抄録
Factor controlling the wet adhesion of the paint film was investigated using various Fe content of Zn-Fe electroplated steel sheets. The wet adhesion of the paint film on Zn-Fe electroplated steel sheets with phosphate film increased with the increase of Fe content. And Zn electroplated steel sheet showed better wet adhesion than Zn-Fe electroplated steel sheets with a little content of Fe. Without phosphate film, wet adhesion of the paint film on Zn-Fe and Zn electroplated steel sheets were excellent. The structure and Fe content of phosphate film changed with Fe content of Zn-Fe electrodeposit. Fe content lower than 30% correspond to the resion of Hopeit, Zn3(PO4)2·4H2O and that higher than 60% to phosphophyllite, Zn2Fe(PO4)2·4H2 O. Fe content of phosphate film increases with the increase of Fe content of Zn-Fe electrodeposits (ED). The higher Fe content of phosphate film brings about good wet adhesion. Phosphate film changes Zn phosphate di hydrate by loosing two crystallin waters during ED coating baking process. In water immersion, they may recover the lost water. The stability of Zn phosphate di hydrate in other words, the non-recoverability, increased with the increase of Fe cotent. It is seemed that the stability of phosphate film plays the decisive role in wet adhesion. In addition to that, the difference of wet adhesion of the paint film on Zn and Zn-Fe with a little Fe content depend on disolution of phosphate film at ED coating process.
