ELECTROPLATING BATH FOR DEPOSITING A BLACK CHROMIUM LAYER AND METHOD FOR ELECTROPLATING A BLACK CHROMIUM LAYER ON A SUBSTRATE

The present invention relates to a very specific electroplating bath for depositing a black chromium layer, and a respective method for electroplating such a layer. The electroplating bath comprises two specific groups of compounds defined as (D) and (E), present in a particularly defined molar ratio ranging from 0.9 to 2.65, based on (E):(D). The black chromium layer is excellently suited for decorative purposes.

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Description
FIELD OF THE INVENTION

The present invention relates to a very specific electroplating bath for depositing a black chromium layer, and a respective method for electroplating such a layer. The electroplating bath comprises two specific groups of compounds defined as (D) and (E), present in a particularly defined molar ratio ranging from 0.9 to 2.65, based on (E):(D). The black chromium layer is excellently suited for decorative purposes.

BACKGROUND OF THE INVENTION

From the very beginning of chromium coatings, a high interest in black chromium coatings was observable due to its great appeal for optical applications.

Beginning with even black hexavalent chromium coatings, the focus today significantly shifted to trivalent chromium coatings due to a higher environmental acceptance. Since some years the demand for dark, even neutral deep dark (also named neutral black), trivalent chromium coatings, is more and more increasing, for example for decorative automotive parts. However, since such a neutral black color tone might be perceived as too cold in some cases, a slight color tone modification is often demanded, which does not compromise the deep black tone itself but is adding a tiny warmth to it to create a more warm black color tone. In principle, both the neutral black color tone as well as the warm black color tone have strong demand in industry although being very similar.

However, the degree of black varies significantly and depends on deposition parameters as well as bath ingredients.

In many cases, the black color obtained from trivalent chromium coatings was not black enough to meet either a neutral black or a warm black color tone, for example to meet requirements for decorative parts in the automotive industry. In other cases, darkness was met but the overall optical impression is not sufficient. In even other cases an insufficient color stability over time was obtained.

WO 2012/150198 A2 refers to a method and plating bath for electrodepositing a dark chromium layer.

WO 2017/053655 A1 refers to a method for adjusting the lightness L* by means of an activated carbon filter as well as a dark electroplated trivalent chromium layer on a workpiece.

CN 107099824 B refers to a black chromium electroplating solution, a composite plating layer and a preparation method thereof. The trivalent black chromium coating formed by this black chromium electroplating solution has a deep black and strong uniform coverage.

US 2020/094526 A1 refers to a black plated resin part comprising a black chromium plating layer exhibiting an b* value of 3.0 or less.

According to US'526 significant progress was made regarding a neutral black color tone and a warm black color tone. However, in all these attempts further improvements are needed for an industrial utilization. For example, in many cases the desired color tone is only obtained through unacceptably long idle times to initiate a natural color ageing, which finally results in the desired color tone. In other cases, the desired color tone is obtained rather quickly but the deposition is not possible on geometrically sophisticated substrates due to haze formation, burnings and skip plating.

Thus, there is a great demand to further improve the available methods and plating baths in order to overcome said problems.

Objective of the Invention

It was therefore the objective of the present invention to provide an electroplating bath and a respective method for electroplating, which allows on the one hand a quick and stable color tone formation (for both a neutral black color tone as well as warm black color tone) and on the other hand allows deposition on a broad variety of substrate geometries without plating defects and thus, providing an excellent optical appearance. Furthermore, both color tones should be specifically and easily targeted and thus obtained.

DETAILED DESCRIPTION OF THE INVENTION

This objective is solved by means of the present invention, an electroplating bath and a respective method for electroplating.

Therefore, the present invention refers to an electroplating bath for depositing a black chromium layer, the electroplating bath comprising:

    • (A) trivalent chromium ions;
    • (B) one or more than one complexing agent for said trivalent chromium ions;
    • (C) optionally, one or more than one pH buffer compound for said electroplating bath;
    • (D) one or more than one compound comprising at least one —SON moiety, salts, esters, and/or isoforms thereof; and
    • (E) one or more than one organic compound, including sulfoxides thereof, comprising at least one —SH moiety and/or at least one —S—(CH2)k—CH3 moiety, wherein k is an integer ranging from 0 to 4,
    • characterized in that
    • (E) and (D) are present in a molar ratio ranging from 0.9 to 2.65, based on (E):(D).

Own experiments have shown (see examples below) that above mentioned problems strongly relate to the molar ratio of (E) to (D) and can be solved by maintaining the molar ratio in a range as defined above. The desired color tones (either neutral black or warm black) are quickly formed. Furthermore, they can be formed even on substrates with sophisticated geometries such that a very uniform deposition quality is provided without plating defects. However, it furthermore turned out that these excellent results are obtained only if the narrowly defined molar ratio range as defined above is kept.

Very preferably, the black chromium layer is a decorative chromium layer. Typical applications are automotive parts, most preferably for the interior of a car. The electroplating bath of the present invention is very suitable in order to obtain such a black chromium layer, most preferably such a black chromium layer as defined throughout the present text.

The black chromium layer in the context of the present invention is very much preferably defined by the L*a*b* color system, preferably as introduced in 1976 by the Commission Internationale de l'Eclairage, if not stated otherwise.

Generally preferred is an electroplating bath of the present invention, wherein the black chromium layer has an L* value of 50 or below, preferably of 49 or below, more preferably of 48 or below, even more preferably 47 or below, yet even more preferably 46 or below, further more preferably 45 or below, most preferably 43 or below. An L* value of 50 or below 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 color tone.

Preferred is an electroplating bath of the present invention, wherein the black chromium layer has an a* value ranging from −1.5 to +3, preferably ranging from −1 to +2.5, most preferably ranging from −0.5 to +2. Preferably, the a* value is at least positive. Most preferably this applies to the neutral black color tone and to the warm black color tone.

A distinction between a neutral black color tone and a warm black color tone is typically based on slightly different b* values.

In some cases, preferred is an electroplating bath of the present invention, wherein the black chromium layer is a neutral black chromium layer. This more preferably means that an electroplating bath of the present invention is preferred, wherein the black chromium layer has an b* value ranging from −2.5 to +2.9, preferably ranging from −2 to +2, more preferably ranging from −1.5 to +1.5, most preferably ranging from −1 to +1.

