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US 4,226,905 AGranted
Manufacture of film from partially crosslinked polyethylene
AssigneeDu Pont Canada Inc.
InventorDavid A. Harbourne
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AssigneeDu Pont Canada Inc.
InventorDavid A. Harbourne
Estimating the term…
The present invention provides a process for the manufacture of a polyethylene film having improved tear strength in the transverse direction. The process involves extruding a partially crosslinked polyethylene into film having a thickness between 10 and 100 .mu.m, by a blown film process. The blow-up ratio is in the range of 1.2:1 to 4:1 and the MD draw-down ratio is in the range of 2 to 60. Polyethylenes used in the present invention had prior to being partially crosslinked a density in the range of 0.940 to 0.970 g/cm.sup.3 and a melt index in the range of 0.2 to 15.0 g/10 min. The polyethylene is crosslinked to an extent sufficient to provide a film having an Elmendorf tear strength in the transverse direction substantially less than the tear strength of film made from the uncrosslinked polyethylene. Crosslinking may be accomplished using any known method e.g. by irradiation, through use of crosslinking agents. The film so produced is useful in packaging operations where transverse cutting or tearing performance of the film is important.
A blown film process in which partially crosslinked polyethylene is extruded into film having a thickness in the range of 10 to 100 .mu.m, said process having a blow-up ratio in the range of 1.2:1 to 4:1 and a MD draw down ratio in the range of 2 to 60, said polyethylene having had before crosslinking, a density in the range of 0.940 to 0.970 g/cm.sup.3 and a melt index in the range of 0.2 to 15.0 g/10 min and having been crosslinked to an extent sufficient to provide, after extrusion in said blown film process, a film having an Elmendorf tear strength in the transverse direction substantially less than the Elmendorf tear strength in the transverse direction of a film produced from the polyethylene, before crosslinking, under the same conditions as the film produced from the partially crosslinked polyethylene.
A blown film produced from partially crosslinked polyethylene consisting essentially of polyethylene which, before being crosslinked, had a density in the range of 0.940 to 0.970 g/cm.sup.3 and a melt index in the range of 0.2 to 15.0 g/10 min. and which, after being crosslinked, exhibits an Elmendorf tear strength in the transverse direction substantially less than the Elmendorf tear strength in the transverse direction of a blown film produced from such polyethylene before being crosslinked under the same conditions as the film produced from the partially crosslinked polyethylene.
Dependencies are inferred from the claim text.