Pigment dispersant, method for producing pigment dispersant, pigment dispersion liquid, and ultraviolet curable ink

Abstract

To provide a pigment dispersant that makes it possible to prepare a pigment dispersion liquid with excellent pigment dispersibility, and low viscosity and high storage stability.SOLUTION: A pigment dispersant has a structure represented by general formula (1). (R1, R2, and R3 each represent a pentadecyl group or the like, R4, R5, and R6 independently represent H, a group represented by formula (2), or a group represented by formula (3), at least one of R4, R5, and R6 represents the group represented by formula (2), and n represents a number selected from 1-10. * represents a bond position, R7 represents an ethylene group or a methyl ethylene group, and m represents a number selected from 14-68. A represents an alkyl group, a dialkylamino alkyl group, a pyridinyl alkyl group, an imidazolyl alkyl group, a pyridinyl group, or an imidazolyl group, and R8 represents H or an alkyl group.)SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a pigment dispersant, a method for producing the pigment dispersant, a pigment dispersion, and an ultraviolet curable ink.

Background Art

[0002] General coating liquids such as paints, inks, and coating agents contain organic solvents. Therefore, since the organic solvents volatilize after the application of these coating liquids, the environmental load is relatively high. Thus, as environmentally friendly coating liquids that substantially do not contain organic solvents, aqueous inks and coating liquids having water as the main liquid medium, powder coating using colored resin powders, etc. have been proposed. Further, coating liquids using vinyl-based, epoxy-based, and oxetane-based monomers instead of organic solvents have also been proposed. Since such coating liquids are of a type that forms a polymer by polymerizing monomers by applying heat or light after application, they are used as active energy ray curable inks such as ultraviolet curable inks and electron beam curable inks that substantially do not contain volatile components.

[0003] In recent years, ultraviolet curable inkjet inks (UVIJ inks) containing a pigment as a colorant, which can record vivid images on demand on substrates such as packaging materials and containers, have been proposed. UVIJ inks are required to exhibit ejection properties suitable for high-speed printing, to have excellent dispersion stability of pigments, and further to have a lower viscosity. That is, there is a demand for a pigment dispersion for UVIJ ink in which the pigment is finely dispersed and has excellent dispersion stability of the pigment.

[0004] When preparing a pigment dispersion, a pigment dispersant is usually used. As the pigment dispersant, low molecular weight dispersants such as surfactants and polymer type dispersants are used. Among them, from the viewpoints of fine dispersibility and dispersion stability of pigments, polymer type dispersants such as vinyl polymers obtained by polymerizing vinyl monomers are frequently used. Note that such pigment dispersants such as vinyl polymers are usually used in the state of a solution diluted with an organic solvent (Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Generally, as described above, polymer-type pigment dispersants are used in a state dissolved in an organic solvent. Therefore, since the UVIJ ink prepared using such a pigment dispersant also contains an organic solvent, the advantages of the UVIJ ink, such as "substantially not containing volatile components and being environmentally friendly", are likely to be impaired. Therefore, there has been a demand for the development of a polymer-based pigment dispersant that substantially does not contain volatile components and has excellent handleability at 100% solid content.

[0007] A polymer-based pigment dispersant that substantially does not contain volatile components can be produced, for example, by removing an organic solvent from an organic solvent solution of a polymer produced by solution polymerization or the like. However, there have been problems that the handleability of the solid content (polymer) obtained by removing the organic solvent is not necessarily good and the manufacturing process becomes complicated. Furthermore, the function of the obtained polymer as a pigment dispersant is not necessarily good, and there is room for further improvement.

[0008] The present invention has been made in view of such problems of the prior art, and an object thereof is to provide a pigment dispersant capable of preparing a pigment dispersion liquid having good dispersibility of pigments, low viscosity, and excellent storage stability.

[0009] Another object of the present invention is to provide a simple method for producing the above pigment dispersant, and a pigment dispersion liquid having good dispersibility of pigments, low viscosity, and excellent storage stability, using the above pigment dispersant. Further, an object of the present invention is to provide an ultraviolet curable ink for inkjet, which uses the above pigment dispersant, has good dispersibility of pigments, low viscosity, excellent storage stability, and substantially does not contain volatile organic compounds.

Means for Solving the Problems

[0010] That is, according to the present invention, the following pigment dispersants are provided. [1] A pigment dispersant having a structure represented by the following general formula (1).

[0011] TIFF0007695217000001.tif42170(In the general formula (1), R1, R2, and R3 independently represent a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, or a 7,10,14-pentadecatrienyl group, and R4, R5, and R6 independently represent a hydrogen atom, a group represented by the following general formula (2), or a group represented by the following general formula (3), and at least one of R4, R5, and R6 is a group represented by the following general formula (2), and n represents a number from 1 to 10)

[0012] TIFF0007695217000002.tif23170(In the general formula (2), * indicates the bonding position, R7 represents an ethylene group or a methylethylene group, and m represents a number from 14 to 68)

[0013] TIFF0007695217000003.tif23170(In the general formula (3), * indicates the bonding position, A represents an alkyl group, a dialkylaminoalkyl group, a pyridinylalkyl group, an imidazolylalkyl group, a pyridinyl group, or an imidazolyl group, and R8 represents a hydrogen atom or an alkyl group)

[0014] Further, according to the present invention, a method for producing the following pigment dispersant is provided. [2] The method for producing a pigment dispersant according to [1], which has a reaction step of reacting a polyepoxy compound represented by the following general formula (4) with a polyalkylene glycol monomethyl ether monoamine.

