Cyanide-free electrolyte for silver deposition

Abstract

To provide an electrolyte of sufficient stability, capable of precipitating a stable alloy composition over a wide range of current density to the extent practicable and sufficiently maintaining a functioning state even after being subjected to a load of a high current density.SOLUTION: There are provided a non-cyanide electrolyte of characteristics as described in claim 1, having storage stability and surely precipitating silver and a silver alloy layer of high gloss, high brilliance and whiteness suitable for technological and decorative applications, and an electrolytic precipitation method using the electrolyte.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrolyte and a method for the electrolytic deposition of silver and silver alloy coatings. The electrolyte according to the invention is non-cyanide, storage stable and ensures the deposition of bright, shiny and white silver and silver alloy layers for technical and decorative applications. [Background technology]

[0002] Industrially, silver is often galvanically deposited from cyanide-based electrolytes. However, due to the toxicity of cyanide, non-cyanide electrolytes are needed. In currently known non-cyanide silver electrolytes, silver is generally used in the form of an organic complex, or an organic silver complex is formed in situ. Many of these non-cyanide silver electrolytes have poor bath stability. Furthermore, the deposited silver coatings are frequently not sufficiently white and / or not glossy enough. Therefore, there is a continuing need to develop stable non-cyanide silver electrolytes for technical and decorative applications.

[0003] Hydantoin derivatives are frequently used as organic complexing agents for silver. Thus, U.S. Patent Application Publication No. 2005 / 0183961 (A1) discloses a galvanic bath for the deposition of silver. Here, silver is used in the form of a non-precipitating, water-soluble salt. The organic complexing agent used is 5,5-dimethylhydantoin or its derivatives, and a pyridyl derivative functions as a brightener. The pH of the bath is 9 to 13. It is particularly advantageous if the bath contains both 2,2-dipyridyl and substituted pyridine compounds as brighteners, as well as a wetting agent. Preferred wetting agents are the substituted glycine derivatives commercially known as Hamposyl® and sulfonated naphthalene-formaldehyde condensates, commercially available as Blancol N or Rhodacal N. Hamposyl® consists of N-acyl sarcosinates, i.e., condensation products of fatty acid acyl residues with N-methylglycine (sarcosine). Silver coatings deposited from these baths are white and bright to high gloss.

[0004] U.S. Patent No. 5,601,696 discloses a galvanic bath for silver deposition and a method for depositing silver using the bath. The bath contains a silver salt of an inorganic acid, such as silver nitrate and silver oxide, and a complexing agent that is a hydantoin derivative. The bath may also optionally contain a brightener, such as at least one organic sulfur compound containing an SH group or a carboxyl group, a sulfur-containing amino acid, or sulfite ions. Examples of brighteners include thiosalicylic acid, thiamine hydrochloride, thiamine nitrate, and potassium sulfite. The bath may also contain a conductive salt, preferably an inorganic salt such as potassium chloride, potassium formate, or a carboxylate. The bath pH is 8 to 13, the bath temperature during deposition is 30 to 90°C, and the current density is 1 to 150 A / dm2 depending on the application. The bath described in U.S. Patent No. 5,601,696 provides a bright silver layer and can be used for up to three passes.

[0005] WO 2008 / 043528 A2 discloses a non-cyanide electrolyte composition for depositing silver or silver alloy layers, comprising a silver ion source, a sulfonic acid or sulfonic acid derivative, a wetting agent, and a hydantoin derivative. The electrolyte composition is useful for depositing crack-free, ductile silver and silver alloy layers. The silver ion source used is at least one silver salt of a sulfonic acid. Optionally, an additional silver ion source selected from silver oxide, silver nitrate, and silver sulfate may be present. When depositing a silver alloy layer, a corresponding alloy metal ion source is used, preferably a sulfonate, oxide, nitrate, or sulfate. The hydantoin derivative for complexing silver has two substituents at the 5-position of the heterocycle, independently selected from hydrogen, an alkyl group having 1 to 5 carbon atoms, and a substituted or unsubstituted aryl group. Optionally, the electrolyte composition may contain a wetting agent, such as a naphthalenesulfonic acid-formaldehyde polycondensate and / or a sulfopropylated polyalkoxylated naphthol. Furthermore, alkali metal bromides, preferably potassium bromide, and / or thiosulfates, preferably alkali metal thiosulfates such as sodium thiosulfate, may be added to the electrolyte. Both alkali metal bromides and thiosulfates function as matting agents. The alkali metal bromides also result in more uniform deposition results in terms of color. The pH of the electrolyte composition is 8 to 14. In practice, it appears that a shiny silver layer has been deposited without the addition of alkali metal bromides or thiosulfates, and no mention is made of gloss. Electrolyte compositions containing alkali metal bromides and / or thiosulfates provide matte silver coatings. WO 2008 / 043528(A2) is silent about the color of the silver layer.

[0006] US Patent Application Publication No. 2011 / 0062030 (A1) describes an electrolyte composition for depositing metals, particularly silver, on solar cells. Silver is used, for example, in the form of its methanesulfonate salt. An imidosuccinate derivative functions as a complexing agent for the metal ions. Optionally, a hydantoin derivative may be used as a second complexing agent. The composition advantageously contains an additive for improving conductivity, preferably a citrate salt, and a wetting agent, preferably one having a polyalkylene oxide chain. The pH of the electrolyte composition is 8 to 12. Apart from the metal to be deposited, which may be in the form of a methanesulfonate salt, the composition preferably contains no additional sulfonic acid derivatives or cyanides. The color and gloss of the deposited layer are not described.

[0007] U.S. Patent Application Publication No. 2012 / 0067733(A1) describes a method for depositing a silver layer on a nickel layer from a non-cyanide electrolytic bath. Suitable silver sources for the bath include silver oxide, silver nitrate, silver sodium thiosulfate, silver gluconate, silver-amino acid complexes such as silver-cysteine ​​complexes, silver alkylsulfonates such as silver methanesulfonate, silver hydantoin compounds, and silver-succinimide complexes. The bath contains at least one imide, such as succinimide, maleimide, phthalimide, or a hydantoin derivative. The silver source is present at a relatively low silver concentration of 0.1 to 5 g / L, while the other imide is used at a concentration of 40 g / L to 120 g / L. Optionally, the bath contains an amidosulfonic acid or alkylsulfonic acid. Furthermore, the bath may optionally contain a surface-active substance, which may be anionic, cationic, or amphoteric. The electrolytic bath has a pH of 8 to 12 and provides a specularly shiny silver layer on the nickel.

[0008] U.S. Patent Application Publication No. 2012 / 0067735(A1) describes a non-cyanide electrolyte for silver deposition, in which silver is complexed with at least one complexing agent selected from hydantoin, hydantoin derivatives, succinimide, and succinimide derivatives. Suitable silver sources for the bath include, for example, silver oxide, silver nitrate, sodium silver thiosulfate, silver gluconate, silver-amino acid complexes such as silver-cysteine ​​complexes, silver alkylsulfonates such as silver methanesulfonate, silver hydantoin compounds, and silver-succinimide complexes. The bath further contains at least one pyridylacrylic acid and at least one organic sulfide selected from dialkyl sulfides and dialkyl disulfides. The combination of pyridylacrylic acid and organic sulfide results in silver deposits with a specular luster, and deposition can also be carried out at high current intensities and high bath temperatures. The electrolyte may further contain a conductive salt and a buffer substance. The pH is between 8 and 14. Using the electrolyte according to US Patent Application Publication No. 2012 / 0067735 A1, specularly shiny silver layers can be deposited galvanically, but the disclosure is silent regarding the color of the deposited layer.

[0009] WO 2015 / 018654 A1 discloses a non-cyanide, acidic, and aqueous electrolyte for depositing silver-based silver-palladium alloys and a method for depositing these layers. In addition to silver and palladium compounds, the electrolyte contains a tellurium or selenium compound, urea or an amino acid, and a sulfonic acid. In this case, the amount of tellurium or selenium affects the silver concentration in the deposited alloy. The urea or amino acid complexes the palladium and improves the stability of the electrolyte. The electrolyte ensures uniform deposition of the corresponding silver-palladium alloy over a wide current density range, which is particularly advantageous for the industrial production of contact materials. The method for depositing the silver-palladium alloy is preferably carried out in a strongly acidic pH range.

[0010] U.S. Patent Application Publication No. 2016 / 0122890(A1) discloses a non-cyanide electrolyte for depositing silver or silver alloys and a method for depositing such layers. The electrolyte according to the invention comprises at least one silver ion source, sulfonic acid and / or sulfonic acid derivatives, a wetting agent, and hydantoin. The silver or silver alloy coatings that can be deposited from this electrolyte are matte and ductile.

