Method for producing colorant excellent in color development
There is provided a method for producing colorants which can exhibit excellent color development even in a small amount and are low in thixotropy. The constituent feature of the present invention comprises: enhancing the molecular extinction coefficient of the coloring matter substance by ion exchanging method, to afford a room for increasing B (resin) of P/B; then a composition is designed and employed to enhance the effect increasing the polar group concentration which is a role of resin and the quality of the effect; it thus becomes possible to achieve the limit value of the molecular extinction coefficient as much as possible and to eliminate the factors adversely affecting the present process.
1. A method for producing a colorant comprising:
contacting a dispersion of a powdery coloring matter substance in deionized water with an anion exchange resin and/or a cation exchange resin to subject the dispersion to ion exchanging until an electrical conductivity of the dispersion reaches 25 μS/cm or lower, thereby obtaining a purified coloring matter substance;
contacting with an anion exchange resin and/or a cation exchange resin an aqueous solution or organic solvent solution of a binder resin prepared so that a carboxyl group concentration or a sum of a carboxyl group concentration and a hydroxyl group concentration is 0.001 mol/ml or higher, to obtain a purified binder resin solution;
kneading the purified coloring matter substance and the purified binder resin solution to obtain a liquid colorant precursor; and
contacting the liquid colorant precursor with an anion exchange resin and/or a cation exchange resin.
2. The method according to claim 1 , further comprising:
subjecting the liquid colorant precursor to an ultra-high speed centrifugal separation at 5000-15000 rpm after the contacting with the anion exchange resin and/or the cation exchange resin.
3. A method according to claim 1 , wherein the binder resin is a copolymer of at least one polymerizable monomer containing a carboxyl group and at least one polymerizable monomer containing neither carboxyl group nor hydroxyl group, a copolymer of at least one polymerizable monomer containing a carboxyl group, at least one polymerizable monomer containing a hydroxyl group and at least one polymerizable monomer containing neither carboxyl group nor hydroxyl group, or a mixture thereof.