CN117425751A - Method of electrodepositing a dark chromium layer, substrate comprising the same, and electroplating bath therefor - Google Patents

Method of electrodepositing a dark chromium layer, substrate comprising the same, and electroplating bath therefor Download PDF

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Publication number
CN117425751A
CN117425751A CN202280040771.6A CN202280040771A CN117425751A CN 117425751 A CN117425751 A CN 117425751A CN 202280040771 A CN202280040771 A CN 202280040771A CN 117425751 A CN117425751 A CN 117425751A
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substrate
trivalent chromium
sulfur
plating bath
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Inventor
B·厄兹卡亚
P·库尔坎普
O·叶夫图申科
M·约纳特
P·瓦赫特
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Germany Aituoteke Co ltd
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Germany Aituoteke Co ltd
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    • 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
    • C25D3/08—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
    • 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

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electroplating And Plating Baths Therefor (AREA)
  • Electroplating Methods And Accessories (AREA)

Abstract

The present invention relates to a method of electrodepositing a dark chrome layer on a substrate, a corresponding electroplating bath for depositing such a dark chrome layer and a corresponding substrate comprising the dark chrome layer. The plating bath includes colloidal particles containing the chemical element aluminum. The substrate comprising the dark chrome layer is mainly suitable for decorative purposes.

Description

Method of electrodepositing a dark chromium layer, substrate comprising the same, and electroplating bath therefor
Technical Field
The present invention relates to a method of electrodepositing a dark chrome layer on a substrate, a corresponding electroplating bath for depositing such a dark chrome layer, and a corresponding substrate comprising the dark chrome layer. The plating bath contains colloidal particles containing the chemical element aluminum. Substrates comprising the dark chrome layer are mainly suitable for decorative purposes.
Background
From the very beginning of the chrome coating, dark chrome coatings have seen high attention to them due to their great attraction to decorative applications.
Even starting from dark hexavalent chromium coatings, the focus today shifts significantly to trivalent chromium coatings due to higher environmental acceptability. As a result of years, for example for decorative automotive parts, the need for dark trivalent chromium coatings has increased. However, in some cases, extremely dark hues may be considered overcooled, such that slight hue modification is typically required to produce multiple shades for various decorative purposes. In general, the degree of obscuration varies significantly depending on the deposition parameters and bath composition.
There is a continuing need to provide a dark chrome layer that allows fine tuning of a slightly warmer hue or a slightly darker hue. It is desirable to have an adjustment that allows this fine tuning to be performed in an easy to handle manner.
In principle, dark trivalent chromium layers are known.
US 2011/155286 A1 refers to a composition for chemical conversion treatment comprising trivalent chromium ions and optionally an inorganic silica sol or alumina sol.
JP 5890394 B2 refers to a chromium plating solution containing trivalent chromium and ceramic particles.
RU 2231581 C1 contains trivalent chromium ion and Al 2 O 3 Chromium electrolyte of the powder.
US 2012/312694 A1 refers to an aqueous acidic trivalent chromium electrolyte comprising trivalent chromium ions and colloidal silica.
US 2015/354085 A1 refers to an apparatus for maintaining the efficiency of trivalent chromium plating baths that utilizes a source of Ultraviolet (UV) radiation that provides UV radiation to the aqueous plating bath so that the plating efficiency of the inhibition bath is reduced.
US 2007/0227895 A1 refers to a process for electrodepositing a crystalline-like chromium deposit on a substrate.
Object of the invention
The object of the present invention is to provide a method of electrodepositing a dark chrome layer starting from a base darkness, but in addition to this, providing (I) a further reduced darkness and (II) a high measure of flexibility in the simultaneous electroplating bath, to slightly change the further reduced darkness to a specific target darkness by decreasing or increasing the brightness lx (according to lxa x b x color space system) according to the required specifications. In addition, such flexibility preferably allows for return to the base darkness without discarding the plating bath.
Disclosure of Invention
These objects are solved by a method of electrodepositing a dark chromium layer on a substrate, comprising the steps of
(a) Providing a substrate, wherein the substrate comprises a plastic substrate,
(b) Providing an aqueous trivalent chromium plating bath comprising
(i) Trivalent chromium ions are used as the ion source,
(ii) One or more complexing agents for said trivalent chromium ions,
(iii) Colloidal particles containing the chemical element aluminum,
(iv) A first sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less, and
(v) Optionally, a second sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less, which is different from (iv),
(c) The substrate is contacted with the electroplating bath and an electrical current is applied such that a dark chromium layer is electrodeposited on the substrate.
Self experiments have shown (see examples below in the text) that a further reduced darkness, mainly represented by a further reduced L-value, is obtained by means of colloidal particles containing the chemical element aluminum, compared to a corresponding electroplating bath not containing said colloidal particles. This is especially the case if the aqueous trivalent chromium plating bath comprises said first sulfur compound, most preferably methionine. However, self-experiments also show that this effect does not necessarily occur in the case of colloidal particles (e.g. colloidal silica) that do not contain aluminum.
Another great benefit of the method of the invention is that the aqueous trivalent chromium plating bath comprises a combination of (iii) and (iv). Most preferably, both act as darkening agents in the context of the present invention. However, they all vary significantly in their properties. Wherein (iii) is formed from particles, (iv) is preferably a soluble compound. This means that (iii) the concentration of (iii) can be adapted by adding such colloidal particles or by partially (or completely) removing the colloidal particles from the electroplating bath. Most preferably, such removal is achieved by physical/mechanical separation means, such as filtration. This generally allows fine tuning of the luminance L depending on the amount present. This removal generally does not significantly affect the presence of (iv). In other words, the total concentration of (iii) is preferably reversibly adapted by physical means without affecting the total concentration of (iv). This allows a very wide variety of dark shades to be used, ideally with the same basic electroplating bath.
Detailed Description
Very preferably, the dark chrome layer is a decorative chrome layer. Are commonly used as automotive parts, most preferably in the interior of automobiles. The electroplating bath used in the method of the invention is well suited to obtain such dark chrome layers, most preferably such dark chrome layers as defined throughout.
