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

Abstract

The invention relates to a very specific electroplating bath for depositing a black chromium layer, to a corresponding method thereof and to a corresponding substrate having said black chromium layer thereon. The substrate comprising said black chromium layer is very well suited for decorative purposes.

Description

Technical Field

[0001] This invention relates to a very specific electroplating bath for depositing a black chromium layer, a corresponding method thereof, and a corresponding substrate having the black chromium layer thereon. The substrate containing the black chromium layer is ideally suited for decorative purposes. Background 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 for visual applications.

[0003] Even though it started with hexavalent chromium coatings, attention has now shifted significantly 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-deep (also known as neutral black) trivalent chromium coatings, for example, for decorative automotive parts. However, because this neutral black tone can feel too cold in some cases, slight tinting modifications are often required. These modifications do not destroy the deep black tone itself, but add a slight warming tone to produce a warmer black. In principle, although neutral black 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 tones, 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 more 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 the 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 of manufacturing thereon.

[0010] US 2020 / 094526 A1 refers to black-plated resin parts that contain a black chrome plating with 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 unacceptably long periods of inactivity, ultimately producing the desired tone. 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 the aforementioned problems. Summary of the Invention

[0013] Therefore, the objective of this invention is to provide an electroplating bath and a corresponding method for electroplating that, on the one hand, allows for rapid and stable tonal formation (for both neutral black and warm black tones), and on the other hand, allows for deposition without plating defects on a wide variety of substrate geometries, resulting in an excellent visual appearance, including excellent gloss. Furthermore, it should be possible to specifically and easily target and obtain both tones. Detailed Implementation

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

[0015] Therefore, the present invention relates to an electroplating bath for depositing a black chromium layer, the electroplating bath comprising:

[0016] (A) Trivalent chromium ions;

[0017] (B) One or more complexing agents for the trivalent chromium ions;

[0018] (C) Optionally, one or more pH buffering compounds for the electroplating bath;

[0019] (D) Thiocyanate, its salts, esters and / or isoforms, in the total volume of the electroplating bath, in the range of 100 mmol / L to 250 mmol / L.

[0020] (E) One or more compounds of formula (I), their salts and / or sulfoxides

[0021] R 1 -S-(CH2) n -CH(NH2)-R 2

[0022] (I),

[0023] in

[0024] -R1 It is a branched or unbranched C1 to C4 alkyl group.

[0025] -R 2 Choose from COOH, its salts, and (CH2). m Groups composed of -OH,

[0026] -n is an integer in the range of 1 to 4, and

[0027] -m is an integer in the range of 1 to 4.

[0028] 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 form on substrates with complex geometries to achieve extremely uniform deposition quality without plating defects. However, it has also been found that these excellent results are only obtained when the relatively narrow concentration range of (D) as defined above is maintained.

[0029] Most preferably, the black chrome layer is a decorative chrome layer. Typical applications include automotive parts, and most preferably, automotive interiors. To obtain such a black chrome layer, and most preferably, a black chrome layer as defined throughout this document, the electroplating bath of the present invention is highly suitable.

[0030] 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.

[0031] Typically, the electroplating bath of the present invention is preferred, wherein the L* value of the black chromium layer is 50 or lower, preferably 49 or lower, more preferably 48 or lower, even more preferably 47 or lower, even more preferably 46 or lower, further more preferably 45 or lower, and most preferably 43 or lower. An L* value of 50 or lower is typically well perceived as black and dark. Generally, the lower the L* value (preferably as defined above), the stronger the impression of a black / dark hue.

[0032] Preferably, the electroplating bath of the present invention contains a* value of the black chromium layer 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.

[0033] The distinction between neutral black tones and warm black tones is typically based on slightly different b* values.

[0034] 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 preference 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, preferably in the range of -2 to +2, more preferably in the range of -1.5 to +1.5, and most preferably in the range of -1 to +1.

[0035] For a neutral black hue, the L* value is preferably 45 or lower, more preferably 44 or lower, even more preferably 43 or lower, even more preferably 42 or lower, and most preferably 41 or lower.

[0036] 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 is more preferred, meaning 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.

[0037] In the context of this invention, both neutral black tones and warm black tones can be specifically targeted and thus obtained, which has great benefits.

[0038] Compound (A) and general bath compounds:

[0039] The electroplating bath of the present invention is preferably an aqueous solution, that is, it contains water, and preferably at least 55% by volume or more, more preferably 65% ​​by volume or more, even more preferably 75% by volume or more, 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, based on the total volume of the electroplating bath. Most preferably, water is the sole solvent.

[0040] 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, even more preferably 2.7 to 3.8, and most preferably 3.0 to 3.5. The pH is preferably adjusted with hydrochloric acid, sulfuric acid, ammonia, potassium hydroxide and / or sodium hydroxide.

[0041] The electroplating bath of the present invention contains (A) trivalent chromium ions.

[0042] The preferred embodiment of the present invention is the electroplating bath, wherein the total concentration of trivalent chromium ions, based on the total volume of the electroplating bath, is in the range of 5 g / L to 35 g / L, preferably 6 g / L to 32 g / L, 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.

