IMPROVING FILM UNIFORMITY OF HIGH-SOLIDS BAKING SYSTEMS

Poor film uniformity resulting from oven sagging or "thermal slump" is recognized as an obstacle to conversion from conventional to higher-solids baking coatings. Various types of additives have been employed as correctives, but have generally been found to lack efficiency or to have adverse effects on application or film properties. This paper describes a new rheology agent, a cationic oligomer, designed to improve film uniformity in a broad range of higher-solids baking coatings with minimal adverse effects. Following a brief review of rheology theory relating to oven sagging, data are presented comparing the new rheology agent versus other chemical types in the three major classifications of higher-solids baking systems: acrylic, alkyd, and polyester. Rheology curves of low shear rate viscosity versus temperature, viscosity versus shear rate, and viscosity recovery with time correlated well with results for sag resistance, and flow of applied films. The results confirmed the efficiency and minimal adverse effects of the new cationic oligomer rheology agent for improving film uniformity of high-solids baking systems.