Metallocene catalyst system for producing LLDPE copolymers with tear resistance and low haze
Ethylene polymers having a density from 0.908 to 0.925 g/cm 3 , a melt index from 0.5 to 3 g/10 min, a ratio of Mw/Mn from 2 to 4, a ratio of Mz/Mw from 1.6 to 2.3, a CY-a parameter from 0.45 to 0.6, and an ATREF profile characterized by a single peak at a peak ATREF temperature from 76 to 88° C., and by less than 4.5 wt. % of the polymer eluting above a temperature of 91° C. These ethylene polymers can be used to produce various articles of manufacture, such as blown and cast films with a beneficial combination of high tear resistance and low haze.
1. A film comprising an ethylene polymer, wherein the film has:
a haze in a range from about 2 to about 10%; and
a MD Elmendorf tear strength in a range from about 200 to about 500 g/mil; and wherein the ethylene polymer has:
a density in a range from about 0.908 to about 0.925 g/cm 3 ;
a melt index in a range from about 0.5 to about 3 g/10 min;
a ratio of Mw/Mn in a range from about 2 to about 4;
a ratio of Mz/Mw in a range from about 1.6 to about 2.3;
a CY-a parameter in a range from about 0.45 to about 0.6; and
an ATREF profile characterized by a single peak at a peak ATREF temperature in a range from about 76 to about 90° C., by less than or equal to about 12 wt % of the ethylene polymer eluting above a temperature of 91° C., and by less than or equal to about 0.1 wt % of the ethylene polymer eluting above a temperature of 100° C.
2. The film of claim 1 , wherein:
the peak ATREF temperature is in a range from about 77 to about 89° C.;
less than or equal to about 11 wt % of the ethylene polymer elutes above a temperature of 91° C.; and
less than or equal to about 0.07 wt % of the ethylene polymer elutes above a temperature of 100° C.
3. The film of claim 1 , wherein:
the haze is in a range from about 2 to about 8%; and
the MD Elmendorf tear strength is in a range from about 250 to about 400 g/mil.
4. The film of claim 3 , wherein the film has:
a ratio of MD Elmendorf tear strength to TD Elmendorf tear strength (MD:TD) in a range from about 0.5:1 to about 0.9:1; and
a dart impact strength of greater than or equal to about 300 g/mil.
5. The film of claim 1 , wherein the ethylene polymer:
has a unimodal molecular weight distribution;
contains less than 0.1 ppm, independently, of hafnium and titanium; and
comprises an ethylene/1-butene copolymer, an ethylene/1-hexene copolymer, an ethylene/1-octene copolymer, or a combination thereof.
6. The film of claim 5 , wherein:
the haze is in a range from about 2 to about 7%; and
the MD Elmendorf tear strength is in a range from about 300 to about 400 g/mil.
7. A film comprising an ethylene polymer, wherein the film has:
a haze of less than or equal to about 8%; and
a MD Elmendorf tear strength in a range from about 250 to about 400 g/mil; and wherein the ethylene polymer has:
a density in a range from about 0.91 to about 0.925 g/cm 3 ;
a melt index in a range from about 0.5 to about 2.5 g/10 min;
a ratio of Mw/Mn in a range from about 2.2 to about 3.8;
a ratio of Mz/Mw in a range from about 1.7 to about 2.1;
a CY-a parameter in a range from about 0.52 to about 0.59; and
an ATREF profile characterized by a single peak at a peak ATREF temperature in a range from about 76 to about 88° C., and by less than or equal to about 4.5 wt % of the ethylene polymer eluting above a temperature of 91° C.
8. The film of claim 7 , wherein:
the density is in a range from about 0.91 to about 0.922 g/cm 3 ; and
the ethylene polymer comprises an ethylene/1-butene copolymer, an ethylene/1-hexene copolymer, an ethylene/1-octene copolymer, or a combination thereof.
9. The film of claim 8 , wherein:
the peak ATREF temperature is in a range from about 79 to about 86° C.; and
less than or equal to about 3.5 wt % of the ethylene polymer elutes above a temperature of 91° C.