[0043] Preferably, the trivalent chromium ions originate from trivalent chromium salts, more preferably from inorganic and / or organic chromium salts, and most preferably from inorganic chromium salts. Preferred inorganic chromium salts contain chloride and / or sulfate anions, more preferably sulfate anions. Extremely preferred inorganic chromium salts are basic chromium sulfates. Preferred organic chromium salts contain carboxylic acid anions, preferably formate, acetate, malate, and / or oxalate anions.

[0044] The preferred embodiment of the present invention is the electroplating bath, wherein the electroplating bath contains sulfate ions, most preferably derived from trivalent chromium salts.

[0045] Preferably, the electroplating bath of the present invention contains, preferably not contains, compounds containing chromium with an oxidation state of +6. Therefore, the electroplating bath contains, preferably not contains, hexavalent chromium.

[0046] Preferably, the electroplating bath of the present invention contains, preferably not contains, cobalt ions. Preferably, the black chrome layer contains, preferably not contains, 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, while not essential 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 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.

[0047] Preferably, the electroplating bath of the present invention contains, 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 to be substantially nickel-free. 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 contains, and preferably does not contain, nickel.

[0048] It is generally preferable to avoid such environments containing potentially contaminated nickel and cobalt ions. This typically results in less complexity for wastewater treatment and bath disposal. Furthermore, neither nickel nor cobalt is required to achieve neutral or warm black tones.

[0049] Preferably, the electroplating bath of the present invention contains, preferably not contains, fluoride ions. More preferably, the black chromium layer contains, preferably not contains, fluoride.

[0050] Preferably, the electroplating bath of the present invention contains, preferably not contains, fluorine-containing compounds. Most preferably, it contains fluorine-containing surfactant compounds. Such compounds are particularly undesirable due to increased environmental restrictions.

[0051] Preferably, the electroplating bath of the present invention contains, preferably not contains, phosphate anions, and more preferably not contains, phosphorus-containing compounds. Preferably, the black chromium layer contains, preferably not contains, phosphorus. However, this does not preclude phosphorus from being deposited in subsequent layers (e.g., passivation layers) on the black chromium layer.

[0052] Preferably, the electroplating bath of the present invention further comprises halide anions, preferably chloride anions. In the context of the present invention, this is preferred, and the corresponding electroplating bath is referred to as a chloride-containing bath. More preferably, the electroplating bath of the present invention comprises chloride ions and sulfate ions.

[0053] Preferably, the electroplating bath of the present invention contains chloride ions at a concentration ranging from 50 g / L to 200 g / L, preferably from 60 g / L to 185 g / L, more preferably from 70 g / L to 170 g / L, even more preferably from 80 g / L to 155 g / L, and most preferably from 90 g / L to 140 g / L, based on the total volume of the electroplating bath. The chloride ions are preferably derived from chloride salts and / or hydrochloric acid, and more preferably from sodium chloride, potassium chloride, ammonium chloride, chromium chloride (at least as a part of all chloride ions), and / or mixtures thereof. Typically, as previously preferably mentioned, the chloride ions are present as anions of conductive salts. Highly preferred conductive salts are ammonium chloride, sodium chloride, and potassium chloride, with ammonium chloride being the most preferred.

[0054] Preferably, the electroplating bath of the present invention further comprises bromide anions. This typically avoids the anodic formation of undesirable hexavalent chromium. 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, 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.

[0055] More preferably, the electroplating bath of the present invention contains chloride ions, bromide ions and sulfate ions, and most preferably has a concentration as defined herein.

[0056] 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 most preferred electroplating bath of the present invention comprises chloride ions, bromide ions, sulfate ions, and Fe(II) ions, and most preferably has concentrations as defined herein. The Fe(II) ions preferably come from the corresponding iron salt, and more preferably from ferric(II) sulfate salts. Typically, iron ions have several beneficial effects on electroplating performance 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 comprises iron, more preferably as defined throughout this document.

[0057] Furthermore, the electroplating bath of the present invention is highly preferred, wherein trivalent chromium ions and Fe(II) ions (if present) are the only transition metals in the plating bath, and most 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 preferably included.

[0058] In some cases, the electroplating bath of the present invention preferably further comprises at least one sulfur-containing compound different from (D) and (E).

[0059] In some cases, the electroplating bath of the present invention preferably contains additional (i.e., in addition to (D) and (E)) saccharin and / or its salts.

[0060] In some cases, the electroplating bath of the present invention preferably contains additional (i.e., in addition to (D) and (E)) sulfur-containing diols, and most preferably in addition to saccharin and / or its salts mentioned above.

[0061] Preferably, the electroplating bath of the present invention further comprises at least one surfactant compound. Preferably, the surfactant compound comprises a cationic or anionic surfactant compound, more preferably anionic. Preferably, the 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.

[0062] Preferred sulfosuccinates include sodium dipentyl sulfosuccinate.

[0063] Preferred alkylbenzene sulfonates having 8 to 20 aliphatic carbon atoms include sodium dodecylbenzene sulfonate.

[0064] Preferred alkyl sulfates having 8 to 20 carbon atoms include sodium lauryl sulfate.

