Electroplating composition for depositing a chromium or chromium alloy layer on a substrate and associated method, use and substrate

Abstract

The present invention relates to an electroplating composition for depositing a chromium or chromium alloy layer on a substrate, the composition comprising (i) trivalent chromium ions, (ii) at least one miscible agent for the trivalent chromium ions, and (iii) at least one oxide-hydroxide particle; a method for depositing various chromium and chromium alloy layers; various uses of the particles; and various substrates comprising the chromium or chromium alloy layer.

Description

[Technical Field]

[0001] The present invention relates to an electroplating composition for depositing a chromium or chromium alloy layer on a substrate, the composition comprising (i) trivalent chromium ions, (ii) at least one miscible agent for the trivalent chromium ions, and (iii) at least one oxide-hydroxide particle; a method for depositing various chromium and chromium alloy layers; various uses of the particles; and various substrates comprising the chromium or chromium alloy layer. [Previous Technology]

[0002] Compared to decorative chromium layers, which are typically less than 1 μm thick, functional chromium layers usually have a much higher average layer thickness, typically ranging from at least 1 μm to hundreds of micrometers. Furthermore, functional chromium layers are characterized by excellent hardness and wear resistance, leading them to be commonly referred to as hard chromium layers.

[0003] The functional chromium layer obtained from an electroplating composition containing hexavalent chromium is known in the prior art and is a mature standard.

[0004] In recent decades, these hexavalent chromium-based electroplating compositions and methods have been increasingly replaced by healthier and more environmentally friendly trivalent chromium-based electroplating compositions and methods.

[0005] Furthermore, trivalent chromium-based electroplating compositions and methods using particles are known in the art.

[0006] In the Journal of the Taiwan Institute of Chemical Engineers, 48, 73-80 (2015), Hung-Hua Sheu et al. mentioned a trivalent chromium bath including Al2O3 particles.

[0007] In the Journal of Protection of Metals and Physical Chemistry of Surfaces, Vol. 46, No. 1, 75-81 (2010), NA Polyakov et al. mentioned a suspension of Cr(III)-oxalate sulfate solution containing Al2O3.

[0008] In Journal Surface & Coating Technology, 350, 1036-1044 (2018), Hung-Hua Sheu et al. mentioned a trivalent chromium bath including Al2O3 particles.

[0009] JP 5890394 B2 mentions an aqueous solution containing trivalent chromium compounds and ceramic particles such as Al2O3.

[0010] RU 2231581 C1 mentions a chromium electrolyte containing Cr(III) salt and Al2O3 powder.

[0011] It has been reported that incorporating Al2O3 particles can reduce the number of cracks in individual chromium and chromium alloy layers. However, even in the presence of these particles, chromium and chromium alloy layers typically do not change their typical bright and lustrous silver-like chromium appearance.

[0012] However, even for hard chrome plating, a less glossy appearance is sometimes required. For example, in some cases, it is necessary to provide a layer with reduced reflection. This can potentially increase safety measures and prevent accidents. Therefore, there is a need for further improvements to existing electroplating compositions in this regard.

[0013] Objective of the present invention Therefore, the objective of the present invention is to provide a trivalent chromium-based electroplating composition for depositing chromium or chromium alloy layers, which can further significantly reduce the number of cracks and their width and additionally reduce the brightness of individual chromium and chromium alloy layers.

[0014] Furthermore, the objective of this invention is to achieve this effect in a simple and effective manner. [Summary of the Invention]

[0015] The objectives mentioned above are achieved by an electroplating composition for depositing a chromium or chromium alloy layer on a substrate, the composition comprising: (i) trivalent chromium ions, (ii) at least one misalignment agent for the trivalent chromium ions, and (iii) at least one oxide-hydroxide particle.

[0016] Our experiments show that, by using at least one oxide-hydroxide particle, the number and width of cracks in individual chromium and chromium alloy layers are further reduced compared to commonly used oxide particles. Furthermore, and importantly, the brightness of the layer is also significantly reduced. In fact, the layer exhibits a much-desired reduction in brightness and can be described as matte (at least with significantly reduced reflection). This is surprising because this combined effect is unexpected. As shown in the following examples, this combined effect was not achieved using particles containing only oxides such as Al2O3.

[0017] Furthermore, the electroplating composition of the present invention is very simple because the combined effect is caused by a specific particle. No combination of particles or multiple compounds is required to achieve this effect. This is particularly important because oxide particles alone do not seem to provide this combined effect.

[0018] In the context of this invention, oxide-hydroxide particles refer to particles that chemically comprise a combination of oxides and hydroxides (i.e., compounds combining oxygen and hydroxides, for example, denoted as XO(OH), wherein X is an opposite ion / part of at least partially compensating for the negative charges of oxygen and hydroxides). Generally, X comprises a metal.

[0019] In the text of this invention, the terms "at least one" or "one or more" respectively mean (and are interchangeable with the following terms) "one, two, three or more" and "one, two, three or more". Furthermore, "trivalent chromium" refers to chromium with an oxidation state of +3. The term "trivalent chromium ion" refers to Cr3+ ions in free or misaligned form. Furthermore, "hexavalent chromium" refers to any compound (including ions) comprising elemental chromium having an oxidation state of +6.

Implementation Method

[0020] Electroplating composition: Preferably, the electroplating composition of the present invention comprises water, preferably 50% by weight or more, more preferably 60% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and even more preferably 90% by weight or more, most preferably 95% by weight or more, based on the total weight of the electroplating composition. Therefore, the electroplating composition of the present invention is preferably aqueous.

[0021] Preferably, the electroplating composition of the present invention has a pH range of 4.1 to 7.0, more preferably 4.5 to 6.5, even more preferably 5.0 to 6.0, and most preferably 5.3 to 5.9. Therefore, the electroplating composition is preferably acidic. The preferred acidic pH range is particularly advantageous for the effective deposition of chromium or chromium alloy layers on substrates having desired qualities (such as hardness and abrasion resistance).

[0022] Preferably, the electroplating composition of the present invention is wherein, based on the total volume of the electroplating composition, the trivalent chromium ions are present at a total concentration in the range of 5 g / L to 40 g / L, more preferably 10 g / L to 30 g / L, even more preferably 14 g / L to 27 g / L, and most preferably 17 g / L to 24 g / L.

