FORMATION OF COATING FILM

PURPOSE:To form an org. coating film having superior heat resistance by depositing colloidal particles on an electrically conductive base material by electrophoresis in a colloidal aq. soln. contg. polyamic acid resin as a precursor of polyimide resin and an arom. maleimide compd. and by carrying out imidation and cross-linking by heating. CONSTITUTION:Polyamic acid resin obtd. by allowing 2,2-bis[4-(3-aminophenoxy) phenyl]propane to react with 3,3',4,4'-benzophenonetetracarboxylic anhydride in N,N-dimethylacetamide is mixed with arom. bismaleimide resin obtd. by allowing 2,2-bis[4-(3-aminophenoxy)phenyl]propane to react with maleic anhydride and water is added to the mixture and stirred to obtain a colloidal aq. soln. for electrophoresis. Colloidal particles are deposited on a body to be treated such as an Al member as the anode by electrophoresis in the colloidal aq. soln. and the Al member is washed and heated to carry out imidation and cross-linking. An org. coating film having superior heat resistance at high temp. is formed on the surface of the Al member.