For a neutral black color tone, most preferably the L* value is 45 or below, more preferably 44 or below, even more preferably 43 or below, yet even more preferably 42 or below, most preferably 41 or below.

In other cases, preferred is an electroplating bath of the present invention, wherein the black chromium layer is a chromium layer having a warm black color tone. This more preferably means that an electroplating bath of the present invention is preferred, wherein the black chromium layer has an b* value ranging from +3 to +6, preferably ranging from +3.5 to +5.8, most preferably from +4 to +5.5.

In the context of the present invention, both the neutral black color tone as well as the warm black color tone can be obtained, which is of great benefit.

Compound (A) and General Bath Compounds:

The electroplating bath of the present invention is preferably aqueous, i.e. it comprises water, preferably at least 55 vol.-% or more is water, based on the total volume of the electroplating bath, more preferably 65 vol.-% or more, even more preferably 75 vol.-% or more, yet even more preferably 85 vol.-% or more, still more preferably 90 vol.-% or more, most preferably 95 vol.-% or more. Most preferably, water is the only solvent.

Preferred is an electroplating bath of the present invention, wherein the electroplating bath is acidic, preferably having a pH ranging from 1.5 to 5.0, more preferably from 2.0 to 4.6, even more preferably from 2.4 to 4.2, yet more preferably from 2.7 to 3.8, most preferably from 3.0 to 3.5. The pH is preferably adjusted with hydrochloric acid, sulfuric acid, ammonia, potassium hydroxide, and/or sodium hydroxide.

The electroplating bath of the present invention comprises (A) trivalent chromium ions.

Preferred is an electroplating bath of the present invention, wherein the trivalent chromium ions have a total concentration ranging from 5 g/L to 35 g/L, based on the total volume of the electroplating bath, preferably from 6 g/L to 32 g/L, more preferably from 7 g/L to 29 g/L, even more preferably from 8 g/L to 26 g/L, yet even more preferably from 9 g/L to 23 g/L, most preferably from 10 g/L to 22 g/L.

Preferably, the trivalent chromium ions are from a trivalent chromium salt, preferably from an inorganic chromium salt and/or an organic chromium salt, most preferably from an inorganic chromium salt. A preferred inorganic chromium salt comprises chloride and/or sulfate anions, preferably sulfate anions. A very preferred inorganic chromium salt is basic chromium sulfate. A preferred organic chromium salt comprises carboxylic acid anions, preferably formate, acetate, malate, and/or oxalate anions.

Preferred is an electroplating bath of the present invention, wherein the electroplating bath comprises sulfate ions, most preferably from a trivalent chromium salt. Sulfate ions are excellently contribute to the conductivity of the electroplating bath.

Preferred is an electroplating bath of the present invention, wherein the electroplating bath is substantially free of, preferably does not comprise, a compound comprising chromium with an oxidation number +6. Thus, the electroplating bath is substantially free of, preferably does not comprise, hexavalent chromium.

Preferred is an electroplating bath of the present invention, wherein the electroplating bath is substantially free of, preferably does not comprise, cobalt ions. Preferably, the black chromium layer is substantially free of, preferably does not comprise, cobalt. Only in very rare cases it is also preferred that the electroplating bath and the black chromium layer, respectively, comprise cobalt, although this is less preferred. However, if cobalt is present, preferably in the black chromium layer more chromium is present than cobalt. The latter preferably means that the atom ratio of chromium to cobalt (i.e. Cr:Co) is more than 1, preferably 2 or more, more preferably 3 or more, most preferably 4 or more. This is most preferably based on the total amount of chromium and cobalt atoms in the black chromium layer.

Preferred is an electroplating bath of the present invention, wherein the electroplating bath is substantially free of, preferably does not comprise, nickel ions. In some cases, a typical Ni-contamination of up to 150 ppm is observed, which is basically acceptable and therefore considered as substantially free of nickel ions. Thus, in some cases the electroplating bath of the present invention preferably comprises nickel ions in a concentration ranging from 0 ppm to 200 ppm, based on the total weight of the electroplating bath, preferably from 1 ppm to 150 ppm, most preferably from 2 ppm to 100 ppm. Preferably, the black chromium layer is substantially free of, preferably does not comprise, nickel.

It is generally preferred to avoid such environmental questionable nickel and cobalt ions. This generally leads to less complicated wastewater treatment and bath disposal. In addition, neither nickel nor cobalt is needed to obtain the neutral black color tone and the warm black color tone.

Preferred is an electroplating bath of the present invention, wherein the electroplating bath is substantially free of, preferably does not comprise, fluoride ions. Preferably, the black chromium layer is substantially free of, preferably does not comprise, fluorine.

Preferred is an electroplating bath of the present invention, wherein the electroplating bath is substantially free of, preferably does not comprise, compounds containing fluorine. This most preferably comprises fluorine-containing surface-active compounds. They are in particular not desired due to increased environmental limitations.

Preferred is an electroplating bath of the present invention, wherein the electroplating bath is substantially free of, preferably does not comprise, phosphate anions, more preferably is substantially free of, preferably does not comprise, phosphorous-containing compounds. Preferably, the black chromium layer is substantially free of, preferably does not comprise, phosphorous. However, this does not exclude phosphorous in a subsequent layer deposited onto the black chromium layer, e.g. a passivation layer.

Preferred is an electroplating bath of the present invention further comprising halogen anions, preferably chloride anions. In the context of the present invention this is preferred and respective electroplating baths are named chloride-containing baths. More preferred is an electroplating bath of the present invention comprising chloride ions and sulfate ions.

Preferred is an electroplating bath of the present invention, wherein the chloride ions have a concentration ranging from 50 g/L to 200 g/L, based on the total volume of the electroplating bath, preferably ranging from 60 g/L to 185 g/L, more preferably ranging from 70 g/L to 170 g/L, even more preferably ranging from 80 g/L to 155 g/L, most preferably ranging from 90 g/L to 140 g/L. Chloride ions are preferably from a chloride salt and/or hydrochloric acid, preferably from sodium chloride, potassium chloride, ammonium chloride, chromium chloride (at least as a part of all chloride ions), and/or mixtures thereof. Typically, chloride ions are present as the anion of a conductivity salt as preferably mentioned before. A very preferred conductivity salt is ammonium chloride, sodium chloride and potassium chloride, ammonium chloride being preferred most.

