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Very low density polyethylene blendsRelated Patent Categories: Synthetic Resins Or Natural Rubbers -- Part Of The Class 520 Series, Natural Rubber Compositions Having Nonreactive Materials (dnrm) Other Than: Carbon, Silicon Dioxide, Glass Titanium Dioxide, Water, Hydrocarbon, Halohydrocarbon, Ethylenically Unsaturated Reactant Admixed With A Preformed Reaction Product Derived From: (a) At Least One Polycarboxylic Acid, Ester, Or Anhydride; (b) At Least One Polyhydroxy Compound; And (c) At Least One Fatty Acid Glycerol Ester, Or A Fatty Acid Or Salt Derived From A Naturally Occurring Glyceride, Tall Oil, Or A Tall Oil Fatty Acid, At Least One Solid Polymer Derived From Ethylenic Reactants Only, Polymer Mixture Of Two Or More Solid Polymers Derived From Ethylenically Unsaturated Reactants Only; Or Mixtures Of Said Polymer Mixture With A Chemical Treating Agent; Or Products Or Processes Of Preparing Any Of The Above Mixtures, Solid Polymer Derived From Ethylene Or PropyleneVery low density polyethylene blends description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060276594, Very low density polyethylene blends. Brief Patent Description - Full Patent Description - Patent Application Claims
1. FIELD OF THE INVENTION [0001] The present invention relates generally to polyolefin blends and films produced from polyolefin blends. More specifically, the present invention is directed to blends of very low density polyethylene produced using metallocene catalysts and linear low density polyethylene, and films formed of such blends. 2. BACKGROUND [0002] Various types of polyethylenes are known in the art. Low density polyethylene ("LDPE") can be prepared at high pressure using free radical initiators, or in gas phase processes using Ziegler-Natta or vanadium catalysts, and typically has a density in the range of 0.916-0.940 g/cm.sup.3. LDPE is also known as "branched" or "heterogeneously branched" polyethylene because of the relatively large number of long chain branches extending from the main polymer backbone. Polyethylene in the same density range, i.e., 0.916 to 0.940 g/cm.sup.3, which is linear and does not contain long chain branching is also known; this "linear low density polyethylene" ("LLDPE") can be produced with conventional Ziegler-Natta catalysts or with metallocene catalysts. Relatively higher density LDPE, typically in the range of 0.928 to 0.940 g/cm.sup.3, is sometimes referred to as medium density polyethylene ("MDPE"). Polyethylenes having still greater density are the high density polyethylenes ("HDPEs"), i.e., polyethylenes having densities greater than 0.940 g/cm.sup.3, and are generally prepared with Ziegler-Natta catalysts. Very low density polyethylene ("VLDPE") is also known. VLDPEs can be produced by a number of different processes yielding polymers with different properties, but can be generally described as polyethylenes having a density less than 0.916 g/cm.sup.3, typically 0.890 to 0.915 g/cm.sup.3 or 0.900 to 0.915 g/cm.sup.3. [0003] U.S. Pat. Nos. 5,272,236 and 5,278,272 disclose polyethylenes termed "substantially linear ethylene polymers" ("SLEPs"). These SLEPs are characterized as having a polymer backbone substituted with about 0.01 long chain branches/1000 carbons to about 3 long chain branches/1000 carbons, more preferably from about 0.01 long chain branches/1000 carbons to about 1 long chain branches/1000 carbons, and especially from about 0.05 long chain branches/1000 carbons to about 1 long chain branches/1000 carbons. As used in U.S. Pat. Nos. 5,272,236 and 5,278,272, "long chain branching" is defined as a chain length of at least about 6 carbons, above which the length cannot be distinguished using .sup.13C NMR spectroscopy. It is further disclosed that the long chain branch can be as long as about the same length as the length of the polymer backbone. [0004] As used in the present disclosure, the term "linear" is applied to a polymer that has a linear backbone and does not have long chain branching; i.e., a "linear" polymer is one that does not have the long chain branches characteristic of a SLEP polymer. [0005] Blends of polyethylenes are also known. Blending has been used to form polymer compositions having altered properties, such as melt index and various processability characteristics. Blending has also been used to form polymer compositions having properties enhanced for particular end uses. For example, polymer blends have been used to form cast or extruded films with altered film properties, such as toughness, tear resistance, shrink properties, and other desired film