Multimodal polyethylene pipe resins and process
View Patent ↗Multimodal polyethylene resins having improved stress crack resistance and melt strength rendering them useful for the manufacture of thick-walled pipe are produced in a process wherein the second stage of the process is a copolymerization conducted at a high temperature with a low comonomer to ethylene ratio and a low hydrogen to ethylene ratio.
1. A multimodal polyethylene resin, said multimodal resin comprised of:
(i) a first polyethylene resin having a first molecular weight and having a density from 0.965 to 0.975 g/cm 3 and MI 2 from 50 to 400 g/10 min and
(ii) a second copolymer resin comprising lower density ethylene-C 3-8 α-olefin copolymer resin having a second molecular weight wherein the second molecular weight is higher than the first molecular weight,
wherein said multimodal resin having a density from 0.947 to 0.950 g/cm 3 , HLMI from 2 to 8 g/10 min and zero shear viscosity from 7×10 6 to 1×10 7 poise.
2. The multimodal polyethylene resin of claim 1 wherein the weight ratio of the first polyethylene resin to the second copolymer resin is from 55:45 to 50:50.
3. The multimodal polyethylene resin of claim 2 wherein the second copolymer resin is an ethylene-butene-1 copolymer.
4. The multimodal polyethylene resin of claim 3 having a density from 0.947 to 0.949 g/cm 3 , HLMI from 3 to 7 g/10 min and zero shear viscosity from 7.2×10 6 to 9.5×10 6 poise.
5. Extruded pipe comprising the multimodal polyethylene resin of claim 1 .
6. The extruded pipe of claim 5 further characterized as meeting the requirements of PE 4710 and PE 100.