Electrolyte for the Cyanide-Free Deposition of Silver

Abstract

The present invention relates to an electrolyte and to a method for the electrolytic deposition of silver coatings and silver alloy coatings. The electrolyte according to the invention is cyanide-free, storage-stable and ensures the deposition of high-gloss, brilliant and white silver and silver alloy layers for technical and decorative applications.

Claims

1. An aqueous cyanide-free electrolyte for the electrolytic deposition of silver and silver alloy coatings, which has the following constituents in dissolved form: a) at least one silver compound in a concentration of 0.1-150 g/l silver, b) at least one compound of an alloy metal in a concentration of 0 to 100 g/l alloy metal, c) at least one compound of formula (I) ##STR00003## wherein R.sub.1, 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 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 selected from at least one amino acid in a concentration of 0.0001- 5 mol/l, in particular 0.01-5 mol/l, and/or ii. at least one pyridinecarboxylic acid in a concentration of 0.01-5 mol/l e) at least one brightening agent selected from sulfonamide, 2,2′-sulfanediyldiethanol, cysteine, methionine, aliphatic and aromatic heterocyclic compounds having 5 to 7 ring atoms, wherein the ring of the aliphatic and aromatic heterocyclic compounds contains at least one heteroatom selected from nitrogen and sulfur, and wherein the aliphatic and aromatic heterocyclic compounds optionally contain one or more further heteroatoms selected from nitrogen, oxygen and sulfur, and also mixtures of these brightening agents, wherein the concentration of the brightening agent or of the mixture of brightening agents is 0.005-25 g/l, wherein, if the at least one brightening agent is selected from cysteine and/or methionine and at least one amino acid according to d)i) is selected as brightener carrier, the brightener carrier amino acid is neither cysteine nor methionine, f) an alkali metal hydroxide selected from lithium hydroxide, sodium hydroxide, potassium hydroxide and mixtures thereof in a concentration of 1-200 g/l, g) wherein the electrolyte has a pH of greater than or equal to 7.

2. The electrolyte Electrolyte according to claim 1, characterized in that wherein the sulfonamide has R.sub.1-SO.sub.2-NR.sub.2R.sub.3 as structural element, wherein R.sub.1, R.sub.2 and R.sub.3 are, independently of one another, a (C.sub.1-C.sub.10) alkyl, a (C.sub.3-C.sub.10) cycloalkyl, a (C.sub.6-C.sub.10) aryl, a (C.sub.5-C.sub.10) heteroaryl, ora (C.sub.5-C.sub.10) heterocycloalkyl.

3. The electrolyte according to 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.

4. The electrolyte according to claim 1, wherein the compound of the at least one alloy metal is selected from compounds of tin, palladium, antimony, cobalt, indium, iron, nickel, ruthenium, rhodium, platinum, copper, zinc, selenium, tellurium, bismuth, iridium, germanium, gallium, rhenium, tungsten, molybdenum, dysprosium, cerium, and gold.

5. The electrolyte according to 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.

6. The electrolyte according to claim 1, wherein the at least one amino acid is selected from glycine, alanine, proline sarcosine and mixtures thereof.

7. The electrolyte according to claim 1, wherein the at least one pyridinecarboxylic acid is selected from picolinic acid, picolinic acid amide, nicotinic acid, nicotinamide, isonicotinic acid, isonicotinamide, and mixtures thereof

8. A method for the electrolytic deposition of silver coatings and silver alloy coatings from an electrolyte according to claim 1, which comprises immersing an electrically conductive substrate in the electrolyte and a flow of current is established between an anode in contact with the electrolyte and the substrate as cathode.

9. The method according to claim 8, characterized in that wherein the temperature of the electrolyte is 20° C. to 90° C.

10. The method according to claim 8, wherein the current density during electrolysis is 0.2 to 100 A/dm.sup.2.

11. The method according to claim 8, which comprises adjusting the pH to range between 9 and 11 during the electrolysis.

12. The method according to claim 8, wherein a soluble silver anode and/or an insoluble anode is used as anode.

Description

EXEMPLARY EMBODIMENTS

[0118] 1 liter of the electrolyte mentioned below is heated using a magnetic stirrer, with stirring with a 60 mm long cylindrical magnetic stirrer rod at at least 200 rpm to the temperature stated in the exemplary embodiment. This stirring and temperature is also maintained during coating.

[0119] After reaching the desired temperature, the pH of the electrolyte is adjusted to the value mentioned in the exemplary embodiment using a KOH solution (c=0.5 g/ml) and methanesulfonic acid (c=70%).

