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 chem istry is described. The competition between the kinetics of the solven t removal and the phase changes, such as the gelation and/or the vitri fication of the polyurethane, need to be taken into account to avoid t he defects in the resulting dried coating. The kinetics of polycondens ation of a two-component polyurethane based on polyester triol and tri isocyanate in a mixture of various solvents was studied as a 100 mu m thick layer on sheet modeling compound (SMC) and zinc plated steel pla tes. Differential scanning calorimetry (DSC) and Fourier-Transform inf rared spectrometry (FTIR) and thermogravimetric analysis (TGA) during isothermal curings allowed us to determine the rate constants and the activation energies by using section and third order autocatalytic mod els.