[0015] TIFF0007695217000004.tif41170(In the general formula (4), R1, R2, and R3 each independently represent a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, or a 7,10,14-pentadecatrienyl group, and R9, R 10 , and R 11 each independently represent a hydrogen atom or a 2,3-epoxypropyl group, and at least one of R9, R 10 , and R 11 is a 2,3-epoxypropyl group, and n represents a number from 1 to 10)

[0016] [3] The method for producing a pigment dispersant according to [2], wherein the compound represented by the general formula (4) is a formalin condensate of cardanol. [4] The reaction step is a step of further reacting the polyepoxy compound with at least one amine compound selected from the group consisting of a primary organic amine, a secondary organic amine, and a polyamine compound, and the polyamine compound is a compound having a primary amino group or a secondary amino group and a tertiary amino group. The method for producing a pigment dispersant according to [2] or [3]. [5] The method for producing a pigment dispersant according to [4], wherein the polyamine compound is at least one selected from the group consisting of dimethylaminopropylamine, diethylaminopropylamine, dibutylaminopropylamine, 4-aminopyridine, 4-(2-aminoethyl)pyridine, and 1-(3-aminopropyl)imidazole.

[0017] Furthermore, according to the present invention, a pigment dispersion liquid shown below is provided. [6] A pigment dispersion liquid containing a pigment, a solvent, and a pigment dispersant for dispersing the pigment in the solvent, wherein the pigment dispersant is the pigment dispersant described in [1]. [7] The pigment dispersion liquid according to [6] above, further containing a pigment derivative having at least one acidic group selected from the group consisting of a carboxy group, a phosphoric acid group, and a sulfonic acid group. [8] The pigment dispersion liquid according to [6] or [7] above, wherein the solvent is an ultraviolet ray / electron beam curable monomer having one or more unsaturated bonds, or an ultraviolet ray / electron beam curable oligomer.

[0018] Further, according to the present invention, an ultraviolet ray curable ink shown below is provided. [9] An ultraviolet ray curable ink for inkjet containing the pigment dispersion liquid according to [8] above.

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a pigment dispersant capable of preparing a pigment dispersion liquid having good dispersibility of the pigment, low viscosity, and excellent storage stability.

[0020] Further, according to the present invention, a simple production method of the above pigment dispersant, and a pigment dispersion liquid having good dispersibility of the pigment, low viscosity, and excellent storage stability using the above pigment dispersant can be provided. Furthermore, according to the present invention, an ultraviolet ray curable ink for inkjet substantially free of volatile organic compounds, having good dispersibility of the pigment, low viscosity, and excellent storage stability using the above pigment dispersant can be provided.

Modes for Carrying Out the Invention

[0021] <Pigment Dispersant> Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. One embodiment of the pigment dispersant of the present invention is a compound (polymer) represented by the following general formula (1). Hereinafter, details of the pigment dispersant of this embodiment will be described.

[0022] TIFF0007695217000005.tif42170(In the general formula (1), R1, R2, and R3 each independently represent a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, or a 7,10,14-pentadecatrienyl group, R4, R5, and R6 each independently represent a hydrogen atom, a group represented by the following general formula (2), or a group represented by the following general formula (3), and at least one of R4, R5, and R6 is a group represented by the following general formula (2), and n represents a number from 1 to 10)

[0023] TIFF0007695217000006.tif23170(In the general formula (2), * indicates the bonding position, R7 represents an ethylene group or a methylethylene group, and m represents a number from 14 to 68)

[0024] TIFF0007695217000007.tif23170(In the general formula (3), * indicates the bonding position, A represents an alkyl group, a dialkylaminoalkyl group, a pyridinylalkyl group, an imidazolylalkyl group, a pyridinyl group, or an imidazolyl group, and R8 represents a hydrogen atom or an alkyl group)

[0025] In the general formula (1), the aromatic ring and the long-chain hydrocarbon groups represented by R1, R2, and R3 are the parts that impart affinity to the pigment. Also, the 7-pentadecenyl group, 7,10-pentadecadienyl group, and 7,10,14-pentadecatrienyl group, which are groups having an unsaturated bond, are all groups capable of generating radicals. Therefore, by using the pigment dispersant of this embodiment having these groups in an ultraviolet-curable ink, these groups can be reacted with the curing components in the ink.

[0026] The group represented by the general formula (2) has a hydroxyl group and an amino group. Also, "(R7O) mExamples of the methoxypolyalkylene glycol chain represented by "CH3" include a methoxypolyethylene glycol chain, a methoxypolypropylene glycol chain, a methoxypolyethylene glycol-polypropylene glycol random structure chain, a methoxypolyethylene glycol-polypropylene glycol diblock structure chain, a methoxypolyethylene glycol-polypropylene glycol-polyethylene glycol triblock structure chain, and a methoxypolyethylene glycol-polypropylene glycol-polyethylene glycol triblock structure chain.

[0027] In the general formula (2), m is from 14 to 68, and "[(R7O) m The molecular weight of the methoxypolyalkylene glycol chain represented by "CH3" is preferably from 1,000 to 3,000. From the viewpoints of easy availability of raw materials and marketability, etc., the methoxypolyalkylene glycol chain represented by "[(R7O) m CH3" is preferably a methoxypolyethylene glycol-polypropylene glycol random structure chain, and the molar ratio of ethylene oxide (EO) to propylene oxide (PO) is preferably in the range of EO / PO = 6 to 58 / 3 to 29. In the general formula (1), one or more of R4, R5, and R6 are groups represented by the general formula (2), and it is preferable that the group represented by the general formula (2) is bonded to more than half of the repeating units, and all of R4, R5, and R6 may be groups represented by the general formula (2).

[0028] In the general formula (3), examples of the alkyl group represented by R8 include a methyl group, an ethyl group, a butyl group, and a hexyl group. In the general formula (3), examples of the dialkylaminoalkyl group represented by A include a dimethylaminoethyl group, a dimethylaminopropyl group, a diethylaminoethyl group, a diethylaminopropyl group, a dibutylaminopropyl group, and a dibutylaminobutyl group. Among them, the dimethylaminopropyl group, the diethylaminopropyl group, and the dibutylaminopropyl group are preferable because they have high basicity and good reactivity.

