Water-base ink composition and process for producing the same

Claim 2

A water-base ink composition comprising: a colorant which is either sparingly soluble or insoluble in water; a solid solvent which is solid at room temperature and soluble in water and can dissolve, in the form of a hot melt or aqueous solution thereof, the colorant and, can form a solid solution together with the colorant; and water.

Claim 3

The water-base ink composition according to claim 1, wherein the colorant is selected from the group consisting of an oil-soluble dye, a disperse dye, and a pigment readily soluble in the solvent.

Claim 4

The water-base ink composition according to claim 1, wherein the solid solvent has a melting point of 30° C. or above.

Claim 5

The water-base ink composition according to claim 1, wherein the solid solvent is selected from the group consisting of carboxylic acid derivatives, urea derivatives, and alkylene carbonates.

Claim 6

The water-base ink composition according to claim 4, wherein the carboxylic acid derivatives are represented by the following formula (I): R.sup.1 --CO--NH--R.sup.2 (I) wherein R 1 represents an unsubstituted or substituted alkyl or unsubstituted or substituted alkoxy group, or a five- or six-membered heteroaromatic ring containing one nitrogen atom, R 2 represents H or an unsubstituted or substituted alkyl group, or R 1 and R 2 are an unsubstituted or substituted alkylene group having 3 to 8 carbon atoms.

Claim 7

The water-base ink composition according to claim 4, wherein the urea derivatives are represented by the following formula (II): R.sup.3 --NH--CO--NH-R.sup.4 (II) wherein R 3 and R 4 each independently represent H or an unsubstituted or substituted alkyl group, or R 3 and R 4 combine with each other to form an alkylene group having 2 to 6 carbon atoms.

Claim 8

The water-base ink composition according to claim 4, wherein the alkylene carbonates are represented by the following formula (III): R.sup.5 --O--CO--O--R.sup.6 (III) wherein R 5 and R 6 each independently represent H or an unsubstituted or substituted alkyl group, or R 5 and R 6 combine with each other to form an alkylene group having 2 to 6 carbon atoms.

Claim 9

The water-base ink composition according to claim 1, wherein the solid solvent is selected from the group consisting of lactamide, acetamide, N-methyl acetamide, methyl carbamate, ethyl carbamate, ε-caprolactam, δ-valerolactam, α-amino-ε-caprolactam, glycolic amide, dimethylol urea, ethylene urea, nicotinamide, and ethylene carbonate.

Claim 10

The water-base ink composition according to claim 8, wherein the solid solvent is selected from the group consisting of lactamide, ε-caprolactam, methyl carbamate, δ-valerolactam, and ethylene carbonate.

Claim 11

The water-base ink composition according to claim 1, wherein the solid solvent is contained in an amount of 1 to 50% by weight of the ink composition.

Claim 12

A process for producing a water-base ink composition according to claim 1, comprising the steps of: heating the solid solvent at the melting point or above to form a hot melt and dissolving a colorant in the melt to prepare a colorant solution; mixing the colorant solution in a hot melt form with water or an aqueous solution containing a water-soluble organic solvent to prepare a dispersion in which particles of the colorant are dispersed; and adding optional components, for forming an ink composition, to the dispersion.

Claim 13

A process for producing a water-base ink composition according to claim 1, comprising the steps of: dissolving a colorant in an aqueous solution to prepare a colorant solution wherein the aqueous solution is an aqueous saturated solid solvent solution or an aqueous solid solvent solution having a high concentration close to the saturation; mixing the colorant solution with water or an aqueous solution containing a water-soluble organic solvent to prepare a dispersion in which particles of the colorant are dispersed; and adding optional components, for forming an ink composition, to the dispersion.

Claim 14

A process for producing a water-base ink composition according to claim 1, comprising the steps of: heating the solid solvent at the melting point or above to form a hot melt and dissolving a colorant in the melt to prepare a colorant solution; cooling the colorant solution to prepare a colorant solid solution containing the colorant and the solid solvent; dissolving the colorant solid solution in water or an aqueous solution containing a water-soluble organic solvent to prepare a dispersion in which particles of the colorant are dispersed; and adding optional components, for forming an ink composition, to the dispersion.

Claim 15

A process for producing a water-base ink composition according to claim 1, comprising the steps of: mixing a solid solvent with a volatile organic solvent, dissolving a colorant in the mixture to prepare a colorant solution, and removing the volatile organic solvent by evaporation to prepare a colorant solid solution; dissolving the colorant solid solution in water or an aqueous solution containing a water-soluble organic solvent to prepare a dispersion in which particles of the colorant are dispersed; and adding optional components, for forming an ink composition, to the dispersion.

Claim 16

A water-base ink composition comprising: a) a colorant which is either sparingly soluble or insoluble in water; said colorant being present in the composition in an amount of 0.5 to 20% by weight, said colorant comprising particles having an average particle diameter of from 10 nm to 10 μm; b) a solid solvent which has a melting point of 30° C. or above and is soluble in water and can dissolve, in the form of a hot melt or aqueous solution, the colorant and can form a solid solution with the colorant, said solid solvent being present in the composition in an amount of 1 to 50% by weight and being selected from the group consisting of carboxylic acid derivatives, urea derivatives and alkylene carbonates; and c) water present in the composition in an amount by weight which exceeds the amount of the solid solvent.

Claim 17

A water-base ink composition comprising: a) a colorant which is either sparingly soluble or insoluble in water; said colorant being present in the composition in an amount of 0.5 to 20% by weight, said colorant comprising particles having an average particle diameter of from 10 nm to 10 μm; b) a solid solvent which has a melting point of 30° C. or above and is soluble in water and can dissolve, in the form of a hot melt or aqueous solution, the colorant and can form a solid solution with the colorant, said solid solvent being present in the composition in an amount of 1 to 50% by weight and being selected from the group consisting of carboxylic acid derivatives, urea derivatives and alkylene carbonates; and c) water present in the composition in an amount by weight which exceeds the amount of the solid solvent.

Claim 18

The water-base ink composition according to claim 15, wherein the composition consists essentially of said colorant, solid solvent and water.

Claim 19

The water-base ink composition according to claim 15, wherein the composition is substantially free of any dispersant.

Claim 20

The water-base ink composition according to claim 17, wherein the solid solvent is a carboxylic acid derivative represented by the following formula (I): R.sup.1 --CO--NH--R.sup.2 (I) wherein R 1 represents an unsubstituted or substituted alkyl or unsubstituted or substituted alkoxy group, or a five or six-membered heteroaromatic ring containing one nitrogen atom, represents H or an unsubstituted or substituted alkyl group, or R 1 and R 2 are an unsubstituted or substituted alkylene group having 3 to 8 carbon atoms.

Claim 21

The water-base ink composition according to claim 17, wherein the solid solvent is a urea derivative represented by the following formula (II): R.sup.3 --NH--CO--NH--R.sup.4 (II) wherein R 3 and R 4 each independently represent H or an unsubstituted or substituted alkyl group, or R 3 and R 4 combine with each other to form an alkylene group having 2 to 6 carbon atoms.

Claim 22

The water-base ink composition according to claim 17, wherein the solid solvent is an alkylene carbonate represented by the following formula (III): R.sup.5 --O--CO--O--R.sup.6 (III) wherein R 5 and R 6 each independently represent H or an unsubstituted or substituted alkyl group, or R 5 and R 6 combine with each other to form an alkylene group having 2 to 6 carbon atoms.