High tear films from hafnocene catalyzed polyethylenes
A polyethylene film having a balance of improved physical and mechanical properties and a method for making the same are provided. In one aspect, the film includes a 1% secant modulus of greater than 25,000 psi, a dart impact resistance of greater than 500 g/mil, and a MD tear strength of greater than 500 g/mil. In one aspect, the method comprises reacting ethylene derived units and a comonomer in the presence of a hafnium-based metallocene at a temperature of from 70° C. and 90° C., an ethylene partial pressure of from 120 psia and 260 psia, and a comonomer to ethylene ratio of from 0.01 to 0.02 to produce an ethylene based polymer. The method further comprises extruding the ethylene based polymer at conditions sufficient to produce a polyethylene film comprising a secant modulus of greater than 25,000 psi, a dart impact resistance of greater than 500 g/mil, and a MD tear strength of greater than 500 g/mil.
1. A method for producing a polyethylene film, comprising:
reacting ethylene and a comonomer in the presence of a hafnium-based metallocene at a temperature of from 70° C. and 90° C., an ethylene partial pressure of from 120 psia and 260 psia, and a comonomer to ethylene ratio of from 0.01 to 0.02 to produce an ethylene based polymer; and
extruding the ethylene based polymer at conditions sufficient to produce a polyethylene film comprising a 1% secant modulus of greater than 25,000 psi, a dart impact resistance of greater than 500 g/mil, and a MD tear strength of greater than 500 g/mil.
2. The method of claim 1 , wherein extruding comprises blown film extrusion or cast film extrusion.
3. The method of claim 1 , wherein the comonomer consists essentially of 1-hexene.
4. The method of claim 1 , wherein the hafnium-based metallocene is represented by the following formula:
Cp A Cp B HfX 2
wherein each X is independently selected from the group consisting of fluorine, chlorine, iodine, bromine, and combinations thereof; and
Cp A and Cp B are independently selected from the from the group consisting of cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl, and a combination thereof.
5. The method of claim 1 , wherein the hafnium-based metallocene is represented by the following formula:
Cp A (A)Cp B HfX n
wherein each X is independently selected from the group consisting of fluorine, chlorine, iodine, bromine, and combinations thereof;
Cp A and Cp B are independently selected from the from the group consisting of cyclopentadienyl, indenyl, tetrahydroindenyl, fluorenyl, and a combination thereof;
A is a divalent hydrocarbon group comprising at least one atom selected from the group consisting of carbon, oxygen, nitrogen, silicon, aluminum, boron, germanium, tin and combinations thereof; and
n is an integer from 0 to 4.
6. The method of claim 1 , wherein the hafnium-based metallocene comprises two symmetrically substituted cyclopentadienyl groups and a dihalide bonded to a hafnium atom.
7. The method of claim 1 , wherein the hafnium-based metallocene is bis(propylcyclopentadienyl) hafnium dichloride.
8. The method of claim 1 , wherein the hafnium-based metallocene is bis(propylcyclopentadienyl) hafnium difluoride.
9. The method of claim 1 , wherein the temperature is from 75° C. to 80° C.
10. The method of claim 2 , wherein the ethylene partial pressure is from 220 psia to 260 psia.
11. The method of claim 3 , wherein the temperature is from 75° C. to 80° C. and the ethylene partial pressure is from 220 psia to 260 psia.
12. The method of claim 4 , wherein the polymer is a co-polymer consisting essentially of 1-hexene and ethylene derived units.
13. The method of claim 12 , wherein the polymer has a 1-hexene to ethylene molar ratio 0.0150 to 0.02.
14. The method of claim 1 , wherein the polymer has a Composition Distribution Breadth Index (CDBI) of from 20% to 50% and a Solubility Distribution Breadth Index (SDBI) of from 18° C. to 22° C.
15. The method of claim 1 , wherein the polymer has a Composition Distribution Breadth Index (CDBI) of from 20% to 35% and a Solubility Distribution Breadth Index (SDBI) of from 18.7° C. to 21.4° C.
16. The method of claim 1 , wherein the polymer has a ratio of Z-average molecular weight to weight average molecular weight of from 2.2 to 3.
17. The method of claim 1 , wherein the polymer has a ratio of Z-average molecular weight to weight average molecular weight of from 2.2 to 2.8.
18. The method of claim 1 , wherein the polymer has a ratio of Z-average molecular weight to weight average molecular weight of from 2.4 to 2.8.
19. The method of claim 1 , wherein the polymer has a Composition Distribution Breadth Index (CDBI) of from 20% to 50%, a Solubility Distribution Breadth Index (SDBI) of from 18° C. to 22° C., and a ratio of Z-average molecular weight to weight average molecular weight of from 2.2 to 3.