Process and aqueous solution for phosphatizing metallic surfaces

US6261384A · kind A · utility

Assignee

• Metallgesellschaft AG · DE

Inventors

• Thomas Kolberg · Heppenheim, DE
• Peter Schubach · Nidderau, DE

Key dates

• Filing date: Mar 10, 1999
• Grant date: Jul 17, 2001
• Expiry date: Mar 10, 2019

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C23C22/184
• WIPO field: Surface technology, coating
• WIPO sector: Chemistry

Abstract

A process is disclosed for preparing an aqueous zinc phosphatizing solution for producing phosphate coatings on metallic surfaces of iron, steel, zinc, zinc alloys, aluminum or aluminum alloys, which comprises: PA1 (1) 0.3 to 5 g Zn.sup.2+ /1; PA1 (2) 0.1 to 3 g nitroguanidine/1 as an accelerator; PA1 (3) phosphate where the acid value is 0.03 to 0.3 indicating the ratio of free acid, calculated as free P.sub.2 O.sub.5 to the total P.sub.2 O.sub.5, and the weight ratio of Zn to P.sub.2 O.sub.5 is 1:5 to 1:30; and PA1 (4) balance water, where the solution produces finely crystallite phosphate coatings in which the crystallites have a maximum edge length <15 .mu.m, which comprises the steps of: PA2 (a) preparing a concentrate comprising the Zn.sup.2+ and the phosphate in water; PA2 (b) supplying additional water to the concentrate so that the Zn.sup.2+ concentration in the phosphatizing solution is 0.3 to 5 g/1; PA2 (c) preparing a stabilized suspension consisting essentially of 100 to 300 g of nitroguanidine/1, 10 to 30 g of sheet silicate/1 as stabilizer and the balance water by suspending the sheet silicate in deionized water and stirring the nitroguanidine into the suspension; an…