TWI713538B

The present invention provides a steel sheet surface treatment agent containing an aqueous urethane resin composition obtained by dispersing in (C) an aqueous medium a urethane resin obtained by reacting (A) a urethane prepolymer having an isocyanate group and (B) a terminator containing (b1) an alcohol solvent, wherein the urethane prepolymer (A) is obtained by reacting (a1) a polyol and (a2) a polyisocyanate containing an aromatic polyisocyanate, wherein the boiling point of the alcohol solvent (b1) is in the range of from 150 to 350°C and wherein the number average molecular weight of the alcohol solvent (b1) is 500 or less. The steel sheet surface treatment agent can form a coating film having excellent heat yellowing resistance, chemical resistance, and corrosion resistance and being capable of preventing deterioration of various types of metal substrates.