JP2011213908A - Pigment dispersion, ink composition using the same, method for forming image, and printed matter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pigment dispersion which includes finely dispersed pigments, and which is excellent in dispersion stability of the pigment even when stored for a long term, exhibits excellent curability when it is used together with a polymerizable compound and is excellent in resistance to an oxidative gas, and to provide an ink composition using the pigment dispersion, a method for forming an image, and printed matter.SOLUTION: The pigment dispersion contains (a) a pigment and (b) a polymer dispersant including a repeating unit having a sulfide group, wherein the content of sulfur atom derived from the sulfide groups is 0.5-8.0 mass% in the polymer dispersant.

Description

  The present invention relates to a pigment dispersion, an ink composition using the pigment dispersion, an image forming method, and a printed material. Specifically, the present invention relates to a pigment dispersion excellent in dispersibility and storage stability, and an ink composition comprising the pigment dispersion and capable of forming a high-quality image and suitable for inkjet printing. is there.

  In various colored compositions, when a pigment is used as a colorant, it is important to ensure the dispersibility and dispersion stability of the solid pigment. An ink composition having a uniform hue can be obtained by using a pigment dispersion excellent in pigment dispersibility and dispersion stability. In particular, pigments excellent in light resistance are widely used as colorants in ink compositions. However, when there is a problem in the dispersibility of the pigments, the color tone may become uneven or the ink used in the ink jet recording method may be used. In the case of the composition, various problems such as a decrease in dischargeability may be caused.

  According to the ink jet recording method, it is possible to print not only on plain paper but also on a non-liquid-absorbing recording medium such as a plastic sheet and a metal plate, in order to realize high speed and high image quality when printing, It is desired to shorten the time required for drying and curing. For this reason, as one of the ink jet recording methods, there is a recording method using ink that can be cured in a short time by irradiation with active energy rays as ink for ink jet recording. According to this method, a sharp image can be formed by irradiating active energy rays immediately after printing and curing the ink droplets. Such a curable ink-jet ink composition is required to have high pigment dispersibility and stability over time in order to form a high-definition image having excellent color developability and to stably discharge the ink composition. It is done.

  In order to impart a clear color tone and high coloring power to the ink composition, it is essential to make the pigment finer. In particular, in an ink composition used for ink jet recording, since the ejected ink droplets greatly affect the sharpness of the image, the amount of ejected droplets is small, and the ink cured formed from the ink composition. It is essential to use finer particles than the film thickness. However, if the pigment particles are further miniaturized in order to obtain a high coloring power, it becomes difficult to disperse the fine particles, and aggregates are likely to be generated. Further, there is a problem that the viscosity of the composition increases due to excessive addition of the dispersant. The occurrence of pigment aggregates and the increase in the viscosity of the ink composition both adversely affect the ink ejection properties. Therefore, it is not preferable to use an ink composition in which pigment aggregation or thickening has occurred for inkjet recording.

  The following various proposals have been made on the dispersant for obtaining a stable ink composition. That is, in order to improve the affinity between the pigment and the dispersant, the ink composition using the pigment derivative as a dispersant (for example, see Patent Documents 1 and 2), and specific pigments such as phthalocyanine and quinacridone series, Dissolving the dispersant and a dispersant such as an ink composition using a polymer having a basic group as the dispersant (for example, see Patent Document 3), poly (ethyleneimine) -poly (12-hydroxystearic acid) graft polymer Ink composition containing a specific monomer to be used and not using an organic solvent (for example, refer to Patent Document 4) or a graft copolymer having a heterocyclic residue that forms an organic pigment as a dispersant The thing (for example, refer patent document 5) is disclosed.

The pigment dispersants and ink compositions disclosed in these documents can surely finely disperse the pigment and the stability of the ink composition is higher than before, but there is still room for improvement in the stability of the ink composition. There was. In addition, the ink composition having excellent stability still has room for improvement in curability when used as a curable ink composition.
JP 2003-119414 A JP 2004-18656 A JP 2003-321628 A JP 2004-131589 A JP 2007-9117 A

  This invention makes it a subject to achieve the following objectives. That is, the object of the present invention is to provide excellent dispersion stability of the pigment even when the pigment is finely dispersed and stored for a long period of time. Further, it has excellent curability when used with a polymerizable compound, and is resistant to oxidizing gas. The present invention also provides an excellent pigment dispersion, an ink composition using the same, an image forming method, and a printed matter. Another object of the present invention is to provide an ink composition that is excellent in dispersion stability of a pigment and is suitable for inkjet recording even after the pigment is finely dispersed and stored for a long period of time or after being subjected to repeated temperature changes. There is to do.

As a result of intensive studies, the present inventors have made the pigment dispersion contain a polymer dispersant containing a repeating unit having a sulfide group and having a specific amount of sulfur atoms derived from the sulfide group. In addition, the polymer has excellent dispersibility and dispersion stability of the pigment, effectively suppresses the decrease in dispersion stability even after long-term storage or repeated temperature changes, and the polymerization in the case of using with a polymerizable compound. The present invention has been completed by finding that a pigment dispersion excellent in curability of a functional compound and excellent in oxidizing gas resistance, and an ink composition, an image forming method and a printed matter using the pigment dispersion can be obtained.
That is, the means for solving the above problems are as follows.

<1> A pigment and (b) a repeating unit having a sulfide group, and a sulfur atom content derived from the sulfide group in the polymer dispersant is 0.5% by mass or more and 8.0% by mass. A pigment dispersion containing the following polymer dispersant.
<2> The pigment dispersion according to <1>, wherein the repeating unit having the sulfide group contained in the polymer dispersant (b) is a repeating unit represented by the following general formula (1). .

In the general formula (1), R ¹ represents a hydrogen atom or a methyl group. A represents —COO—, —CONR ² —, or a phenylene group, and R ² represents a hydrogen atom or an alkyl group. B ¹ and B ² each independently represent a single bond or a divalent linking group selected from the following <Group B>. D represents an alkyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent. n represents an integer of 1 to 3. However, at least one of the sulfur atoms in the general formula (1) is directly bonded to two carbon atoms, and at least one of the carbon atoms is directly bonded to a hydrogen atom.
<Group B>
An alkylene group which may have a substituent, a phenylene group which may have a substituent, a urethane group, a ureylene group, a carbonate group, an ether group, an ester group, an amide group, a sulfonamide group, or an imino group, Or a linking group in which 2 to 5 of these groups are combined

<3> The content of the repeating unit having a sulfide group is 2.5% by mass or more and 40% by mass or less with respect to the whole (b) polymer dispersant, according to <1> or <2>. It is a pigment dispersion.
<4> The pigment dispersion according to any one of <1> to <3>, further comprising (c) a polymerizable compound.
<5> The pigment dispersion according to <1> to <4>, wherein the (b) polymer dispersant has a repeating unit represented by the following general formula (2).

In the general formula (2), R ³ represents a hydrogen atom or a methyl group. J represents a single bond, —CO—, —COO—, —CONR ⁴ —, —OCO—, or a phenylene group, and R ⁴ represents a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group. W represents a single bond or a divalent linking group. P represents a heterocyclic or aromatic ring residue that is the same as or similar to the heterocyclic ring that is a partial structure contained in the organic pigment.

<6> The pigment dispersion according to any one of <1> to <5>, further comprising (d) an oil-soluble dye.
<7> A curable composition containing the pigment dispersion described in <1> to <6>.
<8> An ink composition containing the pigment dispersion according to <1> to <6>.
<9> The ink composition according to <8>, which is for inkjet.
<10> An image forming method comprising a step of forming an image on a recording medium by applying the ink composition according to <9> by an ink jet printer.
<11> A printed material in which an image is formed on a recording medium using the ink composition according to <8> or <9>.

  According to the present invention, even when the pigment is finely dispersed and stored for a long period of time, the pigment has excellent dispersion stability, and further has excellent curability when used with a polymerizable compound, and also has resistance to oxidizing gas. It is possible to provide an excellent pigment dispersion, an ink composition using the same, an image forming method, and a printed matter.

[Pigment dispersion]
The pigment dispersion of the present invention contains at least (a) a pigment, and (b) a polymer dispersant containing a repeating unit having a sulfide group, and the content of sulfur atoms derived from the sulfide group is as follows: It is 0.5 mass% or more and 8.0 mass% or less with respect to the said (b) polymer dispersing agent whole. Hereinafter, “(b) a polymer containing a repeating unit having a sulfide group, and the sulfur content derived from the sulfide group in the polymer dispersant is 0.5% by mass or more and 8.0% by mass or less. The “dispersant” may be referred to as “(b) specific polymer”.
In addition, the pigment dispersion of the present invention is also preferably an embodiment containing (c) a polymerizable compound.

  As described above, the pigment dispersion of the present invention has the (b) specific polymer having a sulfide group, and the content of sulfur atoms derived from the sulfide group is within the above range, whereby the pigment dispersion is oxidized. Excellent gas resistance. That is, the presence of the specific polymer (b) in the pigment dispersion of the present invention suppresses oxidation of the (a) pigment in the pigment dispersion by the oxidizing gas. For example, not only when the pigment dispersion of the present invention is directly exposed to an oxidizing gas atmosphere, but also a film (for example, an image) formed using the pigment dispersion of the present invention is exposed to an oxidizing gas atmosphere. Even in the case, since (b) the specific polymer is contained in the film, (a) the pigment is suppressed from being oxidized by the oxidizing gas and gradually changing in color (fading).

In addition, when the pigment dispersion of the present invention is used as a curable composition to be described later, since the above-mentioned (b) specific polymer is included, compared with the case where the above-mentioned (b) specific polymer is not included. , Curing sensitivity increases. That is, for example, when the polymerizable compound (c) is cured by ultraviolet irradiation, the use of the pigment dispersion of the present invention enables curing with a small ultraviolet irradiation amount.
The specific polymer (b) contained in the pigment dispersion of the present invention has a configuration in which the sulfur atom of the sulfide group is directly bonded to two carbon atoms, and at least one of the carbon atoms is directly bonded to a hydrogen atom. When it has, especially the raise of the said curing sensitivity becomes remarkable. Although the reason is not certain, it is considered that (b) the specific polymer has the above-described configuration, thereby suppressing the inhibition of polymerization by oxygen. In other words, when the growing chain end of the polymerization is stopped as oxygen radicals by oxygen, the hydrogen of the methylene group adjacent to the sulfur atom is extracted by the oxygen radicals, and the generated carbon radicals restart the polymerization to continue the curing reaction. It is thought that it is because it can be made to.

  Even when the pigment dispersion of the present invention contains (a) a pigment at a high concentration, the viscosity increase of the pigment dispersion is small due to the action of the (b) specific polymer, and is contained in the pigment dispersion. The dispersibility of the pigment in the dispersion medium is high, and the dispersion stability can be maintained. Further, (a) a pigment dispersion excellent in color development and colorability by selecting a fine pigment (that is, a pigment having a small particle diameter, for example, a volume average particle diameter in the range of 0.01 μm to 0.4 μm) as the pigment. You can get things.

  Since the pigment dispersion of the present invention has good dispersibility and dispersion stability of the pigment, it can be diluted and used in various applications. For example, from the viewpoint of increasing the productivity of pigment dispersions, once a thick pigment dispersion (mill base) is prepared and diluted, liquid properties, coloring properties, curability, cured film properties, etc. are adjusted, Various applications to ink compositions, colored curable compositions (curable compositions), color filter resists, and the like are possible. The pigment dispersion of the present invention is suitably used in a wide range of applications that require good color developability, applications that require a light-resistant colorant, such as nanoimprint compositions and surface coating agents. sell. Moreover, since the ink composition containing the pigment dispersion of the present invention is excellent in dispersion stability even at a low viscosity, the ejection stability when an image is printed using an ink jet printer is excellent.

  As will be described later, the pigment dispersion of the present invention is cured, for example, by irradiation with active energy rays or heating when it contains a polymerizable compound in addition to (a) the pigment and (b) the specific polymer. It can be suitably used as a curable composition that can be used. Such a curable composition is suitable as a curable ink composition that can be cured by irradiation with active energy rays or heating, particularly as an inkjet ink composition. The ink composition for ink jets to which the pigment dispersion of the present invention is applied has a clear color tone and high coloring power, and can form a high-quality image. In addition, the curable ink composition for inkjet as described above can directly form a high quality image on a non-absorbable recording medium based on digital data. Are also preferably used.