[0065] Preferred alkyl ether sulfate fatty alcohols include sodium lauryl polyethoxylate.

[0066] Preferably, the electroplating bath of the present invention contains a total concentration of at least one surfactant compound in the range 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.

[0067] In contrast, in some cases, the electroplating bath of the present invention is preferred, wherein the electroplating bath is substantially free of, preferably not containing, chloride ions, and preferably not containing halide anions. In the context of the present invention, this is less preferred and the corresponding electroplating bath is referred to as a chloride-free bath. 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, most preferably by means of a conductive salt. The most preferred conductive salts are potassium sulfate, sodium sulfate, ammonium sulfate, or mixtures thereof. In this particular case, the electroplating bath is preferably substantially free of, preferably not containing, bromide ions. However, in some rare cases, such an electroplating bath preferably contains iron ions, preferably Fe(II) ions, most preferably at the concentration defined above.

[0068] Compound (B):

[0069] The electroplating bath of the present invention comprises (B) one or more complexing agents for the trivalent chromium ions. Such compounds retain the trivalent chromium ions in solution. Preferably, one or more complexing agents are not compounds (D) and (E), and are therefore preferably different from (D) and (E).

[0070] Preferred is the electroplating bath of the present invention, wherein one or more complexing agents comprise organic acids and / or their salts, preferably organic carboxylic acids and / or their salts, and most preferably organic carboxylic acids and / or their salts containing one, two or three carboxyl groups.

[0071] Organic carboxylic acids and / or their salts (preferably also organic carboxylic acids and / or their salts containing one, two, or three carboxyl groups) are preferably substituted or unsubstituted. Preferred substituents contain amino and / or hydroxyl groups. Preferably, the substituents do not contain SH groups.

[0072] 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. Preferred (α-)aminocarboxylic acids comprise glycine, aspartic acid, and / or their salts. Preferably, the aminocarboxylic acid (preferably α-aminocarboxylic acid, respectively) is not a compound according to (E), more preferably not a sulfur-containing aminocarboxylic acid (preferably not a sulfur-containing α-aminocarboxylic acid, respectively), and most preferably not methionine. Preferably, one or more complexing agents are different from compounds of formula (E).

[0073] More preferably, the electroplating bath of the present invention contains one or more complexing agents comprising: formic acid, acetic acid, oxalic acid, tartaric acid, malic acid, citric acid, glycine, aspartic acid, and / or their salts, preferably formic acid, acetic acid, oxalic acid, tartaric acid, malic acid, citric acid, and / or their salts, more preferably formic acid, acetic acid, oxalic acid, tartaric acid, malic 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 most preferred embodiment applies if the electroplating bath of the present invention contains chloride ions. In contrast, if the electroplating bath of the present invention is chloride-free, then preferably, one or more complexing agents comprise oxalic acid, tartaric acid, malic acid, citric acid, and / or their salts, and most preferably malic acid and / or their salts.

[0074] The preferred embodiment of the present invention is the electroplating bath in which the total concentration of one or more complexing agents, based on the total volume of the electroplating bath, ranges from 5 g / L to 200 g / L, preferably from 8 g / L to 150 g / L, more preferably from 10 g / L to 100 g / L, even more preferably from 12 g / L to 75 g / L, even more preferably from 15 g / L to 50 g / L, and most preferably from 20 g / L to 35 g / L. This is most preferably applicable if the electroplating bath contains chloride ions, but it is generally also applicable to chlorine-free electroplating baths.

[0075] If the electroplating bath of the present invention is particularly chlorine-free, then the total concentration of one or more complexing agents, based on the total volume of the electroplating bath, 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 preference applies to oxalic acid, tartaric acid, malic acid, citric acid and their salts, and most preferably to malic acid and their salts.

[0076] Preferably, the electroplating bath of the present invention is wherein (B) / (A) forms a molar ratio in the range of 1 to 1.5, preferably in the range of 1.1 to 1.4, and most preferably in the range of 1.2 to 1.3.

[0077] Compound (C):

[0078] The electroplating bath of the present invention comprises (C) optionally one or more pH buffering compounds for the electroplating bath. Most preferably, the electroplating bath of the present invention comprises (i.e., not optionally) one or more pH buffering compounds. In the latter case, the electroplating bath of the present invention is preferred in which one or more pH buffering compounds for 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, preferably do not contain organic acids. In this case, they are counted relative to (B).

[0079] In many cases, the electroplating bath of the present invention is preferred, wherein one or more pH buffer compounds comprise boron-containing compounds, preferably boric acid and / or borates, most preferably boric acid. A preferred borate is sodium borate.

[0080] The electroplating bath of the present invention is most preferably wherein, based on the total volume of the electroplating bath, the total concentration of one or more pH buffer compounds is in the range of 30 g / L to 250 g / L, preferably 35 g / L to 200 g / L, more preferably 40 g / L to 150 g / L, even more preferably 45 g / L to 100 g / L, and most preferably 50 g / L to 75 g / L. This is even more preferably applicable to the boron-containing compounds, and even more preferably applicable to the boric acid and the borates, and most preferably applicable to the boric acid. Most preferably, one or more pH buffer compounds contain boric acid but no borates. Therefore, the electroplating bath of the present invention is most preferably wherein, based on the total volume of the electroplating bath, (C) contains boric acid in a total amount preferably in the range of 35 g / L to 90 g / L, 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.

