METHOD FOR TREATMENT OF A CHROMIUM FINISH SURFACE

Abstract

A method for post-treatment of a chromium finish surface to improve corrosion resistance comprising a) providing a substrate having a chromium finish surface, and at least one intermediate layer between the chromium finish surface and the substrate, selected from the group consisting of nickel, nickel alloys, copper and copper alloys, wherein the chromium finish surface is a surface of a trivalent chromium plated layer, obtained by electroplating the substrate, having the at least one intermediate layer, in a plating bath, the plating bath comprising chromium (III) ions; b) contacting the chromium finish surface with an aqueous solution, comprising a permanganate, at least one compound which is selected from a phosphorus-oxygen compound, a hydroxide, a nitrate, a borate, boric acid, a silicate, or a mixture of two or more of these compounds; c) forming a transparent corrosion protection layer onto the chromium finish surface during step b.

Claims

1. A method for post-treatment of a chromium finish surface to improve corrosion resistance, comprising a) providing a substrate having a chromium finish surface, and at least one intermediate layer between the chromium finish surface and the substrate, wherein the at least one intermediate layer is selected from the group consisting of nickel, nickel alloys, copper and copper alloys, wherein the chromium finish surface is a surface of a trivalent chromium plated layer, obtained by electroplating the substrate having the at least one intermediate layer, in a plating bath, the plating bath comprising chromium (III) ions as a main chromium source; b) contacting the chromium finish surface with an aqueous solution, comprising a permanganate, at least one compound which is selected from a phosphorus-oxygen compound, a hydroxide, a nitrate, a borate, boric acid, a silicate, or a mixture of two or more of these compounds; c) forming a transparent corrosion protection layer onto the chromium finish surface during contacting the chromium surface with the aqueous solution in step b), wherein concentration of the permanganate in the aqueous solution is 0.05-4.5 mol/L.

2. The method of claim 1, wherein the at least one compound is selected from inorganic phosphorus-oxygen compound as a phosphate, a hydrogenphosphate, a dihydrogenphospate, a pyrophosphate, a phosphonate or mixtures thereof; hydroxide; a borate or a nitrate.

3. The method according to claim 1, wherein the plating bath is substantially free of chromium (VI) ions and the trivalent chromium plated layer comprises chromium in an amount of 45-90 at % (atom percent), oxygen in an amount of 5-20 at % with the proviso that the total amount of all chemical elements together will not exceed 100 at % and the chromium amount has in every case the highest amount within the trivalent chromium plated layer.

4. The method according to claim 1, wherein the plating bath is substantially free of chromium (VI) ions and the trivalent chromium plated layer comprises chromium in an amount of 45-90 at %, oxygen in an amount of 5-20 at %, iron in an amount of 0-30 at %, carbon in an amount of 0-15 at %, sulfur in an amount of 0-15 at %, and further metals or nonmetals in an amount of 0-1 at %; with the proviso that the total amount of all chemical elements together will not exceed 100 at % and the chromium amount has in every case the highest amount within the trivalent chromium plated layer.

5. The method according to claim 1, wherein one of the at least one intermediate layer, which is directly in contact with the trivalent chromium plated layer, the trivalent chromium plated layer having pores or pores and cracks, is a bright or satin nickel layer, obtained by electroplating the substrate, and further comprises at least one further intermediate layer which is not a bright nickel layer; or is a MPS nickel layer, obtained by electroplating the substrate, and further comprises at least one further intermediate layer which is not a MPS nickel layer.

6. The method according to claim 1, wherein in step b) an electric potential is applied between the chromium surface and an inert counter electrode, wherein the chromium surface serves as a cathode and the counter electrode as an anode.

7. The method of claim 6, wherein a current density of 0.005-5 A/dm.sup.2, related to the area of the chromium surface, is generated.

8. The method of claim 6, wherein the electric potential is applied for 5-900 seconds.

9. The method of claim 7, wherein the electric potential is applied for 5-900 seconds.

10. The method according to claim 1, comprising, a further step d) treating the chromium surface, after treatment with the aqueous solution in step b), with a component able to reduce and/or dissolve MnO.sub.2.

11. The method according to claim 10, wherein the component is hydrogen peroxide, hydrazine, potassium iodide, sodium sulfite, hydroxylammonium sulfate or a carbohydrate.

12. The method according to claim 10, wherein the component is selected from sulfuric acid, nitric acid, ascorbic acid and acetic acid.

13. The method according to claim 1, comprising, as a further step: rinsing the chromium surface after treatment with the aqueous solution in step b), and before treatment with the acid and/or reducing agent in step d).

14. The method according to claim 1, wherein concentration of the phosphorus-oxygen compound, hydroxide, nitrate, borate, boric acid, or silicate in the aqueous solution is 0.05-2 mol/L.

