Measuring the Rheological Properties of Waterborne Paint during Drying under Controlled Relative Humidity

摘要

Shear rheology has long been used to characterize flow properties of waterborne coatings. However, traditional rheological measurements do not adequately characterize the development of mechanical properties during drying. This is due to the inherent limitations of parallel plate or cone and plate testing fixtures, which do not expose the coating surface to the environment and prevent evaporation. In parallel plates, the drying process is limited by the rate of diffusion from the center of the plate to the outer edge. In this study, novel testing geometries were used to measure changes in viscoelastic properties of waterborne coatings during drying. While traditional parallel plates prevent the majority of sample from drying, these open geometries allow evaporation to occur more readily. Unlike existing methods to study rheological changes during drying, which rely on measuring relative changes of a coating on substrate, this technique provides a quantitative measurement of viscoelastic properties.