[0011] WO 2017 / 067985(A1) describes an electrolyte containing a suitable reducing agent for adjusting the composition of a silver-palladium layer. The reducing agent also contributes to improving the appearance of the layer and increasing the lightness (L value, CIE Lab) of the deposited layer. WO 2017 / 067985(A1) also discloses a method for electrolytically depositing a silver-rich silver-palladium alloy. In addition to silver and palladium compounds, the electrolyte contains a tellurium and / or selenium compound, urea or an amino acid, and a sulfonic acid, as well as a reducing agent. Here, the amount of tellurium and / or selenium affects the silver concentration in the deposited alloy. The urea or amino acid complexes the palladium. The reducing agent serves to adjust the layer composition, since increasing the content of the reducing agent increases the palladium content in the deposited layer. The disclosed method for depositing a silver-palladium alloy is also advantageously carried out in a strongly acidic pH range. Palladium causes the deposited silver-palladium alloy to be darker than a pure silver layer.

[0012] JP 2018-009227 A discloses a method for depositing a palladium-silver alloy layer, in which the weight ratio of Pd to Ag in the layer can be in the range of 1:9 to 9:1. The deposited layer is easily solderable and suitable as an electrical contact material. The electrolyte for depositing the Pd-Ag alloy layer also contains, in addition to a palladium salt and a silver salt, at least one diamine compound and one heterocyclic compound. The diamine compound is advantageously an alkylated diamine, preferably ethylenediamine and 1,3-propanediamine. The heterocyclic compound is hydantoin or a derivative thereof. 1-(hydroxymethyl)-5,5-dimethylhydantoin and 5,5-dimethylhydantoin are particularly advantageous. The pH of the electrolyte is 7.0 to 14.0, most preferably 10.0 to 11.0. Optionally, the electrolyte may contain a conductive salt, a buffer, a brightener, and a wetting agent. The color and gloss of the deposited layer are not described. However, it can be assumed that the deposit will be darker than a pure silver layer because the palladium content is at least 10% by weight. Summary of the Invention [Problem to be solved by the invention]

[0013] Despite the large number of known electrolytes for the electrolytic deposition of silver and silver alloys, there is a further need to provide electrolytes superior to those of the prior art in terms of deposit whiteness and brightness, bath stability, and throughput behavior (metal turnover rate). For industrial use, such electrolytes must have sufficient stability and be capable of depositing stable alloy compositions over as wide a current density range as possible. The electrolytes must remain fully functional even after high current density loading, and the deposits produced with these electrolytes must be homogeneous and advantageous for use in technical and decorative applications. [Means for solving the problem]

[0014] The above object is achieved according to the invention by an electrolyte having the features of claim 1. The subclaims dependent on claim 1 relate to preferred embodiments of the electrolyte according to the invention. Claims 9 to 13 relate to methods for electrolytic deposition using the electrolyte according to the invention.

[0015] by providing an aqueous, cyanide-free electrolyte for the electrolytic deposition of silver and silver alloy coatings, the electrolyte comprising: a) at least one silver compound having a silver concentration of 0.1 to 150 g / L; b) a compound of at least one alloying metal, the concentration of the alloying metal being 0 to 100 g / L; c) at least one compound of formula (I), [ka] During the ceremony, R1, R2, R3, and R4 independently represent hydrogen, a linear or branched alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a hydroxyalkyl group having 1 to 5 carbon atoms, or an aryl group; and at least one compound of formula (I), wherein the at least one compound of formula (I) is present in a concentration of 1 to 350 g / L; d) at least one brightener carrier, i. at least one amino acid at a concentration of 0.0001 to 5 mol / L, in particular 0.01 to 5 mol / L; and / or ii. at least one brightener carrier selected from the group consisting of at least one pyridine carboxylic acid having a concentration of 0.01 to 5 mol / L; e) at least one brightener selected from sulfonamides, 2,2'-sulfanediyldiethanol, cysteine, methionine, aliphatic and aromatic heterocyclic compounds having 5 to 7 ring atoms, the ring of which contains at least one heteroatom selected from nitrogen and sulfur, and which optionally contain one or more further heteroatoms selected from nitrogen, oxygen, and sulfur, and mixtures of these brighteners, wherein the concentration of the brightener or mixture of brighteners is 0.005 to 25 g / L; At least one brightener, wherein when the at least one brightener is selected from cysteine ​​and / or methionine and at least one amino acid according to d)i. is selected as the brightener carrier, the amino acid of the brightener carrier is not cysteine ​​or methionine; f) an alkali metal hydroxide selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, and mixtures thereof, in a dissolved form, in a concentration of 1 to 200 g / L; g) the electrolyte has a pH of 7 or greater; The stated objective is achieved.

[0016] It has surprisingly been found that, using the electrolytes described herein, bright, shiny, and white silver and silver alloy coatings can be deposited on conductive substrates over a wide current density range. Furthermore, the electrolytes according to the present invention have high bath stability and high deposition yields and rates, which are particularly advantageous in industrial applications. The electrolytes of the present invention can also be used to advantageously produce high-quality electrical contact materials in rack and high-speed coating systems. The electrolyte preferably contains only the components listed above. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing the results of determining the L* value. [Figure 2] FIG. 2 is a diagram showing the determination results of the a* value. [Figure 3]FIG. 3 is a diagram showing the determination results of the b* value. DETAILED DESCRIPTION OF THE INVENTION

[0018] The electrolyte according to the present invention is applied to a battery having a current of 0.1 to 100 A / dm 2 It can be used in the current density range of 0.5~20A / dm 2 A current density range of 1000 kJ / s is preferred.

[0019] The color and brightness of the metallic coating are measured in CIEL * a * b (www.cielab.de) * a * b * It is known to those skilled in the art that the measurement of * The value represents the brightness. * Value) is 95-99L * a * b * (The measurement equipment was a Konica Minolta CM-700, and the light source was D65 / 10.) * The value is -0.5 to +0.5, and b * The value is 1.5 to 5.0.

[0020] Gloss can be evaluated by measuring reflection. The silver layer according to the present invention has a value in the range of 91 to 93.5. Reflection was measured using a BYK-Gardner-Micro-TRI gloss meter. Measurements were carried out in accordance with EN ISO 7668 (latest version at the filing date) with the light beam at an angle of incidence of 20° and a reflection angle of 20°. The measurement of surface gloss is known to those skilled in the art; information on this can be found, for example, in "Gloss and reflection measurement of surfaces" [Publication series: Electroplating and surface treatment: Inspecting functional metal coatings], Section 4.3: Gloss and reflection measurement of surfaces, Eugen G. Leuze-Verlag, Saulgau, 1st ed. 1997, pp. 117-125.

[0021] A galvanic bath is a solution containing metal salts that can electrochemically deposit a metal precipitate (coating) onto a substrate (object). Galvanic baths of this type are often also called "electrolytes." Therefore, the cyanide-free aqueous galvanic bath according to the present invention will hereinafter be referred to as "electrolytes."

[0022] The electrolytes for the electrolytic deposition of silver and silver alloy coatings according to the present invention, as well as the methods for depositing such silver and silver alloy coatings, are described below, and the present invention includes all of the embodiments listed below, individually or in combination with each other.

[0023] The electrolyte is a non-cyanide aqueous electrolyte. In this context, it is advantageous if all substances present in the electrolyte are dissolved as completely as possible to avoid contamination of the layer with undissolved materials during deposition. In the context of the present invention, a substance is considered water-soluble if at least 0.1 g of the substance dissolves in 1 liter of water at 25°C. Such substances are also referred to hereinafter as "soluble compounds" or "soluble substances".