Preferred is an electroplating bath of the present invention further comprising bromide anions. This typically avoids an anodic formation of undesired hexavalent chromium species. Preferably, the bromide ions have a concentration ranging from 3 g/L to 20 g/L, based on the total volume of the electroplating bath, preferably ranging from 4 g/L to 18 g/L, more preferably ranging from 5 g/L to 16 g/L, even more preferably ranging from 6 g/L to 14 g/L, most preferably ranging from 7 g/L to 12 g/L. Bromide ions are preferably from a bromide salt, preferably from sodium bromide, potassium bromide, ammonium bromide, and/or mixtures thereof.

More preferred is an electroplating bath of the present invention comprising chloride ions, bromide ions, and sulfate ions, most preferred with concentrations as defined throughout the present text as being preferred.

In some cases an electroplating bath of the present invention is preferred further comprising Fe(II) ions, preferably in a concentration ranging from 0.1 mmol/L to 10 mmol/L, based on the total volume of the electroplating bath, preferably from 0.4 mmol/L to 8 mmol/L, more preferably from 0.6 mmol/L to 6 mmol/L, even more preferably from 0.8 mmol/L to 5 mmol/L, most preferably from 1 mmol/L to 4 mmol/L. This is in particular preferred if the electroplating bath of the present invention comprises chloride ions. Thus, most preferred is an electroplating bath of the present invention comprising chloride ions, bromide ions, sulfate ions, and Fe(II) ions, most preferred with concentrations as defined throughout the present text as being preferred for them. Fe(II) ions are preferably from a respective iron salt, preferably from an iron (II) sulfate salt. Typically, iron ions have several beneficial effects on the electroplating performance and on the deposited black chromium layer obtained by the present invention. In many cases, an increased electroplating rate is observed which allows a thicker layer thickness. Preferably, the black chromium layer comprises iron, preferably up to 15 at.-%, based on all atoms in the black chromium layer, more preferably up to 12 at.-%, even more preferred up to 10 at.-%, yet even more preferably up 8 at.-%, most preferably up to 6 at.-%.

Furthermore very preferred is an electroplating bath of the present invention, wherein the trivalent chromium ions and the Fe(II) ions (if present) are the only transition metals in the plating bath, most preferably chromium ions and iron ions (if present) are the only transition metals in the plating bath. An exception are Ni contaminations as mentioned already above, which are generally acceptable and therefore preferably included.

In some cases, an electroplating bath of the present invention is preferred further comprising at least one sulfur-containing compound being different from (D) and (E).

In some cases, an electroplating bath of the present invention is preferred further (i.e. in addition to (D) and (E)) comprising saccharin and/or salts thereof.

In some cases, an electroplating bath of the present invention is preferred further (i.e. in addition to (D) and (E)) comprising a sulfur-containing diol, most preferably in addition to above mentioned saccharin and/or salts thereof.

Preferred is an electroplating bath of the present invention further comprising at least one surface-active compound. A preferred surface-active compound comprises a cationic or an anionic surface-active compound, preferably an anionic surface-active compound. A preferred anionic surface-active compound comprises sulfosuccinates, alkyl benzene sulfonates having 8 to 20 aliphatic carbon atoms, alkyl sulfates having 8 to 20 carbon atoms, and/or alkyl ether sulfates. Preferably, the at least one surface-active compound is free of fluorine atoms. Most preferably, the at least one surface-active compound is not a compound of (D) and (E). In other words, preferably (D) and (E) are not surface-active compounds.

Preferred sulfosuccinates comprise sodium diamyl sulphosuccinate.

Preferred alkyl benzene sulfonates having 8 to 20 aliphatic carbon atoms comprise sodium dodecyl benzene sulfonate.

Preferred alkyl sulfates having 8 to 20 carbon atoms comprise sodium lauryl sulfate.

Preferred alkyl ether sulfates fatty alcohols comprise sodium lauryl polyethoxy sulfates.

Preferred is an electroplating bath of the present invention, wherein the at least one surface-active compound has a total concentration ranging from 0.001 g/L to 0.05 g/L, based on the total volume of the electroplating bath, preferably from 0.005 g/L to 0.01 g/L.

In contrast, in some cases an electroplating bath of the present invention is preferred, wherein the electroplating bath is substantially free of, preferably does not comprise, chloride ions, preferably does not comprise halogen anions. In the context of the present invention this is less preferred and respective electroplating baths are named chloride-free baths. In such a case, the electroplating bath of the present invention preferably comprises sulfate ions to compensate the missing chloride ions. Even more preferred, the electroplating bath of the present invention comprises sulfate ions in addition to the sulfate ions from the chromium salt, most preferably by means of a conductive salt. A very preferred conductive salt is potassium sulfate, sodium sulfate, ammonium sulfate, or mixtures thereof. In this particular case, the electroplating bath is preferably in some cases substantially free of, preferably does not comprise, bromide ions. However, it is preferred in some rare cases that such an electroplating bath comprises iron ions, preferably Fe(II) ions, most preferably in the concentrations as defined above.

Compound (B):

The electroplating bath of the present invention comprises (B) one or more than one complexing agent for said trivalent chromium ions. Such compounds keep the trivalent chromium ions in solution. Preferably, the one or more than one complexing agent is not a compound of (D) and (E) and is therefore preferably different from (D) and (E).

Preferred is an electroplating bath of the present invention, wherein the one or more than one complexing agent comprises an organic acid and/or salts thereof, preferably an organic carboxylic acid and/or salts thereof, most preferably an organic carboxylic acid comprising one, two, or three carboxylic groups and/or salts thereof.

The organic carboxylic acid and/or salts thereof (preferably also the organic carboxylic acid comprising one, two, or three carboxylic groups and/or salts thereof) are preferably substituted with a substituent or unsubstituted. A preferred substituent comprises an amino group and/or a hydroxyl group. Preferably, the substituent does not comprise a SH moiety and/or a SCN moiety.

More preferably, the organic carboxylic acid and/or salts thereof (preferably also the organic carboxylic acid comprising one, two, or three carboxylic groups and/or salts thereof) comprise amino carboxylic acids (preferably alpha-amino carboxylic acids), hydroxyl carboxylic acids, and/or salts thereof. Preferred (alpha-) amino carboxylic acids comprise glycine, aspartic acid, and/or salts thereof. Preferably, the amino carboxylic acids (preferably alpha-amino carboxylic acids, respectively) is not a compound according to (E), more preferably is not a sulfur-containing amino carboxylic acid (preferably is not a sulfur-containing alpha-amino carboxylic acid, respectively), most preferably is not methionine. It is in particularly preferred that the one or more than one complexing agent is distinct from the compound of formula (E).

