KR20220116477A - Electroplating compositions and methods for depositing chromium coatings on substrates - Google Patents

Abstract

The present invention provides an electroplating composition for forming a chromium coating on a substrate,
(i) a trivalent chromium ion,
(ii) at least one complexing agent for the trivalent chromium ion, and
(iii) at least one additive selected from the group consisting of betaines, polymeric glycols, monomeric diols, and mixtures thereof
It relates to an electroplating composition comprising a.

Description

Electroplating compositions and methods for depositing chromium coatings on substrates

The present invention relates to an electroplating composition and method for depositing a chromium coating on a substrate. In particular, the electroplating composition according to the invention enables the electrolytic deposition of functional chromium coatings, also called hard chromium coatings, on substrates, in particular iron substrates, in particular nickel or nickel alloy coated iron substrates.

Functional chromium coatings generally have a much higher average coating thickness, typically at least 1 μm to several hundreds of micrometers, and are characterized by good hardness and abrasion resistance compared to decorative chromium coatings, which are typically less than 1 μm.

Functional chromium coatings obtained from chromium electroplating compositions containing hexavalent chromium are known and well established standards in the prior art.

In recent decades, hexavalent chromium-based methods are increasingly being replaced by trivalent chromium-based methods, which are much more healthful and environmentally friendly.

A typical chromium-based electroplating method is described in the following prior art.

WO 2015/110627 A1 relates to an electroplating composition for depositing chromium and a method for depositing chromium on a substrate using the electroplating composition.

US 2,748,069 relates to an electroplating solution of chromium, which makes it possible to obtain chromium coatings of very good physical and mechanical properties very quickly. The chrome plating solution can be used in special electrolytic methods such as spot or plugging or penciling electroforming methods. In this particular method, the substrate is typically not immersed in the respective electroplating solution.

WO 2018/185154 A1 discloses a method for the electrolytic deposition of a chromium or chromium alloy coating on a substrate.

US 4,009,085 discloses a lubricating composition and a method for treating metal sheets to impart lubricity and wear resistance thereto.

US 3,432,408 A relates to the prevention of mists and sprays in acidic hexavalent electroplating baths.

US 2016/068983 A1 refers to a method and a plating bath for electrodeposition of a dark chromium layer on a workpiece, the bath comprising for example a diol.

EP 0 100 133 A1 refers to zinc and nickel tolerant trivalent chromium plating baths and plating processes using, for example, betaine.

CN 108034969 A refers to sulphate-based trivalent chromium electroplating baths comprising, for example, diols or polyethylene glycols.

US 2018/245227 A1 relates to the use of ionic liquids in electroplating, and in particular for electroplating thick hard chromium from trivalent salts.

However, when using the trivalent chromium-based method for electroplating according to the prior art, the observed cathode current efficiencies (CCE) are typically higher compared to the cathode current efficiencies observed when using the hexavalent chromium-based method for electroplating. small.

Cathode Current Efficiency (CCE) is based on Faraday's Law, and when all, i.e. 100%, of the metal present in the electroplating composition can be deposited on the substrate, in theory compared to the ideal case, the It is described as the percentage of metal actually deposited on the A typical CCE in a hexavalent chromium-based process for electroplating according to the prior art is between 20% and 25%, whereas a typical CCE in a trivalent chromium-based process for electroplating according to the prior art can be as low as 10%.

An important factor that can influence CCE in trivalent chromium-based methods for electroplating is the type and concentration of complexing agents used to stabilize trivalent chromium ions, particularly in electroplating compositions. Another factor that can affect CCE in trivalent chromium-based methods for electroplating is the type and concentration of additional additives that may be added to the electroplating composition, in particular.

Accordingly, a first object of the present invention is an electroplating composition comprising trivalent chromium ions and a respective method for depositing a chromium coating on a substrate having improved coating quality (such as, for example, hardness and/or abrasion resistance). was to provide

Accordingly, a second object of the present invention was to provide an electroplating composition comprising trivalent chromium ions and a respective method for depositing a chromium coating on a substrate resulting in increased cathode current efficiency (CCE).

Summary of the Invention

The above-mentioned object is solved by an electroplating composition for depositing a chromium coating on a substrate according to a first aspect, the composition comprising:

(i) a trivalent chromium ion,

(ii) at least one complexing agent for the trivalent chromium ion, and

(iii) at least one additive selected from the group consisting of betaines, polymeric glycols, monomeric diols, and mixtures thereof

includes

By using at least one complexing agent for trivalent chromium ions, particularly effective stabilization of trivalent chromium ions in the electroplating composition can be achieved, which enables effective deposition of a chromium coating on the substrate during electroplating.

Surprisingly, with at least one additive selected from the group consisting of betaines, polymeric glycols, monomeric diols and mixtures thereof, a significant increase in cathode current efficiency (CCE) is observed during electroplating, while on the other hand It has been found that a high quality coating is obtained.

