Despite the large amount of research of Cr(VI)-free coated steel sheets being carried out for many years, there have never been products that could provide corrosion resistance and electric conductivity. In this study, as a basic research on Cr(VI)-free thin organic coatings, effects of composition and thickness of organic coatings on corrosion resistance and electric resistance were investigated.
(1) Regarding on barrier effect of organic resins, relationship between O2 permeability coefficient and corrosion resistance was investigated. Amine-modified epoxy resin, providing the lowest coefficient of O2 permeability, showed the best corrosion resistance. (2) In order to provide self-healing effect, effect of silica and phosphate compounds contained in organic coatings on corrosion resistance was investigated. Colloidal silica improved corrosion resistance at 20 to 30 wt%, while fumed silica deteriorated it. A condensed phosphate compound also provided good corrosion resistance. (3) Effect of coating thickness and compositions on electric resistance was investigated. As the coating thickness increased, the electric resistance was deteriorated. However it did not depend on coating compositions.
From the facts described above, a basic concept of Cr(VI)-free thin organic coatings was obtained. In order to provide good corrosion resistance and electric resistance, thin organic composite coatings with barrier effect and self-healing effect are necessary.