[0029] In general formula (3), examples of the pyridinylalkyl group represented by A include a 2-pyridinylmethyl group, a 4-pyridinylmethyl group, a 1-(2-pyridinyl)ethyl group, a 2-(2-pyridinyl)ethyl group, a 1-(4-pyridinyl)ethyl group, and a 2-(4-pyridinyl)ethyl group. Among them, a 4-pyridinyl group having a basic nitrogen at the 4-position and a 2-(4-pyridinyl)ethyl group are preferable. In general formula (3), examples of the imidazolylalkyl group represented by A include a 2-imidazolylethyl group, a 3-imidazolylpropyl group, and a 4-imidazolylbutyl group. Among them, from the viewpoint of easy availability of raw materials, etc., a 3-imidazolylpropyl group is preferable.

[0030] In general formula (1), n represents a number from 1 to 10, and is preferably a number from 2 to 4. When n is 0, the adsorption portion of the main chain is small, so it will desorb from the pigment, and the dispersion stability of the pigment will decrease. On the other hand, when n exceeds 10, the molecular weight is too large, so the viscosity of the resulting pigment dispersion will become excessively high.

[0031] The number average molecular weight (Mn) in terms of polystyrene of the pigment dispersant measured by gel permeation chromatography (GPC) is preferably 1,000 or more and 20,000 or less, and more preferably 3,000 or more and 10,000 or less.

[0032] <Method for producing a pigment dispersant> The above-mentioned pigment dispersant can be produced by the method shown below. That is, one embodiment of the method for producing the pigment dispersant of the present invention is a method for producing the above-mentioned pigment dispersant, and has a reaction step of reacting a polyepoxy compound represented by the following general formula (4) with a polyalkylene glycol monomethyl ether monoamine.

[0033] TIFF0007695217000008.tif41170(In the general formula (4), R1, R2, and R3 each independently represent a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, or a 7,10,14-pentadecatrienyl group, and R9, R 10 , and R 11 each independently represent a hydrogen atom or a 2,3-epoxypropyl group, and at least one of R9, R 10 , and R 11 is a 2,3-epoxypropyl group, and n represents a number from 1 to 10)

[0034] R1, R2, and R3 in the general formula (4) have the same meanings as R1, R2, and R3 in the aforementioned general formula (1). In the general formula (4), at least one of R9, R 10 , and R 11 is a 2,3-epoxypropyl group (hereinafter also simply referred to as an "epoxy group"), preferably 2 or more and not more than n + 2 repeating units.

[0035] As the polyepoxy compound represented by the general formula (4), it is preferable to use a formalin condensate of cardanol. Cardanol has an aromatic ring with a long-chain hydrocarbon group. Since cardanol is a plant-derived raw material, from the perspective of carbon neutrality, it is a raw material that contributes to the reduction of carbon dioxide. Examples of commercially available formalin condensates of cardanol include the product named "Cardolite NC-547" from Caedolite Co., Ltd.

[0036] In the reaction process, a polyalkylene glycol monomethyl ether monoamine is reacted with a polyepoxy compound. Examples of the polyalkylene glycol monomethyl ether monoamine include methoxypolyethylene glycol monoamine, methoxypolypropylene glycol monoamine, methoxypolyethylene glycol polypropylene glycol random structure monoamine, methoxypolyethylene glycol polypropylene glycol diblock structure monoamine, methoxypolyethylene glycol polypropylene glycol polyethylene glycol triblock structure monoamine, methoxypolyethylene glycol polypropylene glycol polyethylene glycol triblock structure monoamine, etc. Among them, methoxypolyethylene glycol polypropylene glycol random structure monoamine is preferred. Commercially available products of polyalkylene glycol monomethyl ether monoamine include the product name "Jeffamine M-" series manufactured by Huntsman Corporation, the product name "Genamin" manufactured by Clariant Corporation, etc.

[0037] The polyalkylene glycol monomethyl ether monoamine can react with all epoxy groups in the polyepoxy compound. By reacting the epoxy group with the amino group in the polyalkylene glycol monomethyl ether monoamine, the epoxy group is ring-opened to form a hydroxyl group and an amino group, and a pigment dispersant having the desired structure can be obtained. The polyalkylene glycol monomethyl ether monoamine may be reacted so as to leave a part of the epoxy groups in the polyepoxy compound. And it is also preferable to further react an amine compound with the remaining epoxy groups to introduce an amino group. The polyalkylene glycol monomethyl ether monoamine is preferably reacted with 50 mol% or more of the epoxy groups in the polyepoxy compound.

[0038] Examples of the amine compound that reacts with the remaining epoxy groups include at least one selected from the group consisting of primary organic amines, secondary organic amines, and polyamine compounds. That is, the reaction step is preferably a step of further reacting a polyepoxy compound with at least one amine compound selected from the group consisting of primary organic amines, secondary organic amines, and polyamine compounds. The polyamine compound is preferably a compound having a primary amino group or a secondary amino group and a tertiary amino group.

[0039] Examples of the primary organic amine include methylamine, ethylamine, butylamine, octylamine, and hydroxyethylamine. Examples of the secondary organic amine include dimethylamine, diethylamine, dibutylamine, and dihydroxyethylamine.

[0040] Examples of the compound having a primary amino group and a tertiary amino group among the polyamine compounds include dimethylaminoethylamine, dimethylaminopropylamine, diethylaminoethylamine, diethylaminopropylamine, dibutylaminopropylamine, 4-aminopyridine, 4-(2-aminoethyl)pyridine, and 1-(3-aminopropyl)imidazole. Examples of the compound having a secondary amino group and a tertiary amino group among the polyamine compounds include diethylaminoethylmethylamine and bis(dimethylaminoethyl)amine.

[0041] The polyamine compound is preferably at least one selected from the group consisting of dimethylaminopropylamine, diethylaminopropylamine, dibutylaminopropylamine, 4-aminopyridine, 4-(2-aminoethyl)pyridine, and 1-(3-aminopropyl)imidazole.

