WO2019027524A1

WO2019027524A1 - Multilayer films and methods of making the same

Info

Publication number: WO2019027524A1
Application number: PCT/US2018/031475
Authority: WO
Inventors: Zhen-yu ZHU; Etienne R.H. LERNOUX; Donald A. WINESETT; Xiao-chuan WANG
Original assignee: Exxonmobil Chemical Patents Inc.
Priority date: 2017-08-02
Filing date: 2018-05-08
Publication date: 2019-02-07

Abstract

Disclosed are multilayer films which can provide a desired balance between MD tear strength and addition of long chain branching.

Description

MULTILAYER FILMS AND METHODS OF MAKING THE SAME

INVENTORS; Zhen-Yu Zhu; Etienne R. H. Lernoux; Donald A. Winesett; Xiao-Chuan Wang CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of Serial No. 62/540,224, filed August 2, 2017, the disclosure of which is hereby incorporated by referenced in its entirety.

FIELD OF THE INVENTION

[0002] This invention is directed to methods for making multilayer films comprising poly ethylenes, films, and silage films made therefrom.

BACKGROUND OF THE INVENTION

[0003] Coextruded blown films are widely used in a variety of packaging as well as other applications. Film properties are often subject to the combined effect of the coextrusion process conditions and polymer compositions selected for the different layers. In order to address requirements of particular end-uses, film producers have to accordingly highlight certain film properties while balancing different mechanical properties to make stronger films for a given thickness and optical properties such as clarity and haze which impact the attractiveness of the packaging and visual inspection of the goods at the point of sale. A three-layer structure has been conventionally employed and refined over time in the art by different applications, in which at least one surface or outer layer is made to facilitate heat-sealing and a core layer may be used to provide strength, impact resistance, stretchability, other main physical properties of the film, or combinations thereof.

[0004] Films having high tear strength in Machine Direction (MD) are desired by packaging applications, such as silage films, food and specialty packages, and heavy-duty sacks, in order to prevent package failure due to tears in the film. While ethylene polymers, such as low density polyethylene (LDPE), linear low density polyethylene (LLDPE) prepared by Ziegler-Natta catalyst in a gas phase process, and blends thereof, have been popular in the packaging market because they can provide relatively low-cost solutions, their potential of improving MD tear strength is limited due to presence of long chain branching (LCB) in ethylene polymers. When ethylene polymers with different levels of LCB are blended, MD tear strength of the blend is generally expected to be lower than that of the polymer with lower level of LCB alone. Efforts to increase MD tear strength may become even less efficient and more difficult as die gap on the extruder grows wider. However, LCB has been demonstrated to contribute to reduced occurrence of tiger stripes caused by vibration and stretching of the film across a very broad processing window, offering the benefit of saving costs and delivering a premium surface appearance. Therefore, film manufacturers have been challenged to overcome the conflict between MD tear strength and presence of LCB with the available selection of ethylene polymers by seeking a convenient approach with higher tolerance for LCB to maintain a desired level of or even allow for further improvement on MD tear strength preferred by end-use, particularly at a wide die gap.

[0005] U.S. Patent No. 9,382,394 relates to ethylene copolymers having a relatively high melt flow ratio and a multimodal profile in a temperature rising elution fractionation (TREF) plot. Such copolymers can be made into film having a dart impact of greater than 500 g/mil, a 1% MD secant modulus of greater than 150 MPa, a 1% TD secant modulus of greater than 175 MPa, and a ratio of MD tear to TD of 0.75 or less under decreased extruder pressures.

[0006] U.S. Patent Publication No. 2014/308480 discloses multilayer thermoplastic films particularly suited for use in liners. The films contain organic fillers to produce opacity when stretched while maintaining an MD Tear Strength of at least 200 gm and a Dart Impact of at least 200 gm. Such performance can be maintained by selection and amounts of resins, organic fillers and processing conditions of the films.

[0007] WO 2014/065989 relates to polymer compositions including (A) 15.0 to 90.0 wt% of a heterogeneously branched ethylene polymer having polymer units derived from at least one C3-C20 alpha-olefin and having a CBDI < 50.0%; and (B) 85.0 to 10.0 wt% of an ethylene-based polymer and films made therefrom.

