PRODUCTION OF POLYETHYLENE BY MULTI-STAGE POLYMERIZATION

PURPOSE:To obtain a polyethylene suitable for flat yarn grades, having excellent extrusion fluidity and balanced strength and elongation, by carrying out continuous multi-stage polymerization by the use of a specific Ziegler catalyst. CONSTITUTION:By the use of a Ziegler catalyst obtained from an organoaluminum compound and a solid reaction product which is obtained by reacting a trivalent halide with a bivalent metallic hydroxide, oxide or carbonate to give a solid reaction product, reacting the reaction product with a halogen-containing transition metallic compound of group 4a or group 5a in the presence of an electron donative compound and then reacting the reaction product with a compound of the transition metallic containing no halogen, ethylene and hydrogen are fed in the molar ratio of ethylene/hydrogen in a gas phase of a polymerizer of 1/1-1/5, 40-60% total polymerization amount is subjected to first-stage polymerization in a saturated hydrocarbon are fed in the molar 1-50kg/cm , then ethylene and hydrogen are fed in the molar ratio of 1/0.05-1/1 and 60-40% total polymerization amount is subjected to second polymerization at 40-100 deg.C under 1-50kg/cm to give a polyethylene having 0.2-2.0 melt index.