U.S. 8,163,839 B2
Dainichiseika Color and Chemicals Mfg. Co. has received a patent for a process for the production of a pigment dispersant comprised of polymerizing (a′) 5% to 30% weight of at least one of an aromatic vinyl monomer and a heterocyclic vinyl monomer, (b′) 10% to 30% weight of a monomer having an acid group, (c′) 40% to 80% weight of a (meth)acrylate ester monomer, and (d′) 5% to 30% weight of a monomer having a poly(C2-6-alkylene glycol) chain or mono(C1-22-alkyl) ether chain of said glycol, said poly(C2-6-alkylene glycol) chain or mono(C1-22-alkyl) ether chain having a number average molecular weight of from 150 to 1,500, a sum of the monomers (a′) to (d′) amounting to 100% weight, with a polymerization initiator in a water-soluble organic solvent to obtain a polymerization mixture with a resultant polymer contained therein,
combining and mixing the polymerization mixture and water together to emulsify or dissolve the polymer in the water such that an emulsion or solution of the polymer is obtained, adding an acid to the emulsion or solution of the polymer to have the polymer precipitated such that a mixture of water and the polymer is obtained, and then, heating the mixture to a temperature of not lower than a cloud point of the polymer, wherein the polymerization initiator is such that a coupling product of radical decomposition products of the polymerization initiator has a boiling point of not lower than 250° C.