A coextruded biaxially oriented polyester film useful for production of flexible packages, especially bag-in-box packages, has outstandingly good adhesion to metals, is easily handled, and shows very good processing properties

摘要

A coextruded biaxially oriented polyester film of high adhesion to metal obtained from a basic layer B and at least one top layer applied to layer B and having strong adhesion to metal, i.e. at least 4 N/25 mm and layer thickness of at most 1.6 micron, preferably at most 1.2 micron, more preferably at most 0.8 micron is new. An Independent claim is included for preparation of the polyester film by feeding layer B, top layer A, and another top layer C to three separate extruders, with removal of any foreign material and contamination from the polymer melt before extrusion by filtration, forming of the melt in a multi-layer nozzle into flat melt films, drawing of the multi-layer film with the aid of an internally cooled polished stainless steel roller, and optionally with a second roller, with fixing to an amorphous pre-film, which is then biaxially stretched and heat fixed removed. Longitudinal stretching of the pre-film is carried out at 80-130 deg C and transverse stretching at 90-150 deg C. The longitudinal stretching ratio is 2.5:1 to 6:1, preferably 3:1 to 5.5:1 and the transverse stretching ratio is 3.0:1 to 5.0:1, preferably 3.5:1 to 4.5:1.