[0081] In some other cases, the electroplating bath of the present invention does not explicitly contain a separate pH buffering compound. Instead, one or more complexing agents for the trivalent chromium ions are present in a certain amount and selected in a certain manner such that they act not only as complexing agents for the trivalent chromium ions but also additionally as pH buffering compounds. In the context of the present invention, this preference is less pronounced but possible.

[0082] Compound (D):

[0083] 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 demonstrate that this compound, along with the aforementioned concentration range, is essential. Preferably, the above concentrations are based on SCN.- That is, based on monobasic thiocyanate. The term "acid" in "thiocyanate" includes its deprotonated / discrete form.

[0084] According to our experiments (see the text under “Examples” below), a sufficiently black chromium layer cannot be obtained if the concentration is significantly below 100 mmol / L. Most importantly, if the concentration of (D) is below 100 mmol / L, the heat treatment in the method of this invention does not significantly affect the final color formation. Furthermore, an undesirable high gloss is obtained, which begins to adversely affect the black visual appearance of the chromium layer.

[0085] 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 becomes unacceptably small. However, this is unacceptable given technical requirements. Additionally, if the (D) concentration significantly exceeds 250 mmol / L, excessively low gloss is achieved, giving the black chromium layer an unacceptably dull appearance.

[0086] In comparison, this invention solves these problems.

[0087] Preferably, the electroplating bath of the present invention comprises (D) thiocyanate, its salts and / or esters in the stated total amount, most preferably thiocyanate and / or its salts in the stated total amount. Preferably, the salt comprises potassium thiocyanate and / or sodium thiocyanate, most preferably in the stated total amount.

[0088] 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, and all other concentration ranges mentioned below, are based on SCN. - This is based on a single-base thiocyanate. Furthermore, it is explicitly preferred that the concentrations mentioned above can be freely combined to form concentration ranges not explicitly disclosed. This most preferred option includes other combinations of lower and upper limits not explicitly mentioned throughout this document.

[0089] In some cases, the electroplating bath of the present invention is preferred, wherein the bath comprises (D), in a total volume of 130 mmol / L to 250 mmol / L, preferably 150 mmol / L to 245 mmol / L, 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.

[0090] 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, 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.

[0091] Compound (E):

[0092] The electroplating bath of the present invention comprises (E) one or more compounds of formula (I), their salts and / or sulfoxides.

[0093] R 1 -S-(CH2) n -CH(NH2)-R 2

[0094] (I),

[0095] in

[0096] -R 1 It is a branched or unbranched C1 to C4 alkyl group.

[0097] -R 2 Choose from COOH, its salts, and (CH2). m Groups composed of -OH,

[0098] -n is an integer in the range of 1 to 4, and

[0099] -m is an integer in the range of 1 to 4.

[0100] In the context of this invention, "sulfoxide" refers to oxygen chemically bonded to a sulfur atom via a double bond, i.e., compounds of formula (I) above include R. 1 -S(=O)-(CH2) n -CH(NH2)-R 2 structure.

[0101] 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, preferably 135 mmol / L to 800 mmol / L, 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.

[0102] In some cases, the electroplating bath of the present invention is preferred, wherein the bath comprises (E), in total volume, ranging from 100 mmol / L to 450 mmol / L, preferably from 120 mmol / L to 400 mmol / L, more preferably from 140 mmol / L to 350 mmol / L, even more preferably from 150 mmol / L to 310 mmol / L, even more preferably from 170 mmol / L to 270 mmol / L, and most preferably from 190 mmol / L to 230 mmol / L. These are particularly preferred concentration ranges for warm black tones.

[0103] In other cases, the preferred method is the electroplating bath of the present invention, wherein the bath comprises (E), in total volume, 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.

[0104] Preferably, the electroplating bath of the present invention has a molar ratio of (E):(D) of 0.9 or greater, preferably 1.0 or greater, more preferably 1.1 or greater, and most preferably 1.2 or greater.

[0105] More preferably, the electroplating bath of the present invention, wherein the molar ratio of (E):(D) is in the range of 0.9 to 2.65, 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.

[0106] 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, preferably 1 to 2, more preferably 1.1 to 1.8, even more preferably 1.15 to 1.5, and most preferably 1.2 to 1.3. In some cases, these are preferred molar ranges for warm black tones.

[0107] 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, preferably 1.9 to 2.6, more preferably 2.05 to 2.55, even more preferably 2.1 to 2.5, even more preferably 2.15 to 2.45, and most preferably 2.2 to 2.4. In some cases, these are preferred molar ranges for neutral black tones.

[0108] Preferably, it is the electroplating bath of the present invention, wherein R 1 It is methyl, ethyl, n-propyl or isopropyl, preferably methyl or ethyl, and most preferably methyl.

[0109] Preferably, it is the electroplating bath of the present invention, wherein R 2 It is COOH and / or its salts. As mentioned, COOH also includes its deprotonated / discrete forms.

