EP2116634B1 - Modified copper-tin electrolyte and method of depositing bronze layers - Google Patents

Abstract

Non-toxic pyrophosphate-containing electrolyte comprises metals (which are to be deposited) in the form of water-soluble salts, a brightener system obtained from the reaction product of epichlorohydrin with hexamethylene tetramine and additionally carbonate ions and/or hydrogen carbonate ions. An independent claim is included for an electrolytically deposition method for galvanic application of decorative bronze layers on consumer goods and technical articles comprising immersing the substrates (that are to be coated) in a electrolyte, which is the electrolyte as above per se.

Description

The invention relates to a modified pyrophosphate-containing copper-tin electrolyte which is free of toxic ingredients such as cyanides or thio compounds. Furthermore, the invention relates to a method for depositing decorative bronze layers on consumer goods and technical objects using the electrolyte according to the invention.

Commodities or articles of daily use, as defined in the Ordinance on Commodities, are refined for decorative reasons and to prevent corrosion with thin, oxidation-stable metal layers. These layers must be mechanically stable and should not show tarnish or signs of wear even after prolonged use. Since 2001, the sale of consumer goods coated with nickel-containing refining alloys is no longer permitted in Europe under EU Directive 94/27 / EC or only under strict conditions, as it is nickel and nickel-containing metal layers about contact allergens. In particular, bronze alloys have become established as a substitute for nickel-containing finishing layers, with which commodity-representing consumer goods in galvanic drum or frame coating processes can be inexpensively refined into allergen-free, handsome products.

When producing bronze layers for the electronics industry, the solderability of the resulting layer and optionally its mechanical adhesive strength are the decisive properties of the layer to be produced. The appearance of the layers is generally less significant than their functionality for use in this area. For the production of bronze layers on consumer goods, however, the decorative effect of the resulting layer in addition to the long shelf life of the layer with unchanged as possible appearance of the essential target parameters.

For the production of bronze layers - in addition to conventional methods using cyanide-containing and thus highly toxic, alkaline baths - various galvanic methods are known, which can be assigned according to the composition of their electrolytes usually one of two observed in the prior art main groups: Process using organosulfonic acid based electrolytes or processes using diphosphoric acid (pyrophosphoric acid) based Bathrooms. "Non-toxic" in the sense of this document is understood to mean that the electrolyte according to the invention thus designated contains no substances which are classified as "toxic" (T) or "very toxic" according to the regulations applicable in Europe for handling dangerous goods and hazardous substances toxic "(T *) are classified.

For example, this describes EP1111097A2 an electrolyte which contains, in addition to an organosulfonic acid and ions of tin and copper dispersants and brighteners, and optionally antioxidants. EP 1 408 141 A1 describes a process for the electrodeposition of bronzes in which an acidic electrolyte is used which, in addition to tin and copper ions, contains an alkylsulfonic acid and an aromatic nonionic wetting agent. The DE 100 46 600 A1 describes an alkyl- or alkanolsulfonic acid-containing bath containing, in addition to soluble tin and copper salts, organic sulfur compounds and a process using this bath.

The EP1146148A2 describes a cyanide-free copper-tin electrolyte based on diphosphoric acid, which contains a cationic surfactant in addition to the reaction product of an amine and an epichlorohydrin in the molar ratio of 1: 1. The amine may be hexamethylenetetramine. In the case of electrolytic deposition, current densities of 0.5, 1.5, 2.5 and 3.0 A / dm ² are used.

The WO2004 / 005528 describes a cyanide-free diphosphoric acid copper-tin electrolyte containing an additive which is composed of an amine derivative, an epichlorohydrin and a glycidyl ether compound in the molar ratio 1: 0.5 - 2: 0.1-5. This document was based on the object, the current density range, in which a uniform deposition of the metals can be achieved in a shiny layer, continue to expand. It is explicitly mentioned that such a deposition can be achieved only if the added additive is composed of all three of the above-mentioned components.