10. The film of claim 7 , wherein:
the ethylene polymer has a unimodal molecular weight distribution;
the haze is in a range from about 2 to about 7%; and
the MD Elmendorf tear strength is in a range from about 300 to about 400 g/mil.
11. An ethylene polymer having:
a density in a range from about 0.91 to about 0.925 g/cm 3 ;
a melt index in a range from about 0.5 to about 2.5 g/10 min;
a ratio of Mw/Mn in a range from about 2.2 to about 3.8;
a ratio of Mz/Mw in a range from about 1.7 to about 2.1;
a CY-a parameter in a range from about 0.5 to about 0.6; and
an ATREF profile characterized by a single peak at a peak ATREF temperature in a range from about 76 to about 88° C., and by less than or equal to about 4.5 wt % of the ethylene polymer eluting above a temperature of 91° C.
12. The ethylene polymer of claim 11 , wherein:
less than or equal to about 3.5 wt % of the ethylene polymer elutes above a temperature of 91° C.;
the density is in a range from about 0.91 to about 0.922 g/cm 3 ; and
the ethylene polymer comprises an ethylene/1-butene copolymer, an ethylene/1-hexene copolymer, an ethylene/1-octene copolymer, or a combination thereof.
13. The ethylene polymer of claim 11 , wherein the ATREF profile is further characterized by from about 0.05 to about 5 wt % of the ethylene polymer eluting below a temperature of 40° C., from about 14 to about 45 wt % of the ethylene polymer eluting between 40 and 76° C., from about 35 to about 53 wt % of the ethylene polymer eluting between 76 and 86° C., and a remainder of the ethylene polymer eluting above a temperature of 86° C.
14. An article of manufacture comprising the ethylene polymer of claim 12 .
15. An ethylene polymer having:
a density in a range from about 0.91 to about 0.925 g/cm 3 ;
a melt index in a range from about 0.5 to about 2.5 g/10 min;
a ratio of Mw/Mn in a range from about 2.2 to about 3.8;
a ratio of Mz/Mw in a range from about 1.7 to about 2.1;
a CY-a parameter in a range from about 0.5 to about 0.6; and
an ATREF profile characterized by a single peak at a peak ATREF temperature in a range from about 76 to about 90° C., by less than or equal to about 12 wt % of the ethylene polymer eluting above a temperature of 91° C., and by less than or equal to about 0.1 wt % of the ethylene polymer eluting above a temperature of 100° C.
16. The polymer of claim 15 , wherein:
the peak ATREF temperature is in a range from about 77 to about 89° C.;
less than or equal to about 10 wt % of the ethylene polymer elutes above a temperature of 91° C.;
less than or equal to about 0.07 wt % of the ethylene polymer elutes above a temperature of 100° C.; and
the ethylene polymer comprises an ethylene/1-butene copolymer, an ethylene/1-hexene copolymer, an ethylene/1-octene copolymer, or a combination thereof.
17. An article of manufacture comprising the ethylene polymer of claim 16 .
18. A polymerization process comprising contacting a catalyst composition with ethylene and an alpha-olefin comonomer in a polymerization reactor system under polymerization conditions to produce an ethylene polymer; wherein:
the catalyst composition comprises an unbridged metallocene compound, an activator, and optionally, a co-catalyst; and
the ethylene polymer has:
a density in a range from about 0.908 to about 0.925 g/cm 3 ;
a melt index in a range from about 0.5 to about 3 g/10 min;
a ratio of Mw/Mn in a range from about 2 to about 4;
a ratio of Mz/Mw in a range from about 1.6 to about 2.3;
a CY-a parameter in a range from about 0.45 to about 0.6; and
an ATREF profile characterized by a single peak at a peak ATREF temperature in a range from about 76 to about 88° C., and by less than or equal to about 4.5 wt % of the ethylene polymer eluting above a temperature of 91° C.
19. The process of claim 18 , wherein:
the comonomer comprises 1-butene, 1-hexene, 1-octene, or a mixture thereof; and
the polymerization reactor system comprises a slurry reactor, a gas-phase reactor, a solution reactor, or a combination thereof.
20. The process of claim 19 , wherein the activator comprises an aluminoxane compound.
21. The process of claim 19 , wherein the activator comprises a fluorided solid oxide and/or a sulfated solid oxide.