[0042] By reacting a polyepoxy compound with a polyalkylene glycol monomethyl ether monoamine and, if necessary, further reacting with an amine compound, the desired pigment dispersant can be obtained. In the reaction step, for example, in the presence of an organic solvent that has no reactivity with epoxy groups or amino groups, it is heated preferably to 60°C or higher, more preferably to 80°C or higher, to react the epoxy group and the amino group. Then, if necessary, the organic solvent is distilled off to obtain a pigment dispersant with a solid content of approximately 100%. The polyepoxy compound is usually a liquid with a relatively low viscosity under the conditions of room temperature to 40°C. Therefore, it is preferable to heat and react it in bulk without using a solvent (in the absence of a solvent).

[0043] The progress of the reaction can be monitored by measuring the infrared absorption spectrum (IR) and confirming the disappearance of the absorption near 910 cm -1 derived from the epoxy group and the generation of the absorption near 3,200 cm -1 derived from the hydroxyl group. Also, the progress of the reaction can be grasped by measuring the epoxy equivalent according to a conventionally known method and confirming the disappearance of the epoxy group. Furthermore, the progress of the reaction can be grasped by confirming an increase in molecular weight by gel permeation chromatography or measuring the amine value according to a conventionally known method. Even if the reaction has not proceeded completely, if the pigment dispersant of the present embodiment having a specific structure has been generated, it can be used as a dispersant for dispersing the pigment.

[0044] <Pigment dispersion liquid> One embodiment of the pigment dispersion liquid of the present invention contains a pigment, a solvent, and a pigment dispersant for dispersing the pigment in the solvent. And this pigment dispersant is the aforementioned pigment dispersant.

[0045] As the pigment, conventionally known pigments can be used. Examples of the pigments include C.I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 94, 95, 97, 109, 110, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 153, 154, 155, 166, 168, 175, 180, 181, 185, 191; C.I. Pigment Orange 16, 36, 43, 51, 55, 59, 61, 64, 71, 73; C.I. Pigment Red 4, 5, 9, 23, 48, 49, 52, 53, 57, 97, 112, 122, 123, 144, 146, 147, 149, 150, 166, 168, 170, 176, 177, 180, 184, 185, 192, 202, 207, 214, 215, 216, 217, 220, 221, 223, 224, 226, 227, 228, 238, 240, 242, 254, 255, 264, 269, 272; C.I. Pigment Violet 19, 23, 29, 30, 37, 40, 50; C.I. Pigment Blue 15, 15:1, 15:3, 15:4, 15:6, 22, 60, 64; C.I. Pigment Green 7, 36, 58; C.I. Pigment Black 7; C.I. Pigment White 6; and the like.

[0046] When these pigments are used in combination, any of the methods of mixing powder pigments, mixing paste-like pigments, and mixing during pigment formation to form a solid solution may be employed. Further, fillers such as zinc oxide, zirconium oxide, silica, and mica can also be used. Additionally, carbon nanotubes, graphite, graphene, carbon nanohorns, carbon nanoribbons, fullerenes, carbon-based quantum dots, and nanodiamonds can also be used.

[0047] As pigments suitable for inkjet inks, from the viewpoints of color development property, dispersibility, weather resistance, etc., C.I. Pigment Yellow 74, 83, 109, 128, 139, 150, 151, 154, 155, 180, 181, 185; C.I. Pigment Red 122, 170, 176, 177, 185, 269; C.I. Pigment Violet 19, 23; C.I. Pigment Blue 15:3, 15:4, 15:6; C.I. Pigment Black 7; C.I. Pigment White 6; etc. can be mentioned.

[0048] The pigment may be an untreated pigment, a self-dispersing pigment having a functional group introduced on its surface, or a treated pigment surface-treated or encapsulated with a surface treatment agent such as a coupling agent or activator or a polymer. Also, unless hiding power is required, it is preferable to use an organic fine particle pigment. Further, when high brilliance and transparency are required, it is preferable to use a pigment micronized by wet grinding or dry grinding such as salt milling. Considering the suppression of nozzle clogging during printing, it is preferable to remove pigments having a particle diameter exceeding 1.0 μm. The average particle diameter of the organic pigment is preferably 0.2 μm or less, and the average particle diameter of the inorganic pigment is preferably 0.4 μm or less.

[0049] (Pigment derivative) The pigment dispersion of this embodiment preferably further contains a pigment derivative having at least one acidic group selected from the group consisting of a carboxy group, a phosphoric acid group, and a sulfonic acid group. The pigment derivative having an acidic group imparts an acidic group to the surface of the pigment by adsorbing on the surface of the pigment. Then, the imparted acidic group and the amino group of the pigment dispersant form an ionic bond, so that the pigment dispersant is more firmly adsorbed on the surface of the pigment to prevent desorption. Therefore, by further containing a pigment dispersant having an acidic group, aggregation and sedimentation of the pigment can be suppressed, and a pigment dispersion having more excellent dispersion stability can be obtained.

[0050] As the pigment derivative, conventionally known pigment derivatives can be used. Specifically, a compound in which at least one acidic group among a carboxy group, a phosphoric acid group, and a sulfonic acid group is bonded to an organic dye skeleton can be used as the pigment derivative. The acidic group is preferably sulfonic acid. Examples of the organic dye skeleton include an azo dye skeleton, an anthraquinone dye skeleton, a quinacridone dye skeleton, a phthalocyanine dye skeleton, a diketopyrrolopyrrole dye skeleton, and an isoindoline dye skeleton. It is preferable that one acidic group is bonded to the organic dye skeleton, and two or more acidic groups may be bonded.

[0051] Examples of the pigment derivative having an azo dye skeleton include a compound represented by the following formula (A). Examples of the pigment derivative having an anthraquinone dye skeleton include a compound represented by the following formula (B). Examples of the pigment derivative having a quinacridone dye skeleton include compounds represented by the following formulas (C) and (D). Examples of the pigment derivative having a phthalocyanine dye skeleton include a compound represented by the following formula (E). Examples of the pigment derivative having a diketopyrrolopyrrole dye skeleton include a compound represented by the following formula (F). Examples of the pigment derivative having an isoindoline dye skeleton include a compound represented by the following formula (G).

