PHOSPHATING SOLUTION FOR ZINC ELECTROPLATED STEEL SHEET

摘要

PURPOSE:To improve the whiteness degree of the surfaces of a zinc electroplated steel sheet after phosphating by adjusting the concn. of nitric acid in a phosphating soln. contg. zinc phosphate as a principal component to a prescribed value. CONSTITUTION:Nitric acid is added to a phosphating soln. contg. zinc phosphate as a principal component for a zinc electroplated steel sheet so as to adjust the concn. of nitric acid in the soln. to =2.5g/l, preferably 2.5-5g/l. For example, the phosphating soln. contains 10g/l phosphoric acid, 2.5g/l zinc, 0.25g/l nickel and 0.15g/l fluorine. Said steel sheet is phosphated with the phosphating soln. Hydrogen generated in the surface layer of the zinc plating is oxidized with nitric acid, the dissolution of zinc proceeds, and the concn. of zinc in the interface is increased. Accordingly, the amount of nickel present in the vicinity of the interface is relatively reduced, and the whiteness degree of the steel sheet is improved.