[0023] Using the concentration range defined above, chromium and chromium alloy layers can be deposited very effectively on the substrate. In many cases, if the total amount of trivalent chromium ions is too low, insufficient deposition is observed, and the deposited chromium is usually of low quality. If the total amount significantly exceeds 40 g / L, the plating composition is no longer stable, which includes the formation of unwanted precipitates.

[0024] Preferably, the electroplating composition of the present invention contains trivalent chromium ions obtained from a soluble source containing trivalent chromium ions, typically a water-soluble salt comprising the trivalent chromium ions. Generally, readily available and cost-effective water-soluble salts are alkaline trivalent chromium sulfate.

[0025] Preferably, the soluble trivalent chromium ion source comprises alkali metal cations accounting for 1% by weight or less of the total weight of the source. In some cases, if the various deposition methods are operated sequentially, this source is preferably used to replenish the trivalent chromium ions. Preferred water-soluble salts comprising the trivalent chromium ions are alkali metal-free trivalent chromium sulfate or alkali metal-free trivalent chromium chloride.

[0026] More preferably, the soluble trivalent chromium ion source includes or is chromium sulfate, more preferably acidic chromium sulfate, and even more preferably chromium sulfate having the general formula Cr2(SO4)3 and a molecular weight of 392 g / mol.

[0027] More preferably, to supplement this, the soluble source containing trivalent chromium ions is preferably an organic anion, more preferably an organic acid anion, and most preferably formate and / or acetate.

[0028] Preferably, the electroplating composition of the present invention contains at least one chelating agent for the trivalent chromium ions selected from organic chelating agents and their salts, preferably carboxylic acids and their salts, more preferably aliphatic carboxylic acids and their salts, and most preferably aliphatic monocarboxylic acids and their salts. Preferably, the aliphatic monocarboxylic acids and their salts are C1-C10 aliphatic monocarboxylic acids and their salts, more preferably C1-C8 aliphatic monocarboxylic acids and their salts, more preferably C1-C6 aliphatic monocarboxylic acids and their salts, and most preferably C1-C3 aliphatic monocarboxylic acids and their salts. More preferably, the at least one chelating agent includes at least formate and / or acetate. Therefore, the trivalent chromium ions can be effectively stabilized in the electroplating composition by the chelating agent, preferably at the pH defined above. Generally, these chelating agents are incorporated as carbon into the chromium or chromium alloy layer.

[0029] Preferably, the electroplating composition of the present invention is wherein, based on the total volume of the composition, the at least one chelating agent for the trivalent chromium ions is present at a total concentration in the range of 50 g / L to 350 g / L, more preferably 70 g / L to 320 g / L, even more preferably 90 g / L to 300 g / L, even more preferably 100 g / L to 250 g / L, and most preferably 120 g / L to 210 g / L.

[0030] The electroplating composition of the present invention comprises (iii) at least one oxide-hydroxide particle. These particles are preferably solids. Therefore, the electroplating composition of the present invention is preferably a suspension. Therefore, the electroplating composition of the present invention is preferably non-colloidal.

[0031] Preferably, the electroplating composition of the present invention comprises at least one oxide-hydroxide particle including a metal, preferably a main group metal and / or a transition metal, wherein main group metals are preferred. Preferred transition metals include ions and / or manganese. Preferred main group metals include aluminum.

[0032] Therefore, more preferably, the metal includes aluminum, and most preferably, the metal is (generally) aluminum and (generally) other metals are preferably not present in the particles.

[0033] Therefore, the preferred electroplating composition of the present invention is the at least one oxide-hydroxide particle comprising aluminum.

[0034] More preferably, the electroplating composition of the present invention includes at least one oxide-hydroxide particle comprising AlO(OH), more preferably α-AlO(OH) and / or γ-AlO(OH), and most preferably γ-AlO(OH).

[0035] The preferred electroplating composition of the present invention contains at least one oxide-hydroxide particle, which is AlO(OH), preferably α-AlO(OH) and / or γ-AlO(OH), and most preferably γ-AlO(OH). Therefore, it is preferable that no other oxide-hydroxide particles are present. Ideally, these are the only particles in the electroplating composition.

[0036] Preferably, the electroplating composition of the present invention contains, based on the total volume of the electroplating composition, at least one oxide-hydroxide particle (i.e., (iii)) having a total amount in the range of 0.1 g / L to 200 g / L, preferably 1 g / L to 100 g / L, more preferably 3 g / L to 80 g / L, even more preferably 5 g / L to 60 g / L, and even more preferably 8 g / L to 40 g / L, most preferably 10 g / L to 30 g / L. If the total amount is too low, i.e., below 0.1 g / L, the combined particles are insufficient, and therefore the desired reduction in brightness and crack reduction are generally not observed. Conversely, in many cases, if the total amount significantly exceeds 200 g / L, the particles tend to settle and result in insufficient particle distribution, which may be accompanied by defects in the chromium and chromium alloy layers.

[0037] Generally, the electroplating composition of the present invention is preferred, wherein the at least one oxide-hydroxide particle has a particle size in the range of 0.05 μm to 15 μm, more preferably 0.08 μm to 10 μm, more preferably 0.11 μm to 8 μm, even more preferably 0.21 μm to 6 μm, and most preferably in the range of 0.31 μm to 3 μm.

[0038] Preferably, the electroplating composition of the present invention contains at least one oxide-hydroxide particle having a particle size D50 in the range of 0.1 μm to 15 μm, more preferably 0.2 μm to 10 μm, more preferably 0.4 μm to 7 μm, even more preferably 0.6 μm to 5 μm, and most preferably 0.8 μm to 3.5 μm.

[0039] Preferably, the electroplating composition of the present invention, wherein the at least one oxide-hydroxide particle has a particle size D10 in the range of 0.05 µm to 2 µm, more preferably 0.1 µm to 1.5 µm, and even more preferably 0.15 µm to 1 µm.

