DRYING OF SOLVENT-BORNE POLYMERIC COATINGS - II - EXPERIMENTAL RESULTS USING FTIR SPECTROSCOPY

The drying behavior of polymeric solvent coatings is investigated usin g FTIR spectroscopy. Poly(vinyl acetate) was dissolved in methanol or benzene or a mixture of these two solvents and subsequently cast on an aluminum substrate. The samples were dried at temperatures of 25 and 40 degrees C and air velocities of 5-70 cm s(-1) parallel to the coati ng surface. The drying time of a polymeric coating is highly dependent on the temperature, and increases with the square of the film thickne ss. The gas-side mass transfer coefficient is less important. This can be explained by a strong decrease in the diffusion coefficient with d ecreasing solvent content. After a short drying time the coating surfa ce is almost dry, forming a barrier for the solvent diffusing from lay ers below. This barrier is the decisive mass-transfer resistance. (C) 1998 Elsevier Science S.A.