POLYETHYLENE COMPOSITION WITH HIGH DEGREE OF SWELLING Russian patent published in 2017 - IPC C08L23/06 C08L23/08 C08F2/34 C08F10/02 C08F210/16 C08J5/00 B29C49/00 

FIELD: chemistry.

SUBSTANCE: invention relates to a polyethylene composition for making moulded articles of different types. Composition has density from 0.953 to 0.960 g/cm³ and ratio of MIF/MIP from 17–29, where MIF is melt flow index at 190 °C with load of 21.60 kg, and MIP is melt flow index at 190 °C with a load of 5 kg. Composition is obtained by polymerisation of ethylene, optionally together with one or more comonomers, in a gas phase reactor in presence of hydrogen and copolymerisation of ethylene with one or more comonomers in other gas-phase reactor in presence of a lower amount of hydrogen, than at step a). In at least one of said gas-phase reactors growing polymer particles flow upward through a first polymerisation zone under fast fluidisation or transfer conditions, come out of said zone, and enter a second polymerisation zone, through which they flow down by gravity, come out of said second polymerisation zone and reenter first polymerisation zone, creating circulation of polymer between polymerisation zones. All copolymerisation steps are carried out in presence of a Ziegler-Natta polymerisation catalyst deposited on MgCl₂. Polyethylene composition contains one or more copolymers of ethylene and not more than 1 wt% of comonomer, selected from olefins of formula CH₂=CHR, where R is alkyl radical, linear or branched, containing from 1 to 10 carbon atoms.

EFFECT: obtained composition is characterised by good balance of physical and mechanical properties, high degree of swelling of extruded flow with surface of high quality and stability of dimensions of end product, environmental stress-cracking resistance (FNCT) and impact strength.

4 cl, 1 dwg, 1 tbl