Polyethylene compositions having high dimensional stability and excellent processability for caps and closures

摘要

A dual reactor solution polymerization process gives high density polyethylene compositions containing a first ethylene copolymer and a second ethylene copolymer and which have high dimensional stability, excellent processability as well as good organoleptic properties and reasonable stress cracking resistance. The polyethylene compositions are suitable for compression molding or injection molding applications and are useful, for example, in the manufacture of caps and closures for bottles, and for example, in bottles containing non-pressurized liquids.

主权项

1. A closure for bottles, the closure comprising a polyethylene composition, the polyethylene composition comprising:
(1) about 10 to about 70 wt % of a first ethylene copolymer having a melt index I2, of from 0.1 to 10 g/10 min; a molecular weight distribution Mw/Mn, of less than 3.0; and a density of from 0.930 to 0.960 g/cm3; and (2) about 90 to about 30 wt % of a second ethylene copolymer having a melt index I2, of from 50 to 10,000 g/10 min; a molecular weight distribution Mw/Mn, of less than 3.0; and a density higher than the density of the first ethylene copolymer, but less than 0.966 g/cm3;
wherein the density of the second ethylene copolymer is less than0.037 g/cm3 higher than the density of the first ethylene copolymer; the ratio (SCB1/SCB2) of the number of short chain branches per thousand carbon atoms in the first ethylene copolymer (SCB1) to the number of short chain branches per thousand carbon atoms in the second ethylene copolymer (SCB2) is greater than 1.0; and wherein the polyethylene composition has a molecular weight distribution Mw/Mn, of from 2 to 7; a density of at least 0.950 g/cm3; a high load melt index I21, of from 150 to 400 g/10 min; a Z-average molecular weight MZ, of less than about 300,000; a melt flow ratio I21/I2, of from 22 to 50; a stress exponent of less than 1.40; and an ESCR Condition B (100% IGEPAL) of at least about 3.5 hrs.