Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/48—Electroplating: Baths therefor from solutions of gold
• • 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
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/62—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of gold

Definitions

• the present invention relates to a gold electroplating solution, its use for electroplating a substrate as well as a method for electroplating a substrate.
• the invention also relates to the use of particular specific gold complexing agents in a method of electroplating gold or gold alloys onto a substrate.
• Gold deposits are commonly used as coatings for functional applications (microelectronics, printed circuit boards, ...) or decorative applications as a corrosion resistant conductive material or simply for its aesthetic decorative appearance in different shades. They are mainly produced by electrodeposition from a gold electroplating bath.
• Gold electroplating baths mainly contain one or more gold salts as well as complexing agents to stabilize the bath and promote deposition, and additives to improve the properties and aesthetics of the deposits.
• a cyanide gold salt is coupled to a phosphorus complexing agent (and another metal salt for alloyed deposition) in an acidic medium.
• This bath operates at a pH of between 3.0 and 7.5 and a temperature ranging from 20 to 80°C depending on the complexing agent used.
• a cyanide gold salt is coupled with a nickel salt, a carboxylic acid and thioglycolic acid to produce white gold deposits.
• the operating pH of the bath is between 3.5 and 4.2 at a temperature of 40-60°C.
• a cyanide gold complex is coupled with one or more complexing agents (EDTA, PTDA and their salts), a copper salt, a ceramic of the boron carbide family and cetylpyridinium chloride.
• sulphite-based bath is given in GB 1 526 215 .
• the gold salt used is an aurosulphite complex and in order to maintain the stability of the bath it may contain various complexing agents, additives, buffers and conducting salts.
• the bath operates at a pH of between 5 and 11 and a temperature of between 20 and 55°C.
• a similar example of a bath is described in US 5 277 790 .
• the bath used is composed of an aurosulphite complex, another source of sulphite ions to be in excess, one or more polyamines and an aromatic compound functionalized by NO 2 to operate at a pH between 4.0 and 6.5.
• the invention now proposes a gold and/or gold alloy electroplating solution which is stable, without requiring the use of highly toxic cyanide compounds.
• the invention relates to a gold electroplating solution comprising gold in the form of a complex with a compound of formula (I) or a salt thereof: R 1 S-Ar-CO 2 H (I) Wherein :
• the gold electroplating solution as defined above is a solution :
• the invention in a second aspect, relates to a use of a gold electroplating solution as defined above for producing an electrodeposit of gold or gold alloy on a substrate.
• the invention relates to a method of electroplating gold or gold alloy on a substrate, comprising the steps of:
• the invention relates to the use of a compound of formula (I) as defined above, as a complexing agent in a method of electroplating gold or gold alloy onto a substrate.
• the invention relates to a gold or gold alloy electroplating substrate obtainable by the method as defined above.
• electrolytic solution means a electrolytic solution which is suitable for use as an electrodeposition bath.
• alkyl means a saturated, linear or branched, hydrocarbon radical of formula -C n H 2n+1 having 1 to 6 carbon atoms.
• alkyl groups include methyl, ethyl, propyl, n-butyl etc ...
• aryl refers to a mono- or bicyclic hydrocarbon aromatic ring system having 6 to 10 ring carbon atoms. Examples include phenyl and naphthyl. Preferred aryl groups include unsubstituted phenyl and naphthyl groups.
• heteroaryl refers to an aromatic group containing 5 to 10 ring carbon atoms in which one or more ring carbon atoms are replaced by at least one hetero atom such as -O-, -N-, or -S-.
• heteroaryl groups include pyrrolyl, furanyl, thienyl, pirazolyl, imidazolyl, thiazolyl, isothiazolyl, isoxazolyl, oxazolyl, oxathiolyl, oxadiazolyl, triazolyl, oxatriazolyl, furazanyl, tetrazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, triazinyl, indolyl, isoindolyl, indazolyl, benzofuranyl, isobenzofuranyl, purinyl, quinazolinyl, quinolyl, isoquinolyl, benzoimidazolyl, benzothiazolyl, benzothiophenyl, thianaphthenyl, benzoxazolyl, benzisoxazolyl, cinnolin
