Modified copper-tin electrolyte and process for the deposition of bronze layers

Abstract

The invention relates to a modified 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. The electrolyte comprises an additive formed from epichlorohydrin and hexamethylenetetramine and contains carbonate or hydrogencarbonate ions.

1 . 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, wherein it comprises a brightener system composed of the reaction product of epichlorohydrin with hexamethylenetetramine and also carbonate ions or hydrogencarbonate ions. 
     
     
         2 . The electrolyte as claimed in  claim 1 , wherein the reaction product has a molar ratio of hexamethylenetetramine to epichlorohydrin of 1:>1-10. 
     
     
         3 . The electrolyte as claimed in  claim 1 , wherein the reaction product is used in an amount of 0.01-5 ml/l of electrolyte. 
     
     
         4 . The electrolyte as claimed in  claim 1 , wherein the carbonate or hydrogencarbonate ions are present in an amount of 1-50 g/l of electrolyte. 
     
     
         5 . The electrolyte as claimed in  claim 1 , wherein the electrolyte comprises copper and tin or copper, tin and zinc as metals to be deposited. 
     
     
         6 . The electrolyte as claimed in  claim 1 , wherein 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 . The electrolyte as claimed in  claim 1 , wherein 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 . The electrolyte as claimed in  claim 1 , wherein the amount of pyrophosphate in the electrolyte is 50-400 g/l. 
     
     
         9 . The electrolyte as claimed in  claim 1 , wherein the pH of the electrolyte is in the range from 6 to 13. 
     
     
         10 . The electrolyte as claimed in  claim 1 , wherein 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 . An 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 as claimed in  claim 1 . 
     
     
         12 . The process as claimed in  claim 11 , wherein the electrolyte is maintained in the temperature range from 20 to 60° C. 
     
     
         13 . The process as claimed in  claim 11 , wherein a current density in the range from 0.2 to 5 ampere per square decimeter is set. 
     
     
         14 . The process as claimed in  claim 11 , wherein 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 . The process as claimed in  claim 11 , wherein 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 . The process as claimed in  claim 11 , wherein 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 Sn 2+  to Sn 4+  is suppressed.