SULFATE BASED, AMMONIUM FREE TRIVALENT CHROMIUM DECORATIVE PLATING PROCESS

Abstract

The present invention refers to an electroplating bath for electroplating a chromium or chromium alloy layer, the bath comprising trivalent chromium ions, organic carboxylic acid, sulfate ions, sodium conductive ions, and additives in the form of inorganic sulfur compound and boric acid as well as a process using such an electroplating bath.

Claims

1-15. (canceled)

16. An electroplating bath for depositing a chromium or chromium alloy layer, the bath comprising: a) at least one source of trivalent chromium ions, b) at least one source of sulfate ions, c) at least one organic acid as a complexing agent, d) sodium saccharin, e) at least one polyalkylene glycol, f) sodium vinyl sulfonate, g) at least one inorganic sulfur compound, h) at least one pH buffer, and, optionally, i) at least one source of ferric or ferrous ions.

17. The bath according to claim 16, wherein the concentration of the ferric or ferrous ions is preferably from 20 to 200 mg/L, more preferably from 30 to 150 mg/L, and even more preferably from 40 to 100 mg/L.

18. The bath according to claim 16, wherein the at least one inorganic sulfur compound is selected from the group of oxyacid anions comprising sulfur having a valence lower than 6, preferably selected from the group consisting of: disulfite or metabisulfite, dithionite or hydrosulfite, thiosulfate, tetrathionate, sulphite and mixtures thereof.

19. The bath according to claim 16, wherein the concentration of the at least one inorganic sulfur compound is from 5 to 500 mg/L, preferably from 10 to 200 mg/L.

20. The bath according to claim 16, wherein the at least one polyalkylene glycol has a molecular weight of lower than 2000 g/mol and is preferably selected from the group consisting of: polyethylene glycol monomethyl ether, ethyleneoxide/propyleneoxyde copolymer, polyethylene glycol and mixtures thereof.

21. The bath according to claim 16, wherein the concentration of the at least one polyalkylene glycols is from 1 to 15 g/L, preferably from 5 to 10 g/L.

22. The bath according to claim 16, wherein the at least one organic acid is i) selected from the group consisting of dicarboxylic acids, preferably selected from the group consisting of malic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, and mixtures thereof, preferably malic acid wherein the at least one organic acid is particularly preferred malic acid; and/or ii) comprised in a concentration from 5 to 40 g/L, preferably from 10 to 30 g/L, more preferably from 15 to 25 g/L.

23. The bath according to claim 16, wherein the at least one pH buffer is selected from the group consisting of boric acid, wherein the pH of the bath is preferably from 1 to 5, more preferably from 2 to 4, and even more preferably from 3.1 to 3.9.

24. The bath according to claim 16, wherein the bath is substantially free of, preferably free of at least one ion selected from the group consisting of chloride ions, ammonium ions, amino carboxylic acid ions, hexavalent chromium ions and combinations thereof.

25. A method for preparing an electroplated product by electroplating a substrate comprising the following steps: A) providing an electroplating bath comprising: a) at least one source of trivalent chromium ions, b) at least one source of sulfate ions, c) at least one organic acid as a complexing agent, d) sodium saccharin, e) at least one polyalkylene glycol, f) sodium vinyl sulfonate, g) at least one inorganic sulfur compound, h) at least one pH buffer, and, optionally, i) at least one source of ferric or ferrous ions; B) immersing a substrate into the electroplating bath and C) applying an electrical current between an anode and the substrate as a cathode for depositing the chromium or chromium alloy layer on the substrate.

26. The method according to claim 25, wherein the cathode current density is in a range from 3 to 14 A/dm.sup.2, preferably from 5 to 10, and/or the anode current density is in a range from 4 to 12 A/dm.sup.2, preferably from 5 to 10 A/dm.sup.2.

27. The method according to claim 25, wherein the at least one anode consists of a mixed metal oxide, preferably a mixed metal oxide selected from the group consisting of mixed metal oxides of at least two of platinum, ruthenium, iridium and tantalum, more preferably a mixed metal oxide of iridium and tantalum.