[0052] TIFF0007695217000009.tif225170

[0053] TIFF0007695217000010.tif189170

[0054] The pigment derivative may be blended when producing the pigment dispersion liquid, or may be pre-treated on the surface of the pigment. Examples of the method for surface-treating the pigment with the pigment derivative include, for example, a method of adding to the pigment after synthesis and then filtering; a method of mixing the pigment derivative with the acidic group as a sodium salt and the pigment, and then making it acidic to insolubilize the pigment derivative for treatment; a method of milling together when micronizing the pigment; and the like. The amount of the pigment derivative with respect to 100 parts by mass of the pigment is preferably 0.5 to 20 parts by mass, and more preferably 1 to 10 parts by mass.

[0055] (Solvent) The solvent is a liquid such as an organic solvent used as a dispersion medium for dispersing pigments. Examples of organic solvents include hydrocarbon solvents such as hexane, toluene, and xylene; alcohol solvents such as methanol, ethanol, isopropanol, butanol, and dodecanol; ketone solvents such as acetone, methyl ethyl ketone, diethyl ketone, and isobutyl methyl ketone; ester solvents such as ethyl acetate, butyl acetate, amyl acetate, dimethyl succinate, dimethyl adipate, methyl lactate, and dimethyl lactate; ether solvents such as dipropyl ether, tetrahydrofuran, and dioxane; carbonate solvents such as dimethyl carbonate, ethylene carbonate, and propylene carbonate; amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide; urea solvents such as tetramethylurea and dimethylimidazolidinone; sulfoxide solvents such as dimethyl sulfoxide; glycol monoether solvents such as ethylene glycol, propylene glycol, diethylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl ether; glycol diether solvents such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and dipropylene glycol dimethyl ether; glycol ether monoether ester solvents such as ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monobutyl ether acetate; ionic liquids such as 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide; and the like. Further, water can also be used as a solvent as needed.

[0056] When the pigment dispersion is used for preparing an ultraviolet-curable ink, the solvent is preferably an ultraviolet- and electron-beam curable monomer having one or more unsaturated bonds or an ultraviolet- and electron-beam curable oligomer. Since these solvents are cured by irradiation with ultraviolet rays or the like, they substantially do not contain volatile components such as organic solvents. Therefore, by using these solvents, a pigment dispersion capable of preparing an environmentally friendly ink can be obtained.

[0057] Examples of the ultraviolet- and electron-beam curable monomers and oligomers include curing components such as monofunctional monomers, polyfunctional monomers, photocurable oligomers, and photocurable polymers. Examples of the monofunctional monomers include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, trimethylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, adamantyl (meth)acrylate, adamantylmethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycidyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polyethylene glycol monomethyl ether (meth)acrylate, 2-ethoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, allyl (meth)acrylate, vinyloxyethoxyethyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, an adduct of phthalic anhydride and 2-hydroxyethyl (meth)acrylate, radical polymerizable monomers such as acryloylmorpholine, and the like.

[0058] Examples of the polyfunctional monomer and the photocurable oligomer include neopentyl glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, poly(n ≥ 2)ethylene glycol di(meth)acrylate, polypropylene glycol (n ≥ 2) di(meth)acrylate, polybutylene glycol (n ≥ 2) di(meth)acrylate, 2,2-bis(4-(meth)acryloxydiethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxydiethoxyphenyl)propane, trimethylolpropane diacrylate, bis(2-(meth)acryloxyethyl)-hydroxyethyl-isocyanurate, trimethylolpropane tri(meth)acrylate, tris(2-(meth)acryloxyethyl) isocyanurate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, epoxy poly(meth)acrylate such as epoxy di(meth)acrylate obtained by reacting bisphenol A type diepoxy with (meth)acrylic acid, 1,Urethane tri(meth)acrylate obtained by reacting a trimer of 6-hexamethylene diisocyanate with 2-hydroxyethyl (meth)acrylate, urethane di(meth)acrylate obtained by reacting isophorone diisocyanate with 2-hydroxypropyl (meth)acrylate, urethane hexa(meth)acrylate obtained by reacting isophorone diisocyanate with pentaerythritol tri(meth)acrylate, urethane di(meth)acrylate obtained by reacting dicyclohexyl diisocyanate with 2-hydroxyethyl (meth)acrylate, urethane di(meth)acrylate obtained by reacting a urethanization reaction product of dicyclohexyl diisocyanate and poly(n = 6 - 15) tetramethylene glycol with 2-hydroxyethyl (meth)acrylate, etc. urethane poly(meth)acrylates, polyester poly(meth)acrylates such as polyester (meth)acrylate obtained by reacting trimethylolethane with succinic acid and (meth)acrylic acid, polyester (meth)acrylate obtained by reacting trimethylolpropane with succinic acid, ethylene glycol, and (meth)acrylic acid, etc. can be mentioned.,

[0059] Examples of the photocurable polymer include polymers in which a plurality of (meth)acryloyloxy groups, which are radically polymerizable groups, are introduced at the terminals or side chains of polymers such as poly(meth)acrylate, polyurethane, polyester, polyamide, polyimide, and epoxy resin. Furthermore, a photocurable polymer having alkali developability into which a carboxy group or the like is introduced can also be used.,

[0060] (Additive) Various additives can be contained in the pigment dispersion. Specific examples of the additives include light stabilizers such as nitroxide compounds, antioxidants such as hindered phenols, dyes, fluorescent brighteners, leveling agents for improving the physical properties and coatability of the coating film, defoaming agents, lubricants, thickeners, antistatic agents, surfactants, silane coupling agents, antioxidants, yellowing inhibitors, bluing agents, infrared absorbers, adhesion promoters, antifouling agents, water repellents, curing catalysts, inorganic fillers such as silica, and metal fine particles, etc. can be mentioned.,

[0061] In addition, the pigment dispersion may contain a photopolymerization initiator. Examples of the photopolymerization initiator include carbonyl compounds such as benzoin, benzoin monomethyl ether, benzoin isopropyl ether, acetoin, benzyl, benzophenone, p-methoxybenzophenone, diethoxyacetophenone, benzyldimethyl ketal, 2,2-diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, methyl phenylglyoxylate, 2-hydroxy-2-methyl-1-phenylpropan-1-one; sulfur compounds such as tetramethylthiuram monosulfide and tetramethylthiuram disulfide; phosphate compounds such as 2,4,6-trimethylbenzoyl diphenylphosphine oxide, 2,4,6-trimethylbenzoyl phenylethoxyphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide; 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1; camphorquinone; and the like.

