Process for producing LLDPE films with improved impact strength

A process for producing a film, which comprises providing a resin which is a linear low density polyethylene comprising at least 80 percent by weight of ethylene units;

• treating the linear low density polyethylene with high temperature peroxide such that a viscosity at 0.1 sec.−1 (190° C.) of 100,000 to 2,000,000 poises is achieved
• extruding said resin through an annular die to form an extruded tube of molten material to provide the tube with a tube diameter which is substantially the annular die diameter the tube having an inner surface and an outer surface;
• while continuously extruding the tube, cooling the tube by flowing a cooling gas in contact with the outer surface of said tube from an annular zone about said extruded tube spaced along the axis thereof and having a diameter sufficient to provide a tube diameter which is substantially the annular die diameter, the annular zone operating to cool the tube in the absence of cooling gas from another annular zone;
• expanding the tube, downstream of said annular die and said annular zone, to attenuate the walls thereof to form the tube of molten material into a bubble of a bubble diameter which exceeds (1) the annular die diameter and (2) the tube diameter;
• wherein said bubble has a frost line which comprises a demarcation line between said molten material and solid biaxially oriented film;
• and producing said film of a thickness ranging from 0.3 to 10.0 mils, exhibiting an improvement in impact strength, determined by ASTM D-1709 of at least 25 percent over a comparable film made from a non-peroxide treated LLDPE under non-stalk film flowing conditions;
• and producing said film.