PHOSPHATING SOLUTION WITH HYDROGEN PEROXIDE AND CHELATING CARBOXYLIC ACIDS
The invention relates to a phosphating solution and a process for the phosphating of metallic surfaces with aqueous, acidic phosphating solutions that comprise zinc and phosphate ions, at least one source of peroxide and one or more aliphatic chelating carboxylic acids containing 2 to 7 carbon atoms; the phosphating solution having a free acid content of one point or less.
1 . An acidic, aqueous phosphating solution comprising:
a.) 0.2 to 3 g/l zinc(II) ions;
b.) 3 to 50 g/l phosphate ions, calculated as PO 4 −3 ;
c.) a source of hydrogen peroxide present in an amount sufficient to provide 15 to 50 g/l hydrogen peroxide in said solution; and
d.) 0.3 to 1.5 g/l of one or more aliphatic chelating carboxylic acids containing 2 to 7 carbon atoms;
said phosphating solution having a free acid content of one point or less.
2 . A phosphating solution according to claim 1 , wherein at least one of the aliphatic chelating carboxylic acids comprises at least two carboxyl groups and at least one hydroxyl moiety that is not part of a carboxyl group.
3 . A phosphating solution according to claim 2 , wherein the aliphatic chelating carboxylic acid comprises one or more of tartronic acid, malic acid, tartaric acid and citric acid.
4 . A phosphating solution according to claim 3 , comprising a source of hydrogen peroxide present in an amount sufficient to provide 20 to 35 g/l hydrogen peroxide in said solution.
5 . A phosphating solution according to claim 4 comprising 0.1 to 4 g/l manganese ions, 0.002 to 0.2 g/l copper ions and not more than 0.05 g/l nickel ions.
6 . A phosphating solution according to claim 4 , additionally comprising one or more of the following cations:
0.1 to 4
g/l manganese(II),
0.2 to 2.5
g/l magnesium(II),
0.2 to 2.5
g/l calcium(II),
0.002 to 0.2
g/l copper(II),
0.1 to 2
g/l cobalt(II), and
0.1 to 2.5
g/l nickel(II).
7 . A phosphating solution according to claim 6 comprising 0.4 to 2 g/l zinc ions, 0.1 to 4 g/l manganese ions and 0.1 to 2.5 g/l nickel ions.
8 . A phosphating solution according to claim 7 additionally comprising free and/or complexed fluoride in amounts of up to 2.5 g/l total fluoride, of which up to 750 mg/l free fluoride, each calculated as F − .
9 . A phosphating solution according to claim 8 , having a free acid value between about 0.3 and 1 point and a total acid value between about 15 and about 35 points.
10 . A phosphating solution according to claim 1 , wherein the aliphatic chelating carboxylic acid comprises one or more of tartronic acid, malic acid, tartaric acid and citric acid.
11 . A phosphating solution according to claim 1 , wherein the aliphatic chelating carboxylic acid comprises is citric acid and the source of hydrogen peroxide comprises ionic peroxide and/or peroxy compounds.
12 . A phosphating solution according to claim 1 , wherein the source of hydrogen peroxide is present in an amount sufficient to provide 20 to 35 g/l hydrogen peroxide in said solution.
13 . A phosphating solution according to claim 12 , additionally comprising one or more of the following cations:
0.1 to 4
g/l manganese(II),
0.2 to 2.5
g/l magnesium(II),
0.2 to 2.5
g/l calcium(II),
0.002 to 0.2
g/l copper(II),
0.1 to 2
g/l cobalt(II),
0.1 to 2.5
g/l nickel(II).
14 . A phosphating solution according to claim 1 comprising 0.1 to 4 g/l manganese ions, 0.002 to 0.2 g/l copper ions and not more than 0.05 g/l nickel ions.
15 . A phosphating solution according to claim 1 comprising 0.1 to 4 g/l manganese ions and 0.1 to 2.5 g/l nickel ions.
16 . A phosphating solution according to claim 1 comprising 0.4 to 2 g/l zinc ions and having a weight ratio of phosphate ions to zinc ions that ranges between 10 and 20.
17 . A phosphating solution according to claim 1 additionally comprising free and/or complexed fluoride in amounts of up to 2.5 g/l total fluoride, of which up to 750 mg/l free fluoride, each calculated as F—.
18 . A phosphating solution according to claim 1 , having a free acid value between about 0.3 and 1 point.
19 . An aqueous concentrate that results in a phosphating solution according to claim 1 upon dilution with water only by a factor of between 10 and 100 weight/weight, and optionally
adjustment of free acid content to a value of one point or less;
adjustment of pH to a working range between 2.7 and 3.6; and
adjustment of concentration of any H 2 O 2 source.
20 . A process for the phosphating of metal surfaces comprising steel, galvanized or alloy galvanized steel and/or aluminum, wherein the metal surfaces are contacted with a phosphating solution according to claim 1 .