[0040] Preferably, the electroplating composition of the present invention contains at least one oxide-hydroxide particle having a particle size D90 in the range of 0.5 µm to 15 µm, more preferably 0.75 µm to 10 µm, more preferably 0.9 µm to 7.5 µm, even more preferably 1.3 µm to 5 µm, and most preferably 1.5 µm to 2.5 µm.

[0041] Preferably, the particle size is based on a volumetric meter, and more preferably by diffraction.

[0042] In the electroplating composition of the present invention, it is preferable that hexavalent chromium is not intentionally added to the electroplating composition. This includes, for example, chromic acid and chromium trioxide. Therefore, the electroplating composition is substantially free of hexavalent chromium, and preferably does not contain hexavalent chromium (except for a very small amount of chromium that may inevitably form on the anode).

[0043] In some cases, the electroplating composition of the present invention is preferred, which further includes transition metal ions that are not chromium, and more preferably iron ions, nickel ions, copper ions and / or zinc ions.

[0044] However, preferably, the electroplating composition of the present invention does not additionally include iron ions.

[0045] However, preferably, the electroplating composition of the present invention does not additionally include nickel ions.

[0046] However, preferably, the electroplating composition of the present invention does not additionally include copper ions.

[0047] However, preferably, the electroplating composition of the present invention does not additionally include zinc ions.

[0048] More preferably, the electroplating composition of the present invention comprises, based on the total weight of all transition metal ions, 90% by weight or more, more preferably 93% by weight or more, more preferably 95% by weight or more, and most preferably 97% by weight or more. In most cases, the electroplating composition of the present invention preferably comprises, wherein the chromium species is the only transition metal species, and most preferably, the trivalent chromium ion is the only transition metal ion.

[0049] The presence of these non-chromium metal ions (so-called metallic alloying elements) usually results in various chromium alloys. However, more typically and preferably, they are non-metallic alloying elements in the individual chromium alloy layers, preferably carbon, nitrogen and / or oxygen.

[0050] In addition, it is preferred to be an electroplating composition comprising one or more compounds selected from the group consisting of: - one or more types of halide ions, preferably bromide ions, - one or more types of alkali metal cations, preferably sodium and / or potassium, - sulfate ions, and - ammonium ions.

[0051] By adding one or more of the compounds mentioned above, the deposition of the chromium or chromium alloy layer during each deposition process can be improved, preferably during the method of the present invention.

[0052] Preferably, the electroplating composition of the present invention comprises one or more types of halide ions, preferably bromide ions and / or chloride ions. Preferably, based on the total volume of the electroplating composition, the bromide ions are present at a concentration of at least 0.06 mol / L, more preferably at least 0.1 mol / L, and even more preferably at least 0.15 mol / L. Bromine anions will particularly effectively suppress the anodic formation of hexavalent chromium species.

[0053] In some cases, the electroplating composition of the present invention preferably includes chloride ions in addition to bromide ions. However, in other cases, it is preferable that the electroplating composition is substantially free of chloride ions. However, this preference does not exclude the presence of other halide ions (preferably bromide ions). Preferably (if chloride ions are present), based on the total volume of the electroplating composition, chloride ions are present at a total concentration in the range of 0.01 mol / L to 1.8 mol / L, more preferably 0.2 mol / L to 1.6 mol / L, more preferably 0.6 mol / L to 1.4 mol / L, and most preferably 0.8 mol / L to 1.2 mol / L.

[0054] Preferably, the electroplating composition comprises one or more types of alkali metal cations, preferably sodium and / or potassium, and its total concentration, based on the total volume of the electroplating composition, is in the range of 0 mol / L to 0.5 mol / L, more preferably 0 mol / L to 0.3 mol / L, even more preferably 0 mol / L to 0.1 mol / L, and most preferably in the range of 0 mol / L to 0.08 mol / L.

[0055] Generally, rubidium ions, francium ions, and cesium ions are not used in electroplating compositions that include trivalent chromium ions, but they are not excluded. However, preferably, one or more types of alkali metal cations include lithium, sodium, and potassium metal cations, most preferably sodium and potassium. However, in some cases, the electroplating composition of the present invention preferably does not include one or more types of alkali metal cations. In this case, ammonium ions are preferred.

[0056] Preferably, the electroplating composition includes ammonium ions, and based on the total volume of the electroplating composition, the concentration is preferably from 1 mol / L to 10 mol / L, more preferably from 2 mol / L to 8 mol / L, even more preferably from 3 mol / L to 7 mol / L, and most preferably in the range of 4 mol / L to 6 mol / L.

[0057] Preferably, the electroplating composition of the present invention includes sulfate ions, and the total amount of sulfate ions is preferably in the range of 50 g / L to 250 g / L based on the total volume of the electroplating composition.

[0058] Preferably, the electroplating composition of the present invention is substantially free of, preferably not free of, boric acid, and preferably not free of, boron-containing compounds.

[0059] Boron-containing compounds are undesirable because they cause environmental problems. Wastewater treatment is expensive and time-consuming when boron-containing compounds are used. Furthermore, boric acid exhibits poor solubility and therefore tends to form precipitates. Although these precipitates can dissolve upon heating, the individual electroplating compositions cannot be used for electroplating during this period. There is a significant risk that these precipitates will promote a decrease in layer quality. Therefore, the electroplating compositions of the present invention are preferably substantially free of, and preferably do not contain, any boron-containing compounds. Surprisingly, the electroplating compositions of the present invention perform very well in the absence of boron-containing compounds, especially within the (preferred) pH range mentioned above.

[0060] In the context of this invention, the terms "does not comprise" and "not comprising" generally mean that individual compounds and / or components are not intentionally added to, for example, the electroplating composition. This does not exclude the possibility that such compounds may be introduced as impurities along with other related chemical substances. However, the total amount of such compounds and components is generally below the detection range and / or not critical in the various embodiments of this invention.

[0061] Generally speaking, it is preferable that the electroplating composition of the present invention is substantially free of, preferably does not include, organic compounds containing divalent sulfur, and is substantially free of, preferably does not include, sulfur-containing compounds having sulfur atoms with an oxidation number lower than +6.

