Biaxially oriented thermoplastic polymer film and method of manufacture

Abstract

The invention is directed to biaxially oriented thermoplastic polymer flexible film having a substantially uniform thickness between about 0.005 and 0.030 of an inch (0.13 mm and 0.76 mm) and characterized by a structure comprised of discrete, platelet-like spherulitic crystalline aggregates compressed transversely to the plane of the film and biaxially oriented in the plane of the film and having a combination of improved properties and also to a rigid conduit or extrudate having a plurality of thermoplastic crystalline polymer layers each of which has a unique microstructure and improved properties. The film is produced by solid state hydrostatic extrusion of a generally cylindrical preform comprised of a plurality of concentric tubular-like discrete layers of polymers through an extrusion zone having converging walls and a diverging geometry, wherein the discrete layers in the preform are substantially simultaneously circumferentially expanded and axially elongated by compressive forces to produce an oriented polymer rigid tubular extrudate comprised of a plurality of concentric tubular-like layers of oriented polymer. The tubular extrudate or preform is slit longitudinally so that the discrete layers of the extrudate can be separated into individual films.