In the context of the present invention, the dark chrome layer is defined by the L x a x b x color system, preferably as described by the 1976 international commission on illumination (Commission Internationalede I' Eclairage), if not otherwise specified.
In step (a) of the method of the present invention, a substrate is provided.
In the method of the present invention, the substrate comprises a plastic substrate.
The method of the present invention is preferred wherein the plastic substrate comprises Acrylonitrile Butadiene Styrene (ABS), acrylonitrile butadiene styrene-polycarbonate (ABS-PC), polypropylene (PP), polyamide (PA), polyurethane (PU), polyepoxide (PE), polyacrylate, polyetherimide (PEI), polyetherketone (PEK), mixtures thereof and/or composites thereof; preferably Acrylonitrile Butadiene Styrene (ABS), acrylonitrile butadiene styrene-polycarbonate (ABS-PC), polyamide (PA), polyurethane (PU), polyepoxide (PE), polyacrylate, mixtures thereof and/or composites thereof. Such plastic substrates are often used in decorative applications, such as automotive parts, in particular ABS and ABS-PC.
The method of the invention is preferred wherein the plastic substrate comprises at least one metal layer (further most preferably). Preferably, the at least one metal layer comprises a copper or copper alloy layer and/or a nickel or nickel alloy layer.
In some other cases, not according to the invention, the substrate is a metal substrate, preferably comprising iron, copper, nickel, aluminum, zinc, mixtures thereof and/or alloys thereof. A very preferred metal substrate comprising iron is steel. The mixture preferably comprises a complex.
The process of the invention is preferred, wherein after step (a) and before step (c), the process of the invention comprises the steps of
(a1) The substrate is pre-treated, preferably cleaned, most preferably degreased and/or rinsed.
Preferably, the degreasing comprises electrolytic degreasing.
Preferably, the pickling comprises contacting with an acid, preferably a mineral acid.
Step (a 1) is preferably followed by a water rinse.
In step (b) of the method of the present invention, the aqueous trivalent chromium plating bath is provided.
The plating bath comprises water, preferably at least 55vol. -% or more, more preferably 65vol. -% or more, even more preferably 75vol. -% or more, yet even more preferably 85vol. -% or more, still more preferably 90vol. -% or more, most preferably 95vol. -% or more of water, based on the total volume of the plating bath. Most preferably, water is the only solvent.
The method of the invention is preferred wherein the aqueous trivalent chromium plating bath is acidic, preferably having a pH in the range of 1.5 to 5.0, more preferably 2.1 to 4.6, even more preferably 2.4 to 4.2, yet more preferably 2.7 to 3.8, most preferably 3.0 to 3.5. The pH is preferably adjusted by means of hydrochloric acid, sulfuric acid, ammonia, potassium hydroxide and/or sodium hydroxide.
The aqueous trivalent chromium plating bath contains (i) trivalent chromium ions.
The method of the present invention is preferred wherein in the plating bath the trivalent chromium ions have a total concentration in the range of 5g/L to 35g/L, preferably 6g/L to 32g/L, more preferably 7g/L to 29g/L, even more preferably 8g/L to 26g/L, yet even more preferably 9g/L to 23g/L, most preferably 10g/L to 22g/L, based on the total volume of the plating bath.
Preferably, the trivalent chromium ion is derived from a trivalent chromium salt, preferably from an inorganic chromium salt and/or an organic chromium salt, most preferably from an inorganic chromium salt. Preferred inorganic chromium salts comprise chloride and/or sulfate anions, preferably sulfate anions. A highly preferred inorganic chromium salt is basic chromium sulfate. Preferred organochromium salts comprise carboxylic acid anions, preferably formate, acetate, malate and/or oxalate anions.
The method of the present invention is preferred, wherein in the aqueous trivalent chromium plating bath trivalent chromium ions together with optional iron ions (as regards iron ions, in some cases iron ions are optional but preferred, see text below) represent all transition metal ions in the aqueous trivalent chromium plating bath in 80mol-% or more, preferably 90mol-% or more, more preferably 93mol-% or more, even more preferably 96mol-% or more, most preferably 98mol-% or more, based on the total volume of the aqueous trivalent chromium plating bath.
An aqueous trivalent chromium plating bath comprising (ii) one or more than one complexing agent for said trivalent chromium ions.
Such compounds keep trivalent chromium ions in solution. Preferably, one or more than one complexing agent is not a compound of (iv), and (v) is therefore preferably different from (iv).
The method of the invention is preferred wherein in the aqueous trivalent chromium plating bath one or more than one complexing agent comprises an organic acid and/or salt thereof, preferably an organic carboxylic acid and/or salt thereof, most preferably an organic carboxylic acid and/or salt thereof comprising one, two or three carboxyl groups.
The organic carboxylic acid and/or salt thereof (preferably also organic carboxylic acid and/or salt thereof comprising one, two or three carboxyl groups) is preferably substituted or unsubstituted with a substituent. Preferred substituents comprise amino and/or hydroxy. Preferably, the substituents do not comprise SH moieties and/or SCN moieties. More preferably, one or more than one complexing agent for the trivalent chromium ions is not a sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less.
More preferably, the organic carboxylic acid and/or salt thereof (preferably also organic carboxylic acid and/or salt thereof comprising one, two or three carboxyl groups) comprises carbamic acid (preferably a-carbamic acid), hydroxy carboxylic acid and/or salt thereof. Preferred (alpha-) carbamates comprise glycine, aspartic acid and/or salts thereof. Preferably, the carbamic acid (preferably respectively α -carbamic acid) is not a compound according to (iv), more preferably is not a sulfur-containing carbamic acid (preferably respectively sulfur-containing α -carbamic acid), most preferably is not methionine. It is particularly preferred that one or more than one complexing agent is different from (iv) and (v).
The process of the present invention is more preferred wherein 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 method of the present invention is preferred wherein one or more than one complexing agent has a total concentration in the range of 5g/L to 200g/L, preferably in the range of 8g/L to 150g/L, more preferably in the range of 10g/L to 100g/L, even more preferably in the range of 12g/L to 75g/L, yet even more preferably in the range of 15g/L to 50g/L, most preferably in the range of 20g/L to 35g/L, based on the total volume of the aqueous trivalent chromium plating bath.
