Screw cap composition
A screw cap is disclosed comprising a composition based on a multimodal ethylene polymer having a standard density (SD) greater than 950 kg/m 3 and a melt flow index MI 2 of less than 10 g/10 min, said multimodal ethylene polymer comprising from 35 to 65 wt %, based on the total weight of the multimodal ethylene polymer, of a fraction of ethylene polymer (A) having an SD(A) of more than 965 kg/m 3 and a melt flow index MI 2 (A) of at least 10 g/10 min, and from 65 to 35 wt % based on the total weight of the multimodal ethylene polymer, of a fraction of a copolymer (B) of ethylene and at least one alpha-olefin containing from 3 to 12 carbon atoms, and having a melt flow index MI 2 (B) of less than 10 g/10 min and a content of said alphaolefin(s) of from 0.1 to 5 mol %. This composition is said to demonstrate an excellent balance between ESCR, injectability and impact resistance, together with excellent organoleptic properties.
1 . Screw cap comprising a composition based on a multimodal ethylene polymer having a standard density (SD) greater than 950 kg/m 3 and a melt flow index MI 2 of less than 2 g/10 min, wherein said multimodal ethylene polymer includes from 45 to 55 wt %, based on the total weight of the multimodal ethylene polymer, of a fraction of ethylene polymer (A) having an SD(A) of more than 965 kg/m 3 and a melt flow index MI 2 (A) of at least 10 g/10 min, and
from 55 to 45wt % based on the total weight of the multimodal ethylene polymer, of a fraction of a copolymer (B) of ethylene and at least one alpha-olefin containing from 3 to 12 carbon atoms, and having a melt flow index MI 2 (B) of less than 10 g/10 min and a content of said at least one alpha-olefin of from 0.1 to 5 mol %.
2 . Screw cap according to claim 1 , wherein the multimodal ethylene polymer has a melt flow index MI 2 of 0.5 to 1.8 g/10 min.
3 . Screw cap according to claim 1 or 2 , wherein the multimodal ethylene polymer has an SD of no more than 960 kg/m 3 .
4 . Screw cap according to claim 1 , wherein MI 2 (B) is less than 0.8 g/10 min.
5 . Screw cap according to claim 4 , wherein MI 2 (B) is less than 0.5 g/10 min.
6 . Screw cap according to claim 1 , wherein MI 2 (A) is at least 80 g/10 min.
7 . Screw cap according to any preceding claim 1 , wherein SD(A) is at least 969 kg/m 3 .
8 . Screw cap according to claim 1 , wherein said multimodal ethylene polymer includes from 48 to 52 wt % of ethylene polymer (A) and from 48 to 52 wt % of copolymer (B).
9 . Screw cap according to claim 1 , wherein copolymer (B) contains monomer units derived from ethylene and butene-1.
10 . Screw cap according to any preceding claim 1 , wherein the multimodal ethylene polymer is obtained by polymerization in at least two reactors connected in series.
11 . Screw cap comprising a composition based on a multimodal ethylene polymer and having an ESCR(B) greater than 800 hours, a notched Charpy impact resistance greater than 7 kJ/m 2 , and an injectability greater than 2.8 s.
12 . Screw cap according to claim 11 , wherein the composition has a standard density greater than 950 kg/m 3 .
13 . Screw cap according to claim 11 or 12 , wherein the composition has a melt flow index MI 2 of less than 10 g/10 min.
14 . Screw cap according to claim 11 , wherein the composition is based on a multimodal ethylene polymer having a standard density (SD) greater than 950 kg/m 3 and a melt flow index MI 2 of less than 2 g/10 min. said multimodal ethylene polymer including from 45 to 55 wt %. based on a total weight of the multimodal ethylene polymer. of a fraction of ethylene polymer (A) having an SD(A) of more than 965 ka/m 3 and a melt flow index MI 2 (A) of at least 10 g/10 min, and
from 55 to 45 wt % based on the total weight of the multimodal ethylene polymer, of a fraction of a copolymer (B) of ethylene and at least one alpha-olefin containing from 3 to 12 carbon atoms, and having a melt flow index MI 2 (B) of less than 10 g/10 min and a content of said at least one alpha-olefin of from 0.1 to 5 mol %.
15 . (Cancelled).
16 . Screw cap according to claim 3 wherein the SD is 951-958 kg/m 3 .