Process for producing metal foil

Abstract

The present invention relates to a process for electrolytically producing metal foil which is diminished in pinhole defects and has a uniform thickness. The metal foil is produced by passing an electric current between a cylindrical cathode immersed in an electrolytic solution and an anode opposed to the cathode, continuously electrodepositing a metal layer on the surface of the cathode while rotating the cathode and thereafter peeling the metal layer off. An auxiliary anode capable of adjusting the current density when electrodeposition is started is disposed at a position downstream from the anode with respect to the direction of flow of the electrolytic solution. The auxiliary anode is an electrode having a coating layer comprising an electrode active substance and formed over an electrically conductive metal substrate, with an intermediate layer of tantalum or a tantalum alloy formed between the coating layer and the substrate.

What is claimed is:  
     
         1 . In producing metal foil by passing an electric current between a cylindrical cathode immersed in an electrolytic solution and an anode opposed to the cathode, continuously electrodepositing a metal layer on a surface of the cathode while rotating the cathode and thereafter peeling the metal layer off, a process for producing metal foil characterized in that an auxiliary anode capable of adjusting the current density when electrodeposition is started is disposed at one side of the cathode where an unelectrolyzed portion thereof is brought into the electrolytic solution, at a position downstream from the anode with respect to the direction of flow of the electrolytic solution, the auxiliary anode being an electrode having a coating layer comprising an electrode active substance containing a platinum group metal or a platinum group metal oxide, or a mixture of an oxide of a valve metal and a platinum group metal or a platinum group metal oxide and formed over an electrically conductive metal substrate comprising titanium or a titanium alloy, with an intermediate layer of tantalum or a tantalum alloy formed between the coating layer and the substrate.  
     
     
         2 . A process for producing metal foil according to  claim 1  wherein the metal foil is copper foil.  
     
     
         3 . A process for producing metal foil according to  claim 1  wherein the titanium alloy is an alloy selected from the group consisting of titanium-tantalum, titanium-tantalum-niobium and titanium-palladium, or a combination of at least two of these alloys.  
     
     
         4 . A process for producing metal foil according to  claim 1  wherein the intermediate layer is formed by sputtering, ion plating or vacuum evaporation.  
     
     
         5 . A process for producing metal foil according to  claim 1  wherein the tantalum alloy is a tantalum-niobium alloy and/or a tantalum-titanium alloy.  
     
     
         6 . A process for producing metal foil according to  claim 1  wherein the intermediate layer is 1 to 10 μm in thickness.  
     
     
         7 . A process for producing metal foil according to  claim 1  wherein the valve metal is selected from the group consisting of titanium, tantalum, niobium and zirconium, or is a combination of at least two of these metals.  
     
     
         8 . A process for producing metal foil according to  claim 1  wherein the electrode active substance is a mixture selected from the group consisting of a mixture of iridium oxide and tantalum oxide, mixture of iridium oxide and titanium oxide, mixture of iridium oxide and ruthenium oxide, mixture of iridium oxide, ruthenium oxide and titanium oxide, mixture of ruthenium oxide and titanium oxide, and mixture of ruthenium oxide and tantalum oxide, or a combination of at least two of these mixtures.  
     
     
         9 . A process for producing metal foil according to  claim 1  wherein the electrode active substance contains a mixture of 60 to 95 wt. % of iridium oxide calculated as metallic iridium and 5 to 40 wt. % of tantalum oxide calculated as metallic tantalum.  
     
     
         10 . A process for producing metal foil according to  claim 1  wherein the electrode active substance contains a mixture of 70 to 95 wt. % of iridium oxide calculated as metallic iridium and 5 to 30 wt. % of tantalum oxide calculated as metallic tantalum.  
     
     
         11 . A process for producing metal foil according to  claim 1  wherein the coating layer is formed by thermal decomposition, electrochemical oxidation or powder sintering.  
     
     
         12 . A process for producing metal foil according to  claim 1  wherein the coating layer is 1 to 50 μm in thickness.