28. The method according to claim 25, wherein the deposition rate during the step bis in the range from 0.01 to 0.5 μm/min, preferably from 0.02 to 0.3 μm/min, and more preferably from 0.03 to 0.2 μm/min.

29. The method according to claim 25, wherein step C) is conducted at a temperature from 35 to 60° C., preferably from 40 to 58° C., more preferably from 45 to 55° C.

30. An alloy obtainable by the method according to claim 25, wherein the alloy comprises from 1 to 5 at % of carbon, from 0.5 to 4 at % of sulfur, from 1 to 5 at % of oxygen, from 0 to 12 at % of iron and/or from 74 to 94.5 at % of chrome.

Description

[0080] With reference to the following FIGURES and examples, the subject-matter according to the present invention is intended to be explained in more detail without wishing to restrict said subject-matter to the specific embodiments shown here.

[0081] FIG. 1 shows the chromium coverage on a Hull cell panel with the three points (HCD, MCD, LCD) used for the examples.

EXAMPLES

[0082] All the examples were carried out in Hull cell (250 mL) using a brass panels nickel plated applying 5A for 5 min at 55° C. using a MMO anodes (Titanium mesh cover by mix metal oxide Ir/Ta).

[0083] The panels were evaluated: the thickness of Chromium using the X-Ray method EN ISO 3497 in three points 1 cm from the left edge define as HCD (High Current Density), 5 cm from the left edge define as MCD (Medium Current Density), 7 cm from the left edge defined as LCD (Low Current Density). The colour at the point defined as MCD was measured by a Colorimeter KONICA MINOLTA CM2600 defining the colour as CIELAB (L, a, b).

[0084] The same panels were evaluated the Chromium deposit coverage measuring the mm from the left edge to the maximum coverage of the deposit to the right. Moreover the Chromium deposit was tested to the PV1073 A that is an automotive standard used to evaluate the corrosion performance of Chromium deposit to the Calcium Chloride.

TABLE-US-00001 g/L Components No1 115 Basic Chromium Sulphate 230 Sodium Sulphate 90 Boric Acid 25 Malic Acid 3 Sodium Saccharin Sodium Hydroxide to have pH 3.5 No2 115 Basic Chromium Sulphate 230 Sodium Sulphate 90 Boric Acid 25 Malic Acid 3 Sodium Saccharin 5 Methyl Polyethylen Glycol Mw 500 Sodium Hydroxide to have pH 3.5 No3 115 Basic Chromium Sulphate 230 Sodium Sulphate 90 Boric Acid 25 Malic Acid 3 Sodium Saccharin 1 Sodium Vinyl sulfonate Sodium Hydroxide to have pH 3.5 No4 115 Basic Chromium Sulphate 230 Sodium Sulphate 90 Boric Acid 25 Malic Acid 3 Sodium Saccharin 0.200 Sodium Dithionite Sodium Hydroxide to have pH 3.5 No5 115 Basic Chromium Sulphate 230 Sodium Sulphate 90 Boric Acid 25 Malic Acid 3 Sodium Saccharin 0.050 FeII or FeIII Sodium Hydroxide to have pH 3.5 No 5 b 115 Basic Chromium Sulphate 230 Sodium Sulphate 90 Boric Acid 25 Malic Acid 3 Sodium Saccharine 1 Sodium Vinyl sulfonate 0.200 Sodium Dithionite 0.050 FeII or FeIII Sodium Hydroxide to have pH 3.5 No5c 115 Basic Chromium Sulphate 230 Sodium Sulphate 90 Boric Acid 25 Malic Acid 3 Sodium Saccharine 5 Methyl Polyethylen Glycol Mw 500 1 Sodium Vinyl sulfonate 0.200 Sodium Dithionite 0.050 FeII or FeIII Sodium Hydroxide to have pH 3.5 No6 115 Basic Chromium Sulphate 230 Sodium Sulphate 90 Boric Acid 25 Malic Acid 3 Sodium Saccharin 5 Methyl Polyethylen Glycol Mw 500 1 Sodium Vinyl sulfonate 0.200 Sodium Dithionite 0.050 FeII or FeIII Sodium Hydroxide to have pH 3.5 No6b 55 Basic Chromium Sulphate 230 Sodium Sulphate 90 Boric Acid 25 Malic Acid 3 Sodium Saccharin 5 Methyl Polyethylen Glycol Mw 500 1 Sodium Vinyl sulfonate 0.200 Sodium Dithionite Sodium Hydroxide to have pH 3.5 No7 Reference test 250 Chromium Trioxide 1 Sulfuric Acid 1 Magnesium Hexafluorosilicate

