JP7126169B2 - pigment dispersion - Google Patents

Description

The present invention relates to a pigment dispersion using a polymer having a specific structure as a pigment dispersant.

As information equipment, next-generation displays such as liquid crystal displays, organic EL displays, and quantum dot displays have been developed in recent years. In addition, with the rapid development of technology, there is a demand for a color filter, which is a component of a liquid crystal display panel with high image quality and excellent cost performance, and a coloring agent for manufacturing such a color filter. there is Furthermore, for organic EL displays and quantum dot displays, there is a demand for a colorant with excellent pigment dispersibility that can constitute a bank material that divides the pixels of the light-emitting layer.

A pigment dispersion liquid used as a coloring agent, which is a material for manufacturing a color filter or the like, contains extremely fine pigments (pigment fine particles) in a finely dispersed state. Such a pigment dispersion liquid has a high surface tension because the pigment is finely divided, and the pigment tends to aggregate easily. Therefore, it is necessary to devise a pigment dispersion liquid to maintain the dispersion stability of the pigment dispersed in the state of fine particles. For example, there have been proposed various colorants for color filters that use a pigment dispersant with good heat resistance and are easily developed with an alkali (Patent Documents 1 to 3).

JP 2008-298967 A JP 2011-068865 A JP 2013-032441 A

As for colorants for next-generation displays, finer particles of pigments are progressing further. In order to stably exhibit high coloring performance while containing finely divided pigments, the finely dispersed state must be maintained without the pigments aggregating even when stored for a long period of time under high temperature conditions. required to be present. However, it cannot be said that conventional colorants can always satisfy these requirements.

The present invention has been made in view of the problems of the prior art, and its object is to achieve low viscosity, exhibit good coloring performance, and improve the dispersion stability and To provide a pigment dispersion which is excellent in long-term storage stability and is useful as various colorants.

That is, according to the present invention, the following pigment dispersion is provided.
[1] A pigment dispersion containing a pigment, an organic solvent, and a polymeric dispersant, wherein the polymeric dispersant is a polymer satisfying the following requirements (1) to (4).
(1) AB block copolymer having polymer chain A and polymer chain B containing 90% by mass or more of methacrylate monomer units.
(2) The polymer chain A is a polymer block having an amine value of 0.5 mgKOH/g or less and a polystyrene equivalent number average molecular weight measured by gel permeation chromatography of 3,000 to 15,000.
(3) The polymer chain B is a polymer block having an amine value of 0 to 150 mgKOH/g and containing a methacrylate-based monomer unit (b) having a functional group represented by the following general formula (1).
(4) The content of the methacrylate-based monomer unit (b) is 30 to 80% by mass based on the entire polymer.

（前記一般式（１）中、Ｒ_１、Ｒ_２、及びＲ_３は、相互に独立に、炭素数１～１８のアルキル基、アルケニル基、又はアリルメチル基を示し、Ｘ_１及びＸ_２は、相互に独立に、フッ素原子又は炭素数１～８のフッ化アルキル基を示す）

(In the general formula (1), R ₁ , R ₂ and R ₃ each independently represent an alkyl group, alkenyl group or allylmethyl group having 1 to 18 carbon atoms, and X ₁ and X ₂ are each independently represents a fluorine atom or a fluorinated alkyl group having 1 to 8 carbon atoms)

[2] The pigment dispersion according to [1] above, wherein the organic solvent is an aprotic solvent having a dielectric constant of 20 or less.
[3] The pigment dispersion according to [1] or [2] above, wherein the pigment has an acidic group of at least one of a carboxy group, a sulfonic acid group, and a phosphoric acid group on its surface.
[4] The pigment dispersion according to any one of [1] to [3], wherein the pigment is a nanocarbon substance.
[5] The pigment dispersion according to [4], wherein the nanocarbon substance is at least one of carbon nanotubes and nanographenes.
[6] The content of the polymer dispersant is 10 to 200 parts by mass with respect to 100 parts by mass of the pigment, and the content of the pigment is 0.5 to 30% by mass based on the entire dispersion. A pigment dispersion liquid according to any one of [1] to [5] above.

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to provide a pigment dispersion that has a low viscosity, exhibits good coloring performance, is excellent in pigment dispersion stability and long-term storage stability, and is useful as various colorants. . The pigment dispersion of the present invention is useful as a colorant for color filters, oil-based inkjet inks, ultraviolet-curable inkjet inks, paints, gravure inks, coating agents, and the like. In addition, the polymer dispersant used in the pigment dispersion of the present invention can stably disperse nanocarbon substances such as carbon nanotubes and nanographenes, which are difficult-to-disperse black pigments, in an organic solvent. . Therefore, according to the present invention, it is also possible to provide a pigment dispersion having a high degree of blackness and jet-blackness, in which the above-described nanocarbon substance, which is a pigment, is stably dispersed at a high concentration.

Embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments. In addition, unless otherwise specified, various physical property values in this specification are values at room temperature (25° C.).

<Pigment dispersion>
The pigment dispersion of the present invention is a so-called "oil-based" pigment dispersion containing a pigment, an organic solvent, and a polymeric dispersant. The polymeric dispersant for dispersing the pigment in the organic solvent is a polymer that satisfies the following requirements (1) to (4). Details of the pigment dispersion of the present invention are described below.
(1) AB block copolymer having polymer chain A and polymer chain B containing 90% by mass or more of methacrylate monomer units.
(2) The polymer chain A is a polymer block having an amine value of 0.5 mgKOH/g or less and a polystyrene equivalent number average molecular weight measured by gel permeation chromatography of 3,000 to 15,000.
(3) The polymer chain B is a polymer block having an amine value of 0 to 150 mgKOH/g and containing a methacrylate-based monomer unit (b) having a functional group represented by the following general formula (1).
(4) The content of the methacrylate-based monomer unit (b) is 30 to 80% by mass based on the entire polymer.

