Effect of resin coating on electropainting behaviour of organic coated steel sheets

Thin organic coated steel sheets have been electropainted for home electrical appliances. Therefore, it is important to make clear the exact mechanism of electropainting on organic coating. In this study, the effect of resin coating on electropainting behaviour of thin organic coated steel sheets was investigated by using an acrylic cationic electropaint for one-coat finish. Measurement an initial current of electropainting, observation of uncured as-deposited paint film by video microscope system and counting of conductive points of organic coated steel sheets were conducted. When resin coating weight of organic coated steel sheets is large, bubbles are left in the paint film, the paint film thickness increase largely and surface of the paint film becomes rough. The reason is that microscopic conductive points of the organic coated steel sheets decrease and electrodeposited paint film becomes random in thickness at the initial stage of electropainting. So the electropainting current concentrates locally on the spots where the paint film is thin, then thick and porous paint film which contains bubbles is formed. It is clear that the electropaintability of organic coated steel sheets depends on the morphology of initially deposited paint film. Therefore, it is possible to improve electropaintability by controlling the microscopic conductive points of resin coating.