POLYETHYLENE MOULDING COMPOSITION WITH IMPROVED STRESS CRACK/STIFFNESS RELATIONSHIP AND IMPACT RESISTANCE

摘要

A high density polyethylene moulding composition having a multimodal molecular weight distribution having a density according to ISO 1183 at 23°C in the range of 945 to 965 kg/m and an MFR according to ISO 1133 in the range of 0.05 to 25 g/10 min said polyethylene moulding composition comprising at least three ethylene polymer fractions having distinct molecular weights: A) 15 to 50 wt% of a low molecular weight ethylene homopolymer fraction with a weight average molecular weight Mw in the range of 15 to 40 kg/mol; B) 15 to 50 wt% of a medium molecular weight ethylene homopolymer fraction with a weight average molecular weight Mw in the range of 70 to 180 kg/mol; and C) 15 to 50 wt% of a high molecular weight ethylene copolymer fraction with a weight average molecular weight Mw in the range of 200 to 400 kg/mol; and wherein the composition has: a tensile modulus according to ISO 527 2: 1993 measured on compression moulded samples of at least 800 MPa; a Charpy impact strength CIS (23°C) according to ISO 179:2000 measured on V notched samples produced by compression moulding of at least 30 kJ/m; and an environmental stress crack resistance ESCR measured as FNCT full notch creep test according to ISO/DIS 16770.3 at 50°C and 6 MPa of at least 20 h.