1. 1. Trommelbeschichtung für Schüttgut und Massenteile:
   • Bei diesem Beschichtungsverfahren werden eher niedrige Arbeitsstromdichten angewendet (Größenordnung 0,05 - 0,5 A/dm²)
2. 2. Gestellbeschichtung für Einzelteile:
   • Bei diesem Beschichtungsverfahren werden mittlere Arbeitsstromdichten angewendet (Größenordnung: 0,2 - 5 A/dm²)
3. 3. High-Speed Beschichtung für Bänder und Drähte in Durchlaufanlagen:
   • In diesem Beschichtungsbereich werden sehr hohe Arbeitsstromdichten angewendet. (Größenordnung 5 - 100 A/dm²)

Usually, different coating methods are used in electroplating, depending on the type and nature of the parts to be coated. The methods differ among other things with regard to the applicable current densities. In essence, 3 different coating methods can be mentioned.

1. 1. Drum coating for bulk material and mass parts:
   • In this coating method rather low operating current densities are used (order of magnitude 0.05 - 0.5 A / dm ² )
2. 2. Frame coating for single parts:
   • Average working current densities are used in this coating method (order of magnitude: 0.2-5 A / dm ² )
3. 3. High-speed coating for strips and wires in continuous flow systems:
   • Very high working current densities are used in this coating area. (Order of magnitude 5 - 100 A / dm ² )

For copper-tin coatings, the first two coating processes (drum and frame) are more important. Depending on the different electrolyte type either drum coating (low current densities) or frame coating (average current densities) is possible.

In view of the above-mentioned prior art, it should be noted that, particularly for rack applications, such deposition methods are particularly advantageous, allowing over the envisaged range of current densities to ensure uniform deposition of metals and on the other hand to operate with electrolytes, which appear less complicated in composition.

It was therefore an object of the present invention to provide an electrolyte and a deposition method which meets these requirements. In particular, the electrolyte should be able to be used even with corresponding current densities, as they are advantageous for frame applications, and to deposit bright, lustrous layers in a uniform manner. Its composition should be simplified compared to those of the prior art, since this appears particularly advantageous from the economic and ecological point of view.

These and other objects which are not mentioned at the moment but which are obvious from the state of the art are solved by specifying an electrolyte having the features of claim 1 and its use in a deposition method according to the invention. preferred Claims relating to these claims can be found in claims 2 to 10 and 12-16.

In that a non-toxic pyrophosphate-containing electrolyte for the deposition of decorative bronze alloy layers on household goods and technical objects indicating which contains the metals to be deposited in the form of water-soluble salts, wherein the electrolyte is a brightener system of the reaction product of epichlorohydrin with hexamethylenetetramine and beyond carbonate ions or Has bicarbonate, you get completely surprising but not less advantageous to solve the tasks. With the electrolyte according to the invention and constructed differently from the prior art, it is possible to obtain excellent electrolytic deposits of bronze alloys, especially in medium current density ranges. The alloy composition remains approximately constant over the wide current density range, was of particular advantage for frame application, and is not suggested by the prior art.

The electrolyte according to the invention has a reaction product of epichlorohydrin with hexamethylenetetramine as brightener component. According to the invention, this additive consists exclusively of a mixture or reaction product of hexamethylenetetramine and epichlorohydrin. The molar ratio of hexamethylenetetramine to epichlorohydrin in the reaction product is preferably 1:> 1-10. Particularly preferred is a ratio of 1: 1.5-5 and most preferably of 1: 2 - 3. Most preferred is a ratio of 1: about 2.7. Such a product is commercially available under the name J146 from URSA Chemie GmbH (Art. No. 33786).

The reaction product may be added in an amount of 0.01 ml / L to 5.0 ml / L, more preferably 0.1 ml / L to 3.0 ml / L, more preferably 0.5 to 2.0 ml, based on the total solution / L and most preferably from 1.0 ml / L to 1.5 ml / L are added to the electrolyte.

The electrolyte according to the invention has a certain concentration of carbonate or hydrogen carbonate ions. These can be added to the electrolyte in the form of soluble salts of the alkali and alkaline earth metals, in particular sodium or potassium carbonate or bicarbonate. However, the embodiment in which the metals used and to be deposited are also completely preferred or partially added in the form of carbonates or bicarbonates to the electrolyte. By adding the abovementioned salts, it is advantageously possible to set a concentration of carbonate or hydrogen carbonate ions in the electrolyte which is between 1 and 50 g / l of electrolyte. Particularly preferably, the concentration is between 5 and 40 g / L and most preferably between 15 and 25 g / L.

