Electroplating bath for depositing a black chromium layer, method for depositing, and substrate comprising such a layer

Abstract

This invention relates to a very specific electroplating bath for depositing a black chromium layer, specific methods thereof, and specific substrates having the black chromium layer thereon. The substrate containing the black chromium layer is ideally suited for decorative purposes.

Description

[Technical Field]

[0001] This invention relates to a very specific electroplating bath for depositing a black chromium layer, various methods thereof, and various substrates having the black chromium layer thereon. The substrate containing the black chromium layer is ideally suited for decorative purposes. [Previous Technology]

[0002] Since the advent of chrome coatings, there has been a great deal of attention paid to black chrome coatings, due to their great appeal in visual applications.

[0003] Even though it started with black hexavalent chromium coatings, attention has now significantly shifted to trivalent chromium coatings due to their higher environmental acceptability. This is because, over the years, there has been a growing demand for dark, even neutral-dark (also known as neutral black) trivalent chromium coatings, for example, for decorative automotive parts. However, because such neutral black tones can feel too cold in some cases, slight tinting modifications are often required. These modifications do not destroy the dark black tone itself, but add a slight warming tone to produce a warmer black. In principle, although neutral black tones and warm black tones are very similar, both are in strong demand in industry.

[0004] However, the degree of blackness varies significantly and depends on the deposition parameters and bath composition.

[0005] In many cases, the black obtained from trivalent chromium coatings is not black enough to satisfy neutral or warm black hues, such as those required for decorative parts in the automotive industry. In other cases, the darkness is sufficient, but the overall visual impression is inadequate. In even other cases, the resulting color stability over time is insufficient.

[0006] WO 2012 / 150198 A2 mentions a method and plating bath for electrodepositing dark chromium layers.

[0007] WO 2017 / 053655 A1 mentions a method for adjusting brightness L* using an activated carbon filter and a dark electroplated trivalent chromium layer on a workpiece.

[0008] CN 107099824 B mentions a black chromium electroplating solution, a composite coating, and a method for preparing the same. The trivalent black chromium coating formed by this black chromium electroplating solution has a deep black color and uniform, strong coverage.

[0009] JP 2014 100809 A mentions a vehicle decorative component with a black coating and a method for manufacturing the same.

[0010] US 2020 / 094526 A1 refers to a black-plated resin component containing a black chrome plating having a b* value of 3.0 or less.

[0011] Significant progress has been made regarding neutral and warm black tones according to US'526. However, further improvements are needed for industrial applications in all these attempts. For example, in many cases, the desired tone is obtained only by inducing natural color aging through an unacceptably long period of inactivity. In other cases, the desired tone is obtained more quickly, but deposition on geometries with complex shapes is impossible due to clouding, burning, and skip plating.

[0012] Therefore, there is a great need to further improve the available methods and plating baths in order to overcome these problems. [Summary of the Invention]

[0013] Therefore, the object of the present invention is to provide an electroplating bath and various methods for electroplating that, on the one hand, allow for rapid and stable tonal formation (for both neutral black and warm black tones), and on the other hand, allow for deposition without plating defects on a wide variety of substrate geometries, thereby achieving an excellent visual appearance, including excellent gloss. Furthermore, it should be possible to specifically and easily target and obtain both tones.

Implementation Method

[0014] This objective is achieved by means of the present invention, the electroplating bath, and various methods for electroplating.

[0015] Therefore, the present invention relates to an electroplating bath for depositing a black chromium layer, the electroplating bath comprising: (A) trivalent chromium ions; (B) one or more chelating agents for the trivalent chromium ions; (C) one or more pH buffering compounds for the electroplating bath, as appropriate; (D) thiocyanate, its salts, esters and / or isoforms, in a total amount in the range of 100 mmol / L to 250 mmol / L based on the total volume of the electroplating bath; (E) one or more compounds of formula (I), their salts and / or monoxide R1-S-(CH2)n-CH(NH2)-R2 (I), wherein -R1 is a branched or unbranched C1 to C4 alkyl group, -R2 is selected from the group consisting of COOH, its salts and (CH2)m-OH, -n is an integer in the range of 1 to 4, and -m is an integer in the range of 1 to 4.

[0016] Our experiments have shown (see examples below) that the problems mentioned above are largely related to the concentration of (D), and can be solved by keeping the concentration of (D) within the range mentioned above. The desired hue (neutral black or warm black) with excellent gloss is rapidly formed and can be specifically targeted. Furthermore, it can even be formed on substrates with complex geometries to achieve extremely uniform deposition quality without plating defects. However, it has also been found that such excellent results can only be obtained when (D) is kept within the relatively narrow concentration range defined above.

[0017] Preferably, the black chrome layer is a decorative chrome layer. Typical applications are automotive parts, and it is best used in automotive interiors. To obtain such a black chrome layer, preferably as defined herein, the electroplating bath of the present invention is highly suitable.

[0018] In the context of this invention, the black chrome layer is preferably defined by the L*a*b* color system, which, unless otherwise specified, is preferably the color system introduced by the International Commission on Illumination (Commission Internationale de l'Eclairage) in 1976.

[0019] Preferably, the electroplating bath of the present invention has an L* value of 50 or lower, more preferably 49 or lower, even more preferably 48 or lower, even more preferably 47 or lower, and even more preferably 46 or lower, further preferably 45 or lower, and most preferably 43 or lower. An L* value of 50 or lower is generally well perceived as black and dark. Generally speaking, the lower the L* value (preferably as defined above), the stronger the impression of a black / dark tone.

[0020] Preferably, the electroplating bath of the present invention has an a* value in the range of -1.5 to +3, more preferably in the range of -1 to +2.5, and most preferably in the range of -0.5 to +2. Preferably, the a* value is at least positive. Most preferably, this is applied to neutral black tones and warm black tones.

[0021] The difference between neutral black tones and warm black tones is usually based on slightly different b* values.

[0022] In some cases, the electroplating bath of the present invention is preferred, wherein the black chromium layer is a neutral black chromium layer. This further means that the electroplating bath of the present invention is preferred, wherein the b* value of the black chromium layer is in the range of -2.5 to +2.9, more preferably in the range of -2 to +2, even more preferably in the range of -1.5 to +1.5, and most preferably in the range of -1 to +1.

[0023] For neutral black tones, the optimal L* value is 45 or lower, better is 44 or lower, even better is 43 or lower, and even better is 42 or lower, with the best being 41 or lower.

[0024] In some cases, the electroplating bath of the present invention is preferred, wherein the black chromium layer is a chromium layer having a warm black hue. This further means that the electroplating bath of the present invention is preferred, wherein the b* value of the black chromium layer is in the range of +3 to +6, preferably +3.5 to +5.8, and most preferably +4 to +5.5.

[0025] In the context of this invention, it is highly beneficial that both neutral black tones and warm black tones can be specifically targeted and obtained.

[0026] Compound (A) and general bath compounds: The electroplating bath of the present invention is preferably an aqueous solution, that is, it contains water, and is preferably at least 55% by volume or more, more preferably 65% ​​by volume or more, even more preferably 75% by volume or more, and even more preferably 85% by volume or more, still more preferably 90% by volume or more, and most preferably 95% by volume or more of water by volume. Preferably, water is the sole solvent.

