MULTIMODAL POLYETHYLENE MOLDING COMPOSITION FOR PRODUCING PIPES HAVING IMPROVED MECHANICAL PROPERTIES

摘要

Polyethylene moulding material (I) with a multi-modal mol. wt. distribution for the production of tubing, comprising (A) 45-55 wt% low-mol. wt. ethylene homopolymer, (B) 20-40 wt% high-mol. wt. copolymer of ethylene and a 4-8C olefin and (C) 15-30 wt% ultrahigh-mol. wt. ethylene copolymer. Independent claims are included for (1) a method for the production of (I) by polymerisation in suspension at 70-100 (preferably 75-90) [deg]C and 2-10 bar in presence of a highly-active Ziegler catalyst comprising a transition metal compound and an organoaluminum compound, carrying out the reaction in 3 stages in 3 reactors in series and adjusting the mol. wt. of the polyethylene produced in each stage with the aid of hydrogen (2) tubes made from (I), with a stress cracking resistance (FNCT) of more than 1500 (preferably more than 2500) hours and a notched impact strength of more than 12.5 kJ/m2> at -30 [deg]C .