[0062] The present invention also relates to a method for depositing a chromium or chromium alloy layer on a substrate, the method comprising the steps of: (a) providing the substrate, preferably a metal substrate; (b) providing an electroplating composition for depositing a chromium or chromium alloy layer, the composition comprising: (i) trivalent chromium ions; (ii) at least one miscible agent for the trivalent chromium ions; and (iii) at least one oxide-hydroxide particle; and (c) contacting the substrate with the electroplating composition and applying an electric current to deposit a chromium or chromium alloy layer on at least one surface of the substrate.

[0063] Preferably, the electroplating composition of the present invention mentioned above (preferably as described above) is also applicable to the method of the present invention (preferably as described below).

[0064] Preferably, the method of the present invention is wherein, in step (c), the current is direct current.

[0065] Preferably, the direct current (DC) is an uninterrupted DC current during electroplating, and more preferably, the DC current is not pulsed (non-pulsed DC). Furthermore, the DC current preferably does not contain reverse pulses.

[0066] Preferably, the method of the present invention, wherein in step (c), the current has a cathode current density of at least 18 A / dm², more preferably at least 20 A / dm², more preferably at least 25 A / dm², even more preferably at least 30 A / dm², and most preferably at least 39 A / dm². Preferably, the cathode current density is in the range of 18 A / dm² to 200 A / dm², more preferably in the range of 20 A / dm² to 180 A / dm², more preferably in the range of 23 A / dm² to 150 A / dm², even more preferably in the range of 25 A / dm² to 120 A / dm², and even more preferably in the range of 27 A / dm² to 90 A / dm², and most preferably in the range of 30 A / dm² to 60 A / dm².

[0067] In some rare cases, the method of the present invention is preferred, wherein in step (c), the current has a cathode current density in the range of 100 A / dm² to 200 A / dm², more preferably 110 A / dm² to 190 A / dm², even more preferably 120 A / dm² to 180 A / dm², most preferably 130 A / dm² to 170 A / dm², and even more preferably 140 A / dm² to 160 A / dm². This is most suitable if step (c) is performed for a relatively short period of time.

[0068] Generally, the substrate provided during the method of the present invention is the cathode during the electroplating process (in step (c)). Preferably, more than one substrate is provided simultaneously in step (c) of the method of the present invention.

[0069] Preferably, the method of the present invention includes a step (c) in which at least one anode is provided, wherein the at least one anode is independently selected from the group consisting of a graphite anode and a titanium anode, and a mixture of metal oxides. These anodes have been shown to be sufficiently resistant in the electroplating compositions of the present invention. Preferably, the at least one anode does not contain any lead or chromium.

[0070] In step (c) of the method of the present invention, a chromium or chromium alloy layer is deposited. Preferably, it is a chromium alloy layer. Preferably, the alloying element is one, more than one, or all elements selected from the group consisting of carbon, nitrogen, and oxygen. More preferably, the chromium alloy layer includes at least carbon and oxygen. Since organic compounds are usually present in the electroplating composition, carbon is usually present. These alloying elements are generally referred to as non-metallic alloying elements.

[0071] More preferably, the only alloying element is carbon, nitrogen and / or oxygen, more preferably carbon and / or oxygen, and most preferably carbon and oxygen. More preferably, based on the total weight of the chromium alloy layer, the chromium alloy layer contains 80% by weight of chromium or more, more preferably 85% by weight or more, even more preferably 90% by weight or more, and most preferably 95% by weight or more.

[0072] In some cases, the method of the present invention is preferred, wherein the chromium alloy layer comprises (in addition to or independently of the non-metallic alloying element) one, more than one, or all elements selected from the group consisting of nickel, copper, and zinc. These alloying elements are generally referred to as metallic alloying elements.

[0073] However, in many cases, the method of the present invention is preferred, wherein the chromium alloy layer does not include one, more than one, or all elements selected from the group consisting of sulfur, nickel, copper, zinc, and tin.

[0074] Particularly preferred is the method of the present invention, wherein the chromium alloy layer is substantially free of, and more preferably free of, sulfur.

[0075] Particularly preferred is the method of the present invention, wherein the chromium alloy layer is substantially free of, and preferably free of, nickel.

[0076] It is particularly preferred that the method of the present invention contains, in which the chromium alloy layer is substantially free of, and more preferably free of, copper.

[0077] Particularly preferred is the method of the present invention, wherein the chromium alloy layer is substantially free of zinc, and preferably free of zinc.

[0078] It is particularly preferred that the method of the present invention contains, in which the chromium alloy layer is substantially free of, and more preferably free of, tin.

[0079] In some cases, the method of the present invention is preferred, wherein the chromium alloy layer is substantially free of, and preferably free of, iron. This is particularly preferred if the at least one oxide-hydroxide particles include aluminum and do not include iron. The same applies if the at least one oxide-hydroxide particles include aluminum and do not include manganese. In this case, it is preferred that the chromium alloy layer (or otherwise) is substantially free of, and preferably free of, manganese.

[0080] Preferably, it is the method of the present invention, wherein in step (c), the electroplating composition has a temperature in the range of 20°C to 90°C, more preferably 30°C to 70°C, even more preferably 40°C to 60°C, and most preferably 45°C to 58°C.

[0081] In step (c), the chromium and chromium alloy layers are deposited in an optimal manner within a preferred temperature range (especially within the optimal temperature range). If the temperature significantly exceeds 90°C, unwanted vaporization will occur, which can adversely affect the concentration of the components in the composition. Furthermore, the suppression of undesirable anode formation of hexavalent chromium is significantly reduced. If the temperature is significantly below 20°C, the deposition is generally insufficient.

[0082] Preferably, the method of the present invention is performed for a period of 5 min to 500 min, more preferably 10 min to 300 min, even more preferably 15 min to 200 min, even more preferably 20 min to 140 min, and most preferably 30 min to 80 min.

[0083] In some rare cases, the method of the present invention is preferred, wherein step (c) is performed for a period of 2 to 10 minutes, preferably 3 to 9 minutes, more preferably 4 to 8 minutes, and even more preferably 5 to 7 minutes. If the current has a relatively high current density, preferably at least 100 A / dm2, more preferably at least 120 A / dm2, and even more preferably at least 140 A / dm2, this is optimal.

