Patent ID: 6261384
Filing Date: 2001-07-17
Classification: C23C

Abstract:
A process for preparing an aqueous zinc phosphatizing solution for producing phosphate coatings on metallic surfaces of iron, steel, zinc, zinc alloys, aluminum, or aluminum alloys wherein the zinc phosphatizing solution comprises:(1) 0.3 to 5 g Zn.sup.2+ /l;(2) 0.1 to 3 g nitroguanidine/l as an accelerator;(3) stabilizer;(4) 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(5) balance water, where the solution produces finely crystallite phosphate coatings in which the crystallites have a maximum edge length <15 .mu.m, wherein said process comprises the steps of:(a) preparing a concentrate comprising the Zn.sup.2+ and the phosphate in water;(b) supplying additional water to the concentrate to form a diluted concentrate so that the Zn.sup.2+ concentration in the zinc phosphatizing solution will be 0.3 to 5 g/l;(c) preparing a stabilized suspension containing 100 to 300 g of nitroguanidine/l, a stabilizer for the suspension and the balance water by suspending the stabilizer for the suspension in deionized water and stirring the nitroguanidine into the suspension; and(d) introducing the stabilized suspension into the dilute concentrate so that the nitroguanidine concentration in the zinc phosphatizing solution is 0.1 to 3 g nitroguanidine/liter.