Patent ID: 7691982

Claim:
A lignin derivative comprising a component unit derived from kraft lignin and/or its salt; a polyalkylene oxide chain; and an anionic functional group, wherein the kraft lignin and/or its salt has a functional group, wherein the polyalkylene oxide chain and anionic functional group are derived from a radical polymerizable water-soluble monomer, wherein the radical polymerizable water-soluble monomer comprises a carboxyl group as the anionic functional group, and wherein the lignin derivative is obtained by reacting the functional group of the kraft lignin and/or its salt with: an alkylene oxide addition compound of an unsaturated alcohol, which is obtained by adding 2 to 300 moles of alkylene oxides to the unsaturated alcohol, to introduce the polyalkylene oxide chain; and the radical polymerizable water-soluble monomer comprising the carboxyl group as the anionic functional group, followed by polymerization.