Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium
  • C25D3/06—Electroplating: Baths therefor from solutions of chromium from solutions of trivalent chromium
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium
  • C25D3/08—Deposition of black chromium, e.g. hexavalent chromium, CrVI
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium
  • C25D3/10—Electroplating: Baths therefor from solutions of chromium characterised by the organic bath constituents used
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/48—After-treatment of electroplated surfaces
  • C25D5/50—After-treatment of electroplated surfaces by heat-treatment

Definitions

• 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.
• 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.
• the present invention refers to an electroplating bath for depositing a black chromium layer, the electroplating bath comprising:
• 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.
• 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.
• 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.
• 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.
• an electroplating bath of the present invention wherein the black chromium layer is a neutral black chromium layer.
• 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.
• 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.
• an electroplating bath of the present invention wherein the black chromium layer is a chromium layer having a warm black color tone.
• 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.
• both the neutral black color tone as well as the warm black color tone can be obtained, which is of great benefit.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the electroplating bath is substantially free of, preferably does not comprise, hexavalent chromium.
• an electroplating bath of the present invention wherein the electroplating bath is substantially free of, preferably does not comprise, cobalt ions.
• 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.
• the electroplating bath of the present invention is substantially free of, preferably does not comprise, nickel ions.
• 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.
• the black chromium layer is substantially free of, preferably does not comprise, nickel.
• an electroplating bath of the present invention wherein the electroplating bath is substantially free of, preferably does not comprise, fluoride ions.
• the black chromium layer is substantially free of, preferably does not comprise, fluorine.
• 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.
• 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.
• 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.
• an electroplating bath of the present invention further comprising halogen anions, preferably chloride anions.
• halogen anions preferably chloride anions.
• chloride-containing baths More preferred is an electroplating bath of the present invention comprising chloride ions and sulfate ions.
• 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.
• 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.
• an electroplating bath of the present invention further comprising bromide anions.
• 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.
• 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.
• 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.
• the electroplating bath of the present invention comprises chloride ions.
• 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.
• 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.
• 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.-%.
• 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.
• an electroplating bath of the present invention is preferred further comprising at least one sulfur-containing compound being different from (D) and (E).
• an electroplating bath of the present invention is preferred further (i.e. in addition to (D) and (E)) comprising saccharin and/or salts thereof.
• 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.
• 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.
• the at least one surface-active compound is free of fluorine atoms.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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).
• 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 are preferably substituted with a substituent or unsubstituted.
• a preferred substituent comprises an amino group and/or a hydroxyl group.
• the substituent does not comprise a SH moiety and/or a SCN moiety.
• the organic carboxylic acid 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.
• the amino carboxylic acids preferably alpha-amino carboxylic acids, respectively
• the one or more than one complexing agent is distinct from the compound of formula (E).
• 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.
• the electroplating bath of the present invention comprises chloride ions.
• 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.
• 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.
• 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.
• the electroplating bath of the present invention comprises (C) optionally, one or more than one pH buffer compound for said electroplating bath.
• the electroplating bath of the present invention comprises (i.e. not optionally) one or more than one pH buffer compound.
• 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).
• 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).
• 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.
• 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.
• the one or more than one pH buffer compound comprises boric acid but no borate.
• 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.
• 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.
• 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.
• —SCN moiety denotes a thiocyanate moiety or group, respectively.
• said compound is organic and/or inorganic, preferably inorganic.
• Preferred organic compounds comprise an alkyl and/or aryl compound thereof, preferably substituted or unsubstituted.
• 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.
• 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.
• the salt comprises potassium thiocyanate and/or sodium thiocyanate.
• acid in “thiocyanic acid” includes its deprotonated/dissociated form.
• a preferred isoform thereof is isothiocyanic acid and/or salts thereof.
• (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.
• 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.
