Patent EA-005091-B1 (EA)
Title: Polyethylene pipe resins and production thereof
Inventor: MISERQUE OLIVER
IPC: C08F2/00
Filed: 2001-10-25
Abstract: 1. A polyethylene resin comprising from 35 to 49 wt.% of a first polyethylene fraction of high molecular weight and from 51 to 65 wt.% of a second polyethylene fraction of low molecular weight, the first polyethylene having a density of up to 0.930 g/cm<3>, and an HLMI of less than 0.6 g/10 min and the second polyethylene fraction comprising a high density polyethylene having a density of at least 0.969 g/cm<3> and an MI2 of greater than 10 g/10 min, and the polyethylene resin, having a density of greater than 0.946 g/cm<3>, an HLMI of from 1 to 100 g/10min, a dynamical viscosity, measured at 0.01 radians/second, greater than 200,000 Pa.s and a ratio of the dynamical viscosities measured at, respectively 0.01 and 1 radians/second greater than 8. 2. A polyethylene resin according to claim 1, wherein for the high density fraction the MI2 is from 100 to 1000 g/10 min. 3. A polyethylene resin according to claim 1 or claim 2 wherein for the low density fraction the HLMI is from 0.001 to 0.5g/10 min. 4. A polyethylene resin according to any one of claims 1 to 3 wherein for the low density fraction the density is from 0.908 to 0.927 g/cm<3>. 5. A polyethylene resin according to any foregoing claim wherein for the high density fraction the density is from 0.970 to 0.990g/cm<3>. 6. A polyethylene resin according to any foregoing claim wherein for the high density fraction the polydispersity index D is from 2 to 4. 7. A polyethylene resin according to any foregoing claim wherein for the low density fraction the polydispersity index D is from 3 to 6. 8. A polyethylene resin according to any foregoing claim wherein the density of the resin is from 0.949 to 0.960g/cm<3>. 9. A polyethylene resin according to any foregoing claim having a capillary viscosity mu2 less than 21,000 dPa.s. 10. A polyethylene resin according to any foregoing claim having a ratio eta0.01/eta1>={(0.293 x Mw/Mn) + 3.594}. 11. A polyethylene resin according to any foregoing claim having a ratio eta0.01/eta1>={(-0.302 x HLMI) + 9.499}. 12. Use, for the manufacture of pipes or fittings, of a polyethylene resin according to any foregoing claim. 13. A pipe or fitting comprising the polyethylene resin of any one of claims 1 to 12. 14. A process for the preparation of a polyethylene resin having a bimodal molecular weight distribution which comprises: (i) contacting ethylene monomer and a first co-reactant with a catalyst system in a first reaction zone under first polymerisation conditions to produce a first polyethylene; and (ii) contacting ethylene monomer and a second co-reactant with a catalyst system in a second reaction zone under second polymerisation conditions to produce a second polyethylene different from the first polyethylene; wherein the first and second polyethylenes are blended together, to form a polyethylene resin comprising a blend of from 35 to 49 wt% of a first polyethylene fraction of high molecular weight and from 51 to 65 wt% of a second polyethylene fraction of low molecular weight, the first polyethylene fraction comprising a linear low density polyethylene having a density of up to 0.930g/cm<3>, and an HLMI of less than 0.6g/10 min and the second polyethylene fraction comprising a high density polyethylene having a density of at least 0.969g/cm<3> and an MI2 of greater than 10 g/10 min, and the polyethylene resin having a density of greater than 0.946 g/cm<3>, an HLMI of from 1 to 100g/10 min,, a dynamical viscosity eta0.01, measured at 0.01 radians/second, greater than 200,000 Pa. s and a ratio of the dynamical viscosities measured at, respectively 0.01 and 1 radians/second eta0.01/eta1 greater than 8, wherein one of the co-reactants is. hydrogen and the other is a comonomer comprising a 1-olefin containing from 3 to 12 carbon atoms, each catalyst system comprising (a) a metallocene catalyst component comprising a bis tetrahydroindenyl compound of the general formula (IndH4)2R"MQ2 in which each IndH4 is the same or different and is tetrahydroindenyl or substituted tetrahydroindenyl, R" is a bridge which comprises a C1-C4 alkylene radical, a dialkyl germanium or silicon or siloxane, or an alkyl phosphine or amine radical, which bridge is substituted or unsubstituted, M is a Group IV metal or vanadium and each Q is hydrocarbyl having 1 to 20 carbon atoms or halogen; and (b) a cocatalyst which activates the catalyst component. 15. A process according to claim 14 wherein the two reactors are connected in series.