Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/58—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of copper
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D17/00—Constructional parts, or assemblies thereof, of cells for electrolytic coating
  • C25D17/002—Cell separation, e.g. membranes, diaphragms
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/60—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of tin

Definitions

• the invention relates to a modified pyrophosphate-containing copper-tin electrolyte which is free of toxic constituents such as cyanides or thio compounds.
• the invention further relates to a process for the deposition of decorative bronze layers on consumer goods and industrial articles using the electrolyte of the invention.
• Consumer goods or consumer articles as are defined in the consumer article regulations are upgraded by means of thin, oxidation-stable metal layers for decorative purposes and to prevent corrosion. These layers have to be mechanically stable and should not display any discoloration due to tarnishing or wear phenomena even on prolonged use.
• the sale of consumer goods coated with nickel-containing upgrading alloys has no longer been permitted in Europe since 2001 in accordance with EU Directive 94/27/EC or is possible only under strict rules since nickel and nickel- containing metal layers are contact allergens.
• Bronze alloys in particular, have become established as a replacement for nickel-containing upgrading layers and these enable such mass-produced consumer goods to be upgraded inexpensively in electrolytic barrel or rack plating processes to give allergen-free, tracked products.
• the solderability of the resulting layer and possibly its mechanical adhesive strength are the critical properties of the layer to be produced.
• the appearance of the layers is generally less important than their functionality.
• the decorative effect of the resulting layer together with long-term durability of the layer with an essentially unchanged appearance are the important target parameters.
• Known processes for producing bronze layers include not only conventional processes which use cyanide-containing and thus highly toxic alkali baths, but also various electromechanical processes which can, according to the composition of their electrolytes, usually be assigned to one of two main groups found in the prior art: processes using electrolytes based on organosulfonic acids or processes using baths based on diphosphoric acid.
• nontoxic means that the electrolyte according to the invention designated in this way does not contain any materials which are classified as “toxic” (T) or “very toxic” (T + ) under the regulations for handling dangerous goods and hazardous materials which apply in Europe.
• EP1 1 1 1097A2 describes an electrolyte which contains not only an organosulfonic acid and ions of tin and of copper and also dispersants and brighteners but also, if appropriate, antioxidants.
• EP 1 408 141 A1 describes a process for the electrochemical deposition of bronzes, in which an acidic electrolyte containing tin and copper ions and also an alkylsulfonic acid and an aromatic, nonionic wetting agent is used.
• DE 100 46 600 A1 describes a bath containing alkylsulfonic or alkanolsulfonic acid together with soluble tin and copper salts and organic sulfur compounds and also a process using this bath.
• EP1 146148A2 describes a cyanide-free copper-tin electrolyte which is based on diphosphoric acid and contains the reaction product of an amine and an epichlorohydrin in a molar ratio of 1 :1 and also a cationic surfactant.
• the amine can be hexamethylenetetramine. Current densities of 0.5, 1.5, 2.5 and 3.0 A/dm 2 are used in the electrolytic deposition.
• WO2004/005528 describes a cyanide-free diphosphoric acid-copper-tin electrolyte which contains an additive composed of an amine derivative, an epichlorohydrin and a glycidyl ether compound in a molar ratio of 1 :0.5 - 2:0.1 - 5. It was an object of this text to achieve a further widening of the current density range in which uniform deposition of the metals in a bright layer can be achieved. It is explicitly stated that such deposition can only be achieved when the additive added is made up of all three of the abovementioned components.
• Different coating processes are usually used in the electroplating industry as a function of the type and nature of the parts to be coated.
• the processes differ, inter alia, in respect of the current densities which can be employed. Mention may be made of essentially three different plating processes.
• medium working current densities are employed (order of magnitude: 0.2 - 5 A/dm 2 )
• the first two plating processes (barrel and rack) are of greatest importance.
• barrel plating relatively low current densities
• rack plating medium current densities
• the electrolyte should be able to be used even at current densities which are advantageous for rack applications and deposit bright, shiny layers in a uniform way. Its composition should be simplified compared to the prior art, since this appears to be particularly advantageous from economic and ecological points of view.
• a 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 and comprises a brightener system composed of the reaction product of epichlorohydrin with hexamethylenetetramine and also carbonate ions or hydrogencarbonate ions, completely surprisingly but nonetheless advantageously achieves the stated objects.
• the electrolytes according to the invention which have a different composition compared to the prior art make it possible to obtain excellent electrolytic deposits of bronze alloys even in a medium current density range.
• the alloy composition remains approximately constant over the wide current density range, which is particularly advantageous for the rack application in particular and is not rendered obvious by the prior art.
• the electrolyte of the invention comprises a reaction product of epichlorohydrin with hexamethylenetetramine as brightener constituent.
• 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. Particular preference is given to a ratio of 1 :1.5 - 5 and very particular preference is given to a ratio of 1 :2 - 3. A ratio of 1 : about 2.7 is especially preferred.
• Such a product can be procured commercially under the name J146 from URSA Chemie GmbH (Cat. No. 33786).