The aqueous trivalent chromium plating bath contains (iii) colloidal particles containing the chemical element aluminum.
The method of the invention is preferred wherein the aqueous trivalent chromium plating bath is a colloidal suspension, preferably a sol. This is due to the presence of the colloidal particles, which are preferably correspondingly smaller.
The method of the invention is preferred wherein the colloidal particles comprise nanoparticles, preferably nanoparticles. Preferably, the colloidal particles comprising the chemical element aluminium have a particle size of less than 1000nm, preferably less than 500nm, more preferably at least 90% of the colloidal particles have a particle size of less than 500nm, most preferably at least 90% of the colloidal particles have a particle size of less than 150nm.
The process of the invention is preferred, wherein the colloidal particles have an average particle diameter D by volume 50 Is 100nm or less, preferably 80nm or less, more preferably 60nm or less, even more preferably 50nm or less, most preferably 40nm or less, most preferably 30nm or less, even most preferably 25nm or less.
The method of the invention is more preferred, wherein the colloidal particles comprise at least particles having a particle size of 100nm or less, preferably 80nm or less, more preferably 60nm or less, even more preferably 50nm or less, most preferably 40nm or less, very most preferably 30nm or less, even most preferably 20nm or less.
The method of the invention is preferred wherein the colloidal particles are present in a total amount in the range of 0.05g/L to 15g/L, preferably 0.1g/L to 12g/L, more preferably 0.5g/L to 10g/L, even more preferably 1.0g/L to 8g/L, most preferably 1.5g/L to 6g/L, even most preferably 1.9g/L to 4g/L, based on the total volume of the aqueous trivalent chromium plating bath.
The method of the invention is more preferred wherein the colloidal particles comprise alumina.
The method of the invention is most preferred, wherein the colloidal particles comprise Al 2 O 3 Preferably consisting essentially of Al 2 O 3 Composition is prepared. Most preferably, these are the only colloidal particles in the aqueous trivalent chromium plating bath.
The aqueous trivalent chromium plating bath includes (iv) a first sulfur compound having a sulfur atom with an oxidation number of +5 or less. Preferably, acids, salts, isomers and betaines thereof are included. However, sulfate anions are not counted in (iv) and (v).
Optionally, the aqueous trivalent chromium plating bath includes (v) a second sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less, different from (iv). Again, this preferably includes the acid, salt, isomer, and betaine thereof.
In some cases, the method of the present invention is preferred, wherein the aqueous trivalent chromium plating bath comprises (iv) and (v). Thus, in this case, (v) is not optional.
The process of the present invention is generally preferred wherein the first and optionally the second sulfur-containing compounds having sulfur atoms with an oxidation number of +5 or less comprise divalent sulfur atoms. The compounds are preferably inorganic or organic.
In some cases, preferably, the first sulfur-containing compound comprises one or more than one organic sulfur-containing compound (preferably as described throughout the text), wherein preferably, the second sulfur-containing compound comprises one or more than one inorganic sulfur-containing compound (preferably as described throughout the text).
The process of the present invention is more generally preferred wherein the first and optionally the second sulfur-containing compounds having sulfur atoms with an oxidation number of +5 or less are selected from the group consisting of (including salts of):
(1) 2- (2-hydroxy-ethylsulfanyl) -ethanol,
(2) Thiazolidine-2-carboxylic acid is used as a base,
(3) Thiodiglycol ethoxylates
(4) 2-amino-3-ethylsulfanyl-propionic acid,
(5) 3- (3-hydroxy-propylsulfanyl) -propan-1-ol
(6) 2-amino-3-carboxymethylsulfanyl-propionic acid,
(7) 2-amino-4-methylsulfanyl-butan-1-ol,
(8) 2-amino-4-methylsulfanyl-butyric acid,
(9) 2-amino-4-ethylsulfanyl-butyric acid,
(10) 3-formamidinylthio-propane-1-sulfonic acid,
(11) 3-formamidinylthio-propionic acid,
(12) A thiomorpholine salt,
(13) 2- [2- (2-hydroxy-ethylsulfanyl) -ethylsulfanyl ] -ethanol,
(14) 4, 5-dihydro-thiazol-2-ylamine,
(15) The reaction product of thiocyanate,
(16) 2-amino-4-methylsulfinyl-butyric acid,
(17) 1, 1-dioxo-1, 2-dihydro-1λ 6 x-benzo [ d ] isothiazol-3-one
(18) Prop-2-yne-1-sulfonic acid,
(19) Methylsulfinyl methane, and
(20) 2- (1, 3-trioxo-1, 3-dihydro-1λ 6 x-benzo [ d ] isothiazol-2-yl) -ethanesulfonic acid
The method of the present invention is also generally preferred, wherein (iv) and (v) together have a total concentration in the range of 16 to 1150mmol/L, preferably 45 to 1000mmol/L, more preferably 80 to 900mmol/L, even more preferably 120 to 800mmol/L, yet even more preferably 150 to 700mmol/L, most preferably 180 to 650mmol/L, based on the total volume of the plating bath. This most preferably applies to all sulfur-containing compounds having sulfur atoms with an oxidation number of +5 or less (i.e., the total concentration within all such compounds) in an aqueous trivalent chromium plating bath.
The method of the present invention is particularly preferred, wherein the aqueous trivalent chromium plating bath comprises (iv) in a total concentration ranging from 15mmol/L to 750mmol/L, preferably 40mmol/L to 650mmol/L, more preferably 70mmol/L to 600mmol/L, even more preferably 100mmol/L to 550mmol/L, yet even more preferably 120mmol/L to 500mmol/L, most preferably 140mmol/L to 470mmol/L, based on the total volume of the plating bath.
The method of the present invention is particularly preferred, wherein the aqueous trivalent chromium plating bath comprises (v) in a total concentration ranging from 1mmol/L to 400mmol/L, preferably from 5mmol/L to 350mmol/L, more preferably from 10mmol/L to 300mmol/L, even more preferably from 20mmol/L to 250mmol/L, yet even more preferably from 30mmol/L to 200mmol/L, most preferably from 40mmol/L to 180mmol/L, based on the total volume of the plating bath.
