LLDPE films with improved impact strength
AssigneeMobil Oil Corporation
InventorPradeep P. Shirodkar
Life of this patent
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Abstract
LLDPE films with superior impact strength are obtained by blowing lightly crosslinked LLDPE resins under film extrusion conditions typically used for blowing HDPE film.
Claims15
A film produced by high stalk extrusion of a peroxide treated LLDPE resin wherein the peroxide treated LLDPE is extruded through a die and a bubble is formed with a diameter which is at least 3:1 times the die diameter, and a film is produced which exhibits impact resistance that is at least 25 percent higher than a comparable LLDPE film (same thickness and density) made from untreated LLDPE under non-stalk extrusion, 0.3 to 10 mils thick, comprising a linear copolymer of ethylene and an alpha olefin of 4 to 10 carbon atoms, contacted with 50 to 500 ppm of high temperature peroxide compound(s), compound comprises 2 to 20 carbon atoms and exhibits a half life at 0.1 hours which is greater than 130.degree. C., wherein the copolymer exhibits a melt strength as determined by complex viscosity at 190.degree. C. and 0.1 sec.sup.-1 in the range of 100,000 to 2,000,000 poises and a melt index of 0.05 to 10 (MI).
A film product produced by a process which comprises providing a resin which is a linear low density polyethylene comprising at least about 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.sup.-1 (190.degree. C.) of 100,000-2,000,000 poises is achieved, wherein the linear low density polyethylene exhibits MI of from 0.05 to 10;
- 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;
- while continuously extruding the tube, expanding the tube, downstream of said annular die, 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, and wherein the bubble diameter is at least 3:1 times the annular die 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;
- wherein said bubble has a frost line which comprises a demarcation line between said molten material and solid film;
- and
- producing said film.
Dependencies are inferred from the claim text.