How to treat chrome finish surfaces

Abstract

To provide a post-treatment method of a chromium-finished surface for improving corrosion resistance.SOLUTION: The method comprises: a) preparing a base material having a chromium-finished surface and at least one intermediate layer between the chromium-finished surface and the base material and selected from the group consisting of nickel, nickel alloys, copper and copper alloys, wherein the chromium-finished surface is a surface of a trivalent chromium plating layer, and is obtained by electroplating the base material having the at least one intermediate layer in a plating bath containing chromium (III) ions as a primary chromium source; b) bringing the chromium-finished surface into contact with an aqueous solution containing permanganate and at least one compound or a mixture of two or more compounds selected from phosphorus-oxygen compound, hydroxide, nitrate, borate, boric acid and silicate; and c) forming a transparent corrosion protective layer on the chromium-finished surface during the contact of the chromium-finished surface with the aqueous solution in the step b).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for the post-treatment of chrome finished surfaces to improve their corrosion resistance, comprising treating said chrome finished surfaces with an aqueous solution, and to the use of said aqueous solution to improve the corrosion resistance and / or passivation of chrome finished surfaces. [Background technology]

[0002] Chromium surfaces are used in a variety of applications, for example in decorative metal finishes for substrates, such as plastic parts in the automotive and sanitary industries, or as wear-resistant coatings for plated parts, such as shock absorbers. The chromium surface is usually the outer surface of a substrate and is obtained by electroplating a chromium layer from a plating bath composition that contains either Cr(III) ions, Cr(VI) ions, or both.

[0003] The resulting decorative chrome surfaces are usually very shiny and meet the aesthetic requirements. Nevertheless, the decorative chrome surfaces of the chrome layers also provide corrosion protection for the substrate and additional underlying layers on the substrate, respectively. However, in some applications of chrome surfaces, for example in the automotive and sanitary industries, the corrosion protection provided by chrome layers deposited from Cr(III)-based electrolytes is not sufficient, for example in the case of the 480-hour ISO 9227 NSS test, which requires that the appearance of the chrome surface remains unchanged. This requirement can currently only be met by plating from Cr(VI)-based electrolytes or by applying post-treatment methods with solutions containing toxic Cr(VI) ions.

[0004] At least one other metal or metal alloy layer is disposed between the chromium layer and the substrate, the at least one metal or metal alloy layer being selected from one or more of a nickel layer, a nickel alloy layer, a copper layer, and a copper alloy layer.

[0005] The chromium layer usually contains microcracks after plating or (thermal) annealing, or pores created, for example, by the underlying microporous nickel layer. Thus, the material of the layer between the chromium layer and the substrate is also exposed to the environment. Thus, the undesired corrosion of the substrate having a chromium layer as its outer surface is caused by the corrosion of the underlying layer. A chromium oxide layer formed on the outer surface of the chromium layer protects said outer surface of the chromium layer from corrosion, but not the underlying layer. Such a multilayer assembly comprising a chromium layer as the outermost layer is disclosed, for example, in US2012 / 0052319 A1.

[0006] Various methods are known in the art for enhancing the corrosion resistance of chromium surfaces and underlying metal and / or metal alloy layers.

[0007] A coating agent comprising a polymer containing 0.05-3% by weight of sulfonate and / or phosphonate groups or their respective esters, which is applied for cathodic electrodeposition of conductive substrates, is disclosed in US Pat. No. 4,724,244. The polymer is deposited on the conductive substrate, thereby forming a corrosion protection layer having a thickness of a few μm, for example 18 μm. Although the corrosion resistance is increased by the treatment, the optical appearance and surface feel of the chrome surface are dramatically altered by the thick polymer layer, which is unacceptable for example for decorative applications of chrome surfaces. Furthermore, the method requires thermal curing of the deposited polymer, which requires high curing temperatures and is therefore not applicable to plastic substrates common in the automotive industry.

[0008] Anodizing of metal surfaces with an aqueous solution containing a compound having a hydrophobic carbon chain with a hydrophilic anionic functional group is disclosed in EP2186928 A1. Although the method can increase corrosion resistance, residues remain on the metal surface, especially on dark chrome surfaces, even after rinsing with water, which creates a dull appearance. Therefore, the method is not suitable for increasing the corrosion resistance of chrome surfaces and preserving the optical properties of the chrome surfaces, i.e., the shiny and decorative optical appearance.

[0009] EP2826890 A1 relates to a method for cathodic corrosion protection of a substrate having a chromium surface and at least one intermediate layer between the substrate and the chromium layer, selected from the group comprising nickel, nickel alloys, copper and copper alloys, in which the chromium surface is contacted with an aqueous solution comprising at least one phosphonate compound, whilst passing an electric current through the substrate, at least one anode and the aqueous solution, in which the substrate acts as the cathode. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] US Patent Application Publication No. 2012 / 0052319 [Patent Document 2] U.S. Pat. No. 4,724,244 [Patent Document 3] European Patent Application Publication No. 2186928 [Patent Document 4] European Patent Application Publication No. 2826890 Summary of the Invention [Problem to be solved by the invention]

[0011] It is an object of the present invention to provide a method for corrosion protection of substrates having a chromium surface, said method preserving the optical appearance of the chromium surface. [Means for solving the problem]

[0012] Summary of the Invention The present invention relates to the application of permanganate-based formulations as post-treatments for chrome-finished surfaces to improve corrosion resistance in wet chemical processes.

