EP1190118B1 - Bath system for galvanic deposition of metals - Google Patents

Description

The invention relates to a bath system for the electrodeposition of metals.

Galvanic baths for the deposition of precious metals and precious metal alloys have long been known both for decorative and technical applications. The soluble noble metal compounds which are used predominantly are based on cyanide (potassium cyanide, potassium silver cyanide), sulfite (gold sulfite complexes) or contain ammonium (palladium complexes). To complex and stabilize the systems either an excess of the salt former (cyanide, sulfite), ammonium and so-called hard complexing agents (derivatives of amino or nitriloacetic acid, etc.) or combinations thereof are selected.

Although systems containing cyanides are generally known for their stability even under difficult conditions of use, they are significant sources of danger due to their toxicity. Since there is a significant interest in replacing the dangerous cyanides have been in the field the noble metal baths continue to make further efforts.

For example, the use of sulfite in gold baths or thiosulfate in silver baths has already been described. However, these systems pose great difficulties in terms of stability. Sulfite also initiates the self-reduction of precious metals, such as gold, in complexed solutions. Thiosulfate in silver baths can not prevent photochemical reactions of free silver ions due to the lower complexation strength. An additional dosage of complexing agents, such as ethylenediaminetetraacetic acid or nitrilotriacetic acid or its derivatives slow down the reaction process, but can not prevent it. In addition, a strict control of the working pH value is required, so that in the workup of rinsing water and spent bathrooms a significant overhead is necessary. So will the case of DE-OS-38 05 627 a gold sulfite complex is used, wherein for the bath as further ingredients harmful pyridine compounds are given as well as the nerve agent antimony.

All hitherto known bathroom systems which are available to experts and have been operated with substitutes instead of cyanide have not been able to assert themselves technically because of the difficult handling. So was in the WO 92/07975 Although already proposed as a complexing agent for palladium resp. To use silver aminoacetic acid and especially glycine; but it is in the pertinent bath solution to a complex special case in metal deposition and as a so-called potentiostatic deposition method, it is not comparable to the commonly used as galvanostatic deposition methods. The potentiostatic separation necessarily requires a separation of anolyte and Katolyt via a membrane, so that this known method for continuous industrial use is not useful. Moreover, the sole use of glycine in a galvanostatic bath process would not lead to the desired results.

By the DE 38 05 627 A According to working example 6, an aqueous bath system for the electrodeposition of metals is known, which contains inter alia a metal (gold), glycine (fission product of a protein), a nitro-containing substance (trinitrobenzenesulfonic acid) and pyridine at a pH of 7.8. By working example 2 of U.S.-A-4,406,755 An aqueous bath system for the electrodeposition of metals is known, which contains inter alia a metal (palladium), succinimide and nicotinamide (vitamin B ₃ ).

In working example 6 of the US-A-4,673,472 discloses an aqueous bath system for the electrodeposition of metals, comprising inter alia a metal salt with a nitrate-containing substance (Palladiumdiaminodinitrit), which is reduced under the influence of an acid in the presence of urea to metal compounds (palladium). The known bath also has glycine (cleavage product of a protein) and succinimide. Example 7 of the same document uses nicotinamide (vitamin B ₃ ) instead of succinimide.

The latter 3 known bath systems all employ pyridine or succinimide according to their working examples, which are known for their harmful effects.

Based on this prior art, the present invention has the object, aqueous bath systems for electrodeposition of metals, in particular of precious metals and their alloys to develop, which are suitable for stable operation both for decorative and technical application and high quality layers of consistent quality in galvanostatic working processes, the bath system free of harmful substances such as cyanides, sulfites and hard complexing agents. Furthermore, the number of complexing of the individual metal-requiring salt formers should be kept as low as possible.

This object is achieved by a bath system with the features of claim 1 in its entirety.

