Process for obtaining a metal-free coextruded bi-oriented of 7 layers film for packaging by triple-bubble process used for sterilization processes up to 135°c

A process of obtaining a metal-free 7-layer co-extruded bi-oriented film for packaging by triple bubble process, the process comprising the steps of:

• a) co-extruding at a temperature between 5-15° C. a tubular strip of 7 layers with a tubular central head, in a first bubble, where said tubular strip has a dimension of 20 to 350 mm to obtain a co-extruded tubular strip;
• b) cooling the co-extruded tubular strip in stage a) by immersing it in water until the strip reaches between 5° and 12° C., to obtain an amorphous multilayer strip;
• c) heating the amorphous tubular multilayer strip obtained in stage b) to a temperature of 70 to 75° C.;
• d) biaxially orienting the tubular multilayer strip heated in stage c) in a second expansion bubble at a temperature of 68 to 75° C. to obtain an amorphous bi-oriented primary film;
• and
• e) heating the amorphous bi-oriented primary film obtained in stage d) until reaching 140 to 150° C. to stabilize it and eliminate thermal shrinkage and possible elongation to obtain a metal-free film for packaging.