[0027] Preferably, the electroplating bath of the present invention is acidic, and preferably has a pH in the range of 1.5 to 5.0, more preferably 2.0 to 4.6, even more preferably 2.4 to 4.2, still more preferably 2.7 to 3.8, and most preferably 3.0 to 3.5. The pH is preferably adjusted using hydrochloric acid, sulfuric acid, ammonia, potassium hydroxide and / or sodium hydroxide.

[0028] The electroplating bath of the present invention contains (A) trivalent chromium ions.

[0029] Preferably, the electroplating bath of the present invention has a total concentration of trivalent chromium ions in the range of 5 g / L to 35 g / L, more preferably 6 g / L to 32 g / L, even more preferably 7 g / L to 29 g / L, even more preferably 8 g / L to 26 g / L, even more preferably 9 g / L to 23 g / L, and most preferably 10 g / L to 22 g / L, based on the total volume of the electroplating bath.

[0030] Preferably, the trivalent chromium ions are derived from trivalent chromium salts, more preferably from inorganic chromium salts and / or organic chromium salts, and most preferably from inorganic chromium salts. The preferred inorganic chromium salts contain chloride and / or sulfate anions, more preferably sulfate anions. The most desirable inorganic chromium salt is basic chromium sulfate. The preferred organic chromium salts contain carboxylic acid anions, more preferably formate, acetate, malate, and / or oxalate anions.

[0031] Preferably, the electroplating bath of the present invention contains sulfate ions, preferably derived from trivalent chromium salts.

[0032] Preferably, the electroplating bath of the present invention contains, and preferably does not contain, compounds containing chromium with an oxidation state of +6. Therefore, the electroplating bath contains, and preferably does not contain, hexavalent chromium.

[0033] Preferably, the electroplating bath of the present invention contains, and preferably does not contain, cobalt ions. Preferably, the black chrome layer contains, or preferably does not contain, cobalt or contains only cobalt in amounts as defined herein. Only in very rare cases is it preferred that both the electroplating bath and the black chrome layer contain cobalt, but this preference is less pronounced. However, although not necessary for a black appearance, relatively low amounts of cobalt are permissible. In this case, the electroplating bath of the present invention is preferred, wherein, based on the total volume of the electroplating bath and based on elemental cobalt, cobalt ions are present in the range of 1 mg / L to 500 mg / L, preferably 2 mg / L to 400 mg / L, more preferably 3 mg / L to 300 mg / L, even more preferably 4 mg / L to 200 mg / L, even more preferably 5 mg / L to 100 mg / L, and most preferably 6 mg / L to 50 mg / L.

[0034] Preferably, the electroplating bath of the present invention is substantially free of, and preferably does not contain, nickel ions. In some cases, typical Ni contamination of up to 150 ppm has been observed, which is substantially acceptable and therefore considered substantially free of nickel ions. Therefore, in some cases, the electroplating bath of the present invention preferably contains nickel ions at a concentration in the range of 0 ppm to 200 ppm, preferably 1 ppm to 150 ppm, and most preferably 2 ppm to 100 ppm by weight of the total weight of the electroplating bath. Preferably, the black chromium layer is substantially free of, and preferably does not contain, nickel.

[0035] It is generally preferable to avoid such environments containing potentially contaminated nickel and cobalt ions. This typically reduces the complexity of wastewater treatment and bath disposal. Furthermore, neither nickel nor cobalt is required to achieve neutral black or warm black tones.

[0036] Preferably, the electroplating bath of the present invention is substantially free of, or preferably does not contain, fluoride ions. Preferably, the black chromium layer is substantially free of, or preferably does not contain, fluoride.

[0037] Preferably, the electroplating bath of the present invention contains, and preferably does not contain, any fluorine-containing compounds. This preferably includes fluorine-containing surfactant compounds. Such compounds are particularly undesirable due to increasing environmental restrictions.

[0038] Preferably, the electroplating bath of the present invention is substantially free of, preferably not free of, phosphate anions, and more preferably substantially free of, phosphorus-containing compounds. Preferably, the black chromium layer is substantially free of, preferably not free of, phosphorus. However, this does not preclude phosphorus from being deposited in subsequent layers (e.g., passivation layers) on the black chromium layer.

[0039] Preferably, the electroplating bath of the present invention further comprises halide anions, more preferably chloride anions. In the context of the present invention, this is preferred, and various electroplating baths are referred to as chloride-containing baths. More preferably, the electroplating bath of the present invention comprises chloride ions and sulfate ions.

[0040] Preferably, the electroplating bath of the present invention contains chloride ions at a concentration ranging from 50 g / L to 200 g / L, more preferably from 60 g / L to 185 g / L, even more preferably from 70 g / L to 170 g / L, and even more preferably from 80 g / L to 155 g / L, most preferably from 90 g / L to 140 g / L, based on the total volume of the electroplating bath. The chloride ions preferably originate from chloride salts and / or hydrochloric acid, and more preferably from sodium chloride, potassium chloride, ammonium chloride, chromium chloride (at least as a portion of all chloride ions), and / or mixtures thereof. Generally, as previously preferred, the chloride ions are present as anions of conductive salts. Preferred conductive salts are ammonium chloride, sodium chloride, and potassium chloride, with ammonium chloride being the most preferred.

[0041] Preferably, the electroplating bath of the present invention further comprises bromide anions. This generally avoids the anode formation of undesirable hexavalent chromium species. Preferably, the bromide ion concentration, based on the total volume of the electroplating bath, is in the range of 3 g / L to 20 g / L, more preferably 4 g / L to 18 g / L, more preferably 5 g / L to 16 g / L, even more preferably 6 g / L to 14 g / L, and most preferably 7 g / L to 12 g / L. The bromide ions are preferably derived from bromide salts, more preferably from sodium bromide, potassium bromide, ammonium bromide, and / or mixtures thereof.

[0042] More preferably, the electroplating bath of the present invention contains chloride ions, bromide ions and sulfate ions, and preferably has the concentrations defined herein as preferred.

[0043] In some cases, the electroplating bath of the present invention preferably further comprises Fe(II) ions, with a concentration preferably in the range of 0.1 mmol / L to 10 mmol / L, more preferably 0.4 mmol / L to 8 mmol / L, more preferably 0.6 mmol / L to 6 mmol / L, even more preferably 0.8 mmol / L to 5 mmol / L, and most preferably 1 mmol / L to 4 mmol / L, based on the total volume of the electroplating bath. This is particularly preferred if the electroplating bath of the present invention contains chloride ions. Therefore, the electroplating bath of the present invention is preferably composed of chloride ions, bromide ions, sulfate ions, and Fe(II) ions, preferably having concentrations as defined herein. The Fe(II) ions are preferably derived from individual iron salts, preferably from ferric(II) sulfate salts. Generally, iron ions have several beneficial effects on electroplating efficiency and the deposited black chromium layer obtained by the present invention. In many cases, an increased electroplating rate has been observed, which allows for a thicker layer thickness. Preferably, the black chromium layer contains iron, which is even better as defined throughout this document.

[0044] Furthermore, the electroplating bath of the present invention is preferably in which trivalent chromium ions and Fe(II) ions (if present) are the only transition metals in the plating bath, and preferably chromium ions and iron ions (if present) are the only transition metals in the plating bath. An exception is Ni contamination as mentioned above, which is generally acceptable and therefore preferred.

[0045] In some cases, the electroplating bath of the present invention preferably further comprises at least one sulfur-containing compound different from (D) and (E).

[0046] In some cases, the electroplating bath of the present invention preferably additionally (i.e., in addition to (D) and (E)) contains saccharin and / or its salts.