The above-mentioned object is solved by a method for depositing a chromium coating on a substrate according to a second aspect, the method comprising the steps of:

(a) providing a substrate;

(b) providing an electroplating composition for depositing a chromium coating on a substrate, the composition comprising:

(i) a trivalent chromium ion,

(ii) at least one complexing agent for the trivalent chromium ion, and

(iii) at least one additive selected from the group consisting of betaines, polymeric glycols, monomeric diols, and mixtures thereof

Providing the electroplating composition comprising,

(c) contacting the substrate with the electroplating composition and applying an electric current such that a chromium coating is deposited on at least one surface of the substrate;

includes

By having in the electroplating composition at least one additive as defined above, a relatively high cathode current efficiency (CCE) is obtained during step (c).

The above-mentioned object is solved by a substrate having a surface according to a third aspect, wherein the surface of the substrate comprises a chromium coating obtained by a film forming method according to the second aspect.

The above-mentioned object is selected from the group consisting of betaines, polymeric glycols, monomeric diols and mixtures thereof for increasing the cathode current efficiency in an electroplating composition for depositing a chromium coating on a substrate according to the fourth aspect is solved by the use of at least one additive.

Brief description of the table

In Table 1, with respect to the resulting cathode current efficiency (CCE), the amount of the different additives in each electroplating composition, expressed as the total amount of additive in g/L, based on the total volume of each electroplating composition. Correlations between the various concentrations are shown. Each bar (C1) to (18) represents a specific electroplating composition. Further details are given in the "Examples" section of the specification below.

DETAILED DESCRIPTION OF THE INVENTION

In the context of the present invention, the terms “at least one” or “one or more” mean (and are interchangeable with) “one, two, three or more” and “one, two, three or more than three” respectively. In addition, "trivalent chromium" denotes chromium having an oxidation number of +3. The term “trivalent chromium ion” refers to Cr ³⁺ ions in free or complexed form. In addition, "hexavalent chromium" denotes chromium having an oxidation number of +6.

The term C _x -C _y when used in the context of the present invention denotes a compound comprising the total number of "x" carbon atoms to "y" carbon atoms. For example, the term C ₁ -C ₂₅ diol denotes a diol comprising a total number from 1 carbon atom to 25 carbon atoms.

The cathode current efficiency (CCE) is determined as described in the specification above and is based on gravimetric analysis (see examples in the specification below).

The electroplating composition of the present invention comprises at least one additive selected from the group consisting of betaine, polymeric glycol, monomeric diol, and mixtures thereof.

In rare cases, an electroplating composition of the present invention is preferred, provided that the at least one additive does not comprise a polymeric glycol. Preferably, the electroplating composition is substantially free or free of polyethylene glycol, more preferably substantially free or free of polyalkylene glycol, and most preferably substantially free of polymeric glycol. or does not include In such a case, the electroplating composition of the present invention preferably comprises at least one additive selected from the group consisting of betaines, monomeric diols, and mixtures thereof.

In very rare cases, an electroplating composition of the present invention is preferred, provided that the at least one additive does not comprise a monomeric diol. Preferably, the electroplating composition is substantially free or free of ethanediol, more preferably substantially free or free of alkanediol, even more preferably substantially free or free of monomeric diol do not include. In such a case, the electroplating composition of the present invention preferably comprises at least one additive selected from the group consisting of betaines, polymeric glycols, and mixtures thereof.

In the electroplating composition of the present invention, hexavalent chromium is not intentionally added to the electroplating composition. Accordingly, the electroplating composition is substantially free or free of hexavalent chromium (except in very small amounts which may form anodic).

Preferably, the electroplating composition of the present invention is an aqueous electroplating composition comprising trivalent chromium ions. Preferably, the electroplating composition comprises further additives and/or metal ions, more preferably iron ions, nickel ions, copper ions and/or zinc ions.

In the context of the present invention, chromium coatings include chromium alloys, ie coatings comprising not only chromium but also alloying elements. In very rare cases, metal alloying elements are preferred, preferably from metal ions as mentioned above. More typical and preferred are non-metal alloying elements, preferably carbon, nitrogen and/or oxygen.

The electroplating composition of the present invention is preferably used more than once to deposit a chromium coating on a plurality of different substrates, preferably during a continuous process. Preferably, the electroplating composition uses during electroplating, preferably at least 100 Ah per liter of electroplating composition, preferably at least 150 Ah per liter, more preferably at least 200 Ah per liter, most preferably at least 300 Ah per liter for it is used repeatedly.

Basically, preference is given to the electroplating composition of the present invention, wherein the betaine comprises at least 5 carbon atoms, more preferably at least 10 carbon atoms, and even more preferably at least 15 carbon atoms. It is preferred not to have more than 50 carbon atoms.

The electroplating composition preferably comprises at least one or more than one betaine, preferably independently comprising at least 5 carbon atoms, more preferably at least 10 carbon atoms, and even more preferably at least 15 carbon atoms. , the electroplating composition of the present invention is preferred. It is preferred not to have more than 50 carbon atoms.

More preferred are the electroplating compositions of the present invention, wherein the electroplating composition comprises at least one or more than one betaine independently comprising at least 10 carbon atoms, preferably at least 15 carbon atoms. It is preferred not to have more than 50 carbon atoms.

This all states that among the selection from betaines, polymeric glycols, monomeric diols, and mixtures thereof, the electroplating composition of the present invention preferably comprises at least betaines having the number of carbon atoms as defined above. it means.