The process of the invention is preferred wherein the molar concentration of (iv) is higher than (v). In some cases, the method of the present invention is preferred wherein the molar ratio of (iv) to (v) in the aqueous trivalent chromium plating bath is greater than 1, preferably 1.1 or greater, most preferably 1.2 or greater. Most preferably, the first sulfur-containing compound has the highest concentration of sulfur-containing compounds having sulfur atoms with an oxidation number of +5 or less.
In some cases, the method of the present invention is more preferred, wherein in the aqueous trivalent chromium plating bath the molar ratio of (iv) to (v) is in the range of 1.05 to 15, preferably 1.10 to 12, more preferably 1.15 to 10, even more preferably 1.20 to 9, most preferably 1.25 to 8. Further, most preferably, the first sulfur-containing compound has the highest concentration of the sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less.
In some cases, the method of the present invention is preferred wherein the first sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less comprises a nitrogen atom, more preferably comprises an amino group, most preferably comprises an amino acid.
Preferably, the amino acid comprises an alpha-amino acid having a sulfur atom with an oxidation number of +5 or less, most preferably a proteinogenic amino acid having a sulfur atom with an oxidation number of +5 or less. Most preferably, this comprises methionine and cysteine.
In some cases, the methods of the invention are more preferred, wherein the first sulfur-containing compound comprises methionine. The aforementioned molar ratios most preferably apply if the first sulfur-containing compound comprises methionine. However, in other cases, the process of the present invention is preferred, wherein instead of the first sulfur-containing compound, the second sulfur-containing compound comprises methionine.
The method of the present invention is preferred, wherein methionine has a total concentration in the range of 100mmol/L to 500mmol/L, preferably 110mmol/L to 450mmol/L, more preferably 120mmol/L to 400mmol/L, even more preferably 130mmol/L to 350mmol/L, yet even more preferably 140mmol/L to 300mmol/L, most preferably 150mmol/L to 250mmol/L, based on the total volume of the plating bath. However, in some cases it is preferred that methionine has even a low total concentration, preferably in the range of 15mmol/L to 100mmol/L, more preferably 20mmol/L to 80 mmol/L.
In some cases, the process of the present invention is preferred wherein the second sulfur-containing compound comprises an inorganic sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less, preferably comprising a thiocyanate anion. However, in some other cases, the process of the present invention is preferred, wherein the first sulfur-containing compound comprises a thiocyanate anion instead of the second sulfur-containing compound. In the context of the present invention, thiocyanate anions (i.e., SCN - ) Organic compounds comprising a thiocyanate moiety are considered to be inorganic. Preferably, the thiocyanate anion is present by thiocyanate (e.g., potassium thiocyanate, sodium thiocyanate, ammonium thiocyanate) and/or by thiocyanate.
The method of the present invention is preferred wherein the thiocyanate anion has a total concentration in the range of 1mmol/L to 400mmol/L, preferably 3mmol/L to 350mmol/L, more preferably 5mmol/L to 300mmol/L, even more preferably 8mmol/L to 250mmol/L, yet even more preferably 12mmol/L to 200mmol/L, most preferably 15mmol/L to 180mmol/L, based on the total volume of the plating bath.
Preferably, the aqueous trivalent chromium plating bath contains other compounds or preferably does not contain specific compounds as outlined below.
The method of the present invention is preferred, wherein the aqueous trivalent chromium plating bath preferably further comprises Fe (II) ions in a concentration ranging from 0.1mmol/L to 10mmol/L, preferably from 0.4mmol/L to 8mmol/L, more preferably from 0.8mmol/L to 6mmol/L, even more preferably from 1.2mmol/L to 5mmol/L, most preferably from 1.5mmol/L to 4.5mmol/L, based on the total volume of the plating bath. In many cases, the Fe (II) ions positively affect plating performance. Furthermore, in some cases, it is preferable that the dark chromium layer contains iron.
The method of the present invention is preferred, wherein in step (b) the aqueous trivalent chromium plating bath further comprises sulfate anions at a concentration preferably in the range of 0.2 to 1.3mol/L, more preferably 0.3 to 1.1mol/L, even more preferably 0.4 to 1.0mol/L, yet even more preferably 0.5 to 0.9mol/L, most preferably 0.6 to 0.8mol/L based on the total volume of the plating bath. Preferably, the sulfate ion is present due to a source of trivalent chromium ions, such as basic chromium sulfate. Sulfate ions contribute very well to the conductivity of the plating bath.
The method of the present invention is preferred, wherein in step (b) the aqueous trivalent chromium plating bath further comprises a total concentration of halogen anions, preferably in the range of 0.1 to 6mol/L, more preferably in the range of 0.5 to 5mol/L, even more preferably 1 to 4.5mol/L, yet even more preferably 1.5 to 4.2mol/L, most preferably 2 to 3.9mol/L, based on the total volume of the plating bath.
The method of the present invention is more preferable in which the halogen anions are contained in a total concentration in the range of preferably 0.5mol/L to 5mol/L, more preferably 0.8mol/L to 4.7mol/L, even more preferably 1.3mol/L to 4.5mol/L, still even more preferably 1.8mol/L to 4mol/L, and most preferably 2.3mol/L to 3.7mol/L, based on the total volume of the plating bath. The chloride ions are preferably derived from a chloride salt and/or hydrochloric acid, preferably from sodium chloride, potassium chloride, ammonium chloride, chromium chloride (at least as part of all chloride ions) and/or mixtures thereof. Typically, chloride ions are present in the form of anions of the conductive salts. Very preferred conductive salts are ammonium chloride, sodium chloride and potassium chloride, with ammonium chloride being most preferred.
