Nippon Paint Compnay, Ltd.

Shoji Oka

Ryoichi Murakami

Akiko Sueyoshi

Tamotsu Sobata

Toshihiro Okai

Kazuo Nobe

Teturo Kishimoto

In a method for phosphating the surface of a metallic substrate by treatment with a phosphating solution containing nitrite ions as the accelerator, an improvement wherein the supply of the nitrite ions to the phosphating solution is carried out by electrolytic reduction of nitrate ions present in the phosphating solution while changing the direction of the current flow at a fixed interval of time, whereby a desired concentration of nitrite ions in the phosphating solution is maintained without accumulation of alkali metal and/or ammonium ions unavailable for the phosphating and also without accumulation of precipitates on the electrode, and a uniform phosphate coating film having satisfactorily good coating properties is formed on said surface.

Phosphating of metallic substrate

In a method for phosphating the surface of a metallic substrate by treament with a phosphating solution comprising nitrite ions as the accelerator, an improvement wherein the supply of the nitrite ions to the phosphating solution is carried out by electrolytic reduction of nitrate ions present in the phosphating solution, whereby a desired concentration of nitrite ions in the phosphating solution is maintained without accumulation of alkali metal and/or ammonium ions unavailable for the phosphating and a uniform phosphate coating film having satisfactorily good coating properties is formed on said surface.

Phosphating of metallic substrate with electrolytic reduction of nitrate

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.

Zinc phosphate coating process

A phosphate coating solution for forming coatings on a metal surface is contacted with an anion-exchanger loaded or contacted with nitrite ions, whereby the nitrate ions present in the coating solution are replaced by the nitrite ions. This process permits continued operation of a phosphate coating process without replenishing a nitrite solution. This process also allows no accumulation of alkali metal and/or ammonium ions unavailable for the phosphate coating and provides uniform coatings with satisfactory coating properties on the metal surface.

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Nara, Japan

Shoji Oka