Preferred are the electroplating compositions of the present invention, wherein the betaine independently comprises (or wherein the betaine represents at least the following):

- a positively charged quaternary nitrogen atom, and

- negatively charged sulfonate groups and/or negatively charged carboxylate groups,

However, positive charges cannot be removed by deprotonation.

Preferred are the electroplating compositions of the present invention, wherein the betaine has a neutral net charge.

Preferred are the electroplating compositions of the present invention, wherein the betaine is a linear betaine.

Preferred are the electroplating compositions of the present invention, wherein the betaine does not contain an aromatic ring structure, and preferably does not contain a ring structure.

The positively charged quaternary nitrogen atom has a substituent such that the positive charge is generated, provided that the substituent is not hydrogen, and the electroplating composition of the present invention is preferred. Preferably, the substituents are independently selected from the group consisting of alkyl, ester and amide.

Preferably, alkyl includes C ₁ -C ₂₀ alkyl, more preferably C ₁ -C ₁₇ alkyl, most preferably C ₁ -C ₁₅ alkyl.

Preferably, the ester comprises a C ₈ -C ₂₀ ester, more preferably a C ₉ -C ₁₇ ester, most preferably a C ₁₀ -C ₁₆ ester.

Preferably, the ester comprises a fatty acid ester, most preferably having the number of carbon atoms as defined above.

Preferably, the amides include C ₈ -C ₂₀ amides, more preferably C ₉ -C ₁₇ amides, most preferably C ₁₀ -C ₁₆ amides.

Preferably, the amide comprises a fatty acid amide, most preferably having the number of carbon atoms as defined above for the amide.

Most preferably, at least one, preferably two substituents are preferably alkyl as defined above, most preferably C ₁ -C ₅ alkyl, even more preferably C ₁ -C ₃ alkyl , also the at least one substituent is preferably an ester as defined above, or preferably an amide as defined above.

Preferred are the electroplating compositions of the present invention, wherein the betaine independently comprises a positively charged quaternary nitrogen atom and a negatively charged sulfonate group, provided that the positive charge cannot be removed by deprotonation.

The electroplating composition of the present invention wherein the betaine is selected from the group consisting of N-substituted-ammonium sulfobetaine and N-substituted-ammonium carboxybetaine is preferred.

The invention, wherein the betaine is selected from the group consisting of N-substituted-N,N-dialkyl-ammonium sulfobetaines, preferably N-substituted-N,N-dialkyl-N-alkyl ammonium sulfobetaines. The electroplating composition of

N-substituted-N,N-dialkyl-ammonium sulfobetaine and N-substituted-N,N-dialkyl-N-alkyl ammonium sulfobetaine are each selected from the group consisting of alkyl, and amidoalkyl Preference is given to the electroplating composition of the present invention, which is N-substituted with a substituent, wherein amidoalkyl is preferably cocoamidopropyl.

Betaine is N,N-dimethyl-N-(3-cocoamidopropyl)-N-(2-hydroxy-3-sulfopropyl) ammonium betaine, N-dodecyl-N,N-dimethyl-3-ammonio -1-propanesulfonate, N-octyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N-decyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N -tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N-octadecyl-N, Preferred are the electroplating compositions of the present invention comprising at least one of N-dimethyl-3-ammonio-1-propanesulfonate, and N,N-dimethyl-N-dodecylglycine betaine.

By selecting the preferred betaine, a particularly advantageous cathode current efficiency (CCE) is achieved, preferably with foam formation for mist suppression during electroplating. Advantageously, the concentration of betaine may be relatively low (see examples).

With regard to the at least one additive, preference is given to the electroplating composition of the present invention, in which in some cases the electroplating composition comprises at least one betaine and preferably further one or more of polymeric glycols and/or monomeric diols. .

Particular preference is given to the electroplating composition of the present invention, wherein the electroplating composition comprises at least one betaine and further at least one monomeric diol.

The electroplating composition has a total concentration of 0.0005 g/L to 1 g/L, preferably 0.001 g/L to 0.5 g/L, more preferably 0.005 g/L to 0.3 g, based on the total volume of the electroplating composition. Preference is given to electroplating compositions of the present invention comprising /L, and most preferably betaine in the range of 0.01 g/L to 0.2 g/L.

Preference is given to the electroplating composition of the invention, wherein the polymeric glycol is a polyalkylene glycol, preferably a polyethylene glycol: Preferably, the polyalkylene glycol, preferably polyethylene glycol, is from 150 Da to 5000 Da, preferably It has an average molecular weight ranging from 200 Da to 2500 Da. Most preferred are polymeric glycols selected from the group consisting of polyethylene glycol 200, polyethylene glycol 600, and polyethylene glycol 1500.

The electroplating composition has a total concentration of 0.01 g/L to 50 g/L, preferably 0.05 g/L to 35 g/L, more preferably 0.1 g/L to 20 g, based on the total volume of the electroplating composition. Preference is given to the electroplating composition of the present invention, comprising a polymeric glycol /L, most preferably in the range from 0.15 g/L to 25 g/L.

In addition, a beneficial increase in the cathode current efficiency (CCE) is obtained when using polymeric glycols as representative of at least one additive.

