Metallocene-produced very low density polyethylenes

Details Metallocene-produced very low density polyethylenes Metallocene-produced very low density polyethylenes

2003-03-24

2004-10-05

Nutter, Nathan M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S216000, C525S232000, C525S240000

Reexamination Certificate

active

06800692

ABSTRACT:

1. FIELD OF THE INVENTION
The present invention relates generally to very low density polyolefins and films produced from very low density polyolefins. More specifically, the present invention is directed to very low density polyethylenes produced using metallocene catalysts, and cast extrusion films formed of metallocene-very low density polyethylenes having improved sealing and mechanical properties relative to conventional low density polyethylene films.
2. BACKGROUND
A variety of polymeric materials have been used successfully in thin cast films. A typical film casting process includes the steps of polymer extrusion, melt feeding through a slot die, melt draw-down in the air gap, chill-roll casting, edge-trim slitting, surface treating if necessary, and winding. The polyolefin film can be extruded onto a substrate of paper, metal foil, or other flexible substrate material to form an extrusion coated substrate. Extrusion of multiple layers of polymeric materials, including polyolefins as well as other materials, a process sometimes termed “coextrusion”, is also well known.
A variety of polymerization processes have been used to make polyolefins, including polyethylene and polypropylene, suitable for extrusion coating applications. Such processes include gas-phase polymerization, solution polymerization and bulk polymerization. More specifically, gas phase polymerization processes using Ziegler-Natta or vanadium-based catalyst systems have been used to make “low density polyethylenes” (“LDPEs”), i.e., polyethylenes having densities of from 0.916 to 0.928 g/cm
3
; “medium density polyethylenes” (“MDPEs”), i.e., polyethylenes having densities of from 0.929 to 0.940 g/cm
3
; and “high density polyethylenes” (“HDPEs”), i.e., polyethylenes having densities greater than 0.940.
The low density polyethylene extrusion coating market is dominated by conventional LDPE made in a high-pressure process. LDPE is generally preferred because it is easy to extrude, has high melt strength thereby minimizing neck-in, and has good sealing characteristics. Linear low density polyethylene (“LLDPE”) offers improved coating toughness, but its relatively narrow molecular weight distribution makes it more difficult to extrude, and it has relatively poor sealing properties; LLDPE makes up about 5% of the low density polyethylene extrusion market.
Although LDPE and LLDPE are widely used, these materials suffer from several disadvantages in extrusion coating applications. In applications requiring adhesion of a coating to polypropylene, LDPE and LLDPE offer relatively poor adhesion, thus necessitating the extra expense and complexity of an adhesive or tic layer. It would thus be desirable to have a polyethylene-based extrusion coating material capable of improved adhesion to polypropylene substrates. In addition, it would be desirable to have an extrusion coating material offering improved mechanical properties and improved sealing performance. Further, it would be desirable to have an extrusion coating material capable of being formed in thinner layer than is conventionally possible with LDPE and LLDPE. Still farther, it would be desirable to have an extrusion coating material providing better organoleptic properties than LLDPE.
U.S. Pat. No. 5,382,631 discloses linear interpolymer blends made from components having narrow molecular weight distribution (e.g. Mw/Mn≦3) and a narrow composition distribution (e.g. CDBI>50%/). The blends have either Mw/Mn>3 and/or CDBI<50%, and combinations of each, and can be bimodal with respect to either or both molecular weight and/or comonomer content. The blends are generally free of blend components having both a higher average molecular weight and a lower average comonomer content than another blend component.
3. SUMMARY OF THE INVENTION
