Surface treatment of polyimide film and polyimide film having a thin metal layer

Abstract

A method of surface treating a polyimide film to impart improved adhesion to metal which comprises treating the surface of a polyimide film having a biphenyltetracarboxylic acid component by contact to a solution containing potassium permanganate and/or sodium permanganate and potassium hydroxide and/or sodium hydroxide and treating said surface with an acid.

What is claimed is:  
     
         1 . A method of surface treating a polyimide film to impart improved adhesion to metal which comprises treating the surface of a polyimide film having a biphenyltetracarboxylic acid component by contact to a solution containing at least one of potassium permanganate and sodium permanganate and at least one of potassium hydroxide and sodium hydroxide and treating said surface with an acid.  
     
     
         2 . The method of surface treating a polyimide film according to  claim 1 , wherein said contact is carried out by immersing the polyimide film in an aqueous solution containing at least one of potassium permanganate and sodium permanganate in a total concentration of 10 to 100 g/l and at least one of potassium hydroxide and sodium hydroxide in a total concentration of 10 to 100 g/l at 20 to 85° C. for 10 to 600 seconds.  
     
     
         3 . The method of surface treating a polyimide film according to  claim 1 , which further comprises plasma treating the surface of the polyimide film after the acid treatment.  
     
     
         4 . The method of surface treating a polyimide film according to  claim 1 , wherein said polyimide film has a multilayer structure composed of a highly heat-resistant polyimide layer based on a biphenyltetracarboxylic acid component having on at least one side thereof a thermoplastic polyimide layer based on a biphenyltetracarboxylic acid component.  
     
     
         5 . A polyimide film having a thin metal layer which comprises a polyimide film having been surface treated by the method according to any one of  claims 1  to  4  to have improved adhesion to metal and a thin metal layer formed on the treated side of said polyimide film by vapor deposition or a combination of vapor deposition and plating.  
     
     
         6 . A polyimide film having a thin metal layer according to  claim 5 , wherein said thin metal layer has a three-layer structure composed of a first metal layer formed on the surface-treated side of the polyimide film by vapor deposition, a second metal layer formed on said first metal layer by vapor deposition and/or plating, and an outermost layer formed on said second metal layer by plating.  
     
     
         7 . The polyimide film having a thin metal layer according to  claim 6 , wherein said first metal layer is made of nickel, chromium, cobalt, palladium, molybdenum, tungsten, titanium, zirconium or a nickel-copper alloy, said first metal layer has a thickness of 1 to 30 nm, said second metal layer is made of nickel, cobalt, a nickel-cobalt alloy or copper, said second metal layer has a thickness of 0.1 to 2.0 μm, and said outermost metal layer is a copper layer having a thickness of 0 to 20 μm.  
     
     
         8 . The polyimide film having a thin metal layer according to  claim 6 , having peel strength of not less than 0.5 kg/cm even when allowed to stand under a heating at 150° C. for 24 hrs, 200° C. for 24 hrs, or 121° C. for 24 hrs at 100% RH under 2 atms.