preferably 85 mol % or less, more preferably 80 mol % or less, even more preferably 70 mol % or less, and still more preferably 65 mol % or less, from the viewpoint of further improving the adhesion to the substrate.

[0037] The acid value of the crosslinked polymer A is preferably 25 mgKOH / g or more, more preferably 30 mgKOH / g or more, and even more preferably 40 mgKOH / g or more, from the viewpoint of further improving the adhesion to the substrate, and is preferably 170 mgKOH / g or less, more preferably 150 mgKOH / g or less, and even more preferably 130 mgKOH / g or less, from the viewpoint of improving the redispersibility of the pigment particles. The acid value of the crosslinked polymer A can be calculated using the following formula. Acid value of crosslinked polymer A (mg KOH / g) = [Acid value of water-dispersible polymer A' (mg KOH / g) × [(100 - crosslinking rate (mol%)) / 100]

[0038] (Composition of Water-Based Pigment Dispersion) The solids concentration of the aqueous dispersion of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, from the viewpoint of further improving adhesion to the substrate, and is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, from the viewpoint of improving the redispersibility of the pigment particles.

[0039] From the viewpoint of print density, the content of the pigment in the aqueous dispersion of the present invention is preferably 3.5% by mass or more, more preferably 5% by mass or more, even more preferably 7% by mass or more, and is preferably 20% by mass or less, more preferably 17% by mass or less, even more preferably 15% by mass or less.

[0040] The mass ratio of the content of the pigment to the content of the water-dispersible polymer A' in the aqueous pigment dispersion of the present invention [pigment / water-dispersible polymer A'] is preferably 0.5 or more, more preferably 0.8 or more, and even more preferably 0.9 or more, from the viewpoint of further improving adhesion to the substrate, and is preferably 4.0 or less, more preferably 3.0 or less, even more preferably 2.5 or less, and even more preferably 1.5 or less, from the viewpoint of further improving redispersibility of the pigment particles.

[0041] The mass ratio of the pigment content to the crosslinked polymer A content in the aqueous pigment dispersion of the present invention [pigment / crosslinked polymer A] is preferably 0.40 or more, more preferably 0.50 or more, even more preferably 0.60 or more, and still more preferably 0.70 or more, from the viewpoint of redispersibility of pigment particles, and from the same viewpoint, is preferably 2.00 or less, more preferably 1.60 or less, even more preferably 1.00 or less, and still more preferably 0.90 or less.

[0042] From the viewpoint of reducing the environmental load, the water content in the aqueous pigment dispersion of the present invention is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% 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.

[0043] The method for producing the water-based pigment dispersion of the present invention is preferably to prepare the dispersion by dispersing the pigment, the water-dispersible polymer A', the polyfunctional epoxy crosslinking agent, and, if necessary, a neutralizing agent, a surfactant, and the like, by a known method. The following method can be used to produce the water-based pigment dispersion. A pigment mixture containing a pigment, a water-dispersible polymer A', an organic solvent, and water is subjected to a dispersion treatment to obtain a dispersion. The organic solvent is then removed from the dispersion, and a polyfunctional epoxy crosslinking agent is added to the obtained pigment aqueous dispersion to crosslink the water-dispersible polymer A'. The mixture is then filtered to remove coarse particles, thereby obtaining an aqueous pigment dispersion in which pigment-containing crosslinked polymer particles are dispersed in an aqueous medium. Specific examples of such methods include those described in paragraphs

[0022] to

[0026] of Japanese Patent Application Laid-Open No. 2022-104084.

[0044] The cumulant average particle size of the pigment-containing crosslinked polymer particles in the aqueous pigment dispersion of the present invention is preferably 50 nm or more, more preferably 70 nm or more, and even more preferably 90 nm or more, from the viewpoints of improving the dispersion stability of the pigment and further improving adhesion to the substrate, and from the same viewpoints, is preferably 600 nm or less, more preferably 500 nm or less, even more preferably 300 nm or less, and still more preferably 200 nm or less. The cumulant average particle size of the pigment-containing crosslinked polymer particles in the aqueous pigment dispersion can be measured by the method described in the Examples.

