Patent ID: 6875798

Claim:
A water based ink comprising a colorant consisting of spherical fine grains colored by a color former, the spherical fine grains consisting of at least one member selected from polyolefins and other polymers containing, as a constitutional unit, at least one monomer selected from the group consisting of acrylonitrile, styrene, acrylic acid, methacrylic acid, methyl acrylate and methyl methacrylate, the colorant being contained in a proportion of 5 to 40 weight %, the color former being a leuco dye color-developed by the use of a developer, the spherical fine grains being obtained by emulsion polymerization and/or suspension polymerization and colored with a leuco dye and a developer for color-developing the leuco dye to obtain a colored ink, said ink being decolorizable or discolorable by at least one of an organic solvent and heat and wherein the ink is acidic.