[0013] The subject matter concerns a method for post-treatment of chrome-finished surfaces to improve corrosion resistance, comprising: a) providing a substrate having a chrome finished surface and at least one intermediate layer between the chrome finished surface and the substrate selected from the group consisting of nickel, nickel alloy, copper, and copper alloy; wherein the chrome-finished surface is a surface of a trivalent chrome plating layer, obtained by electroplating the substrate having at least one intermediate layer in a plating bath containing chromium (III) ions as the main chromium source; b) removing said chrome finished surface by Permanganate At least one compound selected from phosphorus-oxygen compounds, hydroxides, nitrates, borates, boric acid, silicates, or a mixture of two or more of these compounds contacting the aqueous solution containing c) forming a transparent corrosion protection layer on the chrome finished surface during contact of said chrome finished surface with the aqueous solution in step b). The problem is solved by the method, which comprises:

[0014] The enhanced corrosion resistance can be demonstrated by salt spray testing according to ISO 9227 NSS. The achieved corrosion resistance as shown by NSS is at least 120 hours without any change in the appearance of the surface (0% defective area). The method is particularly used for chrome-finished surfaces on substrates in applications for the automotive, white goods and sanitary industry, such as visible decorative chrome-finished surfaces on exterior (outside the passenger compartment) parts of automobiles, such as bumpers, decorative strips, brand name writings, etc.; white goods, such as refrigerators, microwave ovens, washing machines, etc.; interior (inside the passenger compartment) parts of automobiles, such as decorative strips, control buttons, etc.; and sanitary parts, such as shower heads, water taps, etc.

[0015] Moreover, the method of the present invention maintains the appearance, preferably the desired glossy appearance and color of chrome finished surfaces after post-treatment.

[0016] The terms "chrome finish surface" or "chrome surface" in the context of the present invention (used equivalently within the present application) mean that the chrome finish surface of the chrome layer is visible to the naked human eye (visual inspection) and is the last metal layer on the substrate. This last metal layer is only covered by the transparent corrosion protection layer and optionally the transparent organic coating formed in step b). In other words, no further metal layer is applied on the chrome finish surface or on the corrosion protection layer.

[0017] The terms "trivalent chromium plating layer" and "chromium layer" are used interchangeably. "Trivalent chromium plating layer" refers to a chromium layer plated from a chromium bath containing chromium (III) ions as the main chromium source. The chromium layer is limited in size by the "chrome finish surface" or "chrome surface" as described above.

[0018] The term "transparent" in the context of the present invention means that the desired appearance, preferably the glossy appearance, and color of the chrome-finished surface are not significantly altered after post-treatment. In other words, the color difference ΔE between the treated and untreated surface, e.g.

number

[0019] The present invention relates in a further aspect to a process for treating a chrome finished surface to form a transparent corrosion protection layer on said chrome finished surface, in particular to improve the corrosion resistance and / or passivation of the chrome surface, comprising the steps of: Permanganate At least one compound selected from phosphorus-oxygen compounds, hydroxides, nitrates, borates, boric acid, silicates, or a mixture of two or more of these compounds The aqueous solution is preferably used on a chrome finish surface as a decorative chrome finish surface on a substrate in applications for substrates in the automotive, white goods and hygiene industries.

[0020] In one embodiment, after using said aqueous solution, the treated chrome finish surface having a transparent corrosion protection layer does not show any changes in the surface (defect area: 0%) after application of the NSS test (ISO 9227) for at least 120 hours.

[0021] Detailed Description of the Invention The substrate may be, by way of non-limiting example, a plastic, such as ABS, ABS / PC, PA, PI, PP article, (also referred to as a plastic part), a metal article, or a ceramic article. To produce a substrate having a chrome surface and at least one intermediate layer selected from the group consisting of nickel, nickel alloy, copper, and copper alloy between the substrate and the chrome surface, the intermediate layer can be first deposited on the substrate surface (e.g., plastic surface) and then a chrome layer is deposited to produce the chrome surface.

[0022] At least one intermediate layer selected from the group consisting of nickel, nickel alloy, copper and copper alloy is disposed between the substrate and the chromium layer, the surface of which is exposed. The intermediate layer is disposed between the inner part of the substrate and the chromium layer. The so-called inner part of the substrate is the bulk part of the substrate, e.g., the plastic part, and constitutes the bulk volume of the substrate.

[0023] In one embodiment, an ABS substrate can be used having a multi-layer structure in the following order: copper, semi-bright nickel, a middle layer with bright nickel (optionally with non-conductive particles-containing nickel ("microporous nickel")), and a finishing chrome layer.

[0024] In a particular embodiment, the chromium surface is the surface of a trivalent chromium plating layer obtained by electroplating a substrate including an intermediate layer in a plating bath, said plating bath containing chromium (III) ions as the main source of chromium, and wherein said plating bath is essentially free of chromium (VI) ions, which means that the content of chromium (VI) ions is <0.02% by weight. Preferably, no chromium (VI) ions are added to the plating bath.

[0025] The formation of trivalent chromium plating layers and their compositions are known in the art and are described, for example, in EP 2201161 A2.

