JP7695217B2 - Pigment dispersant, method for producing pigment dispersant, pigment dispersion, and ultraviolet curable ink - Google Patents

Description

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

General coating fluids such as paints, inks, and coating agents contain organic solvents. Therefore, the organic solvents evaporate after application of these coating fluids, which places a relatively high burden on the environment. Therefore, as environmentally friendly coating fluids that do not substantially contain organic solvents, water-based inks and coating fluids using water as the main liquid medium, powder coatings using colored resin powders, etc. have been proposed. Furthermore, coating fluids using vinyl-, epoxy-, and oxetane-based monomers instead of organic solvents have also been proposed. Since such coating fluids are of the type in which heat or light is applied after application to polymerize the monomers to form polymers, they are used as active energy ray-curable inks such as ultraviolet-curable inks and electron beam-curable inks that do not substantially contain volatile components.

In recent years, ultraviolet-curable inkjet inks (UVIJ inks) containing pigments as colorants have been proposed that can record colorful images on-demand on substrates such as packaging materials and containers. UVIJ inks are required to exhibit ejection properties suitable for high-speed printing, to have excellent pigment dispersion stability, and to have lower viscosity. In other words, there is a demand for pigment dispersions for UVIJ inks in which the pigments are finely dispersed and have excellent pigment dispersion stability.

When preparing a pigment dispersion, a pigment dispersant is usually used. As the pigment dispersant, a low molecular weight dispersant such as a surfactant, a polymer type dispersant, etc. are used. Among them, from the viewpoint of fine dispersion and dispersion stability of the pigment, 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 form of a solution diluted with an organic solvent (Patent Documents 1 and 2).

JP 2019-157077 A JP 2013-177580 A

As mentioned above, typical polymer-type pigment dispersants are used in a state dissolved in an organic solvent. Therefore, UVIJ inks prepared using such pigment dispersants also contain organic solvents, which tends to undermine the advantages of UVIJ inks, such as being "substantially free of volatile components and environmentally friendly." Therefore, there has been a demand for the development of a polymer-based pigment dispersant that is substantially free of volatile components, has 100% solids, and is easy to handle.

A polymer-based pigment dispersant that is substantially free of volatile components can be produced, for example, by removing the organic solvent from an organic solvent solution of a polymer produced by solution polymerization or the like. However, there are problems in that the solid content (polymer) obtained by removing the organic solvent is not necessarily easy to handle, and the production process becomes complicated. Furthermore, the functionality of the resulting polymer as a pigment dispersant is not necessarily good, and there is room for further improvement.

The present invention was made in consideration of the problems associated with the conventional technology, and its objective is to provide a pigment dispersant that has good pigment dispersibility and is capable of preparing a pigment dispersion that has low viscosity and excellent storage stability.

Another object of the present invention is to provide a simple method for producing the above-mentioned pigment dispersant, and a pigment dispersion liquid using the above-mentioned pigment dispersant that has good pigment dispersibility, low viscosity, and excellent storage stability.A further object of the present invention is to provide an ultraviolet-curable ink for inkjet use using the above-mentioned pigment dispersant that has good pigment dispersibility, low viscosity, excellent storage stability, and does not substantially contain volatile organic compounds.

That is, according to the present invention, there is provided a pigment dispersant as shown below.
[1] A pigment dispersant having a structure represented by the following general formula (1):

（前記一般式（１）中、Ｒ_１、Ｒ_２、及びＲ_３は、相互に独立に、ペンタデシル基、７－ペンタデセニル基、７，１０－ペンタデカジエニル基、又は７，１０，１４－ペンタデカトリエニル基を示し、Ｒ_４、Ｒ_５、及びＲ_６は、相互に独立に、水素原子、下記一般式（２）で表される基、又は下記一般式（３）で表される基を示すとともに、Ｒ_４、Ｒ_５、及びＲ_６のうちの１以上は下記一般式（２）で表される基であり、ｎは１～１０の数を示す）

(In the general formula (1), R ₁ , R ₂ , and R ₃ each independently represent a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, or a 7,10,14-pentadecatrienyl group; R ₄ , R ₅ , and R ₆ 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); at least one of R ₄ , R ₅ , and R ₆ is a group represented by the following general formula (2); and n represents a number from 1 to 10.)

（前記一般式（２）中、＊は結合位置を示し、Ｒ_７はエチレン基又はメチルエチレン基を示し、ｍは１４～６８の数を示す）

(In the general formula (2), * indicates a bonding position, _R7 indicates an ethylene group or a methylethylene group, and m indicates a number from 14 to 68.)