[0047] In some cases, the electroplating bath of the present invention preferably contains additional (i.e., in addition to (D) and (E)) sulfur-containing diols, preferably in addition to saccharin and / or its salts mentioned above.

[0048] Preferably, the electroplating bath of the present invention further comprises at least one surfactant compound. The preferred surfactant compound comprises a cationic or anionic surfactant compound, with anionic surfactant compounds being more preferred. The preferred anionic surfactant compound comprises a sulfosuccinate, an alkylbenzene sulfonate having 8 to 20 aliphatic carbon atoms, an alkyl sulfate having 8 to 20 carbon atoms, and / or an alkyl ether sulfate. Preferably, at least one surfactant compound is free of fluorine atoms.

[0049] Preferred sulfosuccinate includes sodium dipentane sulfosuccinate.

[0050] Preferably, alkylbenzene sulfonates having 8 to 20 aliphatic carbon atoms include sodium dodecylbenzene sulfonate.

[0051] Preferably, the alkyl sulfate having 8 to 20 carbon atoms includes sodium lauryl sulfate.

[0052] Preferred alkyl ether sulfate fatty alcohols include sodium lauryl polyethoxylate.

[0053] Preferably, the electroplating bath of the present invention contains at least one surfactant compound with a total concentration of 0.001 g / L to 0.05 g / L, more preferably 0.005 g / L to 0.01 g / L, based on the total volume of the electroplating bath.

[0054] In contrast, in some cases, the electroplating bath of the present invention is preferred, wherein the electroplating bath substantially does not contain, preferably does not contain, chloride ions, and preferably does not contain halide anions. In the context of the present invention, this preference is less pronounced, and individual electroplating baths are referred to as chloride-free baths. In this case, the electroplating bath of the present invention preferably contains sulfate ions to compensate for the lack of chloride ions. Even more preferably, the electroplating bath of the present invention contains sulfate ions other than sulfate ions from chromium salts, preferably by means of a conductive salt. Preferred conductive salts are potassium sulfate, sodium sulfate, ammonium sulfate, or mixtures thereof. In this particular case, the electroplating bath preferably substantially does not contain, preferably does not contain, bromide ions. However, in some rare cases, such an electroplating bath preferably contains iron ions, preferably Fe(II) ions, preferably at the concentration defined above.

[0055] Compound (B): The electroplating bath of the present invention comprises (B) one or more chelating agents for the trivalent chromium ions. Such compounds retain the trivalent chromium ions in solution. Preferably, one or more chelating agents are not compounds (D) and (E), and are therefore preferably different from (D) and (E).

[0056] Preferably, the electroplating bath of the present invention contains one or more chelating agents comprising an organic acid and / or its salt, preferably an organic carboxylic acid and / or its salt, and most preferably an organic carboxylic acid and / or its salt containing one, two or three carboxyl groups.

[0057] The organic carboxylic acid and / or its salt (preferably an organic carboxylic acid and / or its salt containing one, two or three carboxyl groups) is preferably substituted or unsubstituted. Preferred substituents include amino groups and / or hydroxyl groups. Preferably, the substituents do not contain SH groups.

[0058] More preferably, the organic carboxylic acid and / or its salt (preferably also an organic carboxylic acid and / or its salt containing one, two, or three carboxyl groups) comprises an aminocarboxylic acid (preferably α-aminocarboxylic acid), a hydroxycarboxylic acid, and / or its salt. Preferably, the (α-)aminocarboxylic acid comprises glycine, aspartic acid, and / or its salt. Preferably, the aminocarboxylic acid (preferably α-aminocarboxylic acid) is not a compound according to (E), more preferably not a sulfur-containing aminocarboxylic acid (preferably not a sulfur-containing α-aminocarboxylic acid), and most preferably not methionine. Preferably, one or more chelating agents are different from the compound of formula (E).

[0059] More preferably, the electroplating bath of the present invention contains one or more chelating agents comprising: formic acid, acetic acid, oxalic acid, tartaric acid, malic acid, citric acid, glycine, aspartic acid, and / or their salts, more preferably formic acid, acetic acid, oxalic acid, tartaric acid, malic acid, citric acid, and / or their salts, even more preferably formic acid, acetic acid, and / or their salts, and most preferably formic acid and / or their salts. This is most suitable if the electroplating bath of the present invention contains chloride ions. In contrast, if the electroplating bath of the present invention is chloride-free, more preferably, one or more chelating agents comprise oxalic acid, tartaric acid, malic acid, citric acid, and / or their salts, most preferably malic acid and / or their salts.

[0060] Preferably, the electroplating bath of the present invention contains a total concentration of one or more chelating agents in the range of 5 g / L to 200 g / L, more preferably 8 g / L to 150 g / L, even more preferably 10 g / L to 100 g / L, even more preferably 12 g / L to 75 g / L, and even more preferably 15 g / L to 50 g / L, most preferably 20 g / L to 35 g / L. This is most suitable if the electroplating bath contains chloride ions, but it is also generally suitable for chlorine-free electroplating baths.

[0061] If the electroplating bath of the present invention is particularly chlorine-free, then, based on the total volume of the electroplating bath, the total concentration of one or more chelating agents is in the range of 5 g / L to 100 g / L, preferably in the range of 5.5 g / L to 75 g / L, more preferably in the range of 6 g / L to 50 g / L, even more preferably in the range of 6.5 g / L to 25 g / L, even more preferably in the range of 7 g / L to 18 g / L, and most preferably in the range of 7.5 g / L to 13 g / L. This is preferably applicable to oxalic acid, tartaric acid, malic acid, citric acid and their salts, and most preferably to malic acid and their salts.

[0062] Preferably, the electroplating bath of the present invention is wherein (B) / (A) forms a molar ratio in the range of 1 to 1.5, more preferably in the range of 1.1 to 1.4, and most preferably in the range of 1.2 to 1.3.

[0063] Compound (C): The electroplating bath of the present invention comprises (C), as appropriate, one or more pH buffering compounds for use in the electroplating bath. Preferably, the electroplating bath of the present invention comprises (i.e., regardless of the situation) one or more pH buffering compounds. In the latter case, the electroplating bath of the present invention is preferred, wherein one or more pH buffering compounds for use in the electroplating bath are different from (i.e., different from) (B). In this case, one or more pH buffering compounds do not contain carboxylic acids, and preferably do not contain organic acids. In this case, they are counted relative to (B).

[0064] In many cases, the electroplating bath of the present invention is preferred, wherein one or more pH buffer compounds comprise a boron-containing compound, preferably boric acid and / or borates, most preferably boric acid. A preferred borate is sodium borate.

[0065] Preferably, the electroplating bath of the present invention contains a total concentration of one or more pH buffer compounds in the range of 30 g / L to 250 g / L, more preferably 35 g / L to 200 g / L, even more preferably 40 g / L to 150 g / L, and even more preferably 45 g / L to 100 g / L, most preferably 50 g / L to 75 g / L, based on the total volume of the electroplating bath. This is even more preferably applicable to the boron-containing compound, and even more preferably to the boric acid and the borate, most preferably to the boric acid. Preferably, the one or more pH buffer compounds contain boric acid but no borate. Therefore, the preferred method is the electroplating bath of the present invention, wherein (C) contains boric acid in a total amount preferably in the range of 35 g / L to 90 g / L, more preferably 40 g / L to 80 g / L, more preferably 50 g / L to 70 g / L, and most preferably 56 g / L to 66 g / L, based on the total volume of the electroplating bath.

