Polyethylene Pipe Resin with High Resistance to Slow Crack Growth

Patent metadata

Field	Value
Publication number	US-2023257489-A1
Application number	US-202118014219-A
Country	US
Kind code	A1
Filing date	Jul 7, 2021
Priority date	Jul 10, 2020
Publication date	Aug 17, 2023
Grant date	—

Abstract

The present invention relates to a polyethylene composition comprising a base resin which comprises (A) a first ethylene homo- or copolymer fraction, and (B) a second ethylene-hexene-1 copolymer fraction, wherein fraction (A) has a lower molecular weight than fraction (B) and wherein fraction (B) is present in an amount of from 51.0 to 58.5 wt. %, preferably 52.0 to 57.5 wt. %, more preferably 53.0 to 57.0 wt. % based on the total weight of the base resin, wherein fraction (B) of the base resin has a content of units derived from hexene-1 from 0.80 to 1.45 mol %, preferably of from 0.82 to 1.35 mol % and more preferably of from 0.85 to 1.30 mol %, wherein the base resin has a number average molecular weight Mn of 8,500 g/mol or higher, and wherein the polyethylene composition has a melt flow rate MFRs from 0.10 to 0.30 g/10 min, preferably from 0.15 to 0.28, and still more preferably from 0.16 to 0.25 g/10 min, to a process for producing the polyethylene composition, to an article, especially a pipe comprising the polyethylene composition and to the use of the polyethylene composition for the production of an article, especially a pipe.

First claim

1 . A polyethylene composition comprising a base resin which comprises
(A) a first ethylene homo- or copolymer fraction, and (B) a second ethylene-hexene-1 copolymer fraction,
wherein fraction (A) has a lower molecular weight than fraction (B) and wherein fraction (B) is present in an amount of from 51.0 to 58.5 wt. %, based on the total weight of the base resin,
wherein fraction (B) of the base resin has a content of units derived from hexene-1 from 0.80 to 1.45 mol %,
wherein the base resin has a number average molecular weight Mn of 8,500 g/mol or higher, and
wherein the polyethylene composition has a melt flow rate MFR 5 from 0.10 to 0.30 g/10 min.

2 . Polyethylene composition according to claim 1 wherein the composition has a strain hardening modulus of 80 MPa or higher.

3 . Polyethylene composition according to claim 1 wherein the base resin has a density of at least 945 kg/m 3 .

4 . Polyethylene composition according to claim 1 wherein the base resin has a content of units derived from hexene-1 of 0.44 to 0.70 mol %.

5 . Polyethylene composition according to claim 1 wherein the composition has a Charpy Impact Strength (CIS) at 23° C. of higher than 35 kJ/m 2 , or a Charpy Impact Strength (CIS) at 0° C. of higher than 22.5 kJ/m 2 , or a Charpy Impact Strength (CIS) at −20° C. of higher than 14.7 kJ/m 2 .

6 . Polyethylene composition according to claim 1 wherein fraction (A) of the base resin has an MFR 2 as measured in accordance with ISO 1133 of 150 to 600 g/10 min.

7 . Polyethylene composition according to claim 2 wherein the polyethylene composition has a critical temperature Tc in the rapid crack propagation test of −10° C. or lower.

8 . Polyethylene composition according to claim 1 wherein the composition further comprises carbon black.

9 . Polyethylene composition according to claim 8 wherein fraction (B) of the base resin is present in the base resin in an amount of from 54 to 57 wt. %, based on the total weight of the base resin, or wherein the composition has a density of from 953 to 965 kg/m 3 , or wherein the base resin has a number average molecular weight of 9,000 g/mol or higher.

10 . Polyethylene composition according to claim 1 wherein the composition does not comprise carbon black and the base resin has a total content of units derived from hexene-1 of 0.44 to 0.65 mol %.

11 . Polyethylene composition according to claim 10 wherein fraction (B) of the base resin is present in the base resin in an amount of from 54 to 57 wt. %, based on the total weight of the base resin, or wherein the composition has a density of from 946 to 955 kg/m 3 , or wherein the base resin has a number average molecular weight Mn of 9,300 g/mol or higher.

12 . A process for producing a polyethylene composition according to claim 10 wherein the base resin is produced in a multi-stage polymerization process in the presence of a Ziegler-Natta catalyst.

13 . An article comprising the polyethylene composition according to claim 1 .

14 . The article according to claim 13 being a pipe or pipe fitting.

15 . A method, comprising producing an article using the polyethylene composition of claim 1 .

16 . The polyethylene composition of claim 1 , wherein fraction (B) is present in an amount of from 53.0 to 57.0 wt %.

17 . The polyethylene composition of claim 1 , wherein fraction (B) of the base resin has a content of units derived from hexene-1 from 0.85 to 1.30 mol %.

18 . The polyethylene composition of claim 8 , wherein the base resin has a total content of units derived from hexene-1 of 0.50 to 0.70 mol %.

19 . The polyethylene composition of claim 8 , wherein fraction (B) of the base resin has a content of units derived from hexene-1 from 0.9 to 1.45 mol %.

20 . The polyethylene composition of claim 10 , wherein the composition does not comprise carbon black and wherein fraction (B) of the base resin has a content of units derived from hexene-1 from 0.8 to 1.35 mol %.

Assignees

• Borealis Ag

Inventors

• Buryak Andrey
• Sumerin Victor
• Ruemer Franz
• Aarila Jari
• Cheng Joy Jie

Classifications

• C08F10/02 Primary

  Ethene · CPC title

• C08F210/14

  Monomers containing five or more carbon atoms · CPC title

• C08L23/0815 Primary

  with aliphatic 1-olefins containing 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

• C08K3/04

  Carbon · CPC title