• (D) has not a lower total concentration limit of 100 mmol/L but rather the ranges as defined above.
• all other features as defined throughout the present text for the electroplating bath preferably still apply also to this specific disclosure.
• 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.
• concentration ranges above are based on SCN ⁇ , i.e. are based on monobasic thiocyanate and thiocyanate moieties, respectively.
• 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—(CH 2 ) k —CH 3 moiety, wherein k is an integer ranging from 0 to 4.
• k is 0, 1, 2, 3, or 4, preferably 0, 1, or 2.
• —SH moiety denotes a thiol or sulfhydryl moiety or group, respectively.
• sulfoxides thereof denotes an oxygen chemically linked via a double bond to a sulphur atom, i.e. said organic compound also comprises —S( ⁇ O)—(CH 2 ) k —CHs moieties.
• 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.
• (E) comprises at least a compound of formula (I), salts, and/or sulfoxides thereof
• R 1 is methyl, ethyl, n-propyl, or iso-propyl, preferably methyl or ethyl, most preferably methyl.
• R 2 is COOH and/or salts thereof.
• COOH includes also the deprotonated/dissociated form thereof.
• 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.
• 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.
• 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.
• 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.
• 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.
• the present invention furthermore relates to a method for electroplating a black chromium layer on a substrate, the method comprising the steps
• the aforementioned features regarding the electroplating bath of the present invention 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).
• step (a) the substrate is provided.
• 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.
• the substrate comprises a thermoplastic substrate, preferably an amorphous thermoplastic substrate and/or a semi-crystalline thermoplastic.
• step (a) the substrate comprises butadiene moieties, preferably polybutadiene.
• step (a) the substrate comprises nitrile moieties.
• step (a) the substrate comprises acryl moieties.
• step (a) the substrate comprises polymerized styrene.
• 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).
• ABS acrylonitrile butadiene styrene
• ABS-PC acrylonitrile butadiene styrene-polycarbonate
• 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 ketone (PEKEKK), poly ether ketone ketone (PEKK), and/or mixtures thereof, preferably poly ether ether ketone (PEEK), polyaryletherketone (PAEK), and/or mixtures thereof.
• PAEK polyaryletherketone
• PEEK poly ether ether ketone
• PEEK poly ether ether ketone
• PEEK poly ether ether ketone
• PEEKK poly ether ether ketone ketone
• PEKEKK poly ether ketone ketone
• PEKK polyether ketone ketone
• 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.
• 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.
• 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.
• 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.
• 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.
• a method of the present invention is preferred, wherein the MPS nickel layer is adjacent to the black chromium layer.
• 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.
• the black chromium layer is part of a layer stack.
• 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.
• step (c) 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.
• 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.
• 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.
• step (c) an electrical current is applied.
• the electrical current is a direct current, preferably in a range from 3 A/dm 2 to 30 A/dm 2 , more preferably from 4 A/dm 2 to 25 A/dm 2 , even more preferably from 5 A/dm 2 to 20 A/dm 2 , most preferably from 6 A/dm 2 to 18 A/dm 2 .
• the electrical current is a direct current, preferably in a range from 3 A/dm 2 to 20 A/dm 2 , more preferably from 4 A/dm 2 to 15 A/dm 2 , most preferably from 5 A/dm 2 to 10 A/dm 2 . This most preferably applies if the electroplating bath is a chloride-free electroplating bath.
• 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.
• the electroplated black chromium layer has a layer thickness ranging from 0.05 ⁇ m to 1 ⁇ m, preferably from 0.1 ⁇ m to 0.8 ⁇ m, more preferably from 0.125 ⁇ m to 0.6 ⁇ m, most preferably from 0.15 ⁇ m to 0.5 ⁇ m.
• 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.
• 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.
• the heat-treating is preferably in water.
• this step is carried out in a treatment compartment comprising a treatment composition.
• 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.
• step (d) the heat-treating is a hot water rinse, most preferably by dipping, even most preferably by dipping into the treatment composition.
• step (d) the heat-treating is carried out without an electrical current.
• this step is preferably electroless.
• 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.
• Hull Cell electroplating was performed to evaluate the optical appearance of the black chromium layer depending on the current density distribution.
• copper panels 99 mm ⁇ 70 mm were used as a substrate.
• 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% H 2 SO 4 by volume, and rinsed with water.
• Uniclean® 279 product of Atotech Deutschland GmbH
• the cleansed substrates were deposited with a bright nickel layer (10 min, 4 A/dm 2 , UniBrite 2002, product of Atotech) such that a nickel-plated substrate was obtained and rinsed with water.
• the black chromium layer was deposited by utilizing the following electroplating bath:
• A ca. 20 to 25 g/L Cr 3+ 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 SO 4 •7 H 2 O
• 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.
• 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).
• CM1 first color measurement
• CM2 second color measurement
• 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/dm 2 to 12 A/dm 2 ).
• MCD medium current density
• the substrates were also optically inspected depending on the locally present current densities (abbreviated as “ASD range” in Table 1).
• ASD range 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.
• Example No. 7 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.
• an idle time or also called aging time
• 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.
• 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.

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• 2021
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