（一般式（１）中、Ｒ_１、Ｒ_２、及びＲ_３は、相互に独立に、炭素数１～１８のアルキル基、アルケニル基、又はアリルメチル基を示し、Ｘ_１及びＸ_２は、相互に独立に、フッ素原子又は炭素数１～８のフッ化アルキル基を示す）

(In general formula (1), R ₁ , R ₂ and R ₃ are each independently an alkyl group, alkenyl group or allylmethyl group having 1 to 18 carbon atoms, and X ₁ and X ₂ are each independently represents a fluorine atom or a fluorinated alkyl group having 1 to 8 carbon atoms)

(Polymer dispersant)
A polymer dispersant (pigment dispersant) is a component that functions as a dispersant for dispersing pigments having various shapes such as fine particles, fibers, scales, or rods in an organic solvent (pigment dispersion). , are block copolymers having in their molecular structure a quaternary ammonium base with a specific counter anion. A quaternary ammonium base is adsorbed to a pigment by an electrical action or the like with the particle surface of the pigment. As a result, the dispersion stability of the particulate pigment in the pigment dispersion can be enhanced, and the viscosity of the pigment dispersion is less likely to change over time, thereby exhibiting long-term storage stability. In addition, when an amino group is further present in the molecular structure of the polymer dispersant, it ionically bonds with an acid group such as a carboxyl group, a sulfonic acid group, or a phosphoric acid group on the surface of the pigment particles, so that the pigment and the polymer dispersant are dispersed. Adsorptivity with the agent is improved, and the dispersion stability of the pigment is further improved.

The polymer used as the polymeric dispersant is an AB block copolymer having polymer chains A and polymer chains B containing 90% by mass or more of methacrylate monomer units (requirement (1)). AB block copolymers are polymers with precisely controlled structures and can be prepared by living polymerization, especially living radical polymerization. In particular, in the case of living radical polymerization using an organic iodide as the initiator compound, it is preferred that the iodine atom, which is a terminal propagating group, is bonded to a tertiary carbon atom. Therefore, the AB block copolymer contains 90% by mass or more of methacrylate monomer units.

A methacrylate-based monomer unit is formed, for example, by polymerizing a methacrylate-based monomer. When the content of methacrylate-based monomer units is large, the AB block copolymer has a high glass transition temperature and thermal properties such as heat resistance are improved. Among them, the AB block copolymer preferably has a methacrylate-based monomer unit content of 100% by mass.

Conventionally known methacrylate-based monomers can be used as the methacrylate-based monomer. Examples of methacrylate-based monomers include methacrylic acid; methyl, ethyl, propyl, butyl, hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, tridecyl, hexadecyl, octadecyl, isostearyl, behenyl, cyclohexyl, trimethylcyclohexyl, t-butyl Cyclohexyl, benzyl, methoxyethyl, butoxyethyl, phenoxyethyl, nonylphenoxyethyl, isobornyl, dicyclopentanyl, dicyclopentenyl, dicyclopentenyloxyethyl, glycidyl, 2-hydroxyethyl, 2-hydroxypropyl, 4-hydroxy Monofunctional methacrylates having substituents such as butyl, dimethylaminoethyl, diethylaminoethyl, polyethylene glycol, polypropylene glycol, polyethylene glycol monomethyl ether, polypropylene glycol monomethyl ether, polyepsiloncaprolactone, and polydimethylsiloxane can be mentioned.

Polymer chain A (hereinafter also simply referred to as "A chain") has an amine value of 0.5 mgKOH/g or less and a polystyrene-equivalent number average molecular weight measured by gel permeation chromatography (GPC) of 3,000 to 15. ,000 polymer blocks (requirement (2)). The polymer chain A is a polymer block that is soluble in an organic solvent, and has the function of making the pigment compatible with the organic solvent and suppressing the reaggregation of the pigment dispersed in the organic solvent by its steric repulsion and electrical repulsion.

The amine value of polymer chain A is 0.5 mgKOH/g or less, preferably 0.1 mgKOH/g or less, more preferably 0 mgKOH/g. When the amine value is 0 mgKOH/g, it means that the polymer chain A has substantially no amino groups. On the other hand, polymer chain B (hereinafter also simply referred to as “B chain”) has an amino group and a quaternary ammonium base. These amino groups and quaternary ammonium bases are affinitive or bound to the pigment through ionic bonding, electrical action, hydrogen bonding, π-π stacking, or hydrophobic interaction, so that the polymer chain B adsorbs to the pigment. It is thought that However, when the polymer chain A has more than a certain amount of amino groups, the polymer chain A also tends to be positively adsorbed on the pigment, which tends to lower the dispersibility and storage stability.

The polystyrene-equivalent number average molecular weight (Mn) of the polymer chain A measured by GPC is 3,000 to 15,000, preferably 4,000 to 10,000. Among the polymer blocks constituting the AB block copolymer, the polymer chain B is adsorbed on the pigment, and the polymer chain A is compatible with and dissolved in the organic solvent. This allows the pigment to be dispersed in the organic solvent. The polymer chain A is required to be a polymer block having a molecular weight capable of exhibiting a function of suppressing reaggregation of pigments by steric repulsion or the like. Therefore, if the number average molecular weight of the polymer chain A is less than 3,000, steric repulsion and the like will be insufficient, resulting in insufficient dispersion stability. On the other hand, when the number average molecular weight of the polymer chain A exceeds 15,000, the viscosity of the dispersion may become excessively high or the dispersion may become difficult to dissolve in the organic solvent.

The polymer chain B is a polymer block having an amine value of 0 to 150 mgKOH/g and containing a methacrylate-based monomer unit (b) having a functional group represented by the following general formula (1) (requirement (3)). The content of the polymer chain B in the polymeric dispersant (AB block copolymer) is preferably 50-80% by mass.

（一般式（１）中、Ｒ_１、Ｒ_２、及びＲ_３は、相互に独立に、炭素数１～１８のアルキル基、アルケニル基、又はアリルメチル基を示し、Ｘ_１及びＸ_２は、相互に独立に、フッ素原子又は炭素数１～８のフッ化アルキル基を示す）

(In general formula (1), R ₁ , R ₂ and R ₃ are each independently an alkyl group, alkenyl group or allylmethyl group having 1 to 18 carbon atoms, and X ₁ and X ₂ are each independently represents a fluorine atom or a fluorinated alkyl group having 1 to 8 carbon atoms)

The functional group represented by general formula (1) is a quaternary ammonium base containing a specific counter anion. This functional group is ionic and acts to adsorb to the pigment surface by electronic action. This quaternary ammonium base has low water solubility and is easily soluble in organic solvents, especially low to medium polar organic solvents. In the general formula (1), if the fluorinated alkyl group represented by X ₁ and X ₂ has more than 8 carbon atoms, the water repellency of the fluorinated alkyl group (perfluoroalkyl group) becomes too high. The types of organic solvents may be restricted. The fluorinated alkyl group represented by X ₁ and X ₂ in the general formula (1) preferably has 1 to 4 carbon atoms. When the carbon number of the fluorinated alkyl group is 1 to 4, even though it is an ionic quaternary ammonium salt, it becomes easily soluble in low-polar organic solvents, furthermore, in aprotic organic solvents. Moreover, by using such an ionic quaternary ammonium salt, it becomes easier to adsorb to the pigment by an electrical action or an ionic action, and the dispersibility of the pigment can be improved.