[0045] [Water-based ink] The water-based ink of the present invention contains the above-mentioned water-based pigment dispersion and a water-soluble organic solvent. The aqueous ink of the present invention contains the aqueous pigment dispersion of the present invention, which has excellent redispersibility of pigment particles and, when used for printing on a low-liquid-absorbent printing substrate, has excellent substrate adhesion (tape peel resistance) of the ink coating film of the resulting printed matter, and therefore can be suitably used as an aqueous ink for inkjet printing. When the aqueous ink of the present invention is used for inkjet printing, it also has excellent ejection stability.

[0046] <Water-soluble organic solvent> The water-based ink of the present invention contains a water-soluble organic solvent from the viewpoint of further improving the adhesion to the substrate. In the present invention, the term "water-soluble organic solvent" refers to an organic solvent that dissolves in 100 mL of water at 25°C in an amount of 5 mL or more. The boiling point of the water-soluble organic solvent is preferably 90° C. or higher, more preferably 130° C. or higher, even more preferably 150° C. or higher, and preferably 260° C. or lower, more preferably 250° C. or lower, even more preferably 240° C. or lower. When two or more water-soluble organic solvents are used, the boiling point value is a weighted average value weighted by the content (% by mass) of each water-soluble organic solvent.

[0047] (Alkylene glycol alkyl ether) The water-soluble organic solvent preferably contains an alkylene glycol alkyl ether from the viewpoint of further improving the adhesion to the substrate. From the viewpoint of further improving the adhesion to the substrate, the number of carbon atoms in the alkyl group of the alkylene glycol alkyl ether is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more, and from the same viewpoint, is preferably 6 or less, more preferably 4 or less. The alkyl group may be linear or branched. Here, the number of carbon atoms in the alkyl group is the number of carbon atoms in one alkyl group, and when the alkylene glycol alkyl ether has a plurality of alkyl groups, it is preferable that the number of carbon atoms in each alkyl group is within the above range. The alkylene oxide group of the alkylene glycol alkyl ether is preferably at least one selected from the group consisting of an ethylene oxide group and a propylene oxide group. The alkylene glycol alkyl ether is preferably at least one selected from the group consisting of alkylene glycol monoalkyl ethers and alkylene glycol dialkyl ethers, from the viewpoint of further improving the adhesion to the substrate.

[0048] Examples of alkylene glycol monoalkyl ethers include ethylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, and ethylene glycol monoisobutyl ether; diethylene glycol monoalkyl ethers such as diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, and diethylene glycol monoisobutyl ether; propylene glycol monoalkyl ethers such as propylene glycol monomethyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether; dipropylene glycol monoalkyl ethers such as dipropylene glycol monomethyl ether and dipropylene glycol monopropyl ether; and tripropylene glycol monoalkyl ethers such as tripropylene glycol monomethyl ether. Examples of alkylene glycol dialkyl ethers include diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, and triethylene glycol dimethyl ether. The alkylene glycol alkyl ethers may be used alone or in combination of two or more.

[0049] Among these, from the viewpoint of further improving substrate adhesion, the alkylene glycol alkyl ether is preferably an alkylene glycol monoalkyl ether, more preferably at least one selected from the group consisting of diethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, and dipropylene glycol monoalkyl ether, even more preferably at least one selected from the group consisting of diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and dipropylene glycol monopropyl ether, still more preferably at least one selected from the group consisting of propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monopropyl ether, and diethylene glycol monoisobutyl ether, and still more preferably diethylene glycol monoisobutyl ether.

[0050] (Water-soluble organic solvents other than alkylene glycol alkyl ethers) The water-soluble organic solvent may further contain another water-soluble organic solvent other than alkylene glycol alkyl ether. The other water-soluble organic solvent can be appropriately selected depending on the purpose. Examples of the other water-soluble organic solvent include polyhydric alcohols, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, it is preferable that the water-soluble organic solvent further contains a polyhydric alcohol from the viewpoint of improving tape peel resistance, abrasion resistance, and solid filling ability.