In the electrolyte according to the invention, the metals to be deposited are copper and tin or copper, tin and zinc dissolved in the form of their ions. They are preferably introduced in the form of water-soluble salts, which are preferably selected from the group of pyrophosphates, carbonates, Hydroxidcarbonate, bicarbonates, Sulfrte, sulfates, phosphates, nitrites, nitrates, halides, hydroxides, oxide hydroxides, oxides or combinations thereof. Very particular preference is given to the embodiment in which the metals in the form of the salts with ions are optionally used from the group consisting of pyrophosphate, carbonate, hydroxide carbonate, oxide hydroxide, hydroxide and bicarbonate. Which salts in which amount are incorporated into the electrolyte can be determinative of the color of the resulting decorative bronze layers and can be adjusted according to customer requirements. The metals to be deposited are as indicated for the application of decorative bronze layers on consumer goods and technical items in ionic dissolved form in the electrolyte. The ion concentration of the copper may be in the range of 0.2 to 10 g / L, preferably 0.3 to 4 g / L electrolyte, the ion concentration of the tin in the range 1.0 to 20 g / L, preferably 2-10 g / L Electrolyte and - if present - the ion concentration of zinc in the range 1.0 to 20 g / L, preferably 0 - 3 g / L electrolyte can be adjusted. Particularly preferred for processing consumer goods is the incorporation of the metals to be deposited as pyrophosphate, carbonate or hydroxide carbonate in such a way that the resulting ion concentration in the range of 0.3 to 4 grams of copper, 2 to 10 grams of tin and 0 to 3 grams of zinc, each Liters of electrolyte.

The application of the decorative bronze layers on durable goods and technical articles with the electrolyte according to the invention is carried out as indicated in a galvanic process. It is important that the metals to be deposited are kept permanently in solution during the process, regardless of whether the galvanic coating in a continuous or in a discontinuous Process takes place. In order to ensure this, the electrolyte according to the invention contains pyrophosphate as complexing agent.

The amount of Pyrophosphationen can be adjusted by the skilled person targeted. It is limited by the fact that the concentration in the electrolyte should be above a minimum amount in order to be able to sufficiently accomplish the effect mentioned. On the other hand, the amount of pyrophosphate to be used is oriented on economic aspects. In this context, on the EP1146148 and the information given in this regard. Preferably, the amount of pyrophosphate to be used in the electrolyte is between 50-400 g / L. Particularly preferably, an amount between 250-350 g / l, especially about 300 g / l electrolyte is used. The pyrophosphate, unless it is introduced as a salt component of the metals to be deposited, as alkali or Erdalkalidiphosphat or H ₂ P ₂ O ₇ in combination with an alkali or alkaline earth carbonate / bicarbonate can be used. Preferably, K ₂ P ₂ O _{7 is used} for this purpose.

The pH of the electrolyte is in the range of 6 and 13 required for the electroplating application. A range from 6 to 12 and very particularly preferably from 6 to 10 is preferred. It is most preferred to operate at a pH of about 7 , 9 to 8,1.

In addition to the metals to be deposited, the pyrophosphates used as complexing agents and the brightener system used, the electrolyte may contain further organic additives which perform functions as brighteners, wetting agents or stabilizers. The electrolyte according to the invention can also dispense with the use of cationic surfactants. The addition of further brighteners and wetting agents is preferred only for special requirements on the appearance of the decorative bronze layers to be deposited. With their help - in addition to the color of the bronze layers, which largely depends on the ratio of the metals to be deposited - the layer gloss can be adjusted in all gradations between semi-gloss and high gloss. Preferably, the addition of one or more compounds selected from the group of mono- and dicarboxylic acids, the alkanesulfonic acids, betaines and the aromatic nitro compounds. These compounds act as Elektrolytbadstabilisatoren. Particularly preferred is the use of oxalic acid, of alkanesulfonic acids, especially methanesulfonic acid, or of nitrobenzotriazoles or mixtures thereof. Suitable alkanesulfonic acids can be EP1001054 be removed. Suitable carboxylic acids are, for example, citric acid ( Jordan, Manfred, The galvanic deposition of tin and tin alloys, Saulgau 1993, page 156 ). Betaine to be used are preferably those from WO2004 / 005528 or off Jordan, Manfred (The galvanic deposition of tin and tin alloys, Saulgau 1993, page 156 ) refer to. Particularly preferred are those in the EP636713 are shown. In this context, the use of 1-3 (3-sulfopropyl) pyridinium betaine or 1- (3-sulfopropyl) -2-vinylpyridinium betaine is very particularly preferred. Further additives can be found in the literature ( Jordan, Manfred, The galvanic deposition of tin and tin alloys, Saulgau 1993 ).