[0120] Two plates of fine silver with at least 99.9% purity serve as anodes. These anodes may also be covered with bags made of textiles, filter paper or a semi-permeable membrane such as Nafion.

[0121] The cathode used is a mechanically polished brass sheet having at least 0.2 dm.sup.2 surface area, which was previously coated with at least 5 pm of nickel from an electrolyte which produces high-gloss layers. An approximately 0.1 pm thick gold layer can also be deposited on the nickel layer.

[0122] These cathodes are cleaned before introduction into the electrolyte using electrolytic degreasing (5-7 V) and sulfuric acid-containing pickling (c=5% sulfuric acid). Between each cleaning step and prior to introduction into the electrolyte, the cathode is rinsed with deionized water.

[0123] The cathode is positioned in the electrolyte between the anodes and moved parallel thereto at a minimum of 5 cm/second; the distance between anode and cathode must not change during this process.

[0124] In the electrolyte, the cathode is coated by applying an electric direct current between anode and cathode. The current intensity is selected in such a way that at least 0.5 A/dm.sup.2 is achieved on the surface. Higher current densities can be selected if the electrolyte mentioned in the application example is capable of producing layers which can be used in a technically decorative manner.

[0125] The duration of the current flow is selected in such a way that at least one layer thickness of 1.5 μm on average is achieved over the surface. Higher layer thicknesses can be produced if the electrolyte mentioned in the application example is capable of producing these at a quality which can be used in a technically decorative manner.

[0126] After coating, the cathode is removed from the electrolyte and rinsed with deionized water. After the coating, a customary treatment can be carried out in hot water, complexing agent solution, pickling or a treatment with tarnish protection, e.g. based on octadecanethiols.

[0127] The cathodes can be dried by compressed air, hot air or centrifugation.

[0128] 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 documented and used to determine the average layer thickness and the efficiency of the deposition.

[0129] The color of the deposited layers is determined and documented by an L*a*b* measurement according to CIEL*a*b.

[0130] Experiments and comparative experiments according to the invention are given in the tables below.

[0131] Potassium hydroxide and methanesulfonic acid, which are used to adjust and set the pH, are not explicitly listed in the tables. The person skilled in the art knows how to adjust or set the pH. In the production of the electrolytes according to the invention, it is possible first to prepare an aqueous solution of all components mentioned in the table and to subsequently adjust the pH to the desired value with potassium hydroxide or methanesulfonic acid. Alternatively, it is also possible first to initially charge a potassium hydroxide solution, then add the hydantoin derivative thereto, and subsequently to add all other ingredients and finally to adjust the pH to the desired value with potassium hydroxide or methanesulfonic acid. During the deposition of the silver layers or silver alloy layers, the pH can also be adjusted with potassium hydroxide or methanesulfonic acid.

