Polyethylene composition and film having high stiffness, outstanding sealability and high permeability
A polyethylene composition includes a first polyethylene which is an ethylene copolymer having a weight average molecular weight of from 70,000 to 250,000 and a molecular weight distribution M w /M n of <2.3, a second polyethylene which is an ethylene copolymer or homopolymer having a weight average molecular weight of from 15,000 to 100,000, a molecular weight distribution M w /M n of >2.3, and a third polyethylene which is an ethylene copolymer or homopolymer having a weight average molecular weight of from 70,000 to 250,000 and a molecular weight distribution M w /M n of >2.3, where the first polyethylene has more short chain branching than the second polyethylene or the third polyethylene. The polyethylene composition has a soluble fraction in a CEF analysis of at least 10 weight percent. Film made from the polyethylene composition may have a machine direction 1% secant modulus of 200 ≥MPa (at a film thickness of about 1 mil), a seal initiation temperature (SIT) of ≤90° C. (at a film thickness of about 2 mil), an area of hot tack window (AHTW) of ≥160 Newtons·C° (at a film thickness of about 2 mil) and an oxygen transmission rate (OTR) of ≥600 cm 3 per 100 inch per day (at a film thickness of about 1 mil).
1. A polyethylene composition comprising:
from 5 to 80 wt. % of a first polyethylene which is an ethylene copolymer, the first polyethylene having a weight average molecular weight Mw of from 70,000 to 250,000, a molecular weight distribution M w /M n of <2.3 and from 5 to 100 short chain branches per thousand carbon atoms;
from 5 to 80 wt. % of a second polyethylene which is an ethylene copolymer or an ethylene homopolymer, the second polyethylene having a weight average molecular weight, Mw of from 15,000 to 100,000, a molecular weight distribution M w /M n of >2.3 and from 0 to 20 short chain branches per thousand carbon atoms; and
from 5 to 80 wt. % of a third polyethylene which is an ethylene copolymer or an ethylene homopolymer, the third polyethylene having a weight average molecular weight Mw of from 70,000 to 250,000, a molecular weight distribution M w /M n of >2.3 and from 0 to 35 short chain branches per thousand carbon atoms; wherein,
the number of short chain branches per thousand carbon atoms in the first polyethylene (SCB PE-1 ) is greater than the number of short chain branches per thousand carbon atoms in the second polyethylene (SCB PE-2 ) and the third polyethylene (SCB PE-3 );
the number of short chain branches per thousand carbon atoms in the third polyethylene (SCB PE-3 ) is greater than the number of short chain branches per thousand carbon atoms in the second polyethylene (SCB PE-2 ); and
the weight average molecular weight of the second polyethylene is less than the weight average molecular weight of the first polyethylene and the third polyethylene; wherein,
the polyethylene composition has a density of ≤0.939 g/cm 3 , a melt index I 2 , determined at 190° C., of from 0.1 to 10 dg/min, and has a soluble fraction in a crystallization elution fractionation (CEF) analysis of at least 10 weight percent.
2. The polyethylene composition of claim 1 wherein the polyethylene composition has a unimodal profile in a gel permeation chromatograph (GPC).
3. The polyethylene composition of claim 1 wherein the polyethylene composition has a soluble fraction in a crystallization elution fractionation (CEF) analysis of at least 15 weight percent.
4. The polyethylene composition of claim 1 wherein the polyethylene composition has a melting peak temperature in a differential scanning calorimetry (DSC) analysis at above 125° C.
5. The polyethylene composition of claim 1 wherein the polyethylene composition has two melting peaks in a differential scanning calorimetry (DSC) analysis.
6. The polyethylene composition of claim 1 wherein the first polyethylene has from 30 to 75 short chain branches per thousand carbon atoms.
7. The polyethylene composition of claim 1 wherein the second polyethylene is an ethylene homopolymer.
8. The polyethylene composition of claim 1 wherein the third polyethylene is an ethylene copolymer and has from 5 to 30 short chain branches per thousand carbon atoms.
9. The polyethylene composition of claim 1 wherein the first polyethylene has a weight average molecular weight, Mw of from 75,000 to 175,000.
10. The polyethylene composition of claim 1 wherein the second polyethylene has a weight average molecular weight, Mw of from 25,000 to 80,000.
11. The polyethylene composition of claim 1 wherein the third polyethylene has a weight average molecular weight, Mw of from 80,000 to 200,000.
12. The polyethylene composition of claim 1 wherein the first polyethylene has a density of from 0.860 to 0.916 g/cm 3 .
13. The polyethylene composition of claim 1 wherein the second polyethylene is an ethylene homopolymer having a density of from 0.940 to 0.980 g/cm 3 .
14. The polyethylene composition of claim 1 wherein the third polyethylene is an ethylene copolymer having a density of from 0.880 to 0.936 g/cm 3 .
15. The polyethylene composition of claim 1 wherein the first polyethylene is present in from 5 to 60 wt. %.
16. The polyethylene composition of claim 1 wherein the second polyethylene is present in from 5 to 60 wt. %.
17. The polyethylene composition of claim 1 wherein the first polyethylene is present in from 15 to 60 wt. %.
18. The polyethylene composition of claim 1 wherein the second polyethylene is present in from 10 to 50 wt. %.
19. The polyethylene composition of claim 1 wherein the third polyethylene is present in from 10 to 50 wt. %.
20. The polyethylene composition of claim 1 wherein the first polyethylene is present in from 25 to 50 wt. %.
21. The polyethylene composition of claim 1 wherein the second polyethylene is present in from 20 to 40 wt. %.
22. The polyethylene composition of claim 1 wherein the third polyethylene is present in from 20 to 40 wt. %.
23. The polyethylene composition of claim 1 wherein the first polyethylene has a CDBI 50 of at least 75 wt. %.
24. The polyethylene composition of claim 1 wherein the third polyethylene is a copolymer with a CDBI 50 of less than 75 wt. %.