The process of the present invention is preferred, wherein in step (b), the halogen anion comprises a bromide anion, in some cases preferably in addition to a chloride anion. The bromide ions generally avoid anode formation of undesirable hexavalent chromium species. Preferably, the bromide ion has a concentration in the range of 3g/L to 20g/L, preferably in the range of 4g/L to 18g/L, more preferably in the range of 5g/L to 16g/L, even more preferably in the range of 6g/L to 14g/L, most preferably in the range of 7g/L to 12g/L, based on the total volume of the aqueous trivalent chromium plating bath. The bromide ion is preferably derived from a bromide salt, preferably from sodium bromide, potassium bromide, ammonium bromide and/or mixtures thereof. Preferably, if sulfate ions are used in the aqueous trivalent chromium plating bath, bromide ions are also present.
The method of the present invention is preferred wherein in step (b) the aqueous trivalent chromium plating bath further comprises ammonium ions.
The method of the present invention is preferred wherein in step (b) the aqueous trivalent chromium plating bath further comprises one or more than one pH buffer compound. Most preferably, one or more than one pH buffer compound is different (i.e., different) from (ii). This preferably means that one or more than one pH buffer compound does not comprise a carboxylic acid, preferably does not comprise an organic acid.
In many cases, the method of the invention is preferred wherein in the aqueous trivalent chromium plating bath one or more than one pH buffer compound comprises a boron containing compound, preferably boric acid and/or borate, most preferably boric acid. The preferred borate is sodium borate.
The method of the present invention is generally preferred wherein in the aqueous trivalent chromium plating bath, one or more than one pH buffer compound has a total concentration in the range of 30g/L to 250g/L, preferably in the range of 35g/L to 200g/L, more preferably in the range of 40g/L to 150g/L, even more preferably in the range of 45g/L to 100g/L, most preferably in the range of 50g/L to 75g/L, based on the total volume of the aqueous trivalent chromium plating bath. This applies even more preferably to the boron-containing compound, yet even more preferably to the boric acid together with the borate, most preferably to the boric acid. Most preferably, one or more than one pH buffer compound comprises boric acid, but does not comprise borate. Thus, the method of the present invention is most preferred, wherein the aqueous trivalent chromium plating bath preferably comprises boric acid in a total concentration ranging from 35g/L to 90g/L, preferably from 40g/L to 80g/L, more preferably from 50g/L to 70g/L, most preferably from 56g/L to 66g/L, based on the total volume of the aqueous trivalent chromium plating bath.
However, in some other cases, the aqueous trivalent chromium plating bath does not explicitly include different pH buffer compounds. Conversely, one or more than one complexing agent for the trivalent chromium ions is present in the amount and is selected in such a way that the one or more than one complexing agent not only acts as a complexing agent for the trivalent chromium ions but additionally as a pH buffer compound. In the context of the present invention, this is not preferred, but is possible.
The method of the invention is preferred wherein the aqueous trivalent chromium plating bath is substantially free of ions and/or compounds comprising zinc, preferably free of ions and/or compounds comprising zinc. Preferably, the dark chrome layer is substantially free of zinc, preferably free of zinc.
The method of the invention is preferred wherein the aqueous trivalent chromium plating bath is not a conversion treatment composition. In other words, aqueous trivalent chromium plating baths are not suitable for conversion coating and/or for application on zinc or zinc alloy layers. In other words, the process of the present invention is not a conversion coating process.
The method of the invention is preferred wherein the substrate is substantially free of zinc and zinc alloy layers, preferably free of zinc and zinc alloy layers.
The method of the invention is preferred wherein the aqueous trivalent chromium plating bath is substantially free of fluoride ions, preferably free of fluoride ions. Preferably, the dark chrome layer is substantially free of fluorine, preferably free of fluorine.
The method of the invention is preferred wherein the aqueous trivalent chromium plating bath is substantially free of phosphate anions, preferably free of phosphate anions, more preferably substantially free of phosphorus containing compounds, preferably free of phosphorus containing compounds. Preferably, the dark chrome layer is substantially free of phosphorus, preferably free of phosphorus.
The method of the invention is preferred wherein the aqueous trivalent chromium plating bath is substantially free of sulphite anions, preferably free of sulphite anions.
The method of the invention is preferred wherein the aqueous trivalent chromium plating bath is substantially free of compounds containing chromium having an oxidation number of +6, preferably free of compounds containing chromium having an oxidation number of +6. Thus, the plating bath is substantially free of hexavalent chromium, preferably free of hexavalent chromium. This means in particular that at least hexavalent chromium is not intended to be added to an aqueous trivalent chromium electroplating bath.
In some cases, the method of the invention is preferred wherein the aqueous trivalent chromium plating bath is substantially free of cobalt containing ions and/or compounds, preferably free of cobalt containing ions and/or compounds. Preferably, the dark chrome layer is substantially free of cobalt, preferably free of cobalt. However, in other cases, the method of the invention is preferred wherein the aqueous trivalent chromium plating bath comprises ions and/or compounds containing cobalt. Preferably, the dark chrome layer comprises cobalt. Although cobalt is environmentally questionable, in some cases cobalt provides an additional darkening effect.
The method of the invention is preferred wherein the aqueous trivalent chromium plating bath is substantially free of soluble aluminum compounds (including salts thereof), preferably free of dissolved aluminum ions.
The method of the invention is preferred wherein the aqueous trivalent chromium plating bath is substantially free of nickel ions, preferably free of nickel ions. In some cases, typical Ni contamination of up to 150ppm is observed, which is substantially acceptable and thus considered substantially free of nickel ions. Thus, in some cases, it is preferred that the nickel ions have a concentration in the range of 0ppm to 200ppm, preferably 1ppm to 150ppm, most preferably 2ppm to 100ppm, based on the total weight of the aqueous trivalent chromium plating bath. However, it is most preferred that the aqueous trivalent chromium plating bath be nickel-free. Preferably, the dark chrome layer is substantially free of nickel, preferably free of nickel.
It is generally preferred to avoid environmentally suspected nickel and cobalt species. This generally results in uncomplicated wastewater treatment and bath disposal. In addition, neither nickel nor cobalt is generally required to obtain a dark hue.
The method of the present invention is preferred wherein the aqueous trivalent chromium plating bath is substantially free of sulfamic acid and salts thereof, preferably free of sulfamic acid and salts thereof.
