Process for the preparation of pigment dispersion, pigment dispersion obtained by the same, ink jet recording ink comprising the same, and recording method and recorded material using the same

A process for the preparation of a pigment dispersion which comprises:

• (a) a pigment surface treatment step of introducing at least one hydrophilic dispersibility-providing group onto the surface of a pigment directly and/or with the interposition of a polyvalent group to form a surface treated pigment that is self-dispersible in water and that comprises said at least one hydrophilic dispersibility-providing group in an amount of not lower than 10×10−6 equivalent per gram of particulate pigment,
• (b) a dispersion step of dispersing a surface treated pigment obtained at said surface treatment step in an aqueous medium, wherein said dispersion step involves the dispersion of said surface-treated pigment in admixture with a wetting agent and water wherein the wetting agent is selected from the group consisting of acetylene glycols, acetylene alcohols, glycol ethers and alkylene glycols and is present in an amount that enhances a dispersion efficiency of particles of the surface-treated pigment in water, and
• (c) adding a resin for providing dispersibility and/or fixability during and/or after said dispersion step to form said pigment dispersion, wherein the pigment dispersion has a liquid component comprising polyvalent metal ions in a total amount of not more than 600 ppm,
• wherein the dispersion step results in a dispersion having a pigment concentration of from about 5 to 50% by weight;
• and
• wherein said resin comprises a vinyl polymer obtained by the copolymerization of (a) one or more selected from the group consisting of silicon macromer represented by the following general formula (III) and acrylamide or methacrylamide-based monomer (excluding said monomer having salt-producing groups),
• (b) a polymerizable unsaturated monomer having a salt producing group and (c) a monomer copolymerizable with these monomers in the presence of a radical polymerization initiator:
• X(Y)vSi(R)3-w(Z)W (III)
• wherein X represents a polymerizable unsaturated group;
• Y represents a divalent connecting group;
• R represents a hydrogen atom, a lower alkyl group, an aryl group or an alkoxy group, with the proviso that a plurality of R's may be the same or different;
• Z represents a monovalent siloxane polymer moiety having a number-average molecular weight of at least about 500;
• v represents 0 or 1;
• and w represents an integer of from 1 to 3.

A process for the preparation of a recording liquid comprising the steps of:

• (i) providing a pigment dispersion prepared by a process comprising
• a) a pigment surface treatment step of introducing at least one hydrophilic dispersibility-providing group onto the surface of a pigment directly and/or with the interposition of a polyvalent group to form a surface treated pigment that is self dispersible in water and that comprises said at least one hydrophilic dispersibility-providing group in an amount of not lower than 10×10−6 equivalent per gram of particulate pigment,
• b) a dispersion step of dispersing a surface-treated pigment obtained at said surface treatment step in an aqueous medium, wherein said dispersion step involves the dispersion of said surface-treated pigment in admixture with a wetting agent and water wherein the wetting agent is selected from the group consisting of acetylene glycols, acetylene alcohols, glycol ethers and alkylene glycols and is present in an amount that enhances a dispersion efficiency of particles of the surface-treated pigment in water, and
• (c) adding a resin for providing dispersibility an or fixability during and/or after said dispersion step to form said pigment dispersion, wherein the pigment dispersion has a liquid component comprising polyvalent metal ions in a total amount of not more than 600 ppm, wherein the dispersion step results in a dispersion having pigment concentration of from about 5 to 50% by weight;
• and
• (ii) subsequent to the preparation of said pigment dispersion, mixing the pigment dispersion with at least a solvent to form the recording liquid, wherein step (ii) comprises mixing the pigment dispersion with at least the solvent, a surfactant and water to form the recording liquid, and wherein the recording liquid has a solid component comprising the surface treated pigment and resin and a liquid component comprising the wetting agent, solvent, surfactant, polyvalent metal ions and water, the solid component of the recording liquid being present in an amount by weight that is less than an amount by weight of the wetting agent, solvent, surfactant and polyvalent metal ions present in the liquid component of the recording liquid.