PRETREATMENT FOR PAINTING BY CATIONIC ELECTRODEPOSITION

摘要

PURPOSE:To prevent the occurrence of defects on the appearance of a galvanized steel sheet, e.g., cratering during painting by cationic electrodeposition by applying a soln. of a water soluble cationic thermosetting resin to the steel sheet to coat the steel sheet with an uncured dried film on the resin before the painting. CONSTITUTION:When a galvanized steel sheet is painted by cationic electrodeposition, a soln. of a water soluble cationic thermosetting resin such as epoxy resin contg. quat. ammonium groups is previously applied to the steel sheet by spraying or other method using no electric current. The steel sheet is preferably treated with a phosphate before the soln. is applied. An excess of the soln. applied is then removed and a formed film is dried without curing to coat the steel sheet with an uncured dried film of the resin having 0.5-20g/m2 thickness. By this pretreatment, cratering is prevented during painting by cationic electrodeposition.