In step (c) of the method of the invention, the substrate is contacted with an aqueous trivalent chromium electroplating bath and an electrical current is applied such that a dark chromium layer is electrodeposited on the substrate.
The process of the invention is preferred, wherein the current in step (c) is preferably at 3A/dm 2 To 30A/dm 2 More preferably 4A/dm 2 To 25A/dm 2 Even more preferably 5A/dm 2 To 20A/dm 2 Most preferably 6A/dm 2 To 18A/dm 2 In the range of (3) direct current.
The process of the invention is preferred, wherein in step (c) at least one anode is utilized. The at least one anode is preferably selected from the group consisting of: graphite anode, noble metal anode, and mixed metal oxide anode (MMO).
Preferred noble 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 method of the present invention is preferred wherein the dark chrome layer electrodeposited in step (c) has a layer thickness in the range of 0.05 μm to 1 μm, preferably 0.1 μm to 0.8 μm, more preferably 0.125 μm to 0.6 μm, most preferably 0.15 μm to 0.5 μm.
The process of the present invention is preferred wherein in step (c) the contacting is carried out for 1 to 20 minutes, preferably 2 to 15 minutes, more preferably 3 to 10 minutes.
The process of the present invention is preferred, wherein in step (c) the contacting is performed at a temperature in the range of 20 ℃ to 60 ℃, preferably 25 ℃ to 52 ℃, more preferably 30 ℃ to 45 ℃.
In step (c) of the method of the present invention, the dark chrome layer is preferably electrodeposited (i.e., it is an electroplated chrome layer) on the substrate at a luminance value L of 60 or less, more preferably 58 or less, even more preferably 56 or less, yet even more preferably 53 or less, most preferably 51 or less, according to L x a x b x color space system.
The method of the present invention is more preferred, wherein in step (c) the L-value of the dark chrome layer is in the range of 45 to 59, preferably 47 to 55, most preferably 49 to 53, according to the L-a-b color system. Most preferably, the dark chrome layer comprises the chemical element aluminum. This means that the colloidal particles are preferably incorporated into the dark chrome layer.
The method of the present invention is preferred, wherein in step (c) the dark chrome layer has an a-value in the range of-0.5 to +3.0, preferably 0 to 2.5, more preferably +0.3 to +2, most preferably +0.5 to 1.5, according to the L-a-b color system.
The method of the present invention is preferred wherein the dark chrome layer has a b-value in the range of +3.1 to +7, preferably 3.5 to 6.5, more preferably +4 to +6, most preferably +4.5 to 5.5, according to the L-a-b color system.
The method of the present invention is preferred, said method further comprising at least one metallization step of depositing at least one metal or metal alloy layer, most preferably at least one nickel plating step of depositing at least one nickel or nickel alloy layer, prior to step (c). In many cases, it is preferable to involve two or even three such metallization steps.
Most preferably, the at least one nickel or nickel alloy 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 method of the invention is more preferred, wherein at least one nickel or nickel alloy layer comprises at least one semi-bright nickel layer, preferably at least one semi-bright nickel layer, in addition to the at least one bright nickel layer and/or the at least one satin nickel layer. The at least one semi-bright nickel layer is preferably optional. Most preferably (if applied) at least one semi-bright nickel layer is deposited before the at least one bright nickel layer and/or the at least one satin nickel layer.
The method of the present invention is also preferred, wherein the at least one nickel or nickel alloy layer comprises at least one MPS nickel layer, preferably at least one MPS nickel layer other than the at least one bright nickel layer and/or the at least one satin nickel layer, most preferably at least one MPS nickel layer other than the at least one bright nickel layer and/or the at least one satin nickel layer, and further other than the at least one semi-bright nickel layer. In the context of the present invention MPS means that the MPS nickel layer contains non-conductive micro-particles, which create micro-pores in the subsequent chromium layer, preferably in the dark chromium layer. The at least one MPS nickel layer is preferably optional.
In some cases, the method of the present invention is preferred, wherein the MPS nickel layer is adjacent to the dark chromium layer.
In other cases, the method of the invention is preferred, wherein the dark chrome layer is adjacent to at least one bright nickel layer and/or at least one satin nickel layer, which in most cases is preferred, most preferably in combination with at least one bright nickel layer.
Preferably, the dark chrome layer is part of a layer stack.
The invention further relates to an aqueous trivalent chromium plating bath comprising
(i) Trivalent chromium ions are used as the ion source,
(ii) One or more complexing agents for said trivalent chromium ions,
(iii) Colloidal particles containing the chemical element aluminum,
(iv) A first sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less, and
(v) Optionally, a second sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less, different from (iv).
Preferably, the foregoing description of the method of the invention, particularly the aqueous trivalent chromium plating bath used in the method of the invention, applies equally to the aqueous trivalent chromium plating bath of the invention, most preferably described as a particularly preferred feature.
The invention further relates to a substrate comprising a dark chrome layer, wherein the dark chrome layer comprises a chemical element aluminum and has an L-value of 60 or less, preferably 58 or less, more preferably 56 or less, even more preferably 53 or less, most preferably 51 or less according to the L-a-b color system, wherein the substrate comprises a plastic substrate.
Preferably, the foregoing description of the method of the invention, in particular of the dark chrome layer obtained by the method of the invention, applies equally to the substrate of the invention, most preferably described as a particularly preferred feature. This most preferably applies to the appearance and composition of the dark chrome layer which was mentioned explicitly or implicitly previously in connection with the method of the invention.
The substrate of the present invention is highly preferred wherein the dark chrome layer comprises the chemical element aluminum and has an L-value in the range of 45 to 59, preferably 47 to 55, most preferably 49 to 53, according to the L-a-b color system.
The substrate of the present invention is particularly preferred wherein the a-value of the dark chrome layer is in the range of-0.5 to +3.0, preferably 0 to 2.5, more preferably +0.3 to +2, most preferably +0.5 to 1.5.
The substrate of the present invention is particularly preferred, wherein the b-value of the dark chrome layer is in the range of +3.1 to +7, preferably 3.5 to 6.5, more preferably +4 to +6, most preferably +4.5 to 5.5.