[0066] In some other cases, the electroplating bath of the present invention does not explicitly contain a separate pH buffering compound. Instead, one or more chelating agents for the trivalent chromium ions are present in a certain amount and selected in a certain manner such that they not only act as chelating agents for the trivalent chromium ions but also additionally act as pH buffering compounds. In the context of the present invention, this preference is less pronounced but possible.

[0067] Compound (D): The electroplating bath of the present invention comprises (D) thiocyanate, its salts, esters and / or isoforms, in a total concentration ranging from 100 mmol / L to 250 mmol / L based on the total volume of the electroplating bath. Our experiments have shown that this compound, along with the aforementioned concentration range, is essential. Preferably, the above concentrations are based on SCN-, i.e., based on monobasic thiocyanate. The term "acid" in "thiocyanate" includes its deprotonated / dispersed form.

[0068] According to our experiments (see the text under "Examples" below), a sufficiently black chromium layer cannot be obtained if the concentration is significantly lower than 100 mmol / L. Most importantly, if the concentration of (D) is lower than 100 mmol / L, the heat treatment in the method of the present invention does not significantly affect the final color formation. Furthermore, an undesirable high gloss is obtained, which begins to adversely impair the black visual appearance of the black chromium layer.

[0069] Furthermore, if the concentration of (D) significantly exceeds 250 mmol / L, the number of plating defects increases, especially on substrates with complex surface geometries. Our Hall cell experiments have shown that at excessively high (D) concentrations, the usable current density range is unacceptably small. However, this is unacceptable given technical requirements. Moreover, if the concentration of (D) significantly exceeds 250 mmol / L, excessively low gloss is obtained, giving the black chromium layer an unacceptably dull appearance.

[0070] In contrast, the present invention solves these problems.

[0071] Preferably, the electroplating bath of the present invention contains (D) thiocyanate, its salts and / or esters in the total amount, most preferably in the total amount of thiocyanate and / or its salts. Preferably, the salts contain potassium thiocyanate and / or sodium thiocyanate in the total amount.

[0072] Preferably, the electroplating bath of the present invention comprises (D), the total amount of which, based on the total volume of the electroplating bath, is in the range of 105 mmol / L to 245 mmol / L, preferably 110 mmol / L to 240 mmol / L, more preferably 115 mmol / L to 230 mmol / L, even more preferably 120 mmol / L to 220 mmol / L, even more preferably 125 mmol / L to 210 mmol / L, and most preferably 130 mmol / L to 200 mmol / L. Furthermore, these preferred concentration ranges above, as well as all other concentration ranges mentioned below, are based on SCN-, i.e., based on monobasic thiocyanate. Moreover, it is explicitly preferred that the above concentrations can be freely combined to form concentration ranges not explicitly disclosed. This preferably includes other combinations of lower and upper limits not explicitly mentioned throughout this document.

[0073] In some cases, the electroplating bath of the present invention is preferred, wherein the bath comprises (D), the total amount of which, based on the total volume of the electroplating bath, is in the range of 130 mmol / L to 250 mmol / L, more preferably 150 mmol / L to 245 mmol / L, even more preferably 175 mmol / L to 240 mmol / L, and most preferably 191 mmol / L to 235 mmol / L. These are particularly preferred concentration ranges for neutral black hues.

[0074] In some other cases, the electroplating bath of the present invention is preferred, wherein the bath comprises (D), in total volume of the electroplating bath, in the range of 100 mmol / L to 205 mmol / L, more preferably 105 mmol / L to 200 mmol / L, more preferably 110 mmol / L to 190 mmol / L, even more preferably 115 mmol / L to 180 mmol / L, and most preferably 120 mmol / L to 174 mmol / L. These are particularly preferred concentration ranges for warm black tones.

[0075] Compound (E): The electroplating bath of the present invention comprises (E) one or more compounds of formula (I), their salts and / or monoxide R1-S-(CH2)n-CH(NH2)-R2 (I), wherein -R1 is a branched or unbranched C1 to C4 alkyl group, -R2 is selected from the group consisting of COOH, its salts and (CH2)m-OH, -n is an integer in the range of 1 to 4, and -m is an integer in the range of 1 to 4.

[0076] In the context of this invention, “oxygen” refers to oxygen chemically bonded to a sulfur atom via a double bond, that is, the compound of formula (I) above includes the structure R1-S(=O)-(CH2)n-CH(NH2)-R2.

[0077] Preferably, the electroplating bath of the present invention comprises (E), the total amount of which, based on the total volume of the electroplating bath, is in the range of 100 mmol / L to 950 mmol / L, more preferably 135 mmol / L to 800 mmol / L, even more preferably 150 mmol / L to 650 mmol / L, even more preferably 165 mmol / L to 550 mmol / L, even more preferably 180 mmol / L to 500 mmol / L, and most preferably 195 mmol / L to 450 mmol / L.

[0078] In some cases, the electroplating bath of the present invention is preferred, wherein the bath comprises (E), in total volume of the electroplating bath, in the range of 100 mmol / L to 450 mmol / L, preferably 120 mmol / L to 400 mmol / L, more preferably 140 mmol / L to 350 mmol / L, even more preferably 150 mmol / L to 310 mmol / L, even more preferably 170 mmol / L to 270 mmol / L, and most preferably 190 mmol / L to 230 mmol / L. These are particularly preferred concentration ranges for warm black tones.

[0079] In other cases, the electroplating bath of the present invention is preferred, wherein the bath comprises (E), in total volume of the electroplating bath, in the range of 200 mmol / L to 950 mmol / L, preferably 220 mmol / L to 750 mmol / L, more preferably 250 mmol / L to 580 mmol / L, even more preferably 280 mmol / L to 530 mmol / L, even more preferably 311 mmol / L to 490 mmol / L, and most preferably 330 mmol / L to 420 mmol / L. These are particularly preferred concentration ranges for neutral black hues.

[0080] Preferably, the electroplating bath of the present invention is wherein the molar ratio of (E):(D) is 0.9 or greater, preferably 1.0 or greater, more preferably 1.1 or greater, and most preferably 1.2 or greater.

[0081] More preferably, the electroplating bath of the present invention has a molar ratio of (E):(D) in the range of 0.9 to 2.65, more preferably 1 to 2.6, more preferably 1.05 to 2.55, even more preferably 1.1 to 2.5, even more preferably 1.15 to 2.45, and most preferably 1.2 to 2.40.

[0082] In some cases, the electroplating bath of the present invention is preferred, wherein the molar ratio of (E):(D) is in the range of 0.9 to 2.5, more preferably 1 to 2, even more preferably 1.1 to 1.8, and even more preferably 1.15 to 1.5, most preferably 1.2 to 1.3. In some cases, these are preferred molar ranges for warm black tones.

[0083] In other cases, the electroplating bath of the present invention is preferred, wherein the molar ratio of (E):(D) is in the range of 1.6 to 2.65, more preferably 1.9 to 2.6, even more preferably 2.05 to 2.55, even more preferably 2.1 to 2.5, and even more preferably 2.15 to 2.45, most preferably 2.2 to 2.4. In some cases, these are preferred molar ranges for neutral black tones.

[0084] Preferably, the electroplating bath of the present invention is used, wherein R1 is methyl, ethyl, n-propyl or isopropyl, preferably methyl or ethyl, and most preferably methyl.