• mindestens ein Metall, insbesondere in Form eines Edelmetalles und/oder einer Edelmetall-Legierung in Form eines wasserlöslichen Salzes,
• mindestens einen wasserlöslichen Eiweißstoff und/oder
• mindestens eine wasserlösliche Sulfonsäure und
• mindestens einen wasserlöslichen nitrohaltigen Stoff und
• mindestens ein wasserlösliches Tensid und
• mindestens ein Vitamin, nämlich Vitamin A, B oder H.

enthält, er ein hochwirksames, stabil arbeitendes Abscheidesystem erhält, das frei von Cyaniden, Sulfiten und harten Komplexbildnern gehalten werden kann. Insofern ist das erfindungsgemäße Badsystem ökologisch unbedenklich einsetzbar. Das erfindungsgemäße Badsystem wird auch höchsten Umwelt- und Entsorgungsansprüchen gerecht.It is surprising for a person skilled in the field of galvanic baths that if the bath system according to claim 1

• at least one metal, in particular in the form of a noble metal and / or a precious metal alloy in the form of a water-soluble salt,
• at least one water-soluble protein and / or
• at least one water-soluble sulfonic acid and
• at least one water-soluble nitro-containing substance and
• at least one water-soluble surfactant and
• at least one vitamin, namely vitamin A, B or H.

contains a highly effective, stable separation system that can be kept free of cyanides, sulfites and hard complexing agents. In this respect, the bath system according to the invention is ecologically safe to use. The bath system according to the invention also meets the highest environmental and disposal requirements.

The bath system according to the current main claim also allows the addition of various alloying metals, so that a wide range of alloy compositions can be achieved. In addition, the bath system is characterized by a high quality of the deposited layers with the simplest handling. Furthermore, high current yields are possible, so that the energy input quantities can be reduced and therefore the costs. The bath system according to the invention is little dependent on fluctuations in the bath components and can be easily supplemented by appropriate additives depending on the individual requirements. Furthermore, the bath system has a long service life.

Preferably used as a supplier of proteins protein amino acids with their derivatives (derivatives) and their salts and additionally or alternatively sulfonic acids with their derivatives (derivatives) and their salts.

The mentioned protein amino acids can also have one or more mercapto groups in the molecule in addition to one or more amino groups. Examples of such protein amino acids are glycine, alanine, cysteine and methionine.

The sulfonic acids mentioned may contain one or more alkyl groups and / or one or more amino groups in the molecule. Examples of these sulfonic acids are in particular amidosulfonic acid, methanesulfonic acid and Äthansulfonsäure.

To stabilize and complex the bath system, particularly water-soluble nitro compounds have proved to be favorable as acids and / or their derivatives and / or their salts. The mentioned nitro compounds may have at least one nitro group, a carboxylic acid residue and / or sulfonic acid residue. Examples of these nitro acids are 3-nitrophthalic acid, 4-nitrophthalic acid, m-nitrobenzenesulfonic acids.

To further stabilize the systems, water-soluble nitrogen compounds can be used as acids and / or their derivatives and / or their salts. The nitrogen compounds used contain at least one amino group and / or a carboxylic acid radical and / or sulfonic acid radical. Examples of these nitrogen compounds are nicotinic acid, its derivatives and / or salts and / or succinic acid, their derivatives and / or salts, preferably their amide or sulfo compounds.

Water-soluble derivatives of succinic acid, namely their esters, have proved to be particularly advantageous as surfactants. As a vitamin group, in particular nicotinamide is used, which is the vitamin B complex, in particular the vitamin B ₃ , attributed.

Sulphon derivatives which have one or two aromatic radicals on the sulphone group at the core of which partial substitution of the carbon-bonded hydrogen by metal, nitro groups, amino groups and halogens can be present can be used as brighteners.

It is surprising for a person skilled in the art that he can keep the known baths free of pollutants, in particular cyanide-free by the use of surfactants and vitamins and yet leads to improved results, in particular to increased deposition rates at a comparable or lower power input. In addition, compared to the known bath systems improved surfaces are also obtained in terms of their gloss image.

