| 摘要 |
The invention relates to a polyethylene molding composition having a multimodal molar mass distribution particularly suitable for blow molding films having a thickness in the range from 8 to 200 mum. The molding composition has a density at a temperature of 23 °C in the range from 0. 940 to 0.948 g/cm^3 and an MFR190/5 of the final product after extrusion in the range from 0.10 to 0.50 dg/min. The composition comprises from 40 to 60% by weight of a first ethylene polymer fraction made of a homopolymer A having a first molecular weight, from 25 to 45% by weight of a second ethylene polymer fraction made of a first copolymer B of ethylene and at least one first comonomer from the group of olefins having from 4 to 8 carbon atoms, the first copolymer B having a second molecular weight higher than the first molecular weight, and from 10 to 30% by weight of a third ethylene polymer fraction made of a second copolymer C having a third molecular weight higher than the second molecular weight. The molding composition of the invention allows to produce thin films having improved mechanical properties, in particular in terms of dart drop impact strength, at a high take-off speed without impairing the film bubble stability.
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