Bimodal polyethylene for injection stretch blow moulding applications
A polyethylene resin having a multimodal molecular weight distribution comprising at least two polyethylene fractions A and B, fraction A being substantially free of comonomer and having a lower weight average molecular weight and a higher density than fraction B, each fraction prepared in different reactors of two reactors connected in series in the presence of a Ziegler-Natta catalyst system, the polyethylene resin having a density of from 0.950 to 0.965 g/cm 3 and a melt index MI2 of from 0.5 to 5 g/10 min.
1. A polyethylene resin having a multimodal molecular weight distribution comprising at least two polyethylene fractions A and B, fraction A being substantially free of comonomer and having a lower weight average molecular weight and a higher density than fraction B, each fraction prepared in different reactors of two reactors connected in series in the presence of a Ziegler-Natta catalyst system, the polyethylene resin having a density of from 0.950 to 0.965 g/cm 3 , measured following the method of standard test ASTM 1505 at a temperature of 23° C., a melt index MI2 of from 0.5 to 5 g/10 min, measured following the method of standard test ASTM D 1238 at a temperature of 190° C. and under a load of 2.16 kg, and molecular weight distribution Mw/Mn of from 5 to 20, wherein the fraction B has a high load melt index HL275 of at least 1.5 dg/min and at most 14 dg/min.
2. The polyethylene resin of claim 1 , wherein the Ziegler-Natta catalyst system comprises a Ziegler-Natta catalyst component D and a preactivating agent, wherein the Ziegler Natta catalyst component D is obtained by
a) generating a reaction product A by contacting a magnesium dialkoxide compound with a halogenating agent;
b) contacting reaction product A with a first halogenating/titanating agent to form reaction product B;
c) contacting reaction product B with a second halogenating/titanating agent to form reaction product C; and
d) contacting reaction product C with a third halogenating/titanating agent to form catalyst component D.
3. The polyethylene resin according to claim 2 , wherein the preactivating agent of the Ziegler-Natta catalyst system is an organoaluminium compound.
4. The polyethylene resin according to claim 1 , wherein at least one of the reactors is a slurry loop reactor.
5. The polyethylene resin according to claim 4 , wherein the two reactors are slurry loop reactors.
6. The polyethylene resin according to claim 1 , wherein fraction B is produced in a first reactor of the two reactors and fraction A is produced in a second reactor of the two reactors.
7. The polyethylene resin according to claim 1 , wherein the polyethylene resin has an environmental stress crack resistance of at least 100 h.
8. A process comprising injection stretch blow moulding a polyethylene resin having a multimodal molecular weight distribution comprising at least two polyethylene fractions A and B, fraction A being substantially free of comonomer and having a lower weight average molecular weight and a higher density than fraction B, each fraction prepared in different reactors of two reactors connected in series in the presence of a Ziegler-Natta catalyst system, the polyethylene resin having a density of from 0.950 to 0.965 g/cm 3 , measured following the method of standard test ASTM 1505 at a temperature of 23° C., a melt index MI2 of from 0.5 to 5 g/10 min, measured following the method of standard test ASTM D 1238 at a temperature of 190° C. and under a load of 2.16 kg, and molecular weight distribution Mw/Mn of from 5 to 20.
9. The polyethylene resin of claim 1 , wherein the Ziegler-Natta catalyst system comprises a titanium compound having at least one titanium-halogen bond.
10. The polyethylene resin of claim 1 , wherein the polyethylene resin has a bimodal molecular weight distribution.
11. The polyethylene resin of claim 1 , wherein the fraction B has a density of at least 0.908 g/cm 3 and at most 0.945 g/cm 3 , measured following the method of standard test ASTM 1505 at a temperature of 23° C.
12. The polyethylene resin of claim 1 , wherein the fraction B has a high load melt index HL275 of at least 5 dg/min and at most 10 dg/min.
13. The polyethylene resin of claim 1 , wherein the fraction A has a density of at least 0.953 g/cm 3 and at most 0.978 g/cm 3 , measured following the method of standard test ASTM 1505 at a temperature of 23° C.
14. The polyethylene resin of claim 1 , wherein the polyethylene resin comprises from 36 to 50 wt % of the fraction B and from 50 to 64 wt % of the fraction A.
15. The process of claim 8 , wherein the Ziegler-Natta catalyst system comprises a titanium compound having at least one titanium-halogen bond and an internal electron donor, both on a support, and an organoaluminum compound.
16. The process of claim 8 , wherein the fraction B has a high load melt index HL275 of at least 1.5 dg/min and at most 14 dg/min.