[0026] In a preferred embodiment of the method, the plating bath is essentially free of chromium (VI) ions and the trivalent chromium plating layer comprises chromium in an amount of 45-90 at.% (atomic percent) and oxygen in an amount of 5-20 at.%, with the proviso that the total amount of all chemical elements together does not exceed 100 at.%, and the amount of chromium is in all cases the highest amount in the trivalent chromium plating layer.

[0027] In a more preferred embodiment of the method, the plating bath is essentially free of chromium (VI) ions and the trivalent chromium plating 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%, preferably 5-30 at%, carbon in an amount of 0-15 at%, preferably 5-15 at%, sulfur in an amount of 0-15 at%, preferably 1-10 at%, and further metals or non-metals in an amount of 0-1 at%, with the proviso that the total amount of all chemical elements together does not exceed 100 at%, and the amount of chromium is in all cases the highest amount in the trivalent chromium plating layer.

[0028] In another preferred embodiment of the method, the plating bath is essentially free of chromium (VI) ions and the trivalent chromium plating layer consists of chromium in an amount of 80-85 at.%, oxygen in an amount of 5-15 at.%, carbon in an amount of 5-10 at.%, sulfur in an amount of 0.5-2 at.%, with the proviso that the total amount of all chemical elements together in said trivalent chromium plating layer does not exceed 100 at.%.

[0029] In yet another preferred embodiment of the method, the plating bath is essentially free of chromium (VI) ions and the trivalent chromium plating layer consists of chromium in an amount of 45-80 at.%, oxygen in an amount of 5-20 at.%, iron in an amount of 1-30 at.%, carbon in an amount of 5-20 at.%, sulfur in an amount of 0-10 at.%, with the proviso that the total amount of all chemical elements together in said trivalent chromium plating layer does not exceed 100 at.%.

[0030] The trivalent chromium plating layer produced by said preferred embodiment of the plating bath of said method is preferably used for chrome finishing surfaces on substrates in applications for exterior parts of automobiles, for example for visible decorative chrome finishing surfaces.

[0031] The chromium layer preferably has a thickness of 0.1 to 0.6 μm.

[0032] At least one intermediate layer is used to obtain a smooth and shiny chrome surface because the chrome layer itself is too thin to level out the irregularities caused by the substrate surface.

[0033] The chromium layer usually contains cracks, preferably microcracks, that occur during electroplating or after (thermal) annealing. At least one underlying intermediate layer (in direct contact with the trivalent chromium plating layer) is a nickel layer, a nickel alloy layer, a copper layer or a copper alloy layer formed by an electroplating bath containing Ni or Cu ions. A preferred intermediate layer in direct contact with the trivalent chromium plating layer is a bright or satin nickel layer, which can act as a sacrificial layer for the chromium layer.

[0034] The other chromium layer according to the present invention is preferably crack-free and pore-free.

[0035] This chrome layer, with or without cracks, is preferably used for chrome finishing surfaces on substrates in applications for white goods, automotive parts in passenger compartments, and the sanitary industry, e.g. for visible decorative chrome finishing surfaces.

[0036] Other types of chrome layers with a certain porosity, e.g. microporosity, are formed by electroplating a chrome layer on a nickel or nickel alloy layer or a composite layer of a nickel or nickel alloy layer containing small particles of a non-conductive material, e.g. silicon dioxide and / or aluminum oxide (so-called microporous nickel "MPS nickel" layers). Those chrome layers with pores are preferably used for chrome finish surfaces on substrates in applications for automotive parts outside the passenger compartment, e.g. for visible decorative chrome finish surfaces.

[0037] Preferably, one of the at least one intermediate layer having pores and in direct contact with the trivalent chromium plating layer is a nickel layer, for example a bright nickel layer, a satin nickel layer or a matte nickel layer, obtained by electroplating the substrate with a nickel electroplating bath containing a brightener; an MPS nickel layer, obtained by electroplating the substrate with a nickel electroplating bath containing small particles of a non-conductive substance, for example silicon dioxide and / or aluminum oxide. The substrate has at least one further intermediate layer, which is not a bright nickel layer in the case of bright nickel or is not an MPS nickel layer in the case of an MPS nickel layer.

[0038] The number of pores in a trivalent chromium plating layer derived from the underlying bright or satin nickel layer in direct contact is approximately 100 pores / cm 2 or more, preferably 100-2000 holes / cm 2 The number of pores in the trivalent chromium plating layer derived from the underlying MPS nickel layer in direct contact is approximately 10,000 pores / cm 2 or more, preferably 20,000 holes / cm 2 More, even more preferably 20,000 to 500,000 pores / cm 2 The average diameter of the active pores is about 2 μm. The number of pores can be measured by known tests, for example the Dupernell test, the Cass test or the pore counting test (unpublished DE102016013792.4). In some cases, the chromium surface layer contains about 500-5000 pores / cm and cracks (preferably microcracks).

[0039] The bright nickel layer preferably has a thickness of 2-20 μm. The MPS nickel layer preferably has a thickness of 0.5-3.5 μm. In all those cases the chromium layer does not seal the underlying intermediate metal and / or metal alloy layer. Therefore at least the outermost intermediate layer in direct contact with the chromium layer is also exposed to the environment and corrosive media. The contact may occur through the above-mentioned pores.