The pigment dispersion of the present invention is prepared as an ink composition mixed with a chemical that imparts desired performance in addition to an ink composition such as an inkjet ink composition. Can be used to form a sharp image with excellent color developability and to obtain a high-quality printed matter.
That is, since the ink composition of the present invention has excellent dispersibility of the pigment (a) which is a colorant in an organic medium, it forms an image having a sharp hue even when used as a non-curable ink. can do. That is, a general ink composition containing a film-forming polymer, a colorant, and a solvent, and a film is formed by removing the solvent after coating, for example, a solvent using a volatile solvent such as cyclohexanone as a solvent Ink is also a preferred embodiment of the ink composition in the present invention.

  Further, a colored curable composition (a curable composition described later) obtained by applying the pigment dispersion of the present invention is useful not only for application to an ink composition but also as an optical modeling material. It can also be suitably used for the production of color filters and optical discs.

  Hereinafter, each component in the pigment dispersion of this invention is explained in full detail.

<(A) Pigment>
The pigment dispersion of the present invention contains (a) a pigment as an essential component. In the pigment dispersion of the present invention, the pigment is uniformly and stably dispersed in the pigment dispersion by the action of the specific polymer (b) described later, even if the particle size is small.

  The (a) pigment contained in the pigment dispersion of the present invention is not particularly limited, and various known pigments can be appropriately selected and used according to the purpose.

  Since the pigment dispersion of the present invention contains (a) a pigment, it can be suitably used for applications requiring the weather resistance of a colorant, for example, a colored composition such as an ink composition. Moreover, it is also a preferable aspect to use oil-soluble dye together for hue adjustment and improvement of chroma.

  As the (a) pigment contained in the pigment dispersion of the present invention, generally used organic pigments and inorganic pigments can be used. Usually, any commercially available pigment can be used, and further, a pigment pretreated with a commercially available pigment dispersion or a surface treatment agent can be used as long as the effects of the present invention are not impaired.

  Examples of the pigment (a) include, for example, “Dictionary of Pigments” (2000), edited by Seijiro Ito. Herbst, K.M. Hunger “Industrial Organic Pigments”, Isao Hashimoto “Organic Pigment Handbook” (2006), JP 2002-12607 A, JP 2002-188025 A, JP 2003-26978 A, JP 2003-342503 A Examples thereof include pigments described in publications and the like.

  Examples of the organic pigment include a yellow pigment, a magenta pigment, a cyan pigment, a green pigment, an orange pigment, a brown pigment, a violet pigment, and a black pigment.

  The yellow pigment is a pigment exhibiting a yellow color, for example, a monoazo pigment, a disazo pigment, a non-benzidine azo pigment, an azo lake pigment, a condensed azo pigment, an acidic dye lake pigment, a basic dye lake pigment, an anthraquinone pigment, or a quinophthalone pigment. And pyrazolone pigments, acetolone pigments, metal complex pigments, nitroso pigments, metal complex azomethine pigments, benzimidazolone pigments and isoindoline pigments. Of these, examples of pigments that can be preferably used in the present invention include C.I. I. Pigment Yellow (hereinafter abbreviated as PY) 1, PY3, PY12, PY13, PY14, PY16, PY17, PY18, PY24, PY60, PY74, PY83, PY93, PY94, PY95, PY97, PY100, PY109, PY110, PY115, PY117, PY120, PY128, PY138, PY139, PY150, PY151, PY153, PY154, PY155, PY166, PY167, PY173, PY175, PY180, PY181, PY185, PY194, PY213, PY213, PY213, PY214, PY213 Among them, benzimidazolone pigments such as monoazo pigments, disazo pigments, and acetolone pigments, and isoindoline are preferable, and PY74, PY120, PY150, PY151, PY155, PY180, and PY185 are preferable.

The magenta pigment is a pigment exhibiting red or magenta color. For example, a monoazo pigment, β-naphthol pigment, disazo pigment, azo lake pigment, condensed azo pigment, acidic dye lake pigment, basic dye lake pigment, anthraquinone pigment Thioindigo pigments, perinone pigments, perylene pigments, quinacridone pigments, isoindolinone pigments, alizarin lake pigments, naphtholone pigments, naphthol AS-based lake pigments, naphthol AS pigments, diketopyrrolopyrrole pigments and the like.
Of these, examples of pigments that can be preferably used in the present invention include C.I. I. Pigment Red (hereinafter abbreviated as PR) 1, PR2, PR3, PR4, PR5, PR6, PR21, PR38, PR42, PR46, PR53: 1, PR57: 1, PR52: 1, PR46, PR48, PR81, PR83, PR88, PR144, PR149, PR166, PR179, PR178, PR190, PR224, PR123, PR224, PR19, PR122, PR202, PR207, PR209, PR180, PR83, PR170, PR171, PR172, PR174, PR175, PR176, PR177, PR179, PR185, PR194, PR208, PR214, PR220, PR221, PR242, PR247, PR254, PR255, PR256, PR262, PR268, PR264 PR269, PR272, PR282, C. I. Pigment violet 19 and the like. Of these, quinacridone pigments are preferable, and PR42, PR122, PR202, PR209, PR282, C.I. I. Unsubstituted quinacridone, dimethylquinacridone, dichloroquinacridone, and mixed crystals thereof, such as CI Pigment Violet (hereinafter abbreviated as PV) 19, are preferred.

  The cyan pigment is a pigment exhibiting blue or cyan color, and examples thereof include a disazo pigment, a phthalocyanine pigment, an acid dye lake pigment, a basic dye lake pigment, an anthraquinone pigment, and an alkali blue pigment. Examples of the pigment that can be preferably used in the present invention include C.I. I. Pigment Blue (hereinafter abbreviated as PB) 1, PB15, PB15: 1, PB15: 2, PB15: 3, PB15: 4, PB15: 6, PB16, PB18, PB24, PB25, PB60, PB79 and the like. Among these, a copper phthalocyanine pigment is preferable, and PB15, PB15: 1, PB15: 2, PB15: 3, PB15: 4, and PB15: 6 are preferable.

  The green pigment is a pigment exhibiting green, and examples thereof include phthalocyanine pigments and metal complex pigments. Examples of the pigment that can be preferably used in the present invention include C.I. I. Pigment green (hereinafter abbreviated as PG) 7, PG8, PG10, PG36, and the like.

  The orange pigment is a pigment exhibiting an orange color, for example, an isoindoline pigment, anthraquinone pigment, Β-naphthol pigment, naphthol AS pigment, isoindolinone pigment, perinone pigment, disazo pigment, quinacridone pigment, acetron pigment, Examples include pyrazolone pigments. Examples of the pigment that can be preferably used in the present invention include C.I. I. Pigment Orange (hereinafter abbreviated as PO) 2, PO3, PO4, PO5, PO13, PO15, PO16, PO22, PO24, PO34, PO36, PO38, PO43, PO48, PO49, PO51, PO55, PO60, PO61, PO62, PO64, PO66, PO72, PO74 etc. are mentioned.

The brown pigment is a pigment exhibiting brown color, and examples thereof include naphthron pigments such as PBr25 and PBr32.
The violet pigment is a pigment exhibiting a purple color, and examples thereof include a naphthron pigment, a perylene pigment, a naphthol AS pigment, and a dioxazine pigment. Examples of the pigment that can be preferably used in the present invention include C.I. I. Pigment violet (hereinafter abbreviated as PV) 13, PV17, PV23, PV29, PV32, PV37, PV50, and the like.

  The black pigment is a pigment exhibiting black, and examples thereof include carbon black, indazine pigment, perylene pigment, and the like. I. Pigment black (hereinafter abbreviated as PBk) 1, PBk7, PBk31, PBk32, and the like.

The smaller the average particle size of the pigment (a) used in the present invention, the better the color developability. Therefore, the volume average particle size is preferably 0.01 μm to 0.4 μm, more preferably 0.02 μm to 0.3 μm. The range is as follows. Selection of (a) pigment, polymer (above (b) specific polymer), and above dispersion medium, dispersion conditions, and post-treatment process conditions are set so that the maximum particle size is 3 μm or less, preferably 2 μm or less. It is desirable to do.
In the present invention, the clogging of the ink head nozzles can be suppressed by this particle size control, and the curing sensitivity can be maintained when used for ink storage stability, ink transparency, and a curable composition. In the present invention, since a specific polymer (b) described later is used, the pigment is excellent in dispersibility and dispersion stability, and a uniform and stable pigment dispersion can be obtained even when a fine particle pigment is used.

  The particle diameter of the pigment (a) in the pigment dispersion can be measured by a known measuring method. Specifically, it can be measured by a centrifugal sedimentation light transmission method, an X-ray transmission method, a laser diffraction / scattering method, and a dynamic light scattering method. In addition, the numerical value of the volume average particle diameter of the (a) pigment is a value obtained using a laser diffraction / scattering method, and specifically, a value obtained by the following method. That is, LA-920 (manufactured by Horiba, Ltd.) was used as a measuring device, and measurement was performed using tripropylene glycol methyl ether as a measuring solvent.

  In the present invention, the pigment content (a) is preferably added in an amount of 0.1 to 40% by mass in terms of solid content in the pigment dispersion, and preferably 0.5 to 35% by mass. More preferred.

  For the dispersion of these (a) pigments, for example, ball mill, sand mill, bead mill, attritor, roll mill, jet mill, homogenizer, paint shaker, kneader, agitator, Henschel mixer, colloid mill, ultrasonic homogenizer, pearl mill, wet jet Any known dispersing device such as a mill can be used. In addition, it is preferable to add (b) specific polymer mentioned later when dispersing (a) pigment.

<(B) Specific polymer>
The pigment dispersion of the present invention contains (b) a specific polymer as described above. In the pigment dispersion of the present invention, (b) the specific polymer has a sulfide structure (sulfide group) and the content of sulfur atoms derived from the sulfide group is in the above range. It is considered that there is an effect of suppressing discoloration of a coloring matter (for example, (a) a pigment and a dye described later) in the presence of a gas and an effect of improving curability when used as a curable pigment dispersion.

The content of sulfur atoms derived from the sulfide group in the (b) specific polymer is 0.5% by mass or more and 8.0% by mass or less, and 2.0% by mass with respect to the entire specific polymer (b). % To 7.0% by mass is more preferable. Within this range, (b) the adsorbable segment in the specific polymer (that is, the partial structure that adsorbs to the (a) pigment) and the steric repulsion segment (that is, the partial structure that has an affinity for the dispersion medium) are well balanced, There is a tendency that both the dispersion stability of the pigment in the pigment dispersion and the fading suppression effect by the oxidizing gas can be achieved.

  (B) As the specific polymer, any polymer compound having a sulfide bond (sulfide group) can be used. Specifically, for example, an acrylic resin having a substituent having a sulfide group, a styrene resin, Alternatively, vinyl resin such as acrylamide resin, polyamide resin, polyurethane resin, polyester resin, polyether resin, or polyether sulfide resin can be used.

  As the specific polymer (b) contained in the pigment dispersion of the present invention, the vinyl resin is preferable, and it is particularly preferable to have a repeating unit represented by the following general formula (1).

In the general formula (1), R ¹ represents a hydrogen atom or a methyl group. A represents —COO—, —CONR ² —, or a phenylene group, and R ² represents a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms. B ¹ and B ² each independently represent a single bond or a divalent linking group selected from the following <Group B>. D is a linear, branched, or cyclic alkyl group having 1 to 8 carbon atoms that may have a substituent, an aryl group having 6 to 15 carbon atoms that may have a substituent, or a substituent. Represents a heterocyclic group which may have Examples of the substituent of the alkyl group, aryl group, and heterocyclic group of D include a linear, branched, or cyclic alkyl group having 1 to 8 carbon atoms, a hydroxyl group, a carboxyl group, and a dialkylamino group having 2 to 4 carbon atoms. Or an alkoxy group having 1 to 4 carbon atoms.
The alkyl group or aryl group B ¹ , B ² , and D may be bonded to each other to form a ring. n represents an integer of 1 to 3. However, at least one of the sulfur atoms in the general formula (1) is directly bonded to two carbon atoms, and at least one of the carbon atoms is directly bonded to a hydrogen atom.
<Group B>
An alkylene group which may have a substituent, a phenylene group which may have a substituent, a urethane group, a ureylene group, a carbonate group, an ether group, an ester group, an amide group, a sulfonamide group, or an imino group, Or a linking group in which 2 to 5 of these groups are combined

  The polymer having the structure of the general formula (1) is, for example, a so-called vinyl such as radical polymerization, cationic polymerization, or anionic polymerization of a monomer (monomer) that gives the repeating unit represented by the general formula (1). It can be easily synthesized by polymerization. As the polymerization method, for example, known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, dispersion polymerization, and emulsion polymerization can be used.