（前記一般式（３）中、＊は結合位置を示し、Ａはアルキル基、ジアルキルアミノアルキル基、ピリジニルアルキル基、イミダゾリルアルキル基、ピリジニル基、又はイミダゾリル基を示し、Ｒ_８は水素原子又はアルキル基を示す）

(In the general formula (3), * indicates a bonding position, A indicates an alkyl group, a dialkylaminoalkyl group, a pyridinylalkyl group, an imidazolylalkyl group, a pyridinyl group, or an imidazolyl group, and _R8 indicates a hydrogen atom or an alkyl group.)

According to the present invention, there is also provided a method for producing a pigment dispersant as described below.
[2] A method for producing the pigment dispersant according to the above [1], comprising a reaction step of reacting a polyepoxy compound represented by the following general formula (4) with a polyalkylene glycol monomethyl ether monoamine:

（前記一般式（４）中、Ｒ_１、Ｒ_２、及びＲ_３は、相互に独立に、ペンタデシル基、７－ペンタデセニル基、７，１０－ペンタデカジエニル基、又は７，１０，１４－ペンタデカトリエニル基を示し、Ｒ_９、Ｒ_１０、及びＲ_１１は、相互に独立に、水素原子又は２，３－エポキシプロピル基を示すとともに、Ｒ_９、Ｒ_１０、及びＲ_１１のうちの１以上は２，３－エポキシプロピル基であり、ｎは１～１０の数を示す）

(In the general formula (4), R ₁ , R ₂ , and R ₃ each independently represent a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, or a 7,10,14-pentadecatrienyl group; R ₉ , R ₁₀ , and R ₁₁ each independently represent a hydrogen atom or a 2,3-epoxypropyl group, at least one of R ₉ , R ₁₀ , and R ₁₁ being a 2,3-epoxypropyl group; and n represents a number from 1 to 10.)

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

Furthermore, according to the present invention, there is provided a pigment dispersion liquid as shown below.
[6] A pigment dispersion liquid containing a pigment, a solvent, and a pigment dispersant that disperses the pigment in the solvent, wherein the pigment dispersant is the pigment dispersant described in [1] above.
[7] The pigment dispersion according to [6], further comprising 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], wherein the solvent is an ultraviolet ray or electron beam curable monomer or an ultraviolet ray or electron beam curable oligomer having one or more unsaturated bonds.

According to the present invention, there is also provided the following ultraviolet-curable ink.
[9] An ultraviolet-curable inkjet ink containing the pigment dispersion liquid according to [8] above.

The present invention provides a pigment dispersant that has good pigment dispersibility and can prepare a pigment dispersion that has low viscosity and excellent storage stability.

The present invention also provides a simple method for producing the pigment dispersant, and a pigment dispersion using the pigment dispersant, which has good pigment dispersibility, low viscosity, and excellent storage stability. The present invention also provides an ultraviolet-curable inkjet ink using the pigment dispersant, which has good pigment dispersibility, low viscosity, and excellent storage stability, and which does not substantially contain volatile organic compounds.

<Pigment dispersant>
Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited to the following embodiment. One embodiment of the pigment dispersant of the present invention is a compound (polymer) represented by the following general formula (1). Hereinafter, the pigment dispersant of this embodiment will be described in detail.

（前記一般式（１）中、Ｒ_１、Ｒ_２、及びＲ_３は、相互に独立に、ペンタデシル基、７－ペンタデセニル基、７，１０－ペンタデカジエニル基、又は７，１０，１４－ペンタデカトリエニル基を示し、Ｒ_４、Ｒ_５、及びＲ_６は、相互に独立に、水素原子、下記一般式（２）で表される基、又は下記一般式（３）で表される基を示すとともに、Ｒ_４、Ｒ_５、及びＲ_６のうちの１以上は下記一般式（２）で表される基であり、ｎは１～１０の数を示す）

(In the general formula (1), R ₁ , R ₂ , and R ₃ each independently represent a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, or a 7,10,14-pentadecatrienyl group; R ₄ , R ₅ , and R ₆ 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); at least one of R ₄ , R ₅ , and R ₆ is a group represented by the following general formula (2); and n represents a number from 1 to 10.)

（前記一般式（２）中、＊は結合位置を示し、Ｒ_７はエチレン基又はメチルエチレン基を示し、ｍは１４～６８の数を示す）

(In the general formula (2), * indicates a bonding position, _R7 indicates an ethylene group or a methylethylene group, and m indicates a number from 14 to 68.)