TABLE-US-00001 TABLE 1 Exemplary embodiments according to the invention Example no. Component Concentration 1 2 3 4 5 6 Silver (as silver g/l 20 20 40 0 10 0 methanesulfonate) Silver (as silver nitrate) g/l 0 0 0 45 0 0 Silver (as silver oxide) g/l 0 0 0 0 0 0 Silver (as silver hydantoin g/l 0 0 0 0 0 10 complex) Tin (as potassium g/l 0 0 0 0 30 0 hexahydroxostannate(IV)) Palladium (as palladium(II) g/l 0 0 0 0 0 5 bis(ethylenediamine) sulfate) Rhodium (as rhodium(III) g/l 0 0 0 0 0 0 sulfate) Potassium nitrate g/l 0 0 0 0 0 0 Potassium chloride g/l 0 0 0 0 8 8 Potassium methanesulfonate g/l 0 0 0 0 0 0 Hydantoin g/l 0 0 0 0 0 0 5,5‘-Dimethylhydantoin g/l 150 150 120 160 50 0 5,5‘-Diethylhydantoin g/l 0 0 0 0 0 50 Glycine g/l 40 0 0.5 35 0 0 2,2’-Sulfanediyldiethanol g/l 0 0 0 0 0 0 Tetrahydro-2H-1,4-thiazine ml/l  0.2 0 0.2 0.4 0 0 Cysteine g/l 0 0.2 0 0 0 0 Beta-alanine g/l 0 50 0 0 0 0 Methionine g/l 0 0 0 0 0 0 Proline g/l 0 0 0 0 0 0 Sarcosine g/l 0 0 0 0 0 0 L-Glutamic acid g/l 0 0 0 0 0 0 2-Mercaptonicotinic acid g/l 0 0 0 0 0 0 Picolylamine ml/l  0 0 0 0 0 0 Nicotinic acid g/l 0 0 100 0 0 0 Nicotinamide g/l 0 0 0 100 0 0 Parameters/observations pH 9.6 9.6 10 9 12.1 9.5 Temperature [° C.] 65 55 65 65 40 40 Current density [A/dm2] 0.5-3 0.5-1.5 5-20 0.1-5 1 2 Movement (observation 1) a a c d a a Anode (observation 2) a a b a a a Appearance (observation 3) a a b a b. gray a, gray Layer thickness [μm] 1.5 1.6 2 2.07 1.77 Color [L*a*b*] ND L* 98.7 92.2 98.5 54.32 74.68 a* −0.09 −0.3 −0.10 +2.81 −0.84 b* +1.88 +4.32 1.78 +15.07 −1.37 Silver content [wt %] 100 100 100 100 96.3 92.1 Electrolyte stability a a a a a a (observation 4) Example no. Component Concentration 7 8 9 10 11 12 Silver (as silver g/l 10 10 5 10 10 10 methanesulfonate) Silver (as silver nitrate) g/l 0 0 0 0 0 0 Silver (as silver oxide) g/l 0 0 0 0 0 0 Silver (as silver hydantoin g/l 0 0 0 0 0 0 complex) Tin (as potassium g/l 0 0 0 0 0 0 hexahydroxostannate(IV)) Palladium (as palladium(II) g/l 0 0 0 0 0 0 bis(ethylediamine) sulfate) Rhodium (as rhodium(III) g/l 6 0 0 0 0 0 sulfate) Potassium nitrate g/l 0 0 0 0 0 0 Potassium chloride g/l 8 0 0 0 0 0 Potassium methanesulfonate g/l 0 0 30 0 0 0 Hydantoin g/l 0 0 0 0 0 0 5,5‘-Dimethylhydantoin g/l 50 75 150 60 60 75 5,5‘-Diethylhydantoin g/l 0 0 0 0 0 0 Glycine g/l 0 40 100 30 30 20 2,2’-Sulfanediyldiethanol g/l 0 0 0 0 0 0 Tetrahydro-2H-1,4-thiazine ml/l  0 0 0 0 0 0.2 Cysteine g/l 0 0.5 0 0.2 0.2 0 Beta-alanine g/l 0 0 0 0 0 0 Methionine g/l 0 0 0 0 0 0 Proline g/l 0 0 0 0 0 0 Sarcosine g/l 0 0 0 0 0 0 L-Glutamic acid g/l 0 0 0 0 0 0 Toluenesulfonamide g/l 0 0 0 0 0 0 Mercaptonicotinic acid g/l 0 0 0 0 0 0 Picolylamine ml/l  0 0.05 0 0 0 0 Nicotinic acid g/l 0 0 0 30 0 0 Nicotinamide g/l 0 0 0 0 40 20 Parameters/observations pH 12.8 9.5 8.8 9.5 9.5 9.5 Temperature [° C.] 40 55 55 55 55 65 Current density [A/dm2] 1 0.5 0.5 0.5-1.0 0.25-1.0 0.5-2.0 Movement (observation 1) a b a a a a Anode (observation 2) a a a, b a a a Appearance (observation 3) a a a a a a Layer thickness [μm] 2.39 2 0.1 2 2 2 Color [L*a*b*] ND L* 80.91 97.8 98 98.0 99.4 a* −1.76 −0.44 −0.4 −0.5 −0.09 b* +4.36 +4.06 +3.7 +4.0 +1.4 Silver content [wt %] 93.9 100 100 100 100 100 Electrolyte stability a a a a a a (observation 4) Example no. Component Concentration 13 14 15 16 17 18 Silver (as silver g/l 0 10 10 10 30 30 methanesulfonate) Silver (as silver nitrate) g/l 0 0 0 0 0 0 Silver (as silver oxide) g/l 10 0 0 0 0 0 Silver (as silver hydantoin g/l 0 0 0 0 