Multimodal polyethylene molding composition for producing pipes having improved mechanical properties

Patent metadata

Field	Value
Publication number	US-9051458-B2
Application number	US-99065106-A
Country	US
Kind code	B2
Filing date	Aug 17, 2006
Priority date	Aug 25, 2005
Publication date	Jun 9, 2015
Grant date	Jun 9, 2015

Abstract

A polyethylene molding composition having a multimodal molecular mass distribution and comprising from 45 to 55% by weight of a low molecular weight ethylene homopolymer A, from 20 to 40% by weight of a high molecular weight copolymer B comprising ethylene and another olefin having from 4 to 8 carbon atoms and from 15 to 30% by weight of an ultrahigh molecular weight ethylene copolymer C can be prepared in the presence of a Ziegler catalyst in a three-stage process and is highly suitable for producing pipes having excellent mechanical properties.

First claim

The invention claimed is:

1. A polyethylene molding composition comprising:
(A) 45 to 55% by weight, based on a total weight of the polyethylene molding composition, of a low molecular weight ethylene homopolymer A having a viscosity number VN 1 from 50 to 120 cm 3 /g,
(B) 20 to 40% by weight, based on a total weight of the polyethylene molding composition, of a high molecular weight copolymer B comprising ethylene and from 1 to 8% by weight of another olefin comprising from 4 to 8 carbon atoms, based on the weight of the high molecular weight copolymer B, wherein the mixture of homopolymer A and copolymer B has a viscosity number VN 2 of 200 to 400 cm 3 /g, and
(C) 15 to 30% by weight, based on a total weight of the polyethylene molding composition, of an ultrahigh molecular weight ethylene copolymer C,
wherein the polyethylene molding composition:
(i) has an environmental stress cracking resistance (ESCR) greater than 2500 hours
(ii) has a viscosity number VN 3 from 350 to 490 cm 3 /g,
(iii) has a density between 0.945 and 0.955 g/cm 3 ,
(iv) has a melt flow index, MFI 190/5 , ranging from 0.1 to 0.5 dg/min,
(v) has a trimodal molecular weight distribution, and
(vi) has a notched impact toughness from 8 to 14 kJ/m 2 measured at −30° C.

2. The polyethylene molding composition according to claim 1 , wherein the ultrahigh molecular weight ethylene copolymer C comprises from 1 to 8% by weight of one or more comonomers comprising from 4 to 8 carbon atoms, based on a weight of the ultrahigh molecular weight ethylene copolymer C.

3. A process comprising extruding the molding composition of claim 1 to form a pipe.

4. A pipe comprising a polyethylene molding composition comprising:
(A) 45 to 55% by weight, based on a total weight of the polyethylene molding composition, of a low molecular weight ethylene homopolymer A having a viscosity number VN 1 from 50 to 120 cm 3 /g,
(B) 20 to 40% by weight, based on a total weight of the polyethylene molding composition, of a high molecular weight copolymer B comprising ethylene and from 1 to 8% by weight of another olefin comprising from 4 to 8 carbon atoms, based on the weight of the high molecular weight copolymer B, wherein the mixture of homopolymer A and copolymer B has a viscosity number VN 2 of 200 to 400 cm 3 /g, and
(C) 15 to 30% by weight, based on a total weight of the polyethylene molding composition, of an ultrahigh molecular weight ethylene copolymer C,
wherein the polyethylene molding composition:
(i) has an environmental stress cracking resistance (ESCR) greater than 2500 hours,
(ii) has a viscosity number VN 3 from 350 to 490 cm 3 /g,
(iii) has a density between 0.945 and 0.955 g/cm 3
(iv) has a melt flow index, MFI 190/5 , ranging from 0.1 to 0.5 dg/min,
(v) has a trimodal molecular weight distribution, and
(vi) has a notched impact toughness from 8 to 14 kJ/m 2 measured at −30° C.

Assignees

• Berthold Joachim
• Nitz Hansjörg
• Rothhöft Werner
• Vogt Heinz
• Basell Polyolefine Gmbh

Inventors

• Berthold Joachim
• Nitz Hansjörg
• Rothhöft Werner
• Vogt Heinz

Classifications

• C08F210/08

  Butenes · CPC title

• C08F10/02

  Ethene · CPC title

• C08F10/00

  Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond · CPC title

• C08F2/001

  Multistage polymerisation processes characterised by a change in reactor conditions without deactivating the intermediate polymer (C08F295/00, C08F297/00 take precedence) · CPC title

• C08L2205/03

  containing three or more polymers in a blend · CPC title