Air convective drying and curing of polyurethane-based paints on sheet molding compound surfaces

In this study the kinetics and phase changes which occurred during the convective drying of a model car paint based on the polyurethane chemistry is described. The competition between the kinetics of the solvent removal and the phase changes, such as the gelation and/or the vitrification of the polyurethane, needs to be taken into account to avoid the defects in the resulting dried coating. The kinetics of polycondensation of a two-component polyurethane based on polyester triol and triisocyanate in a mixture of various solvents was studied as a 100 µm thick layer on sheet molding compound (SMC) and zinc plated steel plates. Differential scanning calorimetry (DSC) and Fourier-Transform infrared spectrometry (FTIR) and thermogravimetric analysis (TGA) during isothermal curings allowed us to determine the rate constants and the activation energies by using second and third order autocatalytic models.