[0024] The silver compound contained in the electrolyte according to the present invention is preferably a silver salt soluble in the electrolyte. Here, the silver salt is preferably selected from the group consisting of silver methanesulfonate, silver carbonate, silver phosphate, silver pyrophosphate, silver nitrate, silver oxide, silver lactate, silver fluoride, silver bromide, silver chloride, silver iodide, and silver sulfate. Silver nitrate, silver carbonate, silver methanesulfonate, silver chloride, and silver oxide are particularly preferably used in the electrolyte according to the present invention. Here, those skilled in the art should adhere to the principle that the amount of additional substances added to the electrolyte should be as small as possible. For this reason, those skilled in the art most preferably select silver methanesulfonate, silver carbonate, or silver oxide as the silver salt to be added. It is also possible to use compounds of silver and additional electrolyte components (e.g., silver hydantoate). With regard to the concentration of the silver compound used, those skilled in the art should adhere to the value limitations mentioned above. The silver compound is preferably present in the electrolyte at a concentration of 0.1 to 150 g / L silver, more preferably 2 to 100 g / L silver, and most preferably 4 to 40 g / L silver. The alloying metals are tin, palladium, antimony, cobalt, indium, iron, nickel, ruthenium, rhodium, platinum, copper, zinc, selenium, tellurium, bismuth, iridium, germanium, gallium, gold, rhenium, tungsten, molybdenum, dysprosium, and cerium. 2+ , Sn 4+ , Pb 2+ , Sb 3+ , Co 2+ , In 3+ , Fe 2+ , Fe 3+ , Ni 2+ , Ru 3+ , Ru 4+ , Rh3+ , Pt 2+ , Pt 4+ , Cu 2+ , Cu + 、 Zn 2+ , Se 2+ and Se 4+ , Te 2+ , Bi 3+ , Ir 3+ , Ir 4+ , Ge 2+ , Ge 4+ , Ga 3+ , Au 3+ ,Re 3+ ,Re 4+ , W 6+ , Dy 3+ , and Ce 3+ are added to the baths according to the invention in the form of soluble compounds of the formula:

[0025] Suitable soluble compounds of the alloying metals mentioned are known to those skilled in the art and can be used without departing from the scope of protection of the claims. Advantageously used soluble compounds of the alloying metals are listed below, but the invention also includes soluble compounds of these metals not explicitly mentioned.

[0026] The divalent tin compound is selected from tin(II) fluoride, tin(II) chloride, tin(II) bromide, tin(II) iodide, tin(II) hydroxide, tin(II) oxide, tin(II) pyrophosphate, tin(II) sulfate, tin(II) methanesulfonate. The divalent tin compound is advantageously selected from tin(II) pyrophosphate, tin(II) sulfate, and tin(II) methanesulfonate. The tetravalent tin compound is selected from sodium hexahydroxostannate(IV), potassium hexahydroxostannate(IV), and mixtures thereof.

[0027] Divalent palladium compounds include tetraamminepalladium(II) chloride, tetraamminepalladium(II) bromide, palladium hydroxide, palladium chloride, palladium sulfate, palladium pyrophosphate, palladium methanesulfonate, palladium nitrate, palladium phosphate, palladium bromide, diamminedinitritopalladium(II) chloride, diamminedinitritopalladium(II) bromide, diamminedinitritopalladium(II) sulfate, palladium glycinate, potassium dioxalatopalladate, palladium iodide, palladium(II) cyanide, and pentapalladium. The palladium cyanonitrosylferrate(III) is selected from palladium(II) cyanonitrosylferrate(III), tetraamminepalladium(II) sulfate, bis(ethylenediamino)palladium(II) carbonate, bis(ethylenediamino)palladium(II) sulfate, bis(ethylenediamino)palladium(II) bromide, bis(acetylacetonato)palladium(II), diamminedichloropalladium(II), palladium oxide hydrate, tetraamminepalladium(II) bicarbonate, bis(ethylenediamino)palladium(II) chloride, palladium acetate, and dipotassium cyanopalladate.

[0028] The trivalent antimony compound is selected from antimony(III) oxide, antimony(III) fluoride, antimony(III) chloride, antimony(III) bromide, and potassium antimony tartrate. The trivalent antimony compound is advantageously selected from antimony(III) oxide and potassium antimony tartrate.

[0029] The divalent cobalt compound is selected from cobalt(II) chloride, cobalt(II) oxide, cobalt(II) nitrate, cobalt(II) sulfate, cobalt(II) thiocyanate, and cobalt(II) acetate.

[0030] The trivalent indium compound is selected from indium(III) chloride, indium(III) gluconate, indium(III) sulfate, and indium(III) oxide. The trivalent indium compound is advantageously selected from indium(III) sulfate, indium(III) chloride, and indium(III) gluconate.

[0031] The divalent iron compound is selected from iron(II) sulfate hydrate, iron(II) chloride, iron(II) citrate, iron(II) methanesulfonate, ammonium iron(II) citrate, iron(II) chloride hexahydrate, iron(II) pyrophosphate, ammonium iron(II) oxalate, iron(II) phosphate complex, iron(II) fluoride, iron(II) bromide, iron(II) nitrate, iron(II) thiocyanate, and iron(II) hydroxide.

[0032] The iron(III) compound is selected from iron(III) sulfate hydrate, Fe2(SO4)3, FeCl3, Fe(III) citrate, Fe(III) methanesulfonate, ammonium iron(III) citrate, Fe(III) chloride hexahydrate, Fe(III) pyrophosphate, ammonium iron(III) oxalate, Fe(III) phosphate complex, Fe(III) fluoride, iron(III) bromide, Fe(III) nitrate, Fe(III) thiocyanate, and Fe(III) hydroxide.

[0033] The nickel compound is selected from nickel(II) sulfate heptahydrate, nickel(II) chloride hexahydrate, nickel(II) sulfamate, nickel(II) nitrate hexahydrate, and nickel(II) ethylenediamine complex.

[0034] Ruthenium compounds include ruthenium(III) fluoride, ruthenium(III) chloride, ruthenium(III) bromide, ruthenium(III) iodide, ruthenium(III) nitrosylnitrate, ruthenium(III) acetate, ruthenium isonitrile complexes, and Ru nitride-halo complexes, which have the general formula [RuN(HO)X]. 3- wherein X is a halide ion selected from fluoride, bromide, chloride, and iodide, such as [RuN(HO)Cl] 3- , ruthenium nitrido-hydroxo complexes, and Ru nitrido-oxalato complexes.

[0035] The trivalent rhodium compound is selected from rhodium(III) fluoride, rhodium(III) chloride, rhodium(III) bromide, rhodium(III) iodide, rhodium(III) oxide hydrate, rhodium(III) methanesulfonate, and rhodium(III) sulfate.

[0036] The divalent platinum compound is selected from platinum(II) chloride, tetrachloroplatinic(II) acid H2 (PtCl4), platinum(II) bromide, dinitrosulfatoplatinic(II) acid and its salts, diaminodinitritoplatinum(II), tetraamineplatinum(II) salts, platinum(II) nitrate, and platinum(II) iodide.

[0037] The tetravalent platinum compound is selected from hexachloroplatinic(IV) acid H2 (PtCl6), platinum(IV) fluoride, hexahydroxoplatinic(IV) acid and its salts, and platinum(IV) bromide.

[0038] The divalent copper compound is selected from copper(II) sulfate, copper(II) fluoride, copper(II) chloride, copper(II) bromide, copper(II) iodide, copper(II) hydroxide, copper(II) oxide, copper(II) oxalate, copper(II) carbonate, copper(II) nitrate, copper(II) phosphate, copper(II) pyrophosphate, copper(II) methanesulfonate, copper(II) citrate, copper(II) acetate. The divalent copper compound is advantageously selected from copper(II) sulfate, copper(II) chloride, and copper(II) pyrophosphate.

[0039] The divalent zinc compound is selected from zinc fluoride, zinc chloride, zinc bromide, zinc iodide, zinc sulfate, zinc oxide, zinc hydroxide, zinc pyrophosphate, zinc citrate, zinc methanesulfonate, and is advantageously selected from zinc pyrophosphate, zinc sulfate, and zinc methanesulfonate.

[0040] Suitable selenium and tellurium compounds are those in which selenium or tellurium is present in the +4 or +6 oxidation state. Selenium and tellurium compounds are advantageously used in electrolytes in which selenium or tellurium is present in the +4 oxidation state. Selenium and tellurium compounds are particularly preferably selected from tellurite, selenite, tellurous acid, selenious acid, telluric acid, selenic acid, selenocyanate, tellurocyanate, and selenate and tellurate salts. It is generally preferred here to use tellurium compounds rather than selenium compounds. It is most particularly preferred to add tellurium to the electrolyte in the form of a salt of tellurous acid, for example, potassium tellurite.

[0041] The trivalent bismuth compound is selected from bismuth(III) hydroxide, bismuth(III) hydroxide, bismuth(III) chloride, bismuth(III) citrate, bismuth(III) bromide, bismuth(III) iodide, bismuth(III) methanesulfonate, and is advantageously selected from bismuth(III) citrate and bismuth(III) methanesulfonate.