（前記一般式（３）中、＊は結合位置を示し、Ａはアルキル基、ジアルキルアミノアルキル基、ピリジニルアルキル基、イミダゾリルアルキル基、ピリジニル基、又はイミダゾリル基を示し、Ｒ_８は水素原子又はアルキル基を示す）

(In the general formula (3), * indicates a bonding position, A indicates an alkyl group, a dialkylaminoalkyl group, a pyridinylalkyl group, an imidazolylalkyl group, a pyridinyl group, or an imidazolyl group, and _R8 indicates a hydrogen atom or an alkyl group.)

In general formula (1), the aromatic ring and the long-chain hydrocarbon groups represented by R ₁ , R ₂ , and R ₃ are moieties that impart affinity to the pigment. In addition, the 7-pentadecenyl group, the 7,10-pentadecadienyl group, and the 7,10,14-pentadecatrienyl group, which are groups having an unsaturated bond, are all groups that can generate radicals. For this reason, by using the pigment dispersant of this embodiment having these groups in an ultraviolet-curable ink, it is possible to cause a reaction between these groups and the curing components in the ink.

The group represented by general formula (2) has a hydroxyl group and an amino group. Examples of the methoxypolyalkylene glycol chain represented by "(R ₇ O) _m CH ₃ " 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.

In general formula (2), m is 14 to 68, and the molecular weight of the methoxy polyalkylene glycol chain represented by "(R ₇ O) _m CH ₃ " is preferably 1,000 to 3,000. From the viewpoint of availability of raw materials and marketability, the methoxy polyalkylene glycol chain represented by "(R ₇ O) _m CH ₃ " is preferably a methoxy polyethylene 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 general formula (1), at least one of R ₄ , R ₅ , and R ₆ is a group represented by general formula (2), and it is preferable that a group represented by general formula (2) is bonded to more than half of the repeating units, and all of R ₄ , R ₅ , and R ₆ may be a group represented by general formula (2).

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 these, the dimethylaminopropyl group, the diethylaminopropyl group, and the dibutylaminopropyl group are preferred because of their high basicity and good reactivity.

In the general formula (3), examples of the pyridinyl alkyl group represented by A include 2-pyridinyl methyl group, 4-pyridinyl methyl group, 1-(2-pyridinyl) ethyl group, 2-(2-pyridinyl) ethyl group, 1-(4-pyridinyl) ethyl group, and 2-(4-pyridinyl) ethyl group. Of these, 4-pyridinyl group and 2-(4-pyridinyl) ethyl group, which have a basic nitrogen at the 4-position, are preferred. In the general formula (3), examples of the imidazolyl alkyl group represented by A include 2-imidazolyl ethyl group, 3-imidazolyl propyl group, and 4-imidazolyl butyl group. Of these, 3-imidazolyl propyl group is preferred from the viewpoint of availability of raw materials, etc.

In general formula (1), n is a number between 1 and 10, and is preferably a number between 2 and 4. If n is 0, the adsorption portion of the main chain is small and therefore detaches from the pigment, reducing the dispersion stability of the pigment. On the other hand, if n is greater than 10, the molecular weight is too large, and the viscosity of the resulting pigment dispersion becomes excessively high.

The polystyrene-equivalent number average molecular weight (Mn) 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.

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

（前記一般式（４）中、Ｒ_１、Ｒ_２、及びＲ_３は、相互に独立に、ペンタデシル基、７－ペンタデセニル基、７，１０－ペンタデカジエニル基、又は７，１０，１４－ペンタデカトリエニル基を示し、Ｒ_９、Ｒ_１０、及びＲ_１１は、相互に独立に、水素原子又は２，３－エポキシプロピル基を示すとともに、Ｒ_９、Ｒ_１０、及びＲ_１１のうちの１以上は２，３－エポキシプロピル基であり、ｎは１～１０の数を示す）

(In the general formula (4), R ₁ , R ₂ , and R ₃ each independently represent a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, or a 7,10,14-pentadecatrienyl group; R ₉ , R ₁₀ , and R ₁₁ each independently represent a hydrogen atom or a 2,3-epoxypropyl group, at least one of R ₉ , R ₁₀ , and R ₁₁ being a 2,3-epoxypropyl group; and n represents a number from 1 to 10.)

R ₁ , R ₂ , and R ₃ in the general formula (4) are the same as R ₁ , R ₂ , and R ₃ in the general formula (1) described above. In the general formula (4), at least one of R ₉ , R ₁₀ , and R ₁₁ is a 2,3-epoxypropyl group (hereinafter, also simply referred to as an "epoxy group"), preferably at least 2, and the number of repeating units is n+2 or less.