[0051] Examples of polyhydric alcohols include alkanediols such as ethylene glycol, propylene glycol, 1,2-pentanediol, 1,2-hexanediol, and 1,2-octanediol; polyalkylene glycols such as diethylene glycol and triethylene glycol; glycerin; and trimethylolpropane. Among these, the polyhydric alcohol is preferably one or more selected from the group consisting of propylene glycol, 1,2-hexanediol, triethylene glycol, and glycerin, and more preferably propylene glycol.

[0052] The water-based ink of the present invention may further contain various additives, such as a fixing resin, a surfactant, a humectant, a wetting agent, a wetting / penetrating agent, a viscosity adjuster, an antifoaming agent, an antiseptic, an antifungal agent, and an antirust agent, as necessary. The water-based ink of the present invention is preferably obtained by mixing the above-mentioned water-based pigment dispersion, the water-soluble organic solvent, and various additives. There are no particular limitations on the method for mixing the components.

[0053] (surfactant) Examples of surfactants include nonionic surfactants, anionic surfactants, amphoteric surfactants, etc. Among these, nonionic surfactants are preferred. Examples of nonionic surfactants include polyoxyalkylene alkyl ether surfactants, acetylene glycol surfactants, polyhydric alcohol surfactants, fatty acid alkanolamides, silicone surfactants, and fluorine surfactants. Among these, the nonionic surfactant is preferably at least one selected from the group consisting of acetylene glycol surfactants and silicone surfactants. Preferred examples of the acetylene glycol surfactant include acetylene glycols having 8 to 22 carbon atoms and ethylene oxide adducts of the acetylene glycols, and more preferred is 2,4,7,9-tetramethyl-5-decyne-4,7-diol or an ethylene oxide adduct thereof. Examples of silicone surfactants include polyether-modified silicone, amino-modified silicone, carboxy-modified silicone, fatty acid-modified silicone, alcohol-modified silicone, aliphatic alcohol-modified silicone, epoxy-modified silicone, fluorine-modified silicone, and alkyl-modified silicone. Commercially available nonionic surfactants include, for example, the KF series manufactured by Shin-Etsu Chemical Co., Ltd., the BYK series manufactured by BYK Japan K.K., the Surfynol series manufactured by Nissin Chemical Industry Co., Ltd. and Air Products & Chemicals, and the Acetylenol series manufactured by Kawaken Fine Chemicals Co., Ltd.

[0054] (Composition and properties of water-based ink) From the viewpoint of print density, the content of the pigment in the water-based ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 7% by mass or less.

[0055] The mass ratio of the pigment content to the water-dispersible polymer A' content in the water-based ink of the present invention [pigment / water-dispersible polymer A'] is preferably 0.5 or more, more preferably 0.8 or more, and even more preferably 0.9 or more, from the viewpoint of further improving adhesion to the substrate, and is preferably 4.0 or less, more preferably 3.0 or less, even more preferably 2.5 or less, and even more preferably 1.5 or less, from the viewpoint of further improving redispersibility of the pigment particles.

[0056] The mass ratio of the pigment content to the crosslinked polymer A content in the water-based ink of the present invention [pigment / crosslinked polymer A] is, from the viewpoint of redispersibility of pigment particles, preferably 0.40 or more, more preferably 0.50 or more, even more preferably 0.60 or more, and still more preferably 0.70 or more, and from the same viewpoint, is preferably 2.00 or less, more preferably 1.60 or less, even more preferably 1.00 or less, and still more preferably 0.90 or less.

[0057] The content of the water-soluble organic solvent in the water-based ink of the present invention is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 23% by mass or more, from the viewpoint of further improving adhesion to the substrate, and is preferably 43% by mass or less, more preferably 40% by mass or less, and even more preferably 37% by mass or less, from the viewpoint of redispersibility of the pigment particles.

[0058] The content of alkylene glycol alkyl ether in the water-based ink of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of improving tape peeling resistance, and is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of redispersibility of pigment particles.

[0059] In the present invention, the content of alkylene glycol alkyl ether in the water-soluble organic solvent is preferably 3.5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, from the viewpoint of improving tape peeling resistance, and is preferably 70% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, from the viewpoint of redispersibility of pigment particles.

