Patent ID: 9738777
Date: 2017-08-22
CPC Classifications: B29B,B29C,B29K,B29L,C08F,C08J,C08L

Claim:
1. A polymerization process for preparing a polyethylene composition having the following features: A) a density from 0.945 to less than 0.952 g/cm B) an MIF/MIP ratio from 15-30, where MIF is the melt flow index at 190° C. with a load of 21.60 kg, and MIP is the melt flow index at 190° C. with a load of 5 kg, both determined according to ISO 1133; C) an SIC Index from 2.5-5.5; a) polymerizing ethylene with one or more comonomers in a gas-phase reactor in the presence of hydrogen; b) copolymerizing ethylene with one or more comonomers in another gas-phase reactor in the presence of an amount of hydrogen less than step a); where in at least one of the gas-phase reactors the growing polymer particles flow upward through a first polymerization zone under fast fluidization or transport conditions, leave the riser and enter a second polymerization zone through which they flow downward under the action of gravity, leave the second polymerization zone and are reintroduced into the first polymerization zone for establishing a circulation of polymer between the two polymerization zones, and all polymerizations are performed in the presence of a Ziegler-Natta polymerization catalyst supported on MgCl