[0008] U.S. Patent No. 8,829,137 provides polyethylene films derived from ethylene copolymer compositions made with a suitably substituted phosphinimine catalyst, having a haze of <= 12%, a dart impact of >= 500 g/mil, an MD tear of >= 200 g/mil. Such ethylene copolymers have very narrow molecular weight distributions and broadened comonomer distributions.

[0009] U.S. Patent No. 8,247,065 discloses blends of linear low density polyethylene copolymers with very low density, low density, medium density, high density, and differentiated poly ethylenes and other polymers. This invention also includes articles produced from the linear low density polyethylene and polyethylene blends described therein. [0010] That said, exploring alternative film formulation design to obtain an improved balance between MD tear strength and addition of LCB remains an area of on-going and intense effort.

SUMMARY OF THE INVENTION

[0011] Applicant has found that the above objective can be achieved by applying a first polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers in the outer layer and a second polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers in the core layer, preferably either or both in a blend with other polyethylene(s) at a certain ratio, to prepare a multilayer film. Such multilayer film made therefrom can show a remarkable advantage over currently available solutions in maintaining or even highlighting MD tear strength in presence of LCB with a larger capacity, especially at a wide die gap. Therefore, film manufacturers would be released from the limit of achievable MD tear strength by more leverage for determining LCB addition during formulation design without having to compromise MD tear strength. This makes the inventive multilayer film well suited for specific packaging applications such as a silage film.

[0012] Provided are methods for making multilayer films comprising polyethylenes, films, and silage films made therefrom.

[0013] In one embodiment, the present invention relates to a method for making a multilayer film, comprising the steps of: (a) preparing an outer layer comprising at least about 50 wt% of a first polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the outer layer; (b) preparing an inner layer and a core layer between the outer layer and the inner layer, wherein the core layer comprises at least about 40 wt% of a second polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the core layer; and (c) forming a multilayer film comprising the layers in steps (a) and (b); wherein at least one of the first and the second polyethylenes has a density of from about 0.918 to about 0.921 g/cm³.

[0014] In another embodiment, the present invention encompasses a multilayer film, comprising: an outer layer, an inner layer, a core layer between the outer layer and the inner layer, wherein (a) the outer layer comprises at least about 50 wt% of a first polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the outer layer; and (b) the core layer comprises at least about 40 wt% of a second polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the core layer; wherein at least one of the first and the second polyethylenes has a density of from about 0.918 to about 0.921 g/cm³.

[0015] The multilayer film described herein or made according to any method disclosed herein has a normalized Elmendorf tear of at least about 10.8 g/μιη in MD at a die gap of at least 2.25 mm. Preferably, at least one of the first and the second polyethylenes has one or more of the following: (i) up to about 5 mol% units derived from an a-olefin comonomer; (ii) a melt index (MI), I2.16, of from about 0.1 g/10 min to about 300 g/10 min; (iii) a melt index ratio (MIR), I21.6/I2.16, of from about 15 to about 45; (iv) a weight average molecular weight (M_w) of from about 20,000 to about 200,000; (v) a molecular weight distribution (MWD) of from about 2.0 to about 4.5; (vi) a z-average molecular weight (M_z) to weight average molecular weight (M_w) (Mz/Mw) ratio of from about 1.7 to about 3.5; and (vii) a composition distribution breadth index (CDBI) of from 20% to 35%.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0016] Various specific embodiments, versions of the present invention will now be described, including preferred embodiments and definitions that are adopted herein. While the following detailed description gives specific preferred embodiments, those skilled in the art will appreciate that these embodiments are exemplary only, and that the present invention can be practiced in other ways. Any reference to the "invention" may refer to one or more, but not necessarily all, of the present inventions defined by the claims. The use of headings is for purposes of convenience only and does not limit the scope of the present invention.

[0017] As used herein, a "polymer" may be used to refer to homopolymers, copolymers, interpolymers, terpolymers, etc. A "polymer" has two or more of the same or different monomer units. A "homopolymer" is a polymer having monomer units that are the same. A "copolymer" is a polymer having two or more monomer units that are different from each other. A "terpolymer" is a polymer having three monomer units that are different from each other. The term "different" as used to refer to monomer units indicates that the monomer units differ from each other by at least one atom or are different isomerically. Accordingly, the definition of copolymer, as used herein, includes terpolymers and the like. Likewise, the definition of polymer, as used herein, includes copolymers and the like. Thus, as used herein, the terms "polyethylene," "ethylene polymer," "ethylene copolymer," and "ethylene-based polymer" mean a polymer or copolymer comprising at least 50 mol% ethylene units (preferably at least 70 mol% ethylene units, more preferably at least 80 mol% ethylene units, even more preferably at least 90 mol% ethylene units, even more preferably at least 95 mol% ethylene units or 100 mol% ethylene units (in the case of a homopolymer)). Furthermore, the term "polyethylene composition" means a composition containing one or more polyethylene components.