[0060] From the viewpoint of reducing the environmental impact, the water content in the water-based ink of the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and is preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less.

[0061] The viscosity of the aqueous ink of the present invention at 32°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, even more preferably 4 mPa·s or more, and preferably 12 mPa·s or less, more preferably 9 mPa·s or less, even more preferably 7 mPa·s or less. The viscosity of concentrated aqueous ink can be measured using an E-type viscometer.

[0062] The average particle size of the pigment-containing crosslinked polymer particles in the water-based ink of the present invention is preferably 50 nm or more, more preferably 70 nm or more, and even more preferably 90 nm or more, from the viewpoints of improving the dispersion stability of the pigment and further improving adhesion to the substrate, and from the same viewpoints, is preferably 600 nm or less, more preferably 500 nm or less, even more preferably 300 nm or less, and even more preferably 200 nm or less. The average particle size of the pigment-containing crosslinked polymer particles in the water-based ink can be measured by the method described in the Examples.

[0063] The pH of the water-based ink of the present invention at 25°C is preferably 7.0 or higher, more preferably 7.2 or higher, and even more preferably 7.5 or higher. From the viewpoints of component resistance and skin irritation, the pH is preferably 11 or lower, more preferably 10 or lower, and even more preferably 9.5 or lower. The pH of the water-based ink can be measured by a conventional method.

[0064] (inkjet printing) As described above, the water-based ink of the present invention can be suitably used as a water-based ink for inkjet printing, and is particularly suitable for printing on low-liquid-absorbent printing substrates that use synthetic resins as the printing substrate. In the inkjet printing method, the method for ejecting the water-based ink is preferably a piezo type from the viewpoint of ejection properties. Examples of low-liquid-absorbent printing substrates include low-liquid-absorbent coated paper and resin films. Examples of coated paper include general-purpose glossy paper and multicolor form glossy paper. The resin film may be a film made of a synthetic resin. Examples of such a synthetic resin include polyolefin resins such as polyvinyl chloride resin, polyethylene resin, and polypropylene resin; and polyester resins such as polyethylene terephthalate resin. The resin film may be a biaxially stretched film, a uniaxially stretched film, or a non-stretched film. Furthermore, the film using polyolefin resin or polyester resin is preferably corona discharge treated.

[0065] Among these, from the viewpoint of further improving substrate adhesion, the low-liquid-absorbent printing substrate is preferably a synthetic resin printing substrate, more preferably a low-liquid-absorbent printing substrate using one or more synthetic resins selected from the group consisting of polyvinyl chloride resin, polypropylene resin, and polyethylene terephthalate resin, even more preferably one or more selected from the group consisting of a printing substrate using polyvinyl chloride resin, a printing substrate using polypropylene resin that has been corona discharge treated, and a printing substrate using polyethylene terephthalate resin that has been corona discharge treated, and even more preferably a printing substrate using polyvinyl chloride resin. [Example]

[0066] 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 or calculating each physical property are as follows.

[0067] (1) Measurement of weight average molecular weight of water-dispersible polymer A' The weight-average molecular weight of water-dispersible polymer A' was determined by gel permeation chromatography. The measurement sample was prepared by mixing 0.1 g of polymer with 10 mL of the following eluent in a glass vial, stirring with a magnetic stirrer at 25°C for 10 hours, and filtering through a syringe filter (ADVANTEC "DISMIC-13HP", pore size: 0.2 μm, material: PTFE). The measurement conditions are shown below. GPC equipment: Tosoh Corporation "HLC-8320GPC" Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolumn Super AW-H" manufactured by Tosoh Corporation Eluent: N,N-dimethylformamide dissolved with phosphoric acid and lithium bromide at concentrations of 60mmol / L and 50mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kits with known molecular weights, manufactured by Tosoh Corporation: "PStQuick B (F-550, F-80, F-10, F-1, A-1000)" and "PStQuick C (F-288, F-40, F-4, A-5000, A-500)"

[0068] (2) Measurement of the acid value of water-dispersible polymer A' The resin was dissolved in a titration solvent (toluene:acetone = 2:1 (volume ratio)) mixed with toluene and acetone in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with 0.1 N potassium hydroxide / ethanol solution by potentiometric titration. The inflection point on the titration curve was taken as the endpoint. The acid value (mg KOH / g) of water-dispersible polymer A' was calculated from the titration volume of the potassium hydroxide solution up to the endpoint.