[0042] The trivalent iridium compound is selected from iridium(III) sulfate, iridium(III) chloride, iridium(III / IV) chloride, iridium(IV) chloride, potassium hexabromoiridate(IV), potassium hexachloroiridate(IV), sodium hexabromoiridate(IV), sodium hexachloroiridate(IV), hexachloroiridate(IV), ammonium hexachloroiridate(IV), and ammonium hexabromoiridate(IV).

[0043] The germanium compound is selected from germanium(II) or germanium(IV) halides, germanium(II) selenide, germanium(II) telluride, and germanium(IV) oxide.

[0044] The gallium compound is selected from gallium(III) fluoride, gallium(III) chloride, gallium(III) bromide, gallium(III) iodide, and gallium(III) oxide.

[0045] The gold compound is selected from alkali metal gold(I) sulfite, ammonium gold(I) sulfite, tetrachloroaurate(III) acid, gold as a gold(I) hydantoin complex or a gold(III) hydantoin complex, potassium dicyanoaurate(I), potassium tetracyanoaurate(III), gold(I) cysteine ​​complex, and gold(III) sulfate.

[0046] The rhenium compound is selected from rhenium(III) chloride and rhenium(IV) oxide.

[0047] The tungsten compound is selected from alkali metal tungstates, ammonium tungstate, and tungsten oxide, with tungsten (VI) compounds being preferred.

[0048] The molybdenum compounds are selected from alkali metal molybdates, ammonium molybdate, and molybdenum oxide, with molybdenum (VI) compounds being preferred.

[0049] The dysprosium compound is selected from dysprosium(III) chloride and dysprosium(III) nitrite.

[0050] The cerium compound is selected from cerium(III) chloride and cerium(III) sulfate hydrate.

[0051] The compound of the at least one alloying metal is present in the electrolyte at a concentration of 0 to 100 g / L. In a preferred embodiment, the concentration of the at least one alloying metal in the electrolyte is 0 g / L. In this case, no metals to be deposited are present except for silver, and the electrolyte is conducive to the deposition of a pure silver coating. In an even more preferred embodiment, the compound of the at least one alloying metal is present in the electrolyte at a concentration of more than 0 to a maximum of 100 g / L. In this case, in addition to silver, at least one further metal to be deposited is present, and the electrolyte is conducive to the deposition of a silver alloy coating. Advantageously, the concentration of the at least one alloying metal in the electrolyte is 0.05 to 100 g / L, preferably 0.5 to 20 g / L, and particularly preferably 1 to 10 g / L.

[0052] In the context of the present invention, "compound of at least one alloying metal" includes the following variations: a) Using a single compound of a single alloying metal. b) Using several compounds of a single alloying metal, i.e. the cations of these compounds originate in all cases from the same alloying metal, but the anions are different. The cations may be present in different oxidation states. c) Using compounds of several alloying metals, all compounds have the same anion but different cations. d) Several compounds of several alloying metals are used, i.e., several different anions and several different cations are present.

[0053] In the cases of a) and b), an electrolyte for the deposition of a binary silver alloy is obtained, and in the cases of c) and d), an electrolyte for the deposition of at least a ternary silver alloy is obtained.

[0054] In the electrolyte of the present invention, silver is complexed with at least one compound of formula (I). [ka]

[0055] R1, R2, R3, and R4 independently represent hydrogen, a linear or branched alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a hydroxyalkyl group having 1 to 5 carbon atoms, or an aryl group;

[0056] The straight or branched alkyl group having 1 to 5 carbon atoms is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-methylpropyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2-methylbutyl, 3-methylbutyl, 3-methylbut-2-yl, 2-methylbut-2-yl, 2,2-dimethylpropyl. The alkoxy group having 1 to 5 carbon atoms is selected from methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, 2-methylpropoxy, tert-butoxy, n-pentoxy, 2-pentoxy, 3-pentoxy, 2-methylbutoxy, 3-methylbutoxy, 3-methylbut-2-oxy, 2-methylbut-2-oxy, 2,2-dimethylpropoxy.

[0057] Hydroxyalkyl groups having 1 to 5 carbon atoms are derived from the alkyl groups mentioned, where a hydrogen atom of the specified alkyl group is replaced with a hydroxy group.

[0058] The aryl group is selected from phenol, naphthol, benzene, toluene, xylene, cumene.

[0059] The compounds of formula (I) are hydantoins and their derivatives.

[0060] Advantageously, the at least one compound of formula (I) is selected from 1-methylhydantoin, 1,3-dimethylhydantoin, 5,5-dimethylhydantoin, 1-hydroxymethyl-5,5-dimethylhydantoin, 5,5'-diethylhydantoin and 5,5-diphenylhydantoin, and mixtures thereof. Particularly preferably, the at least one compound of formula (I) is 5,5-dimethylhydantoin.

[0061] The complex of silver and at least one compound of formula (I) is formed in situ from the silver compound used and at least one compound of formula (I). The at least one compound of formula (I) is used in a concentration of 1 to 350 g / L, preferably 5 to 200 g / L, particularly preferably 10 to 100 g / L. In a preferred embodiment of the present invention, silver is used as a complex of formula (I).

[0062] In the electrolyte according to the invention, the molar ratio of silver to the compound according to formula (I) is between 1:2 and 1:6. This applies whether a complex of silver with the compound according to formula (I) is used as the silver compound, or whether a different silver compound that is not a complex of silver with the compound of formula (I) is used; overall, the amount of the compound according to formula (I) in the electrolyte according to the invention is 2 to 5 times higher than the amount of silver, regardless of the proportion of the compound of formula (I) present as a silver complex.

[0063] The electrolyte according to the invention further comprises at least one brightener carrier selected from at least one amino acid in a concentration of 0.0001 to 5 mol / L, preferably 0.001 to 1 mol / L, particularly preferably 0.01 to 0.5 mol / L, and / or at least one pyridinecarboxylic acid in a concentration of 0.01 to 5 mol / L, preferably 0.01 to 1 mol / L, very particularly preferably 0.1 to 0.5 mol / L.

[0064] Those skilled in the art know that amino acids are compounds containing a carboxyl group and an amino group. They may be essential or non-essential amino acids. Furthermore, those skilled in the art know that they may be α-, β-, or γ-amino acids, with α-amino acids having at least two carbon atoms, β-amino acids having at least three carbon atoms, and γ-amino acids having at least four carbon atoms. At least one amino acid may be present in D-, L-, or racemic form. When two or more amino acids are used, each individual amino acid may be present in D-, L-, or racemic form, independently of the other amino acids. Advantageously, the at least one amino acid is selected from alanine, arginine, asparagine, aspartic acid, cystine, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine, sarcosine, and mixtures thereof. With regard to sulfur-containing amino acids, such as cysteine ​​or dimeric cystine, it may be advantageous to use these only in concentrations of 0.0001 to 1 mol / L, preferably 0.0005 to 0.5 mol / L, particularly preferably 0.001 to 0.01 mol / L in the electrolyte.

[0065] In a particularly advantageous embodiment, the at least one amino acid is selected from glycine, alanine, proline, cysteine, and sarcosine, and mixtures thereof. Most preferably, the amino acid is selected from glycine and sarcosine.

[0066] In an advantageous embodiment, the at least one pyridine carboxylic acid is selected from picolinic acid, picolinic acid amide, nicotinic acid, nicotinamide, isonicotinic acid, isonicotinamide, and mixtures thereof.The at least one pyridine carboxylic acid is preferably selected from nicotinic acid, nicotinamide, picolinic acid, and picolinic acid amide.In the context of the present invention, both the free pyridine carboxylic acid and its amide are referred to as "pyridine carboxylic acid".In a highly preferred embodiment, the electrolyte according to the present invention does not contain pyridine carboxylic acid, but contains at least one aminocarboxylic acid as described above as a brightener carrier.

[0067] The at least one brightener is advantageously selected from the group of sulfonamides. Sulfonamides are a group of chemical substances known to those skilled in the art, some of which have antibiotic properties (Beyer Walter, Lehrbuch der organischen Chemie [Textbook of Organic Chemistry], S. Hirzel Verlag Stuttgart, 22nd edition, 1991, pp. 496, 497, 575-577, 784, 785). In a preferred embodiment, the sulfonamide has the structural element R1-SO2-NR2R3, where R1, R2, and R3 are, independently of one another, hydrogen, (C1-C 10 ) Alkyl, (C3-C 10 ) cycloalkyl, (C6-C 10 ) Aryl, (C5-C 10 ) heteroaryl, (C5-C 10 ) heterocycloalkyl. R2 and R3 may also form a saturated or mono- or polyunsaturated ring, which may have 4 or 5 further atoms, in particular C atoms, or 1 or 2 nitrogen or oxygen atoms. This ring may be further substituted.