[0018] As used herein, when a polymer is referred to as comprising a monomer, the monomer is present in the polymer in the polymerized form of the monomer or in the derivative form of the monomer.

[0019] As used herein, when a polymer is said to comprise a certain percentage, wt%, of a monomer, that percentage of monomer is based on the total amount of monomer units in the polymer.

[0020] For purposes of this invention and the claims thereto, an ethylene polymer having a density of 0.910 to 0.940 g/cm³ is referred to as a "low density polyethylene" (LDPE); an ethylene polymer having a density of 0.890 to 0.940 g/cm³, typically from 0.915 to 0.930 g/cm³, that is linear and does not contain a substantial amount of long-chain branching is referred to as "linear low density polyethylene" (LLDPE) and can be produced with conventional Ziegler- Natta catalysts, vanadium catalysts, or with metallocene catalysts in gas phase reactors, high pressure tubular reactors, and/or in slurry reactors and/or with any of the disclosed catalysts in solution reactors ("linear" means that the polyethylene has no or only a few long-chain branches, typically referred to as a gvis of 0.97 or above, preferably 0.98 or above); and an ethylene polymer having a density of more than 0.940 g/cm³ is referred to as a "high density polyethylene" (HDPE).

[0021] As used herein, a "plastomer" means ethylene-based copolymers having a density in the range of about 0.85 to 0.915 g/cm³ ASTM D 4703 Method B and ASTM D1505. Plastomers useful in the compositions described herein typically exhibit a MFR of from about 0.5 to about 30 g/10 min. Plastomers useful in the compositions include copolymers of ethylene derived units and higher a-olefin derived 5 units such as propylene, 1-butene, 1-hexene, and 1-octene.

[0022] As used herein, "core" layer, "outer" layer, and "inner" layer are merely identifiers used for convenience, and shall not be construed as limitation on individual layers, their relative positions, or the laminated structure, unless otherwise specified herein.

[0023] As used herein, "first" polyethylene, "second" polyethylene, "third" polyethylene, and "fourth" polyethylene are merely identifiers used for convenience, and shall not be construed as limitation on individual polyethylene, their relative order, or the number of polyethylenes used, unless otherwise specified herein. Polyethylene Polymer

[0024] In one aspect of the invention, the polyethylene that can be used for the multilayer film made according to the method described herein are selected from ethylene homopolymers, ethylene copolymers, and compositions thereof. Useful copolymers comprise one or more comonomers in addition to ethylene and can be a random copolymer, a statistical copolymer, a block copolymer, and/or compositions thereof. The method of making the polyethylene is not critical, as it can be made by slurry, solution, gas phase, high pressure or other suitable processes, and by using catalyst systems appropriate for the polymerization of polyethylenes, such as Ziegler-Natta-type catalysts, chromium catalysts, metallocene-type catalysts, other appropriate catalyst systems or combinations thereof, or by free-radical polymerization. In a preferred embodiment, the polyethylenes are made by the catalysts, activators and processes described in U.S. Patent Nos. 6,342,566; 6,384,142; and 5,741,563; and WO 03/040201 and WO 97/19991. Such catalysts are well known in the art, and are described in, for example, ZIEGLER CATALYSTS (Gerhard Fink, Rolf Miilhaupt and Hans H. Brintzinger, eds., Springer-Verlag 1995); Resconi et al; and I, II METALLOCENE-BASED POLYOLEFINS (Wiley & Sons 2000).

[0025] Polyethylenes that are useful in this invention include those sold under the trade names ENABLE™, EXACT™, EXCEED™, ESCORENE™, EXXCO™, ESCOR™, PAXON™, and OPTEMA™ (ExxonMobil Chemical Company, Houston, Texas, USA); DOW™, DOWLEX™, ELITE™, AFFINITY™, ENGAGE™, and FLEXOMER™ (The Dow Chemical Company, Midland, Michigan, USA); BORSTAR™ and QUEO™ (Borealis AG, Vienna, Austria); and TAFMER™ (Mitsui Chemicals Inc., Tokyo, Japan).