[0040] Permanganate (i.e., permanganate ion MnO) in an aqueous solution (hereinafter also referred to as "solution") 4 - The concentration of ) is preferably in the range of 0.05 to 4.5 mol / L, more preferably 0.1 to 0.5 mol / L. Suitable permanganate salts include, but are not limited to, sodium permanganate, potassium permanganate or ammonium permanganate.

[0041] The phosphorus-oxygen compound may be an inorganic phosphorus-oxygen compound or an organic phosphorus-oxygen compound.

[0042] The preferred inorganic phosphorus-oxygen compounds are phosphorus oxoacids or their salts. In particular, the inorganic phosphorus-oxygen compounds may be selected from phosphates, hydrogen phosphates, dihydrogen phosphates, pyrophosphates, phosphonates (i.e., salts of phosphonic acid), or their acid forms. Mixtures of one or more of these compounds are also included in the present invention.

[0043] The organic phosphorus-oxygen compound means a phosphorus-oxygen compound containing at least one hydrocarbon group. Preferred organic phosphorus-oxygen compounds are phosphorus oxoacids or salts thereof containing at least one hydrocarbon group. In particular, the organic phosphorus-oxygen compound is an organic phosphonate (R-PO(OH) 2 , R=hydrocarbon group), esters of phosphoric acid, esters of phosphonic acid (also phosphorous acid), phosphite esters or salts thereof. Mixtures of one or more of these compounds are also included in the present invention.

[0044] The concentration of at least one compound selected from phosphorus-oxygen compounds, hydroxides, nitrates, borates, boric acid, silicates, or a combination of two or more of these compounds, is preferably in the range of 0.05-2 mol / L, more preferably 0.2-0.6 mol / L. This concentration is relative to the total concentration of all compounds, if one or more compounds are present. If said compound is an ionic compound, this concentration is relative to the anion, or anions in said compound, e.g. PO 4 3- , H 2 PO 4 - , R 1 PO(OR 2 )O - (In the above formula, R 1 = alkyl, aryl, R 2 =H, alkyl, aryl), NO 3 - , O.H. - , B 4 O 7 2- The compound is added to a buffer, specifically KH 2 PO 4 , Na 2 B 4 O 7 as an acid, e.g. HNO 3 or as a base or brine, e.g. NaOH. When more than one of these compounds are used, the concentrations refer to the total concentration of all these compounds. Depending on the pH of the solution, more than one (i.e. two or more of them) phosphorus-oxygen compounds can be present, e.g. salts and acid forms, e.g. (di)hydrogen phosphate and phosphorous acid, can be present simultaneously. Borates can be present as monoborate, diborate, triborate and / or tetraborate. Suitable cations of the above mentioned compounds, if not acids, are, without limitation, sodium, potassium and ammonium.

[0045] In one embodiment, particularly H 3 PO 4 / HPO 4 - or H 2 PO 4- / HPO 4 2- When used, the pH value of the aqueous solution is in the range of 1-7.

[0046] In another embodiment, particularly OH - When used, the pH value of the aqueous solution is in the range of 7-11.

[0047] In another embodiment, particularly HNO 3 When used, the pH value of the aqueous solution is in the range of 1-5.

[0048] The transparent corrosion protection layer formed on the chromium finished surface during the contact of the chromium finished surface with the aqueous solution in step b) has a thickness of about 1-50 nm, preferably 5-10 nm. Without wishing to be bound by theory, it is believed that chromium (III) oxide is formed by the chromium in the chromium layer by the permanganate treatment, and thus the transparent corrosion protection layer is composed of chromium (III) oxide (Cr) as the main component. 2 O 3 ) is considered to be included.

[0049] A substrate comprising a chrome-finished surface can be contacted with the aqueous solution by immersing the substrate in the aqueous solution, by spraying the aqueous solution onto the substrate, or by brushing the aqueous solution onto the substrate. The contact time for contacting the chrome-finished surface with the aqueous solution is 5 to 900 seconds, preferably 10 to 400 seconds, and preferably 5 to 900 seconds in the case of immersion.

[0050] The method of the present invention can be carried out electrolessly or by applying a current. In one embodiment, in step b) of the method, an electric potential is applied between the chromium surface acting as the anode or cathode and an inert counter electrode, preferably the chromium surface acting as the cathode and the counter electrode acting as the anode. The inert counter electrode can be made of a material selected from the group including, for example, stainless steel, graphite, mixed oxide-coated titanium or platinized titanium.

[0051] Upon application of an electrical potential, a current is passed through a substrate that includes a chromium surface, preferably the chromium surface serving as the cathode.

[0052] Additional application of electric current can be used to improve corrosion resistance, where the achieved corrosion resistance as shown by NSS is more than 120 hours, preferably at least 120 hours to 240 hours, more preferably at least 120 hours to 480 hours, without any change in the surface (defect area: 0%). Without being bound by theory, it is believed that the underlying metal layer, preferably the bright nickel layer, the satin Ni layer or the MPS nickel layer (which is in direct contact with the trivalent chromium plating layer), is also affected to at least partially form a passivation layer adjacent to the cracks or pores and cracks of the chromium layer. In this way, the corrosion half-reactions 1) reduction of oxygen (on the chromium surface, cathodic) and 2) dissolution of nickel (on the underlying nickel surface exposed through the pores or cracks, anodic) are inhibited, resulting in improved corrosion resistance.

