Investigation on the Water Transport in Organic

Coating by Capacitance Measurement

Abstract

In order to scrutinize water absorption process in coatings closely duplicating the actual state of the film on a substrate, a system for monitoring the variation of the parallel capacitance of coatedelectrode in water has been devised. A micro-computer is involved for the data acquisition and theirprocessing. Water content in the film can be calculated from the parallel capacitance by Brasher's equation.
A coating composed of epoxy/blocked polyisocyanate was examined. When baked at lowest temperature, the Arrhenius plot exhibited good linear relationships as for permeability, diffusion and solubility coefficient. With the specimens baked at the higher temperatures, however, data are fluctuated above and breaks of gradients are perceivable. These can be ascribed to the glass transition temperature with the highly crosslinked films existent in the ranges where the present measurement were made.