US Patent 7824600 Biaxially oriented polyolefing film having improved surface properties

The invention relates to a method for raising the surface tension of biaxially-stretched films made of thermoplastic polymers. According to the method, a film is first treated on a surface by means of an atmospheric pressure plasma before being stretched transversally or simultaneously across the width thereof, and the film is additional a subjected to a second treatment by means of a corona or flame after being stretched transversally or simultaneously, the second treatment being done on the same surface which has already been plasma-treated.