0 0 complex) Tin (as potassium g/l 0 0 0 0 0 0 hexahydroxostannate(IV)) Palladium (as palladium(II) g/l 0 0 0 0 0 0 bis(ethylediamine) sulfate) Rhodium (as rhodium(III) g/l 0 0 0 0 0 0 sulfate) Potassium nitrate g/l 10 0 0 0 0 0 Potassium chloride g/l 0 0 0 0 0 0 Potassium methanesulfonate g/l 0 0 0 0 0 0 Hydantoin g/l 0 0 0 0 0 0 5,5‘-Dimethylhydantoin g/l 60 150 75 75 225 150 5,5‘-Diethylhydantoin g/l 0 0 0 0 0 0 Glycine g/l 40 50 20 20 0 40 2,2’-Sulfanediyldiethanol g/l 0 0 1 0 0 0 Tetrahydro-2H-1,4-thiazine ml/l  0 0 0 0.2 0.2 0 Cysteine g/l 0 0 0 0 0.2 0 Beta-alanine g/l 0 0 0 0 0 0 Methionine g/l 0 0 0 0 0.2 1 Proline g/l 0 0 0 0 0 0 Sarcosine g/l 0 0 0 0 0 0 L-Glutamic acid g/l 0 0 0 0 0 0 Toluenesulfonamide g/l 1.0 2.0 0 0 Mercaptonicotinic acid g/l 0.1 0.2 0 0 0 0 Picolylamine ml/l  0 0 0 0 0 0 Nicotinic acid g/l 0 0 0 20 0 0 Nicotinamide g/l 0 0 20 0 0 0 Parameters/observations pH 9.5 9.7 9.5 9.5 9.6 9.6 Temperature [° C.] 50 60 60 60 60 60 Current density [A/dm2] 0.5-1.0 0.5-1.5 0.5-2.0 0.25-1.5 0.1-0.7 0.1-1 Movement (observation 1) a a a a d d Anode (observation 2) a a a a a a Appearance (observation 3) a a a a a a Layer thickness [μm] 2 2 2 2 1.5 1.5 Color [L*a*b*] ND ND L* 98.1 97.4 98.4 98.9 a* −0.5 −0.3 −0.19 −0.11 b* +3.8 +4.6 +2.5 +1.5 Silver content [wt %] 100 100 100 100 100 100 Electrolyte stability a a a a a a (observation 4) Example no. Component Concentration 19 20 21 22 23 24 Silver (as silver g/l 0 20 20 20 20 20 methanesulfonate) Silver (as silver nitrate) g/l 0 0 0 0 0 0 Silver (as silver oxide) g/l 10 0 0 0 0 0 Silver (as silver hydantoin g/l 0 0 0 0 0 0 complex) Tin (as potassium g/l 0 0 0 0 0 0 hexahydroxostannate(IV)) Palladium (as palladium(II) g/l 0 0 0 0 0 0 bis(ethylediamine) sulfate) Rhodium (as rhodium(III) g/l 0 0 0 0 0 0 sulfate) Potassium nitrate g/l 0 0 0 0 0 0 Potassium chloride g/l 0 0 0 0 0 0 Potassium methanesulfonate g/l 0 0 0 0 0 0 Hydantoin g/l 0 0 0 0 0 0 5,5‘-Dimethylhydantoin g/l 60 150 150 150 150 150 5,5‘-Diethylhydantoin g/l 0 0 0 0 0 0 Glycine g/l 40 0 20 0 0 0 2,2’-Sulfanediyldiethanol g/l 0 0 0 0 0 0 Tetrahydro-2H-1,4-thiazine ml/l  0 0.2 0.2 0.2 0.2 0.2 Cysteine g/l 0 0 0 0 0 0 Beta-alanine g/l 0 0 0 0 0 0 Methionine g/l 0.25 0 0 0 0 0 Proline g/l 0 0 0 0 0 150 Sarcosine g/l 0 0 0 115 115 0 L-Glutamic acid g/l 0 0 195 0 0 0 Toluenesulfonamide g/l 0 0 0 0 0 0 Mercaptonicotinic acid g/l 0 0 0 0 0 0 Picolylamine ml/l  0 0 0 0 0 0 Nicotinic acid g/l 0 0 0 0 20 0 Nicotinamide g/l 0 0 0 0 0 0 Parameters/observations pH 9.6 9.6 9.6 9.6 9.6 9.6 Temperature [° C.] 60 65 65 65 65 65 Current density [A/dm2] 0.1-0.7 0.1-0.4 0.1-1 0.1-3 0.1-3 0.1-1 Movement (observation 1) d d d d d d Anode (observation 2) a a a a a a Appearance (observation 3) a a a a a a Layer thickness [μm] 1.5 1.5 1.5 1.5 1.5 1.5 Color [L*a*b*] ND ND ND ND ND L* 98.7 a* −0.2 b* 1.7 Silver content [wt %] 100 100 100 100 100 100 Electrolyte stability a a a a a a (observation 4) Observation 1: a Glass beaker (60 mm stirrer bar; 200 rpm), cathode movement b Glass beaker (60 mm stirrer bar; 200 rpm), barrel c Jet plating (400 l/h) d Hull cell (stirrer bar 40 mm; 600 rpm) Observation 2: a Silver anode b Platinized titanium c Mixed metal oxide Observation 3: a Homogeneous, white, glossy b Homogeneous, white, matte c Yellowish Observation 4: a No precipitation, stable for months, constant quality of the coatings b No precipitation, but no constant quality of the coatings possible c Precipitation after a short time ND not determined

