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. UPRES-A CNRS Q-5007, CPE Lyon, Bat. G308, Campus de la Doua, 69622 Villeurbanne Cedex, France UMR CNRS 5627, Institut National des Sciences Appliquées de Lyon, Bat. 403, 69621 Villeurbanne Cedex, France