• the reaction product can be added to the electrolyte in an amount of from 0.01 ml/I to 5.0 ml/I, more preferably from 0.1 ml/I to 3.0 ml/l, particularly preferably from 0.5 to 2.0 ml/l and especially preferably from 1.0 ml/l to 1.5 ml/I, based on the total solution.
• the electrolyte of the invention has a certain concentration of carbonate or hydrogen- carbonate ions. These can be added in the form of soluble salts of the alkali and alkaline earth metals, in particular sodium or potassium carbonate or hydrogencarbonate, to the electrolyte. However, the embodiment in which the metals used and to be deposited are also added entirely or partly in the form of the carbonates or hydrogencarbonates to the electrolyte is preferred. Addition of the abovementioned salts advantageously enables a concentration of carbonate or hydrogencarbonate ions in the electrolyte which is from 1 to 50 g/l of electrolyte to be set. The concentration is particularly preferably in the range from 5 to 40 g/l and very particularly preferably from 15 to 25 g/l.
• the metals copper and tin or copper, tin and zinc to be deposited are present in the form of their ions. They are preferably introduced in the form of water-soluble salts which are preferably selected from the group consisting of pyrophosphates, carbonates, hydroxidecarbonates, hydrogencarbonates, sulfites, sulfates, phosphates, nitrites, nitrates, halides, hydroxides, oxidehydroxides, oxides and combinations thereof.
• the metals are used in the form of salts with ions selected from the group consisting of pyrophosphate, carbonate, hydroxidecarbonate, oxidehydroxide, hydroxide and hydrogencarbonate.
• the type and amount of salts introduced into the electrolyte can be decisive for the color of the resulting decorative bronze layers and can be set according to customer requirements.
• the metals to be deposited are, as indicated, present in ionically dissolved form in the electrolyte for the application of decorative bronze layers on consumer goods and industrial articles.
• the ion concentration of copper can be in the range from 0.2 to 10 g/l of electrolyte, preferably from 0.3 to 4 g/l of electrolyte
• the ion concentration of tin can be in the range from 1.0 to 20 g/l of electrolyte, preferably 2 - 10 g/l of electrolyte
• the ion concentration of zinc can be in the range from 1.0 to 20 g/l of electrolyte, preferably from 0 to 3 g/l of electrolyte.
• the metals to be deposited as pyrophosphate, carbonate or hydroxidecarbonate so that the resulting ion concentration is in the range from 0.3 to 4 gram of copper, from 2 to 10 gram of tin and from 0 to 3 gram of zinc, in each case per liter of electrolyte.
• the application of the decorative bronze layers on consumer goods and industrial articles by means of using the electrolytes of the invention is carried out, as indicated, in an electrochemical process. It is important here that the metals to be deposited are kept permanently in solution during the process, regardless of whether electrochemical coating is carried out in a continuous process or in a batch process. To ensure this, the electrolyte of the invention contains pyrophosphate as complexing agent.
• the amount of pyrophosphate ions can be set in a targeted manner by a person skilled in the art. It is limited by the fact that the concentration in the electrolyte should be above a minimum amount in order to bring about the intended effect to a satisfactory extent. On the other hand, the amount of pyrophosphate to be used is guided by economic aspects. In this context, reference may be made to EP1146148 and the information given there.
• the amount of pyrophosphate to be used in the electrolyte is preferably 50 - 400 g/l. Particular preference is given to using an amount of 250 - 350 g/l of electrolyte, very particularly preferably about 300 g/l of electrolyte.
• the pyrophosphate can, if it is not introduced as a salt constituent of the metals to be deposited, be used as alkali metal or alkaline earth metal diphosphate or as H 2 P 2 O7 in combination with an alkali metal or alkaline earth metal carbonate/hydrogencarbonate. Preference is given to using K 2 P 2 O 7 for this purpose.
• the pH of the electrolyte is in the range from 6 to 13 required for electroplating use. Preference is given to a range of 6 - 12 and very particularly preferably 6 - 10.
• the process is especially preferably carried out at a pH of from about 7.9 to 8.1.
• the electrolyte can contain, apart from the metals to be deposited, the pyrophosphate used as complexing agent and the brightener system used, further organic additives which act as brighteners, wetting agents or stabilizers.
• the electrolyte of the invention can also dispense with the use of cationic surfactants.
• the addition of further brighteners and wetting agents is only preferred when the appearance of the decorative bronze layers to be deposited have to meet special requirements. These make it possible to adjust, in addition to the color of the bronze layers which depends mainly on the ratio of the metals to be deposited, the brightness of the layer in all gradations between matt silk and high gloss.
• a possible carboxylic acid is, for example, citric acid (Jordan, Manfred, Die galvanische Abscheidung von Zinn und Zinnlegmaschineen, Saulgau 1993, page 156).
• Betaines to be used are preferably those which may be found in WO2004/005528 or in Jordan, Manfred (Die galvanische Abscheidung von Zinn und Zinnlegleiteren, Saulgau 1993, page 156). Particular preference is given to those described in EP636713. In this context, very particular preference is given to using 1 -(3- sulfopropyl)pyridinium betaine or 1 -(3-sulfopropyl)-2-vinylpyridinium betaine. Further additives may be found in the literature (Jordan, Manfred, Die galvanische Abscheidung von Zinn und Zinnlegtechniken, Saulgau 1993).
