Patent ID: 9550208
Date: 2017-01-24
CPC Classifications: B05D,C23C

Claim:
1. A zinc phosphating solution comprising: (a) 5-50 g/l of phosphate ions, (b) 0.3-3 g/l of zinc(II) ions, (c) a concentration of free fluoride, in g/l which is at least 0.005 g/l, and no greater than 8/T g/l wherein T is the temperature at which the solution is used for coating, (d) at least 0.025 g/l, but less than 1.0 g/l of silicon in the form of water-soluble inorganic compounds calculated as SiF said zinc phosphating solution having a free acid point number of at least 0.4 points, but of no more than 3 points and a pH value in the range from 2.2 to 3.6; wherein a product “(Si/mM)·(F/mM)” of concentration of silicon [Si in mM] in the form of water-soluble inorganic compounds and concentration of free fluoride [F in mM] divided by the free acid point number is no greater than 5, wherein the zinc phosphating solution is effective for coating zinc or iron surfaces to form a continuous coating, but forms no continuous coating on aluminum surfaces at under the same coating conditions used for coating zinc or iron surfaces to form a continuous coating.