[0085] Preferably, the electroplating bath of the present invention is wherein R2 is COOH and / or its salt. As mentioned, COOH also includes its deprotonated / dispersed form.

[0086] Preferably, the electroplating bath of the present invention is n, wherein n is 1 or 2, preferably 2.

[0087] Preferably, the electroplating bath of the present invention is used, wherein m is 1 or 2.

[0088] Preferably, the electroplating bath of the present invention contains methionine in the compound of formula (I) in (E). Most preferably, the compound of formula (E) is methionine.

[0089] Electroplating method: Furthermore, the present invention relates to a method for electroplating a black chromium layer on a substrate, the method comprising the steps of: (a) providing a substrate, (b) contacting the substrate with an electroplating bath according to the present invention, preferably as described herein, (c) applying an electric current such that the black chromium layer is electroplated onto the substrate, and (d) heat-treating the substrate obtained in step (c) at a temperature in the range of 30°C to 100°C.

[0090] The foregoing features (including preferred variations) of the electroplating bath of the present invention are also preferably applicable to the electroplating method of the present invention, and most particularly to step (b) of the method. Furthermore, the foregoing content regarding the L*a*b* value is preferably applicable to the black chromium layer electroplated in step (c).

[0091] In step (a), a substrate is provided.

[0092] In some cases, the method of the present invention is preferred, wherein the substrate comprises a plastic substrate, preferably a plastic substrate. In other cases, the method of the present invention is preferred, wherein the substrate comprises a metal substrate, preferably a metal substrate.

[0093] In most cases, the method of the present invention is preferred, wherein in step (a) the substrate comprises a thermoplastic substrate, preferably an amorphous thermoplastic substrate and / or a semi-crystalline thermoplastic substrate.

[0094] More preferably, the method of the present invention is wherein in step (a), the substrate comprises a butadiene portion, preferably polybutadiene.

[0095] Preferably, the method of the present invention is wherein the substrate comprises a nitrile portion in step (a).

[0096] Preferably, the method of the present invention is wherein the substrate comprises a propylene-based portion in step (a).

[0097] The method of the present invention is preferred, wherein in step (a) the substrate comprises polymeric styrene.

[0098] The preferred method of the present invention is wherein, in step (a), the substrate comprises acrylonitrile butadiene styrene (ABS), acrylonitrile butadiene styrene-polycarbonate (ABS-PC), polypropylene (PP), polyamide (PA), polyetherimide (PEI), polyetherketone (PEK), or a mixture thereof, preferably acrylonitrile butadiene styrene (ABS) and / or acrylonitrile butadiene styrene-polycarbonate (ABS-PC). Such plastic substrates, especially ABS and ABS-PC, are commonly used in decorative applications such as automotive parts.

[0099] Preferably, the method of the present invention is wherein the polyether ketone (PEK) comprises polyaryl ether ketone (PAEK), polyether ether ketone (PEEK), polyether ether ether ketone (PEEEK), polyether ether ketone ketone (PEEKK), polyether ketone ether ketone ketone (PEKEKK), polyether ketone ketone (PEKK), and / or mixtures thereof, preferably polyether ether ketone (PEEK), polyaryl ether ketone (PAEK), and / or mixtures thereof.

[0100] In some cases, the method of the present invention is preferred, wherein the substrate is a metal substrate, which preferably comprises iron, copper, nickel, aluminum, zinc, mixtures thereof, and / or alloys thereof. The most preferred metal substrate comprising iron is steel. Mixtures thereof preferably include composites.

[0101] Preferably, the method of the present invention further includes at least one metal plating step to deposit at least one metal layer before step (b), and preferably at least one nickel plating step to deposit at least one nickel layer. In many cases, it is preferred to involve two or even three such metal plating steps.

[0102] Preferably, at least one nickel layer comprises at least one bright nickel layer and / or (preferably) at least one satin nickel layer, with at least one bright nickel layer being the most preferred.

[0103] More preferably, the method of the present invention includes at least one semi-bright nickel layer, and more preferably, it includes at least one semi-bright nickel layer in addition to the at least one bright nickel layer and / or the at least one satin nickel layer. The at least one semi-bright nickel layer is preferably selected as appropriate. Preferably, (if applied) the at least one semi-bright nickel layer is deposited before the at least one bright nickel layer and / or the at least one satin nickel layer.

[0104] Preferably, the method of the present invention includes at least one MPS nickel layer, preferably including at least one MPS nickel layer in addition to the at least one bright nickel layer and / or the at least one satin nickel layer, most preferably including at least one MPS nickel layer in addition to the at least one bright nickel layer and / or the at least one satin nickel layer, and further including at least one semi-bright nickel layer. In the context of the present invention, MPS refers to an MPS nickel layer containing non-conductive microparticles, which, in a subsequent chromium layer, preferably in a black chromium layer, creates micropores. At least one MPS nickel layer is preferably selected as appropriate.

[0105] In some cases, the method of the present invention is preferred, wherein the MPS nickel layer is adjacent to the black chromium layer.

[0106] In other cases, the method of the present invention is preferred, wherein the black chromium layer is adjacent to at least one bright nickel layer and / or at least one satin nickel layer, which is preferred in most cases, and preferably combined with at least one bright nickel layer.

[0107] Preferably, the black chromium layer is part of a stack of layers.

[0108] In step (b), it is preferable to contact the electroplating bath of the present invention with a substrate having at least one nickel layer (preferably as defined above) by immersion.

[0109] Preferably, the method of the present invention is wherein the contact during step (c) is in the range of 1 minute to 30 minutes, more preferably 2 minutes to 20 minutes, more preferably 3 minutes to 15 minutes, even more preferably 4 minutes to 10 minutes, and most preferably 5 minutes to 8 minutes.

[0110] Preferably, the method of the present invention is wherein, in step (c), the temperature of the electroplating bath is in the range of 25°C to 60°C, more preferably 28°C to 50°C, and even more preferably 30°C to 47°C. This is most suitable if the electroplating bath contains chloride ions.

[0111] In some cases, the method of the present invention is preferred, wherein in step (c), the temperature of the electroplating bath of the present invention is in the range of 35°C to 65°C, more preferably 40°C to 63°C, even more preferably 45°C to 61°C, and most preferably 50°C to 59°C. This is most suitable if the electroplating bath is a chlorine-free electroplating bath.

[0112] Apply current in step (c).

[0113] Preferably, the method of the present invention is a direct current, preferably in the range of 3 A / dm2 to 30 A / dm2, more preferably 4 A / dm2 to 25 A / dm2, even more preferably 5 A / dm2 to 20 A / dm2, and most preferably 6 A / dm2 to 18 A / dm2.

[0114] In some cases, the method of the present invention is preferred, wherein the current is direct current, preferably in the range of 3 A / dm² to 20 A / dm², more preferably 4 A / dm² to 15 A / dm², and most preferably 5 A / dm² to 10 A / dm². This is most suitable if the electroplating bath is a chlorine-free electroplating bath.

[0115] Preferably, the method of the present invention utilizes at least one anode in step (c). The at least one anode is selected from the group consisting of graphite anodes, noble metal anodes, and mixed metal oxide anodes (MMO).

[0116] Preferred precious metal anodes include platinum-plated titanium anodes and / or platinum anodes.

[0117] Preferred mixed metal oxide anodes include titanium anodes coated with platinum oxide and / or titanium anodes coated with iridium oxide.