• the electrolyte of the invention is free of hazardous materials classified as toxic (T) or very toxic (T + ). No cyanides, no thiourea derivatives and no thiol derivatives are present.
• the nontoxic electrolyte according to the invention is particularly suitable for electrochemical application of decorative bronze layers on consumer goods and industrial articles. It can be used in barrel, rack, belt or continuous transport plating plants. However, it is preferably employed in rack processes (see introductory explanation and "Praktician Galvanotechnik", Eugen G. Leutze Verlag 1997 page 74 ft). Furthermore, the present invention proposes an electrolytic deposition process for the electrochemical application of decorative bronze alloy layers on consumer goods and industrial articles, in which the substrates to be coated are immersed in an electrolyte according to the invention.
• the preferred embodiments of the electrolyte which have been discussed above apply analogously to the process presented here.
• the process of the invention can be operated at a temperature which a person skilled in the art will choose on the basis of his general technical knowledge. Preference is given to a range from 20 to 60 0 C in which the electrolytic bath is maintained during the electrolysis. Greater preference is given to selecting a range of 30 - 50 0 C.
• the process is especially preferably carried out at a temperature of about 40°.
• An important advantage of the present invention is that the deposition of the alloy composition does not alter significantly over a wide current density range. This also results in a surface quality which appears to be sufficiently homogeneous even at current densities which are relatively high for rack applications. It is possible to obtain the alloy composition of a specific and desirable intermetallic Cu/Sn phase ( ⁇ + ⁇ phase; Ref.: E. Raub, F. Sautter; Der philosophical galvanischer Legleitersniederschlage XII, Metalloberflache 1 1., 1957 number 8) when the deposition is carried out in the range 0.2 A/dm 2 - 5 A/dm 2 .
• the current density in the deposition is preferably 0.5 A/dm 2 - 2 A/dm 2 , particularly preferably 0.75 A/dm 2 - 1.8 A/dm 2 .
• soluble anodes preference is given to using anodes 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. Particular preference is given to combinations of various soluble anodes composed of these materials, and also combinations of soluble tin anodes with insoluble anodes.
• insoluble anodes preference is given to using anodes 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 combinations of these anodes.
• DLC diamond-like carbon
• mixed oxide anodes composed of iridium-ruthenium mixed oxide, iridium-ruthenium-titanium mixed oxide or iridium-tantalum mixed oxide.
• Further materials may be found in Cobley, A.J. et al. (The use of insoluble Anodes in Acid Sulphate Copper Electrodeposition Solutions, Trans IMF, 2001 ,79(3), pp. 113 and 1 14).
• the substrates which are to be provided with decorative bronze layers and represent the cathode are separated by an ion exchange membrane from the insoluble anode so that a cathode space and an anode space are formed.
• the anode space preferably contains an aqueous solution containing only an electrolyte salt such as potassium pyrophosphate, potassium carbonate, potassium hydroxide, potassium hydrogencarbonate or a mixture thereof.
• an electrolyte salt such as potassium pyrophosphate, potassium carbonate, potassium hydroxide, potassium hydrogencarbonate or a mixture thereof.
• ion exchange membranes it is possible to use cationic or anionic exchange membranes. Preference is given to using membranes composed of Nafion which have a thickness of from 50 to 200 ⁇ m.
• the electrolyte of the invention and the present process are therefore distinguished by the use of an additive formed from hexamethylenetetramine and epichlorohydrin in combination with the presence of carbonate or hydrogencarbonate ions in the electrolyte.
• the alloy composition and the brightness of the deposited layers are in this way controlled in a manner which is ideal for rack applications. In rack applications, a medium current density range is important.
• the additive combination enables, firstly, the alloy composition to be kept approximately constant (bronze alloys containing 40 - 70% by weight, preferably 50 - 60% by weight, of copper and 60 - 30% by weight, preferably 50 - 40% by weight, of tin are advantageous) at relatively high current densities over a wide current density range and, secondly, satisfactorily bright and shiny layers to be obtained.
• the desired alloy composition is obtained only in a very narrow current density window which is unusable in industrial practise. Gloss and brightness of the layers are unsatisfactory without the additive combination in the majority of practical applications. The achievement of these advantages by means of the electrolyte according to the invention was not rendered obvious by the prior art.
• the components indicated for the example electrolytes are dissolved in 4 I of distilled water in a 5 I glass beaker provided with magnetic stirrer and movement of the goods.
• the article to be coated is subsequently treated under the conditions indicated.
• Electrolytes for rack deposition of white bronze can have the following composition:
• a higher copper content of the layer results in a darker color of the coating and tends to produce poorer tarnishing behavior.

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• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
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• Electrolytic Production Of Metals (AREA)
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• 2008
  • 2008-05-08 AT AT08008637T patent/ATE486157T1/de active
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• 2009
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