Counter anions for the quaternary ammonium cation include bis(fluorosulfonyl)imide anion, (fluorosulfonyl)(trifluoromethylsulfone)imide anion, bis(trifluoromethylsulfone)imide anion, bis(2,2,2- trifluoroethylsulfone)imide anion, bis(perfluoroethylsulfone)imide anion, bis(perfluoropropylsulfone)imide anion, bis(perfluorobutylsulfone)imide anion, bis(perfluorooctylsulfone)imide anion, 1, 1,2,2,3,3-Hexafluoropropane-1,3-disulfonimide anion and the like can be mentioned. Among them, from the viewpoint of solubility in organic solvents, availability, etc., anions having a perfluoroalkyl group that does not have a large number of carbon atoms are preferable. More preferred is the butylsulfone)imide anion.

Polymer chain B is a polymer block composed of a methacrylate-based monomer having a functional group represented by general formula (1). The functional group represented by general formula (1) is bonded to any organic group. The above methacrylate-based monomers are formed by, for example, reacting an amino group of an amino group-containing methacrylate such as dimethylaminoethyl methacrylate or diethylaminoethyl methacrylate with a quaternizing agent to convert the amino group into a quaternary ammonium base. . For example, a chloride salt of benzyldimethyl-2-methacryloyloxyethylammonium can be obtained by reacting dimethylaminoethyl methacrylate with benzyl chloride.

Quaternary ammonium bases can also be formed by methods other than those described above. Specifically, the following methods (i) to (iii) can be used.
(i) methacrylate, isocyanatoethyl methacrylate, etc. having a glycidyl group are reacted with a compound having a primary or secondary amino group and a tertiary amino group to introduce a tertiary amino group; Let the tertiary amino group be a quaternary ammonium base.
(ii) reacting a methacrylate having a glycidyl group with a tertiary amine to form a quaternary ammonium base;
(iii) reacting a methacrylate having a halogenated alkyl group such as 3-chloro-2-hydroxypropyl methacrylate with a tertiary amine to form a quaternary ammonium base;

In general formula (1), the quaternary ammonium cation represented by "-N ⁺ (-R ₁ ) (-R ₂ ) (-R ₃ )" includes trimethylammonium cation, butyldimethylammonium cation, diethylmethyl ammonium cation, butyldiethylammonium cation, dipropylmethylammonium cation, dibutylmethylammonium cation, benzyldimethylammonium cation, benzyldiethylammonium cation, benzyldipropylammonium cation, benzyldibutylammonium cation, dimethyl(naphthylmethyl)ammonium cation, dimethyl ( anthracenylmethyl)ammonium cation, dimethyl(pyrenemethyl)ammonium cation, and the like.

The content of the methacrylate-based monomer unit (b) having a functional group represented by general formula (1) is 30 to 80% by mass based on the total polymer (requirement (4)). By setting the content of the methacrylate-based monomer unit (b) having a functional group represented by the general formula (1) (hereinafter also simply referred to as “the content of the unit (b)”) to the above range, low polarity It becomes easy to dissolve in the organic solvent and the aprotic organic solvent, and it becomes easy to be adsorbed to the pigment, so that the dispersibility of the pigment can be improved. The content of units (b) is more preferably 50 to 70% by mass based on the total polymer.

The polymer chain B may be substantially composed only of the methacrylate-based monomer unit (b), or may further have structural units (other structural units) other than the methacrylate-based monomer unit (b). Examples of other structural units include structural units derived from the aforementioned methacrylate-based monomers. Among them, it is preferable that the polymer chain B further includes a structural unit derived from a methacrylate-based monomer having an amino group. When an amino group is introduced into the polymer chain B, the adsorptivity to the pigment can be further improved, and the dispersion stability of the pigment can be further improved. In particular, when used in combination with a pigment having an acidic group such as a carboxyl group, a sulfonic acid group, or a phosphoric acid group on its surface, it forms an ionic bond with these acidic groups, thereby improving the adsorptivity between the pigment and the polymer dispersant. At the same time, detachment of the polymer (polymeric dispersant) from the pigment is suppressed, so that the dispersion stability of the pigment can be further improved.

The amine value of polymer chain B is 0 to 150 mgKOH/g, preferably 100 mgKOH/g or less, more preferably 50 mgKOH/g or less. When the amine value of the polymer chain B exceeds 150 mgKOH/g, the amount of amino groups is too large, so the polymer chain B tends to become hydrophilic. In addition, since the polymer is likely to be adsorbed across adjacent pigment particles, it may function as a flocculant and may cause problems such as coloring.

The molecular weight of the polymer chain B may be designed in consideration of the content of the quaternary ammonium base in the polymer chain B, the molecular weight of the polymer chain A, and the like. Specifically, the polystyrene-equivalent number average molecular weight Mn of the polymer chain B measured by GPC is preferably 500 to 15,000, more preferably 1,000 to 10,000.

AB block copolymers used as polymeric dispersants can be produced according to conventionally known methods. Among them, it can be produced by living anionic polymerization, living cationic polymerization, or living radical polymerization, and is preferably produced by living radical polymerization from the viewpoint of conditions, materials, equipment, and the like. Examples of living radical polymerization include atom transfer radical polymerization (ATRP method), nitroxide-mediated radical polymerization (NMP method), reversible addition-fragmentation chain transfer polymerization (RAFT method), and organotellurium-based living radical polymerization (TERP method). ), reversible transfer catalyst polymerization (RTCP method), reversible catalyst-mediated polymerization (RCMP method), and the like. Among them, the RTCP method and the RCMP method using an organic compound as a catalyst and an organic iodide as a starting compound are preferable. These methods use commercially available compounds that are relatively safe, but do not use heavy metals or special compounds. be. Furthermore, since the iodine atom, which is a terminal propagating group, is bonded to a tertiary carbon atom, an AB block copolymer having a specific block structure can be easily produced with high accuracy using general equipment. preferred.