[0069] (3) Calculation of the glass transition temperature (Tg) of water-dispersible polymer A' The glass transition temperature of the water-dispersible polymer A' was 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 was made into a homopolymer according to the Fox equation below. 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 vinyl resin. As the glass transition temperature of the homopolymer of each monomer in the Fox equation, for example, the value described in Polymer Handbook Third Edition (Wiley-Interscience 1989) can be used.

[0070] (4) Measurement of the solids concentration of the solution, aqueous dispersion or aqueous pigment dispersion of the water-dispersible polymer A' Using an infrared moisture meter (Kett Electric Laboratory, "FD-230"), 1.0 g of the measurement sample was dried at a drying temperature of 150°C and measurement mode 96 (monitoring time 2.5 minutes / fluctuation range 0.05%), and the volatile content (%) of the measurement sample was measured, and the solid content (%) was calculated using the following formula. Solid concentration (%) = 100 - Volatile content (%) of the measurement sample

[0071] (5) Measurement of solids concentration of water-based pigment dispersion 10.0 g of sodium sulfate, which had been kept at a constant weight in a desiccator, was weighed out into a 30 mL ointment container, and approximately 1.0 g of the sample was added and mixed. The mixture was then accurately weighed, kept at 105°C for 2 hours to remove volatiles, and left in the desiccator for a further 15 minutes before the mass was measured. The mass of the sample after volatile matter removal was taken as the solid content, and divided by the mass of the added sample to obtain the solid content concentration (%).

[0072] (6) Measurement of the average particle size of pigment-containing crosslinked polymer particles in water-based pigment dispersions or water-based inks Cumulant analysis was performed using a laser particle analysis system ("ELS-8000" manufactured by Otsuka Electronics Co., Ltd.), and the obtained cumulant average particle size was taken as the average particle size of the pigment-containing crosslinked polymer particles in the aqueous pigment dispersion. The measurement sample had a particle concentration of 5 × 10 -3 The dispersion was diluted with water to a concentration of 1.333 (solids content equivalent). The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 integrations. The refractive index of water (1.333) was entered as the refractive index of the dispersion medium.

[0073] (Production of Water-Dispersible Polymer A') Manufacturing Example 1 A reaction vessel equipped with a stirrer, a reflux condenser, and a dropping tank was initially charged with 3.00 parts of isobornyl acrylate, 3.08 parts of acrylic acid, 3.92 parts of butyl acrylate, 7.50 parts of methyl ethyl ketone (hereinafter referred to as "MEK"), and 0.83 parts of water, and the mixture was stirred for 10 minutes while maintaining the temperature of the reaction vessel at 77°C. Next, a mixture of 27.00 parts of isobornyl acrylate, 27.72 parts of acrylic acid, 35.28 parts of butyl acrylate, 76.50 parts of MEK, 8.50 parts of water, 1.60 parts of 4,4'-azobis(4-cyanovaleric acid) as a polymerization initiator, and 1.00 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, yielding a solution of water-dispersible polymer A'1 (solids concentration 55%). 102.70 parts of the resulting water-dispersible polymer A'1 solution was diluted with 58.70 parts of MEK to a solids concentration of 35%. Next, 14.40 parts of triethanolamine (hereinafter referred to as "TEA") was added to the solution so that the degree of neutralization of the carboxyl groups in the water-dispersible polymer A'1 was 40 mol%, and the mixture was stirred at 25°C. Then, 345.70 parts of water was added over 1 hour. After the addition was completed, the MEK was distilled off using an evaporator to obtain an aqueous dispersion of water-dispersible polymer A'1 (TEA neutralized) (polymer solids concentration: 25%). The physical properties of the water-dispersible polymer A'1 are shown in Table 1.