25. The polyethylene composition of claim 1 wherein the first polyethylene is a homogeneously branched ethylene copolymer.
26. The polyethylene composition of claim 1 wherein the third polyethylene is a heterogeneously branched ethylene copolymer.
27. The polyethylene composition of claim 1 wherein the first polyethylene is a made with a single site catalyst.
28. The polyethylene composition of claim 1 wherein the second polyethylene is made with a Ziegler-Natta catalyst.
29. The polyethylene composition of claim 1 wherein the third polyethylene is made with a Ziegler-Natta catalyst.
30. The polyethylene composition of claim 1 wherein the polyethylene composition has a molecular weight distribution M w /M n of from 2.3 to 6.0.
31. The polyethylene composition of claim 1 wherein the polyethylene composition has a molecular weight distribution M w /M n of from 2.3 to 4.5.
32. The polyethylene composition of claim 1 wherein the polyethylene composition has a density of <0.935 g/cm 3 .
33. The polyethylene composition of claim 1 wherein the polyethylene composition has a density of from 0.880 to 0.932 g/cm 3 .
34. The polyethylene composition of claim 1 wherein the polyethylene composition has a melt index, I 2 of from 0.1 to 3.0 dg/min.
35. The polyethylene composition of claim 1 wherein the polyethylene composition has a Mz/M w of less than 3.0.
36. The polyethylene composition of claim 1 wherein the polyethylene composition has a melt index ratio, I 21 /I 2 of from 15 to 50.
37. The polyethylene composition of claim 1 wherein the polyethylene composition has a hexane extractable value of ≤5.5 weight percent.
38. A film layer having a thickness of from 0.5 to 10 mil, comprising the polyethylene composition of claim 1 .
39. The film layer of claim 38 wherein the film layer has a machine direction (MD) 1% secant modulus of ≥200 MPa when measured at a film thickness of about 1 mil.
40. The film layer of claim 38 wherein the film layer has a seal initiation temperature (SIT) of ≤90° C. when measured at a film thickness of about 2 mil.
41. The film layer of claim 38 wherein the film layer has an area of hot tack window (AHTW) of ≥160 Newtons·° C. when measured at a film thickness of about 2 mil.
42. The film layer of claim 38 wherein the film layer has an oxygen transmission rate (OTR) of ≥600 cm 3 per 100 inch 2 per day when measured at a film thickness of about 1 mil.
43. The film layer of claim 38 wherein the film layer has a machine direction (MD) 1% secant modulus of ≥200 MPa when measured at a film thickness of about 1 mil, a seal initiation temperature (SIT) of ≤90° C. when measured at a film thickness of about 2 mil, an area of hot tack window (AHTW) of ≥160 Newtons·° C. when measured at a film thickness of about 2 mil, and an oxygen transmission rate (OTR) of ≥600 cm 3 per 100 inch 2 per day when measured at a film thickness 1 mil.
44. The polyethylene composition of claim 1 , which when made into a film having a thickness of about 1 mil, and when made into a film having a thickness of about 2 mil, satisfies the following relationship:
area of hot tack window (AHTW in Newtons·° C.)>−2.0981 (machine direction (MD) 1% secant modulus in MPa)+564.28;
wherein the AHTW is measured on the film having a thickness of about 2 mil, and the machine direction (MD) 1% secant modulus is measured at a on the film having a thickness of about 1 mil.
45. The polyethylene composition of claim 1 , which when made into a film having a thickness of about 1 mil, satisfies the following relationship:
oxygen transmission rate (OTR in cm 3 per 100 inch per day)>−5.4297 (machine direction (MD) 1% secant modulus in MPa)+1767.8;
wherein the OTR and the machine direction (MD) 1% secant modulus is are measured at ft on the film having a thickness of about 1 mil.
46. The polyethylene composition of claim 1 , which when made into a film having a thickness of about 1 mil, and when made into a film having a thickness of about 2 mil, satisfies the following relationship:
seal initiation temperature (SIT in ° C.)<0.366 (machine direction (MD) 1% secant modulus in MPa)+22.509;
wherein the SIT is measured on the film having a thickness of about 2 mil, and the machine direction (MD) 1% secant modulus is measured at a on the film having a thickness of about 1 mil.
47. The polyethylene composition of claim 1 , which when made into a film having a thickness of about 1 mil, and when made into a film having a thickness of about 2 mil, satisfies the following relationships:
i) area of hot tack window (AHTW in Newtons·° C.)>−2.0981 (machine direction (MD) 1% secant modulus in MPa)+564.28;
ii) oxygen transmission rate (OTR in cm 3 per 100 inch 2 per day)>−5.4297 (machine direction (MD) 1% secant modulus in MPa)+1767.8; and
iii) seal initiation temperature (SIT in ° C.)<0.366 (machine direction (MD) 1% secant modulus in MPa)+22.509;
wherein the AHTW and the SIT are measured on the film having a thickness of about 2 mil, and wherein the machine direction (MD) 1% secant modulus and the OTR are measured on the film having a film thickness of about 1 mil.