As the polyepoxy compound represented by 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 raw material derived from plants, it is a raw material that contributes to reducing carbon dioxide from the perspective of carbon neutrality. An example of a commercially available product of a formalin condensate of cardanol is the product name "Cardolite NC-547" manufactured by Caedolite.

In the reaction step, the polyepoxy compound is reacted with the polyalkylene glycol monomethyl ether monoamine. 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, and methoxypolyethylene glycol polypropylene glycol polyethylene glycol triblock structure monoamine. Among these, methoxypolyethylene glycol polypropylene glycol random structure monoamine is preferred. Examples of commercially available polyalkylene glycol monomethyl ether monoamine include the "Jeffamine M-" series manufactured by Huntsman and the "Genamine" series manufactured by Clariant.

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

The amine compound to be reacted with the remaining epoxy groups may be at least one selected from the group consisting of primary organic amines, secondary organic amines, and polyamine compounds. In other words, the reaction step is preferably a step of further reacting the 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.

Primary organic amines include methylamine, ethylamine, butylamine, octylamine, and hydroxyethylamine. Secondary organic amines include dimethylamine, diethylamine, dibutylamine, and dihydroxyethylamine.

Among polyamine compounds, examples of compounds having a primary amino group and a tertiary amino group include dimethylaminoethylamine, dimethylaminopropylamine, diethylaminoethylamine, diethylaminopropylamine, dibutylaminopropylamine, 4-aminopyridine, 4-(2-aminoethyl)pyridine, and 1-(3-aminopropyl)imidazole. In addition, among polyamine compounds, examples of compounds having a secondary amino group and a tertiary amino group include diethylaminoethylmethylamine and bis(dimethylaminoethyl)amine.

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.

The desired pigment dispersant can be obtained by reacting a polyepoxy compound with a polyalkylene glycol monomethyl ether monoamine, and further reacting with an amine compound as necessary. In the reaction step, for example, in the presence of an organic solvent that is not reactive with epoxy groups or amino groups, the mixture is heated to preferably 60°C or higher, more preferably 80°C or higher, to react the epoxy groups with the amino groups. Thereafter, the organic solvent is distilled off as necessary to obtain a pigment dispersant with a solid content of approximately 100%. Polyepoxy compounds are usually liquids with a relatively low viscosity under conditions of room temperature to 40°C. For this reason, it is preferable to react the mixture in bulk as it is by heating without using a solvent (in the absence of a solvent).

The progress of the reaction can be grasped by measuring infrared absorption spectrum (IR) and confirming the disappearance of the absorption at around 910 cm ⁻¹ derived from the epoxy group and the generation of the absorption at around 3,200 cm ⁻¹ derived from the hydroxyl group. The progress of the reaction can also 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 also be grasped by confirming the increase in molecular weight by gel permeation chromatography or measuring the amine value according to a conventionally known method. Note that even if the reaction has not progressed completely, as long as the pigment dispersant of the present embodiment having a specific structure is generated, it can be used as a dispersant for dispersing pigments.

<Pigment Dispersion>
One embodiment of the pigment dispersion of the present invention contains a pigment, a solvent, and a pigment dispersant that disperses the pigment in the solvent. The pigment dispersant is the pigment dispersant described above.

As the pigment, a conventionally known pigment can be used. Examples of the pigment 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. 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. Examples of pigments include C.I. Pigment Blue 15, 15:1, 15:3, 15:4, 15:6, 22, 60, and 64; C.I. Pigment Green 7, 36, and 58; C.I. Pigment Black 7; and C.I. Pigment White 6.

When these pigments are mixed, any of the following methods may be used: mixing powdered pigments, mixing paste-like pigments, or mixing to form a solid solution when forming the pigment. Fillers such as zinc oxide, zirconium oxide, silica, and mica may also be used. Furthermore, carbon nanotubes, graphite, graphene, carbon nanohorns, carbon nanoribbons, carbon fullerenes, carbon-based quantum dots, and nanodiamonds may also be used.

Pigments suitable for inkjet inks, from the viewpoints of color development, dispersibility, weather resistance, etc., include 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; and the like.

The pigment may be an untreated pigment, a self-dispersing pigment with a functional group introduced on its surface, or a treated pigment that has been surface-treated or encapsulated with a surface treatment agent such as a coupling agent or an activator, or a polymer. In addition, it is preferable to use an organic fine particle pigment unless hiding power is required. Furthermore, in cases where high clarity and transparency are required, it is preferable to use a pigment that has been finely milled by wet grinding such as salt milling or dry grinding. In consideration of preventing nozzle clogging during printing, it is preferable to remove pigments with particle diameters of more than 1.0 μm. The average particle diameter of organic pigments is preferably 0.2 μm or less, and the average particle diameter of inorganic pigments is preferably 0.4 μm or less.