The substrate of the present invention is most preferred wherein the dark chrome layer is substantially free of cobalt, preferably free of cobalt. In contrast, in other cases, it is preferable that the dark chromium layer contains cobalt.
The substrate of the present invention is most preferred wherein the dark chrome layer is substantially free of nickel, preferably free of nickel.
Preferably, the dark chrome layer is not the only metal layer between the dark chrome layer and the substrate.
The substrate of the present invention is preferred wherein the substrate comprises at least one nickel layer or nickel alloy layer under the dark chrome layer.
The substrate of the present invention is preferred wherein the at least one nickel layer or nickel alloy layer comprises at least one bright nickel layer or at least one satin nickel layer. In many cases, this is most preferred.
The substrate of the present invention is preferred wherein said at least one nickel layer or nickel alloy layer comprises at least one semi-bright nickel layer, preferably at least one semi-bright nickel layer other than 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 optional. Most preferably, at least one semi-bright nickel layer is the nickel layer (of all nickel layers) closest to the substrate.
The substrate of the present invention is preferred wherein the at least one nickel layer or nickel alloy layer comprises at least one MPS nickel layer, preferably at least one MPS nickel layer other than the at least one bright nickel layer and/or the at least one satin nickel layer, most preferably at least one MPS nickel layer other than the at least one bright nickel layer and/or the at least one satin nickel layer, and further other than the at least one semi-bright nickel layer. In the context of the present invention MPS means microwells.
The substrate of the present invention is preferred wherein the at least one MPS nickel layer faces the side where the dark chrome layer is located and faces the other side where the at least one bright nickel layer or the at least one satin nickel layer is located.
The substrate of the present invention is preferred wherein the at least one semi-bright nickel layer is located below the at least one bright nickel layer or the at least one satin nickel layer.
The substrate of the invention is even more preferred, wherein the dark chrome layer is part of a layer stack comprising (adjacent or not adjacent) in the dark chrome layer to substrate direction:
(i) A layer of dark chromium which is to be used as a plating solution,
(ii) Optionally, at least one MPS nickel layer,
(iii) At least one bright nickel layer and/or (preferably or) at least one satin nickel layer, and
(iv) Optionally, at least one semi-bright nickel layer.
The specific features described above in relation to the substrate of the invention are preferably equally applicable to the method of the invention, if not stated otherwise.
In some cases, the layer stack preferably comprises a sealant layer and/or an anti-fingerprint (anti-fingerprint) layer, most preferably on a dark chrome layer. If both are applied, it is preferable to first apply the sealant layer, followed by the anti-fingerprint layer, which preferably forms the very outermost layer.
The spirit of the invention is further illustrated in the following examples without limiting the scope of the invention as defined in the claims herein.
Examples
(a) Providing a substrate:
for the following examples, copper plates (99 mm×70 mm) were used as substrates, mainly to simulate plastic substrates with copper layers deposited.
In a first step, the reaction is carried out by using at Room Temperature (RT)279 (An Meite (Atotech) product), 100g/L was subjected to electrolytic degreasing to clean the substrate. Then, 10% by volume of H 2 SO 4 The copper plate was rinsed by dipping and rinsing with water.
In a second step, the cleaned and rinsed substrate was nickel plated to obtain a bright nickel layer on top of the copper plate (parameters: at 4A/dm 2 Setting for 10min;NF electrolyte; an amett product).
(b) Providing an aqueous trivalent chromium plating bath
The following aqueous trivalent chromium alkaline plating baths were used:
the other ingredients and amounts are summarized in tables 1 and 2 below. In table 1, "E" refers to an example according to the present invention, wherein in table 2, "CE" refers to a comparative example not according to the present invention.
The final pH was about 3.
In all examples according to the invention (i.e. E1 to E11), particle sizes D were used 50 Is an alumina nanoparticle of 25nm (Nanobyk-3603; pick chemical Co., ltd. (BYK-Chemie GmbH)). For the comparative example, no particles at all or SiO having a particle diameter of 20nm was used 2 Nanoparticles (Siemens technologies Co., ltd.; thermoFisher; 43110; at least 40% strength).
(c) Contacting a substrate with said electroplating bath
Electroplating was performed in a hel Cell (Hull Cell) with a graphite anode and a mounting substrate as the cathode. The current of 5A was applied to an aqueous trivalent chromium plating bath maintained for 3 minutes at a temperature of about 35 ℃ for all examples (including comparative examples).
Thus, a corresponding dark chromium layer was deposited on top of the nickel-plated copper plate. Subsequently, the substrate with the dark chrome layer was rinsed with water.
The color according to the L x a x b x color space system was determined by a colorimeter (Konica Minolta) CM-700D spectrophotometer. Calibration was performed by black and white standards. Color determination is made at a region in the center of the substrate. The measurement area was placed 1cm from the left edge and 2cm from the lower edge (left edge directed toward the anode).
Table 1: summary of the compositions and results according to the invention
Numbering device Al-nanoparticles [ g/L ]] Fe(II)[mmol/L] Methionine [ g/L ]] L*；a*；b*
E1 1 2 30** 49.9；+1.0；+5.6
E2 1.7 2 30** 49.5；+0.9；+5.6
E3 2.3 2 30** 48.9；+0.9；+5.7
E4 1 2 25 56.0；+0.3；+2.6
E5 1.7 2 25 55.3；+0.4；+2.9
E6 2.3 2 25 55.2；+0.3；+3.1
E7 1 4 25 57.6；+0.1；+1.9
E8 1.7 4 25 56.6；+0.2；+2.3
E9 2.3 4 25 55.7；+0.3；+2.8
E10 1 4 43* 53.9；+0.5；+4.0
E11 2.3 4 43* 52.1；+0.7；+4.7
* Additionally contains about up to 20g/L of ethylene glycol
* Additionally contains about up to 20g/L of thioglycol and thiocyanate anions
Table 2: summary of the compositions and results of the comparative examples
Numbering device SiO 2 Nanoparticles [ ml/L ] ] Fe(II)[mmol/L] Methionine [ g/L ]] L*；a*；b*
CE1 0 2 30** 55.8；+0.4；+3.2
CE2 2 2 30** 55.2；+0.4；+3.3
CE3 3 2 30** 55.3；+0.4；+3.3
CE4 4 2 30** 56.2；+0.4；+3.2
CE5 0 2 25 61.7；-0.3；0
CE6 0 4 25 61.6；-0.1；+0.4
CE7 0 4 43* 58.9；+0.2；+1.3
* Additionally contains about up to 20g/L of ethylene glycol
* Additionally contains about up to 20g/L of thioglycol and thiocyanate anions
Comparative examples CE1 and CE5 to CE7 show the condition of not having any particles but containing only an organic colorant such as methionine. Interestingly, the presence of silica nanoparticles did not significantly reduce the L-value (compare CE1 with CE2 to CE 4); at least not for methionine containing electroplating baths. In these cases, the value of L remains substantially 55. Nevertheless, all the chromium layers obtained are already dark.
