Process for biaxially oriented acrylonitrile polymer barrier film

A process for preparing a biaxially oriented barrier film which comprises preparing a single phase fusion melt of an acrylonitrile polymer and water, said polymer being composed of repeating units derived from about 68 to 93 weight percent acrylonitrile and, correspondingly, 32 to 7 weight percent of one or more monomers copolymerizable with acrylonitrile and containing at least about 10 parts per million of residual monomer;

• extruding said melt through a circular die to form a tubular film, said extruding being directly into a steam-pressurized solidification zone maintained under conditions of saturation, pressure, and temperature which control the rate of release of water from the nascent film;
• introducing steam and air under pressure into the tubular film structure as it is formed by the die to expand and stretch the nascent film in the transverse direction while drawing the film in the longitudinal directly so as to provide biaxial orientation while the film remains within the solidification zone;
• flattening the stretched film for removal from the solidification zone;
• and removing the flattened film from the solidification zone, said film having a residual monomer content substantially less than that of the acrylonitrile polymer employed.