Preferred ethylene homopolymers and copolymers useful in this invention typically have one or more of the following properties:

1. an Mw of 20,000 g/mol or more, 20,000 to 2,000,000 g/mol, preferably 30,000 to

1,000,000, preferably 40,000 to 200,000, preferably 50,000 to 750,000, using a gel permeation chromatograph ("GPC") according to the procedure disclosed herein; and/or

2. a Tin of 30°C to 150°C, preferably 30°C to 140°C, preferably 50°C to 140°C, more preferably 60°C to 135°C, as determined by second melting curve based on ASTM D3418; and/or 3. a crystallinity of 5% to 80%, preferably 10% to 70%, more preferably 20% to 60%, preferably at least 30%, or at least 40%, or at least 50%, as determined by enthalpy of crystallization curve based on ASTM D3418 and calculated by the following formula:

Crystallinity % = Enthalpy (J/g)/ 298 (J/g) ^χ 100%,

wherein 298 (J/g) is enthalpy of 100% crystallinity polyethylene; and/or

4. a heat of fusion of 300 J/g or less, preferably 1 to 260 J/g, preferably 5 to 240 J/g, preferably 10 to 200 J/g, as determined based on ASTM D3418-03; and/or

5. a crystallization temperature (T_c) of 15°C to 130°C, preferably 20°C to 120°C, more preferably 25°C to 110°C, preferably 60°C to 125°C, as determined based on ASTM D3418-03; and/or

6. a heat deflection temperature of 30°C to 120°C, preferably 40°C to 100°C, more preferably 50°C to 80°C as measured based on ASTM D648 on injection molded flexure bars, at 66 psi load (455 kPa); and/or

7. a Shore hardness (D scale) of 10 or more, preferably 20 or more, preferably 30 or more, preferably 40 or more, preferably 100 or less, preferably from 25 to 75 (as measured based on ASTM D 2240); and/or

8. a percent amorphous content of at least 50%, preferably at least 60%, preferably at least 70%, more preferably between 50% and 95%, or 70% or less, preferably 60% or less, preferably 50% or less as determined by subtracting the percent crystallinity from 100.

[0026] The polyethylene may be an ethylene homopolymer, such as HDPE. In one embodiment, the ethylene homopolymer has a molecular weight distribution (M_w/M_n) or (MWD) of up to 40, preferably ranging from 1.5 to 20, or from 1.8 to 10, or from 1.9 to 5, or from 2.0 to 4. In another embodiment, the 1% secant flexural modulus (determined based on ASTM D790A, where test specimen geometry is as specified under the ASTM D790 section "Molding Materials (Thermoplastics and Thermosets)," and the support span is 2 inches (5.08 cm)) of the polyethylene falls in a range of 200 to 1000 MPa, and from 300 to 800 MPa in another embodiment, and from 400 to 750 MPa in yet another embodiment, wherein a desirable polymer may exhibit any combination of any upper flexural modulus limit with any lower flexural modulus limit. The MI of preferred ethylene homopolymers range from 0.05 to 800 dg/min in one embodiment, and from 0.1 to 100 dg/min in another embodiment, as measured based on ASTM D1238 (190°C, 2.16 kg). [0027] In a preferred embodiment, the polyethylene comprises less than 20 mol% propylene units (preferably less than 15 mol%, preferably less than 10 mol%, preferably less than 5 mol%, and preferably 0 mol% propylene units).

[0028] In another embodiment of the invention, the polyethylene useful herein is produced by polymerization of ethylene and, optionally, an alpha-olefin with a catalyst having, as a transition metal component, a bis (n-C3-4 alkyl cyclopentadienyl) hafnium compound, wherein the transition metal component preferably comprises from about 95 mol% to about 99 mol% of the hafnium compound as further described in U.S. Patent No. 6,956,088.