[0074] Production Examples 2 to 8 and Comparative Production Example 1 Aqueous dispersions (each with a polymer solids concentration of 25%) of water-dispersible polymers A'2 to A'8 and A'C1 (all neutralized with TEA) were obtained in the same manner as in Production Example 1, except that the raw material monomer composition constituting 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 degree of neutralization of water-dispersible polymer A' was 40 mol%. The physical properties of water-dispersible polymers A'2 to A'8 and A'C1 are shown in Table 1.

[0075] [Table 1]

[0076] (Production of Water-Based Pigment Dispersion) Example 1-1 (Process 1) To 200.0 parts of an aqueous dispersion (polymer solids concentration 25%) of water-dispersible polymer A'1 (TEA neutralized) was added 28.0 parts of MEK and 372.0 parts of ion-exchanged water, and 50.0 parts of a cyan pigment ("Fastogen Blue CA5380 Pigment Blue 15:3" manufactured by DIC Corporation) was further added to obtain a pigment mixture. The resulting pigment mixture was mixed for 1 hour using a disper blade at 7000 rpm and 20° C. Then, using a microfluidizer (Microfluidics Corporation, high-pressure homogenizer "M-140K"), the mixture was subjected to 10 passes of dispersion treatment at a pressure of 180 MPa to obtain a pigment dispersion.

[0077] (Process 2) From the obtained pigment dispersion, MEK was removed under reduced pressure at 60°C, and then some of the water was removed. After centrifugation, the liquid phase was filtered through a membrane filter ("Minisart Syringe Filter" manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining a pigment aqueous dispersion (i-1) (total concentration of pigment and water-dispersible polymer A': 22%) in which pigment-containing polymer particles were dispersed in an aqueous medium.

[0078] (Step 3) 88.2 parts of the resulting pigment aqueous dispersion (i-1) (total concentration of pigment and water-dispersible polymer A': 22%) was transferred to a screw-cap glass bottle, and 2.88 parts of trimethylolpropane polyglycidyl ether (Denacol EX-321LT, manufactured by Nagase ChemteX Corporation, epoxy group equivalent: 139 g / eq., water solubility: 27%) (hereinafter referred to as "EX321LT") as a multifunctional epoxy crosslinker and 10.2 parts of ion-exchanged water were added. The bottle was then sealed and heated at 80°C for 5 hours with stirring. The temperature was then lowered to room temperature, and the mixture was filtered through a membrane filter (Minisart Syringe Filter, manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding aqueous pigment dispersion D1 (total concentration of pigment and crosslinked polymer A: 22%), consisting of pigment-containing crosslinked polymer particles dispersed in an aqueous medium. The average particle size of aqueous pigment dispersion D1 is shown in Table 2.

[0079] Examples 1-2 to 1-12 and Comparative Example 1-2 Water-based pigment dispersions D2 to D12 and DC2 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.

[0080] Examples 1-13 An aqueous pigment dispersion D13 was obtained in the same manner as in Example 1-3, except that in Example 1-3, 2.40 parts of trimethylolpropane polyglycidyl ether (EX321LT) was replaced with 2.33 parts of 1,6-hexanediol diglycidyl ether ("Denacol EX-212L" manufactured by Nagase ChemteX Corporation, epoxy group equivalent: 135 g / eq., water solubility: 0%) (hereinafter referred to as "EX212L") as the polyfunctional epoxy crosslinking agent, and 8.5 parts of ion-exchanged water was replaced with 8.3 parts.

[0081] Examples 1-14 An aqueous pigment dispersion D14 was obtained in the same manner as in Example 1-3, except that in Example 1-3, 2.40 parts of trimethylolpropane polyglycidyl ether (EX321LT) was replaced with 2.59 parts of 1,4-cyclohexanedimethanol diglycidyl ether ("Denacol EX-216L" manufactured by Nagase ChemteX Corporation, epoxy group equivalent 150 g / eq., water solubility 0%) (hereinafter referred to as "EX216L") as the polyfunctional epoxy crosslinking agent, and 8.5 parts of ion-exchanged water was replaced with 9.2 parts.

