Patent ID: 7264884

Claim:
A process for the manufacture of a multi-layer film which is stretchable and presents a controlled permeability to gases, said process comprising: mixing barrier material comprising an ethylene vinyl alcohol copolymer and plasticizer material inside a double-screw co-rotating extruder immediately before co-extrusion, said mixing comprising pre-melting a polymeric matrix of the barrier material and subsequent injecting the plasticizer material in a liquid phase to the pre-melted polymeric matrix to thereby form plasticized barrier material in a liquid phase to the pre-melted polymeric matrix to thereby form plasticized barrier material, the polymeric matrix having a profile of a plasticization temperature which varies as a function of the percentage of added plasticizer, injecting of the plasticizer occurs at temperature levels which are lower than the relative evaporation temperature of the plasticizer, and if the EVOH polymeric matrix is plasticized at 10% with propylene glycol, the pre-melting of the matrix starts at about 210° C., and the plasticizer is injected at about 180° C.; balloon co-extruding a polymeric stretch material, the plasticized barrier material and an adhesive material fed by respective extruders, said material being arranged so as to form layers of an outer annular layer and an inner annular layer of polymeric stretch material, an intermediate annular layer of plasticized barrier material and annular layers of adhesive material interposed between the preceding layers; squeezing and longitudinal stretching of the balloon by means of a first and of a second pair of parallel and superposed rollers; and cutting and discarding the two longitudinal edges which reciprocally connect the superposed portions of the balloon so as to obtain two films which can be separated, this being performed on the film while under tension, between said two pairs of rollers to form two five-layer films; and separately collecting the two five-layer films obtained; wherein said longitudinal stretching, longitudinal cutting and collecting of the film is obtained on a structure capable of alternately rotating of about 360° around the axis of the balloon.