Polyethylene compositions and closures made from them

摘要

A dual reactor solution process gives high density polyethylene compositions containing a first ethylene copolymer and a second ethylene copolymer and which have good processability, stiffness, and environmental stress crack resistance. The polyethylene compositions are suitable for compression molding or injection molding applications and are particularly useful in the manufacture of caps and closures for bottles.

主权项

1. A closure, said closure comprising a bimodal polyethylene composition comprising:
(1) 10 to 70 weight percent of a first ethylene copolymer having a melt index I2, of less than 0.4 g/10 min; a molecular weight distribution Mw/Mn, of less than 2.7; and a density of from 0.920 to 0.955 g/cm3; and (2) 90 to 30 weight percent of a second ethylene copolymer having a melt index I2, of from greater than 500 to 20,000 g/10 min; a molecular weight distribution Mw/Mn, of less than 2.7; and a density higher than the density of said first ethylene copolymer, but less than 0.967 g/cm3;
wherein the density of said second ethylene copolymer is less than0.037 g/cm3 higher than the density of said first ethylene copolymer; the ratio (SCB1/SCB2) of the number of short chain branches per thousand carbon atoms in said first ethylene copolymer (SCB1) to the number of short chain branches per thousand carbon atoms in said second ethylene copolymer (SCB2) is greater than 1.0; and wherein said bimodal polyethylene composition has a molecular weight distribution Mw/Mn, of from 6 to 13; a density of at least 0.949 g/cm3; a melt index I2, of from 0.2 to 3.0 g/10 min; an MZ of less than 450,000; a stress exponent of less than 1.50, a broadness factor defined as (Mw/Mn)/(Mz/Mw) of at least 2.75 and an ESCR Condition B (10% IGEPAL) of greater than 400 hours.