[0082] Examples 1-15 An aqueous pigment dispersion D15 was obtained in the same manner as in Example 1-3, except that in Example 1-3, 2.40 parts of trimethylolpropane polyglycidyl ether (EX321LT) was used as the multifunctional epoxy crosslinking agent, but 1.99 parts of 1,4-butanediol diglycidyl ether ("Denacol EX-214L" manufactured by Nagase ChemteX Corporation, epoxy group equivalent 115 g / eq., water solubility 100%) (hereinafter referred to as "EX214L"), and 8.5 parts of ion-exchanged water was changed to 7.1 parts.

[0083] Comparative Example 1-1 An aqueous pigment dispersion DC1 was obtained in the same manner as in Example 1-1, except that trimethylolpropane polyglycidyl ether (EX321LT) was not used as the multifunctional epoxy crosslinking agent, and the amount of ion-exchanged water was changed from 10.2 parts to 7.06 parts.

[0084] (Preparation of Water-Based Ink) Example 2-1 To obtain the ink composition (total 100 parts) shown in Table 3, 41.8 parts of Water-Based Pigment Dispersion D1, 22.0 parts of propylene glycol, 4.0 parts of diethylene glycol monoisobutyl ether, 1.0 part of an acetylene glycol surfactant (Nissin Chemical Industry Co., Ltd.'s "Surfynol 104-PG50" (2,4,7,9-tetramethyl-5-decyne-4,7-diol in propylene glycol, active ingredient 50%)), and 31.2 parts of ion-exchange water were added and stirred, and the mixture was filtered through a membrane filter (Sartorius "Minisart Syringe Filter", pore size: 5 μm, material: cellulose acetate) to obtain Water-Based Ink 1. The average particle size of Water-Based Ink 1 is shown in Table 3.

[0085] Examples 2-2 to 2-15 and Comparative Examples 2-1 to 2-2 Water-based inks 2 to 15 and C1 to C2 were obtained in the same manner as in Example 2-1, except that the type and amount of water-based pigment dispersion in Example 2-1 were changed to those shown in Table 2. The average particle size of each water-based ink is shown in Table 3.

[0086] Inkjet printing was carried out by the method described below using the water-based inks 1 to 15 and C1 and C2 obtained in the above Examples and Comparative Examples. The results are shown in Table 3.

[0087] (inkjet printing) In an environment with a temperature of 32°C, an inkjet printing evaluation device (manufactured by Tritec Corporation) equipped with a print head (Kyocera Corporation, "KJ4B-HD06MHG-STDV," piezo type) was filled with water-based ink I-1. The print head voltage was set to 26 V, drive frequency to 30 kHz, ejected droplet volume to 7 pL, print head temperature to 32°C, and print head resolution to 600 dpi. A solid image with a duty of 100% was formed on a low-liquid-absorbency printing substrate (polyvinyl chloride film (3M Japan Ltd., "Scotchcal Graphic Film IJ1220") (hereinafter also referred to as "PVC") heated to 50°C, to obtain a printed matter.

[0088] [evaluation] The water-based inks and printed matter obtained in the examples and comparative examples were evaluated according to the following (1) to (3). The results are shown in Table 3.

[0089] (1) Adhesion to PVC film substrate (tape peel resistance) Tape (Nichiban Co., Ltd., "Cellotape (registered trademark)", 18 mm wide, model number: CT-18S) was applied to the solid image area of ​​the resulting print, and the edge of the tape was quickly peeled off at a 90° angle. The solid image area after peeling was binarized using a print density value that was half the print density value of the solid image area before tape peeling as a threshold value, and the peeled and non-peeled areas were calculated by image analysis. The area ratio of the non-peeled areas was calculated as the coating film remaining rate (%) after the tape peel test. The higher the coating film remaining rate (%), the better the adhesion to the substrate.

