| 摘要 |
PURPOSE:To improve the paint adhesion on a treated surface and to reduce treating cost by treating a defatted and washed zinc surface successively in multi-stage alkali bath group having a specified concn. gradient, and multi-stage acid bath group wherein the liquid in the tank of the final stage is pure water. CONSTITUTION:The defatted and washed zinc surface is immersed successively in multi-stage alkali bath group which have a specified alkali concn. gradient from high to low concns. and controlled to a prescribed value in the alkali concn. of the liquid in the tank of the final stage, whereby said surface is etched. In succession, said surface is immersed successively in multi-stage acid bath group which have a specified acid concn. gradient from high to low concns. and in which the liquid in the tank of the final stage is pure water, whereby the unstable zinc hydroxide layer having some alkali component is neutralized. Then, the zinc hydroxide layer is removed and hardly soluble zinc salt film is formed. The zinc surface formed thereon with such chemically converted film is subjected immediately to a painting stage in a wet state, whereby the paint film having good adhesion is obtained. |