The electrolyte according to the invention is characterized by the fact that it is free of hazardous substances classified as toxic (T) or very toxic (T *). There are no cyanides, no thiourea derivatives and no thiol derivatives. The non-toxic electrolyte according to the invention is particularly suitable for the electroplating of decorative bronze layers on consumer goods and technical articles. It can be used in drum, rack, belt or continuous galvanic systems. However, the preferred application is rack operation (see explanation, introduction and " Practical Electroplating ", Eugen G. Leutze Verlag 1997 page 74 ff .).

Furthermore, the present invention proposes an electrolytic deposition process for the electroplating of decorative bronze alloy layers on consumer goods and technical articles, in which the substrates to be coated are immersed in an electrolyte according to the invention. The preferred embodiments of the electrolyte discussed above apply mutatis mutandis to the process presented here.

The process according to the invention can be operated at a temperature which the person skilled in the art will choose based on his general ability. Preferably, a range of 20 to 60 ° C in question, in which the electrolytic bath is heated during the electrolysis. More preferably, a range of 30-50 ° C is selected. Most preferably, one works at a temperature of about 40 °.

A key advantage of the present invention is that the deposition of the alloy composition does not appreciably change over a wide current density range. This requires relatively high current densities even for frame applications sufficiently homogeneous surface texture. The alloy composition of a specific and desired intermetallic Cu / Sn phase (η + δ phase; E. Raub, F. Sautter; The Construction of Galvanic Alloy Precipitates XII, Metal Surface 11, Jg 1957 Issue 8 ) in the deposition in the range of 0.2 A / dm ² - 5 A / dm ² are obtained. Preferably, the current density in the deposition between 0.5 A / dm ² - 2 A / dm ² , more preferably between 0.75 A / dm ² -1.8 A / dm2.

When using the non-toxic electrolyte according to the invention, various anodes can be used. Soluble or insoluble anodes are also suitable, as is the combination of soluble and insoluble anodes.

As soluble anodes, those made of a material selected from the group consisting of electrolytic copper, phosphorus-containing copper, tin, tin-copper alloy, zinc-copper alloy and zinc-tin-copper alloy are preferably used. Particularly preferred are combinations of different soluble anodes from these materials, as well as the combinations of soluble tin anodes with insoluble anodes.

Preferred insoluble anodes are those made of a material selected from the group consisting of platinized titanium, graphite, iridium-transition metal mixed oxide and special carbon material ("Diamond Like Carbon" DLC) or combinations of these anodes. Especially preferred are mixed oxide anodes of iridium-ruthenium mixed oxide, iridium-ruthenium-titanium mixed oxide or iridium-tantalum mixed oxide. Others can be added Cobley, AJ et al. (The use of insoluble anodes in Acid Sulphate Copper Electrodeposition Solutions, Trans. IMF, 2001, 79 (3), pp. 113 and 114 ) being found.

If insoluble anodes are used, this is a particularly preferred embodiment of the method if the substrates to be provided with decorative bronze layers, which constitute the cathode, are separated from the insoluble anode by an ion exchange membrane in such a way that a cathode space and form an anode space. In such a case, only the cathode compartment is filled with the non-toxic electrolyte according to the invention. In the anode compartment is preferably an aqueous solution containing only a principle such as potassium pyrophosphate, potassium carbonate, potassium hydroxide, potassium bicarbonate or mixture thereof. By such an arrangement, the anodic oxidation of Tin (II) ions to tin (IV) ions, which would adversely affect the coating process prevented. As ion exchange membranes cationic or anionic exchange membranes can be used. Preferably, Nafion membranes having a thickness of 50 to 200 μm are used.

