Ethylene polymer and process for preparing same

Claim 1

A process for the preparation of an ethylene polymer, which comprises polymerizing ethylene, optionally with a small amount of an α-olefin, in the presence of a Ziegler catalyst in multiple stages, wherein by using a polymerization apparatus including at least three polymerization reactors, the following three ethylene polymer components U, H and L are prepared sequentially in an optional order; an ethylene polymer component U having an α-olefin content α u , of 0.1 to 10% by weight and an intrinsic viscosity [η] u satisfying the requirement of 2×[η] w ≦[η] u ≦5×[η] w in which [η] w stands for the intrinsic viscosity of the entire ethylene polymer, the ratio R u of the component U in the entire ethylene polymer satisfying the requirement of 0.35×[η] w ≦[η] u ×R u ≦0.7×[η] w ; an ethylene polymer component H having an α-olefin content α H of up to 20% by weight and an intrinsic viscosity [η] H satisfying the requirement of [η] w ) 2/3 ≦[η] H ≦1.5×[η] w , the ratio R H of the component H in the entire ethylene polymer satisfying the requirement of 0.25×[η] w ≦[η] H ×R H ≦0.7≦[η] w ; and an ethylene polymer component L having an α-olefin content α L of up to 10% by weight and an intrinsic viscosity [η] L satisfying the requirement of 0.2≦[η] L ≦2.0, the ratio R L of the component L in the entire ethylene polymer satisfying the requirement of [η] L ×R L ≧0.05×[η] W ; the three components R U , R H and R L in said ethylene polymer satisfying the requirement of (R U +R H +R L )=1 and each of R U , R H and R L being smaller than 1, said ethylene polymer satisfying the requirement of α U ×R U ≧0.2×(α U ×R U +α H ×R H +α L ×R L ), and wherein the catalyst has a property such that when the component H is prepared independently, the molecular weight distribution Mw/Mn of the obtained ethylene polymer is in the range of from 7 to 17 and the rate constant of deactivation Kd at said polymerization is larger than 0.3 hr +1 , and the intrinsic viscosity [η] W of the entire ethylene polymer is in the range of 1.5≦[η] W ≦4.0.