• heteroarylene or “arylene” refers to a divalent heteroaryl or aryl group. Heteroarylene and arylene groups are preferably unsubstituted, which means that they are not substituted by more than two groups different from H.
• phenylene means a divalent benzene aromatic ring of formula -C 6 H 4 - :
• pyridinylene means a divalent pyridine aromatic ring of formula :
• a first aspect of the present disclosure relates to a gold electroplating solution comprising a gold electroplating solution comprising gold in the form of a complex with a compound of formula (I) or a salt thereof: R 1 S-Ar-CO 2 H (I)
• the gold implemented in the electroplating solution is preferably in the form of gold ions, notably auric (III) or aureous (I) ions, provided by the dissolution of a gold salt, such as chloroauric acid (III), sodium tetrachloroaurate (III), or ammonium aurosulphite (I).
• a gold salt such as chloroauric acid (III), sodium tetrachloroaurate (III), or ammonium aurosulphite (I).
• the complex of gold with the compound of formula (I) may be generated in situ in the electroplating solution, notably in the conditions of gold electrodeposition.
• the gold electroplating solution comprises gold in the form of a complex of a compound of formula (I) or a salt thereof, generally in an aqueous medium.
• the gold electroplating solution is a cyanide-fee electroplating solution, which means that it does not comprise any cyanide compound.
• the electroplating solution does not comprise ammonia.
• Ar is preferably the same at each occurrence.
• Ar may be notably a phenylene or a 5 membered heteroarylene.
• the compound of formula (I) may be selected from nicotinic compounds of formula (Ia) :
• the compound of formula (I) may be selected from thiobenzoic acid compounds of formula (Ib) :
• R 1 is preferably H, methyl or -S-Ar-CO 2 H.
• Ar may be identical or different.
• Ar is identical, which means that :
• the gold electroplating solution may comprise one or more compounds of formula (I) as a gold complexing agent.
• the compound of formula (I) is selected from 2,2'-dithiobenzoic acid, 2-mercaptobenzoic acid, 2-mercaptonicotinic acid, 2-(methylthio)nicotinic acid 4-mercaptobenzoic acid, 6,6'-dithionicotinic acid, 6-mercaptonicotinic acid, 2-(methylthio)benzoic acid, or 3-mercaptobenzoic acid, and/or mixtures thereof.
• the molar ratio of gold relative to the compound of formula (I) may be from 0.5 to 3, notably from 0.5 to 2, in particular from 0.9 to 1.5.
• the gold electroplating solution may further comprise a base for pH regulation.
• the base may be an inorganic base, notably an alkaline or alkaline earth metal hydroxide, such as sodium or potassium hydroxide, or carbonate.
• the pH-value of the electroplating solution may be in the range of from 6 to 8, notably from 7 to 7.5.
• the electroplating solution may further contain a buffer to regulate the pH value of the electroplating solution.
• the buffer may notably be selected from the usual organic and/or inorganic buffer mixtures such as disodium phosphate, alkali metal carbonate.
• the gold electroplating solution may further comprise a conductive salt, in order to improve the conductivity of the electroplating solution.
• the conductive salt may notably be an inorganic salt, such as sodium, potassium, calcium chloride.
• the electroplating solution may be used as an electrodeposition bath in a manner in itself known.
• the gold electroplating solution may further comprise an additional complexing agent selected from hydantoin, hypoxanthine and derivatives thereof.
• the gold electroplating solution may further comprise a soluble species of an alloyable metal for the purpose of producing an alloyed gold electrodeposit.
• the alloyable metal may be useful to modify functional properties of the gold coating such as hardness or colour.
• the alloyable metal may be selected from a salt of copper, silver, iron, indium, palladium, ruthenium, or a combination of two or more thereof.
• the gold electroplating solution may further comprise one or more additives selected from a levelling agent, a brightening agent, a surfactant and/or a mixture thereof.
• the surfactant may be sodium laurylsulfate.
• the concentration of gold in the electroplating solution may range from 0.1 to 10 g/L, preferably from 1 to 5 g/L.
• the concentration of the compound(s) of formula (I) in the electroplating solution may range from 0.1 to 10 g/L, preferably from 1 to 5 g/L.
• the concentration of the base in the electroplating solution may range from 0.1 to 25 g/L, preferably from 1 to 10 g/L.
• the concentration of the conductive salt in the electroplating solution may range of from 1 to 50 g/L, preferably from 5 to 25 g/L.