R ¹ in the general formula (1) represents a hydrogen atom or a methyl group.
A in the general formula (1) represents —COO—, —CONR ² —, or a phenylene group. R ² represents a hydrogen atom or a linear or branched alkyl group, and the alkyl group preferably has 1 to 4 carbon atoms. A is more preferably —COO— or a phenylene group.

B ¹ and B ² in the general formula (1) each independently represent a single bond or a divalent linking group. As the divalent linking group, an alkylene group which may have a substituent, a phenylene group which may have a substituent, a urethane group, a ureylene group, a carbonate group, an ether group, an ester group, an amide group, A sulfonamide group, an imino group, or a linking group obtained by combining 2 to 5 of these groups. In addition, when there are a plurality of B ² in one repeating unit represented by the general formula (1) (that is, n is 2 or 3), each independently represents a single bond or the above divalent linking group. , May be different from each other.
The alkylene group is preferably an unsubstituted, linear or branched alkyl group having 1 to 8 carbon atoms, a hydroxyl group, or an alkylene group having 1 to 6 carbon atoms substituted with an alkoxy group having 1 to 4 carbon atoms. Examples of the phenylene group include an unsubstituted or halogen atom, a hydroxyl group, a linear or branched alkyl group having 1 to 4 carbon atoms, or a phenylene group having 6 to 10 carbon atoms substituted with an alkoxy group having 1 to 4 carbon atoms. preferable. From the viewpoint of enhancing the curability, a single bond as a component of B ¹ and B ^2, urethane group, ureylene group, carbonate group, an ether group, in the case of using an ester group, an amido group, a sulfonamido group, or an imino group Is selected such that at least one sulfur atom is directly bonded to two carbon atoms and at least one of the carbon atoms is bonded to one or more hydrogen atoms.
B ¹ in the general formula (1) is an alkylene group, a combination of an alkylene group, an ether group, and an alkylene group, a combination of an alkylene group, an ester group, and an alkylene group, or a combination of an alkylene group, a urethane group, and an alkylene group. , An alkylene group / ureylene group / alkylene group combination is preferred, and the alkylene group used in these combinations may have a substituent.
B ² in the general formula (1) is an alkylene group, a combination of an alkylene group, an ether group, and an alkylene group, a combination of an alkylene group, an ester group, and an alkylene group, an alkylene group, a urethane group, and an alkylene group. Or a combination of an alkylene group / ureylene group / alkylene group, and the alkylene group used in these combinations may have a substituent. If the B ² there is a plurality, the plurality of B ² may be different.

D in the general formula (1) has a linear, branched or cyclic alkyl group which may have a substituent, an aryl group which may have a substituent, or a substituent. Represents an optionally substituted heterocyclic group. Examples of the substituent for the alkyl group, aryl group, and heterocyclic group of D include a linear, branched or cyclic alkyl group having 1 to 8 carbon atoms, a hydroxyl group, a carboxyl group, a dialkylamino group having 2 to 4 carbon atoms, or Examples thereof include an alkoxy group having 1 to 4 carbon atoms.
As D in the general formula (1), an unsubstituted alkyl group having 1 to 8 carbon atoms, an unsubstituted or substituted aryl group having 6 to 10 carbon atoms, or an unsubstituted or substituted alkyl group. The heterocyclic group having 3 to 5 carbon atoms is preferable, and an unsubstituted alkyl group having 1 to 8 carbon atoms is more preferable. Further, it is one of preferred embodiments that D is bonded to A, B ¹ or B ² to form a 5- to 6-membered ring.
N in the general formula (1) represents an integer of 1 to 3, and is preferably 1 or 2.

The content of the repeating unit having a sulfide group represented by the general formula (1) is preferably 2.5% by mass or more and 40% by mass or less, and more preferably 2.5% by mass or more and 35% by mass with respect to the entire specific polymer (b). More preferably, it is more preferably 5% by mass or more and 30% by mass or less. In the vinyl resin, when the repeating unit represented by the general formula (1) is introduced within this range, as described above, the balance between the adsorptive segment and the steric repulsion segment is good, and the dispersion stability of the pigment in the pigment dispersion is improved. And the fading suppression effect by the oxidizing gas tends to be compatible.
Even when the content of the repeating unit having a sulfide group represented by the general formula (1) is adjusted to the above range, the content of the sulfur atom derived from the sulfide group in the specific polymer (b) The structure of the repeating unit having a sulfide group represented by the general formula (1) and other repeating units should be selected so as to be in the range.

  Preferable specific examples of the monomer (monomer) giving the repeating unit represented by the general formula (1) include the following. However, the present invention is not limited to this.

  The specific polymer (b) used in the pigment dispersion of the present invention preferably contains a repeating unit represented by the following general formula (2) in addition to the repeating unit represented by the general formula (1).

In the general formula (2), R ³ represents a hydrogen atom or a methyl group. J represents —CO—, —COO—, —CONR ⁴ —, —OCO—, or a phenylene group, and R ⁴ represents a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group. W represents a single bond or a divalent linking group. P represents a heterocyclic or aromatic ring residue that is the same as or similar to the heterocyclic ring that is a partial structure contained in the organic pigment.

  The specific polymer containing the repeating unit represented by the above general formula (2) is P in the above general formula (2) (a heterocyclic ring or an aromatic ring which is the same as or similar to the heterocyclic ring which is a partial structure contained in the organic pigment) It is considered that (b) the adsorptivity of the pigment (a) to the specific polymer is very good due to the Van-der-Walls interaction between (residues) and (a) the pigment. For this reason, a pigment dispersion having high affinity between (a) the pigment and (b) the specific polymer can be obtained.

In the general formula (2), R ³ represents a hydrogen atom or a methyl group.
In the general formula (2), J represents —CO—, —COO—, —CONR ⁴ —, —OCO—, or a phenylene group, among which —COO—, —CONR ⁴ —, or a phenylene group is preferable. R ⁴ represents a hydrogen atom, an alkyl group, an aryl group (for example, a phenyl group) or an aralkyl group, and examples of the alkyl group include an alkyl group having 1 to 4 carbon atoms. As the R ^4, among the above, a hydrogen atom or an alkyl group having 1 to 4 carbon atoms are preferred. Of these, J is preferably -COO-, -CONH-, or a phenylene group.

In the general formula (2), W represents a single bond or a divalent linking group.
Examples of the divalent linking group represented by W include a linear, branched, or cyclic alkylene group, an aralkylene group, and the like, and these may have a substituent.

  As the alkylene group represented by W, an alkylene group having 1 to 10 carbon atoms is preferable, and an alkylene group having 1 to 4 carbon atoms is more preferable. Specific examples of the alkylene group include, for example, a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, an octylene group, and a decylene group. Among them, a methylene group, an ethylene group, a propylene group, and the like are particularly preferable. preferable.

The aralkylene group represented by W is preferably an aralkylene group having 7 to 13 carbon atoms, and examples thereof include a benzylidene group and a cinnamylidene group.
The arylene group represented by W is preferably an arylene group having 6 to 12 carbon atoms, and examples thereof include a phenylene group, a cumenylene group, a mesitylene group, a tolylene group, and a xylylene group, and among them, a phenylene group is particularly preferable.
The alkylene group or aralkylene group represented by W may have a substituent, and examples of the substituent include a linear or branched alkyl group having 1 to 4 carbon atoms, a hydroxyl group, or an alkoxy having 1 to 4 carbon atoms. Groups.

  In the divalent linking group represented by W, a group derived from an imino group, an ester group, an ether group, a sulfonamide group, a urethane group, a ureylene group, a carbonate group, an imino group, or a heterocyclic ring ( That is, a group having a heterocyclic ring, specifically, for example, a group obtained by removing two hydrogen atoms from a heterocyclic ring) may be interposed as a linking group.

  W is an unsubstituted or alkyl group in which a single bond, a linear or branched alkylene group having 1 to 8 carbon atoms, an ester group, an ether group, a urethane group, a ureylene group, or an imino group is interposed as a bonding group. , A hydroxyl group or an alkylene group substituted with an amino group and having 1 to 12 carbon atoms.

  In the general formula (2), P represents a heterocyclic or aromatic ring residue that is the same as or similar to the heterocyclic ring that is a partial structure contained in the organic pigment. Here, “the residue of a heterocyclic ring or an aromatic ring that is the same as or similar to a heterocyclic ring that is a partial structure contained in an organic pigment” represented by P is a partial structure that a known organic pigment has in its molecular structure Means a group containing a heterocyclic ring or an aromatic ring having the same or similar structure as the heterocyclic ring (that is, a group obtained by removing one hydrogen from the compound having a heterocyclic ring or an aromatic ring), or a partial skeleton of an organic pigment or Examples thereof include a group containing a heterocyclic ring or an aromatic ring having the same or similar structure as the heterocyclic ring contained as the pigment nucleus (chromophoric atomic group).

  Examples of organic pigments comprising a heterocycle that is the same as or similar to the heterocyclic ring or aromatic ring residue represented by P as a partial structure include known organic pigments. Among them, phthalocyanine-based, insoluble azo Azo lake, anthraquinone, quinacridone, dioxazine, diketopyrrolopyrrole, anthrapyrimidine, antanthrone, indanthrone, flavanthrone, perinone, perylene, thioindigo, quinophthalone, etc. Organic pigments are preferred, quinacridone, benzimidazolone azo, dioxazine, naphthol AS, phthalocyanine, anthraquinone, and perylene organic pigments are more preferred, quinacridone, benzimidazolone azo, anthraquinone, dioxazine The organic pigments are particularly preferred.

  Examples of the heterocyclic or aromatic ring residue represented by P include, for example, quinacridone pigments, benzimidazolone azo pigments, dioxazine pigments, naphthol AS pigments, phthalocyanine pigments, anthraquinone pigments, perylene pigments. A partial structure of any pigment selected from the group consisting of thiophene, furan, xanthene, pyrrole, imidazole, benzimidazole, isoindoline, isoindolinone, benzimidazolone, indole, quinoline, carbazole, acridine, acridone Preferred is a group obtained by removing one hydrogen from a heterocyclic ring which is a partial structure contained in quinacridone, anthraquinone, phthalimide, quinaldine, quinophthalone, naphthalimide, quinaldine and the like. Among these, residues of heterocycles or aromatic rings that are the same as or similar to heterocycles having a structure in which two or more heterocycles are condensed are more preferable. For example, benzimidazole, isoindoline, isoindolinone, benzimidazo And groups obtained by removing one hydrogen from a heterocyclic ring or an aromatic ring such as lon, indole, quinoline, carbazole, acridine, acridone, quinacridone, anthraquinone, phthalimide, quinaldine, quinophthalone, naphthalimide, and quinaldine. In the present invention, the heterocyclic ring or aromatic ring residue is any heterocyclic ring selected from the group consisting of quinacridone, benzimidazolone, indole, quinoline, carbazole, acridine, acridone, anthraquinone, phthalimide, or naphthalimide. Or the group which remove | eliminated one hydrogen from the aromatic ring is the most preferable. These partial structures (that is, the above heterocyclic ring or aromatic ring residue) may further have a substituent.

  Further, the residue of the heterocyclic ring or aromatic ring represented by P is particularly preferably a group having the same or similar structure as the heterocyclic ring of the pigment (a). For example, when the pigment (a) is a quinacridone pigment, P is preferably a heterocyclic or aromatic ring residue having the same or similar structure as the heterocyclic ring of quinacridone. The heterocyclic ring or aromatic ring residue having the same or similar structure as the heterocyclic ring of quinacridone is similar in that it has a quinacridone, acridone, or two benzene rings, a 6-membered ring connecting them, and an acyl group. It is preferably a heterocyclic or aromatic ring residue having a structure such as anthraquinone.

The specific polymer containing the repeating unit represented by the general formula (2) is obtained by introducing a monomer that gives the repeating unit represented by the general formula (2) by a homogeneous polymerization reaction in terms of production stability. It is preferable to synthesize. Monomers that give repeating units of the general formula (2) having a partial skeleton of the pigment tend to have low solubility, but by introducing them by a homogeneous polymerization reaction, the repeating units of the general formula (2) b) It can be stably introduced into the specific polymer at a desired composition ratio.
The specific polymer containing the repeating unit represented by the general formula (2) is a monomer having a structure in which P in the specific polymer (b) is obtained by removing one hydrogen from a pigment molecule (that is, the above complex Monomers having a ring or aromatic ring residue) can also be used for the synthesis. However, for example, a method of introducing a monomer giving the general formula (2) bonded only to the surface of the pigment particles (that is, a monomer having a side chain structure in the general formula (2)) by a heterogeneous polymerization reaction, The polymer having no heterocyclic or aromatic ring residue represented by P in the general formula (2) is reacted with pigment particles (that is, the monomer having the heterocyclic or aromatic ring residue). When the method of introducing P in the general formula (2) is used, it may be difficult to stably control the introduction rate of the repeating unit of the general formula (2).

