Treatment solution for producing chrome and cobalt-free black conversion coatings

1. Treatment solution for producing black chromium- and cobalt-free conversion layers, which contains

a) at least one complex, water-soluble metal cation selected from the group consisting of oxo cations of the formula M′O c d+ , where c is an integer from 1 to 3 and d is an integer from 1 to 3, and/or complex halogen ions of the formula M″X a b− , where X is selected from the group consisting of F, Cl, Br and I, a is an integer from 3 to 6, b is an integer from 1 to 4 and M′ and M″ are selected from the group consisting of Mn, V, Ti, W, Mo, Zr, B, Si and Al

b) at least one oxidant

c) at least one organic sulphur compound selected from the group consisting of compounds of the formulae (1) and (2)

HS—R 1 —COOR 2   (1)

R 5 OOC—R 3 —S—S—R 4 —COOR 6   (2),

where R 1 is selected from among C1-C8-alkyl, linear and branched, and aryl;

R 2 is selected from the group consisting of H, NH 4 + , Li + , Na + , K + and C1-C4-alkyl, linear and branched;

R 3 and R 4 are selected independently from the group consisting of C1-C8-alkyl, linear and branched and aryl; and

R 5 and R 6 ′ are selected independently from the group consisting of H, NH 4 + , Li + , Na + , K + and C1-C4-alkyl, linear and branched.

2. Treatment solution according to claim 1 , wherein M′ is selected from the group consisting of Mn, V, Ti, W, Mo and Zr.

3. Treatment solution according to claim 1 , wherein M″ is selected from the group consisting of B, Al, Si, Ti and Zr.

4. Treatment solution according to claim 1 , which contains at least one oxo cation of the formula M′O c d+ and at least one complex halogen ion of the formula M″X a b− .

5. Treatment solution according to claim 1 , wherein the oxidant is selected from the group consisting of hydrogen peroxide, organic peroxides, alkali metal peroxides, perborates, persulphates, nitrates, organic nitro compounds and organic N-oxixes and mixtures thereof.

6. Treatment solution according to claim 1 , wherein the radicals of the compounds of the formulae (1) and (2) are selected from among:

R 1 is C1-C2-alkyl and

R 3 and R 4 are selected independently from among C1-C2-alkyl.

7. Original) Treatment solution according to claim 6 , wherein R 3 and R 4 are identical.

8. Treatment solution according to claim 1 , wherein the organic sulphur compound is selected from the group consisting of thioglycolic acid, dithiodiglycolic acid, thiolactic acid and 3-thiopropionic acid.

9. Treatment solution according to claim 1 , wherein the oxidant is a peroxide.

10. Treatment solution according to claim 9 , wherein the peroxide is hydrogen peroxide.

11. Treatment solution according to claim 1 , wherein the at least one oxo cation of the formula M′O c d+ is selected from the group consisting of MnO + , VO 3+ , VO 2+ , WO 2 2+ , MoO 2 2+ , TiO 2+ , ZrO 2+ and mixtures thereof.

12. Treatment solution according to claim 1 , wherein the at least one complex halogen ion of the formula M′X a b− is selected from the group consisting of SiF 6 2− , TiF 6 2− and ZrF 6 2− .