(Pigment derivatives)
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 to the surface of the pigment. Then, the imparted acidic group is ionic-bonded to the amino group of the pigment dispersant, so that the pigment dispersant is more firmly adsorbed to the surface of the pigment and prevented from being detached. Therefore, by further containing a pigment dispersant having an acidic group, it is possible to suppress the aggregation and sedimentation of the pigment, and to obtain a pigment dispersion having better dispersion stability.

As the pigment derivative, a conventionally known pigment derivative can be used. Specifically, a compound in which at least one of an acidic group, a carboxyl 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 to the organic dye skeleton.

An example of a pigment derivative having an azo dye skeleton is a compound represented by the following formula (A). An example of a pigment derivative having an anthraquinone dye skeleton is a compound represented by the following formula (B). An example of a pigment derivative having a quinacridone dye skeleton is a compound represented by the following formulas (C) and (D). An example of a pigment derivative having a phthalocyanine dye skeleton is a compound represented by the following formula (E). An example of a pigment derivative having a diketopyrrolopyrrole dye skeleton is a compound represented by the following formula (F). An example of a pigment derivative having an isoindoline dye skeleton is a compound represented by the following formula (G).

The pigment derivative may be added when the pigment dispersion is produced, or the pigment surface may be treated in advance. Examples of methods for surface treating the pigment with the pigment derivative include a method of adding it to the pigment after synthesis and filtering it; a method of mixing the pigment with a pigment derivative in which the acidic group is converted to a sodium salt, and then treating the pigment derivative by acidifying it to make it water-insoluble; and a method of milling the pigment together when finely dividing it. The amount of pigment derivative per 100 parts by weight of pigment is preferably 0.5 to 20 parts by weight, and more preferably 1 to 10 parts by weight.

(solvent)
The solvent is a liquid such as an organic solvent used as a dispersion medium for dispersing the pigment. Examples of the organic solvent 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; ethylene glycol, propylene glycol, diethylene glycol, ethylene glycol methyl Examples of the glycol monoether solvent include 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; and ionic liquids such as 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide. Water can also be used as a solvent if necessary.

When the pigment dispersion is used to prepare an ultraviolet-curable ink, the solvent is preferably an ultraviolet- or electron-beam-curable monomer or an ultraviolet- or electron-beam-curable oligomer having one or more unsaturated bonds. These solvents are cured by irradiation with ultraviolet light or the like, and therefore do not substantially contain volatile components such as organic solvents. Therefore, by using these solvents, it is possible to obtain a pigment dispersion that can be used to prepare an environmentally friendly ink.

Examples of ultraviolet/electron beam curable monomers and oligomers include curing components such as monofunctional monomers, polyfunctional monomers, photocurable oligomers, and photocurable polymers. Examples of 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, adamantyl methyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, Examples of radical polymerizable monomers include 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, and acryloylmorpholine.

Polyfunctional monomers and photocurable oligomers include neopentyl glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, poly(n=2 or more) ethylene glycol di(meth)acrylate, polypropylene glycol (n=2 or more) di(meth)acrylate, polybutylene glycol (n=2 or more) di(meth)acrylate, 2,2-bis(4-(meth)acryloxyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxydiethoxyphenyl)propane, trimethylolpropane diacrylate, bis(2-(meth)acryloxyethoxyphenyl)propane, trimethylolpropane diacrylate ... Epoxies such as (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, and epoxy di(meth)acrylate obtained by reacting bisphenol A diepoxy with (meth)acrylic acid. Poly(meth)acrylate, urethane tri(meth)acrylate obtained by reacting 2-hydroxyethyl (meth)acrylate with a trimer of 1,6-hexamethylene diisocyanate, 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 Examples of such poly(meth)acrylates include urethane di(meth)acrylates obtained by reacting a urethane reaction product of dicyclohexyl diisocyanate and poly(n=6-15)tetramethylene glycol with 2-hydroxyethyl(meth)acrylate, polyester (meth)acrylates obtained by reacting trimethylolethane with succinic acid and (meth)acrylic acid, and polyester poly(meth)acrylates obtained by reacting trimethylolpropane with succinic acid, ethylene glycol, and (meth)acrylic acid.

Examples of photocurable polymers include polymers in which multiple (meth)acryloyloxy groups, which are radical polymerizable groups, have been introduced to the ends or side chains of polymers such as poly(meth)acrylate, polyurethane, polyester, polyamide, polyimide, and polyepoxy resin. In addition, photocurable polymers having alkali developability and in which carboxyl groups or the like have been introduced can also be used.