The content of the repeating unit represented by the general formula (2) is 2% by mass or more with respect to the entire specific polymer (b) from the viewpoint of the adsorptivity to the pigment and the solubility in the dispersion medium and the polymerization solvent. It is preferably 40% by mass or less, more preferably 5% by mass or more and 35% by mass or less, and most preferably 5% by mass or more and 30% by mass or less.
Preferable specific examples of the monomer that gives the repeating unit represented by the general formula (2) include monomers shown below (exemplified monomers: M-1 to M-19). However, the present invention is not limited to this.

  The specific polymer (b) according to the present invention may have other repeating units other than the repeating unit represented by the general formula (1) and the repeating unit represented by the general formula (2). Good. Among these, (b) the specific polymer is a graft copolymer containing a repeating unit derived from a polymerizable oligomer having an ethylenically unsaturated double bond at the terminal (hereinafter also simply referred to as “polymerizable oligomer”). Is particularly preferred. Such a polymerizable oligomer having an ethylenically unsaturated double bond at the terminal is also called a macromonomer because it is a compound having a predetermined molecular weight.

  The specific polymer containing the repeating unit derived from the polymerizable oligomer can disperse the pigment more stably due to the high affinity of the polymerizable oligomer to the liquid medium. For this reason, it is preferable that the said polymerizable oligomer has high affinity with respect to a liquid medium. The affinity of the polymerizable oligomer in the liquid medium can be estimated by, for example, the solubility parameter proposed by HOY. (See, for example, “Journal of Paint Technology” 1970, 42, 76-78.)

  When the solubility parameter δt between the solute and the solvent is close, it is considered that the solubility of the solute in the solvent is good. Therefore, the solubility parameter of the polymerizable oligomer is 80% to 120% of the solubility parameter of the liquid medium. Is preferable, and the range of 85% to 115% is more preferable. The preferable range of the solubility parameter of the polymerizable oligomer is the same in the ink composition to which the pigment dispersion of the present invention is applied. If the value of the solubility parameter is within this range, the structure of the polymerizable oligomer is not particularly limited. When the solubility parameter of the polymerizable oligomer is within this range, the dispersion stability of the pigment contained in the pigment dispersion becomes more excellent.

The polymerizable oligomer consists of a polymer chain part and a part of a polymerizable functional group having an ethylenically unsaturated double bond at its terminal. It is preferable from the viewpoint of obtaining a desired graft polymer that such a group having an ethylenically unsaturated double bond is present only at one end of the polymer chain. As the group having an ethylenically unsaturated double bond, a (meth) acryloyl group and a vinyl group are preferable, and a (meth) acryloyl group is particularly preferable.
The polymer chain portion in the polymerizable oligomer is a homopolymer or copolymer formed from at least one monomer selected from the group consisting of alkyl (meth) acrylate, styrene and derivatives thereof, acrylonitrile, vinyl acetate, and butadiene, It is common to be ethylene oxide, polypropylene oxide, or polycaprolactone.

  The repeating unit derived from the polymerizable oligomer is preferably a repeating unit represented by the following general formula (A).

In the general formula (A), R ¹¹ and R ¹³ each independently represent a hydrogen atom or a methyl group, and R ¹² represents a linear or branched alkylene group having 1 to 12 carbon atoms (preferably a carbon atom). An alkylene group having a number of 2 to 4, which may have a substituent (for example, a hydroxyl group) and may be further linked via an ester bond, an ether bond, a sulfide bond, an amide bond, or the like.
In the general formula (A), Y represents a phenyl group, a phenyl group having an alkyl group of 1 to 4 carbon atoms, or -COOR ^{14. However, R 14} represents an alkyl group, a phenyl group, or an arylalkyl group having 7 to 10 carbon atoms having from 1 to 12 carbon atoms. Y is preferably a phenyl group or —COOR ¹⁴ in which R ¹⁴ is an alkyl group having 1 to 6 carbon atoms.
q represents 15 to 200, preferably 20 to 150, and more preferably 20 to 100.

  The polymerizable oligomer forming the repeating unit of the general formula (A) is preferably a polymerizable oligomer represented by the following general formula (3).

In general formula (3), R ¹¹ and R ¹³ each independently represent a hydrogen atom or a methyl group, and R ¹² represents a linear or branched alkylene group having 1 to 12 carbon atoms (preferably the number of carbon atoms). 2 to 4 alkylene groups, which may have a substituent (for example, a hydroxyl group) and may be further linked via an ester bond, an ether bond, a sulfide bond, an amide bond, or the like).
Y represents a phenyl group, a phenyl group having an alkyl group of 1 to 4 carbon atoms, or -COOR ^{14. However, R 14} represents an alkyl group, a phenyl group, or an arylalkyl group having 7 to 10 carbon atoms having from 1 to 12 carbon atoms. Y is preferably a phenyl group or —COOR ¹⁴ in which R ¹⁴ is an alkyl group having 1 to 6 carbon atoms.
q represents 15 to 200, preferably 20 to 150, and more preferably 20 to 100.

  Preferable examples of the polymerizable oligomer (macromonomer) include, for example, polymethyl (meth) acrylate, poly-n-butyl (meth) acrylate, poly-iso-butyl (meth) acrylate, or one of molecular ends of polystyrene ( A polymer to which a (meth) acryloyl group is bonded can be mentioned. Examples of such a commercially available polymerizable oligomer include, for example, one-end methacryloylated polystyrene oligomer (Mn = 6000, trade name: AS-6, manufactured by Toagosei Chemical Co., Ltd.), one-end methacryloylated polymethyl methacrylate. Oligomer (Mn = 6000, trade name: AA-6, manufactured by Toa Gosei Chemical Co., Ltd.), or one-end methacryloylated poly-n-butyl acrylate oligomer (Mn = 6000, trade name: AB-6, Toa Gosei Chemical) Kogyo Co., Ltd.).

  As a repeating unit derived from the polymerizable oligomer, a repeating unit represented by the following general formula (B) is also one preferred embodiment.

In the general formula (B), R ²¹ represents a hydrogen atom or a methyl group, and R ²² represents a linear or branched alkylene group having 1 to 8 carbon atoms. X ²¹ represents —OR ²³ or —OCOR ²⁴ . Here, R ²³ and R ²⁴ represent a hydrogen atom, an alkyl group, or an aryl group. n represents 2 to 200.

R ²¹ represents a hydrogen atom or a methyl group.
R ²² represents a linear or branched alkylene group having 1 to 8 carbon atoms, among which a linear or branched alkylene group having 1 to 6 carbon atoms is preferable, and an alkylene group having 2 to 3 carbon atoms is more preferable. preferable.
When X ²¹ represents -OR ²³ , R ²³ is preferably a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a phenyl group, or a phenyl group substituted with an alkyl group having 1 to 18 carbon atoms. When X ²¹ represents —OCOR ²⁴ , R ²⁴ is preferably an alkyl group having 1 to 18 carbon atoms.
n represents 2-200, 5-150 is preferable and 10-100 is especially preferable.

The polymerizable oligomer that forms the repeating unit of the general formula (B) is preferably a polymerizable oligomer represented by the following general formula (4).
(C) When a polymerizable compound is used in combination (for example, when (c) the pigment dispersion of the present invention containing the polymerizable compound is used, or (c) the polymerizable compound is added to the pigment dispersion of the present invention. When used as a curable composition), it is particularly preferred that the polymerizable oligomer is appropriately selected according to (c) the polymerizable compound.

In the general formula (4), R ²¹ represents a hydrogen atom or a methyl group, and R ²² represents a linear or branched alkylene group having 1 to 8 carbon atoms. X ²¹ represents —OR ²³ or —OCOR ²⁴ . Here, R ²³ and R ²⁴ represent a hydrogen atom, an alkyl group, or an aryl group. n represents 2 to 200.

R ²¹ represents a hydrogen atom or a methyl group.
R ²² represents a linear or branched alkylene group having 1 to 8 carbon atoms, among which a linear or branched alkylene group having 1 to 6 carbon atoms is preferable, and an alkylene group having 2 to 3 carbon atoms is more preferable. preferable.
When X ²¹ represents -OR ²³ , R ²³ is preferably a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a phenyl group, or a phenyl group substituted with an alkyl group having 1 to 18 carbon atoms. When X ²¹ represents —OCOR ²⁴ , R ²⁴ is preferably an alkyl group having 1 to 18 carbon atoms.
n represents 2-200, 5-150 is preferable and 10-100 is especially preferable.

  Examples of the polymerizable oligomer represented by the general formula (4) include polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol polypropylene glycol mono (meth) acrylate, and polytetramethylene glycol monomethacrylate. These may be commercially available products or may be appropriately synthesized.

  The polymerizable monomer represented by the general formula (4) is also available as a commercial product as described above. Commercially available products include methoxypolyethylene glycol methacrylate (trade names: NK esters M-40G, M-90G, M-230G (manufactured by Shin-Nakamura Chemical Co., Ltd.), Bremer PME-100, PME-200, PME-400. , PME-1000, PME-2000, PME-4000 (above, manufactured by Nippon Oil & Fats Co., Ltd.)), polyethylene glycol monomethacrylate (trade names: Bremmer PE-90, PE-200, PE-350, Nippon Oil & Fats Co., Ltd.) ), Lauryloxypolyethylene glycol acrylate (Brandmer ALE series, manufactured by NOF Corporation), Polypropylene glycol monomethacrylate (Blenmer PP-500, PP-800, PP-1000, NOF Corporation) Manufactured), polyethylene glycol polypro Lenglycol monomethacrylate (Brandmer 70PEP-370B, manufactured by Nippon Oil & Fats Co., Ltd.), Polyethylene glycol polytetramethylene glycol monomethacrylate (Product name: Blenmer 55PET-800, manufactured by Nippon Oils & Fats Co., Ltd) And methylene glycol monomethacrylate (trade name: BLEMMER NHK-5050, manufactured by NOF Corporation).

The polymerizable oligomer preferably has a polystyrene-equivalent weight average molecular weight (Mw) in the range of 500 to 20000, and particularly preferably in the range of 2000 to 15000.
(B) The content of the repeating unit derived from the polymerizable oligomer contained in the specific polymer is preferably 40% by mass or more and 95.5% by mass or less, and 50% by mass or more with respect to the entire specific polymer (b). 92.5 mass% or less is more preferable, and 55 mass% or more and 90 mass% or less is the most preferable. (B) Since the ratio of the repeating unit derived from the polymerizable oligomer in the specific polymer is within this range, the affinity to the liquid medium is good, and (b) the specific polymer to the (a) pigment Since it is more excellent in adsorptivity, the viscosity of the pigment dispersion and the ink composition as an application mode thereof can be effectively suppressed.

  Below, the specific example of the polymerizable oligomer preferably used in this invention is shown. Note that the present invention is not limited to this.

  (B) The specific polymer is a monomer that gives a repeating unit represented by the general formula (1), a monomer that gives a repeating unit represented by the general formula (2), and other copolymerizable with a polymerizable oligomer. It may be a copolymer with the monomer. Examples of the other copolymerizable monomer include, for example, (meth) acrylic acid alkyl ester (eg, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) ) Acrylate), (meth) acrylic acid alkyl aryl esters (eg, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, etc.), (meth) acrylic acid substituted alkyl esters (eg, glycidyl (meth) acrylate, 2- Hydroxyethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, etc.), unsaturated carboxylic acids (eg, (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid), aromatic vinyl compounds (eg, Styrene, α-methylstyrene, vinyl toluene, 2 Vinyl pyridine, 4-vinyl pyridine, N-vinyl imidazole, etc.), carboxylic acid vinyl esters (eg, vinyl acetate and vinyl propionate), vinyl cyanide (eg, (meth) acrylonitrile and α-chloroacrylonitrile), vinyl ether (cyclohexyl) Mention may be made of vinyl ether, 4-hydroxybutyl vinyl and aliphatic conjugated dienes (eg 1,3-butadiene and isoprene), among which (meth) acrylic acid substituted alkyl esters, (meth) acrylic acid alkyl esters ( A meth) acrylic acid alkylaryl ester is preferred.