[0053] 0.005~5A / dm2 for the area of ​​the chromium surface acting as the cathode 2 , preferably 0.02 to 1.5 A / dm 2 can be produced.

[0054] For a chromium surface acting as an anode, 0.5A / dm 2 Less than 0.005 to 0.5 A / dm 2 A current density of is preferably 1000 .mu.m.

[0055] When an electrolytic process is used, the contact time of the article with the solution may be in the same range as for the electroless process. When the chromium surface acts as the cathode, the potential or current may be applied for 5 to 900 seconds, preferably 10 to 400 seconds.

[0056] When the chromium surface serves as the anode, the potential or current may be applied for less than 100 seconds, preferably less than 60 seconds, and most preferably between 5 and 60 seconds.

[0057] The contact of the chromium surface with the aqueous solution can be carried out at a temperature of the solution of 20 to 100°C, preferably 25 to 50°C.

[0058] During the electrolytic process, a substrate comprising a chromium surface can be contacted with the aqueous solution by immersing the substrate in the aqueous solution, by spraying the aqueous solution onto the substrate, or by brushing the aqueous solution onto the substrate, preferably by immersion.

[0059] After step c), the treated chromium surface with the transparent corrosion protection layer may be subjected to a rinsing step with water, preferably DI water, to rinse away said aqueous solution.

[0060] During treatment with permanganate, MnO 2 may be formed on the transparent corrosion protection layer. Preferably, the formed transparent corrosion protection layer after step c) is essentially MnO 2 Not included.

[0061] "Essentially MnO 2 "Free of MnO" refers to the surface of the transparent corrosion protection layer or a part of said surface. 2 means that the amount of discoloration on the chrome finish surface, especially on bright chrome finish surfaces, is so minimal that no discolouration is observable by the naked human eye (visual inspection).

[0062] In some cases, e.g., on dark chrome surfaces, the transparent corrosion protection layer formed is not detectable by visual inspection, but is instead MnO 2 may include.

[0063] Thus, in one embodiment, the method of the invention comprises, as a further step, d) After the treatment with the aqueous solution in step b), the chromium surface is treated with MnO 2 Treating with components capable of reducing or dissolving, especially with acids and / or reducing agents Includes.

[0064] Treatment with said components, especially with reducing agents, can improve or reconstruct the appearance and color of chrome finish surfaces after treatment with permanganate, while the transparent corrosion protection layer remains unchanged and achieves corrosion resistance after 120 hours of NSS.

[0065] It was shown that no visible color change of the chromium surface was observed after the reduction step. When a solution containing phosphorus-oxygen compounds was used in step b), MnO 2 It has been shown that the layer can be reduced to obtain a phosphorus-rich chromium(III) oxide layer. Such a phosphorus-rich layer has been found to have beneficial passivation properties. Without wishing to be bound by theory, it is believed that chromium(III) oxide is formed by the permanganate treatment. However, it has been shown that the method results in the formation of an oxide layer after steps b) and d), the thickness of which is greater than that of the unmodified surface (i.e. the surface not treated by steps b) and d).

[0066] Said component, in particular the reducing agent, may be hydrogen peroxide, hydrazine, potassium iodide, sodium sulfite, hydroxylammonium sulfate or a carbohydrate, preferably a reduced hydrocarbon, preferably a reduced sugar, even more preferably a monosaccharide, such as glucose.

[0067] The acid may be selected from sulfuric acid, nitric acid, ascorbic acid and acetic acid.

[0068] An acid and / or a reducing agent is preferably applied to the solution.

[0069] The treatment temperature with said components, such as acid and / or reducing agent, may be between 25 and 45° C. The application time is preferably between 10 and 600 seconds.

[0070] In one embodiment, the method according to the invention comprises as a further step Rinsing the chromium surface after treatment with the aqueous solution in step b) and before treatment with the component in step d). Includes.

[0071] The aqueous solution may contain a conductivity salt and / or a surfactant. [Brief description of the drawings]

[0072] [Figure 1] FIG. 1 shows the results of XPS analyses carried out on the as-plated chromium surface, the chromium surface after post-treatment, and the chromium surface after the post-treatment and reduction step according to Example 6. [Diagram 2] FIG. 2 shows the surface elemental composition of the chromium surface as plated, after post-treatment, and after the post-treatment and reduction step according to Example 6. [Diagram 3] 3 shows the depth profiles of the as-plated and post-treated reduced surfaces obtained using XPS sputter profiling. The dashed lines indicate the intersection of Cr and O concentrations, which can be taken as a qualitative indication of the oxide thickness according to Example 6. [Figure 4] Figure 4 shows panels after 480 hours of salt spray testing according to ISO 9227. The upper panel shows the chromium surface without post-treatment with visible corrosion products on the surface, and the lower panel shows the post-treated surface, according to Example 1 (without post-treatment) and according to Example 2 (with post-treatment). EXAMPLES

[0073] The invention will now be described with reference to the following non-limiting examples.

[0074] Similar sized ABS substrates containing multiple layers of copper, semi-bright nickel, bright nickel, optional non-conductive particle containing nickel ("microporous nickel") and finish chrome layers, as well as brass panels (10x10mm) containing bright nickel and finish chrome layers, were used for the examples. The chrome layers were either bright or dark chrome layers, as indicated in each example, which were deposited from a trivalent chromium based electrolyte.

