Abstract
In order to see the effect of phosphate coatings on the adhesibility of electro-deposited paint films to steel sheet, the solubility of Hopeite (Zn3(PO4)2⋅4H2O) on the electro-galvanized steel sheet (E. G.) was investigated compared with the solubility of Phosphophyllite (Zn2Fe(PO4)2⋅4H2O) on the cold rolled steel sheet (C. R.). The solubility of hopeite was found in pH region of 2-12 not different from that of Phosphophyllite. The adhesibility of cathodic electro-deposited paint films to C. R. with phosphate coatings of different Phosphophyllite/(Hopeite+Phosphophyllite) (P/(P+H)) was also examined by some testing methods. The forming testing method showed the different result from that by the uniformly testing method, and EPMA images showed the less remained phosphorus on the film stripped surface of C. R. with decreasing P/(P+H) ratio. The adhesibility seems to decrease with the decrease of P/(P+H) ratio.
