RU2001103126A - POLYMER PIPE COMPOSITION - Google Patents

Claims (15)

1. Multimodal polyethylene composition for pipes, in which multimodal polyethylene has a density of 0.930-0.965 g / cm ³ and MFR ₅ 0.2-1.2 g / 10 min, characterized in that the multimodal polyethylene has M _n 8000-15000, M _w 180000-330000 and M _w / M _n 20-35, wherein said multimodal polyethylene contains a low molecular weight (HM) fraction of an ethylene homopolymer and a high molecular weight (HM) fraction of an ethylene copolymer, said HM fraction having a lower molecular weight limit of 3500 and a weight ratio NM fractions to VM fractions equals (35-55) :( 65-45). 2. The composition according to claim 1, in which the multimodal polymer is a bimodal polyethylene obtained by (co) polymerization in at least two stages. 3. The composition according to claim 1, in which the ethylene copolymer of the BM fraction is an ethylene copolymer, and the comonomer is selected from the group consisting of 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene. 4. The composition according to any one of claims 1 to 3, in which the amount of comonomer is 0.4-3.5 mol%. multimodal polymer. 5. The composition according to any one of claims 1 to 4, which has a mass ratio of the NM fraction to the VM fraction (43-51) :( 57-49). 6. The composition according to any one of claims 1 to 5, in which the multimodal polymer has an MFI of ₅ 0.3-1.0 g / 10 min. 7. The composition according to claim 1, in which the polymer is obtained by suspension polymerization in a reactor with the circulation of the NM fraction of ethylene homopolymer, followed by gas-phase polymerization of the BM fraction of ethylene copolymer. 8. The composition according to claim 7, in which suspension polymerization is preceded by a prepolymerization step. 9. The composition of claim 8, in which the polymer is obtained by prepolymerization in a loop reactor followed by suspension polymerization in a loop reactor of the HM fraction of ethylene homopolymer and gas-phase polymerization of the HM fraction of ethylene copolymer. 10. A composition according to any one of claims 7 to 9, wherein the polymerization procatalyst and cocatalyst are introduced only into the first polymerization reactor. 11. The composition of claim 10, in which the polymerization catalyst is a Ziegler-Natta type catalyst. 12. A pipe, characterized in that it is a pressure pipe containing a multimodal polymer composition according to any one of claims 1 to 11, which (pipe) can withstand a pressure of 8.0 MPa, calibrated for 50 years at 20 ° C (MRS8,0) . 13. The pipe according to item 12, in which the pipe is a pressure pipe that can withstand a pressure of 10 MPa, calibrated for 50 years at 20 ° C (MRS10,0). 14. The pipe according to item 12 or 13, in which the pipe has a resistance to rapid crack propagation (BRT) of the S4 test of -1 ° C or lower. 15. The pipe according to 14, in which the pipe has a resistance to rapid crack propagation (BRT) S4-test -7 ° C or lower.