[0118] Preferably, the method of the present invention is wherein the thickness of the electroplated black chromium layer is in the range of 0.05 µm to 1 µm, more preferably 0.1 µm to 0.8 µm, even more preferably 0.125 µm to 0.6 µm, and most preferably 0.15 µm to 0.5 µm.

[0119] In the context of the method of the present invention, the most important step is step (d) heat treatment. It allows for rapid and direct formation of the desired black hue. The temperature applied in step (d) is not the temperature used in step (c) of the electroplating bath. Steps (c) and (d) are distinct steps.

[0120] Preferably, the method of the present invention is wherein the heat treatment is performed at a temperature in the range of 32°C to 99°C, more preferably in the range of 45°C to 92°C, even more preferably in the range of 52°C to 88°C, and most preferably in the range of 60°C to 84°C.

[0121] More preferably, the method of the present invention is wherein, in step (d), the heat treatment is carried out in water, preferably at a temperature in the range of 32°C to 99°C, more preferably in the range of 45°C to 92°C, even more preferably in the range of 52°C to 88°C, and most preferably in the range of 60°C to 84°C.

[0122] As mentioned, heat treatment is preferably carried out in water. This "preferably" means that this step is performed in a treatment compartment containing the treatment composition. Preferably, the treatment composition is an aqueous solution, more preferably containing only water as a solvent, and most preferably consisting essentially of water. Consisting essentially of water means that, apart from minor contamination from previous method steps, the main component of the treatment composition is water and remains water. Generally, such contamination is permissible for the purposes of this step.

[0123] Even more preferably, the method of the present invention is wherein, in step (d), the heat treatment is a hot water rinse, preferably by immersion, or even more preferably by immersion in the treatment composition.

[0124] Preferably, the method of the present invention is wherein, in step (d), heat treatment is performed without current. This means that this step is preferably electrodeless.

[0125] The method of the present invention does not exclude other steps, preferably such as additional rinsing, cleaning, pretreatment and / or posttreatment. Preferably, the steps as defined in the examples below are also applicable to the general methods described throughout this document. Preferred posttreatment steps include sealing steps using inorganic and / or organic sealants, and / or contact steps with the anti-fingerprint composition.

[0126] Substrate containing a black chrome layer: The present invention further relates to a substrate containing a black chrome layer as specifically defined, wherein the black chrome layer has an L* value of 50 or less according to the L*a*b color system and a gloss value in the range of 150 to 230, more preferably 160 to 220, more preferably 165 to 210, and most preferably 170 to 200 at a measurement angle of reference 60°.

[0127] The foregoing description of the electroplating bath and method of the present invention is preferably also applicable to the substrates specifically defined in the present invention (where applicable). This is preferably applicable to the L*a*b* values ​​defined for the electroplating bath and method of the present invention. However, the following characteristics of the substrates of the present invention are also preferably applicable to the method of the present invention (if not mentioned above).

[0128] Preferably, the substrate of the present invention has an L* value of 49 or less, preferably 48 or less, even more preferably 47 or less, even more preferably 46 or less, and even more preferably 45 or less, and most preferably 44 or less.

[0129] Preferably, the substrate of the present invention has an a* value in the range of -1.5 to +3, more preferably in the range of -1 to +2.5, and most preferably in the range of -0.5 to +2, and / or (more preferably and) a b* value in the range of -2.5 to +6, more preferably in the range of -2 to +5.6, and most preferably in the range of -1.5 to +5.

[0130] Preferably, the black chromium layer substantially does not contain, or preferably does not contain, cobalt, or contains cobalt, wherein there is more chromium than cobalt in the black chromium layer. The latter preferably means that the atomic ratio of chromium to cobalt (i.e., Cr:Co) is greater than 1, more preferably 2 or greater, more preferably 3 or greater, and most preferably 4 or greater. This "most preferably" is based on the total amount of chromium and cobalt atoms in the black chromium layer.

[0131] Preferably, the black chrome layer is not the only metal layer between the black chrome layer and the substrate.

[0132] Preferably, the substrate of the present invention comprises at least one nickel layer under the black chromium layer.

[0133] Preferably, the substrate of the present invention comprises at least one bright nickel layer or at least one satin nickel layer. This is preferred.

[0134] Preferably, the substrate of the present invention comprises at least one semi-bright nickel layer, and more preferably, in addition to the at least one bright nickel layer and / or the at least one satin nickel layer, it comprises at least one semi-bright nickel layer. The at least one semi-bright nickel layer is preferably selected as appropriate. Most preferably, the at least one semi-bright nickel layer is the nickel layer (among all nickel layers) closest to the substrate.

[0135] Preferably, the substrate of the present invention comprises at least one MPS nickel layer, more preferably comprising at least one MPS nickel layer in addition to the at least one bright nickel layer and / or the at least one satin nickel layer, most preferably comprising at least one MPS nickel layer in addition to the at least one bright nickel layer and / or the at least one satin nickel layer, and further comprising at least one semi-bright nickel layer. In the context of the present invention, MPS represents micropores.

[0136] Preferably, the substrate of the present invention is wherein the at least one MPS nickel layer faces the black chromium layer on one side and faces the at least one bright nickel layer or the at least one satin nickel layer on the other side.

[0137] Preferably, the substrate of the present invention is wherein the at least one semi-bright nickel layer is under the at least one bright nickel layer or the at least one satin nickel layer.

[0138] Preferably, the substrate of the present invention is a part of a stack of layers, wherein the stack of layers includes (adjacent or non-adjacent) the following in the direction from the black chrome layer to the substrate: (i) a black chrome layer, (ii) at least one MPS nickel layer, (iii) at least one bright nickel layer and / or (preferably) at least one satin nickel layer, and (iv) at least one semi-bright nickel layer.

[0139] This preferably achieves excellent gloss in the context of the present invention, preferably in the range of 150 to 230 degrees with reference to a measurement angle of 60°. This is especially suitable if (iii) is a bright nickel layer.

[0140] Preferably, the substrate of the present invention contains iron (i.e., more than zero atomic percent) based on all atoms in the black chromium layer, preferably up to 15 atomic percent, more preferably up to 12 atomic percent, even more preferably up to 10 atomic percent, and even more preferably up to 8 atomic percent, most preferably up to 6 atomic percent.

[0141] In some cases, the layer stack preferably includes a sealing layer and / or an anti-fingerprint layer, preferably on the black chrome layer. If both are applied, it is preferable to apply the sealing layer first, followed by the anti-fingerprint layer, which preferably forms the outermost layer.

[0142] In the following, the present invention will be described by way of the following non-limiting examples.

[0143] In the following example, Hall cell plating was performed to evaluate the visual appearance of the black chrome layer depending on the current density distribution.

[0144] General procedure: Use a copper plate (99 mm × 70 mm) as the substrate.

[0145] In the first step, the copper plate is cleaned by electrolytic degreasing with 100 g / L Uniclean® 279 (a product of Atotech Deutschland) at room temperature (RT). Then, the substrate is rinsed with water, acid-washed with 10% by volume H2SO4, and rinsed with water.

[0146] In the second step, a bright nickel layer is deposited on the cleaned substrate (10 minutes, 4 A / dm2, UniBrite 2002, Atotech product) to obtain a nickel-plated substrate, and then rinsed with water.