AB block copolymers may be produced by any type of polymerization, including solventless, solution polymerization, and emulsion polymerization. Among them, solution polymerization is preferred. The solvent used in solution polymerization is preferably the same as the organic solvent used in the pigment dispersion. This is because the state of the AB block copolymer solution after polymerization can be used as it is for the pigment dispersion without taking out the AB block copolymer. The above RTCP method and RCMP method can be carried out in the organic solvent used for the pigment dispersion.

Either polymer block of polymer chain A or polymer chain B may be polymerized first, but it is preferable to polymerize polymer chain A first and then polymerize polymer chain B afterwards. This is because if the polymer chain B is polymerized first and the polymerization rate is less than 100%, there is a possibility that the constituent units derived from the remaining monomers will be introduced into the polymer chain A that will be polymerized later. . A quaternary ammonium base can be introduced into the polymer chain B by polymerizing a methacrylate having a quaternary ammonium base. A quaternary ammonium base can also be introduced into the polymer chain B by reacting a quaternizing agent after polymerizing a methacrylate having an amino group. Furthermore, by forming a quaternary ammonium salt whose counter anion is a halide ion, and adding a metal salt having a specific counter anion to carry out ion exchange, a quaternary ammonium salt can be added to the polymer chain B. can be introduced.

(pigment)
As the pigment, conventionally known inorganic pigments and organic pigments can be used. Examples of inorganic pigments include carbon black such as thermal black, ketjen black, and acetylene black, as well as titanium oxide, zinc oxide, red iron oxide, ocher, and composite oxide pigments. Among them, it is preferable to use a pigment having an acidic surface because a polymer dispersant having a basic group is used. For example, as carbon black, it is preferable to use so-called acidic carbon black. Titanium oxide is preferably treated with silica or an acidic silane coupling agent to acidify the surface. Examples of organic pigments include quinacridone pigments, anthraquinone pigments, diketopyrrolopyrrole pigments, perylene pigments, phthalocyanine blue pigments, phthalocyanine green pigments, isoindolinone pigments, indigo/thioindigo pigments, dioxazine pigments, and quinophthalone. Pigments, nickel azo pigments, insoluble azo pigments, soluble azo pigments, high molecular weight azo pigments, organic black pigments and the like can be mentioned. In addition, nanocarbon materials such as carbon nanotubes, graphite, and nanographenes that can be used as black coloring agents can be used.

Pigments for image recording such as inkjet inks include Color Index Number (C.I.) Pigment Blue-15:3, 15:4, C.I. I. Pigment Red-122, 269, C.I. I. Pigment Violet-19, C.I. I. Pigment Yellow-74, 155, 180, 183, C.I. I. Pigment Green-7, 36, 58, C.I. I. Pigment Orange-43, C.I. I. Pigment Black-7, C.I. I. Pigment White-6 and the like can be mentioned. The average primary particle size of these pigments is preferably less than 350 nm.

C. I. Pigment Blue-15:3, 15:4, C.I. I. Pigment Red-122, 269, C.I. I. Pigment Violet-19, C.I. I. Pigment Yellow-74, 155, 180, 183, C.I. I. Pigment Green-7, 36, 58, C.I. I. Pigment Orange-43, and C.I. I. Pigment Black-7 preferably has an average primary particle size of less than 150 nm. Also, C.I. I. Pigment White-6 preferably has an average primary particle size of less than 300 nm. Considering the clogging of the recording head of the inkjet recording apparatus, the sharpness of the recorded image, etc., the smaller the particle diameter of the pigment, the better. A so-called treated pigment, which is surface-treated or encapsulated with a surface-treating agent such as a coupling agent or a surfactant, a synergist, a resin, or the like, can also be used.

As a pigment for image display such as a color filter, it is preferable to use an organic pigment or an inorganic pigment for a black matrix. Examples of red pigments include Color Index (C.I.) Pigment Red (PR) 56, 58, 122, 166, 168, 176, 177, 178, 224, 242, 254, and 255. As a green pigment, C.I. I. Pigment Green (PG) 7, 36, 58, poly(14-16) bromocopper phthalocyanine, poly(12-15) brominated-poly(4-1) chlorinated copper phthalocyanine and the like. As a blue pigment, C.I. I. Pigment Blue 15:1, 15:3, 15:6, 60, 80 and the like.

Examples of complementary color pigments or multicolor pixel pigments for the above pigments include the following. As a yellow pigment, C.I. I. Pigment Yellow (PY) 12, 13, 14, 17, 24, 55, 60, 74, 83, 90, 93, 126, 128, 138, 139, 150, 154, 155, 180, 185, 216, 219, C . I. pigment violet (PV) 19, 23 and the like. As a black pigment for the black matrix, C.I. I. Pigment black (PBK) 6, 7, 11, 26, copper-manganese-iron composite oxides and the like can be mentioned. The surface of these pigments may be treated with a dye derivative (surface modifier) called a synergist, a surfactant, or the like.

The number average particle size of the carbon black and the organic pigment in the pigment dispersion is preferably 10 to 200 nm, more preferably 20 to 150 nm. The number average particle size of the inorganic pigment such as titanium oxide in the pigment dispersion is preferably 50 to 300 nm, more preferably 100 to 250 nm. The number average particle size of the pigment can be observed, measured and calculated using a transmission electron microscope (TEM). A pigment dispersion containing such a finely divided pigment is useful as a coloring agent that provides high color development, high image quality, high gloss, high printability, and the like.

Further, by using the above-mentioned polymer dispersant, it is possible to stably disperse the nanocarbon material, which is a difficult-to-disperse black pigment, in an organic solvent. Examples of nanocarbon materials include carbon nanotubes, graphite, graphene, carbon nanohorns, carbon nanoribbons, carbon fullerenes, carbon-based quantum dots, and nanodiamonds. Among them, at least one of carbon nanotubes and nanographenes is preferable because of its excellent blackness.

Carbon nanotubes are nanocarbon materials composed of graphene sheets rolled into a cylindrical shape. Examples of carbon nanotubes include single-walled carbon nanotubes (SWNT) consisting of a single cylindrical graphene sheet and multi-walled carbon nanotubes (MWNT) consisting of a plurality of concentrically laminated cylindrical graphene sheets. Further, nano-graphenes are nano-sized graphene sheets themselves, and include a single graphene sheet, a laminated sheet in which a plurality of graphene sheets are laminated, and the like. The shape, size, manufacturing method, and the like of the nanocarbon substance are not particularly limited. The nanocarbon material may be doped with a metal such as platinum or palladium or a metal salt.

