Лако-красочные материалы — производство

A moisture-curable urethane resin is simply a urethane prepolymer with free — NCO groups. Typically made from aromatic isocyanates, the free — NCO group of such a resin, when exposed to the envi­ronment after application, will react with ambient moisture and produce urea linkages between prepolymer chains, resulting in formation of the cured coating (Figure 2.64).

The type of isocyanate, MW and — NCO functionality are controlled to balance drying time and film properties. The drying time is signi-

ficantly dependent on the ambient moisture content, temperature and film thickness. Coatings applied at higher film thickness under high humidity frequently show a bubbling defect due to formation of CO2 gas during curing that gets trapped in the film. Due to free — NCO content, such systems have limited shelf-life.