The monomeric diol is a C ₁ -C ₂₅ diol, preferably a C ₂ -C ₂₃ diol, more preferably a C ₂ -C ₂₁ diol, even more preferably a C ₂ -C ₁₉ diol, most preferably a C ₂ -C ₁₈ diol. Phosphorus, the electroplating composition of the present invention is preferred.

In some cases, the monomeric diol is at least one C ₁ -C ₁₀ diol, preferably at least one C ₂ -C ₈ diol, more preferably at least one C ₂ -C ₆ diol, even more preferably at least one C ₂ -C ₅ diols, most preferably at least one C ₂ -C ₄ diol, more preferably the monomeric diol comprises 1,2-propane diol and/or 1,3-propane diol The composition is preferred. Most preferably in combination with one or more betaines.

In some cases, the monomeric diol is in addition to C ₁ -C ₁₀ diols and preferred variations thereof, or alternatively, preferably in addition to C ₁ -C ₁₀ diols and preferred variations thereof, at least one C ₁₁ - C ₂₅ diol, preferably at least one C ₁₂ -C ₂₃ diol, more preferably at least one C ₁₃ -C ₂₁ diol, even more preferably at least one C ₁₄ -C ₂₀ diol, most preferably at least one C Preference is given to the electroplating composition of the present invention, comprising a ₁₅ -C ₁₉ diol, more preferably at least one C ₁₆ -C ₁₈ diol, most preferably in combination with at least one betaine.

Preference is given to the electroplating composition of the present invention, wherein at least one C ₁₁ -C ₂₅ diol, and preferred variants thereof, is selected from the group of saturated and unsaturated C ₁₁ -C ₂₅ diols, preferably saturated C ₁₁ -C ₂₅ diols.

Preferred are the electroplating compositions of the present invention, wherein at least one C ₁₁ -C ₂₅ diol, and a preferred variant thereof, is branched.

Preference is given to the electroplating compositions of the present invention, wherein at least one C ₁₁ -C ₂₅ diol, and preferred variants thereof, comprise 1, 2 or more than 2 iso-propyl moieties.

Preference is given to the electroplating compositions of the present invention, wherein at least one C ₁₁ -C ₂₅ diol, and a preferred variant thereof, comprises an antifoam compound. In many cases, these C ₁₁ -C ₂₅ diols have the potential to function as antifoam compounds. Also, in many cases C ₁ to C ₁₀ diols are often good solvents for the aforementioned antifoam compounds.

The electroplating composition has a total concentration of 0.001 g/L to 60 g/L, preferably 0.1 g/L to 50 g/L, more preferably 1.0 g/L to 40 g, based on the total volume of the electroplating composition. Preference is given to the electroplating compositions of the present invention, comprising monomeric diols/L, even more preferably in the range from 5.0 g/L to 35 g/L and most preferably from 15 g/L to 30 g/L.

In some specific cases, the electroplating composition has a total concentration based on the total volume of the electroplating composition of 0.001 g/L to 10 g/L, preferably 0.01 g/L to 8.0 g/L, more preferably 0.1 the above-described invention comprising monomeric diols ranging from g/L to 6.0 g/L, even more preferably from 0.5 g/L to 4.0 g/L, most preferably from 1.0 g/L to 3.0 g/L. A plating composition is preferred. This most preferred option is preferably, when the electroplating composition of the present invention comprises at least one betaine, most preferably the electroplating composition of the present invention comprises at least one betaine and at least one C ₁₁ -C ₂₅ diol and its It applies if it contains the desired modifications.

Electroplating compositions of the present invention are preferred, wherein the electroplating compositions are substantially free or free of hexavalent chromium ions.

The electroplating composition has a total concentration, based on the total volume of the electroplating composition, of 10 g/L to 30 g/L, preferably 14 g/L to 27 g/L, and most preferably 17 g/L to The electroplating composition of the present invention comprising 24 g/L of trivalent chromium ions is preferred.

With a preferred choice of the concentration range of trivalent chromium ions in the electroplating composition, a particularly effective deposition of a chromium coating on a substrate can be achieved. When the total amount of trivalent chromium ions is significantly less than 10 g/L, insufficient film formation is observed in many cases, and the deposited chromium is generally of low quality. If the total amount significantly exceeds 30 g/L, the electroplating composition is no longer stable, which includes the formation of undesirable deposits.

At least one complexing agent for the trivalent chromium ion is an organic complexing agent and salts thereof, preferably carboxylic acids and salts thereof, more preferably aliphatic carboxylic acids and salts thereof, most preferably aliphatic mono-carboxylic acids and salts thereof, the electroplating composition of the present invention is preferred. Preferred aliphatic mono-carboxylic acids and salts thereof are C ₁ -C ₁₀ aliphatic mono-carboxylic acids and salts thereof, preferably C ₁ -C ₈ aliphatic mono-carboxylic acids and salts thereof, more preferably C ₁ -C ₆ aliphatic mono-carboxylic acids and salts thereof, most preferably C ₁ -C ₃ aliphatic mono-carboxylic acids and salts thereof.

The electroplating composition has a total concentration of 50 g/L to 350 g/L, preferably 100 g/L to 300 g/L, even more preferably 150 g/L to 250 g, based on the total volume of the composition. Preference is given to the electroplating composition of the present invention, comprising at least one complexing agent which is /L.