TABLE-US-00002 TABLE 2 Exemplary embodiments according to the invention Example no. Component Concentration 25 26 27 28 29 Silver (as silver g/l 0 0 40 0 20 methanesulfonate) Silver (as silver nitrate) g/l 0 30 0 5 0 Silver (as silver oxide) g/l 20 0 0 0 0 Silver (as silver hydantoin g/l 0 0 0 0 0 complex) Nickel (as nickel(II) g/l 0 0 0 0 0 sulfate heptahydrate) Tin (as potassium g/l 0 0 0 0 0 hexahydroxostannate(IV)) Palladium (as palladium(II) g/l 0 0 0 0 0 bis(ethylenediamine) sulfate) Rhodium (as rhodium(III) g/l 0 0 0 0 0 sulfate) Potassium nitrate g/l 0 0 0 0 0 Potassium chloride g/l 0 0 0 0 0 Potassium methanesulfonate g/l 0 0 0 0 0 Hydantoin g/l 7 0 0 0 0 5,5‘-Dimethylhydantoin g/l 125 150 120 40 125 5,5‘-Diethylhydantoin g/l 0 0 0 0 0 Glycine g/l 40 60 10 40 Tetrahydro-2H-1,4-thiazine ml/l  0 0 0 0 0 Cysteine g/l 0.5 0.25 0.2 0.25 0.3 4-Amino-N-(2-pyrimidinyl) g/l 0 0 0 0 0 benzenesulfonamide 4-Amino-N-(1,3-thiazol-2-yl) g/l 0.1 0 0 0 0 benzenesulfonamide 4-Aminobenzenesulfonamide g/l 0 1.0 0 0.5 0 4-Amino-N-(diaminomethylene) g/l 0 0 0 0 0.1 benzenesulfonamide Polyethyleneimine (Lupasol FG) ml/l  0 0 0.1 0 0 Trans-3-(3-pyridyl)acrylic acid g/l 0 0 1 0 0 Beta-alanine g/l 0 0 0 0 0 Methionine g/l 0 0 0 0 0 Proline g/l 0 0 0 0 0 Sarcosine g/l 0 0 0 0 0 Nicotinic acid g/l 0 0 100 0 0 Nicotinamide g/l 0 0 0 0 0 Parameters/observations pH 9.2 9.5 9.8 8.8 9.6 Temperature [° C.] 50 60 60 45 50 Current density [A/dm2] 0.25-2.0 0.5-5.0 0.5-10.0 0.1-1.0 0.25-2.0 Movement (observation 1) a d c b b Anode (observation 2) a a b a a Appearance (observation 3) c a,b a a a Layer thickness [μm] 2 2 2 0.2 10 Color [L*a*b*] ND L* 96.6 98.4 98.1 98 a* −1.6 −0.3 −0.4 −0.4 b* 10.3 5.8 3.3 3.5 Silver content [wt %] Electrolyte stability a a a a a (observation 4) Example no. Component Concentration 30 31 32 33 34 Silver (as silver g/l 0 0 30 0 0 methanesulfonate) Silver (as silver nitrate) g/l 40 0 0 40 0 Silver (as silver oxide) g/l 0 20 0 0 0 Silver (as silver hydantoin g/l 0 0 0 0 40 complex) Nickel (as nickel(II) g/l 0 0 0 0 0 sulfate heptahydrate) Tin (as potassium g/l 0 0 0 0 0 hexahydroxostannate(IV)) Palladium (as palladium(II) g/l 0 0 0 0 0 bis(ethylenediamine) sulfate) Rhodium (as rhodium(III) sulfate) g/l 0 0 0 0 0 Potassium nitrate g/l 0 0 0 0 0 Potassium chloride g/l 0 0 0 0 0 Potassium methanesulfonate g/l 0 0 10 0 0 Hydantoin g/l 5,5‘-Dimethylhydantoin g/l 120 125 125 120 0 5,5‘-Diethylhydantoin g/l 0 0 0 0 120 Glycine g/l 0 0 40 0 0 Tetrahydro-2H-1,4-thiazine ml/l  0 0.2 0 0 0 Cysteine g/l 0.25 0 0.3 0.25 0.25 4-Amino-N-(2-pyrimidinyl) g/l 0.5 0 0.5 0 0 benzenesulfonamide 4-Amino-N-(1,3-thiazol-2-yl) g/l 0 0 0 0 0 benzenesulfonamide 4-Aminobenzenesulfonamide g/l 0 0.25 0 0 2 4-Amino-N-(diaminomethylene) g/l 0 0.1 0 0.2 0 benzenesulfonamide Polyethyleneimine (Lupasol FG) ml/l  0.05 0 0 0 0 Trans-3-(3-pyridyl)acrylic