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CA-3188493-C - POLYETHYLENE PIPE RESIN WITH HIGH RESISTANCE TO SLOW CRACK GROWTH

CA3188493CCA 3188493 CCA3188493 CCA 3188493CCA-3188493-C

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/10min, preferably from 0.15 to 0.28, and still more preferably from 0.16 to 0.25 g/10min, 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.

Inventors

  • Andrey Buryak
  • Victor SUMERIN
  • Franz Ruemer
  • Jari Aarila
  • JOY JIE CHENG

Assignees

  • BOREALIS AG

Dates

Publication Date
20260505
Application Date
20210707
Priority Date
20200710

Claims (19)

  1. We Claim: 1. A polyethylene composition comprising a base resin which comprises (A) a first ethylene homo- or copolymer fraction~ and (8) a second ethylene-hexene-1 copolymer fraction, wherein fraction (A) has a lower molecular weight than fraction (8) and wherein fraction (8) is present in an amount of from 51.0 to 58.5 wt.% based on the total weight of the base resin, wherein fraction (8) of the base resin has a content of units derived from hexene-1 from 0.80 to 1.45 moI%, 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 MFR5 from 0.10 to 0.30 g/1 0min.
  2. 2. The polyethylene composition according to claim 1, wherein fraction (A) has a lower molecular weight than fraction (8) and wherein fraction (8) is present in an amount of from 52.0 to 57.5 wt.% based on the total weight of the base resin, wherein fraction (8) of the base resin has a content of units derived from hexene-1 from 0.82 to 1.35 mo!%, 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 MFR5 from 0.15 to 0.28 g/1 0min.
  3. 3. The polyethylene composition according to claim 1, wherein fraction (A) has a lower molecular weight than fraction (B) and wherein fraction (8) is present in an amount of from 53.0 to 57.0 wt.% based on the total weight of the base resin, wherein fraction (8) of the base resin has a content of units derived from hexene-1 from 0.85 to 1.30 mo!%, 36 'I I I .. 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 0.16 to 0.25 g/1 0min.
  4. 4. The polyethylene composition according to any one of claims 1 to 3, wherein the composition has a strain hardening modulus of 80 MPa or higher.
  5. 5. The polyethylene composition according to any one of claims 1 to 4, wherein the base resin has a density of at least 945 kg/m 3 .
  6. 6. The polyethylene composition according to any one of claims 1 to 5, wherein the base resin has a content of units derived from hexene-1 of 0.44 to 0. 70 mo I%.
  7. 7. The polyethylene composition according to any one of claims 1 to 6, wherein the composition has a Charpy Impact Strength (CIS) at 23 °C of higher than 35 kJ/m 2, and/or a Charpy Impact Strength (CIS) at 0 °C of higher than 22.5 kJ/m 2, and/or a Charpy Impact Strength (CIS) at -20 °c of higher than 14. 7 kJ/m 2.
  8. 8. The polyethylene composition according to any one of claims 1 to 7, wherein fraction (A) ·of the base resin has an MFR2 as measured in accordance with ISO 1133 of 150 to 600 g/1 0min. ·
  9. 9. The polyethylene composition according to any one of claims 1 to 8, wherein the polyethylene composition has a critical temperature Tc in the rapid crack propagation test of -10 °C or lower. ,._
  10. 10. The polyethylene composition according to any one of claims 1 to 9, wherein the composition comprises carbon black.
  11. 11. The polyethylene composition according to claim 10, wherein the base resin has a total content of units derived from hexene-1 of 0.50 to 0. 70 mo I%, and/or wherein fraction (B) of the base resin has a content of units derived from hexene-1 from 0.90 to 1.45 mol%.
  12. 12. The polyethylene composition according to claim 10 or claim 11 wherein fraction (B) of the base resin is present in the base resin in 37 "I I Ir .. . , . an amount of from 54 to 57 wt.% based on the total weight of the base resin and/or wherein the composition has a density of from 953 to 965 kg/m 3 and/or wherein the base resin has a number average molecular weight of 9,000 g/mol or higher.
  13. 13. The polyethylene composition according to any one of claims 1 to 9 wherein the composition does not comprise carbon black.
  14. 14. The polyethylene composition according to claim 13, wherein the base resin has a total content of units derived from hexene-1 of 0.44 to 0.65 mo!%, and/or wherein fraction (B) of the base resin has a content of units derived from hexene-1 from 0.8 to 1.35 mo I%.
  15. 15. The polyethylene composition according to any one of claims 13 or 14 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, and/or wherein the composition has a density of from 946 to 955 kg/m 3 and/or wherein the base resin has a number average molecular weight Mn of 9,300 g/mol or higher.
  16. 16. A process for producing the polyethylene composition according to any one of claims 1 to 15, wherein the base resin is produced in a multi-stage polymerization process in the presence of a Ziegler-Natta catalyst.
  17. 17. An article comprising the polyethylene composition according to any one of claims 1 to 15.
  18. 18. The article according to claim 17 being a pipe or pipe fitting.
  19. 19. Use of the polyethylene composition according to any one of claims 1 to 15 for producing an article. 38

