Polyethylene composition for high pressure resistant pipes

8:

• A polyethylene composition obtainable by a multistage process, the multistage process comprising the following steps:
• a) polymerizing ethylene in the presence of a solid Ziegler-Natta catalyst component in a first reactor for obtaining a first intermediate material, the first intermediate material having a melt flow rate MFR2 (190° C., 2.16 kg) of 5.0 to 300 g/10 min,
• b) transferring the first intermediate material to a second reactor,
• (i) feeding ethylene to the second reactor,
• (ii) further polymerizing the first intermediate material,
• for obtaining a second intermediate material, the second intermediate material having a melt flow rate MFR2 (190° C., 2.16 kg) of 80 to 300 g/10 min;
• and
• c) transferring the second intermediate material to a third reactor,
• (i) feeding ethylene and comonomer selected from alpha-olefins having from 4 to 12 carbon atoms to a fourth reactor,
• (ii) further polymerizing the second intermediate material in the presence of a silane type external donor,
• for obtaining a base resin having density of from 950.0 kg/m3 to 962.0 kg/m3, determined according to ISO 1183, and
• d) extruding the base resin into a polyethylene composition having a melt flow rate MFR21 (190° C., 21.16 kg), of from 1.0 to 9.0 g/10 min, determined according to ISO 1133, and a viscosity at a constant shear stress of 747 Pa eta747 of from 3500 kPa·s to 20000 kPa·s.

10:

• The process according to claim 9, wherein the multistage process comprises the following steps:
• a) polymerizing ethylene in the presence of a solid Ziegler-Natta catalyst component in a first reactor for obtaining a first intermediate material, the first intermediate material having a melt flow rate MFR2 (190° C., 2.16 kg) of 5.0 to 300 g/10 min,
• b) transferring the first intermediate material to a second reactor,
• (i) feeding ethylene to the second reactor,
• (ii) further polymerizing the first intermediate material,
• for obtaining a second intermediate material, the second intermediate material having a melt flow rate MFR2 (190° C., 2.16 kg) of 80 to 300 g/10 min;
• and
• c) transferring the second intermediate material to a third reactor,
• (i) feeding ethylene and comonomer selected from alpha-olefins having from 4 to 12 carbon atoms to the fourth reactor,
• (ii) further polymerizing the second intermediate material in the presence of a silane type external donor,
• for obtaining a base resin having density of from 950.0 kg/m3 to 962.0 kg/m3, determined according to ISO 1183, and
• d) extruding the base resin into the polyethylene composition.