acid g/l 0 0 0 0 0 Beta-alanine g/l 0 40 0 0 0 Methionine g/l 0 0 1 0 0 Proline g/l 0 0 0 0 0 Sarcosine g/l 0 0 10 0 0 Nicotinic acid g/l 100 0 0 0 50 Nicotinamide g/l 0 0 0 100 50 Parameters/observations pH 9.5 9 9.6 9.5 9.5 Temperature [° C.] 60 50 60 60 60 Current density [A/dm2] 1-10 0.25-3.0 1-5 0.5-5 0.5-3 Movement (observation 1) c a d d d Anode (observation 2) b a a a a Appearance (observation 3) a a a a a Layer thickness [μm] 2 10 2 2 2 Color [L*a*b*] ND ND ND L* 98.2 98 a* −0.4 −0.2 b* 4.2 2.6 Silver content [wt %] 100 100 100 100 100 Electrolyte stability a a a a a (observation 4) Example no. Component Concentration 35 36 37 38 39 Silver (as silver g/l 10 0 10 20 0 methanesulfonate) Silver (as silver nitrate) g/l 0 0 0 0 20 Silver (as silver oxide) g/l 0 0 0 0 0 Silver (as silver hydantoin g/l 0 10 0 0 0 complex) Nickel (as nickel(II) g/l 0 0 0 1 0 sulfate heptahydrate) Tin (as potassium g/l 30 0 0 0 0 hexahydroxostannate(IV)) Palladium (as palladium(II) g/l 0 5 0 0 0 bis(ethylenediamine)sulfate) Rhodium (as rhodium(III) sulfate) g/l 0 0 6 0 0 Potassium nitrate g/l 0 0 0 0 10 Potassium chloride g/l 8 8 8 0 0 Potassium methanesulfonate g/l 0 0 0 0 0 Hydantoin g/l 0 0 0 0 0 5,5‘-Dimethylhydantoin g/l 50 0 50 0 150 5,5‘-Diethylhydantoin g/l 0 50 0 50 0 Glycine g/l 0 0 0 20 0 Tetrahydro-2H-1,4-thiazine ml/l  0 0 0 0 0.2 Cysteine g/l 0 0 0 0.5 0 4-Amino-N-(2-pyrimidinyl) g/l 0 0 0 0 0 benzenesulfonamide 4-Amino-N-(1,3-thiazol-2-yl) g/l 0 0 0 0 0 benzenesulfonamide 4-Aminobenzenesulfonamide g/l 0 0 0 1 0 4-Amino-N-(diaminomethylene) g/l 0 0 0 0 0 benzenesulfonamide Polyethyleneimine (Lupasol FG) ml/l  0 0 0 0 0 Trans-3-(3-pyridyl)acrylic acid g/l 0 0 0 0 0 Beta-alanine g/l 0 0 0 0 0 Methionine g/l 0 0 0 0 0 Proline g/l 0 0 0 0 150 Sarcosine g/l 0 0 0 0 0 Nicotinic acid g/l 0 0 0 0 0 Nicotinamide g/l 0 0 0 0 0 Parameters/observations pH 12.1 9.5 12.8 9.5 10 Temperature [° C.] 40 40 40 50 65 Current density [A/dm2] 1 2 1 1 0.1-1 Movement (observation 1) a a a a d Anode (observation 2) a a a a a Appearance (observation 3) b,c gray a, gray a a a Layer thickness [μm] 2.1 1.8 2.4 2 1.5 Color [L*a*b*] ND L* 54.3 74.7 80.9 95.8 a* +2.8 −0.8 −1.7 −0.6 b* +15.1 −1.4 +4.3 7.3 Silver content [wt %] 96.3 92.1 93.9 98.3 Electrolyte stability a a a a a (observation 4) Observation 1: a Glass beaker (60 mm stirrer bar; 200 rpm), cathode movement b Glass beaker (60 mm stirrer bar; 200 rpm), barrel c Jet plating (400 l/h) d Hull cell (stirrer bar 40 mm; 600 rpm) Observation 2: a Silver anode b Platinized titanium c Mixed metal oxide Observation 3: a Homogeneous, white, glossy b Homogeneous, white, matte c Yellowish Observation 4: a No precipitation, stable for months, constant quality of the coatings b No precipitation, but no constant quality of the coatings possible c Precipitation after a short time ND not determined

