Structure and property development during solidification of VOC compliant automotive refinish clearcoats

A model volatile organic compound (VOC) compliant two component (2K) acrylic polyol refinish clearcoat was prepared and used to study the effects of a cellulose-based additive on drying, curing, rheology and stress development at room temperature. Results were compared with commercially available VOC compliant and traditional non-compliant clearcoats. Most of the drying of the low VOC coatings occurred before appreciable (20%) crosslinking. Tensile stress developed in the same timeframe as drying and then relaxed over a longer time scale. All coatings had relatively low levels of peak stress (<0.25 MPa) compared to other polymer coatings. Model low VOC coatings prepared with the additive had higher peak stresses than those without the additive. In addition, rheological data showed that the additive resulted in greater viscosity buildup after application. Both effects are attributed to the high glass transition temperature of the additive (∼70 °C).