A gold bath designed to remove fine gold according to the invention contains the gold, for example, as a protein amino acid derivative of class a), preferably in the form of a gold cysteine complex, the gold concentration being between 0.5 and 30 g / l bath, preferably between 1 and 10 g / l bath, lies. The pH of the bath can be adjusted between 7 and 14, preferably between 8 and 12, in particular between 9 and 10. The adjustment and stabilization of the pH can be carried out with borate buffer, phosphate buffer, citrate buffer or other conventional buffer systems in electroplating. The working temperature of a pertinent bath is set between 20 ° C and 80 ° C, preferably between 40 ° C and 60 ° C. The applicable cathodic current density is between 0.1 A / dm ² and 15 A / dm ² , preferably between 0.5 Ndm ² and 5 A / dm ² .

The exemplary gold bath designed according to the bath system according to the invention contains an excess of the protein derivative used for depositing the fine gold and may contain, in addition to the mentioned sulfonic acids, one of the indicated nitro acids for stabilization and / or additionally a water-soluble nitrogen compound. This water-soluble nitrogen compound may, in addition to the complexation of the gold in a wide pH range, preferably the complexation optionally take over existing alloy metals. The added water-soluble nitrogen compound is preferably at least one heterocyclic organic compound. This heterocyclic organic compound may preferably consist of aromatic heterocycles. However, amides of nicotinic acid have proven to be particularly advantageous. As additional stabilizing agents it is also possible to add amides of succinic acid.

A silver bath for depositing fine silver prepared according to the invention contains the silver, for example, as sulfonate of compound class b), preferably in the form of silver methanesulfonate, the silver concentration being between 0.5 and 60 g / l bath, preferably between 2 and 40 g / l Bath, lies. For stabilization, the bath may contain additional portions of the sulfonate used. For complexing the free silver and for protection against photometric reaction, at least one water-soluble protein-amino acid compound of compound class a) is added to the bath according to the invention. The water-soluble protein-amino acid compound is present in excess of the stoichiometric ratio to silver.

To further stabilize the bath, at least one water-soluble organic nitrogen compound may additionally be added to the bath system according to the invention. In addition to the complexation of the silver in a wide pH range, this water-soluble nitrogen compound can preferably take over the complexing of any alloying metals present. The added water-soluble nitrogen compound is preferably at least one heterocyclic organic compound. This heterocyclic organic compound may preferably be aromatic heterocycles. Particularly advantageous have thereby amides of nicotinic acid proved. As additional stabilization also amides of succinic acid can be added.

The pH of the bath can be adjusted between 7 and 14, preferably between 8 and 12, in particular between 9 and 10. The adjustment and stabilization of the pH value can be carried out with borate buffer, phosphate buffer, citrate buffer or other conventional buffer systems in electroplating. The working temperature of a pertinent bath is between 10 ° C and 50 ° C, preferably between 20 ° C and 40 ° C. The applicable cathodic current density can be set between 0.1 A / dm ² and 15 A / dm ² , preferably between 0.5 A / dm ² and 5 A / dm ² .

It is particularly advantageous that substrates of brass can be directly coated in the silver baths according to the invention. The previously required pre-silvering of brass substrates in pre-silver baths can therefore be omitted and thus a complete operation can be saved.

The baths according to the invention for the deposition of fine coatings of noble metals can be added in a known manner alloying metals. Suitable alloy metals are all known metals of the Periodic Table which can be deposited together with the respective noble metal from an aqueous solution. In particular, these are the above-mentioned precious metals gold, silver, palladium and combinations of these precious metals with each other. Other preferred alloy metals for gold are copper, zinc, tin, iron and bismuth. As alloying metals for silver, especially tin and bismuth have proved to be advantageous.

After the baths according to the invention, the individual alloying partners can be electrodeposited by enrichment or depletion in the baths in proportions of between 0 and 100%.

In the following, the low-pollutant to schadschofffree aqueous system for the electrodeposition of precious metals and precious metal alloys is presented in more detail with reference to two embodiments.