TABLE-US-00003 TABLE 3 Comparative examples Example no. Component Concentration 1 2 3 4 Silver (as silver g/l 0 0 30 0 methanesulfonate) Silver (as silver nitrate) g/l 0 0 0 16 Silver (as silver hydantoin g/l 0 0 0 0 complex) Silver (as silver oxide) g/l 40 40 0 0 Potassium chloride g/l 0 0 0 8 Amidosulfonic acid g/l 35 35 0 0 Hydantoin g/l 0 0 0 0 5,5‘-Dimethylhydantoin g/l 117.5 117.5 80 50 Thiosalicylic acid g/l 0 0 0 1 Potassium methanesulfonate g/l 0 0 150 0 Imidosuccinate, sodium salt g/l 0 0 0 0 2,2’-Sulfanediyldiethanol g/l 2 2 0 0 3-Trans-(3-pyridyl)acrylic acid g/l 4 4 0 0 Tripotassium citrate monohydrate g/l 0 0 0 0 Naphthalenesulfonic acid- g/l 0 0 15 0 formaldehyde polycondensate Sulfopropylated polyalkoxylated g/l 0 0 2.5 0 naphthol, potassium salt Polyethylene glycol octyl g/l 0 0 0 0 (3-sulfopropyl) diether, potassium salt Potassium nitrate g/l 15 15 0 0 Parameters/observations pH 9.5 9.6 9.8 9.5 Temperature [° C.] 60 60 55 50 Current density [A/dm2] 5 1 1 1.5 Movement (observation 1) c c a a Anode (observation 2) a a a a Appearance (observation 3) a,b c b,c c Layer thickness [μm] 1.5 1.5 1 2 Color [L*a*b*] L* 97.1 96.4 68.7 87.5 a* −0.5 −0.6 −0.7 −2.7 b* +5.6 +6.4 +7.1 +14.2 Silver content [wt %] 100 100 100 100 Electrolyte stability a a c c (observation 4) Example no. Component Concentration 5 6 7 Silver (as silver g/l 0 0 30 methanesulfonate) Silver (as silver nitrate) g/l 16 0 0 Silver (as silver hydantoin g/l 0 0 0 complex) Silver (as silver oxide) g/l 0 11 0 Potassium chloride g/l 8 8 0 Amidosulfonic acid g/l 0 0 0 Hydantoin g/l 40 40 0 5,5‘-Dimethylhydantoin g/l 0 0 130 Thiosalicylic acid g/l 0 0 0 Potassium methanesulfonate g/l 0 0 0 Imidosuccinate, sodium salt g/l 0 0 10 2,2’-Sulfanediyldiethanol g/l 0 0 0 3-Trans-(3-pyridyl)acrylic acid g/l 0 0 0 Tripotassium citrate monohydrate g/l 0 0 40 Naphthalenesulfonic acid- g/l 0 0 0 formaldehyde polycondensate Sulfopropylated polyalkoxylated g/l 0 0 0 naphthol, potassium salt Polyethylene glycol octyl g/l 0 0 0 (3-sulfopropyl) diether, potassium salt Parameters/observations pH 9.5 9 10.3 Temperature [° C.] 40 45 40 Current density [A/dm2] 1 1 2 Movement (observation 1) a a c Anode (observation 2) a a a Appearance (observation 3) c, matte c, matte b Layer thickness [μm] 1 1 2 Color [L*a*b*] ND ND ND L* a* b* Silver content [wt %] 100 100 100 Electrolyte stability (observation 4) b b c Observation 1: a Glass beaker (60 mm stirrer bar; 200 rpm), cathode movement b Glass beaker (60 mm stirrer bar; 200 rpm), barrel c Glass beaker (60 mm stirrer bar; 400 rpm), cathode movement d Jet plating (400 l/h) Observation 2: a Silver anode b Platinized titanium c Mixed metal oxide Observation 3: a Homogeneous, white, glossy b Homogeneous, white, matte c Yellowish Observation 4: a No precipitation, stable for months, constant quality of the coatings b No precipitation, but no constant quality of the coatings possible c Precipitation after a short time ND = not determined

