Polyethylene pipe
View Patent ↗Multi-layered pipe comprising a main layer of polyethylene compound having a resistance to stress cracking NPT measured according to ISO 13479 standard of less than 8000 hours and an internal layer of polyethylene compound having a resistance to stress cracking NPT of higher than 8000 hours, the thickness of the internal layer being between 1 and 25% of the total pipe thickness but not less than 0.3 mm.
1. Multi-layered pipe comprising a main layer of polyethylene compound having a resistance to stress cracking NPT measured according to ISO 13479 standard of less than 8000 hours and an internal layer of polyethylene compound having a resistance to stress cracking NPT of higher than 8000 hours, the thickness of the internal layer being between 1 and 25% of the total pipe thickness but not less than 0.3 mm.
2. Pipe according to claim 1 , wherein the polyethylene compound of the internal layer has a resistance to stress cracking NPT of at least 10000 hours.
3. Pipe according to claim 1 , wherein the polyethylene compound of the internal layer has a MRS classification according to ISO/TR 9080 standard of at least 10.
4. Pipe according to claim 1 , wherein the polyethylene compound of the internal layer comprises at least 95% by weight of a polyethylene resin comprising from 30 to 70% by weight of an ethylene polymer having a density of at least 960 kg/m 3 and a melt index MI 2 of at least 100 g/10 min and from 30 to 70% by weight of an ethylene-hexene copolymer comprising from 0.4 to 10 weight % of hexene, having a density between 910 and 938 kg/m 3 and a melt index MI 5 of between 0.01 to 2 g/10 min.
5. Pipe according to claim 1 , wherein the polyethylene compound of the main layer has a MRS classification according to ISO/TR 9080 standard of at least 10.
6. Pipe according to claim 1 , wherein the pipe comprises an external layer having an improved scratch resistance.
7. Pipe according to claim 6 , wherein the external layer comprises a crosslinked silane-grafted polyethylene compound.
8. Pipe according to claim 6 , wherein the external layer comprises a polyethylene compound having a resistance to stress cracking NPT measured according to ISO 13479 standard of higher than 8000 hours.
9. Pipe according to claim 6 , wherein the internal layer, the main layer and the external layer comprise a polyethylene compound having a MRS classification of at least 10.
10. Pipe according to claim 6 , wherein the thickness of the external layer is between 1 and 35% of the total pipe thickness but not less than 0.3 mm.