[0029] In another embodiment of the invention, the polyethylene is an ethylene copolymer, either random or block, of ethylene and one or more comonomers selected from C3 to C20 a- olefins, typically from C3 to C10 a-olefins. Preferably, the comonomers are present from 0.1 wt% to 50 wt% of the copolymer in one embodiment, and from 0.5 wt% to 30 wt% in another embodiment, and from 1 wt% to 15 wt% in yet another embodiment, and from 0.1 wt% to 5 wt% in yet another embodiment, wherein a desirable copolymer comprises ethylene and C3 to C20 a- olefin derived units in any combination of any upper wt% limit with any lower wt% limit described herein. Preferably the ethylene copolymer will have a weight average molecular weight of from greater than 8,000 g/mol in one embodiment, and greater than 10,000 g/mol in another embodiment, and greater than 12,000 g/mol in yet another embodiment, and greater than 20,000 g/mol in yet another embodiment, and less than 1,000,000 g/mol in yet another embodiment, and less than 800,000 g/mol in yet another embodiment, wherein a desirable copolymer may comprise any upper molecular weight limit with any lower molecular weight limit described herein.

[0030] In another embodiment, the ethylene copolymer comprises ethylene and one or more other monomers selected from the group consisting of C3 to C20 linear, branched or cyclic monomers, and in some embodiments is a C3 to C12 linear or branched alpha-olefin, preferably butene, pentene, hexene, heptene, octene, nonene, decene, dodecene, 4-methyl-pentene-l,3- methyl pentene-l,3,5,5-trimethyl-hexene-l, and the like. The monomers may be present at up to 50 wt%, preferably from up to 40 wt%, more preferably from 0.5 wt% to 30 wt%, more preferably from 2 wt% to 30 wt%, more preferably from 5 wt% to 20 wt%, based on the total weight of the ethylene copolymer.

[0031] Preferred linear alpha-olefins useful as comonomers for the ethylene copolymers useful in this invention include C3 to Cs alpha-olefins, more preferably 1 -butene, 1 -hexene, and 1-octene, even more preferably 1 -hexene. Preferred branched alpha-olefins include 4-methyl-l - pentene, 3 -methyl- 1 -pentene, 3,5,5-trimethyl-l-hexene, and 5-ethyl-l -nonene. Preferred aromatic-group-containing monomers contain up to 30 carbon atoms. Suitable aromatic-group- containing monomers comprise at least one aromatic structure, preferably from one to three, more preferably a phenyl, indenyl, fluorenyl, or naphthyl moiety. The aromatic-group- containing monomer further comprises at least one polymerizable double bond such that after polymerization, the aromatic structure will be pendant from the polymer backbone. The aromatic-group containing monomer may further be substituted with one or more hydrocarbyl groups including but not limited to Ci to Cio alkyl groups. Additionally, two adjacent substitutions may be joined to form a ring structure. Preferred aromatic-group-containing monomers contain at least one aromatic structure appended to a polymerizable olefinic moiety. Particularly, preferred aromatic monomers include styrene, alpha-methylstyrene, para- alkylstyrenes, vinyltoluenes, vinylnaphthalene, allyl benzene, and indene, especially styrene, paramethyl styrene, 4-phenyl-l -butene and allyl benzene.

[0032] Preferred di olefin monomers useful in this invention include any hydrocarbon structure, preferably C4 to C30, having at least two unsaturated bonds, wherein at least two of the unsaturated bonds are readily incorporated into a polymer by either a stereospecific or a non- stereospecific catalyst(s). It is further preferred that the diolefin monomers be selected from alpha, omega-diene monomers (i.e., di-vinyl monomers). More preferably, the diolefin monomers are linear di-vinyl monomers, most preferably those containing from 4 to 30 carbon atoms. Examples of preferred dienes include butadiene, pentadiene, hexadiene, heptadiene, octadiene, nonadiene, decadiene, undecadiene, dodecadiene, tridecadiene, tetradecadiene, pentadecadiene, hexadecadiene, heptadecadiene, octadecadiene, nonadecadiene, icosadiene, heneicosadiene, docosadiene, tricosadiene, tetracosadiene, pentacosadiene, hexacosadiene, heptacosadiene, octacosadiene, nonacosadiene, triacontadiene, particularly preferred dienes include 1 ,6-heptadiene, 1,7-octadiene, 1 ,8-nonadiene, 1 ,9-decadiene, 1, 10-undecadiene, 1, 1 1- dodecadiene, 1, 12-tridecadiene, 1, 13 -tetradecadiene, and low molecular weight polybutadienes (Mw less than 1000 g/mol). Preferred cyclic dienes include cyclopentadiene, vinylnorbornene, norbornadiene, ethylidene norbomene, divinylbenzene, dicyclopentadiene, or higher ring containing diolefins with or without substituents at various ring positions.