With customary pyrophosphate-containing electrolytes, the current densities typical for frame applications can likewise be achieved. However, the deposition of the metals does not take place in optically perfect quality. In general, such electrolytes tend to have dark, streaky deposits (in the range customary for rack operation).

Only with the use of the electrolyte according to the invention is the deposition of bright and shiny layers possible over the entire current density range customary for frame applications. The formation of dark streaks is clearly suppressed.

The electrolyte according to the invention and the subject process are therefore characterized by the use of an additive formed from hexamethylenetetramine and epichlorohydrin in combination with the presence of carbonate or hydrogen carbonate ions in the electrolyte. This controls the alloy composition and the gloss of the deposited layers in a manner ideal for rack applications. For rack applications, a medium current density range is significant. By means of the additional combination, the alloy composition can be kept approximately constant at higher current densities over a wide current density range (advantageous are bronze alloys which are 40-70% by weight, preferably 50-60% by weight copper and 60-30% by weight, preferably 50-40 wt .-% tin) and on the other hand sufficiently bright and shiny layers are obtained. Without this additional combination, the desired alloy composition is obtained only in a very narrow, practically unusable, current density window. The gloss and brightness of the layers are not sufficient without the additional combination for the majority of practical applications.

The invention of these advantages by means of the electrolyte according to the invention was by no means suggested by the prior art.

Examples: Coating of test sheets:

Substrates: 0.5 and 0.75 dm ² brass sheets

coating:

0.5 - 2 μm copper-tin at different current densities (0.5, 1.0, 1.5 and 2.0 A / dm ² )

Experimental setup:

The components specified for the example electrolyte are distilled in a 5 L beaker with magnetic stirrer and goods movement in 4 L dest. Water dissolved. Subsequently, the object to be coated is treated under the specified conditions.

example electrolytes

White-bronze electrodeposition supports may have the following composition:

1. Example electrolyte

300 g / l potassium pyrophosphate 20 ml / l Methanesulfonic acid, 70% 20 g / l potassium carbonate 5.21 g / l Copper (II) carbonate 8.66 g / l pyrophosphate 5.55 g / l pyrophosphate 1.25 ml / l Reaction product of hexamethylenetetramine and epichlorohydrin Temperature: 40 ° C PH value: 7.4

2. Example electrolyte

300 g / l Kaliumyrophosphat 20 ml / l methane 20 g / l potassium carbonate 5.21 g / l Copper (II) carbonate 8.66 g / l pyrophosphate 5.55 g / l pyrophosphate 0.125 ml / l Reaction product (J146) temperature 40 ° C PH value: 8.0

3. Example electrolyte

100 g / l potassium pyrophosphate 50 ml / l methane 50 g / l potassium carbonate 2.0 g / l copper sulphate 20 g / l tin sulfate 5.0 ml / l Conversion product (J146) PH value: 9.0 Temperature: 30 ° C

4. Example electrolyte

160 g / l potassium pyrophosphate 20 ml / l methane 5 g / l sodium 4 g / l Hydroxo copper 5 g / l pyrophosphate 0.5 ml / l Reaction product of hexamethylenetetramine and epichlorohydrin PH value: 7.5 Temperature: 45 ° C

5. Example electrolyte

200 g / l potassium pyrophosphate 30 ml / l ethanesulfonic 50 g / l citric acid 5 g / l potassium 3 g / l copper sulphate 15 g / l tin sulfate 1 ml / l Reaction product of hexamethylenetetramine and epichlorohydrin Temperature: 45 ° C PH value: 8.5

• a) durch optischen Eindruck
• b) durch Messung von Glanz und Helligkeit
• c) Messung der Legierungszusammensetzung (je höher der Kupferanteil, desto dunkler die Schichten)
• d) Anlauftests, Korrosionstests

The assessment of the layers takes place

• a) by visual impression
• b) by measurement of gloss and brightness
• c) Measurement of the alloy composition (the higher the copper content, the darker the layers)
• d) start-up tests, corrosion tests

Results:

a) Optical impression:
The deposited layers were uniformly bright and shiny.
b) Brightness values (L * values, measured according to CIE-LAB, http://www.cielab.de/) Comparison "Example electrolyte 2 ° vs." state of the art " Current densities A / dm ² 0.5 0.75 1.0 1.5 2.0 Example electrolyte 2 84.08 85.9 85.74 86.86 86.1 State of the art 81.0 82.9 3.1 83.2 82.8
c) alloy composition
Comparison "Sample Electrolyte 2" vs. "State of the art" Current densities A / dm ² 0.5 1.0 1.5 2.0 Example electrolyte 2 60% Cu 50% Cu 47% Cu 48% Cu 40% Sn 50% Sn 53% Sn 52% Sn State of the art 62% Cu 55% Cu 52% Cu 53% Cu 48% Sn 45% Sn 48% Sn 47% Sn

Higher copper content in the layer means darker coating color and tends to have worse start-up behavior.