However, after addition of colloidal particles containing chemical element aluminum, especially alumina nanoparticles, a significant further reduction in L x value (i.e. further darkening) was observed. In detail: CE1 (L55.8) = > E1 to E3 (L48.9 to 49.9; at least about 10% reduction); CE5 (L61.7) = > E4 to E6 (L55.2 to 56.0; at least about 9% reduction); CE6 (L61.6) = > E7 to E9 (L55.7 to 57.6; at least about 6% reduction); and CE7 (L58.9) = > E10 and E11 (L52.1 to 53.9; at least about 8% reduction).
In each case, i.e., in each comparative example and its corresponding inventive example, the L-x value is reduced by between about 6% and 10%.
As also shown in tables 1 and 2, in all examples, the a values remain substantially constant. However, the addition of colloidal particles containing the chemical element aluminum significantly affects the b-value, which increases substantially all the time. In detail: CE1 (b+3.2) = > E1 to E3 (b+about+5.6); CE5 (b x 0) = > E4 to E6 (b x+2.6 to +3.1); CE6 (b+0.4) = > E7 to E9 (b+1.9 to +2.8); and CE7 (b+1.3) = > E10 and E11 (b+4.0 to +4.7). Thus, in the case of colloidal particles containing the chemical element aluminum, a warmer light brown hue is obtained.
The dark chrome layer obtained by the present invention is glossy.

Claims (15)

1. A method of electrodepositing a dark chrome layer on a substrate, the method comprising the steps of
(a) Providing the substrate, wherein the substrate comprises a plastic substrate,
(b) Providing an aqueous trivalent chromium plating bath comprising
(i) Trivalent chromium ions are used as the ion source,
(ii) One or more complexing agents for said trivalent chromium ions,
(iii) Colloidal particles containing the chemical element aluminum,
(iv) A first sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less, and
(v) Optionally, a second sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less, which is different from (iv),
(c) The substrate is contacted with the electroplating bath and a current is applied such that the dark chromium layer is electrodeposited on the substrate.
2. The method according to claim 1, wherein the aqueous trivalent chromium plating bath is a colloidal suspension, preferably a sol.
3. A method according to claim 1 or 2, wherein the colloidal particles comprise nanoparticles, preferably nanoparticles.
4. The method of any one of the preceding claims, wherein the colloidal particles have an average particle diameter D by volume 50 Is 100nm or less, preferably 80nm or less, more preferably 60nm or less, even more preferably 50nm or less, most preferably 40nm or less, most preferably 30nm or less, even most preferably 25nm or less.
5. The method according to any one of the preceding claims, wherein the colloidal particles comprise at least particles having a particle size of 100nm or less, preferably 80nm or less, more preferably 60nm or less, even more preferably 50nm or less, most preferably 40nm or less, very most preferably 30nm or less, even most preferably 20nm or less.
6. The method according to any one of the preceding claims, wherein the colloidal particles are present in a total amount in the range of 0.05g/L to 15g/L, preferably 0.1g/L to 12g/L, more preferably 0.5g/L to 10g/L, even more preferably 1.0g/L to 8g/L, most preferably 1.5g/L to 6g/L, even most preferably 1.9g/L to 4g/L, based on the total volume of the aqueous trivalent chromium plating bath.
7. The method of any one of the preceding claims, wherein the colloidal particles comprise alumina.
8. The method of any one of the preceding claims, wherein the colloidal particles comprise Al 2 O 3 Preferably substantially of Al 2 O 3 Composition is prepared.
9. The method according to any one of the preceding claims, wherein the first sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less comprises a nitrogen atom, more preferably an amino group, most preferably an amino acid.
10. The method of any one of the preceding claims, wherein the first sulfur-containing compound comprises methionine.
11. The method of any one of the preceding claims, wherein the second sulfur-containing compound comprises an inorganic sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less, preferably comprises a thiocyanate anion.
12. An aqueous trivalent chromium plating bath comprising
(i) Trivalent chromium ions are used as the ion source,
(ii) One or more complexing agents for said trivalent chromium ions,
(iii) Colloidal particles containing the chemical element aluminum,
(iv) A first sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less, and
(v) Optionally, a second sulfur-containing compound having a sulfur atom with an oxidation number of +5 or less, different from (iv).
13. A substrate comprising a dark chrome layer, wherein the dark chrome layer comprises a chemical element aluminum and has an L value of 60 or less, preferably 58 or less, more preferably 56 or less, even more preferably 53 or less, most preferably 51 or less according to an L.a.b color system,
Wherein the substrate comprises a plastic substrate.
14. A substrate according to claim 13, wherein the a-x value of the dark chrome layer is in the range of-0.5 to +3.0, preferably 0 to 2.5, more preferably +0.3 to +2, most preferably +0.5 to 1.5.
15. A substrate according to claim 14, wherein the dark chrome layer has a b-x value in the range of +3.1 to +7, preferably 3.5 to 6.5, more preferably +4 to +6, most preferably +4.5 to 5.5.
CN202280040771.6A 2021-06-10 2022-06-08 Method of electrodepositing a dark chromium layer, substrate comprising the same, and electroplating bath therefor Pending CN117425751A (en)

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