[0110] The preferred embodiment is the electroplating bath of the present invention, wherein n is 1 or 2, preferably 2.

[0111] Preferably, the electroplating bath of the present invention is used, wherein m is 1 or 2.

[0112] Preferably, the electroplating bath of the present invention contains the compound of formula (I) in (E) comprising methionine. Most preferably, the compound of formula (E) is methionine.

[0113] Electroplating method:

[0114] Furthermore, the present invention relates to a method for electroplating a black chromium layer on a substrate, the method comprising the following steps:

[0115] (a) Providing a substrate,

[0116] (b) Bring the substrate into contact with the electroplating bath according to the invention, preferably as described herein.

[0117] (c) Apply an electric current to electroplate a black chromium layer onto the substrate.

[0118] (d) Heat-treat the substrate obtained in step (c) at a temperature ranging from 30°C to 100°C.

[0119] The foregoing features of the electroplating bath of the present invention (including preferred variations thereof) are preferably also 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 most preferably applicable to the black chromium layer electroplated in step (c).

[0120] In step (a), a substrate is provided.

[0121] 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.

[0122] 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.

[0123] More preferably, the method of the present invention includes a butadiene portion, preferably polybutadiene, in step (a).

[0124] Also preferred is the method of the present invention, wherein in step (a) the substrate comprises a nitrile portion.

[0125] Also preferred is the method of the present invention, wherein in step (a) the substrate comprises a propylene-based portion.

[0126] The method of the present invention is most preferably wherein the substrate comprises polymeric styrene in step (a).

[0127] Most preferably, the method of the present invention comprises, in step (a) an 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 typically used for decorative applications, such as automotive parts.

[0128] The preferred embodiment of the method of the present invention is the polyetherketone (PEK) comprising polyaryl etherketone (PAEK), polyetheretherketone (PEEK), polyetheretheretherketone (PEEEK), polyetheretherketoneketone (PEEKK), polyetherketoneketoneketone (PEKEKK), polyetherketoneketone (PEKK), and / or mixtures thereof, preferably polyetheretherketone (PEEK), polyaryl etherketone (PAEK), and / or mixtures thereof.

[0129] In some cases, the method of the present invention is preferred, wherein the substrate is a metallic substrate, preferably comprising iron, copper, nickel, aluminum, zinc, mixtures thereof, and / or alloys thereof. Iron-containing metallic substrates are most preferably steel. Mixtures thereof preferably comprise composites.

[0130] 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 most preferably at least one nickel plating step to deposit at least one nickel layer. In many cases, two or even three such metal plating steps are preferred.

[0131] Most 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.

[0132] More preferably, the method of the present invention includes at least one semi-bright nickel layer, preferably comprising at least one semi-bright nickel layer in addition to the at least one bright nickel layer and / or the at least one satin-finish nickel layer. The at least one semi-bright nickel layer is preferably optional. Most preferably, (if applied) the at least one semi-bright nickel layer is deposited prior to the at least one bright nickel layer and / or the at least one satin-finish nickel layer.

[0133] Also preferred is the method of the present invention, wherein at least one nickel layer comprises at least one MPS nickel layer, 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 in addition to the at least one semi-bright nickel layer. In the context of the present invention, MPS refers to an MPS nickel layer comprising non-conductive microparticles that create micropores in a subsequent chromium layer, preferably in a black chromium layer. At least one MPS nickel layer is preferably optional.

[0134] In some cases, the method of the present invention is preferred, wherein the MPS nickel layer is adjacent to the black chromium layer.

[0135] 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 most preferably combined with at least one bright nickel layer.

[0136] Preferably, the black chrome layer is part of a layer stack.

[0137] In step (b), the substrate preferably having at least one nickel layer (preferably as defined above) is preferably brought into contact with the electroplating bath of the present invention by immersion.

[0138] The preferred method of the present invention is wherein the contact during step (c) is in the range of 1 minute to 30 minutes, 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.

[0139] The preferred embodiment of 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, preferably 28°C to 50°C, and more preferably 30°C to 47°C. This is most preferably applicable if the electroplating bath contains chloride ions.

[0140] 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, preferably 40°C to 63°C, more preferably 45°C to 61°C, and most preferably 50°C to 59°C. This most preferred method is applicable if the electroplating bath is a chlorine-free electroplating bath.

[0141] In step (c), a current is applied.

[0142] The preferred embodiment of the method of the present invention is a direct current, preferably 3A / dm. 2 Up to 30A / dm 2 , preferably 4A / dm 2 Up to 25A / dm 2 , or even better, 5A / dm 2 Up to 20A / dm 2 Optimal selection 6A / dm 2 Up to 18A / dm 2 Within the range.

[0143] In some cases, the method of the present invention is preferred, wherein the current is direct current, preferably at 3A / dm. 2 Up to 20A / dm 2 , preferably 4A / dm 2 Up to 15A / dm 2 Optimal selection 5A / dm 2 Up to 10A / dm 2 Within the specified range. This is most preferably applicable if the electroplating bath is a chlorine-free electroplating bath.

[0144] 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).

[0145] Preferred precious metal anodes include platinum-plated titanium anodes and / or platinum anodes.

