| 主权项 |
1. A trimodal polyethylene comprising three polymeric weight fractions A,B,C, wherein the low molecular weight fraction A is a homopolymer and the medium and the high molecular weight fractions B and C, respectively, are copolymers of ethylene and 1-butene as the comonomer,
the polyethylene comprising 50 to 60% (w/w) of homopolymer A, 22 to 28% (w/w) of copolymer B, 18 to 24% (w/w) of copolymer C, and 0 to 5% (w/w) of non-polymeric additives and/or polymeric lubricants selected from the group consisting of: (i) colorants, (ii) antioxidants; (iii) stabilizers; (iv) inorganic or carbonic acids or acid anhydrides; (v) non-polymeric lubricants; (vi) a fluoropolymer lubricant; and (vii) polybutene-1, based on the total weight of the polymer, and wherein the polyethylene is obtained by stepwise polymerization in the presence of a solid Ziegler-Natta catalyst component, where the solid catalyst is the product of a process comprising (a) reacting magnesium diethoxide with titanium tetrachloride carried out in a hydrocarbon at a temperature of 50-100° C., (b) subjecting the reaction mixture obtained in (a) to a heat treatment at a temperature of 110° C. to 200° C. for a time ranging from 3 to 25 hours (c) isolating and washing with a hydrocarbon the solid obtained in (b), said solid catalyst component having a Cl/Ti molar ratio higher than 2.5, wherein the trimodal polyethylene has a density of 0.950 to 0.960 g/cm3, a melt index (HLMI) according to ASTM D-1238, at 190° C. and 21.6 kg, of 2.9-6 g/10 min, and the polyethylene is produced by polymerization with a Ziegler-Natta catalyst. |
