Temperature dependence of rheological behavior of a metallic automotive waterborne basecoat

The temperature dependence of the rheological behavior of a metallic automotive waterborne basecoat was studied with the temperature ranging from 10 to 45 °C. It is found that the paint exhibits both shear thinning and thixotropic behavior. The degree of shear thinning and thixotropy increases as the temperature increases. Small amplitude oscillatory shear tests show that the basecoat displays more elasticity at higher temperature. Both steady shear viscosity and dynamic properties indicate that the paint gradually develops a network structure as the temperature increases, which leads to increased viscosity. The viscosity at very low shear rate at 45 °C is about 500 times greater than that at 20 °C. The high shear viscosity decreases with the increase of temperature in the range of 10-35 °C, and then increases with temperature up to 45 °C. The Ford cup #4 measurements show good agreement with the steady-state viscosity at high shear rate.