In particular, by using the preferred selection of the complexing agent mentioned above, the trivalent chromium ion can be efficiently stabilized in the electroplating composition by the complexing agent.

The electroplating composition of the present invention preferably has a pH of 4.1 to 7.0, preferably 4.5 to 6.5, more preferably 5.0 to 6.0, and most preferably 5.3 to 5.9.

The preferred acidic pH range is particularly advantageous for effectively depositing chromium coatings on substrates of the desired quality.

Particular preference is given to the electroplating composition of the present invention, wherein the electroplating composition comprises at least one betaine and at least one monomeric diol.

provided that the at least one monomeric diol includes at least one C ₁₁ -C ₂₅ diol comprising one, two or more than two isopropyl moieties.

Even more preferred are the electroplating compositions of the present invention, wherein the electroplating composition comprises at least one betaine and at least one monomeric diol.

only,

- at least one of the more than one monomeric diols comprises at least one C ₁₁ -C ₂₅ diol comprising one, two or more than two iso-propyl moieties (or another preferred diol among the aforementioned C ₁₁ -C ₂₅ diols) ), including

- at least one of the more than one monomeric diol comprises at least one C ₂ -C ₈ diol (or another preferred diol among the C ₂ -C ₈ diols mentioned above).

Electroplating compositions of the present invention are preferred, wherein the electroplating composition is substantially free or free of boric acid, preferably substantially free or free of boron-containing compounds.

Boron containing compounds are undesirable because they are environmentally problematic. When using boron-containing compounds, wastewater treatment is expensive and time consuming. In addition, boric acid is usually poorly soluble and tends to form precipitates. These precipitates can solubilize upon heating, but during this time the respective electroplating composition cannot be utilized for electroplating. Such deposits pose a significant risk of promoting deterioration of the chrome coating. Accordingly, the electroplating composition of the present invention is preferably substantially free or free of boron-containing compounds. Surprisingly, the electroplating compositions of the present invention perform very well without boron-containing compounds, especially in the preferred pH ranges mentioned above.

The present invention, wherein the electroplating composition is substantially free or free of organic compounds containing divalent sulfur, preferably substantially free or free of sulfur containing compounds having sulfur atoms having an oxidation number lower than +6. The electroplating compositions of the invention are preferred.

Omitting divalent sulfur-containing organic compounds from the electroplating composition is particularly advantageous when using the electroplating composition for the deposition of hard functional chromium coatings.

The term "free" typically means that the respective compound and/or component is not intentionally added to, for example, an electroplating composition. This does not preclude such compounds being introduced as impurities in other chemicals. However, typically the total amount of such compounds and components is below the detection range and is therefore not critical in various aspects of the present invention.

An electroplating composition further comprising at least one compound selected from the group consisting of

- at least one type of halogen ion, preferably bromide,

- at least one type of alkali metal cation, preferably sodium and/or potassium,

- sulfate ions, and

- Ammonium ions.

By adding one or more of the compounds mentioned above, the deposition of chromium can be improved during the electroplating process, most preferably during the process of the present invention.

Preferably, the electroplating composition of the present invention is one in a concentration of at least 0.06 mol/L, more preferably at least 0.1 mol/L, even more preferably at least 0.15 mol/L, based on the total volume of the electroplating composition. more than one type of halogen ion, preferably bromide. In particular, the bromide anion effectively inhibits the formation of hexavalent chromium species at at least one anode.

Preferably, the electroplating composition is from 0 mol/L to 0.5 mol/L, more preferably from 0 mol/L to 0.3 mol/L, even more preferably from 0 mol/L, based on the total volume of the electroplating composition. one or more types of alkali metal cations, preferably sodium and/or potassium, in a total concentration of from 0 mol/L to 0.08 mol/L, and most preferably from 0 mol/L to 0.08 mol/L.

Typically, rubidium, francium and cesium ions are not utilized in electroplating compositions comprising trivalent chromium ions. Accordingly, preferably the one or more types of alkali metal cations include metal cations of lithium, sodium and potassium, usually sodium and potassium.

Preferred are the electroplating compositions of the present invention, wherein the trivalent chromium ions of the electroplating composition are obtained from a soluble trivalent chromium ion-containing source, typically a water-soluble salt comprising said trivalent chromium ions. Preferably, the source containing soluble trivalent chromium ions comprises a total amount of alkali metal cations of up to 1% by weight, based on the total weight of said source. In some cases, preferably, this source is utilized to replenish trivalent chromium ions when the method is operated continuously. Preferred water-soluble salts comprising trivalent chromium ions are alkali metal-free trivalent chromium sulfate or alkali metal-free trivalent chromium chloride. In some cases, it is preferred that the electroplating compositions of the present invention contain sulfate ions, preferably in a total amount ranging from 50 g/L to 250 g/L, based on the total volume of the electroplating composition.

Preferably, the soluble trivalent chromium ion containing source is or comprises chromium sulfate, more preferably acidic chromium sulfate, even more preferably chromium sulfate having the general formula Cr ₂ (SO ₄ ) ₃ and a molecular weight of 392 g/mol. do.

