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
  • C25D3/08—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
  • C25D3/06—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
  • C25D15/00—Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires
• • 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
  • C25D5/10—Electroplating with more than one layer of the same or of different metals
  • C25D5/12—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium
  • C25D5/14—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium two or more layers being of nickel or chromium, e.g. duplex or triplex layers
• • 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
• • 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
  • C25D5/60—Electroplating characterised by the structure or texture of the layers
  • C25D5/605—Surface topography of the layers, e.g. rough, dendritic or nodular layers
  • C25D5/611—Smooth layers
• • 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
  • C25D5/627—Electroplating characterised by the visual appearance of the layers, e.g. colour, brightness or mat appearance

Definitions

• the present invention relates to a very specific electroplating bath for depositing a black chromium layer, a respective method thereof, and a respective substrate with said black chromium layer thereon.
• the substrate comprising said 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.
• JP 2014 100809 A refers to a vehicular decorative component having black plating film and method for manufacturing the same.
• 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:
• R 1 is a branched or unbranched C1 to C4 alkyl
• R 2 is selected from the group consisting of COOH, salts thereof, and (CH 2 ) m -OH,
• - n is an integer ranging from 1 to 4, and
• - m is an integer ranging from 1 to 4.
• 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 I'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 specifically targeted and thus, 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.
• an electroplating bath of the present invention wherein the electroplating bath comprises sulfate ions, most preferably from a trivalent chromium salt.
• 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, or only in amounts as defined in the text below. 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, comparatively low amounts of cobalt can be tolerated although they are not necessary for the black appearance.
• an electroplating bath of the present invention wherein cobalt ions are present in a range from 1 mg/L to 500 mg/L, based on the total volume of the electroplating bath and based on the element cobalt, preferably from 2 mg/L to 400 mg/L, more preferably from 3 mg/L to 300 mg/L, even more preferably from 4 mg/L to 200 mg/L, yet even more preferably from 5 mg/L to 100 mg/L, most preferably from 6 mg/L to 50 mg/L.
• 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(ll) 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(ll) ions, most preferred with concentrations as defined throughout the present text as being preferred for them.
• Fe(ll) 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, more preferably as defined throughout the text.
• an electroplating bath of the present invention wherein the trivalent chromium ions and the Fe(ll) 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 addi- tion 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.
• 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(ll) 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.
• 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 group.
• 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 electro- plating 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.
• 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 40 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.
• (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 40 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) thiocyanic acid, salts, esters, and/or isoforms thereof, in a total amount ranging from 100 mmol/L to 250 mmol/L, based on the total volume of the electroplating bath.
• concentration above is based on SCN; i.e. based on monobasic thiocyanate.
• acid in “thiocyanic acid” includes its deprotonated/dissociated form.
• (D) comprises thiocyanic acid, salts, and/or esters thereof in said total amount, most preferably thiocyanic acid and/or salts thereof in said total amount.
• the salt comprises potassium thiocyanate and/or sodium thiocyanate, most preferably in said total amount.
• an electroplating bath of the present invention wherein the bath comprises (D) in a total amount ranging from 105 mmol/L to 245 mmol/L, based on the total volume of the electroplating bath, preferably from 110 mmol/L to 240 mmol/L, more preferably from 115 mmol/L to 230 mmol/L, even more preferably from 120 mmol/L to 220 mmol/L, yet even more preferably from 125 mmol/L to 210 mmol/L, most preferably from 130 mmol/L to 200 mmol/L.
• these preferred concentration ranges above are based on SCN; i.e.
• an electroplating bath of the present invention comprises (D) in a total amount ranging from 130 mmol/L to 250 mmol/L, based on the total volume of the electroplating bath, preferably from 150 mmol/L to 245 mmol/L, more preferably from 175 mmol/L to 240 mmol/L, most preferably from 191 mmol/L to 235 mmol/L.
• concentration ranges for a neutral black color tone are particularly preferred.