characteristics. [0006] U.S. Pat. No. 5,972,444 discloses a polyolefin shrink film made from a polymer mixture which includes a first ethylene polymer component having a single differential scanning calorimetry (DSC) melting peak or a single Analytical Temperature Rising Elution Fractionation (ATREF) peak and a second ethylene polymer component having one or more DSC melting peaks, wherein the density differential between the two component polymers about 0 to about 0.03 g/cm.sup.3. Preferably, the first ethylene polymer component is a substantially linear ethylene polymer (SLEP) and the second component polymer is a heterogeneously branched linear ethylene polymer. Commonly assigned PCT publication WO 98/21276 discloses similar films. [0007] U.S. Pat. No. 5,707,751 discloses shrink film compositions comprising precise combinations of "narrow, substantially singular" melting point polyethylene with a higher melting point (by at least about 10.degree. C.) polyethylene. [0008] U.S. Pat. No. 5,382,631 discloses polymer blends and single or multilayer films made from the blends. The blends are made from components having a narrow molecular weight distribution (e.g., Mw/Mn 3) and a narrow composition distribution (e.g., CDBI>50%). The blend components of the blend can all have the same molecular weight but different comonomer contents, the same comonomer content but different molecular weights, or comonomer contents which increase with molecular weight. 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. [0009] U.S. Pat. Nos. 5,907,943 and 5,922,441 disclose a thermoplastic stretch wrap film containing at least three layers, the inner layer of which comprises a blend of a "low dispersity polymer" and either a high pressure low density polyethylene resin, a very low density polyethylene resin or a combination thereof. The low dispersity polymer has a density of from about 0.88 to 0.94 g/cm.sup.3. 3. SUMMARY [0010] 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.sup.3, and a linear low density polyethylene (LLDPE) polymer, having a density of from 0.916 to 0.940 g/cm.sup.3. Preferably the VLDPE and LLDPE polymers are metallocene-catalyzed polymers. [0011] In another embodiment, the present invention is directed to a polymer blend, the blend including a metallocene-produced VLDPE polymer, preferably a gas-phase metallocene-produced VLDPE polymer, the VLDPE polymer being a copolymer of ethylene and at least one C.sub.3 to C.sub.12 alpha olefin and having a density of from 0.900 to 0.915 g/cm.sup.3 and a melt index of from 0.5 to 20 g/10 min; and a metallocene-produced LLDPE polymer, the LLDPE polymer being a copolymer of ethylene and at least one C.sub.3 to C.sub.12 alpha olefin and having a density of from 0.916 to 0.940 g/cm.sup.3 and a melt index of from 0.5 to 20 g/10 min. The blend can include, for example, 5-85% by weight of the VLDPE polymer and 95-15% by weight of the LLDPE polymer, based on the total weight of the VLDPE and LLDPE polymers. [0012] 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, 4-methyl-1-pentene, or 1-octene and having a density of from 0.910 to 0.915 g/cm.sup.3, a melt index of from 0.5 to 20 g/10 min, a composition distribution breadth index of 60 to 80 wt %, and a molecular weight distribution (Mw/Mn) of 2.2 to 2.8; and a metallocene-produced LLDPE polymer, the LLDPE polymer being a copolymer of ethylene and 1-butene, 1-hexene, 4-methyl-1-pentene or 1-octene and having a density of from 0.916 to 0.925 g/cm.sup.3 and a melt index of from 0.5 to 20 g/10 min. In this embodiment, the blend preferably includes 10-50% by weight of the VLDPE polymer and 90-50% by weight of the LLDPE polymer, based on the total weight of the VLDPE and LLDPE polymers. [0013] In one embodiment, the present invention is directed to a VLDPE/LLDPE 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. [0014] In another embodiment, the present invention is directed to monolayer films formed from the polymer blends of the invention. [0015] In another embodiment, the present invention is directed to multilayer films, wherein at least one layer of the multilayer film is formed of a polymer blend of the invention. [0016] In other embodiments, the invention is directed to articles including the films of the invention, articles wrapped with the films of the invention, and substrates coated with the films of the invention. 