Polymer composition for caps and closures
Polyethylene composition having a density of 950-960 kg/m 3 , a SHI (1,100) of 4-12, a melt index MI 2 between 0.2 and 2 g/10 min, and a relationship between spiral flow ‘SF’ (measured in mm at 250° C./1000 bar/100 mm/s) and ESCR ‘E’ (measured in hours) of E>200−SF. The composition contains 48-62 wt % of an ethylene polymer (A) and 38-52 wt % of an ethylene copolymer (B). Copolymer (B) has a higher weight average molecular weight than polymer (A), and both of fractions (A) and (B) have a reverse comonomer distribution such that comonomer content increases with increasing molecular weight in the individual fraction.
1. Polyethylene composition having a density of 950-960 kg/m 3 , a SHI (1,100) of 4-12, a melt index MI 2 between 0.2 and 2 g/10 min, and a relationship between spiral flow ‘SF’ (measured in mm at 250° C./1000 bar/100 mm/s) and ESCR ‘E’ (measured in hours) of E>200−SF, wherein the composition comprises 48-62 wt % of an ethylene polymer (A) and 38-52 wt % of an ethylene copolymer (B), copolymer (B) having a higher weight average molecular weight than copolymer (A), and both of fractions (A) and (B) have a reverse comonomer distribution such that comonomer content increases with increasing molecular weight in the individual fraction.
2. Composition according to claim 1 , wherein the relationship between spiral flow ‘SF’ (measured in mm at 250° C./1000 bar/100 mm/s) and ESCR ‘E’ (measured in hours) is E>370−2SF.
3. Polyethylene composition having a density of 950-960 kg/m 3 , of SHI (1,100) of 4-12, a melt index MI2 between 0.2 and 2 g/10 min, and a relationship between spiral flow ‘SF’ (measured in mm at 250° C./1000 bar/100 mm/s), ESCR ‘E’ (measured in hours) and melt index ‘MI2’ (measured in g/10 min according to ISO 1133 at 190° C. at load of 2.16 kg) of E>(9800−36SF−1000MI2)/60.
4. Composition according to claim 3 , wherein the relationship between spiral flow ‘SF’, ESCR ‘E’ and melt index ‘MI2’ is E>(11000−36SF−1000MI2)/60.
5. Composition according to claim 1 , which has a SHI (1,100) between 4 and 10.
6. Composition according to claim 1 , which has a molecular weight distribution (Mw/Mn) (measured by GPC analysis) between 5 and 13.
7. Composition according to claim 1 , which has a relationship between spiral flow ‘SF’ (measured in mm at 250° C./1000 bars/100 mm/s) and solubles ‘S’ (measured in g/kg) of S<0.1SF.
8. Composition according to claim 1 , which comprises 50-60 wt % of ethylene polymer (A) and 40-50 wt % of ethylene copolymer (B).
9. Composition according to claim 1 , wherein ethylene polymer (A) is a copolymer, and has a density between 969 and 974 kg/m3 and a MI2 of from 10 to 800 g/10 min.
10. Composition according to claim 1 , which has a density between 950 to 954 kg/m3 and an MI2 of between 1 and 2 g/10 min.
11. Composition according to claim 1 , which has a density between 954 to 960 kg/m3 and an MI2 of between 0.1 and 1 g/10 min.
12. Composition according to claim 1 , which has a density between 950 to 954 kg/m3 and an MI2 of between 1 and 2 g/10 min, wherein the density of copolymer (B) is between 919 and 936 kg/m3 and the HLMI of copolymer (B) is from 3 to 6 g/10 min.
13. Composition according to claim 1 , which has a density between 954 to 960 kg/m3 and an MI2 of between 0.1 and 1 g/10 min, wherein the density of copolymer (B) is between 929 and 947 kg/m3 the HLMI of the copolymer (B) is from 0.2 to 2 g/10 min.
14. Composition according to claim 3 , which has a SHI (1,100) between 4 and 10.
15. Composition according to claim 3 , which has a molecular weight distribution (Mw/Mn) (measured by GPC analysis) between 5 and 13.
16. Composition according to claim 3 , which has a relationship between spiral flow ‘SF’ (measured in mm at 250° C./1000 bars/100 mm/s) and solubles ‘S’ (measured in g/kg) of S<0.1SF.
17. Composition according to claim 3 , which comprises 48-62 wt % of an ethylene polymer (A) and 38-52 wt % of an ethylene copolymer (B), copolymer (B) having a higher weight average molecular weight Mw than polymer (A).
18. Composition according to claim 3 , wherein ethylene polymer (A) is a copolymer, and has a density between 969 and 974 kg/m3 and a MI2 of from 10 to 800 g/10 min.
19. Composition according to claim 3 , which has a density between 950 to 954 kg/m3 and an MI2 of between 1 and 2 g/10 min.
20. Composition according to claim 3 , which has a density between 954 to 960 kg/m3 and an MI2 of between 0.1 and 1 g/10 min.
21. Composition according to claim 3 , which has a density between 950 to 954 kg/m3 and an MI2 of between 1 and 2 g/10 min, wherein the density of copolymer (B) is between 919 and 936 kg/m3 and the HLMI of copolymer (B) is from 3 to 6 g/10 min.
22. Composition according to claim 3 , which has a density between 954 to 960 kg/m3 and an MI2 of between 0.1 and 1 g/10 min, wherein the density of copolymer (B) is between 929 and 947 kg/m3 the HLMI of the copolymer (B) is from 0.2 to 2 g/10 min.
23. Composition according to claim 2 , wherein the relationship between spiral flow ‘SF’ (measured in mm at 250° C./1000 bar/100 mm/s) and ESCR ‘E’ (measured in hours) is E>540−3SF.
24. Composition according to claim 4 , wherein the relationship between spiral flow ‘SF’, ESCR ‘E’ and melt index ‘MI2’ is E>(12000−36SF−1000MI2)/60.
25. Composition according to claim 5 , which has a SHI (1,100) between 4 and 8.
26. Composition according to claim 7 , which has a relationship between spiral flow ‘SF’ (measured in mm at 250° C./1000 bars/100 mm/s) and solubles ‘S’ (measured in g/kg) of S<0.1SF−2.5.
27. Composition according to claim 26 , which has a relationship between spiral flow ‘SF’ (measured in mm at 250° C./1000 bars/100 mm/s) and solubles ‘S’ (measured in g/kg) of S<0.1SF−5.