• an electroplating bath of the present invention comprises (D) in a total amount ranging from 100 mmol/L to 205 mmol/L, based on the total volume of the electroplating bath, preferably from 105 mmol/L to 200 mmol/L, more preferably from 110 mmol/L to 190 mmol/L, even more preferably from 115 mmol/L to 180 mmol/L, most preferably from 120 mmol/L to 174 mmol/L.
• concentration ranges for a warm black color tone preferably from 100 mmol/L to 205 mmol/L, based on the total volume of the electroplating bath, preferably from 105 mmol/L to 200 mmol/L, more preferably from 110 mmol/L to 190 mmol/L, even more preferably from 115 mmol/L to 180 mmol/L, most preferably from 120 mmol/L to 174 mmol/L.
• the electroplating bath of the present invention comprises (E) one or more than one compound of formula (I), salts, and/or sulfoxides thereof
• R 1 is a branched or unbranched C1 to C4 alkyl
• R 2 is selected from the group consisting of COOH, salts thereof, and (CH 2 ) m -OH,
• - n is an integer ranging from 1 to 4, and
• - m is an integer ranging from 1 to 4.
• an electroplating bath of the present invention wherein said bath comprises (E) in a total amount ranging from 100 mmol/L to 950 mmol/L, based on the total volume of the electroplating bath, preferably from 135 mmol/L to 800 mmol/L, more preferably from 150 mmol/L to 650 mmol/L, even more preferably from 165 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.
• an electroplating bath of the present invention wherein said bath comprises (E) in a total amount ranging from 100 mmol/L to 450 mmol/L, based on the total volume of the electroplating bath, preferably from 120 mmol/L to 400 mmol/L, more preferably from 140 mmol/L to 350 mmol/L, even more preferably from 150 mmol/L to 310 mmol/L, yet even more preferably from 170 mmol/L to 270 mmol/L, most preferably from 190 mmol/L to 230 mmol/L.
• con- centration ranges for a warm black color tone preferably from 120 mmol/L to 450 mmol/L, based on the total volume of the electroplating bath, preferably from 120 mmol/L to 400 mmol/L, more preferably from 140 mmol/L to 350 mmol/L, even more preferably from 150 mmol/L to 310 mmol/L, yet even more
• an electroplating bath of the present invention wherein said bath comprises (E) in a total amount ranging from 200 mmol/L to 950 mmol/L, based on the total volume of the electroplating bath, preferably from 220 mmol/L to 750 mmol/L, more preferably from 250 mmol/L to 580 mmol/L, even more preferably from 280 mmol/L to 530 mmol/L, yet even more preferably ranging from 311 mmol/L to 490 mmol/L, most preferably from 330 mmol/L to 420 mmol/L.
• concentration ranges for a neutral black color tone preferably from 200 mmol/L to 950 mmol/L, based on the total volume of the electroplating bath, preferably from 220 mmol/L to 750 mmol/L, more preferably from 250 mmol/L to 580 mmol/L, even more preferably from 280 mmol/L to 530 m
• an electroplating bath of the present invention wherein the molar ratio of (E) : (D) is ranging from 0.9 to 2.65, preferably from 1 to 2.6, more preferably from 1.05 to 2.55, even more preferably from 1.1 to 2.5, yet more preferably from 1.15 to 2.45, most preferably from 1.2 to 2.40.
• an electroplating bath of the present invention wherein the molar ratio of (E) : (D) is ranging from 0.9 to 2.5, preferably from 1 to 2, more preferably from 1.1 to 1.8, yet even more preferably from 1.15 to 1.5, most preferably from 1.2 to 1.3. These are in some cases preferred molar ranges for a warm black color tone.
• 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.
• R 1 is methyl, ethyl, n-propyl, or /so-propyl, preferably methyl or ethyl, most preferably methyl.
• R 2 is COOH and/or salts thereof.
• COOH includes also the deprotonated/dissociated form thereof.
• the present invention furthermore relates to a method for electroplating a black chromium layer on a substrate, the method comprising the steps
• step (d) heat-treating the substrate obtained from step (c) at a temperature ranging from 30°C to 100°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. Also preferred is a method of the present invention, wherein in 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 65°C, 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 pm to 1 pm, preferably from 0.1 pm to 0.8 pm, more preferably from 0.125 pm to 0.6 pm, most preferably from 0.15 pm to 0.5 pm.