[0146] Preferred mixed metal oxide anodes include titanium anodes coated with platinum oxide and / or titanium anodes coated with iridium oxide.

[0147] The preferred 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, preferably 0.1 μm to 0.8 μm, more preferably 0.125 μm to 0.6 μm, and most preferably 0.15 μm to 0.5 μm.

[0148] In the context of the method of this invention, step (d) is the most important. It allows for the rapid and direct formation of the desired black hue. The temperature applied in step (d) is not the same as the temperature used in step (c) of the electroplating bath. Steps (c) and (d) are distinct steps.

[0149] The preferred 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.

[0150] 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.

[0151] As mentioned, heat treatment is preferably carried out in water. This preference 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. Typically, for the purposes of this step, such contamination is permissible.

[0152] Even more preferred is the method of the present invention, wherein in step (d), the heat treatment is a hot water rinse, most preferably by immersion, and even more preferably by immersion in the treatment composition.

[0153] The preferred method of the present invention involves heat treatment in step (d) without current. This means that this step is preferably electrodeless.

[0154] The method of the present invention does not exclude other steps, preferably such as additional rinsing, cleaning, pretreatment, and / or post-treatment. Preferably, the steps defined in the examples below are also applicable to the general methods described throughout this document. Preferred post-treatment steps include a sealing step, preferably using inorganic and / or organic sealants, and / or a contact step with the anti-fingerprint composition.

[0155] Substrate containing a black chromium layer:

[0156] The present invention further relates to a substrate comprising a black chromium layer as specifically defined, wherein the black chromium 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, preferably 160 to 220, more preferably 165 to 210, and most preferably 170 to 200 at a measurement angle of reference 60°.

[0157] The foregoing description of the electroplating bath and method of the present invention preferably also applies to the substrates specifically defined in the present invention (if applicable). This is most 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 substrate of the present invention are also preferably applicable to the method of the present invention (if not mentioned above).

[0158] Preferably, the substrate of the present invention has an L* value of 49 or less, preferably 48 or less, more preferably 47 or less, even more preferably 46 or less, even more preferably 45 or less, and most preferably 44 or less.

[0159] Preferably, the substrate of the present invention has the following characteristics:

[0160] The a* value is within the range of -1.5 to +3, preferably within the range of -1 to +2.5, and most preferably within the range of -0.5 to +2, and / or (preferably) the sum of the values.

[0161] The b* value is preferably in the range of -2.5 to +6, and most preferably in the range of -2 to +5.6, and most preferably in the range of -1.5 to +5.

[0162] Preferably, the black chromium layer contains, and preferably does not contain, cobalt.

[0163] or

[0164] It contains cobalt, wherein in the black chromium layer, there is more chromium than cobalt. The latter preferably means that the atomic ratio of chromium to cobalt (i.e., Cr:Co) is greater than 1, preferably 2 or greater, more preferably 3 or greater, and most preferably 4 or greater. This most preferred option is based on the total amount of chromium and cobalt atoms in the black chromium layer.

[0165] Preferably, the black chromium layer is not the only metal layer between the black chromium layer and the substrate.

[0166] Preferably, the substrate of the present invention comprises at least one nickel layer under a black chromium layer.

[0167] Preferably, the substrate of the present invention comprises at least one bright nickel layer or at least one satin-finished nickel layer. This is the most preferred embodiment.

[0168] 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-finished nickel layer, it comprises at least one semi-bright nickel layer. The at least one semi-bright nickel layer is preferably optional. Most preferably, the at least one semi-bright nickel layer is the nickel layer (of all nickel layers) closest to the substrate.

[0169] Preferably, the substrate of the present invention comprises at least one MPS nickel layer, 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-finish 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-finish nickel layer, and further comprising the at least one semi-bright nickel layer. In the context of the present invention, MPS represents micropores.

[0170] 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.

[0171] 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.

[0172] Preferably, the substrate of the present invention is wherein the black chromium layer is part of a layer stack, and the layer stack comprises (adjacent or non-adjacent) layers along the direction from the black chromium layer to the substrate:

[0173] (i) Black chrome layer,

[0174] (ii) Optionally, at least one MPS nickel layer

[0175] (iii) at least one bright nickel layer and / or (preferably) at least one satin nickel layer, and

[0176] (iv) Optionally, at least one semi-bright nickel layer.

[0177] This preferred embodiment achieves excellent gloss in the context of the invention, with reference to a measurement angle of 60°, and most preferably in the range of 150 to 230°. This is especially preferred if (iii) is a bright nickel layer.

[0178] Preferred is the substrate of the present invention, wherein the black chromium layer contains iron (i.e., greater 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, even more preferably up to 8 atomic percent, and most preferably up to 6 atomic percent.

[0179] In some cases, the layer stack preferably includes a sealing layer and / or an anti-fingerprint layer, most preferably on a black chrome layer. If both are applied, then it is preferable to apply the sealing layer first, followed by the anti-fingerprint layer, which preferably forms the outermost layer.

[0180] In the following text, the invention is illustrated by the following non-limiting examples.

[0181] Example

[0182] In the following sections, Hall cell plating is performed to evaluate the visual appearance of the black chromium layer based on the current density distribution.