(Additives)
The pigment dispersion liquid may contain various additives. 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 application properties of the coating film, defoamers, lubricants, thickeners, antistatic agents, surfactants, silane coupling agents, antioxidants, yellowing inhibitors, bluing agents, infrared absorbing agents, adhesion promoters, antifouling agents, water repellents, curing catalysts, inorganic fillers such as silica, and metal fine particles.

The pigment dispersion may also contain a photopolymerization initiator. Examples of photopolymerization initiators include carbonyl compounds such as benzoin, benzoin monomethyl ether, benzoin isopropyl ether, acetoin, benzil, benzophenone, p-methoxybenzophenone, diethoxyacetophenone, benzil dimethyl ketal, 2,2-diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, methylphenyl glyoxylate, and 2-hydroxy-2-methyl-1-phenylpropan-1-one; tetramethylthiuram monosulfide, tetramethylthiuram disulfide, and the like. Examples of such compounds include sulfur compounds such as phosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide; 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1; camphorquinone; and the like.

The pigment dispersion liquid can be prepared according to a conventional method. For example, the pigment dispersion liquid of this embodiment can be prepared by using a solvent as a dispersion medium and dispersing the pigment in the solvent using a pigment dispersant. The content of the organic pigment in the pigment dispersant is preferably 1 to 30 mass %, and more preferably 10 to 25 mass %. The content of the inorganic pigment in the pigment dispersion liquid is preferably 5 to 70 mass %, and more preferably 30 to 50 mass %.

First, a mixture of pigment, pigment dispersant, and solvent is processed using a paint shaker, ball mill, attritor, sand mill, horizontal media mill, colloid mill, roll mill, etc. to finely disperse the pigment of a specified particle size and obtain a dispersion adjusted to a specified liquid chromaticity. After that, it is preferable to remove coarse particles from the obtained dispersion using a centrifuge or filter. Next, various additives can be added as necessary to prepare the pigment dispersion.

The viscosity of the pigment dispersion may be adjusted to suit the properties of the pigment and the application method. The viscosity of a pigment dispersion using an organic pigment is preferably 2 to 100 mPa·s at 25°C. The viscosity of a pigment dispersion using an inorganic pigment is preferably 5 to 200 mPa·s at 25°C.

The pigment dispersion of the present embodiment is useful as a pigment dispersion for applications such as paints, gravure inks, coating agents, stationery, etc. In addition, when the ratio of ethylene oxide (EO) in the methoxypolyalkylene glycol chain represented _by "( _R7O ) _mCH3 " in general formula (2) is 50 mol% or more, the water solubility of the methoxypolyalkylene glycol chain is improved, and therefore the pigment dispersion can also be used in aqueous inks.

<UV-curable ink>
The pigment dispersant described above preferably does not substantially contain volatile components. Therefore, the pigment dispersant of this embodiment does not substantially contain volatile components and is useful as a material for constituting an ultraviolet-curable ink or an electron beam curable ink in which most of the components form a coating film. Furthermore, by using the pigment dispersant of this embodiment, the pigment can be stably and finely dispersed in a medium, and the resulting dispersion has high storage stability. Therefore, the pigment dispersant and pigment dispersion of this embodiment are suitable as materials used in an ultraviolet-curable ink for inkjet. That is, the ultraviolet-curable ink of this embodiment is an inkjet ink that contains the pigment dispersion described above using an ultraviolet/electron beam curable monomer or an ultraviolet/electron beam curable oligomer as a solvent and does not substantially contain volatile components.

The UV-curable ink of this embodiment contains a pigment dispersion, the above-mentioned photopolymerization initiator used as needed, a UV-curable/electron beam curable monomer or UV-curable/electron beam curable oligomer, and various additives. The UV-curable ink can be obtained by mixing and thoroughly stirring the components, and then filtering the mixture as needed. The content of the photopolymerization initiator in the UV-curable ink is preferably 3 to 12% by mass. If the content of the photopolymerization initiator is less than 3% by mass, curing may be poor. On the other hand, if the content of the photopolymerization initiator is more than 12% by mass, excess photopolymerization initiator may remain, or the image may be colored by the photopolymerization initiator.

By using the UV-curable ink of this embodiment, it is possible to record (print) images (printed films) that are highly saturated and have excellent durability, such as color development, adhesion, and abrasion resistance, on various substrates using a general inkjet recording method. Examples of substrates include paper, photographic paper, glossy photographic paper, plastic film, fabric, ceramics, and metal.

The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. Note that "parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified.