[0062] The pigment dispersion can be prepared according to a conventionally known method. For example, the pigment dispersion of the present embodiment can be prepared by using a solvent as a dispersion medium and dispersing the pigment in the solvent with a pigment dispersant. The content of the organic pigment in the pigment dispersant is preferably 1 to 30% by mass, more preferably 10 to 25% by mass. Also, the content of the inorganic pigment in the pigment dispersion is preferably 5 to 70% by mass, more preferably 30 to 50% by mass.

[0063] First, a mixture of a pigment, a pigment dispersant, and a solvent is processed using a paint shaker, a ball mill, an attritor, a sand mill, a horizontal media mill, a colloid mill, a roll mill, etc., to finely disperse the pigment with a predetermined particle size and obtain a dispersion adjusted to a predetermined liquid chromaticity. Thereafter, it is preferable to remove coarse particles from the obtained dispersion using a centrifuge or a filter. Next, a pigment dispersion can be prepared by adding various additives as necessary.

[0064] The viscosity of the pigment dispersion may be adjusted to a viscosity suitable for the properties of the pigment and the coating method. The viscosity of the pigment dispersion using an organic pigment at 25°C is preferably 2 to 100 mPa·s. Also, the viscosity of the pigment dispersion using an inorganic pigment at 25°C is preferably 5 to 200 mPa·s.

[0065] The pigment dispersion of the present embodiment is useful as a pigment dispersion in applications such as paints, gravure inks, coating agents, and stationery. Further, in the general formula (2), when the proportion of ethylene oxide (EO) in the methoxypolyalkylene glycol chain represented by “(R7O) m CH3” is 50 mol% or more, the water solubility of the methoxypolyalkylene glycol chain is improved, so it can also be used in aqueous inks.

[0066] <UV-curable ink> The aforementioned pigment dispersant preferably contains substantially no volatile components. Therefore, the pigment dispersant of the present embodiment contains substantially no volatile components, and most of the components are useful as materials for forming ultraviolet-curable inks or electron-beam curable inks that form a coating film. Further, when the pigment dispersant of the present embodiment is used, the pigment can be stably and finely dispersed in the medium, and the storage stability of the resulting dispersion is also high. For this reason, the pigment dispersant and the pigment dispersion of the present embodiment are suitable as materials used in ultraviolet-curable inks for inkjet. That is, the ultraviolet-curable ink of the present embodiment is an inkjet ink that contains the aforementioned pigment dispersion using an ultraviolet / electron-beam curable monomer or an ultraviolet / electron-beam curable oligomer as a solvent and substantially contains no volatile components.

[0067] The ultraviolet-curable ink of the present embodiment contains a pigment dispersion, the aforementioned photoinitiator used as necessary, an ultraviolet / electron-beam curable monomer, an ultraviolet / electron-beam curable oligomer, and various additives. After mixing each component and sufficiently stirring, the ultraviolet-curable ink can be obtained by filtering with a filter as necessary. The content of the photoinitiator in the ultraviolet-curable ink is preferably 3 to 12% by mass. If the content of the photoinitiator is less than 3% by mass, curing failure may occur. On the other hand, if the content of the photoinitiator exceeds 12% by mass, an excessive photoinitiator may remain, or the image may be colored by the photoinitiator.

[0068] When the ultraviolet-curable ink of the present embodiment is used, an image (printed film) having high color density and excellent durability such as color development property, adhesion property, and abrasion resistance can be recorded (printed) on various substrates by a general inkjet recording method. Examples of the substrate include paper, printing paper, photographic glossy paper, plastic film, fabric, ceramics, and metal.

Examples

[0069] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are based on mass unless otherwise specified.

[0070] <Production of Pigment Dispersant> (Example 1) Into a reaction apparatus, 75 parts of cardanol novolak type polyepoxy resin (NC-547) and 215 parts (0.1 mol) of a one-terminal aminoated polypropylene glycol polyethylene glycol monomethyl ether copolymer (trade name "Jeffamine M2005", manufactured by Huntsman Corporation, PPG / PEG = 29 / 6 (molar ratio), measured amine value: 26.1 mgKOH / g, molecular weight calculated from amine value: 2,151) (M2005) were put. As the cardanol novolak type polyepoxy resin, the product named "Cardlite NC-547" (manufactured by Cardlite, epoxy equivalent: 750 g / mol) was used. Cardanol has a structure in which a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, and a 7,10,14-pentadecatrienyl group are bonded to the 4-position of the phenol skeleton. While bubbling nitrogen, it was heated to 80 °C and reacted for 8 hours to obtain a pigment dispersant NCA-1. A part of the reaction solution was sampled and the infrared absorption spectrum (IR) was measured. It was confirmed that the absorption of the epoxy group (904 cm -1 ) almost completely disappeared, and the absorption of the hydroxyl group (3,500 cm -1 ) increased. The number average molecular weight (Mn) in terms of polystyrene of the pigment dispersant NCA-1 measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as the developing solvent was 2,700, and the dispersity (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) was 6.13. Almost no peaks derived from NC-547 and M2005 used as raw materials were observed. The amine value of the pigment dispersant NCA-1 measured by a potentiometric automatic titrator using a 0.1 mol / L isopropanolic hydrochloric acid solution was 20.9 mgKOH / g. The solid content of the heating residue that reached a constant weight at 180 °C (measurement value measured using a moisture meter) was approximately 100%.