[0084] Preferably, it is the method of the present invention, wherein in step (c), the electroplating composition is stirred, preferably at a stirring rate in the range of 100 rpm to 900 rpm, more preferably 200 rpm to 700 rpm, more preferably 300 rpm to 600 rpm, and most preferably 350 rpm to 500 rpm. Stirring is preferred to provide (iii) excellent homogenization / distribution in the electroplating composition. If the stirring is too low, (iii) tends to result in unwanted settling. If the stirring is too strong, the surface of the electroplating composition is in excessive motion, and insufficient fog suppression is achieved.

[0085] By performing step (c) of the method within the preferred temperature range and / or (preferably) for a preferred time period and / or (preferably) at a preferred stirring rate mentioned above, particularly favorable deposition kinetics during step (c) can be ensured.

[0086] Preferably, the method of the present invention further includes step (d) heat treatment after step (c) to obtain the substrate from step (c).

[0087] Preferably, the method of the present invention is carried out in step (d) at a temperature ranging from 80°C to 600°C, more preferably from 100°C to 400°C, even more preferably from 120°C to 350°C, and even more preferably from 135°C to 300°C, and most preferably from 150°C to 250°C.

[0088] Preferably, the method of the present invention is used, wherein in step (d), the heat treatment is performed for a period of 1 hour to 10 hours, preferably 2 hours to 4 hours.

[0089] By performing the heat treatment of the substrate more preferably at a better temperature and / or a better time period as described above, the properties of the chromium and chromium alloy layers are generally further improved in many cases (e.g., hardness).

[0090] Preferably, the method of the present invention includes a substrate comprising a metal or a metal alloy, more preferably comprising one or more metals selected from the group consisting of copper, iron, nickel and aluminum, more preferably comprising one or more metals selected from the group consisting of copper, iron and nickel, and most preferably comprising at least iron. The metals mentioned above comprise various alloys, including at least one of these metals.

[0091] More preferably, the substrate is a tie rod.

[0092] In many cases, the substrate preferably includes at least one pre-coated substrate, the at least one pre-coating preferably including a metal layer, more preferably including a metal layer of at least one transition metal, even more preferably including a metal layer of a fourth period (according to the periodic table) transition metal, most preferably including a metal layer of nickel and / or chromium, even more preferably a nickel or nickel alloy layer, on which chromium and chromium alloy layers are respectively applied during step (c) of the method of the present invention. Particularly preferred is a steel substrate pre-coated with a metal layer as defined above, preferably a nickel or nickel alloy layer. Alternative or additional pre-coatings preferably include a chromium metal layer. However, alternatively or additionally, other pre-coatings are present. In many cases, this pre-coating will significantly increase corrosion resistance compared to a metal substrate without such pre-coatings. However, in some cases, the substrate is not easily corroded due to a corrosive inert environment (e.g., in an oil composition). In this case, a pre-coating is not necessarily required, preferably a nickel or nickel alloy layer.

[0093] Therefore, in some cases, the method of the present invention is preferred, wherein the substrate does not include nickel and nickel alloy layers located below the chromium and chromium alloy layers, respectively. Since at least one oxide-hydroxide particle in the electroplating composition used in the method of the present invention significantly improves the corrosion resistance of the chromium and chromium alloy layers, the need for this pre-coating is further reduced.

[0094] Generally, the method of the present invention is preferred, wherein in step (c), the chromium and chromium alloy layers each have a thickness in the range of 1.1 μm to 500 μm, more preferably 2 μm to 450 μm, more preferably 4 μm to 400 μm, even more preferably 6 μm to 350 μm, and even more preferably 8 μm to 300 μm, and most preferably 10 μm to 250 μm. These are generally the thicknesses of so-called hard chromium layers to provide sufficient wear resistance. Therefore, the chromium and chromium alloy layers obtained in the text of the present invention are preferably not decorative layers.

[0095] In some other cases, the method of the present invention is preferred, wherein in step (c), the chromium and chromium alloy layers have a thickness of 15 μm or higher, more preferably 20 μm or higher, and even more preferably 30 μm or higher.

[0096] As mentioned at the beginning, the present invention results in a reduction in brightness and / or reflectivity. Preferably, the method of the present invention includes, in step (c), the chromium and chromium alloy layers each having an L* value of 70 or less as defined by CIELAB. Preferably, the L* value is measured in a mode that includes a specular reflection component (also referred to as SCI mode). This means that specular reflection and diffuse reflection are included during the measurement process. More preferably, it has an L* value of 69 or less, and even more preferably 68 or less. This L* value is significant because, in the absence of (iii), the L* value is significantly higher than 70, for example 75 or higher, more preferably 77 or higher. However, within the text of this invention, an L* value of 70 or slightly less is not considered dark. Therefore, the method of the present invention is preferred, wherein in step (c), the chromium and the chromium alloy layer respectively have an L* value in the range of 57 to 70, more preferably 58 to 69, even more preferably 59 to 68, and most preferably 60 to 68.

[0097] Preferably, the method of the present invention is wherein, in step (c), the chromium and the chromium alloy layer respectively have an a* value in the range of -2 to +2 and / or a b* value in the range of -2 to +2 as defined by CIELAB.

[0098] Preferably, the method of the present invention is wherein, in step (c), the chromium and the chromium alloy layer respectively have an a* value in the range of -1.5 to +1.5 and / or a b* value in the range of -1.5 to +1.5 as defined by CIELAB.

[0099] Even more preferably, the method of the present invention, wherein in step (c), the chromium and the chromium alloy layer respectively have an a* value in the range of -1 to +1 and / or a b* value in the range of -1 to +1 as defined by CIELAB.

[0100] The preferred method of the present invention is wherein, in step (c), the chromium and the chromium alloy layer respectively have an a* value in the range of -0.5 to +0.5 and / or a b* value in the range of -0.5 to +0.5 as defined by CIELAB.

[0101] Preferably, it is the method of the present invention, wherein after step (c), the chromium and chromium alloy layers have a hardness (HV) in the range of 650 to 950, more preferably 680 to 900, even more preferably 700 to 850, and most preferably 720 to 800.

[0102] More preferably, the method of the present invention, wherein after step (d), the chromium and the chromium alloy layer each have a hardness (HV) of 950 or greater. Preferably, after step (d), the hardness (HV) is in the range of 950 to 1900, more preferably from 1000 to 1700, more preferably from 1050 to 1500, and most preferably from 1100 to 1300.