[0068] In this context, (C1-C10) alkyl is a saturated or mono- or polyunsaturated alkyl radical, which may be linear or optionally branched. These are preferably selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-methylpropyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2-methylbutyl, 3-methylbutyl, 3-methylbut-2-yl, 2-methylbut-2-yl, and 2,2-dimethylpropyl. The radicals considered here may be substituted by heteroatoms, which are preferably selected from the group consisting of oxygen, nitrogen, or sulfur. Likewise, the heteroatoms may in turn be substituted by further organic radicals. These radicals are particularly preferably selected from hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-methylpropyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2-methylbutyl, 3-methylbutyl, 3-methylbut-2-yl, 2-methylbut-2-yl, 2,2-dimethylpropyl.

[0069] In this context, (C3~C 10 Cycloalkyl is a cyclic alkyl radical, such as, for example, cyclopropyl, cyclopentyl, or cyclohexyl. These radicals may have double bonds. The radicals considered here may be substituted by heteroatoms, which are preferably selected from the group consisting of oxygen, nitrogen, or sulfur. Likewise, the heteroatoms may in turn be substituted by further organic radicals. These radicals are particularly preferably selected from hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-methylpropyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2-methylbutyl, 3-methylbutyl, 3-methylbut-2-yl, 2-methylbut-2-yl, and 2,2-dimethylpropyl.

[0070] (C6~C 10) Aryl is an aromatic ring compound that can be optionally substituted with further radicals selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-methylpropyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2-methylbutyl, 3-methylbutyl, 3-methylbut-2-yl, 2-methylbut-2-yl, and 2,2-dimethylpropyl. Most preferably, they are selected from the group consisting of phenol, naphthol, benzene, toluene, xylene, and cumene. The radicals considered here may be substituted with heteroatoms, which are preferably selected from the group consisting of oxygen, nitrogen, or sulfur. Likewise, the heteroatoms can in turn be substituted with further organic radicals. These radicals are particularly preferably selected from hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-methylpropyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2-methylbutyl, 3-methylbutyl, 3-methylbut-2-yl, 2-methylbut-2-yl, 2,2-dimethylpropyl.

[0071] (C5~C 10 ) heteroaryl or (C5-C 10 Heterocycloalkyls are derived from the above-mentioned cycloalkyl and aryl radicals, in which at least one C atom in the ring is replaced by a heteroatom. They are therefore preferably aliphatic or aromatic heterocyclic compounds having 5 to 10 ring atoms, the ring of which contains at least one heteroatom selected from nitrogen and sulfur, and the latter optionally contains one or more further heteroatoms selected from nitrogen, oxygen, and sulfur. Likewise, these ring systems can in turn be substituted by further organic radicals. These radicals are particularly preferably selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-methylpropyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2-methylbutyl, 3-methylbutyl, 3-methylbut-2-yl, 2-methylbut-2-yl, and 2,2-dimethylpropyl. (C5-C10 ) heteroaryl or (C5-C 10 ) Heterocycloalkyl radicals may be substituted with heteroatoms, which are preferably selected from the group consisting of oxygen, nitrogen, or sulfur. Likewise, the heteroatoms may in turn be substituted with further organic radicals. These radicals are particularly preferably selected from hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-methylpropyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, 2-methylbutyl, 3-methylbutyl, 3-methylbut-2-yl, 2-methylbut-2-yl, and 2,2-dimethylpropyl.

[0072] In a further advantageous embodiment, at least one brightener is a sulfonamide, which has as radicals R1, R2, and R3 an aromatic (optionally heterocyclic) compound having 5 to 10 ring atoms, the ring having at least one nitrogen and / or sulfur atom. Sulfonamides having as radicals R1, R2, and R3 an aromatic (optionally heterocyclic) compound that can be used as brighteners in the context of the present invention preferably have 5 to 7 ring atoms, at least one of which is a nitrogen or sulfur atom. Optionally, one or more additional heteroatoms selected from oxygen, nitrogen, and sulfur may also be present. These additional heteroatoms may likewise be constituents of the aromatic ring, but may also be present in side chains and groups attached to the ring. Suitable aliphatic and aromatic heterocyclic compounds are derivatives of tetrahydrothiophene, thiophene, tetrahydrofuran, furan, pyrrolidine, pyrrole, imidazolidine, pyrazolidine, imidazole, pyrazole, oxazolidine, isoxazolidine, oxazole, isoxazole, thiazolidine, isothiazolidine, thiazole, isothiazole, dioxolane, dithiolane, triazole, furazan, oxadiazole, thiadiazole, dithiazole, tetrazole, piperidine, pyridine, tetrahydropyran, pyran, thiane, thiopyran, piperazine, pyrimidine, diazine, morpholine, oxazine, thiomorpholine, thiazine, dioxane, dioxine, dithiane, dithiin, hexahydro-1,3,5-triazine, triazine, trioxane, trithiane, tetrazine, pentazine, azepane, azepine, oxepane, oxepine, thiepine, diazepane, diazepine, thiazepine. Aniline and pyrimidine, pyridine and pyrazine are particularly preferred in this context. Those skilled in the art know that organic compounds are carbon-based. For the purposes of the present invention, organic hetero compounds are compounds that contain at least one additional atom in addition to carbon and hydrogen. This additional atom is a "heteroatom". Advantageously, it is nitrogen, oxygen, or sulfur. The aliphatic and aromatic heterocyclic compounds mentioned can have functional groups.These functional groups are advantageously thio, thiol, carbonyl, carboxyl, alkyl, hydroxyl, sulfonyl, and sulfonylalkyl groups.

[0073] Likewise, in a particularly advantageous embodiment, the at least one brightener is a (C6-C 10) aryl radical-substituted sulfonamides, such as 4-aminobenzene-sulfonamide, 4-amino-N-pyridin-2-yl-benzenesulfonamide, 4-amino-N-(2-pyrimidinyl)benzenesulfonamide, 4-amino-N-(6-chloropyrazin-2-yl)benzenesulfonamide, 4-amino-N-(6-chloro-3-pyridazinyl)benzenesulfonamide, 4-amino-N-(5-methoxy-2-pyrimidinyl)benzenesulfonamide, 4-amino-N-(1,3-thiazol-2-yl)benzenesulfonamide, 4-amino-N-(5-methyl-1,3,4-thiadiazol-2yl)benzenesulfonamide, 4-amino-N-(4-methyl-1,3-thiazol-2yl)benzenesulfonamide, 4-amino-N-(4-methoxy-1,2,5-thiadiazol-3-yl)benzenesulfonamide, 4-amino-N-(5-methyl-3-isoxazolyl)benzenesulfonamide, 4-amino-N-(5-methyl-3-isoxazolyl)benzenesulfonamide, Amino-N-(4-methyl-2-pyrimidinyl)benzenesulfonamide, 4-amino-N-(5-methylpyrimidinyl)benzenesulfonamide, 4-amino-N-(6-methoxypyridazin-3-yl)benzenesulfonamide, 4-amino-N-(3-methoxy-2-pyrazinyl)benzenesulfonamide, 4-amino-N-(4,5-dimethyl-1,3-oxazol-2-yl)benzenesulfonamide, 4-amino-N-(3,4-dimethyl-5-isoxazolyl) Benzenesulfonamide, N-(3,3-dimethylacroyl)sulfanilamide, 4-amino-N-(4,6-dimethyl-2-pyrimidinyl)benzenesulfonamide, 4-amino-N-(2,6-dimethyl-2-pyrimidin-4-yl)benzenesulfonamide, 4-amino-N-(6-methoxy-2-methylpyrimidin-4-yl)benzenesulfonamide, 4-amino-N-(2,6-dimethoxy-4-pyrimidinyl)benzenesulfonamide, 4-amino-N-(5,The sulfanilamide is selected from the group consisting of 6-dimethoxy-4-pyrimidinyl)benzenesulfonamide, 4-amino-N-(2-phenylpyrazol-3-yl)benzenesulfonamide, 2-hydroxy-5-(2-(pyridinyl)sulfonyl)phenyl)azo)benzoic acid, 4-aminophenyl-sulfonylthiourea, 1-(4-aminobenzenesulfonyl)urea, 4-(aminomethyl)benzenesulfonamide, N-(p-aminophenyl-sulfonyl)acetamide, and 4-amino-N-(diaminomethylene)benzenesulfonamide (https: / / de.wikipedia.org / wiki / Sulfanilamid).