[0183] General procedures:

[0184] A copper plate (99mm × 70mm) was used as the substrate.

[0185] In the first step, by using 100 g / L at room temperature (RT) 279 (a product of Atotech Deutschland, Germany) was used to clean the copper plate by electrolytic degreasing. The substrate was then rinsed with water, acid-washed with 10% by volume H2SO4, and rinsed again with water.

[0186] In the second step, a bright nickel layer is deposited on the cleaned substrate (10 minutes, 4 A / dm). 2 (UniBrite2002, a product of Anmet) thus obtains a nickel-plated substrate, which is then rinsed with water.

[0187] In the third step, a black chromium layer is deposited using the following electroplating bath:

[0188] (A) Approximately 20 to 25 g / L Cr 3+ Ions (provided in the form of basic chromium sulfate),

[0189] (B) Approximately 30 g / L formic acid,

[0190] (C) Approximately 60 g / L boric acid,

[0191] (D) Table 1 Potassium thiocyanate,

[0192] (E) Table 1 Methionine,

[0193] Approximately 10 g / L ammonium bromide,

[0194] Approximately 100 g / L ammonium chloride,

[0195] Approximately 100 g / L potassium chloride, and

[0196] Approximately 0.5 g / L Fe SO4·7H2O

[0197] 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 or nickel. However, other experiments indicate that relatively small amounts of cobalt (not shown) are permissible.

[0198] Adjust the pH to 3.2.

[0199] Compounds (D) and (E) are used in various concentrations, as outlined in Table 1 below.

[0200] Unless otherwise stated, each electroplating bath was tested in a Hall cell with a graphite anode, with the nickel-plated substrate mounted as the cathode. A current of 5 A was applied for 3 minutes at temperatures ranging from 35°C to 45°C (see Table 1 for other details).

[0201] 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 then the second color measurement was performed (abbreviated as "CM2" in Table 1).

[0202] 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 hot water rinsing. 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 hot water rinsing. 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 approximately 10 A / dm). 2 Up to 12A / dm 2 The typical medium current density (MCD) is used. The comparative example is abbreviated as "CE".

[0203] In addition to the color measurements mentioned above, 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 chromium layer (i.e., a homogeneous black chromium layer without turbidity or burnt areas) is determined and recalculated to the corresponding current density range ("ASD range"). A relatively wide range of recalculated current densities is considered preferred because it demonstrates the ability to obtain a defect-free black chromium layer from low to high current densities.

[0204] The gloss was measured using a reflectometer (REFO 3-D, Dr. Lange) with a reference measurement angle of 60°.

[0205] Table 1. Electroplating bath composition and results

[0206]

[0207] * indicates the electroplating bath temperature of 35℃.

[0208] **Indicates the electroplating bath temperature of 45℃.

[0209] *** indicates the temperature of the rinsing water.

[0210] Under the "Level" rating, evaluate overall performance as follows:

[0211] + indicates that the color measurement (i.e., CM1 and CM2) or ASD range meets the requirements; however, this is insufficient and therefore undesirable.

[0212] ++ indicates that both color measurements (i.e., CM1 and CM2) and ASD range meet the requirements; this is required.

[0213] +++ indicates that the color measurements (i.e., CM1 and CM2) and ASD range both meet the requirements exceptionally well; this is absolutely necessary.

[0214] -CE1 displays require a certain concentration of (D) to achieve a sufficiently black / dark hue. The concentration of (D) is significantly lower than 100 mmol / L. Furthermore, the lack of (D) in its display cannot be compensated for by a relatively high concentration of (E).

[0215] Other comparative examples CE2 to CE4 are based on US 2020 / 094526 A1:

[0216] -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. Despite the relatively wide ASD range, the color immediately after plating is not dark enough.

[0217] As shown in Table 1 of US'526, only in example 7 was a very dark (and neutral black) hue obtained through an "accelerated test" 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 test"). 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 through 13 in US'526 have at least the following drawbacks: First, an 18 or 19-day idle time (or aging time) is considered unacceptable given industry requirements. Second, the same chemical composition yields different visual results depending on the idle time and conditions of the application. Neither is desirable. A clear black hue (neutral or warm black hue) is expected to be obtained quickly. As shown above, this can be achieved through the present invention.

[0218] Therefore, our experiments clearly demonstrate that the total concentration of (D) (e.g., thiocyanate) below 100 mmol / L is too low to be significantly affected by hot water rinsing.

[0219] -CE3 corresponds to sample 14 in Table 2 of US'526, with a total thiocyanate content of 15 g / L (i.e., 254 mmol / L), which is significantly higher than the total content in sample 5 of US'526. This is followed by a concentration of approximately 10 A / dm 2 Following plating, color measurements CM1 showed L*; a*; b* values ​​of 47; 1.0; 5.7, which are consistent with those disclosed in Table 2, No. 14, “Initial,” of US’526. However, without any hot water rinsing, our experiments also demonstrated 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 concentrations significantly above 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 resolved by the present invention with concentrations not exceeding 250 mmol / L.

[0220] -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 plating on precision or complex substrates requiring a significantly wider current density range.