  (B) In addition to the repeating unit represented by the general formula (1), the repeating unit represented by the general formula (2), and the repeating unit derived from the polymerizable oligomer, When having a repeating unit derived from another polymerizable monomer, it is preferable to have a repeating unit derived from the other monomer in a range of 30% by mass or less of all repeating units contained in the specific polymer (b). .

  (B) The preferred weight average molecular weight (Mw) of the specific polymer is preferably in the range of 10,000 to 500,000, particularly preferably in the range of 15,000 to 200,000, from the viewpoint of the dispersion stability of the pigment and the viscosity of the pigment dispersion. Here, the weight average molecular weight is a polystyrene-reduced weight average molecular weight measured by gel permeation chromatography (carrier: N-methylpyrrolidone containing 1 mM lithium bromide).

  (B) Although the example of the graft copolymer which is a suitable aspect of a specific polymer is shown below, this invention is not restrict | limited to these.

P-1) monomer S-1 / monomer M-17 / 3- (dimethylaminopropyl) acrylamide / polymerizable oligomer N-1 (AA-6, manufactured by Toagosei Co., Ltd.) (10: 15: 10: 65, (Mass ratio) copolymer (content of sulfur atoms derived from sulfide groups: 2.00% by mass)
P-2) Copolymer of monomer S-1 / monomer M-4 / 3- (dimethylaminopropyl) acrylamide / polymerizable oligomer N-1 (30: 10: 10: 50, mass ratio) (derived from sulfide group) Sulfur atom content: 6.00% by mass)
P-3) Copolymer of monomer S-1 / monomer M-17 / 3- (dimethylaminopropyl) acrylamide / polymerizable oligomer N-1 (2.5: 15: 10: 72.5, mass ratio) ( Content of sulfur atom derived from sulfide group: 0.50% by mass)
P-4) Copolymer of monomer S-1 / monomer M-10 / 3- (dimethylaminopropyl) acrylamide / polymerizable oligomer N-1 (40: 10: 10: 40, mass ratio) (derived from sulfide group) Sulfur atom content: 8.00% by mass)
P-5) Copolymer of monomer S-3 / monomer M-4 / t-butylaminoethyl methacrylate / polymerizable oligomer N-1 (25: 10: 10: 55, mass ratio) (sulfur derived from sulfide group) Atom content: 3.07% by mass)
P-6) Copolymer of monomer S-1 / t-butylaminoethyl methacrylate / polymerizable oligomer N-1 (15:25:60, mass ratio) (content of sulfur atoms derived from sulfide groups: 3. 00% by mass)
P-7) Monomer S-5 / Monomer M-4 / N, N- (Dimethylamino) ethyl methacrylate / Polymerizable oligomer N-5 (Blenmer PME-4000, manufactured by NOF Corporation) (10:10:20 : 60, mass ratio) copolymer (content of sulfur atom derived from sulfide group: 1.17% by mass)
P-8) monomer S-10 / monomer M-17 / 3- (dimethylaminopropyl) acrylamide / polymerizable oligomer N-3 (AX-707 (manufactured by Toagosei Co., Ltd.)) (10: 15: 10: 65, (Mass ratio) copolymer (content of sulfur atoms derived from sulfide groups: 1.11% by mass)
P-9) Monomer S-9 / Monomer M-4 / N, N- (Dimethylamino) ethyl acrylate / Polymerizable oligomer Polymerizable oligomer N-6 (Blemmer ALE-800, manufactured by NOF Corporation) (10: 10:10:70, mass ratio) copolymer (content of sulfur atoms derived from sulfide groups: 1.70 mass%)
P-10) Monomer S-1 / Monomer M-4 / t-Butylaminoethyl methacrylate / Methyl methacrylate / Polymerizable oligomer N-2 (AB-6, manufactured by Toagosei Co., Ltd.) (10: 10: 10: 15 : 55, mass ratio) copolymer (content of sulfur atom derived from sulfide group: 2.00% by mass)

  The pigment dispersion of the present invention may contain only one type of (b) specific polymer, or two or more types may be used in combination. The content of the specific polymer (b) in the pigment dispersion is preferably 1 part by mass or more and 100 parts by mass or less, and more preferably 5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the pigment (a). preferable.

<Other pigment dispersants>
In addition to the (b) specific polymer, a known pigment dispersant can be used in combination with the pigment dispersion of the present invention as long as the effect is not impaired. The amount added is preferably in the range of 5 to 50 parts by mass with respect to 100 parts by mass of the (b) specific polymer. Furthermore, it is also possible to use synergists (synergists) corresponding to the various (a) pigments as dispersion aids as necessary. The dispersion aid is preferably added in the range of 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the pigment (a).

<Dispersion medium>
In the pigment dispersion of the present invention, (a) a dispersion medium used for dispersing various components such as a pigment can be appropriately selected according to the purpose. For example, a solvent may be used as a dispersion medium, (c) a polymerizable compound described later may be used without a solvent (without using a solvent) as a dispersion medium, or a solvent and (c) a polymerizable compound are used in combination. May be.
When a solvent is used as the dispersion medium, a known alcohol solvent, ester solvent, ether solvent, hydrocarbon solvent or the like is preferably used as the solvent. Specifically, alkylene oxide monoalkyl ether, alkylene oxide monoalkyl ether acetate, alkylene glycol diacetate, dicarboxylic acid dialkyl ester, (meth) acrylates, divinyl ethers and the like are preferable.
When the pigment dispersion is applied to a colored curable composition (curable composition) such as an active energy ray-curable ink composition, it is preferable that the pigment dispersion does not contain a volatile solvent and has a boiling point of 180. It is preferable to use a high-boiling solvent having a temperature of at least ° C or no solvent. In such a case, it is preferable to use the polymerizable compound (c) as a dispersion medium.

<(C) Polymerizable compound>
The pigment dispersion of the present invention preferably contains (c) a polymerizable compound. As described above, particularly when the pigment dispersion of the present invention is applied to a curable composition, it is preferable to use a polymerizable compound as a dispersion medium without using a solvent (without using a solvent). It is preferable to use a polymerizable compound (c) having a low viscosity (for example, a viscosity of 30 mPa · s or less). At this time, if necessary, a small amount of solvent may be used as long as the effect is not impaired.
(C) The polymerizable compound is not particularly limited as long as it is a compound that causes a polymerization reaction by being imparted with some energy and cures, and can be used regardless of the type of monomer, oligomer, or polymer. Various known polymerizable monomers known as radically polymerizable monomers and cationically polymerizable monomers that cause a polymerization reaction by an initiation species generated from a polymerization initiator added by the above are preferable. Among these, from the viewpoint of stability, a radical polymerizable monomer and a cationic polymerizable monomer containing no oxirane compound are more preferable.

  (C) The polymerizable compound may be used in combination of one or more for the purpose of adjusting the reaction rate, cured film properties, and ink properties if the pigment dispersion is applied to the ink composition. it can. The polymerizable compound (c) may be a monofunctional compound or a polyfunctional compound. When the proportion of the monofunctional compound is large, the cured product tends to be flexible, and when the proportion of the polyfunctional compound is large, the curability tends to be excellent. Accordingly, the ratio between the monofunctional compound and the polyfunctional compound is arbitrarily determined according to the application.

(C) As a polymeric compound, the various well-known radically polymerizable monomer which produces a polymerization reaction with the start seed | species generate | occur | produced from a photoradical initiator can also be used, for example.
Examples of the radical polymerizable monomer include vinyl compounds such as (meth) acrylates, (meth) acrylamides, aromatic vinyls, N-vinyl compounds, and vinyl ethers. In the present specification, when referring to both or one of “acrylate” and “methacrylate”, when referring to both “(meth) acrylate” and “acryl” and / or “methacryl”, “(meth) acryl” And may be described respectively.

Examples of these include, for example, (meth) acrylate compounds, (meth) acrylamide compounds, vinyl ether compounds, styrene compounds, N-vinyl compounds and the like described in JP-A-2008-208190 and 2008-266561. Can be mentioned.
Among these, in the present invention, it is preferable to use one or more monomers selected from a (meth) acrylate compound, a (meth) acrylamide compound, and a vinyl ether compound as the radical polymerizable monomer. It is also preferable to use a polyfunctional polymerizable monomer having a plurality of polymerizable functional groups and a monofunctional polymerizable monomer in view of curing speed, viscosity of the pigment dispersion, and film physical properties of the print sample.

  When the pigment dispersion of the present invention contains (c) a polymerizable compound, the content of the (c) polymerizable compound is from 50% by mass to 95% by mass with respect to the total mass of the pigment dispersion from the viewpoint of curability. The following is preferable, and more preferably 55% by mass or more and 92% by mass or less.

<Oil-soluble dye>
In addition to (a) the pigment, it is also preferable to use an oil-soluble dye together with the pigment dispersion of the present invention in order to adjust the hue and increase the color density. Since the pigment dispersion of the present invention includes (b) the specific polymer, (a) not only the oxidation gas resistance to the pigment but also the oxidation gas resistance to the oil-soluble dye is improved.
Known oil-soluble dyes can be used as the oil-soluble dye. The oil-soluble dye preferably has a melting point of 200 ° C. or lower, more preferably has a melting point of 150 ° C. or lower, and still more preferably has a melting point of 100 ° C. or lower. By using an oil-soluble dye having a low melting point, the precipitation of pigment crystals in the pigment dispersion is suppressed, and the storage stability of the pigment dispersion is improved.

  Examples of the oil-soluble dye include the dyes described in paragraphs [0023] to [0053] of JP-A No. 2002-114930, and the following. Specific examples of the oil-soluble dye include C.I. I. Solvent Black 3, 7, 27, 29 and 34; I. Solvent Yellow 14, 16, 19, 29, 30, 56, 82, 93 and 162; I. Solvent Red 1, 3, 8, 18, 24, 27, 43, 49, 51, 72, 73, 109, 122, 132 and 218; I. Solvent Violet 3; C.I. I. Solvent Blue 2, 11, 25, 35, 38, 67 and 70; C.I. I. Solvent Green 3 and 7; I. Solvent orange 2 and the like are preferred. In addition, as oil-soluble dyes, Nubian Black PC-0850, Oil Black HBB, Oil Yellow 129, Oil Yellow 105, Oil Pink 312, Oil Red 5B, Oil Scallet 308, Vali Fast Blue 2606, Oil Blue B Blue GNH (manufactured by Hodogaya Chemical Co., Ltd.), Neopen Yellow 075, Neopen Magenta SE1378, Neopen Blue808, Neopen Blue FF4012, Neopen Cyan FF4238 (manufactured by BASF).

  Further, in order to further improve the discoloration, particularly resistance to oxidizing substances such as ozone and curing characteristics, it is desirable to use an oil-soluble dye having a noble (high) oxidation potential. For this reason, as the oil-soluble dye used in the present invention, those having an oxidation potential of 1.0 V (vs SCE) or more are preferably used. The oxidation potential is preferably higher, the oxidation potential is more preferably 1.1 V (vs SCE) or more, and particularly preferably 1.15 V (vs SCE) or more.

As the yellow dye, a compound having a structure represented by the general formula (Y-I) described in JP-A No. 2004-250483 is preferable.
Particularly preferred dyes are dyes represented by the general formulas (Y-II) to (Y-IV) described in paragraph [0034] of JP-A No. 2004-250483. And the compounds described in paragraph numbers [0060] to [0071] of JP-A-250483. The oil-soluble dye of the general formula (Y-I) described in the publication may be used not only for yellow but also for inks of any color such as black ink and red ink.

The magenta dye is preferably a compound having a structure represented by the general formulas (3) and (4) described in JP-A No. 2002-114930. Specific examples include paragraphs of JP-A No. 2002-114930. Examples include the compounds described in [0054] to [0073].
Particularly preferred dyes are azo dyes represented by the general formulas (M-I) to (M-II) described in paragraph numbers [0084] to [0122] of JP-A No. 2002-121414. Examples thereof include compounds described in paragraph numbers [0123] to [0132] of JP-A No. 2002-121414. The oil-soluble dyes represented by the general formulas (3), (4), (M-I) to (M-II) described in the publication are used not only for magenta but also for inks of any color such as black ink and red ink. May be.

