Nippon Paint Compnay, Ltd.

Teturo Kishimoto

Tamotsu Sobata

Minoru Ishida

Shoji Oka

Kazuo Nobe

A metal surface is processed with dipping by a first zinc phosphating solution in which a fluoride complex and a simple fluoride are contained and a concentration of this simple fluoride is 200 to 300 mg/l on a basis converted into the HF concentration and that of the fluoride complex is in a mole ratio with the simple fluoride converted into the HF as shown as, [fluoride complex]/[simple fluoride].gtoreq.0.01, and then the surface is processed with spraying by a second zinc phosphating solution in which a simple fluoride concentration is 500 mg/l or less and higher than that in said first zinc phosphating solution. Thus, on a metal surface is formed a zinc phosphate coating film which is suitable for electrodeposition coating, particular for cationic electrodeposition coating, and superior in coating film adhesion, corrosion-resistance, particularly resistance for warm brine, and prevention of scab-corrosion.

Process for phosphating metal surface to make thereon a zinc phosphate

Zinc phosphate coating solution contains phosphate ions in an amount of at least 0.5 percent by weight and in the phosphate ion to nitrate ion molar weight ratio of from 1 : 0.7 to 1 : 1.3. This solution also contains zinc ions in an amount, preferably, of at least 0.03 percent by weight and in a ratio of zinc ion to phosphate ion of less than 0.116 to 1. Nickel ions may be added in an amount of at least 0.01 percent by weight and in the nickel ion to zinc ion ratio of less than 1.89 to 1. The pH value of this solution ranges from about pH 3.3 to pH 3.8, whereby the consumption of nitrites employed as accelerators is reduced and sludges are formed in less amounts as in the form easily removable from an apparatus where the phosphating is effected. The zinc phosphate coating solution is preferably employed for an apparatus in which little or no solution is discharged out of the phosphating system.

Growing community of inventors

Osaka, Japan

Teturo Kishimoto