Claims (16)

1. Nontoxic pyrophosphate-containing electrolyte for the deposition of decorative bronze alloy layers on consumer goods and industrial articles, which contains the metals to be deposited in the form of water-soluble salts, characterized in that the electrolyte comprises a brightener system composed of the reaction product of epichlorohydrin with hexamethylenetetramine and also carbonate ions or hydrogencarbonate ions.
2. Electrolyte according to Claim 1, characterized in that the reaction product has a molar ratio of hexamethylenetetramine to epichlorohydrin of 1:>1 - 10.
3. Electrolyte according to Claim 1 and/or 2, characterized in that the reaction product is used in an amount of 0.01 - 5 ml/l of electrolyte.
4. Electrolyte according to one or more of Claims 1 to 3, characterized in that the carbonate or hydrogencarbonate ions are present in an amount of 1 - 50 g/l of electrolyte.
5. Electrolyte according to one or more of Claims 1 to 4, characterized in that the electrolyte comprises copper and tin or copper, tin and zinc as metals to be deposited.
6. Electrolyte according to one or more of Claims 1 to 5, characterized in that the water-soluble salts of the metals to be deposited are selected from the group consisting of pyrophosphates, carbonates, hydroxidecarbonates, hydrogencarbonates, sulfites, sulfates, phosphates, nitrites, nitrates, halides, hydroxides, oxidehydroxides, oxides and combinations thereof.
7. Electrolyte according to one or more of Claims 1 to 6, characterized in that the metals to be deposited are present in ionically dissolved form, with the ion concentration of copper being in the range from 0.2 to 10 g/l of electrolyte, the ion concentration of tin being in the range from 1.0 to 20 g/l of electrolyte and, if present, the ion concentration of zinc being in the range from 1.0 to 20 g/l of electrolyte.
8. Electrolyte according to one or more of Claims 1 to 7, characterized in that the amount of pyrophosphate in the electrolyte is 50 - 400 g/l.
9. Electrolyte according to one or more of Claims 1 to 8, characterized in that the pH of the electrolyte is in the range from 6 to 13.
10. Electrolyte according to one or more of Claims 1 to 9, characterized in that one or more compounds having a stabilizing action selected from the group consisting of monocarboxylic and dicarboxylic acids, alkanesulfonic acids, betaines and aromatic nitro compounds are present.
11. Electrolytic deposition process for the electrochemical application of decorative bronze alloy layers on consumer goods and industrial articles, wherein the substrates to be coated are immersed in an electrolyte according to one or more of Claims 1 to 10.
12. The process according to Claim 11, characterized in that the electrolyte is maintained in the temperature range from 20 to 60°C.
13. Process according to Claim 11 and/or 12, characterized in that a current density in the range from 0.2 to 5 ampere per square decimeter is set.
14. Process according to one or more of Claims 11 - 13, characterized in that a soluble anode composed of a material selected from the group consisting of electrolytic copper, phosphorus-containing copper, tin, tin-copper alloy, zinc-copper alloy and zinc-tin-copper alloy or a combination of these anodes is used.
15. Process according to one or more of Claims 11 to 14, characterized in that an insoluble anode composed of a material selected from the group consisting of platinized titanium, graphite, iridium-transition metal mixed oxide and a specific carbon material ("diamond-like carbon", DLC) or a combination of these anodes is used.
16. Process according to one or more of Claims 11 to 15, characterized in that the cathode and the insoluble anode are separated from one another by an ion-exchange membrane to form a cathode space and an anode space and only the cathode space contains the nontoxic electrolyte so that anodic oxidation of Sn²⁺ to Sn⁴⁺ is suppressed.