4. DETAILED DESCRIPTION [0017] 4.1 The VLDPE Component [0018] The polymer blends and films of the present invention include a very low density polyethylene (VLDPE) polymer. As used herein, the terms "very low density polyethylene" polymer and "VLDPE" polymer refer to a polyethylene copolymer having a density of less than 0.916 g/cm.sup.3. Polymers having more than two types of monomers, such as terpolymers, are also included within the term "copolymer" as used herein. The comonomers that are useful in general for making VLDPE copolymers include .alpha.-olefins, such as C.sub.3-C.sub.20 .alpha.-olefins and preferably C.sub.3-C.sub.12 .alpha.-olefins. The .alpha.-olefin comonomer can be linear or branched, and two or more comonomers can be used, if desired. Examples of suitable comonomers include linear C.sub.3-C.sub.12 .alpha.-olefins, and .alpha.-olefins having one or more C.sub.1-C.sub.3 alkyl branches, or an aryl group. Specific examples include propylene; 1-butene, 3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-pentene with one or more methyl, ethyl or propyl substituents; 1-hexene with one or more methyl, ethyl or propyl substituents; 1-heptene with one or more methyl, ethyl or propyl substituents; 1-octene with one or more methyl, ethyl or propyl substituents; 1-nonene with one or more methyl, ethyl or propyl substituents; ethyl, methyl or dimethyl-substituted 1-decene; 1-dodecene; and styrene. It should be appreciated that the list of comonomers above is merely exemplary, and is not intended to be limiting. Preferred comonomers include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene and styrene, more preferably 1-butene, 1-hexene, and 1-octene. [0019] Although not generally preferred, other useful comonomers include polar vinyl, conjugated and non-conjugated dienes, acetylene and aldehyde monomers, which can be included in minor amounts in terpolymer compositions. Non-conjugated dienes useful as co-monomers preferably are straight chain, hydrocarbon di-olefins or cycloalkenyl-substituted alkenes, having 6 to 15 carbon atoms. Suitable non-conjugated dienes include, for example: (a) straight chain acyclic dienes, such as 1,4-hexadiene and 1,6-octadiene; (b) branched chain acyclic dienes, such as 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; and 3,7-dimethyl-1,7-octadiene; (c) single ring alicyclic dienes, such as 1,4-cyclohexadiene; 1,5-cyclo-octadiene and 1,7-cyclododecadiene; (d) multi-ring alicyclic fused and bridged ring dienes, such as tetrahydroindene; norbornadiene; methyl-tetrahydroindene; dicyclopentadiene (DCPD); bicyclo-(2.2.1)-hepta-2,5-diene; alkenyl, alkylidene, cycloalkenyl and cycloalkylidene norbornenes, such as 5-methylene-2-norbornene (MNB), 5-propenyl-2-norbornene, 5-isopropylidene-2-norbornene, 5-(4-cyclopentenyl)-2-norbornene, 5-cyclohexylidene-2-norbornene, and 5-vinyl-2-norbornene (VNB); and (e) cycloalkenyl-substituted alkenes, such as vinyl cyclohexene, allyl cyclohexene, vinyl cyclooctene, 4-vinyl cyclohexene, allyl cyclodecene, and vinyl cyclododecene. Of the non-conjugated dienes typically used, the preferred dienes are dicyclopentadiene, 1,4-hexadiene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, and tetracyclo-(.DELTA.-11,12)-5,8-dodecene. Particularly preferred diolefins are 5-ethylidene-2-norbornene (ENB), 1,4-hexadiene, dicyclopentadiene (DCPD), norbornadiene, and 5-vinyl-2-norbornene (VNB). Note that throughout this description the terms "non-conjugated diene" and "diene" are used interchangeably. [0020] It should be appreciated that the amount of comonomer used will depend upon the desired density of the VLDPE polymer and the specific comonomers selected. For one embodiment of the VLDPE polymer comprising an ethylene/butene copolymer, the molar ratio of butene to ethylene should be from about 0.015 to 0.035, preferably from 0.020 to 0.030. For one embodiment of the VLDPE polymer comprising an ethylene/hexene copolymer, the molar ratio of hexene to ethylene should be from about 0.015 to 0.035, preferably from 0.020 to 0.030. For one embodiment of the VLDPE polymer comprising an ethylene/octene copolymer, the molar ratio of octene to ethylene should be from about 0.015 to 0.035, preferably from 0.020 to 0.030. In general, the comonomer may be present in an amount of 25% or less by weight, preferably 20% or less by weight and more preferably 15% or less by weight. In one embodiment, the comonomer may be present in an amount of 5% or more by weight. It is well-understood in the art that, for a given comonomer, the density of the VLDPE polymer produced therefrom decreases as the comonomer content increases. One skilled in the art can readily determine the appropriate comonomer content appropriate to produce a VLDPE polymer having a desired density. Continue reading about Very low density polyethylene blends... 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