Polymer composition for pipes

US6441096B1 · kind B1 · utility

Assignee

• Borealis Technology Oy · FI

Inventors

• Mats Bäckman · Gothenburg, SE
• Eeva-Leena Heino · Helsinki, FI
• Solveig Johansson · Stenungsund, SE
• Jussi Laurell · Porvoo, FI
• Arja Lehtinen · Helsinki, FI
• Jarmo Lindroos · Stathelle, NO
• Marja Ora · Porvoo, FI
• Elisabeth Ribarits · Spekeröd, SE
• Teija Sihvonen · Karis, FI
• Jari {umlaut over (Aa)}rilä · Karis, FI

Key dates

• Filing date: Apr 10, 2001
• Grant date: Aug 27, 2002
• Expiry date: Apr 10, 2021

Classification

• Technology area (CPC Y): Emerging Cross-Sectional Technologies
• CPC primary: Y10S138/07
• WIPO field: Macromolecular chemistry, polymers
• WIPO sector: Chemistry

Abstract

A multimodal polymer composition for pipes is disclosed as well as a pipes made thereof. The polymer is a multimodal polyethylene with a density of 0.930-0.965 g/cm3, and a viscosity at a shear stress of 747 Pa (&eegr;747 Pa) of at least 650 Pa.s, said multimodal polyethylene comprising a low molecular weight (LMW) ethylene homopolymer fraction and a high molecular weight (HMW) ethylene copolymer fraction, said HMW fraction having a weight ratio of the LMW fraction to the HMW fraction of (35-55):(65-45). Preferably, the multimodal polyethylene has a viscosity at a shear stress of 2.7 kPa (&eegr;2.7 kPa) of 260-450 kPa.s; and a shear thinning index (SHI) defined as the ratio of the viscosities at shear stresses of 2.7 and 210 kPa, respectively, of SHI27/210=50-150, and a storage modulus (G′) at a loss modulus (G″) of 5 kPa, of G′5 kPa≧3000 Pa. The pipe is made of the multimodal polymer composition and withstands a stress of 8.0 MPa gauge during 50 years at 20° C. (MRS8.0). Preferably, the pipe has a rapid crack propagation (RCP) S4-value, determined according to ISO 13477:1997(E), of −5° C. or lower and a slow crack propagation resistance, determin…