Examples of the cyan dye include dyes represented by formulas (I) to (IV) described in JP-A No. 2001-181547, and paragraphs [0063] to [0078] of JP-A No. 2002-121414. The dyes represented by the general formulas (IV-1) to (IV-4) described above are preferred, and specific examples include paragraph numbers [0052] to [0066] of JP-A No. 2001-181547. Examples thereof include the compounds described in paragraph Nos. [0079] to [0081] of Kai 2002-121414.
Particularly preferred dyes are phthalocyanine dyes represented by general formulas (CI) and (C-II) described in paragraphs [0133] to [0196] of JP-A No. 2002-121414, A phthalocyanine dye represented by formula (C-II) is preferred. Specific examples thereof include the compounds described in JP-A No. 2002-121414, paragraph numbers [0198] to [0201]. The oil-soluble dyes of the formulas (I) to (IV), (IV-1) to (IV-4), (CI) and (C-II) are not only cyan but also black ink or green ink. The ink may be used for any color ink.

[Curable composition]
The pigment dispersion of the present invention has a characteristic that the pigment can be finely and stably dispersed even in a so-called polymerizable compound having a polymerizable functional group such as an ethylenic double bond or a cyclic ether. It is suitably used as a coloring component.
That is, the curable composition of the present invention is a colored curable composition containing the pigment dispersion of the present invention, and is cured by applying energy such as heat and light.
The curable composition of the present invention is not particularly limited as long as it contains the pigment dispersion of the present invention, but further contains a polymerization initiator and a polymerizable compound from the viewpoint of improving effectiveness. Is preferred. That is, when (c) a polymerizable compound is contained in the pigment dispersion of the present invention, it is preferable to add a polymerization initiator to the pigment dispersant of the present invention to obtain a curable compound. When the pigment dispersion uses a solvent as a dispersion medium and does not contain the above (c) polymerizable compound, the pigment dispersion of the present invention is further added with (c) a polymerizable compound and a polymerization initiator. It is preferable to use a compound.

<Polymerization initiator>
As a polymerization initiator, either a thermal polymerization initiator or a photopolymerization initiator may be used. When a thermal polymerization initiator is included, the curable composition exhibits good curability when heated. Moreover, when a photoinitiator is included, a curable composition will harden | cure by irradiation of an active energy ray. For example, when an image is formed using the curable composition of the present invention, it is preferable to instantaneously cure the curable composition in order to obtain a sharp image. For this reason, it is preferable to use a photoinitiator as a polymerization initiator in the curable composition of this invention. In addition, since the curable composition of the present invention has good dispersion stability of the pigment, it is also one of the characteristics that storage stability in the presence of a photopolymerization initiator is good.

  Here, the active energy ray is not particularly limited as long as it can impart energy capable of generating a starting species in the ink composition by irradiation, and α ray, γ ray, X ray, ultraviolet ray, Includes visible light, electron beam, etc. Among these, from the viewpoint of curing sensitivity and device availability, ultraviolet rays or electron beams are preferable, and ultraviolet rays are more preferable. Therefore, the curable composition of the present invention is preferably one that can be cured by irradiating ultraviolet rays as radiation. As a light source for generating ultraviolet rays, a light source having a light emission wavelength of 300 nm to 400 nm is preferable. Low pressure mercury lamps, high pressure mercury lamps, short arc discharge lamps, ultraviolet light emitting diodes, semiconductor lasers, fluorescent lamps and the like, which are known ultraviolet lamps, are used. A xenon lamp belonging to a high-pressure mercury lamp, a metal halide lamp, or a short arc discharge lamp belonging to a high-pressure discharge lamp is preferably used depending on the light amount and wavelength suitable for the initiator. Moreover, an ultraviolet light emitting diode is also preferably used from the viewpoint of energy saving.

The curable composition of the present invention preferably contains a polymerization initiator for radical polymerization, and more preferably contains a photopolymerization initiator.
Hereinafter, the photopolymerization initiator will be described in more detail.

<Photopolymerization initiator>
As described above, the curable composition of the present invention may contain a photopolymerization initiator. A photopolymerization initiator is a compound that generates a chemical change through the action of light or interaction with the electronically excited state of a sensitizing dye to generate at least one of radicals, acids, and bases. .

  The photopolymerization initiator is an actinic ray to be irradiated, for example, an ultraviolet ray having a wavelength of 400 nm to 200 nm, a far ultraviolet ray, a g ray, an h ray, an i ray, a KrF excimer laser beam, an ArF excimer laser beam, an electron beam, an X ray, Those having sensitivity to a molecular beam or an ion beam can be appropriately selected and used.

  As the photopolymerization initiator, those known to those skilled in the art can be used without limitation. Monroe et al., Chemical Review, 93, 435 (1993). R. S. By Davidson, Journal of Photochemistry and biologic A: Chemistry, 73.81 (1993). J. P. Fausier “Photoinitiated Polymerization—Theory and Applications”: Rapra Review vol. 9, Report, Rapra Technology (1998). M. Tsunooka et al. , Prog. Polym. Sci. , 21, 1 (1996). Can be used. In addition, chemical amplification type photoresists and compounds used for photocation polymerization described in “Organic Materials for Imaging” edited by Organic Electronics Materials Research Group, Bunshin Publishing (1993), pages 187-192 are used. can do. Further, F.I. D. Saeva, Topics in Current Chemistry, 156, 59 (1990). G. G. Maslak, Topics in Current Chemistry, 168, 1 (1993). H., et al. B. Shuster et al, JACS, 112, 6329 (1990). , I. D. F. Eaton et al, JACS, 102, 3298 (1980). A group of compounds that undergo oxidative or reductive bond cleavage through interaction with the electronically excited state of a sensitizing dye as described in the above.

  Examples of the photopolymerization initiator include (i) aromatic ketones, (ii) aromatic onium salt compounds, (iii) organic peroxides, (iv) hexaarylbiimidazole compounds, (v) ketoxime ester compounds, vi) a borate compound, (vii) an azinium compound, (viii) a metallocene compound, (ix) an active ester compound, (x) a compound having a carbon halogen bond, and the like are preferable. The photoinitiator described in 0225 can be mentioned.

  The photoinitiator as a polymerization initiator can be used individually by 1 type or in combination of 2 or more types. The content of the photopolymerization initiator is preferably in the range of 0.1% by mass to 20% by mass in the curable composition, and preferably 0.5% by mass to 15% by mass. More preferably, it is 1 mass% or more and 10 mass% or less.

The curable composition of the present invention may contain a polymerizable compound, a polymerization initiator, etc. in addition to the essential components of (a) the pigment and (b) the specific dispersant, and further a sensitizing dye and a co-sensitizer. Etc. can be used in combination according to the purpose.
As the sensitizing dye, for example, sensitizing dyes described in paragraphs [0228 to 0237] of JP2010-13630A can be preferably used.
Examples of the co-sensitizer include the co-sensitizers described in paragraphs [0238 to 0240] of JP2010-13630A.
In addition to this, for example, an ultraviolet absorber can be used from the viewpoint of improving the weather resistance of the obtained image and preventing fading.
In addition, an antioxidant can be added to improve the stability of the curable composition. Below, the additive which can be used for the curable composition of this invention is mentioned.

<Polymerization inhibitor>
A polymerization inhibitor can be added to the curable composition of the present invention. Polymerization inhibitors include phenolic hydroxyl group-containing compounds, quinones, N-oxide compounds, piperidine-1-oxyl free radical compounds, pyrrolidine-1-oxyl free radical compounds, N-nitrosophenylhydroxylamines, And a compound selected from the group consisting of cationic dyes.

  Specifically, haloquinone, p-methoxyphenol, di-t-butyl-p-cresol, pyrogallol, resorcinol, catechol, t-butylcatechol, hydroquinone monoalkyl ether (for example, hydroquinone monomethyl ether, hydroquinone monobutyl ether), Benzoquinone, 4,4-thiobis (3-methyl-6-tert-butylphenol), 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 2,2,6,6-tetramethylpiperidine and its Derivatives, di-t-butyl nitroxide, 2,2,6,6-tetramethylpiperidine-N-oxide and derivatives thereof, piperidine 1-oxyl free radical, 2,2,6,6-tetramethylpiperidine 1-oxyl Free radicals, 4- Oxo-2,2,6,6-tetramethylpiperidine 1-oxyl free radical, 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl free radical, 4-acetamido-2,2,6 6-tetramethylpiperidine 1-oxyl free radical, 4-maleimido-2,2,6,6-tetramethylpiperidine 1-oxyl free radical, 4-phosphonoxy-2,2,6,6-tetramethylpiperidine 1-oxyl Free radical, 3-carboxy-2,2,5,5-tetramethylpyrrolidine 1-oxyl free radical, N-nitrosophenylhydroxylamine cerium salt, N-nitrosophenylhydroxylamine aluminum salt, crystal violet, methyl violet, Ethyl violet , And Victoria Pure Blue BOH, and the like.

  Among the above, hydroquinone monoalkyl ethers such as hydroquinone monomethyl ether and hydroquinone monobutyl ether, 4,4′-thiobis (3-methyl-6-tert-butylphenol), 2,2′-methylenebis (4-methyl-6-t) Hindered phenols such as -butylphenol) are preferred.

  As content in the curable composition of a polymerization inhibitor, 1000-20000 ppm is preferable with respect to the total mass of a curable composition, 2000-17000 ppm is more preferable, 4000-15000 ppm is more preferable.

<Other ingredients>
The curable composition of the present invention includes various organic and metal complex anti-fading agents, and conductive materials such as potassium thiocyanate, lithium nitrate, ammonium thiocyanate, dimethylamine hydrochloride for the purpose of controlling injection properties. In addition to using salts and the like, a very small amount of an organic solvent can be added to improve the adhesion to the recording medium.

Various polymer compounds can be added to the curable composition of the present invention for the purpose of adjusting film properties. High molecular compounds include acrylic polymers, polyvinyl butyral resins, polyurethane resins, polyamide resins, polyester resins, epoxy resins, phenol resins, polycarbonate resins, polyvinyl butyral resins, polyvinyl formal resins, shellacs, vinyl resins, acrylic resins. Rubber resins, waxes and other natural resins can be used. Two or more of these may be used in combination.
A nonionic surfactant, a cationic surfactant, an organic fluoro compound, or the like may be added to the curable composition of the present invention for adjusting the liquid physical properties.
In addition to this, for example, leveling additives, matting agents, waxes for adjusting film physical properties, polymerization to improve adhesion to recording media such as polyolefin and PET, and the like. A tackifier or the like that does not inhibit the above can be contained.

[Ink composition]
The ink composition of the present invention contains at least the pigment dispersion of the present invention. The ink composition of the present invention preferably contains (c) a polymerizable compound and has a pigment concentration of 1% by mass to 15% by mass. In addition, the ink composition of the present invention is one of suitable application forms that includes (c) a polymerizable compound and / or an organic solvent.

  The ink composition of the present invention can be obtained, for example, by adding at least one of (c) a polymerizable compound and an organic solvent to (a) the pigment and (b) the specific polymer. The ink composition may contain a polymerization initiator and the like in addition to the above components. The ink composition of the present invention preferably contains (c) a polymerizable compound, and is also preferably used as an active energy ray-curable curable ink composition in combination with a photopolymerization initiator.

  When the ink composition of the present invention is used as a curable ink composition, the content of the pigment (a) with respect to the ink composition is 0.1% by mass or more and 20% by mass or less (more) in terms of color developability and viscosity. Preferably, the sum of the content of the polymerizable compound (c) and the organic solvent in the ink composition is preferably 50% by mass to 95% by mass, and more preferably. Is 55% by mass or more and 92% by mass or less.

  When the ink composition of the present invention is used as a curable ink composition, it is preferably prepared using a pigment dispersion of an embodiment containing a polymerizable compound among the pigment dispersions of the present invention. Details of each component ((a) pigment, (b) specific polymer, (c) polymerizable compound, organic solvent, etc.) that can be contained in the pigment dispersion and the preferred embodiment thereof are described in the pigment dispersion described above. As detailed in the description of the object.

One of the preferred embodiments of the ink composition of the present invention is an ink composition for inkjet.
The ink composition of the present invention can be prepared, for example, as an active energy ray-curable ink composition, and in this case, after applying the ink composition on a recording medium, it is cured by irradiation with radiation. It is preferable that the solvent is not contained or is contained in an extremely small amount even if it is contained. This is because if the solvent remains in the cured ink image, there is a concern that the solvent resistance deteriorates, the blocking property decreases, the curing failure, and the physical properties of the ink image change over time due to the remaining solvent. . From such a point of view, (c) a polymerizable compound is used as a dispersion medium, and in particular, a polymerizable compound having a low viscosity can be selected. (A) Dispersibility of pigments and the like, and improved handling of the ink composition And from the viewpoint of inkjet discharge suitability. The ink composition to which the pigment dispersion is applied is cured with high sensitivity by active radiation even when used together with the polymerizable compound (c) as described above, and the viscosity is increased due to a decrease in dispersion stability of the pigment. As described later, it is suitably used for ink jet inks used in ink jet recording methods that require viscosity stability.