[0103] This invention also relates to the use of at least one oxide-hydroxide particle in a trivalent chromium electroplating composition for depositing a hard chromium or hard chromium alloy layer having an L* value of 70 or less as defined by CIELAB.

[0104] Preferably, the electroplating composition of the present invention mentioned above (preferably as described above) and / or the method of the present invention (preferably as described above) are also applicable to the uses of the present invention.

[0105] Furthermore, the present invention relates to a first substrate comprising a chromium or chromium alloy layer, the substrate further comprising: - at least one pre-coating layer between the substrate and the chromium or chromium alloy layer as needed, wherein the chromium and chromium alloy layers each comprise at least one oxide-hydrogenate particle.

[0106] Preferably, the electroplating composition (preferably as described above) and / or the method (preferably as described above) mentioned above are also applicable to the first substrate of the present invention.

[0107] Preferably, the chromium and chromium alloy layer on the first substrate used in the present invention is obtained by means of the apparatus of the method of the present invention.

[0108] The substrate of the present invention is preferred, wherein the at least one pre-coating includes (preferably) a metal layer, more preferably a metal layer including at least one transition metal, even more preferably a metal layer including at least one fourth-period transition metal, preferably a metal layer including nickel and / or chromium, even more preferably a nickel or nickel alloy layer.

[0109] Particularly preferred is the first substrate of the present invention, wherein the chromium and chromium alloy layers each have an L* value of 70 or less as defined by CIELAB. More preferably, it is an L* value as defined above in the method of the present invention.

[0110] Preferably, the present invention relates generally to a hard chromium layer. Therefore, the first substrate of the present invention is preferred, wherein the chromium and chromium alloy layers have thicknesses in the range of 1.1 μm to 500 μm, more preferably 2 μm to 450 μm, more preferably 4 μm to 400 μm, even more preferably 6 μm to 350 μm, even more preferably 8 μm to 300 μm, and most preferably 10 μm to 250 μm.

[0111] Preferably, the first substrate of the present invention includes or is a metal rod.

[0112] Furthermore, the present invention relates to a more general substrate comprising a chromium or chromium alloy layer, the substrate further comprising: - at least one pre-coating layer between the substrate and the chromium or chromium alloy layer as needed, wherein the chromium and chromium alloy layers respectively - comprise carbon, - have an L* value of 70 or less as defined by CIELAB, and - have a thickness of 4 μm or higher.

[0113] Preferably, the electroplating composition (preferably as described above) and / or the method (preferably as described above) mentioned above regarding the present invention are also applicable to the more general substrates of the present invention.

[0114] The substrate of the present invention is preferred, wherein the at least one pre-coating layer includes (preferably) a metal layer, more preferably a metal layer including at least one transition metal, even more preferably a metal layer including at least one fourth-period transition metal, preferably a metal layer including nickel and / or chromium, even more preferably a nickel or nickel alloy layer.

[0115] Preferably, the substrate of the present invention is more general, wherein the chromium and chromium alloy layers have a thickness of 5 μm or higher, more preferably 6 μm or higher, even more preferably 8 μm or higher, and even more preferably 10 μm or higher, and most preferably 15 μm or higher.

[0116] Even more preferably, the substrate of the present invention is a more general one, wherein the chromium and chromium alloy layers have a thickness of 4 µm to 500 µm, more preferably 5 µm to 450 µm, even more preferably 6 µm to 400 µm, even more preferably 8 µm to 350 µm, and most preferably in the range of 10 µm to 300 µm.

[0117] More preferably, the substrate of the present invention is a more general one, wherein the chromium and chromium alloy layers have an L* value of 69 or less, more preferably 68 or less.

[0118] Even more preferably, the substrate of the present invention is a more general one, wherein the chromium and chromium alloy layers have L* values ​​in the range of 57 to 70, more preferably 58 to 69, more preferably 59 to 68, and most preferably 60 to 68.

[0119] A more general substrate of the present invention is used, wherein, based on the total weight of the layer, the chromium and chromium alloy layers each comprise a total amount of carbon of 0.1 wt% or more, preferably 0.5 wt% or more, and more preferably 0.1 wt% or more. Preferably, based on the total weight of the layer, the carbon is present in a total amount ranging from 0.1 wt% to 10 wt%, preferably from 0.5 wt% to 8 wt%, and more preferably from 1 wt% to 6 wt%. Preferably, this also applies explicitly to the first substrate of the present invention.

[0120] A more general substrate of the present invention is used, wherein, based on the total weight of the layer, the chromium and chromium alloy layers each comprise less than 98% by weight, preferably 97% by weight or less, more preferably 96% by weight or less, even more preferably 95% by weight or less, and even more preferably 94% by weight or less of chromium. Even more preferably, the substrate of the present invention comprises, based on the total weight of the layer, the chromium and chromium alloy layers each comprise a total amount of chromium ranging from 88% by weight to 98% by weight, preferably from 89% by weight to 97% by weight, more preferably from 90% by weight to 96% by weight, and most preferably from 91% by weight to 95% by weight. Preferably, this also applies explicitly to the first substrate of the present invention.

[0121] More preferably, the substrate of the present invention is a more general one, wherein, based on the total weight of the layers, the chromium and chromium alloy layers each contain oxygen in a preferred total amount ranging from 1% to 5% by weight, and more preferably from 1.5% to 4% by weight. Preferably, this also applies explicitly to the first substrate of the present invention.

[0122] In some cases, the more general substrate system of the present invention is preferred, wherein the chromium and chromium alloy layers are substantially free of, and preferably free of, sulfur.

[0123] More preferably, the substrate of the present invention is more general, wherein the chromium and chromium alloy layers have a hardness (HV) in the range of 650 to 2000, more preferably 700 to 1700, more preferably 750 to 1500, and most preferably 800 to 1300.

[0124] Preferably, if the chromium and chromium alloy layers are deposited from a trivalent chromium plating composition, the characteristics regarding the amounts of chromium, carbon, and oxygen mentioned above are generally obtained. This is most applicable to the presence of carbon, which is a typical and very prominent element obtained from the deposition of a trivalent chromium plating composition. The characteristics mentioned above (most notably carbon) are preferably typical differences on the corresponding layers deposited from a hexavalent chromium plating bath.