[0033] In a preferred embodiment, one or more dienes are present in the polyethylene at up to 10 wt%, preferably at 0.00001 wt% to 2 wt%, preferably 0.002 wt% to 1 wt%, even more preferably 0.003 wt% to 0.5 wt%, based upon the total weight of the polyethylene. In some embodiments, diene is added to the polymerization in an amount of from an upper limit of 500 ppm, 400 ppm, or 300 ppm to a lower limit of 50 ppm, 100 ppm, or 150 ppm.

[0034] Preferred ethylene copolymers useful herein are preferably a copolymer comprising at least 50 wt% ethylene and having up to 50 wt%, preferably 1 wt% to 35 wt%, even more preferably 1 wt% to 6 wt% of a C3 to C20 comonomer, preferably a C4 to Cs comonomer, preferably hexene or octene, based upon the weight of the copolymer. Preferably these polymers are metallocene poly ethylenes (mPEs).

[0035] Useful mPE homopolymers or copolymers may be produced using mono- or bis- cyclopentadienyl transition metal catalysts in combination with an activator of alumoxane and/or a non-coordinating anion in solution, slurry, high pressure or gas phase. The catalyst and activator may be supported or unsupported and the cyclopentadienyl rings may be substituted or unsubstituted.

[0036] In one embodiment, the multilayer film made according to the method described herein comprises in the outer layer a first polyethylene (as a polyethylene defined herein) derived from ethylene and one or more C3 to C20 a-olefin comonomers. In another embodiment, the multilayer film made according to the method described herein comprises in the core layer a second polyethylene (as a polyethylene defined herein) derived from ethylene and one or more C3 to C20 a-olefin comonomers. In various embodiments, the first polyethylene may be the same as or different from the second polyethylene. Preferably, the first polyethylene is the same as the second polyethylene.

[0037] In one preferred embodiment, at least one of the first and the second polyethylene polymers may have one or more of the following properties: (i) up to about 5 mol% units derived from an a-olefin comonomer; (ii) an MI, Γ2.16, of from about 0.1 g/10 min to about 300 g/10 min; (iii) an MIR, I21.6/I2.16, of from about 15 to about 45; (iv) an M_w of from about 20,000 to about 200,000; (v) an MWD of from about 2.0 to about 4.5; (vi) an M_z/M_w ratio of from about 1.7 to about 3.5; and (vii) a composition distribution breadth index (CDBI) of from 20% to 35%. The CDBI may be determined using techniques for isolating individual fractions of a sample of the resin. The preferred technique is Temperature Rising Elution Fraction ("TREF"), as described in Wild, et al, J. Poly. Sci., Poly. Phys. Ed., Vol. 20, p. 441 (1982), which is incorporated herein for purposes of U. S. practice. [0038] In another preferred embodiment, at least one of the first and the second polyethylenes has a density of from about 0.918 to about 0.921 g/cm³.

[0039] In yet another preferred embodiment, at least one of the first and the second polyethylenes is produced by gas-phase polymerization of ethylene with a catalyst having as a transition metal component a bis(n-C3-4 alkyl cyclopentadienyl) hafnium compound, wherein said transition metal component comprises from about 95 mol% to about 99 mol% of said hafnium compound.

[0040] In one preferred embodiment, the multilayer film made according to the method described herein may comprise in the inner layer a fourth polyethylene (as a polyethylene defined herein) derived from ethylene and one or more C3 to C20 a-olefin comonomers. In various embodiments, the fourth polyethylene may conform to characteristics as set out above for the first or the second polyethylene. Preferably, the fourth polyethylene is the same as the first or the second polyethylene.