15. The method according to claim 1, further comprising using the chromium finish surface as a decorative chromium finish surface on a substrate in the automotive, white goods, or sanitary industry.

16. The method according to claim 1, further comprising applying a NSS test (ISO 922 7), wherein the treated chromium finish surface having the transparent corrosion protection layer does not show any alteration of the surface (area of defects: 0%) after applying the NSS test (ISO 922 7) for at least 120 h.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0081] FIG. 1 demonstrates the results of XPS analyses performed on as-plated chromium surface, chromium surface after post treatment and chromium surface after post-treatment and reduction step according to Example 6.

[0082] FIG. 2 indicates the elemental surface composition of as-plated chromium surface, chromium surface after post-treatment and chromium surface after post-treatment and reduction step according to Example 6.

[0083] FIG. 3 is a view showing the depth profiles of as-plated and post-treated and reduced surface acquired by means of XPS sputter profiling. Dashed line shows the cross-over point of Cr and O concentration, which can be taken as a qualitative indicator of oxide film thickness according to Example 6.

[0084] FIG. 4 shows the panels after 480 h neutral salt spray test according to ISO 9227. Upper panels show the chromium surface without post treatment with visible corrosion products on the surface and lower panels demonstrate the post treated surfaces according to Example 1 (without post-treatment and according to Example 2 (with post-treatment).

EXAMPLES

[0085] The invention will now be illustrated by reference to the following non-limiting examples.

[0086] ABS substrates of the same size which comprise a multilayer of copper, semi-bright nickel, bright nickel, optional non-conductive particle containing nickel (‘microporous Nickel’) and a final chromium layer as well as brass panels (10×10 mm) which comprise a layer of bright nickel and a final chromium layer were used for the examples. The chromium layer was either a bright chromium layer or a dark chromium layer as indicated in the respective example which has been deposited from a trivalent chromium based electrolyte.

[0087] The optical appearance of the chromium surface was visually inspected prior to the neutral salt spray tests.

[0088] Neutral salt spray (NSS) tests were performed according to ISO 9227. The results are given with the respective examples.

EXAMPLE 1 (COMPARATIVE)

[0089] A bright chromium surface (brass panel) was investigated without any post-treatment by a neutral salt spray test according to ISO 9227 NSS.

[0090] The untreated bright chromium surface possess a significant change of appearance when visually inspected after 120 h of the chromium surface (area of defects >5-10%).

EXAMPLE 2

[0091] A bright chromium surface (brass panel) was treated with an aqueous solution comprising 40 g/L potassium permanganate (KMnO.sub.4) and 50 g/L monopotassium dihydrogenophosphate (KH.sub.2PO.sub.4) for 90 seconds at 25° C. while applying a current density of 1 A/dm.sup.2 to the chromium surface as the cathode. Afterwards the chromium surface was rinsed with DI-water and dipped into a solution consisting of H.sub.2SO.sub.4 and H.sub.2O.sub.2 for 5 seconds at 25° C.

[0092] The optical appearance was not significantly changed after the post-treatment and the treated chromium surface passed the corrosion test when visually inspected after 480 h neutral salt spray test without any alteration (area of defects: 0%).

EXAMPLE 3 (COMPARATIVE)

[0093] A bright chromium surface (ABS cap with non-conductive particle containing nickel within the multilayer) was investigated without any post-treatment by a neutral salt spray test according to ISO 9227 NSS.

[0094] The untreated bright chromium surface possess when visually inspected after 120 h a significant change of appearance of the chromium surface (area of defects >10-25%).

EXAMPLE 4

[0095] A bright chromium surface (ABS cap without non-conductive particle containing nickel within the multilayer) was treated with an aqueous solution comprising 40 g/L potassium permanganate (KMnO.sub.4) and 50 g/L monopotassium dihydrogenophosphate (KH.sub.2PO.sub.4) for 90 seconds at 25° C. while applying a current density of 1 A/dm.sup.2 to the chromium surface as the cathode. Afterwards the chromium surface was rinsed with DI-water and dipped into a solution consisting of H.sub.2SO.sub.4 and H.sub.2O.sub.2 for 5 seconds at 25° C.

[0096] The optical appearance was not significantly changed after the post-treatment and the treated chromium surface passed the corrosion test when visually inspected after 480 h neutral salt spray test without any alteration (area of defects: 0%).

EXAMPLE 5

[0097] A bright chromium surface (ABS cap with non-conductive particle containing nickel within the multilayer) was treated with an aqueous solution comprising 40 g/L sodium permanganate (NaMnO.sub.4) and 50 g/L monopotassium dihydrogenophosphate (KH.sub.2PO.sub.4) for 10 minutes at 50° C. without applying an external current to said chromium surface.