[0125] Unless otherwise stated, the features of the more general substrate mentioned above in relation to the present invention are also preferably applicable to the first substrate of the present invention.

[0126] The invention is described in more detail by way of the following non-limiting examples.

[0127] Examples For multiple experiments, individual test electroplating compositions (volume: approximately 850 mL) were prepared, as shown in Table 1 as comparative examples not according to the invention and in Table 2 as embodiments according to the invention. Generally, and unless otherwise stated, these compositions contain approximately 20 g / L trivalent chromium ions, approximately 4 mol / L formic acid anions, approximately 90 mmol / L bromide ions, and approximately 0.5 mol / L chloride ions. These compositions are free of boric acid or any boron-containing compounds, and free of organic compounds having divalent sulfur. The pH was adjusted to 5.4 with ammonia. Experiments were conducted using different particle sizes, particle concentrations, layer thicknesses, and cathode current densities (CCD) (see Tables 1 and 2 for more information).

[0128] In each experiment, the respective electroplating compositions were electroplated to obtain respective chromium or chromium alloy layers on a substrate (a soft steel rod with a diameter of 10 mm). A graphite anode was used as the anode. Electrodeposition was carried out for 30 to 60 minutes at 50°C and with stirring (450 rpm) at various current densities (see Tables 1 and 2). The layer thickness was consistently in the range of 10 µm to 40 µm, depending on the applied current density (see Tables 1 and 2).

[0129] In each experiment (i.e., comparative and according to the invention), each chromium or chromium alloy layer comprised 1 to 5% by weight of carbon. The total amount of chromium was less than 98% by weight.

[0130] Table 1: Overview of comparative examples of experimental setups. Example particle c [g / L] D 50 [µm] d [µm] CCD [A / dm 2 ] C1 -- -- -- 10 30 C2 -- -- -- 25 30 C3 -- -- -- 10 40 C4 -- -- -- 25 40 C5 γ-Al2O3 10 1 10 30 C6 γ-Al2O3 10 1 25 30 C7 γ-Al2O3 10 1 10 40 C8 γ-Al2O3 10 1 25 40 C9 γ-Al2O3 20 1 10 30 C10 γ-Al2O3 20 1 25 30 C11 γ-Al2O3 20 1 10 40 C12 γ-Al2O3 20 1 25 40 C13 γ-Al2O3 10 8.2 10 30 C14 γ-Al2O3 10 8.2 25 30 C15 γ-Al2O3 10 8.2 10 40 C16 γ-Al2O3 10 8.2 25 40 C17 γ-Al2O3 20 8.2 10 30 C18 γ-Al2O3 20 8.2 25 30 C19 γ-Al2O3 20 8.2 10 40 C20 γ-Al2O3 20 8.2 25 40 C21 α-Al2O3 10 4.6 10 30 C22 α-Al2O3 10 4.6 25 30 C23 α-Al2O3 10 4.6 10 40 C24 α-Al2O3 10 4.6 25 40 C25 α-Al2O3 20 4.6 10 30 C26 α-Al2O3 20 4.6 25 30 C27 α-Al2O3 20 4.6 10 40 C28 α-Al2O3 20 4.6 25 40 C29 α-Al2O3 10 6.5 10 30 C30 α-Al2O3 10 6.5 25 30 C31 α-Al2O3 10 6.5 10 40 C32 α-Al2O3 10 6.5 25 40 C33 α-Al2O3 20 6.5 10 30 C34 α-Al2O3 20 6.5 25 30 C35 α-Al2O3 20 6.5 10 40 C36 α-Al2O3 20 6.5 25 40 "c [g / L]" refers to the total number of particles; "D50 [µm]" refers to the particle size; "d [µm]" refers to the thickness of the deposited layer; "CCD" represents the cathode current density.

[0131] According to Table 1, only comparative examples are shown. No particles are used in the control electroplating compositions of Examples (C1) to (C4), thereby defining a typical reference color for a substrate having a hard chromium layer obtained from a particle-free trivalent chromium deposition bath. Compared to layers obtained from a hexavalent chromium deposition bath, these hard chromium layers are glossy and have a very similar brightness.

[0132] According to Table 1, alumina particles were used and a plurality of parameters were changed in several further experiments (C5) to (C36). In the context of this invention, these particles are not oxide-hydroxide particles, but only oxide particles.

[0133] The comparative electroplating composition of Comparative Example (C4) was further tested without any chloride (but otherwise identical; data not shown). No optical difference was observed compared to (C4).

[0134] However, in each comparative example, the following colors were measured: L* 78-79; a* -0.1 to +0.1; b* +0.6 to +1. As mentioned above, in each comparative example, the deposited layer was shiny with a silver-like luster.

[0135] Table 2: Overview of experimental setup examples according to the present invention. Example particle c [g / L] D 50 [µm] d [µm] CCD [A / dm 2 ] E1 γ-AlO(OH) 5 0.9 10 30 E2 γ-AlO(OH) 5 0.9 25 30 E3 γ-AlO(OH) 5 0.9 10 40 E4 γ-AlO(OH) 5 0.9 25 40 E5 γ-AlO(OH) 10 0.9 10 30 E6 γ-AlO(OH) 10 0.9 25 30 E7 γ-AlO(OH) 10 0.9 10 40 E8 γ-AlO(OH) 10 0.9 25 40 E9 γ-AlO(OH) 20 0.9 10 30 E10 γ-AlO(OH) 20 0.9 25 30 E11 γ-AlO(OH) 20 0.9 10 40 E12 γ-AlO(OH) 20 0.9 25 40 E13 γ-AlO(OH) 20 0.9 25 50 E14 γ-AlO(OH) 20 0.9 25 60 E15 γ-AlO(OH) 20 0.9 20 70 E16 γ-AlO(OH) 20 0.9 15 80 E17 γ-AlO(OH) 20 0.9 15 100 E18 γ-AlO(OH) 10 1.8 10 30 E19 γ-AlO(OH) 10 1.8 25 30 E20 γ-AlO(OH) 10 1.8 10 40 E21 γ-AlO(OH) 10 1.8 25 40 E22 γ-AlO(OH) 20 1.8 10 30 E23 γ-AlO(OH) 20 1.8 25 30 E24 γ-AlO(OH) 20 1.8 10 40 E25 γ-AlO(OH) 20 1.8 25 40 E26 γ-AlO(OH) 10 2.7 10 30 E27 γ-AlO(OH) 10 2.7 25 30 E28 γ-AlO(OH) 10 2.7 10 40 E29 γ-AlO(OH) 10 2.7 25 40 E30 γ-AlO(OH) 20 1.8 10 30 E31 γ-AlO(OH) 20 1.8 25 30 E32 γ-AlO(OH) 20 1.8 10 40 E33 γ-AlO(OH) 20 1.8 25 40 "c [g / L]" refers to the total number of particles; "D50 [µm]" refers to the particle size; "d [µm]" refers to the thickness of the deposited layer; "CCD" represents the cathode current density.

