Polyethylene composition having high stress cracking resistance

Patent metadata

Field	Value
Publication number	US-9879099-B2
Application number	US-201515527158-A
Country	US
Kind code	B2
Filing date	Oct 27, 2015
Priority date	Nov 18, 2014
Publication date	Jan 30, 2018
Grant date	Jan 30, 2018

Abstract

A polyethylene composition made from or containing a polyethylene, having the following features:
1) a density from about 0.930 to about 0.945 g/cm 3 , determined according to ISO 1183 at 23° C.; 2) a ratio of MIF/MIP from about 30 to about 55; 3) a MIF from about 3 to about 25 g/10 min.; 4) a Mz equal to or greater than about 1,500,000 g/mol; and 5) a long-chain branching index, LCBI, equal to or lower than about 0.55, wherein the LCBI is the ratio of the measured mean-square radius of gyration R g , measured by GPC-MALLS, to the mean-square radius of gyration for a linear PE having about the same molecular weight of 1,000,000 g/mol.

First claim

What is claimed is:

1. A polyethylene composition comprising:
1) a density from about 0.930 to about 0.945 g/cm 3 , determined according to ISO 1183 at 23° C.;
2) a ratio of MIF/MIP from about 30 to about 55, where MIF is the melt flow index at 190° C. with a load of 21.60 kg, and MIP is the melt flow index at 190° C. with a load of 5 kg, both determined according to ISO 1133;
3) a MIF from about 3 to about 25 g/10 min;
4) a Mz equal to or greater than 1,500,000 g/mol, measured by GPC-MALLS (Gel Permeation Chromatography coupled with Multi-angle laser-light scattering); and
5) a long-chain branching index, LCBI, equal to or lower than about 0.55, at a molecular weight of 1,000,000 g/mol,
wherein LCBI is the ratio of the measured mean-square radius of gyration R g , measured by GPC-MALLS, to the mean-square radius of gyration for a linear PE having about the same molecular weight.

2. The polyethylene composition of claim 1 , wherein the polyethyelene has Mw equal to or higher than about 300,000 g/mol.

3. The polyethylene composition of claim 1 , wherein the polyethylene comprises ethylene copolymer.

4. The polyethylene composition of claim 1 , wherein the polyethylene is prepared by a process using a Ziegler-Natta polymerization catalyst.

5. The polyethylene composition of claim 4 , wherein the Ziegler-Natta polymerization catalyst comprises a product of a reaction between:
a) a solid catalyst component comprising a Ti compound supported on MgCl 2 , obtained by contacting the titanium compound with the MgCl 2 , or a precursor Mg compound, optionally in the presence of an inert medium, at a temperature from 130 to 150° C.;
b) an organo-Al compound; and optionally
c) an external electron donor compound.

6. The polyethylene composition of claim 1 , wherein the polyethylene has a property selected from the group consisting of:
a) a ratio of Mw/Mn from about 36 to about 48;
b) a MIP in the range from about 0.05 to about 1.5 g/10 min.;
c) an elongational hardening at 0.5 s −1 , T=150° C. of about 0.9 or higher;
d) an elongational hardening at 0.1 s −1 , T=150° C. of about 0.9 or higher; and
e) a comonomer content equal to or less than about 8% by weight, based upon the total weight of the polyethylene.

7. The polyethylene composition of claim 1 , wherein the polyethylene comprises:
A) about 40 to about 60% by weight of an ethylene homopolymer or copolymer, based upon the total weight of the polyethylene, having
i) a density equal to or greater than about 0.945 g/cm 3 and
ii) a melt flow index MIE at 190° C. with a load of 2.16 kg, according to ISO 1133, of about 1 about 25 g/10 min.; and

B) about 40 to about 60% by weight of an ethylene copolymer, based upon the total weight of the polyethylene, having
i) a MIE value lower than the MIE value of component A.

8. An article of manufacture comprising:
A) a polyethylene composition comprising:
1 ) a polyethylene having the properties of
a) a density from about 0.930 to about 0.945 g/cm 3 , determined according to ISO 1183 at 23° C.; b) a ratio of MIF/MIP from about 30 to about 55, where MIF is the melt flow index at 190° C. with a load of 21.60 kg, and MIP is the melt flow index at 190° C. with a load of 5 kg, both determined according to ISO 1133; c) a MIF from about 3 to about 25 g/10 min; d) a Mz equal to or greater than 1,500,000 g/mol, measured by GPC-MALLS (Gel Permeation Chromatography coupled with Multi-angle laser-light scattering); and e) a long-chain branching index, LCBI, equal to or lower than about 0.55, at a molecular weight of 1,000,000 g/mol, wherein LCBI is the ratio of the measured mean-square radius of gyration R g , measured by GPC-MALLS, to the mean-square radius of gyration for a linear PE having about the same molecular weight.

9. The article of manufacture according to claim 8 , being a membrane having a layer comprising:
a) the polyethylene composition.

10. A process for preparing a polyethylene composition comprising the step of contacting ethylene with a Ziegler-Natta catalyst supported on MgCl 2 under polymerization conditions, wherein the polyethylene composition has the following properties:
1) a density from about 0.930 to about 0.945 g/cm 3 , determined according to ISO 1183 at 23° C.;
2) a ratio of MIF/MIP from about 30 to about 55, where MIF is the melt flow index at 190° C. with a load of 21.60 kg, and MIP is the melt flow index at 190° C. with a load of 5 kg, both determined according to ISO 1133;
3) an MIF from about 3 to about 25 g/10 min;
4) an Mz equal to or greater than 1,500,000 g/mol, measured by GPC-MALLS (Gel Permeation Chromatography coupled with Multi-angle laser-light scattering); and
5) a long-chain branching index, LCBI, equal to or lower than about 0.55, at a molecular weight of 1,000,000 g/mol, wherein LCBI is the ratio of the measured mean-square radius of gyration R g , measured by GPC-MALLS, to the mean-square radius of gyration for a linear PE having about the same molecular weight.

11. The process of claim 10 , comprising the following steps, in any mutual order:
a) polymerizing ethylene, optionally together with one or more comonomers, in a gas-phase reactor in the presence of hydrogen; and
b) copolymerizing ethylene with one or more comonomers in another gas-phase reactor in the presence of an amount of hydrogen less than step a);

wherein, in at least one of the gas-phase reactors, the growing polymer particles flow upward through a first polymerization zone under fast fluidization or transport conditions, leave the riser and enter a second polymerization zone through which the particles flow downward under the action of gravity, leave the second polymerization zone and are reintroduced into the first polymerization zone, thus establishing a circulation of polymer between the two polymerization zones.

Assignees

• Basell Polyolefine Gmbh

Inventors

• Mannebach Gerd
• Marczinke Bernd Lothar
• Meier Gerhardus
• Schuller Ulf
• Vittorias Iakovos
• Mavridis Harilaos

Classifications

• C08L2314/02

  Ziegler natta catalyst · CPC title

• C08L2308/00

  Chemical blending or stepwise polymerisation process with the same catalyst · CPC title

• C08L2205/025

  containing two or more polymers of the same hierarchy C08L, and differing only in parameters such as density, comonomer content, molecular weight, structure · CPC title

• C08L23/08

  Copolymers of ethene (C08L23/16 takes precedence) · CPC title

• C08L23/06

  Polyethylene · CPC title