Manufacturing method of galvanized steel sheet with excellent white rust resistance, paint adhesion and alkali degreasing resistance

摘要

PROBLEM TO BE SOLVED: To obtain a galvanized steel sheet excellent in resistance against white color rust, adhesion property with a coating material, resistance against alkali degreasing without causing environmental pollution by applying a specified amt. of a soln. containing a silicate ester and an inorg. salt or aluminum on a zinc-plated steel sheet and heating to dry. SOLUTION: The mixture of silicate and aluminum is incorporated in such a manner that the proportion of the inorg. salt is 0.01 to 0.75 molar ratio of Al/(Al+Si), and further polyethylene glycol having 4106 average mol.wt. is added by 0.01 to 1 time of the mole of the silicate. The soln. is applied on a zinc-plated steel sheet in such a manner that the sum amt. of Al and Si deposited is 5 to 1000mg/m2 , and then the applied soln. is dried by heating. At least one kind of colloidal silica or fumed silica is preferably added by 0.01 to 2 times of the moles of the silicate.