[0075] The optical appearance of the chrome surfaces was visually inspected prior to the salt spray test.

[0076] The NSS tests were carried out according to ISO 9227. The results are presented with each example.

[0077] Example 1 (comparison): A bright chrome surface (brass panel) without any post-treatment was investigated by a salt spray test according to ISO 9227 NSS.

[0078] Untreated bright chrome surfaces have a significant change in appearance (defect area >5-10%) when the chrome surface is visually inspected after 120 hours.

[0079] Example 2 Polished chrome surfaces (brass panels) were stained with 40 g / L potassium permanganate (KMnO 4 ) and 50 g / L monopotassium dihydrogen phosphate (KH 2 PO 4 ) for 90 seconds at 25°C while applying a current density of 1 A / dm2 to the chromium surface as the cathode. 2 The chromium surface was then rinsed with DI water and 2 SO 4 and H 2 O 2 The specimen was immersed in a solution consisting of the following for 5 seconds at 25°C.

[0080] The optical appearance did not change significantly after post-treatment, and the treated chrome surface did not show any changes when visually inspected after 480 hours of salt spray testing, and passed the corrosion test (defect area: 0%).

[0081] Example 3 (Comparison) A bright chrome surface (ABS cap with non-conductive particles containing nickel in a multilayer structure) without post-treatment was investigated by a salt spray test according to ISO 9227 NSS.

[0082] The untreated bright chrome surfaces had a significant change in the appearance of the chrome surface when visually inspected after 120 hours (defect area >10-25%).

[0083] Example 4 The bright chrome surface (ABS cap, without nickel containing non-conductive particles in the multilayer structure) was pretreated with 40 g / L potassium permanganate (KMnO 4 ) and 50 g / L monopotassium dihydrogen phosphate (KH 2 PO 4 ) for 90 seconds at 25°C while applying a current density of 1 A / dm2 to the chromium surface as the cathode. 2 The chromium surface was then rinsed with DI water and 2 SO 4 and H 2 O 2 The specimen was immersed in a solution consisting of the following for 5 seconds at 25°C.

[0084] The optical appearance did not change significantly after post-treatment, and the treated chrome surface did not show any changes when visually inspected after 480 hours of salt spray testing, and passed the corrosion test (defect area: 0%).

[0085] Example 5 A bright chrome surface (ABS cap with non-conductive particles containing nickel in a multi-layer structure) was etched with 40 g / L sodium permanganate (NaMnO 4 ) and 50 g / L monopotassium dihydrogen phosphate (KH 2 PO 4 ) for 10 minutes at 50° C., and no external current was applied to the chromium surface.

[0086] The optical appearance did not change significantly after post-treatment, and the treated chrome surface did not show any changes when visually inspected after 120 hours of salt spray testing, passing the corrosion test (defect area: 0%).

[0087] Example 6 A bright chrome surface (ABS cap with non-conductive particles containing nickel in a multi-layer structure) was etched with 40 g / L sodium permanganate (NaMnO 4 ) and 50 g / L monopotassium dihydrogen phosphate (KH 2 PO 4 ) for 60 seconds at 25°C while applying a current density of 0.5 A / dm2 to the chromium surface as the cathode. 2 The chromium surface was then rinsed with DI water and 2 SO 4 and H 2 O 2 The specimen was immersed in a solution consisting of the following for 5 seconds at 25°C.

[0088] The optical appearance did not change significantly after post-treatment, and the treated chromium surface passed the corrosion test without any change when visually inspected after 120 hours of salt spray testing (defect area: 0%). Even after 480 hours of salt spray testing, the chromium surface showed only slight changes of the chromium surface (defect area <0.5%).

[0089] Example 7 A bright chrome surface (ABS cap with non-conductive particles containing nickel in a multi-layer structure) was etched with 40 g / L potassium permanganate (KMnO 4 ) and 50 g / L monopotassium dihydrogen phosphate (KH 2 PO 4 ) for 3 min at 25°C while applying a current density of 0.5 A / dm2 to the chromium surface as the cathode. 2 The chromium surface was then rinsed with DI water and 2 SO 4 and H 2 O 2 The specimen was immersed in a solution consisting of the following for 5 seconds at 25°C.

[0090] The optical appearance did not change significantly after post-treatment, and the treated chrome surface did not show any changes when visually inspected after 480 hours of salt spray testing, and passed the corrosion test (defect area: 0%).

[0091] Example 8 A bright chrome surface (ABS cap with non-conductive particles containing nickel in a multi-layer structure) was etched with 40 g / L sodium permanganate (NaMnO 4 ) and 50 mL / L sodium hydroxide solution (NaOH, 30 mass%) at 50 °C for 30 seconds, while applying a current density of 0.5 A / dm2 to the chromium surface as the cathode. 2 The chromium surface was then rinsed with DI water and 2 SO 4 and H 2 O 2 The specimen was immersed in a solution consisting of the following for 5 seconds at 25°C.

[0092] The optical appearance did not change significantly after post-treatment, and the treated chrome surface did not show any changes when visually inspected after 120 hours of salt spray testing, passing the corrosion test (defect area: 0%).