More preferred is an electroplating bath of the present invention, wherein the one or more than one complexing agent comprises formic acid, acetic acid, oxalic acid, tartaric acid, malic acid, citric acid, glycine, aspartic acid, and/or salts thereof, preferably formic acid, acetic acid, oxalic acid, tartaric acid, malic acid, citric acid, and/or salts thereof, more preferably formic acid, acetic acid, oxalic acid, tartaric acid, malic acid, and/or salts thereof, even more preferably formic acid, acetic acid, and/or salts thereof, most preferably formic acid and/or salts thereof. This most preferably applies, if the electroplating bath of the present invention comprises chloride ions. In contrast, if the electroplating bath of the present invention is chloride-free, preferably the one or more than one complexing agent comprises oxalic acid, tartaric acid, malic acid, citric acid, and/or salts thereof, most preferably malic acid and/or salts thereof.

Preferred is an electroplating bath of the present invention, wherein the one or more than one complexing agent has a total concentration ranging from 5 g/L to 200 g/L, based on the total volume of the electroplating bath, preferably ranging from 8 g/L to 150 g/L, more preferably ranging from 10 g/L to 100 g/L, even more preferably from 12 g/L to 75 g/L, yet even more preferably ranging from 15 g/L to 50 g/L, most preferably ranging from 20 g/L to 35 g/L. This most preferably applies if the electroplating bath comprises chloride ions but generally also applies to a chloride-free electroplating bath.

If the electroplating bath of the present invention is particularly chloride-free, the one or more than one complexing agent has a total concentration ranging from 5 g/L to 100 g/L, based on the total volume of the electroplating bath, preferably ranging from 5.5 g/L to 75 g/L, more preferably ranging from 6 g/L to 50 g/L, even more preferably from 6.5 g/L to 25 g/L, yet even more preferably ranging from 7 g/L to 18 g/L, most preferably ranging from 7.5 g/L to 13 g/L. This preferably applies to oxalic acid, tartaric acid, malic acid, citric acid, and salts thereof, most preferably to malic acid and salts thereof.

Preferred is an electroplating bath of the present invention, wherein (B)/(A) forms a molar ratio ranging from 1 to 1.5, preferably ranging from 1.1 to 1.4, most preferably ranging from 1.2 to 1.3.

Compound (C):

The electroplating bath of the present invention comprises (C) optionally, one or more than one pH buffer compound for said electroplating bath. Most preferably, the electroplating bath of the present invention comprises (i.e. not optionally) one or more than one pH buffer compound. In the latter case, an electroplating bath of the present invention is preferred, wherein the one or more than one pH buffer compound for said electroplating bath is distinct (i.e. different) from (B). In such a case, the one or more than one pH buffer compound does not comprise a carboxylic acid, preferably does not comprise an organic acid. In such a case they are counted to (B).

In many cases an electroplating bath of the present invention is preferred, wherein the one or more than one pH buffer compound comprises a boron-containing compound, preferably boric acid and/or a borate, most preferably boric acid. A preferred borate is sodium borate.

Very preferred is an electroplating bath of the present invention, wherein the one or more than one pH buffer compound has a total concentration ranging from 30 g/L to 250 g/L, based on the total volume of the electroplating bath, preferably ranging from 35 g/L to 200 g/L, more preferably ranging from 40 g/L to 150 g/L, even more preferably ranging from 45 g/L to 100 g/L, most preferably ranging from 50 g/L to 75 g/L. This even more preferably applies to said boron-containing compound, yet even more preferably to said boric acid together with said borate, most preferably to said boric acid. Most preferably the one or more than one pH buffer compound comprises boric acid but no borate. Thus, most preferred is an electroplating bath of the present invention, wherein (C) comprises boric acid, preferably in a total amount ranging from 35 g/L to 90 g/L, based on the total volume of the electroplating bath, preferably from g/L to 80 g/L, more preferably from 50 g/L to 70 g/L, most preferably from 56 g/L to 66 g/L.

In some other cases the electroplating bath of the present invention does not explicitly comprise a distinct pH buffer compound. Rather, the one or more than one complexing agent for said trivalent chromium ions are present in such an amount and selected in such a way that they do not only serve as complexing agent for the trivalent chromium ions but additionally serve as pH buffer compound. In the context of the present invention this is less preferred but possible.

Compound (D):

The electroplating bath of the present invention comprises (D) one or more than one compound comprising at least one —SCN moiety, salts, esters, and/or isoforms thereof. The term “—SCN moiety” denotes a thiocyanate moiety or group, respectively.

Preferably, said compound is organic and/or inorganic, preferably inorganic. Preferred organic compounds comprise an alkyl and/or aryl compound thereof, preferably substituted or unsubstituted.

Preferred is an electroplating bath of the present invention, wherein in (D) said compound has all together 1 to 30 carbon atoms, preferably 2 to 25, more preferably 3 to 20, even more preferably 4 to 17, most preferably 5 to 14. This most preferably applies if said compound is an organic compound.

Preferably, in (D) said compound has all together 1 to 10 carbon atoms, more preferably 1 to 8, even more preferably 1 to 6, most preferably 1 to 4.

Very preferably in (D) said compound has one single carbon atom only, most preferably (D) comprises at least thiocyanic acid, isoforms, and/or salts thereof, preferably at least thiocyanic acid and/or salts thereof. Preferably the salt comprises potassium thiocyanate and/or sodium thiocyanate.

The term “acid” in “thiocyanic acid” includes its deprotonated/dissociated form.

A preferred isoform thereof is isothiocyanic acid and/or salts thereof.

In the context of the present invention, (D) is present in a total amount ranging from 100 mmol/L to 750 mmol/L, based on the total volume of the electroplating bath, preferably in a total amount ranging from 100 mmol/L to 600 mmol/L, preferably from 100 mmol/L to 450 mmol/L, more preferably from 100 mmol/L to 300 mmol/L, even more preferably from 115 mmol/L to 250 mmol/L, most preferably from 130 mmol/L to 200 mmol/L.