• the gold electroplating solution is characterised in that it comprises :
• a second aspect of the present disclosure relates to a use of a gold electroplating solution as defined above, for producing an electrodeposit of gold or gold alloy on a substrate.
• the substrate notably comprises at least an electrically conductive portion.
• This portion may be notably the surface of an electrically conductive substrate or an electrically conductive layer deposited on the substrate, such as a metal layer coating.
• the substrate may be made of metal or metal alloy.
• undercoating which may be a metal or metal alloy layer coating, located between a substrate's surface and the gold or gold alloy electrodeposit.
• the substrate may notably be selected from stainless steel, tin, brass, nickel.
• the undercoating may be selected notably from white brass, palladium, nickel, palladium-nickel alloys.
• a third aspect of the present disclosure relates to a method of electroplating gold or gold alloy on a substrate, said method comprising the steps of:
• the electroplating method is carried out in a deposition tank comprising an anode and a cathode which form the substrate to be coated.
• the device is provided with temperature control and heating means, bath stirring and circulation means and a bath filtration system.
• step b) at a temperature in the range of 10 to 80°C, preferably 20 to 55 °C, more preferably from 40 to 60°C and/or at a cathodic current density from 0.1 to 1 amperes per dm 2 (A/dm 2 ).
• the electric current may be a "pulsed current", that is a current wherein the polarity of the wave varies.
• This so-called “pulsed current” mode avoids competition between the diffusion of the reactive species (gold ions) and the reduction of the solvent. This avoids an increase in the concentration of certain species such as hydroxyl ions and therefore an increase in the pH near the electrode.
• This mode also makes it possible to influence the structural properties of the gold coating (crystalline organization, grain size) and thus the functional properties (hardness, adhesion).
• the bath can be used with single pulse sequences (alternating t on where current is applied and t off where current is zero), or reverse pulses which can include a current reversal time within the sequence.
• the method may further comprise a surface treatment step d) of the gold or gold alloy electrodeposit.
• this treatment may be useful to completely (for a bronze appearance) or partially (for aged or patinated bronze appearance) remove any thin black deposit which may be formed on the surface of the obtained gold layer.
• Appropriate surface treatment step d) may include abrasion, notably a mechanical brushing or polishing of the surface.
• the method may further comprise a step e) of applying a transparent protective layer to the gold or gold alloy electrodeposit after step c) or d), such as a varnish coating.
• a transparent protective layer may be applied by conventional techniques, such as by immersion, spray, for thick coatings, or electrophoretic process, for thin coatings.
• the invention relates to the use of a compound of formula (I) as defined above, as a complexing agent in a method of electroplating gold or gold alloy onto a substrate.
• a gold or gold alloy electroplating substrate obtainable by the method of the invention
• the invention relates to a gold or gold alloy electroplated substrate obtainable by the method as defined above.
• the electroplated substate may be notably a decorative part (watch cases, bracelets, glasses, belt buckles, palettes, bag chains, etc.).
• the gold or gold alloy coatings deposited from the electroplating solution of the invention may have a thickness ranging from 0,3 à 5 ⁇ m.
• the invention relates to a complex of gold together with a compound of formula (I) as defined above or a salt thereof, said compound of formula (I) being selected from 2,2'-dithiobenzoic acid, 2-mercaptobenzoic acid, 2-(methylthio)nicotinic acid 4-mercaptobenzoic acid, 6,6'-dithionicotinic acid, 6-mercaptonicotinic acid, 2-(methylthio)benzoic acid, or 3-mercaptobenzoic acid, and/or mixtures thereof.
• the deposits obtained are adherent with a high covering power, with a thin black layer on the surface.

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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)

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Citations (16)

• 2022
  • 2022-03-15 EP EP22305294.5A patent/EP4245893A1/fr active Pending
• 2023
  • 2023-03-13 WO PCT/EP2023/056352 patent/WO2023174871A1/fr unknown

Patent Citations (16)

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