Urethane Polyol Modifiers for Aminoplast-Crosslinked High-Performance Coatings
Ravi Ravichandran, Vice-President, Reswearch & Development, King Industries
Water-soluble urethane polyol resins have been developed for coatings systems crosslinked with aminoplast resins. These polymer modifiers are capable of imparting superior mechanical properties, and chemical resistance in high-performance amino-formaldehyde crosslinked coating applications. They are water soluble, but do not contain neutralizing amines, surfactants or co-solvents. As resin modifiers, the hydroxyl functionality and urethane backbone of these resins allow formulators to enhance performance of aminoplast-crosslinked coatings by incorporating urethane groups into the backbone of the cured polymer matrix. Especially their water dispersibility, superior flexibility, flow and leveling properties combined with improved adhesion, salt spray, overbake, acid etch resistance and stone chip resistance make them very suitable for use as modifier for waterborne primers. In addition, development of optimal urethane polyol-to-crosslinker ratios leads to a highly crosslinked film with features such as improved corrosion and humidity resistance, as well as higher hardness with maintained flexibility. Furthermore, reactivity differences between primary and secondary hydroxyl functional urethane polyols in the crosslinking reactions and their subsequent effect on melamine self-condensation will be discussed.