Cross-linkable polyethylene resin for pipes made by a single-site catalyst
View Patent ↗An ethylene polymer with a density of less than 955 kg/m 3 obtained by polymerisation with a single-site catalyst and having a shear thinning index SHI 2.7/210 of less than 5 wherein ethylene polymer comprises two components.
1. A process for the preparation of a unimodal ethylene homopolymer with a density of less than 955 kg/m 3 and having a shear thinning index SHI 2.7/210 of less than 5 comprising:
(I) polymerizing ethylene in a first stage in the presence of a single site catalyst;
(II) polymerizing ethylene in a second stage in the presence of the same single site catalyst and in the presence of the product of step (I);
so as to form the unimodal ethylene homopolymer having an Mw/Mn of less than 3.
2. The process according to claim 1 wherein the unimodal ethylene homopolymer comprises a first component and a second component.
3. The process according to claim 2 wherein the first component comprises a loop phase polymer.
4. The process according to claim 2 wherein the second component is made in a gas phase process.
5. The process according to claim 1 wherein the unimodal ethylene homopolymer comprises an ash content of less than 250 ppm.
6. The process according to claim 2 wherein the first component comprises an ash content of at least 250 ppm.
7. The process according to claim 1 wherein the unimodal ethylene homopolymer comprises an SHI 2.7/210 of less than 4.
8. The process according to claim 1 wherein the unimodal ethylene homopolymer comprises an MFR 21 of less than 5 g/10 min.
9. The process according to claim 1 wherein the unimodal ethylene homopolymer comprises a single peak in its GPC curve.
10. The process according to claim 2 wherein a weight ratio between the two components in the unimodal ethylene homopolymer is 40:60 to 60:40.
11. A process for the preparation of a cross-linked polyethylene comprising:
cross-linking the unimodal ethylene homopolymer prepared according to the process of claim 1 ;
so as to form the cross-linked polyethylene.
12. The process according to claim 11 wherein the cross-linked polyethylene comprises a cross-linking degree of at least 70% (ASTM D2765-01, method A using Trig 145 E85).
13. A process for the preparation of a cross-linked pipe comprising:
conducting RAM extrusion with the cross-linked polyethylene prepared according to the process of claim 9 .
14. The process according to claim 13 wherein a cross-linking agent comprises a peroxide.