Polyethylene composition for blow molding having high stress cracking resistance

Patent metadata

Field	Value
Publication number	US-9725541-B2
Application number	US-201414900955-A
Country	US
Kind code	B2
Filing date	Jun 19, 2014
Priority date	Jun 25, 2013
Publication date	Aug 8, 2017
Grant date	Aug 8, 2017

Abstract

The present technology relates to a polyethylene composition suitable for producing small articles such as flexible and collapsible tubes by blow molding comprising:
1) a density from 0.948 to 0.955 g/cm 3 ; 2) a MIF/MIP ratio from 12 to 25; 3) a MIF from 25 to 40 g/10 min; 4) a Mz from 1000000 to 2000000 g/mol; and 5) a long-chain branching index, LCBI, equal to or greater than 0.55.

First claim

What is claimed is:

1. A polyethylene composition comprising:
1) a density from 0.948-0.955 g/cm 3 as determined according to ISO 1183 at 23° C.;
2) an MIF/MIP ratio from 12-25, 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 25-40 g/10 min;
4) an M z from 1000000-2000000 g/mol; and
5) a long-chain branching index (LCBI) equal to or greater than 0.60;
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 the same molecular weight.

2. The polyethylene composition of claim 1 , further comprising:
6) an eta (0.02) value from 25,000-35,000 Pa·s;
wherein eta (0.02) is the complex shear viscosity at an angular frequency of 0.02 rad/s, measured with dynamic oscillatory shear in a plate-plate rotational rheometer at a temperature of 190° C.

3. The polyethylene composition of claim 1 , wherein the polyethylene composition comprises one or more ethylene copolymers.

4. The polyethylene composition of claim 3 , wherein the polyethylene composition has a comonomer content from 1-3%.

5. The polyethylene composition of claim 1 , wherein the polyethylene composition is obtained by using a Ziegler-Natta polymerization catalyst.

6. The polyethylene composition of claim 5 , wherein the Ziegler-Natta polymerization catalyst comprises the product of the reaction of:
a) a solid catalyst component comprising a Ti compound supported on MgCl 2 , said component being obtained by contacting the titanium compound with the MgCl 2 , or a precursor Mg compound, optionally in the presence of an inert medium, obtaining an intermediate product a′), then subjecting a′) to prepolymerization and contact with an electron donor compound;
b) an organo-Al compound; and optionally
c) an external electron donor compound.

7. The polyethylene composition of claim 1 , having at least one of the following additional features:
a Mw equal to or lower than 300000 g/mol;
a Mw/Mn from 15-30;
an MIP from 1.0-2.5 g/10 min;
an SIC Index from 1.5-3;
wherein the SIC Index is the Shear-Induced Crystallization Index, determined according to the following equation:
SIC Index=( t onset,SIC @1000 ×t onset,quiescent )/(MIF)

where t onset,SIC @1000 is measured in seconds and is the time required for crystallization onset under shear rate of 1000 s −1 , the t onset, quiescent is measured in seconds and is the crystallization onset time at temperature of 125° C. under no shear, as determined in isothermal mode by differential scanning calorimetry.

8. The polyethylene composition of claim 1 , comprising:
A) 40-60% by weight of an ethylene homopolymer or copolymer with density equal to or greater than 0.960 g/cm 3 and melt flow index MIE at 190° C. with a load of 2.16 kg, according to ISO 1133, of 20-120 g/10 min;
B) 40-60% by weight of an ethylene copolymer having a MIE value lower than 0.5 g/10 min.

9. A manufactured article comprising the polyethylene composition of claim 1 .

10. The manufactured article of claim 9 , comprising a blow-molded article having a capacity from 250-5000 ml.

11. A process for preparing the polyethylene composition of claim 1 , wherein the process is carried out in the presence of a Ziegler-Natta polymerization catalyst supported on MgCl 2 .

12. The process of claim 11 , comprising:
a) polymerizing ethylene, optionally together with one or more comonomers, in a gas-phase reactor in the presence of hydrogen;
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);
where 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 they flow downward under the action of gravity, leave the second polymerization zone and are reintroduced into the first polymerization zone for establishing a circulation of polymer between said two polymerization zones.

13. The polyethylene composition of claim 1 , comprising an M z from 1000000-1500000 g/mol.

Assignees

• Basell Polyolefine Gmbh

Inventors

• Meier Gerhardus
• Schuller Ulf
• Dotsch Diana
• Marczinke Bernd Lothar
• Wiesecke Jens

Classifications

• C08L23/0815 Primary

  with aliphatic 1-olefins containing one carbon-to-carbon double bond · CPC title

• B29K2023/06

  PE, i.e. polyethylene · CPC title

• C08L2314/02

  Ziegler natta 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

• C08F210/16 Primary

  Copolymers of ethene with alpha-alkenes, e.g. EP rubbers · CPC title