When the ink composition of the present invention is used in an ink jet recording method, the ink viscosity at the temperature at the time of ejection is preferably 30 mPa · s or less, preferably 20 mPa · s or less in consideration of the ejection properties of the ink composition. More preferably, the composition ratio is suitably adjusted and determined so as to be in the above range.
The ink viscosity at 25 ° C. (room temperature) is 0.5 mPa · s to 200 mPa · s, preferably 1 mPa · s to 100 mPa · s, more preferably 2 mPa · s to 50 mPa · s. . By setting the viscosity at room temperature high, even when a porous recording medium is used, ink penetration into the recording medium is prevented, and in the case of a curable ink composition, uncured monomers are reduced. In addition to being able to reduce odor, dot bleeding at the time of ink droplet landing can be suppressed, resulting in improved image quality. When the ink viscosity at 25 ° C. is larger than 200 mPa · s, a problem occurs in the delivery of the ink liquid.

  The surface tension when the ink composition of the present invention is used for inkjet is preferably 20 mN / m or more and 40 mN / m or less, more preferably 23 mN / m or more and 35 mN / m or less. When recording on various recording media such as polyolefin, PET, coated paper, uncoated paper, 20 mN / m or more is preferable from the viewpoint of bleeding and penetration, and 35 mN / m or less is preferable from the viewpoint of wettability.

The ink composition thus adjusted is suitably used as an inkjet recording ink. When the ink composition is printed on a recording medium by an ink jet printer and a curable ink composition is used, the printed ink composition is cured by irradiation with radiation and recording is performed.
The ink composition is not limited to the curable ink composition as described above, and may be in any form as long as it contains the pigment dispersion of the present invention. That is, for example, it may be a general ink composition containing a film-forming polymer, a colorant, and a solvent, and the film is cured by removing the solvent after coating, specifically, for example, cyclohexanone. Solvent ink using a solvent such as

  The pigment dispersion of the present invention may be used in addition to image formation with ink. In particular, since the curable compound containing the pigment dispersion of the present invention is cured by irradiation with radiation such as ultraviolet rays to obtain a cured film having a high strength, for example, the curable compound is converted into an ink receiving layer (image portion) of a lithographic printing plate. ) May be used.

  Next, an ink jet recording method and an ink jet recording apparatus that can be employed when the ink composition of the present invention is applied to an ink jet ink composition will be described below.

-Inkjet recording method-
In the recording method using an ink jet printer, it is preferable to eject the ink composition after controlling the ink composition to a temperature range of 25 ° C. or more and 80 ° C. or less and setting the viscosity of the ink composition to 30 mPa · s or less. Therefore, high injection stability can be realized.
In general, a water-insoluble ink composition generally has a higher viscosity than a water-based ink, and therefore has a large viscosity fluctuation range due to temperature fluctuations during printing. This viscosity variation of the ink composition directly affects the droplet size and droplet ejection speed as it is, which causes image quality deterioration. Therefore, it is necessary to keep the ink composition temperature as constant as possible during printing. is there. The control range of the ink composition temperature is preferably set temperature ± 5 ° C., more preferably set temperature ± 2 ° C., and particularly preferably set temperature ± 1 ° C.

  One characteristic of the ink jet recording apparatus used in the ink jet recording method is that it includes a means for stabilizing the temperature of the ink composition, and the part to be kept at a constant temperature is from the ink tank (the intermediate tank if there is an intermediate tank) to the nozzle. All piping systems and members up to the injection surface are targeted.

  The temperature control method is not particularly limited, but for example, it is preferable to provide a plurality of temperature sensors in each piping portion and perform heating control according to the ink composition flow rate and the environmental temperature. Moreover, it is preferable that the head unit to be heated is thermally shielded or insulated so that the apparatus main body is not affected by the temperature from the outside air. In order to shorten the printer start-up time required for heating or to reduce the loss of thermal energy, it is preferable to insulate from other parts and reduce the heat capacity of the entire heating unit.

When the ink composition of the present invention contains a photopolymerization initiator as a polymerization initiator and further contains (c) a polymerizable compound that causes a polymerization reaction by an initiation species generated from the photopolymerization initiator, the active radiation curable type Of the ink composition.
The irradiation conditions of actinic radiation in such an ink composition will be described. A basic irradiation method is disclosed in JP-A-60-132767. Specifically, a light source is provided on both sides of the head unit, and the head and the light source are scanned by a shuttle method. Irradiation is performed after a certain period of time after ink landing. Further, the curing is completed by another light source that is not driven. In WO99 / 54415, as an irradiation method, a method using an optical fiber or a method in which a collimated light source is applied to a mirror surface provided on the side surface of the head unit to irradiate the recording unit with UV light is disclosed. In the present invention, these irradiation methods can be used.

In addition, when the ink composition of the present invention is used, it is desirable that the ink composition is heated to a certain temperature and the time from landing to irradiation is 0.01 seconds to 0.5 seconds, preferably The irradiation is performed after the elapse of 0.01 seconds to 0.3 seconds, more preferably 0.01 seconds to 0.15 seconds. Thus, by controlling the time from landing to irradiation to an extremely short time, it is possible to prevent the landing ink from bleeding before being cured.
Also, since the ink composition can be exposed to a porous recording medium before it penetrates deeper than the light source reaches, unreacted monomer remains, and as a result, odor can be reduced. Can do.
By using the inkjet recording method and the ink composition of the present invention in combination, a great synergistic effect is brought about. In particular, when an ink composition having an ink viscosity of 200 mPa · s or less at 25 ° C. is used, a great effect can be obtained.
By adopting such an ink jet recording method, the dot diameter of the landed ink can be kept constant even on various recording media having different surface wettability, and the image quality is improved. In addition, in order to obtain a color image, it is preferable to superimpose in order from the color with the lowest brightness. When inks with low lightness are overlapped later, it is difficult for the irradiation line to reach the lower ink, and inhibition of curing sensitivity, increase of residual monomers, generation of odor, and deterioration of adhesion tend to occur. Irradiation can be performed by injecting all the colors and exposing them together, but exposure for each color is preferable from the viewpoint of promoting curing.

There is no restriction | limiting in particular as an inkjet recording device used for this invention, A commercially available inkjet recording device can be used. That is, in the present invention, a printed matter can be produced by recording on a recording medium using a commercially available ink jet recording apparatus and forming an image.
According to the preferable ejection conditions, the ink composition of the present invention repeats heating and lowering, but the ink composition of the present invention has a pigment dispersibility even when stored under such temperature conditions. This is advantageous in that it is possible to suppress the deterioration of the color, to obtain excellent color developability over a long period of time, and to suppress the deterioration of the dischargeability due to the aggregation of the pigment.

[Recording medium]
The recording medium to which the ink composition of the present invention can be applied is not particularly limited, and various non-absorbing resin materials used for ordinary non-coated paper, coated paper, and so on, so-called soft packaging, or the like. A resin film formed into a film shape can be used, and examples of various plastic films include PET film, OPS film, OPP film, ONy film, PVC film, PE film, and TAC film. In addition, examples of the plastic that can be used as a recording medium material include polycarbonate, acrylic resin, ABS, polyacetal, PVA, and rubbers. Metals and glasses can also be used as the recording medium.

[Printed matter]
The printed matter of the present invention has the recording medium and the image formed on the recording medium with the ink composition. That is, for example, the ink composition of the present invention is printed on a recording medium by an ink jet printer, and then, preferably, the printed ink composition is irradiated with active energy or heated to be cured to obtain a printed matter. be able to.
The printed matter produced by the ink composition of the present invention contains a high-quality image excellent in color development and sharpness because the ink used for image formation contains fine pigment particles uniformly and stably dispersed. And is excellent in weather resistance of the image, it can be applied to a wide range of fields.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the embodiments in these examples.

<Synthesis of specific polymer>
-Synthesis of monomer S-3-
To a solution obtained by diluting 2.1 g of methionol (manufactured by Tokyo Chemical Industry Co., Ltd.) and 20.2 g of triethylamine (manufactured by Wako Pure Chemical Industries, Ltd.) with 10 g of acetonitrile, 3.1 g of 2-isocyanatoethyl methacrylate (Karenz MOI, manufactured by Showa Denko KK) And stirred at room temperature for 5 hours. The resulting solution was purified by column chromatography to obtain 4.8 g of monomer S-3.
-Synthesis of monomer M-4-
9 g (10H) acridone (Wako Pure Chemical Industries, Ltd.) 15 g and sodium hydroxide (Wako Pure Chemical Industries, Ltd.) 3.4 g are dissolved in dimethyl sulfoxide (Wako Pure Chemical Industries, Ltd.) 84 g and heated to 45 ° C. To this, 17.6 parts of CMS-P (chloromethylstyrene, manufactured by Seimi Chemical Co., Ltd.) is added dropwise, and the mixture is further heated and stirred at 50 ° C. for 5 hours. The reaction solution was poured into a mixed solution of 30 g of distilled water and 30 g of methanol (manufactured by Wako Pure Chemical Industries, Ltd.) with stirring, and the resulting precipitate was separated by filtration and washed with 300 g of a solution in which distilled water and methanol were mixed in the same mass. As a result, 17.5 g of monomer M-4 was obtained.

-Synthesis of Monomer M-17-
355.0 g of 1,8-naphthalimide (manufactured by Kanto Chemical Co., Inc.) is dissolved in 1500 mL of N-methylpyrrolidone (manufactured by Wako Pure Chemical Industries), and 0.57 g of nitrobenzene (manufactured by Wako Pure Chemical Industries, Ltd.) is added at 25 ° C Here, 301.4 g of DBU (diazabicycloundecene) (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise. After stirring for 30 minutes, 412.1 g of CMS-P was added dropwise, and the mixture was further heated and stirred at 60 ° C. for 4 hours. To this reaction solution, 2.7 L of isopropanol (manufactured by Wako Pure Chemical Industries, Ltd.) and 0.9 L of distilled water were added and stirred while cooling to 5 ° C. The obtained precipitate was filtered off and washed with 1.2 L of isopropanol to obtain 544.0 g of monomer M-17.

-Synthesis of specific polymer P-1-
2.0 g of 2- (methylthio) ethyl methacrylate, 2.0 g of 3- (dimethylamino) propylacrylamide (manufactured by Wako Pure Chemical Industries), 3.0 g of monomer M-17, polymerizable oligomer N-1 [methacryloyl at the terminal A poly (methyl methacrylate) macromonomer having a group, trade name: AA-6, manufactured by Toagosei Co., Ltd., weight average molecular weight 5300] 13.0 g, and methyl ethyl ketone 20 g were introduced into a nitrogen-substituted three-necked flask, and a stirrer ( The mixture was stirred with Shinto Kagaku Co., Ltd. (Three-One Motor) and heated to 75 ° C. while flowing nitrogen into the flask. To this, 140 mg of dimethyl 2,2′-azobis (2-methylpropionate dimethylvaleronitrile (V-601, manufactured by Wako Pure Chemical Industries, Ltd.)) was added, and the mixture was heated and stirred at 75 ° C. for 2 hours. Further, 140 mg of V-601 was added, and the mixture was stirred with heating for 3 o'clock The obtained reaction solution was poured into 1000 mL of hexane with stirring, and the resulting precipitate was heated and dried to obtain graft copolymer 1. Graft copolymer 1. 1 is the graft copolymer (monomer S-1 / monomer M-17 / 3- (dimethylaminopropyl) acrylamide / copolymer synthesized from polymerizable oligomer N-1) described above as the specific polymer P-1. is there.
As a result of measuring the weight average molecular weight (polystyrene conversion) of the graft copolymer 1 by GPC, it was 150,000, It confirmed that the specific polymer (polymer) was obtained.

-Synthesis of specific polymers P-2 to P-5 and comparative polymers 1 to 3-
Specified in the same manner as the specific polymer P-1, except that the type of monomer used in the synthesis of the specific polymer P-1 and the amount used thereof, and the amount of the polymerization initiator were changed as described in Table 1 below. Polymers P-2 to P-5 and comparative polymers 1 to 3 were synthesized. Table 1 shows the weight average molecular weight of the produced specific polymer (polymer) by GPC.
In the table, DMAPAAm is 3- (dimethylamino) propylacrylamide (manufactured by Wako Pure Chemical Industries), tBuAEMA is 2- (tert-butylamino) ethyl methacrylate (manufactured by Aldrich), and M-10 is 9-vinylcarbazole (Tokyo). Kasei Kogyo Co., Ltd.).

