PROCESS FOR PRODUCING A HOMOGENEOUS POLYETHYLENE MATERIAL INTHE PRESENCE OF A CATALYST

摘要

The present invention concerns a process for producing homogeneous polyethylene materials and processes for making high density, medium density and low density films therefrom. The process comprises producing a polyethylene composition in a multistage reaction sequence of successive polymerization stages in the presence of an ethylene-polymerizing catalyst system. According to the invention, the process is carried out using an unsupported catalyst comprising magnesium and titanium as active constituents, in at least one loop polymerization stage and at least one gas phase polymerization stage and, operated with different amounts of hydrogen and comonomers to produce a high molecular weight portion in one of the polymerization stages and a low molecular weight portion in another so as to provide a polyethylene composition with the low molecular weight part having an MFR2 of 250 g/10 min or more. By means of the process it is possible to obtain homogeneous bimodal polyethylene material.