[0098] The optical appearance was not significantly changed after the post-treatment and the treated chromium surface passed the corrosion test when visually inspected after 120 h neutral salt spray test without any alteration (area of defects: 0%).

EXAMPLE 6

[0099] A bright chromium surface (ABS cap with non-conductive particle containing nickel within the multilayer) was treated with an aqueous solution comprising 40 g/L sodium permanganate (NaMnO.sub.4) and 50 g/L monopotassium dihydrogenophosphate (KH.sub.2PO.sub.4) for 60 seconds at 25° C. while applying a current density of 0.5 A/dm.sup.2 to the chromium surface as the cathode. Afterwards the chromium surface was rinsed with DI-water and dipped into a solution consisting of H.sub.2SO.sub.4 and H.sub.2O.sub.2 for 5 seconds at 25° C.

[0100] The optical appearance was not significantly changed after the post-treatment and the treated chromium surface passed the corrosion test when visually inspected after 120 h neutral salt spray test without any alteration (area of defects: 0%). Even after 480 h neutral salt spray test the chromium surface exhibit of only slight changes of the chromium surface (area of defects <0.5%).

EXAMPLE 7

[0101] A bright chromium surface (ABS cap with non-conductive particle containing nickel within the multilayer) was treated with an aqueous solution comprising 40 g/L potassium permanganate (KMnO.sub.4) and 50 g/L monopotassium dihydrogenophosphate (KH.sub.2PO.sub.4) for 3 minutes at 25° C. while applying a current density of 0.5 A/dm.sup.2 to the chromium surface as the cathode. Afterwards the chromium surface was rinsed with DI-water and dipped into a solution consisting of H.sub.2SO.sub.4 and H.sub.2O.sub.2 for 5 seconds at 25° C.

[0102] The optical appearance was not significantly changed after the post-treatment and the treated chromium surface passed the corrosion test when visually inspected after 480 h neutral salt spray test without any alteration (area of defects: 0%).

EXAMPLE 8

[0103] A bright chromium surface (ABS cap with non-conductive particle containing nickel within the multilayer) was treated with an aqueous solution comprising 40 g/L sodium permanganate (NaMnO.sub.4) and 50 mL/L sodium hydroxide solution (NaOH, 30 ww %) for 30 seconds at 50° C. while applying a current density of 0.5 A/dm.sup.2 to the chromium surface as the cathode. Afterwards the chromium surface was rinsed with DI-water and dipped into a solution consisting of H.sub.2SO.sub.4 and H.sub.2O.sub.2 for 5 seconds at 25° C.

[0104] The optical appearance was not significantly changed after the post-treatment and the treated chromium surface passed the corrosion test when visually inspected after 120 h neutral salt spray test without any alteration (area of defects: 0%).

EXAMPLE 9

[0105] A bright chromium surface (ABS cap with non-conductive particle containing nickel within the multilayer) was treated with an aqueous solution comprising 40 g/L sodium permanganate (NaMnO.sub.4) and 15 g/L sodium tetraborate (Na.sub.2B.sub.4O.sub.7.10H.sub.2O) 10 minutes at 50° C. without applying an external current to said chromium surface. Afterwards the chromium surface was rinsed with DI water and dipped into a solution consisting of H.sub.2SO.sub.4 and H.sub.2O.sub.2 for 5 seconds at 25° C.

[0106] The optical appearance was not significantly changed after the post-treatment and the treated chromium surface shows an enhancement of the corrosion resistance compared to the untreated: When visually inspected after 120 h neutral salt spray test the treated chromium surface exhibits only of slight changes of the chromium surface (area of defects <0.25%).

EXAMPLE 10 (COMPARATIVE)

[0107] A dark chromium surface (ABS cap with non-conductive particle containing nickel within the multilayer) was investigated without any post-treatment by a neutral salt spray test according to ISO 9227 NSS.

[0108] The untreated bright chromium surface possesses when visually inspected after 120 h a significant change of appearance of the chromium surface (area of defects >50%).

[0109] EXAMPLE 11

[0110] A dark chromium surface (ABS cap without non-conductive particle containing nickel within the multilayer) was treated with an aqueous solution comprising 40 g/L potassium permanganate (KMnO.sub.4) and 50 g/L monopotassium dihydrogenophosphate (KH.sub.2PO.sub.4) for 90 seconds at 25° C. while applying a current density of 1 A/dm.sup.2 to the chromium surface as the cathode. Afterwards the chromium surface was rinsed with DI water and dipped into a solution consisting of H.sub.2SO.sub.4 and H.sub.2O.sub.2 for 5 seconds at 25° C.

[0111] The optical appearance was not significantly changed after the post-treatment and the treated chromium surface passed the corrosion test when visually inspected after 120 h neutral salt spray test without any alteration (area of defects: 0%). Even after 480 h neutral salt spray test the chromium surface exhibit of only slight changes of the chromium surface (area of defects <0.25%).