The pigment is preferably a pigment having at least one acidic group of a carboxy group, a sulfonic acid group, and a phosphoric acid group on its surface. When the polymeric dispersant is an AB block copolymer having an amino group in its molecular structure, the acidic group on the surface of the pigment particles ionically bonds with the amino group, thereby adsorbing the polymeric dispersant to the pigment. easier. This improves the affinity between the polymer dispersant and the pigment, suppressing detachment of the polymer dispersant from the pigment, further improving the dispersion stability of the pigment and further suppressing reaggregation of the pigment. can do.

The acidic group can be introduced onto the surface of the pigment by a conventionally known method. Specifically, the surface of the pigment is (i) oxidized; (ii) treated with a treating agent such as a silane coupling agent having an acidic group; (iii) treated with an aromatic diazonium salt having an acidic group. Coupling treatment; (iv) surface treatment with a synergist (dye derivative) having an acidic group; or the like can introduce acidic groups onto the surface of the pigment.

As a synergist for surface-treating a pigment (to be used in combination with a pigment), a compound having a pigment skeleton and having at least one acidic group of a carboxy group, a sulfonic acid group, and a phosphoric acid group can be used. Among them, a synergist having a sulfonic acid group is preferable because it is easily adsorbed by forming an ionic bond with the polymer dispersant described above.

(organic solvent)
Conventionally known organic solvents can be used as the organic solvent. Incidentally, the organic solvent may contain a small amount of water. 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; ethyl acetate. , butyl acetate, amyl acetate, dimethyl succinate, dimethyl adipate, methyl lactate, dimethyl lactate and other ester solvents; dipropyl ether, tetrahydrofuran, dioxane and other ether solvents; dimethyl carbonate, ethylene carbonate, propylene carbonate and other carbonates System solvent; amides such as N,N-dimethylformamide, N,N-dimethylacetamide, pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide urea solvents such as tetramethylurea and dimethylimidazolidinone; sulfoxide solvents such as dimethylsulfoxide; ethylene glycol, propylene glycol, diethylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol monobutyl ether, tri Glycol monoether solvents such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether; ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, etc. and glycol ether 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 the like.

Reactive monomers such as (meth)acrylic monomers, vinyl ether monomers, epoxy compounds, and oxetane compounds can also be used as organic solvents. By using a reactive monomer as an organic solvent, it is possible to obtain a dispersion liquid that can be applied to ultraviolet-curable or electron-beam-curable inks and coating agents.

As the organic solvent, it is preferable to use an aprotic solvent. Furthermore, the organic solvent contains an aprotic low-polarity solvent and an aprotic non-polar solvent, but preferably does not substantially contain a protic solvent. Aprotic solvents are solvents that do not have hydrogen atoms to protonate (H ⁺ ). Also, the polarity of an aprotic solvent can be defined by the dielectric constant under temperature conditions of 20 to 25°C. The dielectric constant of the aprotic solvent is preferably 20 or less, more preferably 10 or less. Aprotic solvents having a dielectric constant of 20 or less include ethyl acetate (6.0), butyl acetate (5.0), cyclohexanone (18.3), methyl ethyl ketone (18.5), and tetrahydrofuran (7.5). ), toluene (2.4), propylene glycol monomethyl ether acetate (8.0), 3-methoxy-3-methyl-1-butanol (13), butyl acrylate (5.1) and the like ( Numerical values in parentheses indicate dielectric constants at 25°C). The dielectric constant of the aprotic solvent may be an actually measured value, or may be a value described in manufacturer's catalogs and information, literature such as solvent pocketbooks, chemical handbooks, chemical encyclopedias, etc. .

General polymers having a quaternary ammonium base, which is an ionic group, are difficult to dissolve in aprotic solvents, especially aprotic low-polar solvents and aprotic non-polar solvents. For this reason, protic polar solvents are usually used to dissolve common polymers with quaternary ammonium bases. In contrast, the polymer used as the polymer dispersant in the pigment dispersion of the present invention has a quaternary ammonium base with a specific counter anion, so it is easily dissolved in an aprotic solvent and stabilizes the pigment. It can be dispersed in a state of Furthermore, by using an aprotic solvent, it is possible to improve the drying property, hygroscopicity, workability, etc. of inks and paints, and there are advantages such as facilitating mixing with other reactive substances. .

(other ingredients)
The pigment dispersion may further contain conventionally known components such as additives and resins (other components). Examples of additives include dyes, resins, light stabilizers, ultraviolet absorbers, leveling agents, antifoaming agents, photopolymerization initiators, and the like.

As the resin, a photosensitive or non-photosensitive resin varnish or the like can be used. Examples of photosensitive resin varnishes include photosensitive cyclized rubber resins, photosensitive phenolic resins, photosensitive polyacrylate resins, photosensitive polyamide resins, photosensitive polyimide resins, unsaturated polyester resins, and polyester acrylate resins. Varnishes such as resins, polyepoxyacrylate-based resins, polyurethane acrylate-based resins, polyether acrylate-based resins, and polyol acrylate-based resins can be used. Furthermore, varnishes obtained by adding a monomer as a reactive diluent to these varnishes can also be used.

Non-photosensitive resin varnishes include cellulose acetate resins, nitrocellulose resins, styrene (co)polymers, polyvinyl butyral resins, amino alkyd resins, polyester resins, amino resin-modified polyester resins, and polyurethane resins. Resin, acrylic polyol urethane resin, soluble polyamide resin, soluble polyimide resin, soluble polyamideimide resin, soluble polyesterimide resin, hydroxyethyl cellulose, water-soluble salt of styrene-maleic acid ester copolymer, (meth) Varnishes such as water-soluble salts of acrylic ester (co)polymers, water-soluble aminoalkyd resins, water-soluble aminopolyester resins, and water-soluble polyamide resins can be mentioned.

The pigment dispersion can be prepared, for example, by blending the components described above and dispersing the pigment in an organic solvent using a polymer dispersant. The resin-treated pigment may be prepared by adding a polymer dispersant when converting the raw pigment into a pigment, or adding a polymer dispersant when making the pigment finer (fine particles). . The content of the pigment in the pigment dispersion is preferably 0.1 to 70% by mass, more preferably 0.5 to 30% by mass, more preferably 5 to 20% by mass, based on the total dispersion. is particularly preferred. If the pigment content is less than 0.5% by mass, the coloring may be insufficient. On the other hand, if the pigment content exceeds 30% by mass, the viscosity of the pigment dispersion may become excessively high. The content of the polymer dispersant in the pigment dispersion is preferably 5 to 100 parts by mass, more preferably 10 to 200 parts by mass, based on 100 parts by mass of the pigment.