• 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.
• Substrate comprising a black chromium layer:
• the present invention furthermore relates to a specifically defined substrate comprising a black chromium layer, wherein the black chromium layer has, according to the L*a*b color system, an L* value of 50 or less, and a gloss value ranging from 150 to 230, referenced to a measuring angle of 60°, preferably from 160 to 220, more preferably from 165 to 210, most preferably 170 to 200.
• the aforementioned regarding the electroplating bath of the present invention and the method of the present invention preferably applies likewise to the specifically defined substrate of the present invention (if technical applicable). This most preferably applies to the L*a*b* values defined for the electroplating bath of the present invention and the method of the present invention.
• the following features of the substrate of the present invention preferably also apply to the method of the present invention (if not already mentioned in the text above).
• the black chromium layer has an L* value of 49 or less, preferably 48 or less, more preferably of 47 or less, even more preferably of 46 or less, yet even more preferably of 45 or less, most preferably of 44 or less.
• 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, and/or (preferably and) an b* value ranging from -2.5 to +6, preferably ranging from -2 to +5.6, most preferably ranging from -1.5 to +5.
• the black chromium layer is substantially free of, preferably does not comprise, cobalt, or comprises cobalt, wherein 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 black chromium layer is not the only metal layer between the black chromium layer and the substrate.
• the at least one nickel layer comprises at least one bright-nickel layer or at least one satin nickel layer. This is most preferred.
• 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 the at least one semi-bright nickel layer is the nickel layer (of all nickel layers) closest to the substrate.
• 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 micro porous.
• the black chromium layer comprises iron (i.e. is more than zero at.-%), 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.- %.
• the layer stack preferably comprises a sealer layer and/or an antifingerprint layer, most preferably on the black chromium layer. If both is applied, preferably the sealer layer is applied first, followed by the anti-fingerprint layer, which preferably forms the very outermost layer.
• 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 x 70 mm were used.
• 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.
• Uniclean® 279 product of Atotech GmbH
• the cleaned 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:
• 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.
• 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.
• Gloss was determined with a reflectometer (REFO 3-D, Dr. Lange), referenced to a measuring angle of 60°.
• +++ 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
• - CE2 corresponds to Sample No. 5 in Table 1 (which represents all samples ranging from 5 to 13 in Table 1), wherein the total amount of thiocyanic acid is again below 100 mmol/L (i.e. 100 ml/L Trichrome Graphite Makeup and 30 ml/L Trichrome Graphite Maintenance result in less than 100 mmol/L thiocyanic acid); 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.
• 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 [0064] 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 following disadvantages according to our own observations: First, an idle time (or also called aging time) of 18 or 19 days is considered inacceptable in view of industry requirements. Second, the same chemical composition provides different optical results depending on the idle time and conditions applied. Both is not desired. 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.
• - CE3 corresponds to Sample No. 14 in Table 2 in LIS’526, wherein the total amount of thiocyanic acid is 15 g/L (i.e. 254 mmol/L), which is significantly higher than in Sample No. 5 of LIS’526.
• the color measurement CM1 showed an L*; a*; b* of 47; 1.0; 5.7 immediately after plating at ca. 10 A/dm 2 , which is in good agreement with what is disclosed in LIS’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.
• the examples of the present invention clearly show that a thiocyanic acid concentration below 250 mmol/L allows not only the desired color tone but additionally broadens the ASD range.
• a total amount significantly above 250 mmol/L 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 not exceeding 250 mmol/L.
• 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). Compared to CE3 the total amount of thiocyanic acid was significantly further increased. 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 a either a neutral black color tone or a warm black color tone can be specifically addressed and obtained within an acceptable short time.
• the concentration of (D) is high enough to obtain an effect from the hot water rinse but is not exceeding a critical concentration such that a relative broad current density range is still guaranteed.

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• 2021
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