[0147] In the third step, a black chromium layer is deposited using the following electroplating bath: (A) approximately 20 to 25 g / L Cr3+ ions (provided in the form of alkaline chromium sulfate), (B) approximately 30 g / L formic acid, (C) approximately 60 g / L boric acid, (D) potassium thiocyanate (Table 1), (E) methionine (Table 1), approximately 10 g / L ammonium bromide, approximately 100 g / L ammonium chloride, approximately 100 g / L potassium chloride, and approximately 0.5 g / L FeSO4•7H2O. The electroplating bath further contains a small amount (up to 4 g / L) of saccharin and S-containing diols between 5 g / L and 50 g / L. Cobalt and nickel ions are absent. Therefore, the black chromium layer does not contain cobalt and nickel. However, other experiments have shown that a relatively small amount of cobalt (not shown) is permissible.

[0148] Adjust the pH value to 3.2.

[0149] Compounds (D) and (E) are used in various concentrations as outlined in Table 1 below.

[0150] Unless otherwise stated, each electroplating bath is tested in a Hall cell with a graphite anode, and a nickel-plated substrate is mounted as the cathode. A current of 5 A is passed through the bath for 3 minutes at a temperature ranging from 35°C to 45°C (see Table 1 for other details).

[0151] After plating, the substrate was rinsed with water and dried for the first color measurement (abbreviated as "CM1" in Table 1). After "CM1", the substrate was rinsed with hot water at 70°C and 80°C for 10 minutes respectively, dried, and the second color measurement was performed (abbreviated as "CM2" in Table 1).

[0152] In the first set of experiments (abbreviated as Examples E1.1 to E1.7 in Table 1), a warm black hue (b* in the range of approximately +3 to +6) was formed immediately after rinsing with hot water. In the second set of experiments (abbreviated as Examples E2.1 to E2.3 in Table 1), a neutral black hue (b* approximately or less than zero) was formed immediately after rinsing with hot water. Color measurements according to the L*a*b* color space system were performed using a colorimeter (Konica Minolta CM-700d; measurement mode: SCI; observation angle: 10°; light source: D65) at a position approximately 3.5 cm from the left edge of the substrate and 2 cm from the bottom edge (representing a typical medium current density (MCD) of approximately 10 A / dm² to 12 A / dm²). Comparative examples are abbreviated as "CE".

[0153] In addition to the color measurement mentioned above, the visual inspection of the substrate also depends on the local current density (abbreviated as "ASD range" in Table 1). For this purpose, the area of ​​the defect-free black chrome layer (i.e., a homogeneous black chrome layer without turbidity or charring) is determined and recalculated to the corresponding current density range ("ASD range"). A relatively wide range of recalculated current densities is considered preferable because it demonstrates the achievement of a defect-free black chrome layer from low to high current densities.

[0154] Gloss was measured using a reflectometer (REFO 3-D, Dr. Lange) at a measurement angle of 60°. Table 1, Electroplating Bath Composition and Results serial number (D) [mmol / L] (E) [mmol / L] (E) / (D) T*** [℃] CM1 L*;a*;b* CM2 L*;a*;b* ASD range grade E1.1* 101 202 2 70 53; 0.5; 3.8 49;1.0;4.9 3-50 ++ E1.2* 131 306 2.3 70 51;0.6;4.6 46;1.4;5.6 3-20 ++ E1.3** 131 306 2.3 80 50;1.0;5.5 44;1.5;4.5 5-50 +++ E1.4* 152 202 1.3 70 52;0.6;4.2 44;1.5;4.4 3-25 +++ E1.5* 163 155 1 70 53;0.5;3.8 50;0.8;4.8 3-50 ++ E1.6* 163 206 1.3 70 52;0.6;4.4 46;1.4;5.2 3-35 +++ E1.7* 202 202 1 70 50;0.7;4.7 43;1.6;3.6 4-25 +++ E2.1** 162 357 2.2 80 50; 0.8; 5.1 41; 1.6; 0.6 4-50 +++ E2.2** 182 406 2.2 80 48; 1.2; 6.4 40; 1.0; -1.4 4-20 +++ E2.3** 234 406 1.7 80 48; 1.1; 6.3 41; 0.3; -2.4 4-15 ++ CE1 49 202 4.1 70 55; 0.4; 3.3 53; 0.6; 4.3 3-50 + * Indicates a 35°C plating bath temperature. ** Indicates a 45°C plating bath temperature. *** Indicates the rinsing water temperature. Under the "Grade" rating, overall performance is evaluated as follows: + Indicates that color measurements (i.e., CM1 and CM2) or ASD range meet requirements; however, this is insufficient and therefore undesirable; ++ Indicates that both color measurements (i.e., CM1 and CM2) and ASD range meet requirements; this is desirable; +++ Indicates that both color measurements (i.e., CM1 and CM2) and ASD range meet requirements exceptionally well; this is highly desirable; - CE1 indicates that a certain concentration of (D) is required to obtain a sufficiently black / dark tone. The concentration of (D) is significantly below 100 mmol / L. Furthermore, it indicates that the lack of (D) cannot be compensated for by a relatively high concentration of (E).

[0155] Other comparative examples CE2 to CE4 based on US 2020 / 094526 A1: - CE2 corresponds to sample 5 in Table 1 (which represents all samples in the range of 5 to 13 in Table 1), where the total amount of thiocyanate is also less than 100 mmol / L (i.e., 100 ml / L Trichrome Graphite Makeup and 30 ml / L Trichrome Graphite Maintenance produce less than 100 mmol / L of thiocyanate); the color measurement CM1 immediately after plating shows L*; a*; b* of 54; 0.5; 3.8, and ASD in the range of 7 to 50. Although the ASD range is relatively wide, the color immediately after plating is not black / dark enough.

[0156] As shown in Table 1 of US'526, only in Example 7 was a very dark (and neutral black) hue obtained by "accelerated testing" with L*; a*; b* (measured at high current density) of 44; 0.8; 0.4, which included an 18-day waiting period under predetermined conditions (see

[0064] Ions US'526). Furthermore, a sufficient warm black hue was obtained only in Example 6 (which was left to stand in ambient air for 18 days) and Example 13 (which underwent another 18-day "accelerated testing"). Our experiments showed that a 10-minute hot water rinse had no significant effect on obtaining a warm or neutral black hue for CE2. Therefore, based on our observations, Examples 5 to 13 in US'526 have at least the following disadvantages: First, an 18 or 19-day rest period (or aging time) is considered unacceptable given industry requirements. Second, the visual results obtained from the same chemical composition differ depending on the rest period and conditions of the application. Both are undesirable. The desire is to quickly obtain a clear black tone (neutral black tone or warm black tone). As shown above, this can be achieved by the present invention.

[0157] Therefore, our experiments clearly demonstrate that the total concentration of (D) (e.g., thiocyanate) less than 100 mmol / L is too low to be significantly affected by hot water rinsing.

[0158] - CE3 corresponds to sample 14 in Table 2 of US'526, where the total amount of thiocyanate is 15 g / L (i.e., 254 mmol / L), which is significantly higher than the total amount in sample 5 of US'526. Immediately after plating at approximately 10 A / dm², color measurements CM1 showed L*; a*; b* of 47; 1.0; 5.7, which are consistent with the contents disclosed in Table 2, Item 14, "Initial," of US'526. However, regardless of any hot water rinsing, our experiments also showed an unacceptably narrow ASD range (only about 1 ASD) in the Hall cell setup. In contrast, the examples of the present invention clearly demonstrate that thiocyanate concentrations below 250 mmol / L not only achieve the desired hue but also further expand the ASD range. Therefore, total amounts significantly higher than 250 mmol / L adversely affect the possible current density range on the substrate and thus greatly increase the likelihood of plating defects. This can be unexpectedly solved by the present invention with a concentration not exceeding 250 mmol / L.

