Multimodal polyethylene resin for pipe made by a single-site catalyst
View Patent ↗The present invention relates to a polyethylene composition comprising a polyethylene base resin, which comprises a. an ethylene copolymer as fraction (A), and b. an ethylene homo- or copolymer as fraction (B), with fraction (A) having a lower molecular weight than fraction (B), wherein the polyethylene base resin is obtainable in a polymerisation process in which a single-site catalyst. (SSC) is used in the polymerisation of at least one of fractions (A) and (B), and the base resin has (i) a density of below 940 kg/m 3 , and (ii) a MFR 2 at 190 ° C./2.16 kg of 0.001 to 10 g/10 min, and the composition has (iii) a flexural modulus of from 300 to 820 MPa, and to a process for the production of such a composition, and to a pipe produced from such a composition.
1. A polyethylene composition comprising, a polyethylene base resin, which comprises:
a. an ethylene copolymer as fraction (A), and
b. an ethylene homo- or copolymer as fraction (B),
with fraction (A) having a lower molecular weight than fraction (B),
wherein the polyethylene base resin is obtained by a polymerization process in which a single-site catalyst (SSC) is used in the polymerization of at least one of fractions (A) and (B), and the polyethylene base resin has:
(i) a density of below 940 kg/m3, and
(ii) a MFR2 at 190 20 C. / 2.16 kg of 0.01 to 10 g/10 min;
wherein the polyethylene composition has a flexural modulus of from 400 to 820 MPa;
wherein the polyethylene composition has a shear thinning index (SHI 2.7/2.10 ) below 20; and
wherein a loop reactor, used in the polymerization process, is operated at a temperature of between 70 to 90° C.
2. The polyethylene composition according to claim 1 , wherein the polyethylene composition has a Charpy impact strength at 0° C. of at least 10 kJ/m 2 , measured according to ISO 179.
3. The polyethylene composition according to claim 1 , wherein the polyethylene composition has a critical temperature in the RCP-S4 test of +2° C. or lower, measured according to ISO 13477.
4. The polyethylene composition according to claim 1 , wherein the polyethylene composition has a slow crack growth value in a pipe notch test according to ISO 13479 at 80° C. and 5.4 MPa of at least 165 hours.
5. The polyethylene composition according to claim 1 , wherein the polyethylene composition has an MRS rating of at least 6.3, measured according to ISO /TR 9080.
6. The polyethylene composition according to claim 1 , wherein the molecular weight distribution of the polyethylene base resin is from 5 to 25.
7. The polyethylene composition according to claim 1 , wherein fraction (A) is a copolymer of ethylene and C 4 to C 20 alpha-olefin comortomers.
8. The polyethylene composition according to claim 1 , wherein fraction (A) has a density from 920 to 962 kg/m3.
9. The polyethylene composition according to claim 1 , wherein fraction (A) has a melt flow rate (190° C. / 2.16 kg) MFR 2 of 10 to 300 g/10 min.
10. The polyethylene composition according to claim 1 , wherein in the polyethylene base resin the weight ratio between fraction (A) and fraction (B) is between 60:40 to 40:60.
11. A pipe made of the polyethylene composition according to claim 1 .