[Example 1]
-Preparation of ink 1-
In a 200 mL beaker, 8.0 g of (b) specific polymer P-1 (pigment dispersant) and 72.0 g of (c) polymerizable compound (phenoxyethyl acrylate, trade name: AMP-10G, Shin-Nakamura Chemical Co., Ltd.) Made). Further, 20 g of (a) pigment (benzimidazolone-based yellow pigment PY-120, trade name: Novoperperm Yellow H2G, manufactured by Clariant) was added and mixed with a magnetic stirrer for 1 hour for preliminary dispersion. The obtained dispersion was dispersed for 2.0 hours at a peripheral speed of 9.0 m / s using a bead mill (motor mill M50, manufactured by Eiger, beads: zirconia beads, diameter 0.65 mm) to obtain a mill base. Ink 1 of Example 1 was prepared by adding 10.0 g of the obtained mill base and (c) a polymerizable compound, a photopolymerization initiator, and a polymerization inhibitor described in Table 2 and mixing and stirring, followed by pressure filtration with a membrane filter. It was created.

[Examples 2 to 5, Comparative Examples 1 to 4]
-Creation of inks 2-9-
In the preparation of ink 1, (b) the type of specific polymer (pigment dispersant) used, the amount of millbase added, (c) the amount of polymerizable compound added, the amount of photopolymerization initiator added, and the polymerization inhibitor Inks 2 to 9 of Examples 2 to 5 and Comparative Examples 1 to 4 were obtained in the same manner except that the addition amount was changed as described in Table 2. In the table, “NVC” is N-vinylcaprolactam (manufactured by Aldrich), “PEA” is 2-phenoxyethyl acrylate (trade name SR339, manufactured by Sartomer), and “Irg819” is a photopolymerization initiator bis (2 , 4,6-trimethylbenzoyl) phenylphosphine oxide (trade name: Irgacure 819, manufactured by Ciba Specialty Chemicals), “ST-1” is a PEA solution of tris (N-nitroso-N-phenylhydroxylamine) aluminum salt (commercial product) Name: FIRSTCURE ST-1, manufactured by ALBEMARLE), “MEHQ” represents 4-methoxyphenol (manufactured by Tokyo Chemical Industry Co., Ltd.), and so on. In Comparative Example 2, a basic comb-type pigment dispersant Solsperse 24000GR (manufactured by Lubrizol Co., Ltd.) having no sulfur atom as a repeating unit was used as a commercially available comparative dispersant.

[Evaluation of inks 1 to 9]
The obtained ink was evaluated for ink jet according to the following evaluation method. The results are shown in Table 3. Table 3 also shows the sulfur atom content (mass%) derived from the sulfide group in the pigment dispersant (specific polymer, etc.) used.

-Viscosity-
The viscosity of each ink at 40 ° C. was measured using an E-type viscometer (manufactured by Toki Sangyo).
A: Less than 25 mPas B: 25 mPas or more, less than 30 mPas C: 30 mPas or more (a level causing a discharge problem)

-Viscosity stability-
The dispersion state after each ink was stored at 60 ° C. for 1 week was evaluated by viscosity.
A: Increase in viscosity is 2 or more and less than 10%, and there is no problem with ejection properties.
B: A level at which the ejection stability decreases when the increase in viscosity is 10% or more and less than 20%.
C: A level at which the increase in viscosity is 20% or more and the ejection stability is significantly reduced.

-Particle size-
For each mill base, a volume-based integrated 50% particle diameter D50 was measured and evaluated using a laser diffraction / scattering particle size distribution analyzer (LA920, manufactured by Horiba, Ltd.). The evaluation criteria are as follows.
A: D50 is less than 250 nm B: D50 is 250 nm or more, less than 400 nm C: D50 is 400 nm or more

-Curability-
Each obtained ink-jet ink was solid-printed on a vinyl chloride film using a piezo-type ink-jet head (CA3 head, manufactured by Toshiba Tec Corporation, printing density 300 dpi, droplet ejection frequency 4 kHz, nozzle number 64). The film was exposed with a Deep UV lamp (US-7, SP-7) under the condition of 900 mJ / cm ² energy. A print sample was obtained. Exposure was repeated until the cured film was touched with a finger and no stickiness was observed.
The number of exposures required for curing was evaluated as follows.
A: 4 times or less B: 5 times C: 6 times or more

-Ozone resistance-
Ink is coated on a vinyl chloride film, inks 1 to 9 are applied with a bar, exposed at an exposure amount of 6000 mJ / cm ^{2 with} the UV lamp, and measured with a color transmission / reflection densitometer (X-Rite 310TR, manufactured by Sakata Inx Engineering). A sample having a reflection density of 1.0 was prepared. This sample was stored for 3 days under the condition of an ozone concentration of 50 ppm, and the image density before and after exposure to ozone was measured using the reflection densitometer, and the dye residual ratio was determined and evaluated as follows.
A: When the dye residual ratio is 95% or more B: When the dye residual ratio is 90% or more and less than 95% C: When the dye residual ratio is less than 90%

  From Table 3, each inkjet ink of the Example using a specific polymer as a pigment dispersant could be stably stored even at high temperatures. The particle size is also fine. Furthermore, it turned out that it is excellent in sclerosis | hardenability of printed matter. On the other hand, in the case of the inks 6 and 7 using the comparative polymer, although the stability is good, the curability is insufficient, the stability of the ink 8 is high, and the ink 9 is hard and hard. The stability of both was lacking.

[Example 6]
-Preparation of ink 10-
In a 200 mL beaker, 9.0 g of (b) specific polymer P-1 (pigment dispersant) and 71.0 g of (c) polymerizable compound (phenoxyethyl acrylate, trade name: AMP-10G, Shin-Nakamura Chemical Co., Ltd.) Made). Further, 20 g of (a) pigment (quinacridone magenta pigment PR-42, trade name: CINQUASIA MAGEBNTA RT-355D, manufactured by Ciba Specialty Chemicals) was added and mixed with a magnetic stirrer for 1 hour to perform preliminary dispersion. The obtained dispersion was dispersed for 2.0 hours at a peripheral speed of 9.0 m / s using a bead mill (motor mill M50, manufactured by Eiger, beads: zirconia beads, diameter 0.65 mm) to obtain a mill base. After 8.0 g of the obtained mill base and (c) polymerizable compound, photopolymerization initiator, polymerization inhibitor, and oil-soluble dye D-1 shown in Table 4 were added and mixed and stirred, pressure filtration was performed with a membrane filter. Ink 10 of Example 6 was prepared.

  In the preparation of ink 10, (b) the type of specific polymer (pigment dispersant) used, the amount of millbase added, (c) the amount of polymerizable compound added, the amount of photopolymerization initiator added, the addition of a polymerization inhibitor Inks 11 to 13 of Examples 7 and 8 and Comparative Example 5 were obtained in the same manner except that the amount and the addition amount of the oil-soluble dye were changed as described in Table 4. The oil-soluble dye D-1 having the following structure was used.

[Evaluation of inks 10 to 13]
The obtained ink was evaluated for ink jet according to the following evaluation method. The results are shown in Table 5.

-Viscosity-
The viscosity of each ink at 40 ° C. was measured using an E-type viscometer (manufactured by Toki Sangyo).
A: Less than 25 mPas B: 25 mPas or more, less than 30 mPas C: 30 mPas or more (a level causing a discharge problem)

-Viscosity stability-
The dispersion state after each ink was stored at 60 ° C. for 1 week was evaluated by viscosity.
A: Increase in viscosity is 2 or more and less than 10%, and there is no problem with ejection properties.
B: A level at which the ejection stability decreases when the increase in viscosity is 10% or more and less than 20%.
C: A level at which the increase in viscosity is 20% or more and the ejection stability is significantly reduced.

-Particle size-
For each mill base, a volume-based integrated 50% particle diameter D50 was measured and evaluated using a laser diffraction / scattering particle size distribution analyzer (LA920, manufactured by Horiba, Ltd.). The evaluation criteria are as follows.
A: D50 is less than 250 nm B: D50 is 250 nm or more, less than 400 nm C: D50 is 400 nm or more

-Curability-
Each obtained ink-jet ink was solid-printed on a vinyl chloride film using a piezo-type ink-jet head (CA3 head, manufactured by Toshiba Tec Corporation, printing density 300 dpi, droplet ejection frequency 4 kHz, nozzle number 64). The film was exposed with a Deep UV lamp (US-7, SP-7) under the condition of energy of 1000 mJ / cm ² . A print sample was obtained. The cured film was touched with a finger and exposure was repeated until the stickiness disappeared.
The number of exposures required for curing was evaluated as follows.
A: 3 times or less B: 4 times C: 5 times or more

-Ozone resistance-
The ink was applied onto a vinyl chloride film with a bar of ink 10-13, exposed with an exposure amount of 6000 mJ / cm 2 with the UV lamp, and measured with a color transmission / reflection densitometer (X-Rite 310TR, manufactured by Sakata Inx Engineering). A sample having a reflection density of 1.0 was prepared. This sample was stored for 3 days under the condition of an ozone concentration of 0.5 ppm, and the image density before and after exposure to ozone was measured using the reflection densitometer, and the dye residual ratio was determined and evaluated as follows.
A: When the dye residual ratio is 95% or more B: When the dye residual ratio is 90% or more and less than 95% C: When the dye residual ratio is less than 90%

  From Table 5, each inkjet ink of the Example using the specific polymer as a pigment dispersant was not only excellent in curability but also excellent in durability under an ozone atmosphere. On the other hand, in the case of the ink 13 using the comparative polymer, the results were inferior to the examples in terms of stability and ozone resistance.

  As described above, by using a pigment dispersant having a sulfide group as a pigment dispersant, a pigment dispersion and an ink composition excellent in storage stability, ozone resistance, and curability when used as a curable ink can be obtained. It was. Since the pigment dispersion of the present invention is excellent in pigment dispersion stability, it can be ejected by an ink jet printer as in Examples, and can be suitably used.

Claims (11)

  (A) containing a pigment and (b) a repeating unit having a sulfide group, and the content of sulfur atoms derived from the sulfide group in the polymer dispersant is 0.5% by mass or more and 8.0% by mass or less. A pigment dispersion containing a polymer dispersant. The pigment dispersion according to claim 1, wherein the repeating unit having the sulfide group contained in the polymer dispersant (b) is a repeating unit represented by the following general formula (1).


[In General Formula (1), R ¹ represents a hydrogen atom or a methyl group. A represents —COO—, —CONR ² —, or a phenylene group, and R ² represents a hydrogen atom or an alkyl group. B ¹ and B ² each independently represent a single bond or a divalent linking group selected from the following <Group B>. D represents an alkyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent. n represents an integer of 1 to 3. However, at least one of the sulfur atoms in the general formula (1) is directly bonded to two carbon atoms, and at least one of the carbon atoms is directly bonded to a hydrogen atom.
<Group B>
An alkylene group which may have a substituent, a phenylene group which may have a substituent, a urethane group, a ureylene group, a carbonate group, an ether group, an ester group, an amide group, a sulfonamide group, or an imino group, Or a linking group in which 2 to 5 of these groups are combined]   3. The pigment dispersion according to claim 1, wherein the content of the repeating unit having a sulfide group is 2.5% by mass or more and 40% by mass or less with respect to the whole (b) polymer dispersant. .   The pigment dispersion according to any one of claims 1 to 3, further comprising (c) a polymerizable compound. The pigment dispersion according to claim 1, wherein the (b) polymer dispersant has a repeating unit represented by the following general formula (2).


[In General Formula (2), R ³ represents a hydrogen atom or a methyl group. J represents a single bond, —CO—, —COO—, —CONR ⁴ —, —OCO—, or a phenylene group, and R ⁴ represents a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group. W represents a single bond or a divalent linking group. P represents a heterocyclic or aromatic ring residue that is the same as or similar to the heterocyclic ring that is a partial structure contained in the organic pigment. ]   The pigment dispersion according to any one of claims 1 to 5, further comprising (d) an oil-soluble dye.   A curable composition containing the pigment dispersion according to claim 1.   An ink composition comprising the pigment dispersion according to claim 1.   The ink composition according to claim 8, which is for inkjet.   An image forming method comprising a step of forming an image on a recording medium by applying the ink composition according to claim 9 by an ink jet printer.   A printed matter in which an image is formed on the recording medium with the ink composition according to claim 8 or 9.