[0071] (Examples 2 and 3) Pigment dispersants NCA-2 and 3 were obtained in the same manner as in Example 1 above, except that the formulations shown in Table 1 were used. The meanings of the abbreviations in Table 1 are shown below. · M1000: Mono-end amino-modified polypropylene glycol polyethylene glycol monomethyl ether copolymer, trade name "Jeffamine M1000", manufactured by Huntsman · M41: Mono-end amino-modified polypropylene glycol polyethylene glycol monomethyl ether copolymer, trade name "Genamin M41 / 2000", manufactured by Clariant

[0072] TIFF0007695217000011.tif145170

[0073] (Example 4) 75 parts of NC-547, 158.2 parts (0.074 mol) of M41, and 2.67 parts (0.026 mol) of 3-dimethylaminopropylamine (DMAPA) were placed in a reaction apparatus. The mixture was heated to 80 °C with nitrogen bubbling and reacted for 8 hours to obtain pigment dispersant NCA-4. A part of the reaction solution was sampled and measured by IR, and it was confirmed that the absorption of epoxy groups almost completely disappeared and the absorption of hydroxyl groups increased. The Mn of pigment dispersant NCA-4 measured by GPC was 2,100, the PDI was 4.09, and almost no peaks derived from NC-547 and M41 used as raw materials were observed. Also, the amine value of pigment dispersant NCA-4 was 31.3 mgKOH / g, and the solid content was 99.3%.

[0074] (Examples 5 and 6) Pigment dispersants NCA-5 and 6 were obtained in the same manner as in Example 4 above, except that the formulations shown in Table 2 were used. The meanings of the abbreviations in Table 2 are shown below. · AEP: 2-(2-aminoethyl)pyridine · API: 1-(3-aminopropyl)imidazole

[0075] TIFF0007695217000012.tif159170

[0076] (Comparative Production Example 1) 17.6 parts of a phenol novolak type polyepoxy resin (trade name "Araldite EPN 1180", manufactured by Huntsman Corporation, epoxy equivalent weight: 176 g / mol) (EPN1180) and 214 parts (0.1 mol) of M41 were placed in a reaction apparatus. While bubbling nitrogen, the mixture was heated to 80 °C and reacted for 8 hours to obtain a pigment dispersant H-1. A part of the reaction solution was sampled and IR was measured. It was confirmed that the absorption of epoxy groups almost completely disappeared and the absorption of hydroxyl groups increased. The Mn of the pigment dispersant H-1 measured by GPC was 1,800, the PDI was 4.22, and almost no peaks derived from EPN1180 and M41 used as raw materials were observed. Also, the amine value of the pigment dispersant H-1 was 24.5 mgKOH / g and the solid content was 99.5%.

[0077] (Comparative Production Example 2) (a) Synthesis of an acrylic type polyepoxy compound 98.2 parts of propylene glycol monomethyl ether acetate (PGMAc) was placed in a reaction apparatus and charged. After heating to 65 °C while bubbling nitrogen, 3.4 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Corporation) (V65) was added. A solution prepared by mixing 51.2 parts (0.36 mol) of glycidyl methacrylate, 37.5 parts (0.36 mol) of styrene, and 4.3 parts (0.04 mol) of 1-thioglycerol (trade name "Blemmer TGL", manufactured by NOF Corporation) was added dropwise over 1 hour. After polymerization at 65 °C for 1 hour, 0.9 part of V65 was added. Further, after polymerization at 65 °C for 2 hours, 0.9 part of V65 was added and polymerization was carried out for 4 hours to obtain a PGMAc solution of an acrylic type polyepoxy compound. When IR was measured, absorption of epoxy groups could be confirmed. The Mn of the acrylic type polyepoxy compound measured by GPC was 2,800 and the PDI was 2.49. Also, the epoxy equivalent weight was 273 g / mol and the solid content was 50.1%.

[0078] (b) Production of a pigment dispersant 54.5 parts of a PGMAc solution of an acrylic type polyepoxy compound, 0.1 part of 4-methoxyphenol, and 214 parts (0.1 mol) of M41 were placed in a reaction apparatus. While nitrogen bubbling was carried out, the mixture was heated to 80 °C and reacted for 8 hours to obtain a pigment dispersant H-2. A part of the reaction solution was sampled and IR was measured, and it was confirmed that the absorption of the epoxy group almost completely disappeared and the absorption of the hydroxyl group increased. The Mn of the pigment dispersant H-2 measured by GPC was 3,500, the PDI was 3.05, and almost no peaks derived from the acrylic type polyepoxy compound and M41 used as raw materials were observed. Also, the amine value of the pigment dispersant H-2 was 23.8 mgKOH / g, and the solid content was 89.8%.

[0079] <Production of Pigment Dispersion for UV-Curable Ink> (Examples 7 to 12, Comparative Examples 1 and 2) Each component of the type and amount shown in Table 3 was blended. After stirring for 2 hours with a dissolver, dispersion treatment was carried out using a horizontal media disperser to produce pigment dispersions for UV-curable inks of yellow (Y) color, magenta (M) color, cyan (C) color, and black (Bk) color. In Table 3, "Synergist 1", "Synergist 2", and "Synergist 3" are pigment derivatives having acidic groups represented by the following structural formulas (I) to (III), respectively. In Table 3, "PY-150" is Levasolin Yellow (manufactured by Lanxess), and "PR-122" and "PB-15:4" are both pigments manufactured by Dainichi Seika Kogyo Co., Ltd. In Table 3, "PEA" is 2-phenylethyl acrylate, and as carbon black, the product name "MB-1000" (manufactured by Mitsubishi Chemical Corporation) was used.

