Process for producing polyolefin film composition and films prepared thereof

Abstract

The present invention deals with a process for producing a multimodal ethylene polymer composition suitable for producing films by blow moulding and comprising the steps of (i) homopolymerising ethylene or copolymerising ethylene and an alpha-olefin comonomer in a first polymerisation step in the presence of a silica supported Ziegler-Natta catalyst to produce a first ethylene homo- or copolymer (PEI) having a density of from 940 to 980 kg/mand a melt flow rate MFRof from 2 to 1000 g/10 min, provided that if the first ethylene homo- or copolymer (PE1) is a copolymer, MFRthereof is in the range of 2 to 100 g/10 min; (ii) homopolymerising ethylene or copolymerising ethylene and an alpha-olefin comonomer in a second polymerisation step in the presence of the first ethylene homo- or copolymer to produce a first ethylene polymer mixture (PEM1) comprising the first ethylene homo- or copolymer and a second ethylene homo- or copolymer (PE2), said first ethylene polymer mixture having a density of from 940 to 980 kg/mand a melt flow rate MFRof from 10 to 1000 g/10 min; (iii) copolymerising ethylene and an alpha-olefin comonomer in a third polymerisation step in the presence of the first ethylene polymer mixture (PEM1) to produce a second ethylene polymer mixture (PEM2) comprising the first ethylene polymer mixture (PEM1) and a third ethylene copolymer (PE3), said second ethylene polymer mixture (PEM2) having a density of from 915 to 940 kg/mand a melt flow rate MFRof from 0.3 to 5 g/10 min, and wherein the second ethylene polymer mixture comprises from 10 to 35% by weight of the first ethylene homo- or copolymer, from 10 to 35% by weight of the second ethylene homo- or copolymer and from 45 to 70% by weight of the third ethylene copolymer.