PRETREATMENT FOR PAINTING BY CATIONIC ELECTRODEPOSITION

摘要

PURPOSE:To improve the adhesion of a plate-shaped metallic structure to a paint film formed by cationic electrodeposition by immersing the structure in a phosphating soln. contg. essential components such as phosphate ions at a specified concn. each and further contg. Mn ions to form a phosphate film. CONSTITUTION:A phosphating soln. contg. 0.2-2.0g/l Mn ions besides F ions, phosphate (PO4) ions and 0.7-2.2g/l Zn ions and having 0.6-1.4 point free acidity (FA) is prepd. so as to satisfy (9-64):1 ratio of total F ions (g/l)Xphosphate ions (g/l):Zn ions (g/l) and (7-33):1 ratio of phosphate ions:Zn ions. A plate-shaped metallic structure composed essentially of a cold rolled steel sheet and an alloyed galvanized steel sheet is immersed in the phosphating soln. Ni ions may be added to the soln. as required. By this pretreatment, superior adhesion to a paint film formed by cationic electrodeposition can be provided to the structure.