Quinacridone pigments that are surface-functionalized with glycidyl methacrylate, maleic anhydride, or 4-methacryloxyethyl trimellitic anhydride to create a functionalized pigment. The functional groups are then activated to bond hydrophobic polymers, thereby coating the pigment with the hydrophobic polymers. The quinacridone pigments can be used for a variety of applications. They are well-suited for use in electro-optic materials, such as electrophoretic media for use in electrophoretic displays.

Polymer shells similar to those described in U.S. Pat. No. 6,822,782 can be formed on pigment particles by (a) physi-sorping a reagent comprising polymerizable groups on to the pigment particles by treating the particle with a reagent having a polymerizable or polymerization-initiating group, such that the reagent will not desorb from the particle surface when the particle is placed in a hydrocarbon medium; or (b) treating pigment particles bearing nucleophilic groups with a reagent having a polymerizable or polymerization-initiating group, and an electrophilic group, thus attaching the polymerizable or polymerization-initiating groups to the particle surface. The zeta potential of the pigment particles can be varied by a process similar to (b) but using a reagent which does not have a polymerizable or polymerization-initiating group.

Polymer shells similar to those described in U.S. Pat. No. 6,822,782 can be formed on pigment particles by (a) physi-sorping a reagent comprising polymerizable groups on to the pigment particles by treating the particle with a reagent having a polymerizable or polymerization-initiating group, such that the reagent will not desorb from the particle surface when the particle is placed in a hydrocarbon medium; or (b) treating pigment particles bearing nucleophilic groups with a reagent having a polymerizable or polymerization-initiating group, and an electrophilic group, thus attaching the polymerizable or polymerization-initiating groups to the particle surface. The zeta potential of the pigment particles can be varied by a process similar to (b) but using a reagent which does not have a polymerizable or polymerization-initiating group.

The present invention provides a process for producing a colored fine particle dispersion suitably used in a water-based ink for ink-jet printing which can be produced by an emulsion polymerization method even when using a pigment having a quinacridone skeleton, is excellent in storage stability, and can provide printed characters or images having excellent rub fastness when printed on a recording medium; the colored fine particle dispersion; and a process for producing a water-based ink for ink-jet printing which includes the colored fine particle dispersion. The present invention relates to [1] a process for producing a colored fine particle dispersion including the step of subjecting a dispersion including a pigment, a polymerizable monomer, a surfactant, a polymerization initiator and water to emulsion polymerization, the pigment being a pigment having a quinacridone skeleton; the surfactant being an anionic or nonionic surfactant; and the polymerization initiator including an anionic or nonionic azo-based compound, [2] a colored fine particle dispersion including colored fine particles having an average particle size of not less than 10 nm and not more than 300 nm, and [3] a process for producing a water-based ink for ink-jet printing, including the step of mixing the obtained colored fine particle dispersion and an organic solvent B.

The present invention provides a process for producing a colored fine particle dispersion suitably used in a water-based ink for ink-jet printing which can be produced by an emulsion polymerization method even when using a pigment having a quinacridone skeleton, is excellent in storage stability, and can provide printed characters or images having excellent rub fastness when printed on a recording medium; the colored fine particle dispersion; and a process for producing a water-based ink for ink-jet printing which includes the colored fine particle dispersion. The present invention relates to [1] a process for producing a colored fine particle dispersion including the step of subjecting a dispersion including a pigment, a polymerizable monomer, a surfactant, a polymerization initiator and water to emulsion polymerization, the pigment being a pigment having a quinacridone skeleton; the surfactant being an anionic or nonionic surfactant; and the polymerization initiator including an anionic or nonionic azo-based compound, [2] a colored fine particle dispersion including colored fine particles having an average particle size of not less than 10 nm and not more than 300 nm, and [3] a process for producing a water-based ink for ink-jet printing, including the step of mixing the obtained colored fine particle dispersion and an organic solvent B.

Provided are a pigment dispersant, a pigment dispersion, and an aqueous ink composition for inkjet that satisfactorily inhibit a magenta pigment from aggregating and makes it possible to obtain an aqueous ink applicable by printing in an inkjet system. The pigment dispersant of the present invention is a pigment dispersant for dispersing a magenta pigment, wherein a copolymer composed of a polymer alcohol and an ester, or an acrylic dispersant is dispersed in a dispersion medium, and the copolymer composed of the polymer alcohol and the ester, and the acrylic dispersant have an acid value.

Provided are a pigment dispersant, a pigment dispersion, and an aqueous ink composition for inkjet that satisfactorily inhibit a magenta pigment from aggregating and makes it possible to obtain an aqueous ink applicable by printing in an inkjet system. The pigment dispersant of the present invention is a pigment dispersant for dispersing a magenta pigment, wherein a copolymer composed of a polymer alcohol and an ester, or an acrylic dispersant is dispersed in a dispersion medium, and the copolymer composed of the polymer alcohol and the ester, and the acrylic dispersant have an acid value.

Quinacridone pigments that are surface-functionalized with glycidyl methacrylate, maleic anhydride, or 4-methacryloxyethyl trimellitic anhydride to create a functionalized pigment. The functional groups are then activated to bond hydrophobic polymers, thereby coating the pigment with the hydrophobic polymers. The quinacridone pigments can be used for a variety of applications. They are well-suited for use in electro-optic materials, such as electrophoretic media for use in electrophoretic displays.

An ink composition contains (a) a pigment represented by chemical formula 1a or chemical formula 1b, (b) a polymer having a structure unit having a diphosphonic acid group and represented by Chemical formula 2, (c) a hydrosoluble solvent, and (d) water. ##STR00001## ##STR00002## ##STR00003##

There is provided a photoelectric conversion film including a quinacridone derivative represented by the following General formula (1) and a subphthalocyanine derivative represented by the following General formula (2).

##STR00001##