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

Thin organic coated steel sheets have been electropainted for home electric al 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 wa s investigated by using an acrylic cationic electropaint for one-coat finis h. Measurement an initial current of electropainting, observation of uncure d as-deposited paint film by video microscope system and counting of conduc tive points of organic coated steel sheets were conducted. When resin coati ng weight of organic coated steel sheets is large, bubbles are left in the paint firm, the paint film thickness increase largely and surface of the pa int film becomes rough. The reason is that microscopic conductive points of the organic coated steel sheets decrease and electrodeposited paint film b ecomes random in thickness at the initial stage of electropainting. So the electropainting current concentrates locally on the spots where the paint f ilm is thin, then thick and porous paint film which contains bubbles is for med. It is clear that the electropaintability of organic coated steel sheet s depends on the morphology of initially deposited paint film. Therefore, i t is possible to improve electropaintability by controlling the microscopic conductive points of resin coating.