[0074] The at least one brightener may likewise be selected from the compound 2,2-sulfanediyldiethanol, cysteine, methionine, aliphatic and aromatic heterocyclic compounds having 5 to 7 ring atoms, the ring of which contains at least one heteroatom selected from nitrogen and sulfur, and which optionally contain one or more further heteroatoms selected from nitrogen, oxygen, and sulfur, and mixtures of these brighteners.

[0075] Aliphatic and aromatic heterocyclic compounds that can be used as brighteners in this regard have 5 to 7 ring atoms. At least one of these ring atoms is a nitrogen or sulfur atom. Optionally, one or more additional heteroatoms selected from oxygen, nitrogen, and sulfur may also be present. These additional heteroatoms may likewise be components of the aromatic or aliphatic ring, but may also be present in side chains and functional groups attached to the ring.

[0076] Suitable aliphatic heterocyclic compounds in this context are derivatives of tetrahydrothiophene, thiophene, tetrahydrofuran, furan, pyrrolidine, pyrrole, imidazolidine, pyrazolidine, imidazole, pyrazole, oxazolidine, isoxazolidine, oxazole, isoxazole, thiazolidine, isothiazolidine, thiazole, isothiazole, dioxolane, dithiolane, triazole, furazan, oxadiazole, thiadiazole, dithiazole, tetrazole, piperidine, pyridine, tetrahydropyran, pyran, thiane, thiopyran, piperazine, diazine, morpholine, oxazine, thiomorpholine, thiazine, dioxane, dioxine, dithiane, dithiin, hexahydro-1,3,5-triazine, triazine, trioxane, trithiane, tetrazine, pentazine, azepane, azepine, oxepane, oxepine, thiepine, diazepane, diazepine, thiazepine.

[0077] The aliphatic and aromatic heterocyclic compounds mentioned may have functional groups, which are advantageously thio, thiol, carbonyl, carboxyl, alkyl, hydroxyl, sulfonyl and sulfonylalkyl groups.

[0078] In a particularly advantageous embodiment in this regard, the at least one brightener is an aliphatic or aromatic heterocyclic compound having 5 to 7 ring atoms, the ring containing a nitrogen atom and a sulfur atom.

[0079] In a highly advantageous embodiment in this respect, the at least one brightener is selected from cysteine, 2,2-sulfanediyldiethanol, 2-mercaptonicotinic acid, pyridine-3-sulfonic acid, thiomorpholine, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,2,5-thiadiazole, and 1,3,4-thiadiazole, and derivatives thereof. Particularly preferred is thiomorpholine, also called tetrahydro-2H-1,4-thiazine according to the IUPAC nomenclature.

[0080] When the at least one brightener is selected from cysteine ​​and / or methionine and at least one amino acid is selected as the brightener carrier, the amino acid of the brightener carrier is not cysteine ​​or methionine.

[0081] The use of cysteine ​​and / or methionine in the electrolyte according to the invention as brightener carrier or brightener as defined above is illustrated below by means of some examples. a) At least one brightening agent is selected from cysteine ​​and / or methionine. next, - If at least one amino acid is selected as the brightener carrier, the amino acid of this brightener carrier is not cysteine ​​or methionine. Optionally, the electrolyte according to the invention may contain at least one pyridine carboxylic acid. b) At least one brightener is selected from 2,2'-sulfanediyldiethanol or aliphatic and aromatic heterocyclic compounds as defined above. next, When at least one amino acid is selected as a brightening agent, it may be an essential or non-essential amino acid according to the above definition, including cysteine ​​and / or methionine. Optionally, the electrolyte according to the invention may contain at least one pyridine carboxylic acid.

[0082] When the at least one brightening agent is selected from cysteine ​​and / or methionine, each of these two amino acids can be present, independently of the other, in the D-, L- or racemic form.

[0083] Furthermore, the following combinations of brightener carriers and brighteners are also possible. c) At least one brightener carrier is at least one pyridine carboxylic acid as defined above. No amino acids are used as brightener carriers. The brightener is selected from 2,2'-sulfanediyldiethanol, cysteine, methionine, and aliphatic and aromatic heterocyclic compounds as defined above.

[0084] The terms "brightener carrier" and "brightener" are known to those skilled in the art. Brightener carriers are also called "primary brighteners." Galvanic deposition of layers from electrolytes results in a certain brightness, but not high brightness, which often occurs only over a limited current density range. Brightener carriers often act to reduce particle size. Brighteners are also called "secondary brighteners." They result in highly glossy deposited layers, but are also often only effective over a limited current density range. High brightness over a wide current density range may be possible with the combination of a suitable brightener carrier and brightener.

[0085] The brightening agent or mixture of brightening agents is present in the electrolyte in a concentration of 0.005 to 25 g / L, preferably 0.01 to 5 g / L, particularly preferably 0.05 to 1 g / L.

[0086] The electrolyte according to the invention further contains an alkali metal hydroxide selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, and mixtures thereof, in a concentration of 1 to 200 g / L, preferably 5 to 150 g / L, particularly preferably 10 to 100 g / L. In an advantageous embodiment, the alkali metal hydroxide is potassium hydroxide. The pH of the electrolyte according to the invention is 8 or higher, advantageously 9 to 11.

[0087] The non-cyanide aqueous electrolyte according to the present invention optionally contains one or more humectants.

[0088] In a preferred embodiment, the at least one wetting agent is selected from: Nonionic wetting agents, such as β-naphthene ethoxylate potassium salt, fatty alcohol polyglycol ethers, polyethyleneimine, polyethylene glycol, and mixtures thereof. Wetting agents with a molecular weight of less than 2000 g / mol are particularly advantageous. Anionic wetting agents, such as N-dodecanoyl-N-methylglycine, (N-lauroylsarcosine) Na salt, alkyl collagen hydrolysate, 2-ethylhexyl sulfate Na salt, lauryl ether sulfate Na salt, and mixtures thereof. Cationic wetting agents, such as 1H-imidazolium 1-ethenyl (or 3-methyl)-, methyl sulfate homopolymers.

[0089] In the electrolyte according to the present invention, anionic and nonionic surfactants can typically be used as wetting agents, such as polyethylene glycol adducts, fatty alcohol sulfates, alkyl sulfates, alkyl sulfonates, aryl sulfonates, alkylaryl sulfonates, heteroaryl sulfates, betaines, fluorosurfactants, and salts and derivatives thereof (see also Kanani, N: Galvanotechnik [Electroplating technology]; Hanser Verlag, Munich Vienna, 2000; pp. 84 et seq.).

[0090] In a further advantageous embodiment, the electrolyte according to the present invention contains at least one additional salt. The anion of these salts is selected from the group consisting of sulfate, fluoride, chloride, bromide, iodide, carbonate, formate, acetate, propionate, butyrate, valerate, nitrate, nitrite, sulfonate, alkylsulfonate, in particular methanesulfonate, amidosulfonate, sulfamate, aminocarboxylic acid, and N-heterocyclic carboxylic acid anions. The cation of these salts is selected from ammonium, lithium, sodium, and potassium ions. In the case of polyprotonated acids, one or all hydrogen atoms may be replaced by the mentioned cations. If two or more hydrogen atoms are replaced by one of the mentioned cations, these cations may be the same or different. The at least one additional salt is hereinafter also referred to as a "conductive salt." The at least one conductive salt is selected from sodium, potassium, and ammonium salts of sulfate, hydrochloride, methanesulfonate, carbonate, nitrate, and phosphate. In an advantageous embodiment, the at least one conductive salt is a potassium salt, particularly preferably potassium methanesulfonate and / or potassium nitrate. In an advantageous embodiment, the at least one conductive salt is used in a concentration of 1 to 200 g / L, preferably 10 to 100 g / L.

[0091] The present invention also relates to a method for electrolytically depositing silver and silver alloy coatings from the electrolyte according to the invention, in which a conductive substrate is immersed in the electrolyte and a current flow is established between an anode in contact with the electrolyte and the substrate as the cathode. It should be noted that the embodiments described as preferred for the electrolyte also apply mutatis mutandis to the method covered herein.

[0092] The temperatures prevailing during the deposition of silver and silver alloy coatings can be selected as desired by those skilled in the art. They are therefore determined, on the one hand, by a sufficient deposition rate and the applicable current density range, and, on the other hand, by economical aspects or the stability of the electrolyte. It is advantageous to set the temperature between 20°C and 90°C, preferably between 40°C and 80°C, and particularly preferably between 50°C and 70°C.