<Production of Pigment Dispersant>
Example 1
Into a reaction vessel were placed 75 parts of cardanol novolac type polyepoxy resin (NC-547) and 215 parts (0.1 mol) of one-end aminated polypropylene glycol polyethylene glycol monomethyl ether copolymer (trade name "Jeffamine M2005", manufactured by Huntsman, PPG/PEG=29/6 (molar ratio), measured amine value: 26.1 mgKOH/g, molecular weight calculated from the amine value: 2,151) (M2005). As the cardanol novolac type polyepoxy resin, a trade name "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. The mixture was heated to 80°C while bubbling with nitrogen and reacted for 8 hours to obtain pigment dispersant NCA-1. A part of the reaction solution was sampled and infrared absorption spectrum (IR) was measured, and it was confirmed that the absorption of epoxy groups (904 cm ^-1 ) had almost completely disappeared and that the absorption of hydroxyl groups (3,500 cm ^-1 ) had increased. The number average molecular weight (Mn) of pigment dispersant NCA-1 in terms of polystyrene, measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a 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 pigment dispersant NCA-1, measured by a potentiometric automatic titrator using a 0.1 mol/L isopropanol hydrochloric acid solution, was 20.9 mgKOH/g. The solid content of the heating residue which reached a constant weight at 180° C. (measured using a moisture meter) was about 100%.

(Examples 2 and 3)
Pigment dispersants NCA-2 and 3 were obtained in the same manner as in Example 1 above, except that the formulation was as shown in Table 1. The meanings of the abbreviations in Table 1 are as follows.
M1000: one-terminated aminated polypropylene glycol polyethylene glycol monomethyl ether copolymer, trade name "Jeffamine M1000", manufactured by Huntsman M41: one-terminated aminated polypropylene glycol polyethylene glycol monomethyl ether copolymer, trade name "Genamine M41/2000", manufactured by Clariant

Example 4
Into a reaction apparatus, 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. The mixture was heated to 80°C while bubbling with nitrogen and reacted for 8 hours to obtain pigment dispersant NCA-4. A part of the reaction solution was sampled and IR was measured, and it was confirmed that the absorption of the epoxy group had almost completely disappeared and that the absorption of the hydroxyl group had increased. The Mn and PDI of the pigment dispersant NCA-4 measured by GPC were 2,100 and 4.09, respectively, and almost no peaks derived from the raw materials NC-547 and M41 were observed. In addition, the amine value of the pigment dispersant NCA-4 was 31.3 mgKOH/g, and the solid content was 99.3%.

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

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

(Comparative Production Example 2)
(a) Synthesis of acrylic polyepoxy compound 98.2 parts of propylene glycol monomethyl ether acetate (PGMAc) was charged into a reaction vessel, and heated to 65°C while bubbling with nitrogen, and then 3.4 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (V65) were 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 "Blenmar TGL", manufactured by NOF Corporation) was dropped over 1 hour. After polymerization at 65°C for 1 hour, 0.9 parts of V65 were added. After further polymerization at 65°C for 2 hours, 0.9 parts of V65 was added and polymerization was continued for 4 hours to obtain a PGMAc solution of an acrylic polyepoxy compound. IR measurement confirmed the absorption of epoxy groups. The Mn of the acrylic polyepoxy compound measured by GPC was 2,800, and the PDI was 2.49. The epoxy equivalent was 273 g/mol, and the solid content was 50.1%.

(b) Production of pigment dispersant Into a reaction vessel, 54.5 parts of a PGMAc solution of an acrylic polyepoxy compound, 0.1 parts of 4-methoxyphenol, and 214 parts (0.1 mol) of M41 were placed. The mixture was heated to 80°C while bubbling with nitrogen and reacted for 8 hours to obtain 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 had almost completely disappeared and that the absorption of the hydroxyl group had increased. The Mn and PDI of pigment dispersant H-2 measured by GPC were 3,500 and 3.05, respectively, and almost no peaks derived from the acrylic polyepoxy compound and M41 used as raw materials were observed. In addition, the amine value of pigment dispersant H-2 was 23.8 mgKOH/g, and the solid content was 89.8%.

<Production of Pigment Dispersion for UV-Curable Ink>
(Examples 7 to 12, Comparative Examples 1 and 2)
The types and amounts of each component shown in Table 3 were mixed. After stirring for 2 hours with a dissolver, a horizontal media disperser was used to carry out a dispersion process, and pigment dispersions for ultraviolet-curable inks of yellow (Y), magenta (M), cyan (C), and black (Bk) were produced. In Table 3, "SYNERGIST 1", "SYNERGIST 2", and "SYNERGIST 3" are pigment derivatives having an acidic group represented by the following structural formulas (I) to (III), respectively. In Table 3, "PY-150" is REVASCULINE YELLOW (manufactured by LANXESS), and "PR-122" and "PB-15:4" are pigments manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd. In Table 3, "PEA" is 2-phenylethyl acrylate, and the trade name "MB-1000" (manufactured by Mitsubishi Chemical Corporation) was used as carbon black.