Polymer dispersant, pigment, and organic solvent are mixed, and if necessary, various additives are further mixed, and then dispersed using a disperser or the like until the pigment becomes fine particles with the desired particle size. By doing so, a pigment dispersion can be obtained. A pigment dispersion can also be obtained by mixing a polymer dispersant, a pigment, and an organic solvent, premixing the mixture if necessary, and then performing a dispersion treatment using a disperser or the like. As the dispersing machine, conventionally known various dispersing machines can be used. Examples of dispersing machines include kneaders, attritors, ball mills, sand mills using glass or zircon, horizontal media dispersing machines, colloid mills, and the like. In order to improve the reliability of the resulting pigment dispersion, it is preferred that after the dispersion treatment, it is further treated using a centrifugal separator, an ultracentrifuge, or a filter to remove coarse particles slightly present. .

Since the pigment dispersion liquid of the present invention is a so-called "oil-based" dispersion liquid in which a pigment is dispersed in an organic solvent, it can be used as a coloring agent blended in conventional inks, paints, and the like. In addition, coloring agents for oil-based inkjet inks, coloring agents for UV-curable inks, coloring agents for UV-curable inkjet inks, coloring agents for display members for color filters, and coloring agents for suspension or emulsion polymerization toners. It can also be used as an agent. Further, a pigment dispersion using a nanocarbon material as a pigment is useful as a coloring agent for applications requiring jet-blackness, such as automobiles, musical instruments, and decorative displays.

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited by the following examples as long as the gist thereof is not exceeded. "Parts" and "%" regarding component amounts are based on mass unless otherwise specified.

<Synthesis of quaternary ammonium base-containing polymer (polymeric dispersant)>
(Synthesis example 1)
A reactor equipped with a stirrer, a backflow condenser, a thermometer, and a nitrogen inlet tube attached to a separable flask was prepared. In this reactor, 438 parts of diethylene glycol monobutyl ether (BDG), 4.1 parts of iodine, 2,2-azobis (2,4-dimethylvaleronitrile) (trade name "V-65", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) ) (V-65) 11.9 parts, diphenylmethane (DPM) 0.7 parts, methyl methacrylate (MMA) 80 parts, butyl methacrylate (BMA) 80 parts, and 2-ethylhexyl methacrylate (EHMA) 80 The mixture was stirred while bubbling nitrogen, heated to 60° C., and polymerized for 4.5 hours to synthesize a polymer (A chain). A part of the reaction solution was sampled and measured to have a solid content of 36.8%, and the polymerization rate calculated based thereon was about 100%. The polystyrene-equivalent number average molecular weight (Mn) of the A chain measured by GPC using tetrahydrofuran (THF) as a developing solvent was 4,500, and the polydispersity (PDI) was 1.22. Mn was measured by a differential refractive index detector of GPC.

Then, 5.4 parts of V-65 and 180 parts of 2-(dimethylamino)ethyl methacrylate (DMAEMA) were added, heated to 60° C. and polymerized for 4 hours. As a result, a polymer (B chain) was formed to obtain a polymer solution containing a block copolymer, polymer BP-1. A part of the reaction solution was sampled and measured to have a solid content of 49.9%, and the polymerization rate calculated based thereon was about 100%. Polymer BP-1 had an Mn of 7,700, a PDI of 1.26, and an amine value (measured) of 153.2 mgKOH/g. The amine value (actual measurement) of the polymer was measured by diluting the sample with toluene and 2-propanol, using a 0.1 mol/L hydrochloric acid 2-propanol solution as a titration solution, and using an automatic potentiometric titrator.

After cooling the polymer BP-1 to room temperature, a mixed solution of 144.9 parts of benzyl chloride (BzCl) and 144.9 parts of BDG was added dropwise over 30 minutes. The temperature was raised to 80° C. and the mixture was reacted for 5 hours to quaternary ammonium salt the amino group derived from DMAEMA to obtain a solution of polymer PP-1 (prepolymer) having a solid content of 49.8%. The amine value (actually measured) of polymer PP-1 was about 0 mgKOH/g, confirming that all amino groups in polymer BP-1 became quaternary ammonium bases. The counter anion for the quaternary ammonium cation in polymer PP-1 is the chloride ion (Cl ⁻ ).

276.4 parts of polymer PP-1 and 2487.6 parts of water were placed in a vat fitted with a stirrer and stirred to give a clear solution. When a mixture of 82.2 parts of bis(trifluoromethanesulfonyl)imide lithium (TFSILi) and 739.8 parts of water was added dropwise, the system became cloudy and a precipitate was formed. It is presumed that the precipitate was formed due to the high hydrophobicity of the quaternary ammonium salt with bis(trifluoromethanesulfonyl)imide anion (TFSI) as a counterion generated by the salt exchange. After the precipitate was filtered by suction, it was washed with water and dried to obtain a quaternary ammonium base-containing polymer (polymer SIB-1) as a white solid. Since the amine value of polymer SIB-1 is 0 mgKOH/g, the amine value of the B chain is also 0 mgKOH/g.

(Synthesis Examples 2 and 3)
Polymers SIB-2 and SIB-, which are quaternary ammonium base-containing polymers, were prepared in the same manner as in Synthesis Example 1 described above, except that raw materials such as monomers of the types and amounts (unit: parts) shown in Table 1 were used. got 3. Abbreviations in Table 1 have the following meanings.
・BzMA: benzyl methacrylate ・PME200: poly(n≈4) ethylene glycol monomethyl ether methacrylate ・DMQ: quaternary ammonium salt produced by reacting BzCl with DMAEMA ・DMTFSI: the chloride ion of DMQ was exchanged with TFSI quaternary ammonium salt

The amine value (calculation) of the B chain of the polymer SIB-3 obtained in Synthesis Example 3 was calculated as follows, with the molecular weight of DMAEMA set to 157.1 and the molecular weight of KOH set to 56.1. That is, since the B chain is composed of DMAEMA and DMTFSI, the DMAEMA content of the B chain is "23.9 / (23.9 + 40.1) × 100 = 0.3734", and the amine value of the B chain (calculated ) becomes “(0.3734/157.1)×56.1=133.3 mgKOH/g”.