However, preferred is an electroplating bath according to the present disclosure, wherein said bath comprises (D) in a total amount ranging from 20 mmol/L to 750 mmol/L, based on the total volume of the electroplating bath, preferably from 50 mmol/L to 600 mmol/L, more preferably from 75 mmol/L to 450 mmol/L, even more preferably from 100 mmol/L to 300 mmol/L, yet even more preferably from 115 mmol/L to 250 mmol/L, most preferably from 130 mmol/L to 200 mmol/L. Thus, in this case (D) has not a lower total concentration limit of 100 mmol/L but rather the ranges as defined above. However, all other features as defined throughout the present text for the electroplating bath preferably still apply also to this specific disclosure.

The aforementioned concentration ranges most preferably apply to said compound in (D) having preferably all together 1 to 10 carbon atoms, more preferably 1 to 8, even more preferably 1 to 6, most preferably 1 to 4. Even most preferably it applies to thiocyanic acid, isoforms, and/or salts thereof.

Preferably, concentration ranges above are based on SCN−, i.e. are based on monobasic thiocyanate and thiocyanate moieties, respectively.

Furthermore, it is explicitly preferred that above concentrations can be freely combined to form not explicitly disclosed concentration ranges. This includes most preferably further combinations of lower limits with higher limits not explicitly mentioned throughout the text.

Compound (E):

The electroplating bath of the present invention comprises (E) one or more than one organic compound, including sulfoxides thereof, comprising at least one —SH moiety and/or at least one —S—(CH2)k—CH3 moiety, wherein k is an integer ranging from 0 to 4.

Preferably, k is 0, 1, 2, 3, or 4, preferably 0, 1, or 2. The term “—SH moiety” denotes a thiol or sulfhydryl moiety or group, respectively.

In the context of the present invention “sulfoxides” thereof denotes an oxygen chemically linked via a double bond to a sulphur atom, i.e. said organic compound also comprises —S(═O)—(CH2)k—CHs moieties.

Preferred is an electroplating bath of the present invention, wherein said bath comprises (E) in a total amount ranging from 1 mmol/L to 950 mmol/L, based on the total volume of the electroplating bath, preferably from 50 mmol/L to 800 mmol/L, more preferably from 100 mmol/L to 650 mmol/L, even more preferably from 140 mmol/L to 550 mmol/L, yet even more preferably from 180 mmol/L to 500 mmol/L, most preferably from 195 mmol/L to 450 mmol/L.

Preferred is an electroplating bath of the present invention, wherein in (E) said organic compound independently comprises an amino moiety.

Preferred is an electroplating bath of the present invention, wherein in (E) said organic compound independently comprises a carboxylic acid moiety and/or salts thereof.

Preferred is an electroplating bath of the present invention, wherein in (E) said organic compound independently comprises an amino acid and/or salts thereof, preferably an alpha-amino acid.

Preferred is an electroplating bath of the present invention, wherein (E) comprises at least a compound of formula (I), salts, and/or sulfoxides thereof


R1—S—(CH2)n—CH(NH2)—R2  (I),

    • wherein
      • R1 is a branched or unbranched C1 to C4 alkyl,
      • R2 is selected from the group consisting of COOH, salts thereof, and (CH2)m—OH,
      • n is an integer ranging from 1 to 4, and
      • m is an integer ranging from 1 to 4.

Preferred is an electroplating bath of the present invention, wherein R1 is methyl, ethyl, n-propyl, or iso-propyl, preferably methyl or ethyl, most preferably methyl.

Preferred is an electroplating bath of the present invention, wherein R2 is COOH and/or salts thereof. Preferably, COOH includes also the deprotonated/dissociated form thereof.

Preferred is an electroplating bath of the present invention, wherein n is 1 or 2, preferably 2.

Preferred is an electroplating bath of the present invention, wherein m is 1 or 2.

Preferred is an electroplating bath of the present invention, wherein (E) comprises at least methionine.

According to own experiments (see in the text below under “Examples”) if the molar ratio of (E):(D) is outside a range from 0.9 to 2.65 no sufficiently black chromium layer is obtained. Most important, if the molar ratio is exceeding 2.65, the heat-treating in the method of the present invention does not significantly affect the final color formation.

Furthermore, if the molar ratio is below 0.9 the number of plating defects is increasing, in particular on substrates with sophisticated surface geometry. Own hull cell experiments have shown that with a molar ratio significantly below 0.9 an unacceptable small range of current densities is available. However, this is not acceptable in view of technical demands.

In contrast, these problems are overcome with the present invention.

Preferred is an electroplating bath of the present invention, wherein the molar ratio of (E):(D) is ranging from 0.95 to 2.6, preferably from 1 to 2.55, more preferably from 1.1 to 2.5, even more preferably from 1.2 to 2.45, most preferably from 1.25 to 2.4.

In some cases preferred is an electroplating bath of the present invention, wherein the molar ratio of (E):(D) is ranging from 0.9 to 2.5, preferably from 0.95 to 2, more preferably from 1 to 1.8, yet even more preferably from 1.05 to 1.5, most preferably from 1.1 to 1.3. These are in some cases preferred molar ranges for particularly a warm black color tone.

Thus, a respective electroplating bath of the present invention is preferably for a black chromium layer having a b* value ranging from +3 to +5.5, according to the L*a*b* color system, preferably ranging from +3.5 to +5.0.

In other cases preferred is an electroplating bath of the present invention, wherein the molar ratio of (E):(D) is ranging from 1.6 to 2.65, preferably from 1.9 to 2.6, more preferably from 2.05 to 2.55, even more preferably from 2.1 to 2.5, yet even more preferably from 2.15 to 2.45, most preferably from 2.2 to 2.4. These are in some cases particularly preferred molar ranges for a neutral black color tone.

Thus, a respective electroplating bath of the present invention is preferably for a black chromium layer having a b* value ranging from −1.5 to +1.5, according to the L*a*b* color system, preferably ranging from −1 to +1.0.

Method for Electroplating:

The present invention furthermore relates to a method for electroplating a black chromium layer on a substrate, the method comprising the steps

    • (a) providing the substrate,
    • (b) contacting the substrate with an electroplating bath according to the present invention, preferably an electroplating bath as described as being preferred throughout the present text, or according to the present disclosure (see text above),
    • (c) applying an electrical current such that the black chromium layer is electroplated onto the substrate,
    • (d) heat-treating the substrate obtained from step (c) at a temperature ranging from 30° C. to 100° C.