[0090] (2) Concentrated viscosity of water-based ink The water-based ink was placed in a petri dish (diameter 35 mm, height 11 mm) and dried for 18 hours at 40°C and a relative humidity of 25%. The resulting concentrated ink was scraped up and the concentrated viscosity was measured under the following conditions. Measuring equipment: MCR301 rheometer (manufactured by Anton Paar) Corn plate: CP50-1 Temperature: 25℃ Shear rate conditions: The shear rate was increased from 0.01 (1 / s) to 1000 (1 / s) in a logarithmic manner with a measurement interval of 3 seconds, so as to measure 16 points, and then the shear rate was decreased from 1000 (1 / s) to 0.01 (1 / s) in a logarithmic manner with a measurement interval of 3 seconds, so as to measure 16 points. The viscosity value at a shear rate of 1 (1 / s) in the region where the shear rate was decreased was taken as the concentrated viscosity value. The lower the concentrated viscosity, the better the fluidity and the more excellent the ejection stability.

[0091] (3) Redispersibility of water-based ink Using a micropipette, 10 μL of the water-based ink was dropped onto the center of the bottom of a screw tube No. 5 (manufactured by Maruemu Co., Ltd.), and the tube was left uncovered at 40°C and 25% RH for 8 hours to evaporate and dry the water-based ink. 10 mL of ion-exchanged water was added to the solid matter remaining at the bottom of the screw tube, and the mixture was stirred at 150 rpm for 1 minute. The redispersibility of the solid matter was visually observed, and the redispersibility of the water-based ink was evaluated according to the following criteria. The redispersibility of the water-based ink can be evaluated by evaluating the redispersibility of the water-based pigment dispersion contained in the water-based ink. (Evaluation criteria) A: The solids were uniformly redispersed. B: Most of the solids were redispersed and the water was deeply colored, but there was a small residue. C: The solids redispersed and the water became deeply colored, but there was a large amount of residue. D: Some of the solid matter was redispersed and the water was slightly colored, but most of the solid matter remained as a residue. E: The solid matter did not redisperse and the water was not colored.

[0092] [Table 2]

[0093] [Table 3]

[0094] Table 3 shows that the aqueous inks using the aqueous pigment dispersions of the Examples of the present invention have better redispersibility of pigment particles and better adhesion (substrate adhesion) between the ink coating and PVC film, which is a low-absorbency printing substrate, than the aqueous inks using the aqueous pigment dispersions of the Comparative Examples. Furthermore, the aqueous inks using the aqueous pigment dispersions of the Examples of the present invention have a lower concentrated viscosity than the aqueous inks using the aqueous pigment dispersions of the Comparative Examples, and are therefore thought to have better ejection stability when used as inkjet printing inks. [Industrial Applicability]

[0095] According to the present invention, it is possible to provide an aqueous pigment dispersion and an aqueous ink using the aqueous pigment dispersion, which have excellent re-dispersibility of pigment particles and, when used for printing on a low-liquid-absorbent printing substrate, provide an ink coating film of the resulting printed matter with excellent substrate adhesion (tape peel resistance).

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 the 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 isobornyl (meth)acrylate (a-1).

2. The water-based pigment dispersion according to claim 1, wherein the water-dispersible polymer A' further contains a structural unit derived from one or more ionic monomers (a-2) having a carboxy group selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid.

3. The water-based pigment dispersion according to claim 1 or 2, wherein the crosslinked polymer A has an acid value of 25 mgKOH / g or more and 170 mgKOH / g or less.

4. 3. The water-based pigment dispersion according to claim 1, wherein the isobornyl (meth)acrylate (a-1) is isobornyl acrylate.

5. 3. The water-based pigment dispersion according to claim 1, wherein the content of structural units derived from isobornyl (meth)acrylate (a-1) in all structural units of the water-dispersible polymer A' is 20% by mass or more and 90% by mass or less.

6. 3. The water-based pigment dispersion according to claim 1, wherein the water-dispersible polymer A' has an acid value of 60 mgKOH / g or more and 300 mgKOH / g or less.

7. 3. 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.

8. 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'.

9. A water-based ink comprising the water-based pigment dispersion according to claim 1 or 2 and a water-soluble organic solvent.

10. The water-based ink of claim 9 for inkjet printing.

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