[0093] Example 9 A bright chrome surface (ABS cap with non-conductive particles containing nickel in a multi-layer structure) was etched with 40 g / L sodium permanganate (NaMnO 4 ) and 15 g / L sodium tetraborate (Na 2 B 4 O 7 10H 2 The chromium surface was then treated with an aqueous solution containing 1,2-dichloroethane (HO) for 10 minutes at 50° C., and no external current was applied to the chromium surface. The chromium surface was then rinsed with DI water and 2 SO 4 and H 2 O 2 The specimen was immersed in a solution consisting of the following for 5 seconds at 25°C.

[0094] The optical appearance is not significantly changed after post-treatment and the treated chromium surface exhibits enhanced corrosion resistance compared to untreated, and when visually inspected after 120 hours of salt spray testing, the treated chromium surface shows only minor changes to the chromium surface (defect area <0.25%).

[0095] Example 10 (Comparison) The dark chrome surface (ABS cap with non-conductive particles containing nickel in a multi-layer structure) was investigated without any post-treatment by a salt spray test according to ISO 9227 NSS.

[0096] The untreated dark chrome surface has a significant change in the appearance of the chrome surface (>50% defect area) when visually inspected after 120 hours.

[0097] Example 11 The dark chrome surface (ABS cap, without nickel containing non-conductive particles in the multilayer structure) was pretreated with 40 g / L potassium permanganate (KMnO 4 ) and 50 g / L monopotassium dihydrogen phosphate (KH 2 PO 4 ) for 90 seconds at 25°C while applying a current density of 1 A / dm2 to the chromium surface as the cathode. 2 The chromium surface was then rinsed with DI water and 2 SO 4 and H 2 O 2 The specimen was immersed in a solution consisting of the following for 5 seconds at 25°C.

[0098] The optical appearance did not change significantly after post-treatment, and the treated chrome surface passed the corrosion test without any change when visually inspected after 120 hours of salt spray testing (defect area: 0%). Even after 480 hours of salt spray testing, the chrome surface shows only slight changes of the chrome surface (defect area <0.25%).

[0099] Example 12 The dark chrome surface (brass panel) was stained with 40 g / L potassium permanganate (KMnO 4 ) and 50 g / L monopotassium dihydrogen phosphate (KH 2 PO 4 ) for 90 seconds at 25°C while applying a current density of 1 A / dm2 to the chromium surface as the cathode. 2 The chromium surface was then rinsed with DI water and 2 SO 4and H 2 O 2 The specimen was immersed in a solution consisting of the following for 5 seconds at 25°C.

[0100] The optical appearance did not change significantly after post-treatment, and the treated chrome surface passed the corrosion test without any change when visually inspected after 120 hours of salt spray testing (defect area: 0%). After 240 hours of salt spray testing, the chrome surface shows only slight changes of the chrome surface (defect area <0.1%).

[0101] Example 13 The dark chrome surface (ABS cap with non-conductive particles containing nickel in a multi-layer structure) was pretreated with 40 g / L potassium permanganate (KMnO 4 ) and 50 g / L monopotassium dihydrogen phosphate (KH 2 PO 4 ) for 10 minutes at 50° C., and no external current was applied to the chromium surface. The chromium surface was then rinsed with DI water and 2 SO 4 and H 2 O 2 The specimen was immersed in a solution consisting of the following for 5 seconds at 25°C.

[0102] The optical appearance did not change significantly after post-treatment, and the treated chromium surface showed a significant enhancement in corrosion resistance compared to the untreated one; when visually inspected after 480 hours of salt spray testing, the treated chromium surface showed only minor changes to the chromium surface (defect area <0.1%).

[0103] Example 14 The dark chrome surface (ABS cap with non-conductive particles containing nickel in a multi-layer structure) was pretreated with 40 g / L potassium permanganate (KMnO 4 ) and 50 g / L nitric acid (HNO 3 ) for 10 minutes at 50° C., and no external current was applied to the chromium surface. The chromium surface was then rinsed with DI water and 2 SO 4 and H 2 O2 The specimen was immersed in a solution consisting of the following for 5 seconds at 25°C.

[0104] The optical appearance did not change significantly after post-treatment, and the treated chrome surface passed the corrosion test without any change when visually inspected after 120 hours of salt spray testing (defect area: 0%). After 240 hours of salt spray testing, the chrome surface shows only slight changes of the chrome surface (defect area <0.1%).

[0105] Example 15 A bright chrome surface (ABS cap with non-conductive particles containing nickel in a multi-layer structure) was etched with 40 g / L potassium permanganate (KMnO 4 ) and 50 g / L monopotassium dihydrogen phosphate (KH 2 PO 4 ) for 90 seconds at 25°C while applying a current density of 0.1 A / dm2 to the chromium surface as the cathode. 2 The chrome surface was then rinsed with DI water.

[0106] The optical appearance did not change significantly after post-treatment, and the treated chrome surface passed the corrosion test without any changes in the surface when visually inspected after 480 hours of salt spray testing (defect area: 0%).

[0107] Example 16 A bright chrome surface (ABS cap with non-conductive particles containing nickel in a multi-layer structure) was etched with 40 g / L potassium permanganate (KMnO 4 ) and 50 g / L monopotassium dihydrogen phosphate (KH 2 PO 4 ) for 90 seconds at 25°C while applying a current density of 1.5 A / dm2 to the chromium surface as the cathode. 2 The chrome surface was then rinsed with DI water.