The aforementioned features regarding the electroplating bath of the present invention (or according to the present disclosure), including the preferred variants thereof, preferably apply likewise to the method for electroplating of the present invention, most particular to step (b) of said method. Furthermore, the aforementioned regarding the L*a*b* values (and possibly other parameters of the black chromium layer) most preferably applies to the black chromium layer electroplated in step (c).

In step (a) the substrate is provided.

In some cases, a method of the present invention is preferred, wherein the substrate comprises a plastic substrate, preferably is a plastic substrate. In other cases, a method of the present invention is preferred wherein the substrate comprises a metallic substrate, preferably is a metallic substrate.

In many cases a 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.

More preferred is a method of the present invention, wherein in step (a) the substrate comprises butadiene moieties, preferably polybutadiene.

Also preferred is a method of the present invention, wherein in step (a) the substrate comprises nitrile moieties.

Also preferred is a method of the present invention, wherein in step (a) the substrate comprises acryl moieties.

Very preferred is a method of the present invention, wherein in step (a) the substrate comprises polymerized styrene.

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

Preferred is a method of the present invention, wherein the polyetherketone (PEK) comprises polyaryletherketone (PAEK), poly ether ether ketone (PEEK), poly ether ether ether ketone (PEEEK), poly ether ether ketone ketone (PEEKK), poly ether ketone ether ketone ketone (PEKEKK), poly ether ketone ketone (PEKK), and/or mixtures thereof, preferably poly ether ether ketone (PEEK), polyaryletherketone (PAEK), and/or mixtures thereof.

In some cases, a 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. A very preferred metallic substrate comprising iron is steel. A mixture thereof preferably includes composites.

Preferred is a method of the present invention further comprising prior to step (b) at least one metal plating step to deposit at least one metal layer, 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 preferably involved.

Most preferably, the at least one nickel layer comprises at least one bright-nickel layer and/or (preferably or) at least one satin nickel layer, most preferably at least one bright-nickel layer.

More preferred is a method of the present invention, wherein the at least one nickel layer comprises at least one semi-bright nickel layer, preferably at least one semi-bright-nickel layer in addition to said at least one bright-nickel layer and/or said at least one satin nickel layer. The at least one semi-bright nickel layer is preferably optionally. Most preferably (if applied) the at least one semi-bright nickel layer is deposited prior to said at least one bright-nickel layer and/or said at least one satin nickel layer.

Also preferred is a method of the present invention, wherein the at least one nickel layer comprises at least one MPS nickel layer, preferably at least one MPS nickel layer in addition to said at least one bright-nickel layer and/or said at least one satin nickel layer, most preferably at least one MPS nickel layer in addition to said at least one bright-nickel layer and/or said at least one satin nickel layer, and further to said at least one semi-bright nickel layer. In the context of the present invention MPS denotes that the MPS nickel layer comprises non-conductive micro-particles, which cause micro-pores in a subsequent chromium layer, preferably in the black chromium layer. The at least one MPS nickel layer is preferably optionally.

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

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

Preferably, the black chromium layer is part of a layer stack.

In step (b) the substrate, preferably with the at least one nickel layer (preferably as defined above as being preferred) is contacted with the electroplating bath of the present invention, preferably by dipping.

Preferred is a method of the present invention, wherein the contacting during step (c) ranges from 1 minute to 30 minutes, preferably from 2 minutes to 20 minutes, more preferably from 3 minutes to 15 minutes, even more preferably from 4 minutes to 10 minutes, most preferably from 5 minutes to 8 minutes.

Preferred is a method of the present invention, wherein in step (c) the electroplating bath has a temperature in a range from 25° C. to 60° C., preferably from 28° C. to 50° C., more preferably from 30° C. to 47° C. This most preferably applies if the electroplating bath comprises chloride ions.

In some cases, a method of the present invention is preferred, wherein in step (c) the electroplating bath of the present invention has a temperature in a range from 35° C. to preferably from 40° C. to 63° C., more preferably from 45° C. to 61° C., most preferably from 50° C. to 59° C. This most preferably applies if the electroplating bath is a chloride-free electroplating bath.

In step (c) an electrical current is applied.

Preferred is a method of the present invention, wherein the electrical current is a direct current, preferably in a range from 3 A/dm2 to 30 A/dm2, more preferably from 4 A/dm2 to 25 A/dm2, even more preferably from 5 A/dm2 to 20 A/dm2, most preferably from 6 A/dm2 to 18 A/dm2.

In some cases a method of the present invention is preferred, wherein the electrical current is a direct current, preferably in a range from 3 A/dm2 to 20 A/dm2, more preferably from 4 A/dm2 to 15 A/dm2, most preferably from 5 A/dm2 to 10 A/dm2. This most preferably applies if the electroplating bath is a chloride-free electroplating bath.

Preferred is a method of the present invention, wherein in step (c) at least one anode is utilized. The at least one anode is selected from the group consisting of graphite anodes, precious metal anodes, and mixed metal oxide anodes (MMOs).

Preferred precious metal anodes comprise platinized titanium anodes and/or platinum anodes.

Preferred mixed metal oxide anodes comprise platinum oxide coated titanium anodes and/or iridium oxide coated titanium anodes.

Preferred is a method of the present invention, wherein the electroplated black chromium layer has a layer thickness ranging from 0.05 μm to 1 μm, preferably from 0.1 μm to 0.8 μm, more preferably from 0.125 μm to 0.6 μm, most preferably from 0.15 μm to 0.5 μm.

Most important in the context of the method of the present invention is step (d), the heat-treating. It allows a quick and direct formation of the desired black color tone. The temperature applied in step (d) is not the temperature utilized in step (c) for the electroplating bath. Steps (c) and (d) are distinct steps.

Preferred is a method of the present invention, wherein the heat-treating is at a temperature ranging from 32° C. to 99° C., more preferably ranging from 45° C. to 92° C., even more preferably ranging from 52° C. to 88° C., most preferably ranging from 60° C. to 84° C.

More preferred is a method of the present invention, wherein in step (d) the heat-treating is carried out in water, preferably having a temperature ranging from 32° C. to 99° C., more preferably ranging from 45° C. to 92° C., even more preferably ranging from 52° C. to 88° C., most preferably ranging from 60° C. to 84° C.