The bath components listed in the examples below were dissolved in the amounts indicated and the solution was made up to 1 l with deionized water. In the bath parameters given in the individual examples, specimens were coated with the appropriate metal or metal alloy.

Bath 1:

2 g / l Gold as a gold cysteine complex 5 g / l Methanesulfonic acid solution (70% neutralized with potassium hydroxide solution) 5 g / l cysteine 20 g / l borax 2 g / l 3-nitrophthalic 20 g / l Bernsteinsäuresulfimid 5 g / l Nicotinic acid amide (vitamin) 1 ml / l Tegotain 485 (commercial surfactant, 1% aqueous solution) 0.1 ml / l Brightener (commercially available sulphonone derivative, 1% aqueous solution)

• Temperature: 50 - 60 ° C pH: 9.5 - 10.5
• Current density: approx. 0.5 A / dm ²
• Anodes: Platinized titanium
• Test item: Silver plated brass sheet metal sections angled

The specimens are coated over the entire surface. The color of the metallic coating corresponds to the typical fine gold color.

Bath 2:

10 g / l Silver as silver methanesulfonate 5 g / l Methanesulfonic acid solution (70% neutralized with potassium hydroxide solution) 5 g / l cysteine 20 g / l borax 2 g / l 2-nitrophthalic 25 g / l Nicotinic acid amide (vitamin) 3 ml / l Tegotain 485 (commercial surfactant, 1% aqueous solution) 0.1 ml / l Brightener (commercially available sulfone derivative, 1% aqueous solution)

• Temperature: 25 - 30 ° C
• pH: 9.5 - 10.5
• Current density: approx. 1 A / dm ²
• Anodes: fine silver
• Test item: Angled brass sheet sections

The specimens are coated over the entire surface. The color of the metallic coating corresponds to the typical fine silver color.

Claims (10)

1. Bath system for galvanic separation of metals, comprising:

   - at least one metal, especially in the form of a precious metal and/or a precious metal alloy in the form of a water soluble salt,

   - at least one water soluble protein and/or

   - at least one water soluble sulphonic acid, and

   - at least one water soluble nitrous material, and

   - at least one water soluble surfactant, and

   - at least one vitamin, namely vitamin A, B, or H.
2. Bath system according to Claim 1, characterised in that the relevant water soluble protein is present as a part of water soluble protein amino acids in form of an acid and/or its derivative and/or salts of the same in a quantity of 0.1 to 150 g/l of bath.
3. Bath system according to Claim 1 or 2, characterised in that the relevant water soluble sulphonic acid is present in form of an acid and/or a derivative and/or a salt in a quantity of 0.1 to 200 g/l of bath.
4. Bath system according to one of the Claims 1 to 3, characterised in that the relevant water soluble nitrous material is present in form of an acid and/or in form of a derivative and/or of salt form in a quantity of 0.1 to 200 g/l of bath, especially of 0.1 to 50 g/l of bath.
5. Bath system according to one of the Claims 1 to 4, characterised in that the relevant water soluble surfactant is present in a quantity of 0.1 to 5 g/l of bath.
6. Bath system according to one of the Claims 1 to 5, characterised in that nicotine acid is used as the vitamin.
7. Bath system according to one of the Claims 3 to 6, characterised in that a water soluble sulphone derivative is present in a quantity of 0.001 to 5 g/l of bath.
8. Bath system according to one of the Claims 1 to 7, characterised in that the pH value is adjusted to between 7 and 14, especially to between 8 and 12, by means of buffering.
9. Bath system according to one of the Claims 1 to 8, characterised in that the gold concentration in a pure gold bath lies between 0.5 and 30 g/l of bath, preferably between 1 and 10 g/l of bath.
10. Bath system according to one of the Claims 1 to 8, characterised in that the silver concentration in a pure silver bath lies between 0.5 and 60 g/l of bath, preferably between 2 and 40 g/l of bath.