[0108] The optical appearance was unchanged after post-treatment, and the treated chrome surface passed the corrosion test (defect area <0.1%) without any change in the surface when visually inspected after 480 hours of salt spray testing.

[0109] Example 17 A bright chrome surface (ABS cap with non-conductive particles containing nickel in a multi-layer structure) was etched with 40 g / L potassium permanganate (KMnO 4 ) and 50 g / L monopotassium dihydrogen phosphate (KH 2 PO 4 ) for 90 seconds at 25°C while applying a current density of 1.0 A / dm2 to the chromium surface as the cathode. 2 The chrome surface was then rinsed with DI water.

[0110] The optical appearance was unchanged after post-treatment, and the treated chrome surface passed the corrosion test without any changes in the surface when visually inspected after 480 hours of salt spray testing (defect area: 0%).

Claims

1. 1. A method for post-treating a chrome finished surface to improve corrosion resistance, comprising the steps of: a) providing a substrate having a chrome finished surface and at least one intermediate layer between the chrome finished surface and the substrate selected from the group consisting of nickel, a nickel alloy, copper, and a copper alloy; wherein the chrome finish surface is a surface of a trivalent chrome plating layer, obtained by electroplating the substrate having the at least one intermediate layer in a plating bath containing chromium (III) ions as the main chromium source; b) removing said chrome finished surface by Permanganate At least one compound selected from phosphorus-oxygen compounds, hydroxides, nitrates, borates, boric acid, silicates, or a mixture of two or more of these compounds. contacting the aqueous solution containing c) forming a transparent corrosion protection layer on the chrome finished surface during contact of said chrome finished surface with the aqueous solution in step b). The method comprising:

2. 2. The method of claim 1, wherein the at least one compound is selected from inorganic phosphorus and oxygen compounds as phosphates, hydrogen phosphates, dihydrogen phosphates, pyrophosphates, phosphonates or mixtures thereof, hydroxides, borates or nitrates.

3. 3. The method according to claim 1 or 2, wherein the plating bath comprises less than 0.02% by weight of chromium (VI) ions, and the trivalent chromium plating layer formed comprises chromium in an amount of 45-90 at% (atomic percent) and oxygen in an amount of 5-20 at%, with the proviso that the total amount of all chemical elements together does not exceed 100 at%, and the amount of chromium is in all cases the highest amount in the trivalent chromium plating layer.

4. 4. The method according to claim 1, wherein the plating bath contains less than 0.02% by weight of chromium (VI) ions and the trivalent chromium plating layer contains chromium in an amount of 45 to 90 at.%, oxygen in an amount of 5 to 20 at.%, iron in an amount of 0 to 30 at.%, carbon in an amount of 0 to 15 at.%, sulfur in an amount of 0 to 15 at.%, and further metals or non-metals in an amount of 0 to 1 at.%, with the proviso that the total amount of all chemical elements together does not exceed 100 at.%, and the amount of chromium is in all cases the highest amount in the trivalent chromium plating layer.

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

6. 6. The method according to claim 1, wherein in step b) an electrical potential is applied between the chrome-finished surface and an inert counter electrode, the chrome-finished surface acting as a cathode and the counter electrode acting as an anode.

7. Current density of 0.005 to 5 A / dm2 for the area of ​​the chrome-finished surface 2 The method of claim 6, wherein:

8. The method of claim 6 or 7, wherein the potential is applied for 5 to 900 seconds.

9. As a further step, d) The chrome-finished surface after treatment with the aqueous solution in step b) is treated with MnO 2 Treating with a component that can reduce or dissolve The method according to any one of claims 1 to 8, comprising:

10. 10. The method of claim 9, wherein the component is hydrogen peroxide, hydrazine, potassium iodide, sodium sulfite, hydroxylammonium sulfate, or a carbohydrate.

11. 11. The method of claim 9 or 10, wherein the component is selected from sulfuric acid, nitric acid, ascorbic acid and acetic acid.

12. As a further step, 12. The method of any one of claims 9 to 11, comprising rinsing the chrome finished surface after step b) and before step d).

13. The method according to any one of claims 1 to 12, wherein the concentration of permanganate in the aqueous solution is 0.05 to 4.5 mol / L.

14. 14. The method according to claim 1, wherein the concentration of phosphorus-oxygen compounds, hydroxides, nitrates, borates, boric acid or silicates in the aqueous solution is 0.05 to 2 mol / L.

15. 15. The method of any one of claims 1 to 14, wherein the chrome finish surface is a decorative chrome finish surface.

16. treating a chrome finish surface to form a transparent corrosion protection layer on said chrome finish surface to improve the corrosion resistance and / or passivation of said chrome finish surface; Permanganate At least one compound selected from phosphorus-oxygen compounds, hydroxides, nitrates, borates, boric acid, silicates, or a mixture of two or more of these compounds. Use of an aqueous solution comprising The use, wherein the aqueous solution is used on a chrome finish surface as a decorative chrome finish surface on a substrate in applications for substrates in the automotive, white goods and sanitary industries.

17. 17. Use according to claim 16, wherein the treated chrome-finished surface with a transparent corrosion protection layer does not show any changes in the surface, i.e. 0% defect area, after application of the NSS test according to ISO 9227 for at least 120 hours.

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