(Synthesis Example 4)
225 parts of polymer PP-3 and 2137.5 parts of water were placed in a vat equipped with a stirrer and stirred to obtain a clear solution (resin: about 5%). When a mixture of 74.7 parts of bis(nonafluorobutanesulfonyl)imide lithium (NFSILi) and 672.3 parts of water was added dropwise, the system became cloudy and a precipitate was formed. It is presumed that the precipitate was formed due to the high hydrophobicity of the quaternary ammonium salt with bis(nonafluorobutanesulfonyl)imide anion (NFSI) as a counterion, which was produced by the salt exchange. After the precipitate was filtered by suction, it was washed with water and dried to obtain a white solid quaternary ammonium base-containing polymer (polymer SIB-4).

(Synthesis Example 5)
A quaternary compound with bis(fluorosulfonyl)imide anion (FSI) as a counterion in the same manner as in Synthesis Example 4 described above, except that the raw materials of the types and amounts (unit: parts) shown in Table 2 were used. An ammonium base-containing polymer (polymer SIB-5) was obtained. Abbreviations in Table 2 have the following meanings.
- FSILi: bis(fluorosulfonyl)imide lithium - DMNFSI: quaternary ammonium salt in which the chloride ion of DMQ has been exchanged for NFSI - DMFSI: quaternary ammonium salt in which the chloride ion of DMQ has been exchanged for FSI

(Comparative Synthesis Examples 1 and 2)
Tetrafluoroborate anion (BF ₄ ⁻ ) and hexafluorophosphate anion (PF ₆ ⁻ ) were obtained as quaternary ammonium base-containing polymers (polymers HB-1 and HB-2), respectively. Abbreviations in Table 3 have the following meanings.
NaBF ₄ : Sodium tetrafluoroborate NaPF ₆ : Sodium hexafluorophosphate DMBF ₄ : Quaternary ammonium salt in which chloride ions of DMQ are exchanged with tetrafluoroboric acid DMPF ₆ : Chloride ions of DMQ quaternary ammonium salt exchanged for hexafluorophosphate

Table 4 shows the physical properties of the quaternary ammonium group-containing polymers obtained in Synthesis Examples 1 to 5 and Comparative Synthesis Examples 1 and 2, and the solubility in various solvents and acrylic monomers. Abbreviations in Table 4 have the following meanings.
・MEK: methyl ethyl ketone ・THF: tetrahydrofuran ・PGMAc: propylene glycol monomethyl ether acetate ・PEA: phenylethyl acrylate ・BzA: benzyl acrylate

In addition, evaluation criteria for "solubility" in Table 4 are as shown below.
○: Soluble (transparent solution)
△: Translucent solution ×: Insoluble (precipitate)

As shown in Table 4, polymers HB-1 and HB-2 in which the counter anion of the quaternary ammonium cation is BF ₄ ^- or PF ₆ ^- are difficult to dissolve in various organic solvents. Therefore, even if polymers HB-1 and HB-2 are used, it is practically impossible to disperse pigments and nanocarbons in these organic solvents.

<Preparation of pigment dispersion (1)>
(Examples 1-3)
(a) Refinement Treatment of Pigments PR254, PG58, and PB15-6 were prepared as pigments for color filters. 100 parts of a pigment, 400 parts of sodium chloride, and 130 parts of diethylene glycol were placed in a kneader equipped with a pressurized lid (pressurized kneader manufactured by Moriyama Co., Ltd.). After pre-mixing in the kneader until a uniformly moist mass was formed, the pressurized lid was closed, and the contents were kneaded and ground for 7 hours while pressing the contents at a pressure of 6 kg/cm ² to obtain a ground product. The resulting ground product was added to 3,000 parts of 2% sulfuric acid and stirred for 1 hour. After removing sodium chloride and diethylene glycol by filtration, the product was thoroughly washed with water, dried and pulverized to obtain each pigment powder. The number average particle diameter of the pigment powder measured and calculated by observation with a transmission electron microscope (TEM) was all about 30 nm.

(b) Preparation of polymer dispersant solution 50 parts each of polymers SIB-1 to 3 and 116.7 parts of PGMAc were placed in a beaker. A stirrer was added and a magnetic stirrer was used to stir until the polymer was completely dissolved to obtain polymeric dispersant solutions SIB-1S, SIB-2S and SIB-3S. The solids content of the resulting polymeric dispersant solutions was 30.0% (SIB-1S), 29.9% (SIB-2S), and 29.9% (SIB-3S), respectively.

(c) Preparation of Pigment Dispersion The components shown in the upper part of Table 5 in kind and amount (unit: part) were mixed and stirred for 2 hours using a dissolver. After confirming that there were no lumps of the pigment, a dispersion treatment was performed using a horizontal media dispersing machine to prepare a pigment dispersion. In Table 5, "Synergist 1" is a compound (dye derivative) represented by the following formula (I), "Synergist 2" is a compound represented by the following formula (II), and "Synergist 3" is the following It is a compound represented by formula (III). As the "acrylic resin" in Table 5, a polymer having a monomer composition of BzMA/MAA = 80/20 (mass ratio), Mn 5,500, and PDI 2.02 was used. The Mn of the polymer was measured using a PGMAc solution with a solid content of 30%.

(d) Evaluation of pigment dispersion The number average particle diameter (nm) of the pigment in the pigment dispersion, the initial viscosity (mPa s) of the pigment dispersion, and the pigment dispersion after storage at 45 ° C. for 3 days The measurement results of viscosity (viscosity after storage; mPa·s) are shown in the lower part of Table 5. The number average particle size of the pigment was measured using a dynamic light scattering particle size distribution analyzer. The viscosity of the pigment dispersion was measured using an E-type viscometer under the conditions of 60 rpm and 25°C.

<Application to color filter resist>
(Application examples 1 to 3)
(a) Preparation of color filter resist inks The types and amounts (units: parts) of each component shown in Table 6 were blended and thoroughly mixed using a mixer to obtain color filter resist inks of each color. rice field. "Photosensitive acrylic resin varnish" in Table 6 is an acrylic resin obtained by reacting a BzMA/MAA copolymer with glycidyl methacrylate (Mn 6,100, PT 14,400, PDI 2.39, acid value 111 mgKOH/g ) is a varnish containing Abbreviations in Table 6 have the following meanings.
・TMPTA: trimethylolpropane triacrylate ・HEMPA: 2-hydroxyethyl 2-methylpropionic acid ・DEAP: 2,2-diethoxyacetophenone

(b) Evaluation of Color Filter Resist Ink A glass substrate treated with a silane coupling agent was set on a spin coater. Each color resist ink was spin-coated on the glass substrate at 300 rpm for 5 seconds. After pre-baking at 80° C. for 10 minutes, the glass substrates of each color (red glass substrate-1, green glass substrate-1, and blue glass substrate-1) were exposed with a light amount of 100 mJ/cm ² using an ultra-high pressure mercury lamp. manufactured.