[0093] The current density established between the cathode and the anode during the deposition process in the electrolyte according to the invention can be selected by a person skilled in the art according to the efficiency and quality of the deposition. Depending on the application and the type of coating facility, the current density in the electrolyte is advantageously between 0.1 and 100 A / dm 2 If necessary, the current density can be increased or decreased by adjusting the system parameters, such as the coating cell design, flow rate, anode or cathode conditions, etc. The current density is set to 0.1 to 100 A / dm 2 is advantageous, 0.2 to 50.0 A / dm 2 is preferable, and 0.5 to 30 A / dm 2 is most preferred.

[0094] In the context of the present invention, the low, medium and high current density ranges are defined as follows: -Low current density range: 0.1~0.75A / dm 2 , - Medium current density range: 0.75A / dm 2 Super~5A / dm 2 , -High current density range: 5A / dm 2 Super.

[0095] The electrolyte according to the invention and the method according to the invention can be used for the electrolytic deposition of silver and silver alloy coatings, for example for technical applications such as electrical plug connections and printed circuit boards, and for decorative applications such as jewellery and watches. In an advantageous embodiment of the invention, a low current density range is used for the electrolytic deposition of silver and silver alloy coatings, and the at least one brightener carrier contains 0.2 to 3 mol / L of at least one amino acid and 0.01 to 0.5 mol / L of at least one pyridine carboxylic acid.

[0096] In an advantageous embodiment of the present invention, a medium current density range is used for the electrolytic deposition of silver and silver alloy coatings, and the at least one brightener carrier contains 0.1 to 1.5 mol / L of at least one amino acid and 0.1 to 1 mol / L of at least one pyridine carboxylic acid.

[0097] In an advantageous embodiment of the present invention, a high current density range is used for the electrolytic deposition of silver and silver alloy coatings, and the at least one brightener carrier contains 0.01 to 0.1 mol / L of at least one amino acid and 0.25 to 2.5 mol / L of at least one pyridine carboxylic acid.

[0098] As already indicated, the electrolyte according to the present invention is alkaline. The pH should be greater than or equal to 7, particularly preferably between 8 and 11, and even better between 9 and 10.5. Changes in the pH value of the electrolyte may occur during electrolysis. Therefore, in a preferred embodiment of the method, the skilled person will continue to monitor the pH value during electrolysis and, if necessary, adjust it to the nominal value. Advantageously, potassium hydroxide or methanesulfonic acid is used to adjust the pH. Alternatively, instead of potassium hydroxide, lithium hydroxide or sodium hydroxide or a mixture of these alkali metal hydroxides can also be used.

[0099] In using the electrolyte, a variety of anodes can be used. Soluble or insoluble anodes are suitable, as are combinations of soluble and insoluble anodes. When a soluble anode is used, silver anodes are particularly preferred.

[0100] Preferred insoluble anodes are those made from materials selected from the group consisting of platinized titanium, graphite, mixed metal oxides, glassy carbon anodes, and specialty carbon materials (DCL, "diamond-like carbon"), or combinations of these anodes. Platinized titanium or titanium coated with a mixed metal oxide is advantageous, with the mixed metal oxide preferably selected from iridium oxide, ruthenium oxide, tantalum oxide, and mixtures thereof. Also advantageously used in the practice of the present invention are mixed oxide anodes made of iridium-transition metal oxides, more preferably iridium-ruthenium mixed oxide, iridium-ruthenium-titanium mixed oxide, or iridium-tantalum mixed oxide. Further information can be found in Cobley, AJ et al. (The Use of Insoluble Anodes in Acid Sulphate Copper Electrodeposition Solutions, Trans IMF, 2001, 79(3), pp. 113 and 114).

[0101] Depending on the embodiment, the deposited silver and silver alloy coatings can have a thickness of up to several millimeters, preferably 0.005 to 500 μm, particularly preferably 0.01 to 25 μm, very particularly preferably 0.5 to 10 μm.

[0102] For example, thin layer thicknesses of silver in the range of 0.1 to 0.3 μm are typically used in the coating of plastic caps in rack operation. Here, low current densities in the range of 0.25 to 0.75 A / dm² are used. A further application of low current densities is the coating of contact pins, for example, with drum or vibration techniques. Here, approximately 0.5 to 3 μm of silver is applied at current densities in the range of 0.25 to 0.75 A / dm². Layer thicknesses in the range of 1 to 10 μm are typically deposited with rack operation, primarily for decorative applications, using current densities in the range of 1 to 5 A / dm². For technical applications, layer thicknesses of up to 25 μm may also be deposited. In continuous systems, layer thicknesses are achieved at the highest possible deposition rate, and therefore at the highest possible current densities, of 5 to 30 A / dm². 2 are deposited over a relatively wide range of about 0.5 to about 5 μm. In addition, there are special applications for depositing relatively high layer thicknesses of several tens of μm up to several millimeters, for example in the case of electroforming.

[0103] Instead of direct current, pulsed direct current can also be used, whereby the current is interrupted for a certain period of time (pulse plating). In reverse pulse plating, the polarity of the electrodes is changed, which causes partial anodic stripping of the coating. In this way, the layer buildup is controlled by successive alternations with cathodic pulses. Simple pulse conditions, for example, a current (t) of 1 second at a medium current density, on ) and a 0.5 second pulse pause (t off ) resulted in a uniform, glossy white coating.

[0104] Suitable substrate materials typically used herein are copper-based materials such as pure copper, brass, or bronze, iron-based materials such as iron or stainless steel, nickel, gold, and silver. The substrate material may also be a multilayer system coated galvanically or with another coating technique. This relates, for example, to circuit board materials or iron materials that have been nickel- or copper-plated and then optionally gold-plated or pre-silver-coated. Another substrate material is a wax core pre-coated with silver conductive varnish (electroforming).

[0105] A special silver electrolyte for the purposes of this invention is a pre-silver or silver stripping electrolyte. This is intended to mean an electrolyte that typically contains a small amount of silver and a large amount of complexing agent. As a result, silver can be deposited only by applying a voltage, rather than by charge exchange. Layers deposited by charge exchange have poor adhesion, so a thin layer of pre-silver is often deposited before applying a thicker silver layer using a different electrolyte (see Example 4).

[0106] The electrolyte according to the invention has long-term stability and high anodic solubility. The method according to the invention for electrolytic deposition of silver and silver alloy coatings from this electrolyte produces very white coatings, the color of which is comparable to that of L. * a * b * It is close to the white point of the color space. * = 100, and a * and b * is equal to zero. Even at high layer thicknesses of more than 5 μm, the coatings are highly glossy, lustrous, and very tarnish-resistant, i.e., no subsequent yellowing occurs. Such coatings could previously only be deposited with cyanide-based electrolytes. Thanks to the electrolyte according to the invention, silver and silver alloy coatings can be deposited over a very wide current density range.

[0107] Exemplary embodiments:

[0108] One liter of the following electrolyte is stirred using a magnetic stirrer with a 60 mm long cylindrical magnetic stir bar at at least 200 rpm and heated to the temperature described in the exemplary embodiment, and this stirring and temperature are maintained during coating.

[0109] After reaching the desired temperature, the pH of the electrolyte is adjusted to the value described in the exemplary embodiment using a solution of KOH (c=0.5 g / mL) and methanesulfonic acid (c=70%).

[0110] Two pure silver plates with a purity of at least 99.9% serve as anodes, which may also be covered with a bag made of fabric, filter paper, or a semipermeable membrane such as Nafion.

[0111] The cathode used is a mechanically polished brass sheet with a surface area of ​​at least 0.2 dm², which is pre-coated with at least 5 µm of nickel from an electrolyte to produce a high-gloss layer, and a gold layer approximately 0.1 µm thick may be deposited on top of the nickel layer.

[0112] These cathodes are cleaned using electrolytic degreasing (5-7 V) and acid cleaning with sulfuric acid (c = 5% sulfuric acid) before introduction into the electrolyte. Between each cleaning step and before introduction into the electrolyte, the cathodes are rinsed with deionized water.

[0113] The cathode is placed between the anodes in the electrolyte and moved parallel to them at a minimum of 5 cm / sec; the distance between the anode and cathode must not change during this process.

[0114] The cathode is coated by applying a direct current between the anode and the cathode in the electrolyte, the current strength being at least 0.5 A / dm on the surface. 2 A higher current density can be chosen if the electrolyte mentioned in the application example is capable of producing layers that can be used in technical decorative ways.

[0115] The duration of the current is selected so that an average layer thickness of at least 1.5 μm is achieved on the surface. Higher layer thicknesses can be achieved if the electrolytes mentioned in the application examples are capable of producing them in a quality that can be used in technical decorative applications.