As mentioned, the heat-treating is preferably in water. This preferably means that this step is carried out in a treatment compartment comprising a treatment composition. Preferably, the treatment composition is aqueous, more preferably comprising as solvent only water, most preferably essentially consisting of water. Essentially consisting of water means that besides tiny contaminations from previous method steps, the main component of the treatment composition is and remains water. Typically, said contaminations are tolerable for the purpose of this step.

Even more preferred is a method of the present invention, wherein in step (d) the heat-treating is a hot water rinse, most preferably by dipping, even most preferably by dipping into the treatment composition.

Preferred is a method of the present invention, wherein in step (d) the heat-treating is carried out without an electrical current. This means that this step is preferably electroless.

The method of the present invention does not exclude further steps, preferably such as additional rinsing, cleaning, pre-treating, and/or post-treating. Preferably, steps as defined in the examples below apply likewise to the general method described throughout the present text. A preferred post-treating step comprises a sealing step, preferably with an inorganic and/or organic sealer, and/or a contacting step with an anti-fingerprint composition.

Below, the present invention is illustrated by the following non-limiting examples.

EXAMPLES

In the following, Hull Cell electroplating was performed to evaluate the optical appearance of the black chromium layer depending on the current density distribution.

General Procedure:

As a substrate, copper panels (99 mm×70 mm) were used.

In a first step, the copper panels were cleaned by electrolytic degreasing with Uniclean® 279 (product of Atotech Deutschland GmbH), 100 g/L at room temperature (RT). Afterwards the substrates were rinsed with water, pickled with 10% H2SO4 by volume, and rinsed with water.

In a second step, the cleansed substrates were deposited with a bright nickel layer (10 min, 4 A/dm2, UniBrite 2002, product of Atotech) such that a nickel-plated substrate was obtained and rinsed with water.

In a third step, the black chromium layer was deposited by utilizing the following electroplating bath:

(A) ca. 20 to 25 g/L Cr3+ ions (provided as basic chromium sulfate), (B) ca. 30 g/L Formic acid, (C) ca. 60 g/L Boric acid, (D) Tbl. 1 Potassium thiocyanate, (E) Tbl. 1 Methionine, ca. 10 g/L Ammonium bromide, ca. 100 g/L Ammonium chloride, ca. 100 g/L Potassium chloride, and ca. 0.5 g/L Fe SO4•7 H2O

The electroplating baths further comprised small amounts (up to 4 g/L) of saccharin and between 5 g/L and 50 g/L of a S-containing diol. No cobalt ions and no nickel ions were present. Thus, the black chromium layer did not comprise cobalt and nickel. However, further experiments indicate that relatively small amounts of cobalt can be tolerated (not shown).

The pH value was adjusted to 3.2.

Compounds (D) and (E) were utilized in various concentrations and resulting molar ratios as summarized in Table 1 below.

If not stated otherwise, each electroplating bath was tested in a Hull cell having a graphite anode and the nickel-plated substrate was installed as the cathode. An electrical current of 5 A was passed through for 3 minutes at temperatures ranging from 35° C. to 45° C. (see Table 1 for further details).

After plating, the substrates were rinsed with water and dried for a first color measurement (abbreviated as “CM1” in Table 1). After “CM1”, the substrate was subjected to a hot water rinse for 10 minutes at 70° C. and 80° C., respectively, dried and a second color measurement was carried out (abbreviated as “CM2” in Table 1).

In a first set of experiments (abbreviated as Examples E1.1 to E1.7 in Table 1), a warm black color tone (b* ranging from ca. +3 to +6) was immediately created after the hot water rinse, wherein in a second set of experiments (abbreviated as Examples E2.1 to E2.3 in Table 1) a neutral black color tone (b* about or less than zero) was immediately created after the hot water rinse. Color measurements according to the L*a*b* color space system were carried out with a colorimeter (Konica Minolta CM-700d; measuring mode: SCI; Observer angle: 10°; Light source: D65) and at a position of ca. 3.5 cm from the left edge of the substrate and 2 cm from the lower edge (representing a typical medium current density (MCD) of approximately 10 A/dm2 to 12 A/dm2). Comparative Examples are abbreviated as “CE”.

Besides above mentioned color measurement, the substrates were also optically inspected depending on the locally present current densities (abbreviated as “ASD range” in Table 1). For that, the area of defect-free black chromium layer (i.e. having a homogeneous black chromium layer without haze and burnings) was determined and re-calculated as a corresponding current density range (“ASD range”). A comparatively broad range of re-calculated current densities is considered better because it shows that from low to high current densities a defect-free black chromium layer is obtained.

Table 1, electroplating bath compositions and results

(D) (E) (E)/ T*** CM1 CM2 ASD No. [mmol/L] [mmol/L] (D) [° C.] L*; a*; b* L*; a*; b* range Rating 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 + *denotes 35° C. electroplating bath temperature **denotes 45° C. electroplating bath temperature ***denotes rinse water temperature Under “Rating” the over-all performance is evaluated as follows: + denotes that either the color measurement (i.e. CM1 and CM2) or the ASD range are meeting the requirements; however, this is not sufficient and therefore not desired; ++ denotes that both the color measurement (i.e. CM1 and CM2) and the ASD range are meeting the requirements; this is desired; +++ denotes that both the color measurement (i.e. CM1 and CM2) and the ASD range are excellently meeting the requirements; this is very much desired CE1 shows that a molar ratio of (E)/(D) of 4.1 does not result in a sufficiently black/dark color tone (L* = 53). The molar ratio is far exceeding the defined maximum value of 2.65.

Additional Comparative Examples CE2 to CE4 were carried out based on US 2020/094526 A1:

    • CE2 corresponds to Sample No. 5 in Table 1 (which represents all samples ranging from 5 to 13 in Table 1), having a (E)/(D) molar ratio of approximately 2.7 (100 ml/L Trichrome Graphite Makeup and 30 ml/L Trichrome Graphite Maintenance result in a molar ratio exceeding 2.65); the color measurement CM1 showed an L*; a*; b* of 54; 0.5; 3.8 immediately after plating and an ASD range from 7 to 50. Although the ASD range is relatively broad, the color is not sufficiently black/dark immediately after plating.