[0080] TIFF0007695217000013.tif214170

[0081] TIFF0007695217000014.tif143170

[0082] <Evaluation of Pigment Dispersion> The viscosity (initial viscosity) of the produced pigment dispersion and the particle diameter of the pigment (initial particle diameter (median diameter; D50 )) was measured. Also, the viscosity after storing the pigment dispersion at 70°C for one week (viscosity after storage) and the particle diameter of the pigment (particle diameter after storage (median diameter; D 50 )) were measured. The measurement results are shown in Table 4. The particle diameter of the pigment was measured using a dynamic light scattering type particle size distribution measuring device (trade name "SZ-100", manufactured by Horiba, Ltd.).

[0083] TIFF0007695217000015.tif73170

[0084] As shown in Table 4, the M-color pigment dispersion-3 produced in Comparative Example 2 showed a certain degree of good dispersibility, but it contained PGMAc which is a volatile component, and it is inappropriate as a pigment dispersion for an ultraviolet curable ink that substantially does not contain volatile components.

[0085] <Preparation of Ultraviolet Curable Ink> (Examples 13 to 18, Comparative Example 3) Using each component of the type and amount (parts) shown in Table 5, an ultraviolet curable ink (pigment ink) for inkjet was prepared. Specifically, each component of the type and amount shown in Table 5 was mixed, stirred well using a dissolver, and then filtered through a membrane filter with a pore size of 10 μm. It was further filtered through a 5-μm membrane filter to obtain a pigment ink. In Table 5, "Lucirin TPO", "Irgacure 819", and "Irgacure 127" are all trade names of photoinitiators manufactured by BASF Corporation.

[0086] TIFF0007695217000016.tif163170

[0087] <Evaluation of Ultraviolet Curable Ink> The viscosity (initial viscosity) of the prepared ultraviolet curable ink (pigment ink) and the particle diameter of the pigment (initial particle diameter (median diameter; D 50 )) were measured. Also, the viscosity after storing the pigment ink at 70°C for one week (viscosity after storage) and the particle diameter of the pigment (particle diameter after storage (median diameter; D 50 )) were measured. The measurement results are shown in Table 6.

[0088] TIFF0007695217000017.tif83170

[0089] <Examples of Ink Usage> (Examples 1 to 6) Each of the pigment inks prepared in Examples 13 to 18 was filled into an ink cartridge and mounted on an inkjet printer (trade name "EB100", manufactured by Konica Minolta). Using this inkjet printer, a solid image was continuously printed on a polyethylene terephthalate (PET) film for 1 hour. As a result, in each case of using the pigment inks, the head did not clog and smooth printing was possible. Also, defects such as streaks and warping did not occur, and the ejection stability was good.

Industrial Applicability

[0090] The pigment dispersant of the present invention is useful as a material for ultraviolet curable inks considering the environment, and is also useful as a pigment dispersion for environmentally friendly printing inks, and is suitable as a material for inks used in printing such as food packaging, electronic component packaging, and labels.

Claims

1. A pigment dispersant having a structure represented by the following general formula (1). (In the general formula (1), R １ , R ２ , and R ３ each independently represents a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, or a 7,10,14-pentadecatrienyl group, and R ４ , R ５ , and R ６ each independently represents a hydrogen atom, a group represented by the following general formula (2), or a group represented by the following general formula (3), and one or more of R ４ , R ５ , and R ６ are groups represented by the following general formula (2), and n represents a number from 1 to 10) (In the general formula (2), * indicates the bonding position, R ７ represents an ethylene group or a methylethylene group, and m represents a number from 14 to 68) (In the general formula (3), * indicates the bonding position, A represents an alkyl group, a dialkylaminoalkyl group, a pyridinylalkyl group, an imidazolylalkyl group, a pyridinyl group, or an imidazolyl group, and R ８ represents a hydrogen atom or an alkyl group)

2. A method for producing the pigment dispersant according to Claim 1, comprising a reaction step of reacting a polyepoxy compound represented by the following general formula (4) with a polyalkylene glycol monomethyl ether monoamine. (In the general formula (4), R １ , R ２ , and R ３ each independently represents a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, or a 7,10,14-pentadecatrienyl group, and R ９ , R １０ , and R １１ each independently represents a hydrogen atom or a 2,3-epoxypropyl group, and R ９ , R １０ , and R １１One or more of them are 2,3-epoxypropyl groups, and n represents a number from 1 to 10)

3. The method for producing a pigment dispersant according to claim 2, wherein the compound represented by the general formula (4) is a formalin condensate of cardanol.

4. The reaction step is a step of further reacting the polyepoxy compound with at least one amine compound selected from the group consisting of a primary organic amine, a secondary organic amine, and a polyamine compound, The method for producing a pigment dispersant according to claim 2 or 3, wherein the polyamine compound is a compound having a primary amino group or a secondary amino group and a tertiary amino group.

5. The method for producing a pigment dispersant according to claim 4, wherein the polyamine compound is at least one selected from the group consisting of dimethylaminopropylamine, diethylaminopropylamine, dibutylaminopropylamine, 4-aminopyridine, 4-(2-aminoethyl)pyridine, and 1-(3-aminopropyl)imidazole.

6. A pigment dispersion liquid containing a pigment, a solvent, and a pigment dispersant for dispersing the pigment in the solvent, The pigment dispersion liquid, wherein the pigment dispersant is the pigment dispersant according to claim 1.

7. The pigment dispersion liquid according to claim 6, further containing a pigment derivative having at least one acidic group selected from the group consisting of a carboxy group, a phosphoric acid group, and a sulfonic acid group.

8. The pigment dispersion liquid according to claim 6 or 7, wherein the solvent is an ultraviolet / electron beam curable monomer having one or more unsaturated bonds, or an ultraviolet / electron beam curable oligomer.

9. An ultraviolet curable ink for inkjet containing the pigment dispersion liquid according to claim 8.

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