[0159] - CE4 corresponds to sample 17 in Table 2 of US'526, with a total thiocyanate content of 40 g / L (i.e., 677 mmol / L). Compared to CE3, the total thiocyanate content is significantly increased further. Although deposition is possible, a strong and undesirable white turbidity covers most of the Hall cell substrate, indicating that the acceptable current density range is even smaller than that of CE3. Therefore, CE4 confirms the findings of CE3 and supports the conclusion that CE4 is unsuitable for electroplating precision or complex substrates requiring a significantly wider current density range.

[0160] Examples of the present invention demonstrate that a neutral black tone or a warm black tone can be specifically determined and obtained within an acceptable time. (D) The concentration is high enough to obtain a hot water flushing effect, but does not exceed a critical concentration, so as to still ensure a relatively wide range of current densities.

[0161] Furthermore, for Examples E1.1 to E1.7, gloss was measured after rinsing with hot water, and the results are as follows: E1.1: >210 to 230; E1.2 to E1.6: 185 to 210; E1.7: 160 to <185. These results demonstrate that gloss is indirectly related to the concentration of (D). According to the results, very low (D) concentrations produce relatively high gloss, for example, greater than 210 (see E1.1). In contrast, the (D) concentration ranges in Examples E1.2 to E1.6 produce the desired gloss in the range of 185 to 210. In contrast, higher (D) concentrations, such as in E1.7, have shown an acceptable but reduced gloss in the range of 160 to <185. This indicates that significantly higher (D) concentrations, especially above 250 mmol / L, substantially weaken the gloss of individual black chrome layers by significantly reducing gloss to below 150, resulting in an increased (and undesirable) matte / dull surface impression. Conversely, if the (D) concentration is too low, i.e., (significantly) below 100 mmol / L, the gloss is relatively high (e.g., >230), but this impairs visual perception, creating an impression that the black tone is not dark enough or black enough. This perception is undesirable.

[0162] Other examples according to the invention were carried out, wherein the electroplating bath was modified in a manner that did not include chloride ions (specific details not shown). In these experiments, Hall cell experiments were not performed; instead, electroplating tests were conducted in beakers having the same Hall cell substrate but at a specific current density of 10 A / dm². In these examples, warm black tones with L*; a*; b* values ​​of 45; 1.3; 3.8 were obtained.

Claims

1. An electroplating bath for depositing a black chromium layer, the electroplating bath comprising: (A) trivalent chromium ions; (B) one or more chelating agents for the trivalent chromium ions; (D) thiocyanate, its salts, esters and / or isoforms, the total amount of which is in the range of 130 mmol / L to 250 mmol / L based on the total volume of the electroplating bath; (E) one or more compounds of formula (I), their salts and / or monoxide R1-S-(CH2)n-CH(NH2)-R2 (I), wherein R1 is a branched or unbranched C1 to C4 alkyl group, R2 is selected from the group consisting of COOH, its salts and (CH2)m-OH, n is an integer in the range of 1 to 4, and m is an integer in the range of 1 to 4, wherein the total amount of which is in the range of 150 mmol / L to 950 mmol / L based on the total volume of the electroplating bath. (E) in the range of mmol / L, and the (E):(D) molar ratio in the range of 0.9 to 2.

65.

2. The electroplating bath of claim 1 further comprises one or more pH buffering compounds for use in the electroplating bath.

3. The electroplating bath, as requested in item 1 or 2, further comprises halogen anions.

4. The electroplating bath of claim 1 or 2, wherein the bath contains (D) in a total amount ranging from 150 mmol / L to 245 mmol / L based on the total volume of the electroplating bath.

5. The electroplating bath of claim 1 or 2, wherein the bath contains (E) in a total amount ranging from 200 mmol / L to 950 mmol / L based on the total volume of the electroplating bath.

6. The electroplating bath as requested in item 1 or 2, wherein the molar ratio of (E):(D) is in the range of 1 to 2.

3.

7. The electroplating bath as requested in item 1 or 2, wherein R1 is methyl, ethyl, n-propyl or isopropyl.

8. The electroplating bath as requested in item 1 or 2, wherein R2 is COOH and / or its salt.

9. The electroplating bath as requested in item 1 or 2, where n is 1 or 2.

10. The electroplating bath of claim 1 or 2, wherein the compound of formula (I) in (E) contains methionine.

11. The electroplating bath of claim 1 or 2, wherein the trivalent chromium ions are derived from an inorganic or organic trivalent chromium salt having anions selected from the group consisting of: sulfate anion, formate anion, acetate anion, malate anion and oxalate anion.

12. The electroplating bath of claim 1, wherein cobalt ions are present in the range of 1 mg / L to 500 mg / L or not contained in the electroplating bath.

13. A method for electroplating a black chromium layer on a substrate, the method comprising the steps of: (a) providing the substrate, (b) contacting the substrate with an electroplating bath as claimed in any one of claims 1 to 12, (c) applying an electric current to electroplat the black chromium layer onto the substrate, and (d) heat-treating the substrate obtained in step (c) at a temperature in the range of 30°C to 100°C.

14. The method of claim 13, wherein in step (d), the heat treatment is carried out in water.

15. The method of claim 13 or 14, wherein in step (d), the heat treatment is a hot water rinse.

16. The method of claim 13 or 14, wherein the black chromium layer has an a* value in the range of -1.5 to +3, or a b* value in the range of -2.5 to +6, or both an a* value in the range of -1.5 to +3 and a b* value in the range of -2.5 to +6.

17. A substrate comprising a black chrome layer formed by an electroplating bath as claimed in any one of claims 1 to 12, wherein the black chrome layer has an L* value of 50 or less according to the L*a*b color system and a gloss value in the range of 150 to 230 degrees at a measurement angle of reference 60°.

18. The substrate of claim 17, wherein the black chromium layer has an a* value in the range of -1.5 to +3, or a b* value in the range of -2.5 to +6, or both an a* value in the range of -1.5 to +3 and a b* value in the range of -2.5 to +6.

19. The substrate of claim 17 or 18, wherein the black chrome layer is part of a stack of layers comprising, along the direction from the black chrome layer to the substrate: (i) the black chrome layer, and (iii) at least one bright nickel layer and / or at least one satin nickel layer.

20. The substrate of claim 17 or 18, wherein the black chrome layer is part of a stack of layers comprising, along the direction from the black chrome layer to the substrate: (i) the black chrome layer, (ii) at least one MPS nickel layer, and (iii) at least one bright nickel layer and / or at least one satin nickel layer.

21. The substrate of claim 17 or 18, wherein the black chrome layer is part of a stack of layers comprising, along the direction from the black chrome layer to the substrate: (i) the black chrome layer, (iii) at least one bright nickel layer and / or at least one satin nickel layer, and (iv) at least one semi-bright nickel layer.

22. The substrate of claim 17 or 18, wherein the black chrome layer is part of a stack of layers comprising, along the direction from the black chrome layer to the substrate: (i) the black chrome layer, (ii) at least one MPS nickel layer, (iii) at least one bright nickel layer and / or at least one satin nickel layer, and (iv) at least one semi-bright nickel layer.

23. The substrate of claim 17 or 18, wherein the black chromium layer is substantially free of cobalt, or contains cobalt, wherein there is more chromium than cobalt in the black chromium layer.