As shown in US′526, Table 1, a really dark (and neutral black) color tone is obtained only in Example No. 7 with L*; a*; b* of 44; 0.8; 0.4 (measured at high current density) with an “Acceleration test”, which includes a waiting time under pre-determined conditions for 18 days (see ion US′526). Furthermore, a sufficiently warm black color tone was obtained only in Example No. 6 (allowed to stand at ambient air for 18 days) and Example No. 13 (again with “Acceleration test for 18 days). Own experiments show that a 10 minutes hot water rinse has no significant effect on CE2 to obtain a warm black color tone or a neutral black color tone. Examples 5 to 13 in US'526 therefore have at least the disadvantage that an idle time (or also called aging time) of 18 or 19 days is considered inacceptable in view of industry requirements. However, it is desired to quickly obtain a well-defined black color tone (either a neutral black color tone or a warm black color tone). As shown above, this can be achieved with the present invention and maintaining a comparatively narrow molar ratio range.

Thus, our own experiments show that a molar ratio of 0.9 to 2.65, based on (E)/(D) must be maintained to obtain a significant effect caused by a hot water rinse.

    • CE3 corresponds to Sample No. 14 in Table 2 in US'526, wherein the total amount of thiocyanic acid is 15 g/L, i.e. 254 mmol/L, which results in a (E)/(D) molar ratio of 0.8. This is significantly lower molar ratio than in Sample No. 5 of US'526. The color measurement CM1 showed an L*; a*; b* of 47; 1.0; 5.7 immediately after plating at ca. 10 A/dm2, which is in good agreement with what is disclosed in US'526, Table 2, No. 14, “Initial”. However, irrespective of any hot water rinse, our experiment also showed that the ASD range is unacceptably narrow (only ca. 1 ASD) in the Hull Cell setup. In contrast, the examples of the present invention clearly show that a (E)/(D) molar ratio range from 0.9 to 2.65 allows not only the desired color tone but additionally broadens the ASD range. Thus, a molar ratio below 0.9 very negatively affects the possible current density range on a substrate and therefore strongly increases the possibility of plating defects. This can be surprisingly solved by the present invention by maintaining a (E)/(D) molar ratio ranging from 0.9 to 2.65.
    • CE4 corresponds to Sample No. 17 in Table 2 of US'526, wherein the total amount of thiocyanic acid is 40 g/L (i.e. 677 mmol/L), which results in a (E)/(D) molar ratio of even below 0.4. Although a deposition is possible, a strong and undesired white haze is covering major parts of the hull cell substrate indicating that the range of an acceptable current density range is even smaller compared to CE3. Thus, CE4 confirms the finding of CE3 and supports the conclusion that CE4 is not suitable for electroplating sophisticated or complex substrates which require a significantly broader current density range.

The examples according to the invention show that either a neutral black color tone or a warm black color tone can be obtained within an acceptable short time. The molar ratio (E)/(D) is chosen in such a way to obtain an effect from the hot water rinse and that a relative broad current density range is still guaranteed.

Further examples according to the invention were carried out, wherein the electroplating bath was modified in such a way that no chloride ions were included (specific data not shown). In these experiments no hull cell experiments were carried out but rather electroplating trials in a beaker with the same hull cell substrates but at a specific current density of 10 A/dm2. In these examples a warm black color tone with an L*; a*; b* of 45; 1.3; 3.8 was obtained.

Claims

1. An electroplating bath for depositing a black chromium layer, the electroplating bath comprising:

(A) trivalent chromium ions;
(B) one or more than one complexing agent for said trivalent chromium ions;
(C) optionally, one or more than one pH buffer compound for said electroplating bath;
(D) one or more than one compound comprising at least one —SCN moiety, salts, esters, and/or isoforms thereof, in a total amount ranging from 100 mmol/L to 750 mmol/L, based on the total volume of the electroplating bath; and
(E) one or more than one organic compound, including sulfoxides thereof, comprising at least one —SH moiety and/or at least one —S—(CH2)k—CH3 moiety, wherein k is an integer ranging from 0 to 4,
characterized in that
(E) and (D) are present in a molar ratio ranging from 0.9 to 2.65, based on (E):(D).

2. The electroplating bath according to claim 1, wherein the electroplating bath further comprises sulfate ions.

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

4. The electroplating bath according to claim 1 further comprising Fe(II) ions.

5. The electroplating bath according to claim 1, wherein (C) comprises boric acid.

6. The electroplating bath according to claim 1, wherein said bath comprises (D) in a total amount ranging from 100 mmol/L to 600 mmol/L, based on the total volume of the electroplating bath.

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

8. The electroplating bath according to claim 1, wherein (E) comprises at least a compound of formula (I), salts, and/or sulfoxides thereof

R1—S—(CH2)n—CH(NH2)—R2  (I),
wherein R1 is a branched or unbranched C1 to C4 alkyl, R2 is selected from the group consisting of COOH, salts thereof, and (CH2)m—OH, n is an integer ranging from 1 to 4, and m is an integer ranging from 1 to 4.

9. The electroplating bath according to claim 8, wherein R1 is methyl, ethyl, n-propyl, or iso-propyl.

10. The electroplating bath according to claim 8, wherein R2 is COOH and/or salts thereof.

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

12. The electroplating bath according to claim 1, wherein (E) comprises at least methionine.

13. The electroplating bath according to claim 1, wherein the molar ratio of (E):(D) is ranging from to 2.6.

14. A method for electroplating a black chromium layer on a substrate, the method comprising the steps

(a) providing the substrate,
(b) contacting the substrate with an electroplating bath according to claim 1,
(c) applying an electrical current such that the black chromium layer is electroplated onto the substrate,
(d) heat-treating the substrate obtained from step (c) at a temperature ranging from 30° C. to 100° C.

15. The method of claim 14, wherein in step (d) the heat-treating is carried out in water.

Patent History
Publication number: 20240026557
Type: Application
Filed: Dec 10, 2021
Publication Date: Jan 25, 2024
Applicant: Atotech Deutschland GmbH & Co. KG (Berlin)
Inventors: Berkem ÖZKAYA (Berlin), Philipp WACHTER (Berlin), Michael JONAT (Berlin)
Application Number: 18/256,480
Classifications
International Classification: C25D 3/08 (20060101); C25D 3/10 (20060101); C25D 5/50 (20060101);