Film formation from cationic electropaint systems containing resins with different glass transition temperature

Some phenomena in the deposition process of electropainting have not been w ell elucidated till now. In this paper, to investigate an influence of glas s transition temperature (T-g) on film formation, the deposited film was ob served with an atomic force microscope and the electrochemistry was investi gated, using two kinds of cationic acrylate resin with different T-g (methy l methacrylate system (MMAs): T-g = 70 degreesC, and methyl acrylate system (MAs): T-g = 5 degreesC). Electrodeposition was performed under constant v oltage or current condition. At constant voltage, the deposition behavior i n the two resin systems differed extremely. The MMAs, the resin with high T -g, produced a high resistance film. The MAs, the resin with low T-g, was d eposited forming a film at a voltage lower than 20 V At constant current, t he film formation did not result in a rise in voltage. It behaved like a co nductive film. When the resin with high T-g was used, particulate deposits were observed by AFM even in the induction period. The resin with low T-g f ormed flat deposits. These results suggest that paint deposition is initiat ed once electrolysis of water starts. In addition, there are two types of f ilm formation on the cationic electropainting: high resistance film formati on for the resin with high T-g, and ion-permeable film formation for the re sin with low T-g. In both cases, film growth occurs at the film/bulk soluti on interface. Published by Elsevier Science B.V.