[0136] According to Table 2, only examples according to the present invention are shown, all electroplating compositions include oxide-hydroxide particles. The hard chromium layer thus obtained is less glossy than that of the comparative examples and particularly exhibits a dull, matte appearance. In all examples according to the present invention, the following colors were measured: L* 68 to 69; a* -0.1 to +0.1; b* -0.1 to +0.2. Furthermore, in all examples according to the present invention, the optical appearance is the same, which is therefore substantially independent of the various parameters changed in (E1) to (E33). Furthermore, in all examples according to the present invention, the hardness (HV) after step (c) is between 700 and 800, and is therefore slightly lower than the hardness obtained after step (c) of the comparative examples (C1) to (C4).

[0137] Furthermore, (E8) was further tested without any chloride (but otherwise identical; data not shown). No optical differences were observed compared to (E8) or any other example according to the invention.

[0138] As shown in Table 2, only the mixed oxide-hydroxide species exhibited the desired matte appearance. In the comparative experiment using only oxide particle species, this desired change in brightness did not occur.

[0139] Furthermore, the number and width of cracks were studied. A comparison between (C1) to (C4) and (C5) to (C12) shows that the use of oxide particles can reduce the number of microcracks on the cross-section of the layer by about 10%. However, a comparison between (C1) to (C4) and all examples of the present invention shows that if oxide-hydroxide particles are present, the reduction is 60 to 80%.

[0140] In addition, the presence of oxide-hydroxide particles significantly reduces the width of the remaining crack.

[0141] Interestingly, (C13) to (C36) show no improvement at all, that is, the number of cracks is not reduced compared to (C1) to (C4).

Claims

1. An electroplating composition for depositing a chromium or chromium alloy layer on a substrate, the composition comprising: (i) trivalent chromium ions, (ii) at least one chelating agent for the trivalent chromium ions, and (iii) at least one oxide-hydroxide particle, wherein the electroplating composition has a pH in the range of 5.3 to 7.

0.

2. The electroplating composition of claim 1, having a pH in the range of 5.3 to 6.

5.

3. The electroplating composition of claim 1 or 2, wherein the at least one oxide-hydroxide particle comprises aluminum.

4. The electroplating composition of claim 1 or 2, wherein the at least one oxide-hydroxide particle comprises AlO(OH).

5. The electroplating composition of claim 1 or 2, wherein the at least one oxide-hydroxide particles have a total amount in the range of 0.1 g / L to 200 g / L based on the total volume of the electroplating composition.

6. The electroplating composition of claim 1 or 2, wherein the at least one oxide-hydroxide particles have a particle size D50 in the range of 0.1 μm to 15 μm.

7. The electroplating composition of claim 1 or 2, wherein the electroplating composition does not contain zinc.

8. A method for depositing a chromium or chromium alloy layer on a substrate, the method comprising the following steps: (a) providing the substrate, (b) providing an electroplating composition for depositing a chromium or chromium alloy layer, the composition comprising: (i) trivalent chromium ions, (ii) at least one chelating agent for the trivalent chromium ions, and (iii) at least one oxide-hydroxide particle, wherein the electroplating composition has a pH in the range of 5.3 to 7.0, (c) contacting the substrate with the electroplating composition and applying an electric current to deposit the chromium or chromium alloy layer on at least one surface of the substrate.

9. The method of claim 8, wherein in step (c), the chromium or chromium alloy layer has a thickness in the range of 1.1 μm to 500 μm.

10. The method of claim 8 or 9, wherein in step (c), the chromium or chromium alloy layer has an L* value of 70 or less as defined by CIELAB.

11. The method of claim 8 or 9, wherein in step (c), the chromium or chromium alloy layer has an a* value in the range of -2 to +2 and / or a b* value in the range of -2 to +2 as defined by CIELAB.

12. The method of claim 8 or 9, wherein after step (c), the chromium or chromium alloy layer has a hardness (HV) in the range of 650 to 950.

13. Use of at least one oxide-hydroxide particle in a trivalent chromium electroplating composition for depositing a chromium or chromium alloy layer having an L* value of 70 or less as defined by CIELAB.

14. A substrate comprising a chromium or chromium alloy layer, wherein the chromium or chromium alloy layer comprises at least one oxide-hydroxide particle, and wherein the chromium or chromium alloy layer has an a* value in the range of -2 to +2 as defined by CIELAB and / or a b* value in the range of -2 to +2, and / or the chromium or chromium alloy layer has a hardness (HV) in the range of 650 to 950.

15. The substrate of claim 14, wherein the chromium or chromium alloy layer has an L* value of 70 or less as defined by CIELAB.

16. The substrate of claim 14, wherein the chromium or chromium alloy layer has a thickness in the range of 1.1 μm to 500 μm.

17. A substrate comprising a chromium or chromium alloy layer, wherein the chromium or chromium alloy layer - comprises carbon, - has an L* value of 70 or less as defined by CIELAB, and - has a thickness of 4 μm or more, and wherein the chromium or chromium alloy layer has an a* value in the range of -2 to +2 and / or a b* value in the range of -2 to +2 as defined by CIELAB, and / or the chromium or chromium alloy layer has a hardness (HV) in the range of 650 to 950.