| 摘要 |
<p>The invention relates to a polymer comprising units derived from ethylene, said polymer having: a) a Melt Index of from 0.05 to 20 g/10 min as determin ed by ASTM-1238 Condition E; b) at least 10 per 1000 C-atoms of short chain branches, containing five carbon atoms or less, as determined by C13 NMR, an d less than 3.5 mol %, of units derived from a copolymerizable ethylenically unsaturated ester, c) a density of from 0.90 to 0.94 g/cm3, preferably 0.91 to 0.935 g/cm3, especially 0.92 to 0.93 g/cm3 as determined by ASTM D1505, and d) a relaxation time as described herein of at least 10 s. Such polymers are obtainable by polymerization by free radical polymerization using a chain transfer agent that incorporates into the polymer chain such as an alpha- olefin, preferably propylene, as a chain transfer agent, preferably in a tubular reactor under circumstances to favor LCB formation in a down stream part of the tubular reactor. The polymer may be used for stretch hood film, preferably as a blown film coextruded tube comprising: a) a core of the abov e polymer; and b) a skin layer, on each side of the core which may be of the same or different composition, comprising at least 60 wt % of an LLDPE havin g density of 0.91 to 0.94 g/cm3 as determined by ASTM-D 1238 Condition E and hexane extractablesless than 1.5 wt %, said skin layer containing less than 7500 ppm of anti-block particulates and said film having an elastic recovery after a 100 % stretch of at least 40 % and providing a normalized holding force per 100 ~m thickness pre-stretch at 85 % stretch after an initial stretch of 100 % of at least 20 N/50 mm at a deformation rate of less than 1 0 % of the starting length per second.</p> |