[0116] After coating, the cathode is removed from the electrolyte and rinsed with deionized water. After coating, the cathode may be treated as usual with hot water, complexing agent solution, acid wash, or with a tarnish protectant, for example based on octadecanethiol.

[0117] The cathode may be dried with compressed air, hot air, or by centrifugation.

[0118] The surface area of ​​the cathode, the magnitude and duration of the applied current, and the weight of the cathode before and after coating are recorded and used to determine the average layer thickness and efficiency of deposition.

[0119] The color of the precipitate layer is expressed as CIEL * a * According to b L * a * b * Determined by measurement and recorded.

[0120] Tests according to the invention and comparative tests are shown in the table below.

[0121] The potassium hydroxide and methanesulfonic acid used to adjust and set the pH are not specified in the table. Methods for adjusting or setting the pH are known to those skilled in the art. In preparing the electrolyte according to the present invention, an aqueous solution of all the components listed in the table can be first prepared, and then the pH can be adjusted to the desired value using potassium hydroxide or methanesulfonic acid. Alternatively, the potassium hydroxide solution can be added first, followed by the addition of the hydantoin derivative, followed by the addition of all other components, and finally the pH can be adjusted to the desired value using potassium hydroxide or methanesulfonic acid. During the deposition of the silver or silver alloy layer, the pH can also be adjusted using potassium hydroxide or methanesulfonic acid. [Table 1] [Table 2] [Table 3] [Table 4] Observation 1: a Glass beaker (60 mm stirring bar, 200 rpm), cathode movement b Glass beaker (60 mm stirring rod, 200 rpm), barrel c. Jet plating (400L / h) d Hull cell (stirring rod 40 mm, 600 rpm) Observation 2: a Silver anode b Platinum-plated titanium c Mixed metal oxide Observation 3: a Homogeneous, white, glossy b Homogeneous, white, matte c Yellowish Observation 4: a No sedimentation, stable for several months, consistent quality coating b No precipitation, but consistent coating quality is not possible c Precipitates after a short time ND Not measured [Table 5] [Table 6] [Table 7] Observation 1: a Glass beaker (60 mm stirring bar, 200 rpm), cathode movement b Glass beaker (60 mm stirring rod, 200 rpm), barrel c. Jet plating (400L / h) d Hull cell (stirring rod 40 mm, 600 rpm) Observation 2: a Silver anode b Platinum-plated titanium c Mixed metal oxide Observation 3: a Homogeneous, white, glossy b Homogeneous, white, matte c Yellowish Observation 4: a No sedimentation, stable for several months, consistent quality coating b No precipitation, but consistent coating quality is not possible c Precipitates after a short time ND Not measured [Table 8] [Table 9] Observation 1: a Glass beaker (60 mm stirring bar, 200 rpm), cathode movement b Glass beaker (60 mm stirring rod, 200 rpm), barrel c Glass beaker (60 mm stirring bar, 400 rpm), cathode movement d. Jet plating (400L / h) Observation 2: a Silver anode b Platinum-plated titanium c Mixed metal oxide Observation 3: a Homogeneous, white, glossy b Homogeneous, white, matte c Yellowish Observation 4: a No sedimentation, stable for several months, consistent quality coating b No precipitation, but consistent coating quality is not possible c Precipitates after a short time ND Not measured [Table 10] Determining color values

[0122] For the silver layer deposited from the electrolyte according to the invention and three comparative examples, L * a * The color values ​​were measured according to the b color space. Test conditions: Capacity: 1 liter Magnetic stirrer: IKA RET CV Agitation: 200 and 400 rpm, 3 A / dm 2 At current densities above 1000 kJ / s, high stirring speeds were used. Stirring rod: 60mm Cathode: moved parallel to the anode, 5 cm / sec Cathode surface: 0.2dm 2 ,brass Cathode current density: 0.5~3A / dm 2 Layer thickness: 1.5 μm. Anode: 99.9% silver

[0123] Temperature: 40°C to 65°C depending on the stability of the solution. Comparative Example 4 was tested at 40°C because at 50°C (the original parameters of Example 5 of U.S. Pat. No. 5,601,696), more silver was deposited than theoretically electrochemically possible. This indicates that chemical deposition is occurring in addition to galvanic deposition, the latter of which is undesirable. pH: 9.5-10 depending on example. Measurement equipment: Konica Minolta Spectrophotometer CM-700, SCI 10° / D65 L * Determining Values

[0124] L * a * b * In color space, L * The axis represents the color brightness, with values ​​ranging from 0 (black) to 100 (white).

[0125] In each case, a 1.5 μm thick layer was deposited at a current density of 0.5 to 3.0 A / dm2. [Table 11]

[0126] Figure 1 shows the L * The result of the value determination is shown below. a * Determining Values

[0127] L * a * b * In color space, a * The axis represents the green or red portion of the color, with negative values ​​indicating green and positive values ​​indicating red.

[0128] In each case, a 1.5 μm thick layer was applied at 0.5 to 3.0 A / dm 2 The deposition was carried out at a current density of . [Table 12]

[0129] Figure 2 shows a * The result of the value determination is shown below. b * Determining Values

[0130] L * a * b * In color space, b * The axis represents the blue or yellow portion of the color, with negative values ​​indicating blue and positive values ​​indicating yellow.

[0131] In each case, a 1.5 μm thick layer was applied at 0.5 to 3.0 A / dm 2 The deposition was carried out at a current density of . [Table 13]

[0132] Figure 3 shows the * The result of the value determination is shown below.

Claims

1. 1. An aqueous, cyanide-free electrolyte for the electrolytic deposition of silver alloy coatings, comprising: a) at least one silver compound having a silver concentration of 4 to 40 g / L; b) a compound of at least one alloying metal having a concentration of 1 to 10 g / L of alloying metal, said alloying metal being selected from tin, nickel, and rhodium; c) at least one compound of formula (I), 【Chemistry 1】 During the ceremony, R1, R2, R3, and R4 independently represent hydrogen, a linear or branched alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, a hydroxyalkyl group having 1 to 5 carbon atoms, or an aryl group; and, at least one compound of formula (I), wherein said at least one compound of formula (I) is present in a concentration of 10 to 100 g / L, d) at least one brightener carrier, i. at least one amino acid at a concentration of 0.0001 to 5 mol / L; e) at least one brightener selected from sulfonamides at a concentration of 0.005 to 25 g / L; f) an alkali metal hydroxide selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, and mixtures thereof, in a concentration of 1 to 200 g / L; in dissolved form, g) the electrolyte has a pH of 7 or greater; The sulfonamide has R １ -SO ２ -NR ２ R ３ and In the formula, R １ , R ２ , and R ３ are independently hydrogen, (C １ ~C １０ ) alkyl, (C ３ ~C １０ ) cycloalkyl, (C ６ ~C １０ ) aryl, (C ５ ~C １０ ) heteroaryl, (C ５ ~C １０ ) heterocycloalkyl, and (C ６ ~C １０ ) an electrolyte characterized in that the aryl has an amino group in the para position on the aryl radical.

2. 2. The electrolyte of claim 1, wherein the silver compound is selected from silver methanesulfonate, silver carbonate, silver phosphate, silver pyrophosphate, silver nitrate, silver oxide, silver lactate, silver fluoride, silver bromide, silver chloride, silver iodide, and silver sulfate.

3. 2. The electrolyte of claim 1, wherein the at least one compound of formula (I) is selected from 1-methylhydantoin, 1,3-dimethylhydantoin, 5,5-dimethylhydantoin, 1-hydroxymethyl-5,5-dimethylhydantoin, 5,5'-diethylhydantoin, and 5,5-diphenylhydantoin, and mixtures thereof.

4. 2. The electrolyte of claim 1, wherein the at least one amino acid is selected from glycine, alanine, proline, and sarcosine, and mixtures thereof.

5. 10. A method for electrolytically depositing a silver alloy coating from the electrolyte of claim 1, comprising: A conductive substrate is immersed in the electrolyte, and a current flow is established between an anode in contact with the electrolyte and the substrate as a cathode; A method characterized in that the current density during electrolysis is 0.5 to 30 A / dm 2 .

6. 6. The method of claim 5, wherein the temperature of the electrolyte is between 20°C and 90°C.

7. 6. The method according to claim 5, wherein the pH is continuously adjusted to a range of 9 to 11 during the electrolysis.

8. 6. The method according to claim 5, characterized in that a soluble silver anode and / or an insoluble anode is used as the anode.

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