EXAMPLE 12

[0112] A dark chromium surface (brass panel) was treated with an aqueous solution comprising 40 g/L potassium permanganate (KMnO.sub.4) and 50 g/L monopotassium dihydrogenophosphate (KH.sub.2PO.sub.4) for 90 seconds at 25° C. while applying a current density of 1 A/dm.sup.2 to the chromium surface as the cathode. Afterwards the chromium surface was rinsed with DI water and dipped into a solution consisting of H.sub.2SO.sub.4 and H.sub.2O.sub.2 for 5 seconds at 25° C.

[0113] The optical appearance was not significantly changed after the post-treatment and the treated chromium surface passed the corrosion test when visually inspected after 120 h neutral salt spray test without any alteration (area of defects: 0%). After 240 h neutral salt spray test the chromium surface exhibit of only slight changes of the chromium surface (area of defects <0.1%).

EXAMPLE 13

[0114] A dark chromium surface (ABS cap with non-conductive particle containing nickel within the multilayer) was treated with an aqueous solution comprising 40 g/L potassium permanganate (KMnO.sub.4) and 50 g/L monopotassium dihydrogenophosphate (KH.sub.2PO.sub.4) for 10 minutes at 50° C. without applying an external current to said chromium surface. Afterwards the chromium surface was rinsed with DI water and dipped into a solution consisting of H.sub.2SO.sub.4 and H.sub.2O.sub.2 for 5 seconds at 25° C.

[0115] The optical appearance was not significantly changed after the post-treatment and the treated chromium surface shows an significant enhancement of the corrosion resistance compared to the untreated: When visually inspected after 480 h neutral salt spray test the treated chromium surface exhibits of only slight changes of the chromium surface (area of defects <0.1%).

EXAMPLE 14

[0116] A dark chromium surface (ABS cap with non-conductive particle containing nickel within the multilayer) was treated with an aqueous solution comprising 40 g/L potassium permanganate (KMnO.sub.4) and 50 g/L nitric acid (HNO.sub.3) for 10 minutes at 50° C. without applying an external current to said chromium surface. Afterwards the chromium surface was rinsed with DI water and dipped into a solution consisting of H.sub.2SO.sub.4 and H.sub.2O.sub.2 for 5 seconds at 25° C.

[0117] The optical appearance was not significantly changed after the post-treatment and the treated chromium surface passed the corrosion test when visually inspected after 120 h neutral salt spray test without any alteration (area of defects: 0%). After 240 h neutral salt spray test the chromium surface exhibit of only slight changes of the chromium surface (area of defects <0.1%).

EXAMPLE 15

[0118] A bright chromium surface (ABS cap with non-conductive particle containing nickel within the multilayer) was treated with an aqueous solution comprising 40 g/L potassium permanganate (KMnO.sub.4) and 50 g/L monopotassium dihydrogenophosphate (KH.sub.2PO.sub.4) for 90 seconds at 25° C. while applying a current density of 0.1 A/dm.sup.2 to the chromium surface as the cathode. Afterwards the chromium surface was rinsed with DI-water.

[0119] The optical appearance was not significantly changed after the post-treatment and the treated chromium surface passed the corrosion test when visually inspected after 480 h neutral salt spray test without any alteration of the surface (area of defects: 0%).

EXAMPLE 16

[0120] A bright chromium surface (ABS cap with non-conductive particle containing nickel within the multilayer) was treated with an aqueous solution comprising 40 g/L potassium permanganate (KMnO.sub.4) and 50 g/L monopotassium dihydrogenophosphate (KH.sub.2PO.sub.4) for 90 seconds at 25° C. while applying a current density of 1.5 A/dm.sup.2 to the chromium surface as the cathode. Afterwards the chromium surface was rinsed with DI-water.

[0121] The optical appearance was not changed after the post-treatment and the treated chromium surface passed the corrosion test when visually inspected after 480 h neutral salt spray test without any alteration of the surface (area of defects: <0.1%).

EXAMPLE 17

[0122] A bright chromium surface (ABS cap with non-conductive particle containing nickel within the multilayer) was treated with an aqueous solution comprising 40 g/L potassium permanganate (KMnO.sub.4) and 50 g/L monopotassium dihydrogenophosphate (KH.sub.2PO.sub.4) for 90 seconds at 25° C. while applying a current density of 1.0 A/dm.sup.2 to the chromium surface as the cathode. Afterwards the chromium surface was rinsed with DI-water.

[0123] The optical appearance was not changed after the post-treatment and the treated chromium surface passed the corrosion test when visually inspected after 480 h neutral salt spray test without any alteration of the surface (area of defects: 0%).