MANUFACTURING METHOD OF URETHANE MODIFIED POLYESTER RESIN, ITS PRODUCT MANUFACTURED THEREBY AND A PAINT COMPOSITION FOR PCM CONTAINING THE SAME

摘要

An urethane-modified polyester resin is provided to solve problems of discoloration and self polymerization of resin by a remaining -NCO group due to the delay of reaction time and to ensure excellent chemical resistance and corrosion resistance. A method for manufacturing a urethane-modified polyester resin for under coating of a pre-coated metal steel sheet comprises a step of addition reaction at 100-120°C in the amount of 30-70% of isocyanate compound to a polyester resin based on an equivalent ratio of the polyester resin. The polyester resin is formed by condensation between a glycol component and an acid component and has a hydroxyl group value of 10-30 mgKOH/g and an average molecular weight of 20,000 or more.