Description

POLYETHYLENE PIPE RESIN WITH HIGH RESISTANCE TO SLOW CRACK GROWTH The present invention relates to a multimodal polyethylene composition for the production of a high-pressure pipe, to a process for obtaining the composition, to an article, especially a pipe, comprising the composition. Polyolefin pipes and especially polyethylene pipes are conventionally used for transport of water, gas as well as industrial liquids and slurries. Due to their versatility, ease of production and installation as well as non-corrosivity, their use is constantly increasing. New installation techniques, such as trenchless and sand bed-free installation, demand polyethylene pipe resins with higher and higher resistance to slow crack growth. The requirements for slow crack growth become more and more stringent and many of the existing products fail to consistently meet those requirements. At the same time, there is the need to improve the impact resistance of the HOPE pipe resins in order to avoid pipelines' failure by rapid crack propagation. Depending on the pressure pipes made from a polyethylene composition can withstand at 20°C over 50 years lifetime, the compositions are classified for example as PESO or PE 100. According to ISO 9080 polyethylene pipes are classified by their minimum required strength, i.e. their capability to withstand different hoop stresses during 50 years at 20 °C without fracturing. Thereby, pipes withstanding a hoop stress of 8.0 MPa (MRSs.o) are classified as PESO pipes, and pipes withstanding a hoop stress of 10.0 MPa (MRS10.o) are classified as PE100 pipes. The service temperature for PE100 is usually within the temperature range from about 0 °C to about 50 °C. To meet the PESO requirements with multimodal resins manufactured by conventional Ziegler-Natta catalysts, the density needs to be at least 940 kg/m3 and to meet PE100 requirements the density needs to be above 945 kg/m3 . However, the density of a polyethylene resin is directly connected with its crystallinity. The higher the crystallinity of a polyethylene resin the lower its slow crack growth resistance. In other words, all polyethylene materials for pressure resistance of a pipe suffer from the dependency of crystallinity and insofar density and the slow crack growth. When the density is increased, the resistance to slow crack growth (SCG) decreases. 1 The manufacture of polyethylene materials to be used in pressure pipes is discussed for example in an article by Scheirs et al (Scheirs, Bohm, Boot and Leevers: PE 100 Resins for Pipe Applications, TRIP Vol. 4, No 12 (1996) pp. 408- 415). WO 00/22040 discloses a pipe having good mechanical properties made from a bimodal resin. EP 1 985 660 A 1 discloses a pipe or a supplementary pipe article with improved slow crack growth resistance comprising a polyethylene composition comprising a base resin, which comprises a first ethylene homo- or copolymer fraction (A), and a second ethylene homo- or copolymer fraction (B), wherein fraction (A) has a lower average molecular weight than fraction (B), and wherein the base resin has a density in the range of 945 to 949 kg/m 3, an MFRs in the range of 0.2 to 0.4 g/10 min., a comonomer content of higher than 2.0 wt.% and a SHl(2.?1210) in the range of 55 to 100. It is an object of the present invention to provide a polyethylene pipe material which meets the requirements for a PE100 resin and, at the same time, has a combination of an improved slow crack growth resistance, a very good rapid crack propagation resistance and a very good impact resistance. The present invention is based on the surprising finding that such a pipe material can be provided by a selecting a specific combination of the properties of a multimodal polyethylene base resin in terms of a high number average molecular weight, a selected hexene comonomer content in the high Mw fraction, and a selected amount of the high Mw fraction. The present invention therefore provides 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 2 wherein the polyethylene composition has a melt flow rate MF Rs from 0.10 to 0.30 g/1 0min, preferably from 0.15 to 0.28, and still more preferably from 0.16 to 0.25 g/1 0min. The polyethylene composition of the invention due to its combination of design parameters allows to achieve excellent resistance to slow crack g