[0221] Examples of the invention demonstrate that a neutral black tone or a warm black tone can be specifically determined and obtained within an acceptable time. The concentration of (D) is high enough to achieve a hot water flushing effect, but does not exceed a critical concentration to still ensure a relatively wide range of current densities.

[0222] Additionally, for Examples E1.1 to E1.7, gloss was measured after rinsing with hot water, with the following results: E1.1: >210 to 230; E1.2 to E1.6: 185 to 210; E1.7: 160 to <185. These results demonstrate an indirect correlation between gloss and 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, (D) concentration ranges such as those in Examples E1.2 to E1.6 produce the highly desired gloss in the range of 185 to 210. Higher (D) concentrations, such as in E1.7, have shown 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 the corresponding black chrome layer by significantly reducing the gloss to below 150, resulting in an increased (and undesirable) matte / dull surface impression. In contrast, if the (D) concentration is too low, i.e., (significantly) below 100 mmol / L, then the gloss is relatively high (e.g., >230), but this impairs visual perception, creating the impression that the black tone is not dark enough or black enough. This perception is undesirable.

[0223] Other embodiments according to the invention were carried out, wherein the electroplating bath was used to modify the material in a manner that did not include chloride ions (specific data not shown). Hall cell experiments were not performed in these experiments; instead, they were conducted in beakers with the same Hall cell substrate at a rate of 10 A / dm. 2 Electroplating experiments were conducted at specific current densities. In these examples, warm black tones with L*, a*, and b* values ​​of 45, 1.3, and 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 complexing agents for the trivalent chromium ions, said complexing agent being formic acid, acetic acid, oxalic acid, tartaric acid, malic acid, citric acid, glycine and / or salts thereof; (C) Optionally, one or more pH buffering compounds for the electroplating bath; (D) Thiocyanate, its salts, esters and / or isoforms, in a total amount ranging from 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 sulfoxides R 1 -S-(CH2) n -CH(NH2)-R 2 (I)， in - R 1 It is a branched or unbranched C1 to C4 alkyl group. - R 2 Choose from COOH, its salts, and (CH2). m Groups composed of -OH, - n is an integer in the range of 1 to 4, and - m is an integer in the range of 1 to 4. The electroplating bath contains (E) in a total concentration ranging from 150 mmol / L to 950 mmol / L, based on the total volume of the electroplating bath. The molar ratio of (E):(D) is between 0.9 and 2.

65.

2. The electroplating bath according to claim 1, further comprising halogen anions.

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

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

5. The electroplating bath according to claim 1, wherein the molar ratio of (E):(D) is in the range of 1 to 2.

3.

6. The electroplating bath according to claim 1, wherein R 1 It can be methyl, ethyl, n-propyl or isopropyl.

7. The electroplating bath according to claim 1, wherein R 2 It is COOH and / or its salt.

8. The electroplating bath according to claim 1, wherein n is 1 or 2.

9. The electroplating bath according to claim 1, wherein the compound of formula (I) in (E) comprises methionine.

10. A method for electroplating a black chromium layer on a substrate, the method comprising the steps of: (a) Providing the substrate, (b) Bring the substrate into contact with the electroplating bath according to claim 1. (c) Applying an electric current to electroplate the black chromium layer onto the substrate, and (d) Heat-treat the substrate obtained in step (c) at a temperature ranging from 30°C to 100°C.

11. The method of claim 10, wherein in step (d), the heat treatment is carried out in water.

12. An electroplating bath for depositing a black chromium layer, the electroplating bath comprising: (A) Trivalent chromium ions; (B) One or more complexing agents for the trivalent chromium ions, said complexing agent being formic acid, acetic acid, oxalic acid, tartaric acid, malic acid, citric acid, glycine and / or salts thereof; (C) One or more pH buffering compounds for use in the electroplating bath; (D) Thiocyanate, its salts, esters and / or isoforms, in a total amount ranging from 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 sulfoxides R 1 -S-(CH2) n -CH(NH2)-R 2 (I)， in - R 1 It is a branched or unbranched C1 to C4 alkyl group. - R 2 It is COOH and / or its salt. - n is an integer in the range of 1 to 4, and - m is an integer in the range of 1 to 4. The electroplating bath contains (E) in a total concentration ranging from 140 mmol / L to 950 mmol / L, based on the total volume of the electroplating bath. The molar ratio of (E):(D) is between 0.9 and 2.

65.

13. The electroplating bath according to claim 1, wherein the trivalent chromium ions are derived from inorganic or organic trivalent chromium salts having anions selected from sulfate anions, formate anions, acetate anions, malate anions, and oxalate anions.

14. The electroplating bath according to claim 1, wherein the concentration of cobalt ions in the electroplating bath is from 1 mg / L to 500 mg / L, or the electroplating bath does not contain cobalt ions.

15. The method of claim 10, wherein in step (d), the heat treatment is a hot water rinse.

16. The method of claim 10, wherein the black chromium layer comprises: a* values ​​in the range of -1.5 to +3, or b* values ​​in the range of -2.5 to +6, or The following two: a* values ​​in the range of -1.5 to +3 and b* values ​​in the range of -2.5 to +6.

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