INVESTIGATION OF THE INTERNAL REFLECTANCE AND PREDICTION OF INFRARED DIFFUSE-REFLECTANCE OF THE POLYMERIC COATING ON ALUMINUM SUBSTRATE

This study employs the ray tracing method to develop and analyze mathe matical formulae for the IR diffuse reflectance of the polymeric coati ng on a metal substrate. The effects of the thickness and the absorpti on property of the polymer film on the internal reflectance are also i nvestigated. In addition, the diffuse reflectance of the coating/subst rate system which is irradiated with a perfect diffuse source is formu lated as well. Analysis results indicate that the internal reflectance of the internal front surface (polymer/air interface) is not a consta nt which depends on the film thickness and absorption property. Closel y examining the internal multiple reflections between the front and th e substrate surface reveals that the diffuse reflectance of the coatin g/substrate system can be obtained by summing the fractions of rays em erging from the front surface. By knowing the refractive index and the extinction coefficient of the polymer, the diffuse reflectance of the coating/substrate system can be calculated by the formulae presented here. In addition an alkyd resin coating/aluminum substrate system is also implemented to compare the experimental reflectances with the cal culated ones. According to the comparisons the analysis and developed formulae are guile effective. (C) 1998 Elsevier Science B.V.