<Evaluation of Pigment Dispersion>
The viscosity (initial viscosity) and pigment particle size (initial particle size (median size; _D50 )) of the produced pigment dispersion were measured. In addition, the viscosity (viscosity after storage) and pigment particle size (particle size after storage (median size; _D50 )) of the pigment dispersion after storage at 70°C for 1 week were measured. The measurement results are shown in Table 4. The pigment particle size was measured using a dynamic light scattering particle size distribution measuring device (product name "SZ-100", manufactured by Horiba, Ltd.).

As shown in Table 4, M pigment dispersion-3 produced in Comparative Example 2 showed a fairly good dispersibility, but it contained PGMAc, a volatile component, and is therefore unsuitable as a pigment dispersion for UV-curable inks that contain substantially no volatile components.

<Preparation of UV-curable ink>
(Examples 13 to 18, Comparative Example 3)
An inkjet UV-curable ink (pigment ink) was prepared using the types and amounts (parts) of each component shown in Table 5. Specifically, the types and amounts of each component shown in Table 5 were mixed and thoroughly stirred using a dissolver, and then filtered through a membrane filter with a pore size of 10 μm. The mixture was further filtered through a membrane filter with a pore size of 5 μm to obtain a pigment ink. In Table 5, "Lucirin TPO", "Irgacure 819", and "Irgacure 127" are all trade names of photopolymerization initiators manufactured by BASF.

<Evaluation of UV-curable ink>
The viscosity (initial viscosity) and pigment particle diameter (initial particle diameter (median diameter; _D50 )) of the prepared UV-curable ink (pigment ink) were measured. In addition, the viscosity (viscosity after storage) and pigment particle diameter (particle diameter after storage (median diameter; _D50 )) of the pigment ink after storage for one week were measured. The measurement results are shown in Table 6.

<Ink usage examples>
(Usage examples 1 to 6)
The pigment inks of each color prepared in Examples 13 to 18 were filled into ink cartridges, and the cartridges were then loaded into an inkjet printer (product name "EB100", manufactured by Konica Minolta, Inc.). Using this inkjet printer, solid images were printed continuously for one hour on a polyethylene terephthalate (PET) film. As a result, no head clogging occurred when any of the pigment inks was used, and printing was smooth. Furthermore, no defects such as streaks or twisting occurred, and ejection stability was good.

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

Claims (9)

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 represent a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, or a 7,10,14-pentadecatrienyl group; R ₄ , R ₅ , and R ₆ 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); at least one of R ₄ , R ₅ , and R ₆ is a group represented by the following general formula (2); and n represents a number from 1 to 10.)

(In the general formula (2), * indicates a bonding position, _R7 indicates an ethylene group or a methylethylene group, and m indicates a number from 14 to 68.)

(In the general formula (3), * indicates a bonding position, A indicates an alkyl group, a dialkylaminoalkyl group, a pyridinylalkyl group, an imidazolylalkyl group, a pyridinyl group, or an imidazolyl group, and _R8 indicates a hydrogen atom or an alkyl group.) A method for producing the pigment dispersant according to claim 1, comprising the steps of:
A method for producing a pigment dispersant, 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 represent a pentadecyl group, a 7-pentadecenyl group, a 7,10-pentadecadienyl group, or a 7,10,14-pentadecatrienyl group; R ₉ , R ₁₀ , and R ₁₁ each independently represent a hydrogen atom or a 2,3-epoxypropyl group, at least one of R ₉ , R ₁₀ , and R ₁₁ being a 2,3-epoxypropyl group; and n represents a number from 1 to 10.) 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. 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,
4. The method for producing a pigment dispersant according to claim 2, wherein 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 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. A pigment dispersion liquid containing a pigment, a solvent, and a pigment dispersant for dispersing the pigment in the solvent,
A pigment dispersion liquid, wherein the pigment dispersant is the pigment dispersant according to claim 1. The pigment dispersion according to claim 6, further comprising 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 dispersion according to claim 6 or 7, wherein the solvent is an ultraviolet-ray/electron-beam-curable monomer or an ultraviolet-ray/electron-beam-curable oligomer having one or more unsaturated bonds. An ultraviolet-curable inkjet ink comprising the pigment dispersion liquid according to claim 8.