Patent No. U.S. . 7,108,728 B2
Taisei Chemical Industries has been granted a patent for a process for producing a colorant comprised of a hydrophobic coloring matter substance, an amphoteric electrolyte and water. The process is comprised of dissolving and/or dispersing the hydrophobic coloring matter substance in an organic solvent miscible with water to obtain a coloring matter substance solution in which the concentration of the hydrophobic coloring matter substance is in the range of 1-10% weight; contacting the coloring matter substance solution with an anion exchange resin and/or a cation exchange resin to obtain a purified coloring matter substance solution; adding dropwise, while stirring, the purified coloring matter substance solution into a solution containing an amphoteric electrolyte, being an amino acid or an amphoteric oligomer having a weight average molecular weight of 1,000 or less, in de-ionized water at a concentration of 10% weight or less to obtain a water-containing organic solvent solution of the purified coloring matter substance; removing the organic solvent component from the water-containing organic solvent solution of the purified coloring mailer substance by an azeotropic distillation of water and said organic solvent, while supplying de-ionized water and/or an organic solvent if necessary, under an ambient or a reduced pressure, to obtain an aqueous solution containing the coloring matter substance and the amphoteric electrolyte; subjecting said aqueous solution containing a coloring matter substance and an amphoteric electrolyte to high-speed centrifugation; and collecting as a product, a resulting aqueous colorant composition containing the coloring matter substance and an amphoteric electrolyte.