REDUCING OR AVOIDING SURFACE IRREGULARITIES IN ELECTROPHORETIC PAINTING OF PHOSPHATED METAL SURFACES

摘要

The phenomenon of 'mapping' (surface defects) after electrophoretic painting over phosphate conversion coatings passivated with hexavalent chromium containing passivating compositions can be avoided or reduced by keeping the surface being treated constantly wet from the time it is conversion coated until it is electrophoretically painted, by preceding the passivating step by treatment with an aqueous liquid treatment composition comprising at least one of the following components: (A) a water soluble and/or water dispersible polymer with a weight average molecular weight of at least 500; (B) fluorometallic acids and anions thereof, the molecules of which consist of (i) at least one atom of boron, silicon, zirconium, iron, aluminum, or titanium, (ii) at least four fluorine atoms, and, optionally, (iii) one or more atoms of oxygen, hydrogen, or both; (C) zirconium salts of ethylenediamine tetraacetic acid; and (D) alkali metal and ammonium zirconyl carboxylates and carbonates; or by replacing the chromium containing passivating composition with an aqueous liquid treatment composition of the same type as described above.