In one embodiment, the present invention is directed to a polymer blend, the blend including a very low density polyethylene (VLDPE) polymer having a density of less than 0.916 g/cm
3
, and a low density polyethylene (LDPE) polymer, having a density of from 0.916 to 0.940 g/cm
3
. Preferably the VLDPE and LDPE polymers are metallocene-catalyzed polymers.
In another embodiment, the present invention provides a polymer blend suitable for use as a film or a coating, the polymer blend including from 1 to 99% by weight of a metallocene-produced VLDPE polymer having a density less than 0.916 g/cm
3
, and from 1 to 99% by weight of an LDPE polymer having a density of from 0.916 to 0.928 g/cm
3
wherein the sum of VLDPE and the LDPF is 100%. Alternatively, the blend can have from 5 to 95%, from 10 to 90%, or from 15 to 85% by weight of the LDPE polymer. The VLDPE polymer can have a melt index of from 6 to 15 dg/min, or from 9 to 12 dg/min. The VLDPE polymer can be an ethylene homopolymer, or a copolymer of ethylene and a C
3
to C
12
alpha-olefin. The LDPE polymer can have a melt index of from 0.5 to 15 dg/min, or from 1 to 10 dg/min. The LDPE polymer can be an ethylene homopolymer, or a copolymer of ethylene and a C
3
to C
12
alpha-olefin.
In another embodiment, the present invention is directed to a polymer blend, the blend including a gas-phase metallocene-produced VLDPE polymer, the VLDPE polymer being a copolymer of ethylene and at least one C
3
to C
12
alpha olefin and having a density of from 0.900 to 0.915 g/cm
3
and a melt index of from 5 to 20 g/10 min; and a metallocene-produced LDPE polymer, the LDPE polymer being a copolymer of ethylene and at least one C
3
to C
12
alpha olefin and having a density of from 0.916 to 0.940 g/cm
3
and a melt index of from 0.5 to 15 g/10 min. In this embodiment, the blend includes 5-95% by weight of the VLDPE polymer and 95-5% by weight of the LDPE polymer, based on the total weight of the VLDPE and LDPE polymers.
In another embodiment, the present invention is directed to a polymer blend, the blend including a gas-phase metallocene-produced VLDPE polymer, the VLDPE polymer being a copolymer of ethylene and 1-butene, 1-hexene or 1-octene and having a density of from 0.910 to 0.915 g/cm
3
, a melt index of from 5 to 20 g/10 min, a composition distribution breadth index (CDBI) of 60 to 80 wt % and a molecular weight distribution (MWD) of 2.2 to 2.8; and a metallocene-produced LDPE polymer, the LDPE polymer being a copolymer of ethylene and 1-butene, 1-hexene or 1-octene and having a density of from 0.916 to 0.925 g/Cm
3
and a melt index of from 0.5 to 10 g/10 min. In this embodiment, the blend preferably includes 10-90% by weight of the VLDPE polymer and 90-10% by weight of the LDPE polymer, based on the total weight of the VLDPE and LDPE polymers.
In one embodiment, the present invention is directed to a VLDPE/LDPE polymer blend, the blend including a metallocene-produced VLDPE polymer comprising an ethylene copolymer with a comonomer content of 25% or less by weight, preferably 20% or less by weight, and more preferably 15% or less by weight.
In another embodiment, the present invention is directed to a polymer blend, the blend including from 1 to 99% by weight of a copolymer derived from ethylene and one or more C
3
-C
20
alpha olefin comonomers, and from 1 to 99% by weight of a low density polyethylene polymer having a density of from 0.916 to 0.928 g/cm
3
, wherein the sum of the weight of the copolymer and low density polyethylene polymer is 100%. The copolymer is further characterized by properties including one or more of the following: a comonomer content of from 5 to 15 wt. %, a density of less than 0.916 g/cm
3
, a composition distribution breadth index in the range of from 55% to 70%, a molecular weight distribution Mw/Mn of from 2 to 3, and a molecular weight distribution Mz/Mw of less than 2.
In another embodiment, the present invention is directed to an article, the article including a substrate and a film disposed on the substrate. The film includes a polymer blend, the polymer blend including from 1 to 99% by weight of a copolymer derived from ethylene and one or more C
3
-C
20
alpha olefin comonomers, and from 1 to 99% by weight of a low density polyethylene

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