TABLE-US-00004 Comparative example 1 U.S. 2012/0067733 A1 Example 4 Comparative example 2 U.S. 2012/0067733 A1 Example 4 Comparative example 3 U.S. 2016/0122890 A1 Example 1 Comparative example 4 U.S. Pat. No. 5,601,696 Example 5 Comparative example 5 U.S. Pat. No. 5,601,696 Example 1 Comparative example 6 U.S. Pat. No. 5,601,696 Example 2 Comparative example 7 U.S. 2011/0062030 Example 1

Determination of Color Values

[0132] Color values were measured according to the L*a*b color space for a silver layer deposited from an electrolyte according to the invention and for three comparative examples.

Experimental Conditions:

[0133] Volumes: 1 liter
Magnetic stirrer: IKA RET CV
Stirring: 200 and 400 rpm; the higher stirring rate was used at current densities above 3 A/dm.sup.2.

Stirrer bar: 60 mm

[0134] Cathode: moved parallel to anodes, 5 cm/s
Cathode surface: 0.2 dm.sup.2, brass
Cathodic current density: 0.5 to 3 A/dm.sup.2
Layer thicknesses: 1.5 μm.
Anodes: 99.9% silver

[0135] Temperature: 40° C.-65° C., depending on the stability of the solution. Comparative example 4 was tested at 40° C. because more silver was deposited at 50° C. (original parameter of example 5 in U.S. Pat. No. 5,601,696) than is theoretically electrochemically possible. This is a sign that, in addition to galvanic deposition, chemical deposition also takes place, the latter being undesirable.

pH: 9.5 to 10, depending on the example.
Measuring instrument: Konica Minolta Spectrophotometer CM-700, SCI 10°/D65
Determination of the L* values

[0136] In the L*a*b* color space, the L* axis describes the lightness of the color with values from 0 (black) to 100 (white).

[0137] In each case, layers of 1.5 μm thickness were deposited at current densities of 0.5 to 3.0 A/dm.sub.2.

TABLE-US-00005 Current L* value density Exemplary Comparative Comparative Comparative [A/dm.sup.2] embodiment 1 example 2 example 3 example 4 0.5 98.3 97.2 75.4 87.4 1.0 98.7 96.4 68.7 88.6 1.5 98.7 96.7 87.5 2.0 98.7 96.9 78.8 2.5 98.7 96.4 78.8 3.0 98.8 97.2 88.6 FIG. 1 shows the results of determining the L* values.

Determination of the a* Values

[0138] In the L*a*b* color space, the a* axis describes the green or red portion of a color, wherein negative values stand for green and positive values for red.

[0139] In each case, layers of 1.5 pm thickness were deposited at current densities of 0.5 to 3.0 A/dm.sup.2.

TABLE-US-00006 Current a* value density Exemplary Comparative Comparative Comparative [A/dm.sup.2] embodiment 1 example 2 example 3 example 4 0.5 −0.13 −0.45 −2.15 −3.06 1.0 −0.13 −0.59 −0.72 −3.12 1.5 −0.09 −0.65 −2.65 2.0 −0.08 −0.39 −0.31 2.5 −0.10 −0.65 −3.12 3.0 −0.07 −0.39 −0.31 FIG. 2 shows the results of determining the a* values.

Determination of the b* Values

[0140] In the L*a*b* color space, the b* axis describes the blue or yellow portion of a color, wherein negative values stand for blue and positive values for yellow.

[0141] In each case, layers of 1.5 μm thickness were deposited at current densities of 0.5 to 3.0 A/dm.sup.2.

TABLE-US-00007 Current b* value density Exemplary Comparative Comparative Comparative [A/dm.sup.2] embodiment 1 example 2 example 3 example 4 0.5 +2.60 +5.41 +6.63 +3.97 1.0 +1.97 +6.37 +7.13 +3.43 1.5 +1.88 +6.99 +14.21 2.0 +1.74 +5.11 +8.33 2.5 +1.81 +5.11 +3.43 3.0 +1.54 +6.99 +14.21 FIG. 3 shows the results of determining the b* values.