More preferably, for replenishment, a source containing soluble trivalent chromium ions is preferred, wherein the anion is an organic anion, preferably an organic acid anion, most preferably formate and/or acetate.

The invention according to a second aspect provides a method for depositing a chromium coating on a substrate, the method comprising the steps of:

(a) providing a substrate;

(b) providing an electroplating composition (preferably as described above, most preferably as described as preferred) for depositing a chromium coating on a substrate, said composition comprising:

(i) a trivalent chromium ion,

(ii) at least one complexing agent for the trivalent chromium ion, and

(iii) at least one additive selected from the group consisting of betaines, polymeric glycols, monomeric diols, and mixtures thereof

A step of providing the electroplating composition comprising a.

(c) contacting the substrate with the electroplating composition and applying an electric current such that a chromium coating is deposited on at least one surface of the substrate;

includes

Preferably, what has been said above with respect to the electroplating composition of the invention (preferably as described above as preferred) also applies to the method of the invention (preferably as described below as preferred) as well.

In step (c) the current is direct current, the method of the present invention is preferred

Preferably, the direct current (DC) is an uninterrupted direct current during electroplating, more preferably the direct current is not pulsed (non-pulsed DC). Moreover, the direct current preferably contains no reverse pulses.

In step (c) the current is at least 18 A/dm ² , preferably at least 20 A/dm ² , more preferably at least 25 A/dm ² , even more preferably at least 30 A/dm ² , most preferably at least 39 A Preference is given to the process of the invention, with a cathode current density of /dm ² . Preferably, the cathode current density is between 18 A/dm ² and 60 A/dm ² , more preferably between 25 A/dm ² and 55 A/dm ² , most preferably between 30 A/dm ² and 50 A/dm is the range of ² .

Typically, the substrate provided during the method of the present invention is the cathode during the electroplating process (ie in step (c)). Preferably, more than one substrate is provided simultaneously in step (c) of the process of the invention.

Preference is given to the process of the invention, wherein in step (c) at least one anode is provided, wherein the at least one anode is independently selected from the group consisting of graphite anode and mixed metal oxides on titanium anode. Such anodes have been shown to be sufficiently resistant in the electroplating compositions of the present invention. Preferably, the at least one anode does not contain lead or chromium.

In step (c) of the process of the invention the chromium coating is deposited as pure or as an alloy. Preferably, the chrome coating is an alloy. Preferred alloying elements are carbon, nitrogen and oxygen, preferably carbon and oxygen. Carbon is typically present due to organic compounds normally present in the electroplating composition. In many cases, the process of the invention is preferred, wherein the chromium coating does not comprise one, more than one or all elements selected from the group consisting of sulfur, nickel, copper, aluminum, tin and iron. More preferably, the only alloying elements are carbon, nitrogen and/or oxygen, more preferably carbon and/or oxygen, most preferably carbon and oxygen. Preferably, the chromium coating contains at least 90% by weight, more preferably at least 95% by weight of chromium, based on the total weight of the chromium coating.

wherein the electroplating composition in step (c) has a temperature in the range from 20°C to 90°C, preferably from 30°C to 70°C, more preferably from 40°C to 60°C, most preferably from 45°C to 58°C; The method of the invention is preferred.

In the preferred temperature range (in particular the most preferred temperature range) the chromium coating is optimally deposited in step (c). If the temperature significantly exceeds 90° C., undesirable vaporization may occur, which may negatively affect the concentration of the composition components. Moreover, undesirable anode formation of hexavalent chromium is significantly less inhibited. If the temperature is significantly less than 20 DEG C, electrodeposition is insufficient.

Preference is given to the process of the invention, wherein step (c) is carried out for a period in the range from 10 minutes to 100 minutes, preferably from 20 minutes to 90 minutes, more preferably from 30 minutes to 60 minutes.

Preference is given to the process of the invention, in which the electroplating composition in step (c) is stirred, preferably at a stirring speed in the range from 100 rpm to 500 rpm, most preferably from 200 rpm to 400 rpm.

Electrodeposition kinetics particularly advantageous during step (c) by carrying out process step (c) in the above-mentioned preferred temperature range and/or for a (preferably and) preferred period and/or at a (preferably and) preferred stirring rate (electrodeposition kinetics) can be guaranteed.

Preference is given to the process of the present invention further comprising the following steps after step (c):

(d) heat-treating the chrome-coated substrate obtained in step (c).

The heat treatment in step (d) is carried out at a temperature ranging from 100°C to 250°C, preferably from 120°C to 240°C, more preferably from 150°C to 220°C, most preferably from 170°C to 200°C. method is preferred.

Preference is given to the method of the present invention, wherein in step (d), the heat treatment is carried out for a period of 1 hour to 10 hours, preferably 2 hours to 4 hours.

By preferably performing heat treatment of the substrate, more preferably at a desired temperature and/or for a desired period, the properties of the chromium coating can in some cases be further improved (eg hardness).

Preference is given to the process of the present invention, wherein the cathode current efficiency (CCE) in step (c) is at least 11%, preferably at least 12% and most preferably at least 13%. This applies most preferably when the same method is carried out except that the electroplating composition contains no additives.