[0085] The results of the examples are shown in the table below. The table shows how each component has a different effect in terms of thicknesses, coverage, color and performance versus PV 1073 A corrosion test.

[0086] In particular the reference example n° 7 where the deposit was carried out from Hexavalent Chromium electrolyte shows a very bluish color due to a very negative values of a and b but it didn't pass the PV1073 A test.

[0087] The present invention refers to the alloy carried out with the example n° 6 characterized in that the alloy composition contains 5-10 at % of Fe, 1-3 at % of S, 2-4 at % of C, 2-4 at % of O, remaining at % Cr (up to 100 at %) and reaching a comparable color to the reference example and a good deposition rate, with the features of claim 1 and the method for preparing an electroplated product by using the electroplating bath with the features of claim 10.

[0088] In the example n° 5b, the bath did not contain Methyl Polyethylen Glycol (Mw 500). The disadvantage of omitting said compound in the bath is that the obtained thickness at HCD is much lower than with the bath according to the invention (bath n° 6). Besides, in the absence of said compound, the oxyacid sulphur anion (anion of sodium dithionite) (alone) is not able to increase the compliance regarding the color, the coverage and the PV 1073A.

[0089] In the example n° 5c, the bath did not contain an oxyacid sulphur anion, i.e. did not contain sodium dithionite in the present case. The disadvantage of omitting said compound in the bath is that the thicknesses at HCD, MCD and LCD are much lower than with the bath according to the invention (bath n° 6). Color, coverage and PV 1073A are complying.

[0090] The example n° 6b shows a similar results to the n° 6 but with the better colour performance. In particular the b value reaches a very close value to the reference CrVI, wherein the efficiency is just a little bit, i.e. not significantly, reduced.

[0091] Table Showing the Results:

TABLE-US-00002 Thickness Color in MCD Alloy Composition by Example HCD MCD LCD L a b Coverage PV1073 A XPS profile (at %)* 1 0,12 0,1 0,05 82,8 −0,2   0,92 85/100 Corrosion 2 0,25 0,11 0,05 82,8 −0,21   0,90 86/100 Corrosion 3 0,11 0,1 0,04 83,2 −0,5 −0,1 86/100 Corrosion 4 0,18 0,4 0,18 83 −0,3   0,8 80/100 Corrosion 2-4% C 2-4% O; 1-3% S; remaining % Cr 5 0,11 0,1 0,04 82 −0,1   1,05 98/100 Unchanged 5b 0,12 0,4 0,02 83 −0,5 −0,1 95/100 Unchanged 5-10% Fe; 2-4% 2-4% O; 1-3% S 5c 0,25 0,18 0,05 83 −0,5   0,3 98/100 Unchanged 5-10% Fe; 2-4% 2-4% O; 1-3% S 6 0,35 0,4 0,02 83,5 −0,5 −0,1 95/100 Unchanged 5-10% Fe; 2-4% 2-4% O; 1-3% S 6b 0,25 0,25 0,15 84,5 −0,5 −1,0 90/100 Unchanged 2-4% C 1-4% O; 1-3% S 7 0,92 0,2 0,07 85,2 −1,1 −1,2 75/100 Corrosion 96-98% Cr; 2-4% O *Regarding the alloy composition, if not indicated otherwise, remaining % are represented by Cr.