Each of the obtained glass substrates of each color had excellent spectral curve characteristics and excellent fastness such as light resistance and heat resistance. Moreover, all glass substrates were excellent in optical properties such as light transmittance and contrast ratio.

<Preparation of pigment dispersion (2)>
(Examples 4-8)
(a) Preparation of Polymeric Dispersant Solution 50 parts each of polymers SIB-4 and SIB-5 and 116.7 parts PEA were placed in a beaker. A stirrer was added and a magnetic stirrer was used to stir until the polymer was completely dissolved to obtain polymeric dispersant solutions SIB-4S and SIB-5S. The solids content of the resulting polymeric dispersant solutions was 29.9% (SIB-4S) and 30.0% (SIB-5S), respectively.

(b) Preparation of Pigment Dispersion The types and amounts (unit: part) of each component shown in the upper part of Table 7 were mixed and stirred for 2 hours using a dissolver. After confirming that there were no lumps of the pigment, a dispersion treatment was performed using a horizontal media dispersing machine to prepare a pigment dispersion. In Table 7, "Synergist 4" is a compound (dye derivative) represented by the following formula (IV). In Table 7, as "PY-150", the trade name "Revasclin Yellow" (manufactured by LANXESS) was used. Also, as “PR-122” and “PB-15:4”, pigments manufactured by Dainichi Seika Kogyo Co., Ltd. were used. Further, as the “carbon black”, the trade name “MB-1000” (manufactured by Mitsubishi Chemical Corporation) was used, and as the “titanium oxide”, the trade name “JR-405” (manufactured by Tayca Corporation) was used.

(c) Evaluation of pigment dispersion liquid Number average particle diameter (nm) of pigment in initial pigment dispersion liquid, number average particle diameter (nm) of pigment in pigment dispersion after storage at 70 ° C. for 1 week, pigment The measurement results of the initial viscosity (mPa·s) of the dispersion and the viscosity (mPa·s) of the pigment dispersion after storage at 70° C. for 1 week are shown in the lower part of Table 7.

As shown in Table 7, the pigment dispersions of each color of Examples 4 to 8 are suitable as colorants for UV curable inks because the pigments are highly dispersed and have high storage stability. . In particular, since the pigment hardly agglomerates and is stably dispersed in the form of fine particles for a long period of time, it is particularly suitable as a colorant for UV-curable inkjet inks that require ejection stability and high-speed printability. be.

<Preparation of pigment dispersion (3)>
(Examples 9-11)
(a) Preparation of polymer dispersant solution Polymers SIB-2 to 50 parts each and 3-methoxy-3-methyl-1-butyl acetate (trade name “Solfit AC”, manufactured by Kuraray Co., Ltd.) 116.7 parts was placed in a beaker. A stirrer was added and a magnetic stirrer was used to stir until the polymer was completely dissolved to obtain polymeric dispersant solutions SIB-2A, SIB-3A and SIB-4A. The solids content of the resulting polymeric dispersant solutions was 29.8% (SIB-2A), 29.8% (SIB-3A), and 30.1% (SIB-4A), respectively.

(b) Preparation of Pigment Dispersion (Nanocarbon Dispersion) The types and amounts (unit: part) of each component shown in the upper part of Table 8 were mixed and stirred for 2 hours using a dissolver. After confirming that the lumps of nanocarbon disappeared, a dispersion treatment was performed using a horizontal media dispersing machine to prepare a nanocarbon dispersion. In Table 8, as "graphene", the product name "N006-P" (manufactured by Ishihara Chemical Co., Ltd.) was used. Also, as the “graphite”, the trade name “xGnP-M-5” (manufactured by XG Science) was used. Furthermore, as "CNT", the product name "AMC" (manufactured by Ube Industries, Ltd.) was used.

(c) Evaluation of pigment dispersion (nanocarbon dispersion) Measurement results of initial viscosity (mPa s) of pigment dispersion and viscosity (mPa s) of pigment dispersion after storage at 70 ° C. for 1 week is shown in the lower part of Table 8.

The pigment dispersion of the present invention is suitable as a colorant for image display materials such as color filters and a colorant for image recording materials such as inkjet inks.

Claims (6)

containing a pigment, an organic solvent, and a polymeric dispersant,
A pigment dispersion in which the polymeric dispersant is a polymer satisfying the following requirements (1) to (4).
(1) AB block copolymer having polymer chain A and polymer chain B containing 90% by mass or more of methacrylate monomer units.
(2) The polymer chain A is a polymer block having an amine value of 0.5 mgKOH/g or less and a polystyrene equivalent number average molecular weight measured by gel permeation chromatography of 3,000 to 15,000.
(3) The polymer chain B is a polymer block having an amine value of 0 to 150 mgKOH/g and containing a methacrylate-based monomer unit (b) having a functional group represented by the following general formula (1).
(4) The content of the methacrylate-based monomer unit (b) is 30 to 80% by mass based on the entire polymer.

(In the general formula (1), R ₁ , R ₂ and R ₃ each independently represent an alkyl group, alkenyl group or allylmethyl group having 1 to 18 carbon atoms, and X ₁ and X ₂ are each independently represents a fluorine atom or a fluorinated alkyl group having 1 to 8 carbon atoms) 2. The pigment dispersion according to claim 1, wherein the organic solvent is an aprotic solvent having a dielectric constant of 20 or less. 3. The pigment dispersion liquid according to claim 1, wherein the pigment has at least one acidic group selected from a carboxy group, a sulfonic acid group and a phosphoric acid group on its surface. The pigment dispersion according to any one of claims 1 to 3, wherein the pigment is a nanocarbon material. 5. The pigment dispersion according to claim 4, wherein the nanocarbon substance is at least one of carbon nanotubes and nanographenes. The content of the polymer dispersant is 10 to 200 parts by mass with respect to 100 parts by mass of the pigment,
The pigment dispersion according to any one of claims 1 to 5, wherein the content of the pigment is 0.5 to 30% by mass based on the total dispersion.