By significantly increasing the cathode current efficiency (CCE) above 11%, the overall method is more effective and economical. Also, less energy is wasted and less hydrogen gas is produced during step (c).

Preference is given to the method of the present invention, wherein the substrate comprises a metal rod.

The substrate comprises a metal or a metal alloy, preferably at least one metal selected from the group consisting of copper, iron, nickel and aluminum, more preferably at least one metal selected from the group consisting of copper, iron and nickel and most preferably at least iron.

In many cases, a substrate comprising a pre-coating is preferred, the pre-coating preferably being a nickel or nickel alloy coating, most preferably a semi-gloss nickel coating, over which a chromium coating is applied in step (c) of the method of the present invention. ) is applied during Steel substrates precoated with a nickel or nickel alloy coating are particularly preferred. However, preferably other pre-coatings are alternatively or additionally present. In many cases, such pre-coating significantly increases corrosion resistance compared to metal substrates without such pre-coating. However, in some cases the substrate is not susceptible to corrosion due to a corrosion inert environment (eg, in an oil composition). In such a case, a pre-coating, preferably a nickel or nickel alloy pre-coating, is not necessarily required.

In general, the thickness of the chromium coating in step (c) is from 1.1 μm to 500 μm, preferably from 2 μm to 450 μm, more preferably from 4 μm to 400 μm, even more preferably from 6 μm to 350 μm, even more Even more preferably 8 μm to 300 μm, and most preferably 10 μm to 250 μm are preferred.

In some cases, the thickness of the chromium coating in step (c) is at least 0.5 μm, preferably at least 0.75 μm, more preferably at least 0.9 μm, even more preferably at least 1.0 μm, even more preferably at least 1.5 μm. Above, and most preferably at least 2.0 μm, the method of the present invention is preferred. In some further cases, preference is given to the process of the invention, in which, in step (c), the thickness of the chromium coating is at least 15 μm, preferably at least 20 μm.

in step (c) the concentration of at least one additive selected from the group consisting of betaine, polymeric glycol, monomeric diol, and mixtures thereof (preferably at least betaine) is continuously or semi-continuously monitored, The method of the invention is preferred, wherein

- the monitored concentration is compared with a target concentration (preferably of said betaine) of said at least one additive,

- at least one additive (preferably betaine) is added to the electroplating composition if the monitored concentration is lower than the target concentration;

What has been said above with regard to betaine in particular in electroplating compositions applies likewise to the process of the invention.

The present invention according to a third aspect provides a substrate having a surface, wherein the surface of the substrate comprises a chromium coating obtained by the method for forming a film according to the second aspect.

Preferred are the substrates of the present invention, wherein the chrome-coated substrate comprises or is a metal rod.

those mentioned above in relation to the electroplating composition of the invention (preferably the electroplating composition as described as being preferred) and the above-mentioned in relation to the method of the invention (preferably the method for forming a film as described as being preferred) This preferably applies likewise to the substrate of the invention.

In particular, a preferred embodiment of the electroplating composition of the first aspect and a preferred embodiment of the method for forming a film according to the second aspect are also preferred embodiments for the substrate according to the third aspect. This applies particularly and most preferably to the properties of the chromium coating.

The present invention according to a fourth aspect provides at least one selected from the group consisting of betaines, polymeric glycols, monomeric diols and mixtures thereof for increasing the cathode current efficiency in an electroplating composition for depositing a chromium coating on a substrate. The use of one additive is provided.

those mentioned above in relation to the electroplating composition of the invention (preferably the electroplating composition as described as being preferred) and the above-mentioned in relation to the method of the invention (preferably the method for forming a film as described as being preferred) This preferably applies likewise to the use of the present invention.

The invention is illustrated in more detail by the following non-limiting examples.

Example:

For multiple experiments, 10 g/L to 30 g/L trivalent chromium ion (source: basic chromium sulfate), 50 g/L to 250 g/L sulfate ion, at least one organic complexing compound (aliphatic monocarboxyl Each test electroplating composition comprising organic acid), ammonium ion, and bromide ion was prepared (volume: about 850 mL). The composition contained neither boric acid nor boron containing compounds, nor organic compounds containing divalent sulfur. The pH ranged from 5.4 to 5.7.

The reference electroplating composition (C1) contains no additives defining the reference cathode current efficiency (CCE). In a number of further experiments, various additives at different concentrations were tested (see Table 1 below).

In each test, each electroplating composition was electroplated to obtain a chromium coating on a substrate (mild steel rod with a diameter of 10 mm). A graphite anode was used as the anode. Electrodeposition was performed at 40 A/dm ² for 45 minutes at 50° C. under mild stirring.

CCE was determined based on Faraday's law and gravimetric analysis.

Very similar results were obtained for 1,2-propanediol, diethylene glycol and triethylene glycol (data not shown), confirming the results shown in Table 1.

The results in Table 1 show that the tested compounds increase the CCE by 40% compared to the CCE of the reference experiment. In addition, according to Experiments 1 to 12, a relatively high additive concentration is required compared to the additives used in Experiments 13 to 18. Therefore, betaine can significantly increase CCE at relatively low concentrations. In addition, experiments 13 to 18 were observed to exhibit foaming. In a further experiment foaming was performed with an anti-foam compound (tetramethyldecanediol (monomeric C ₁₁ -C ₂₅ diol) containing two isopropyl moieties), solubilized in propylene glycol (monomeric C ₃ diol) prior to addition. was limited by the addition (total amount of diol in the electroplating composition was less than 4.0 g/L).

