AQUEOUS SOLUTION AND METHOD FOR THE FORMATION OF A PASSIVATION LAYER
The present invention generally relates to an aqueous solution for the formation of a passivation layer on a zinc layer or zinc-alloy layer. More particularly, the invention relates to the formation of a black passivation layer on a zinc layer or zinc-alloy layer, which passivation layer is substantially free of hexavalent chromium. Furthermore, the present invention relates to method for the formation of a passivation layer on a zinc layer or zinc-alloy layer, as well as a passivation layer on a zinc layer or zinc-alloy layer itself. The solution used contains trivalent chromium ions, nitrate ions, an organic acid and a dithioglycolate.
1 - 8 . (canceled)
9 . A method for the formation of a passivation layer on a zinc layer or zinc-alloy layer, the method comprising the steps:
depositing a zinc or zinc-alloy layer on a substrate surface;
treating the deposited zinc or zinc-alloy layer with an aqueous process solution according to claim 18 .
10 . The method according to claim 9 wherein the zinc or zinc-alloy layer is deposited from an acidic electrolyte.
11 . The method according to claim 9 or 10 , wherein the zinc or zinc-alloy layer is deposited from an electrolyte comprising a thiodiglycol ethoxylate.
12 . The method according to claim 11 , wherein the zinc or zinc-alloy layer is deposited at a temperature ≦30° C.
13 . The method according to claim 9 or 10 , wherein subsequent to the formation of the passivation layer, the surface is treated with a film building polymeric solution to improve the corrosion resistance.
14 . Use of a compound according to the general formula
wherein R is H, Li, Na, K, NH 4 , or a branched or unbranched alkyl group having 1 to 8 carbon atoms as additive in a composition for the deposition or passivation of metals on the surface of a substrate.
15 . Passivation layer on a zinc layer or zinc-alloy layer, characterized in that the passivation layer has an average optical surface reflectance at a wavelength within the range of 360 nm to 710 nm of less than 8%, preferably less than 7%, wherein the fluctuation range of the reflectance is ≦2%, preferably ≦1%.
16 . The method of claim 9 for forming a passivation layer on a zinc layer or zinc-alloy layer, the method comprising the steps:
the depositing the zinc or zinc alloy layer on a substrate surface; and
the treating the deposited zinc or zinc-alloy layer with an aqueous process solution according to claim 1 or 2 ;
wherein the depositing the zinc or zinc alloy layer comprises deposition at a temperature ≦30° C. from an acidic electrolyte comprising between 0.01 mol/l to 0.1 mol/l of a thiodiglycol ethoxylate; and
wherein the treating comprises treatment with a solution comprising between 4 mmol to 0.2 mol/l of the trivalent chromium ions, between 0.1 mmol/l and 1 mol/l of the dithioglycolate, between 0 and 2 mol/l of the nitrate ions; and
wherein the organic acid is at least one acid of the group consisting of citric acid, malonic acid, formic acid, tartaric acid, lactic acid, malic acid, gluconic acid, ascorbic acid, oxalic acid, succinic acid, and adipic acid.
17 . The method of claim 16 wherein the dithioglycolate in the treatment solution is ammonium dithioglycolate.
18 . An aqueous process solution useful for forming a passivation layer on a zinc or zinc alloy layer comprising a combination of:
a source of trivalent chromium ions;
a source of nitrate ions selected from the group consisting of ammonium nitrate and alkali metal nitrates;
a dithiodiglycolate salt;
a carboxylic acid; and
water.
19 . An aqueous process solution as set forth in claim 18 wherein said dithiodiglycolate salt comprises ammonium dithiodiglycolate.
20 . An aqueous process solution as set forth in claim 18 or 19 wherein said carboxylic acid comprises a monocarboxylic acid selected from the group consisting of formic acid, acetic acid, propionic acid, and lactic acid.
21 . An aqueous process solution as set forth in any of claims 18 to 20 wherein said carboxylic acid comprises a polycarboxylic acid selected from the group consisting of succinic acid, oxalic acid, citric acid and malonic acid.
22 . An aqueous process solution as set forth in any of claims 18 to 23 wherein said carboxylic acid comprises an α-hydroxy acid.
23 . An aqueous process solution as set forth in any of claims 18 to 23 further comprising fluoride or bifluoride ions.
24 . An aqueous process solution as forth in any of claims 18 to 23 wherein said source of trivalent chromium ions is selected from the group consisting of chromium sulfate and chromium chloride.
25 . An aqueous process solution set forth in claim 24 wherein said source of trivalent chromium ions comprises chromium sulfate.
26 . An aqueous process solution as set forth in any of claims 18 to 25 that is substantially free of phosphite ions.
27 . An aqueous process solution as set forth in any of claims 18 to 26 that is substantially free of zinc ions.
28 . An aqueous process solution as set forth in any of claims 18 to 27 further comprising ions of a metal selected from the group consisting of Sc, Y, Ti, Zr, Mo, W, Mn, Fe, Co, Ni, B, Al and Si.
29 . An aqueous solution as set forth in any of claims 18 to 28 further comprising ethylene diamine tetraacetic acid, nitrilo triacetic acid, and ethylene diamine disuccinic acid.