In a further comparative example and in view of US 3,432,408, the sulfobetaines utilized in experiments 13 and 16 were tested in a hexavalent chromium electroplating composition (55° C., 50 A/dm ² ). The CCE was about 25% without additive and about 25% with 0.04 g/L additive. Therefore, no significant increase in CCE was observed, confirming that the positive effect of increasing CCE was limited to the electroplating composition containing trivalent chromium ions.

Claims (15)

An electroplating composition for depositing a chromium coating on a substrate, comprising:
(i) a trivalent chromium ion,
(ii) at least one complexing agent for the trivalent chromium ion, and
(iii) at least one additive selected from the group consisting of betaines, polymeric glycols, monomeric diols, and mixtures thereof
comprising, an electroplating composition. The method of claim 1,
The electroplating composition comprises at least one or more than one betaine independently comprising at least 10 carbon atoms, preferably at least 15 carbon atoms. 3. The method of claim 1 or 2,
The betaine is independently
- a positively charged quaternary nitrogen atom, and
- comprises negatively charged sulfonate groups and/or negatively charged carboxylate groups,
provided that the positive charge cannot be removed by deprotonation. 4. The method according to any one of claims 1 to 3,
wherein said betaine is selected from the group consisting of N-substituted-N,N-dialkyl-ammonium sulfobetaines, preferably N-substituted-N,N-dialkyl-N-alkyl ammonium sulfobetaines; plating composition. 5. The method according to any one of claims 1 to 4,
The betaine is N,N-dimethyl-N-(3-cocoamidopropyl)-N-(2-hydroxy-3-sulfopropyl) ammonium betaine, N-dodecyl-N,N-dimethyl-3-ammonium o-1-propanesulfonate, N-octyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N-decyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, N-octadecyl-N An electroplating composition comprising at least one of ,N-dimethyl-3-ammonio-1-propanesulfonate, and N,N-dimethyl-N-dodecylglycine betaine. 6. The method according to any one of claims 1 to 5,
wherein the electroplating composition comprises at least one betaine and further at least one monomeric diol. 7. The method according to any one of claims 1 to 6,
The electroplating composition has a total concentration of 0.0005 g/L to 1 g/L, preferably 0.001 g/L to 0.5 g/L, more preferably 0.005 g/L to based on the total volume of the electroplating composition. An electroplating composition comprising 0.3 g/L, and most preferably betaine in the range of 0.01 g/L to 0.2 g/L. 8. The method according to any one of claims 1 to 7,
The electroplating composition has a pH of 4.1 to 7.0, preferably 4.5 to 6.5, more preferably 5.0 to 6.0, and most preferably 5.3 to 5.9. 9. The method according to any one of claims 1 to 8,
wherein the electroplating composition comprises at least one betaine and at least one monomeric diol;
provided that the at least one monomeric diol comprises at least one C ₁₁ -C ₂₅ diol comprising one, two or more than two isopropyl moieties. A method for depositing a chromium coating on a substrate, comprising:
(a) providing the substrate;
(b) providing an electroplating composition for depositing a chromium coating on the substrate, the composition comprising:
(i) a trivalent chromium ion,
(ii) at least one complexing agent for the trivalent chromium ion, and
(iii) at least one additive selected from the group consisting of betaines, polymeric glycols, monomeric diols, and mixtures thereof
A step of providing the electroplating composition comprising a.
(c) contacting the substrate with the electroplating composition and applying an electric current such that the chromium coating is deposited on at least one surface of the substrate;
A method for depositing a chromium coating on a substrate comprising: 10. The method of claim 9,
A method for depositing a chromium coating on a substrate, wherein the cathode current efficiency (CCE) in step (c) is at least 11%, preferably at least 12% and most preferably at least 13%. 11. The method according to claim 9 or 10,
In step (c) the thickness of the chromium coating is from 1.1 μm to 500 μm, preferably from 2 μm to 450 μm, more preferably from 4 μm to 400 μm, even more preferably from 6 μm to 350 μm, even more A method for depositing a chromium coating on a substrate, preferably between 8 μm and 300 μm, and most preferably between 10 μm and 250 μm. 12. The method according to any one of claims 9 to 11,
In step (c) the concentration of at least one additive selected from the group consisting of betaine, polymeric glycol, monomeric diol, and mixtures thereof is continuously or semi-continuously monitored, wherein
- the monitored concentration is compared with a target concentration of said at least one additive,
- a method for depositing a chromium coating on a substrate, wherein said at least one additive is added to said electroplating composition when said monitored concentration is lower than said target concentration. A substrate having a surface, wherein the surface of the substrate comprises a chromium coating obtained by the method for forming a film according to any one of claims 10 to 13. Use of at least one additive selected from the group consisting of betaines, polymeric glycols, monomeric diols and mixtures thereof for increasing the cathode current efficiency in an electroplating composition for depositing a chromium coating on a substrate.