[0041] The polyethylene polymer that can be used as the first, the second, or the fourth polyethylene in the multilayer film made according to the method described herein comprises from 70.0 mol% to 100.0 mol% of units derived from ethylene. The lower limit on the range of ethylene content may be from 70.0 mol%, 75.0 mol%, 80.0 mol%, 85.0 mol%, 90.0 mol%, 92.0 mol%, 94.0 mol%, 95.0 mol%, 96.0 mol%, 97.0 mol%, 98.0 mol%, or 99.0 mol% based on the mol% of polymer units derived from ethylene. The polyethylene polymer may have an upper ethylene limit of 80.0 mol%, 85.0 mol%, 90.0 mol%, 92.0 mol%, 94.0 mol%, 95.0 mol%, 96.0 mol%, 97.0 mol%, 98.0 mol%, 99.0 mol%, 99.5 mol%, or 100.0 mol%, based on polymer units derived from ethylene. For polyethylene copolymers, the polyethylene polymer may have less than 50.0 mol % of polymer units derived from a C3-C20 olefin, preferably, an alpha-olefin, e.g., hexene or octene. The lower limit on the range of C3-C20 olefin-content may be 25.0 mol%, 20.0 mol%, 15.0 mol%, 10.0 mol%, 8.0 mol%, 6.0 mol%, 5.0 mol%, 4.0 mol%, 3.0 mol%, 2.0 mol%, 1.0 mol%, or 0.5 mol%, based on polymer units derived from the C3-C20 olefin. The upper limit on the range of C3-C20 olefin-content may be 20.0 mol%, 15.0 mol%, 10.0 mol%, 8.0 mol%, 6.0 mol%, 5.0 mol %, 4.0 mol%, 3.0 mol%, 2.0 mol%, or 1.0 mol%, based on polymer units derived from the C3 to C20 olefin. Any of the lower limits may be combined with any of the upper limits to form a range. Comonomer content is based on the total content of all monomers in the polymer. [0042] In a class of embodiments, the polyethylene polymer may have minimal long chain branching (i.e., less than 1.0 long-chain branch/1000 carbon atoms, preferably particularly 0.05 to 0.50 long-chain branch/1000 carbon atoms). Such values are characteristic of a linear structure that is consistent with a branching index (as defined below) of g'_vis > 0.980, 0.985, > 0.99, > 0.995, or 1.0. While such values are indicative of little to no long chain branching, some long chain branches may be present (i.e., less than 1.0 long-chain branch/1000 carbon atoms, preferably less than 0.5 long-chain branch/1000 carbon atoms, particularly 0.05 to 0.50 long- chain branch/1000 carbon atoms).

[0043] In some embodiments, the polyethylene polymers may have a density in accordance with ASTM D-4703 and ASTM D-1505/ISO 1183 of from about 0.910 to about 0.925 g/cm³, from about 0.910 to about 0.923 g/cm³, from about 0.910 to about 0.920 g/cm³, from about 0.915 to about 0.921 g/cm³, from about 0.912 to about 0.918 g/cm³, or from about 0.918 to about 0.921 g/cm³.

[0044] The weight average molecular weight (M_w) of the polyethylene polymers may be from about 15,000 to about 500,000 g/mol, from about 20,000 to about 200,000 g/mol, from about 25,000 to about 150,000 g/mol, from about 150,000 to about 400,000 g/mol, from about 200,000 to about 400,000 g/mol, or from about 250,000 to about 350,000 g/mol.

[0045] The polyethylene polymers may have a molecular weight distribution (MWD) or (Mw/Mn) of from about 1.5 to about 5.0, from about 2.0 to about 4.5, from about 3.0 to about 4.0, or from about 2.5 to about 4.0. MWD is measured using a gel permeation chromatograph ("GPC") on a Waters 150 gel permeation chromatograph equipped with a differential refractive index ("DRI") detector and a Chromatix KMX-6 on line light scattering photometer. The system is used at 135°C with 1 ,2,4-trichlorobenzene as the mobile phase using Shodex (Showa Denko America, Inc.) polystyrene gel columns 802, 803, 804, and 805. This technique is discussed in "Liquid Chromatography of Polymers and Related Materials III," J. Cazes editor, Marcel Dekker, 1981, p. 207, which is incorporated herein by reference. Polystyrene is used for calibration. No corrections for column spreading are employed; however, data on generally accepted standards, e.g., National Bureau of Standards Polyethylene 1484 and anionically produced hydrogenated polyisoprenes (alternating ethylene-propylene copolymers) demonstrate that such corrections on MWD are less than 0.05 units. M_w/M_n is calculated from elution times. The numerical analyses are performed using the commercially available Beckman/CIS customized LALLS software in conjunction with the standard Gel Permeation package. Reference to M_w/M_n implies that the Mw is the value reported using the LALLS detector and M_n is the value reported using the DRI detector described above.

[0046] The polyethylene polymers may have a z-average molecular weight (M_z) to weight average molecular weight (M_w) (M_z/M_w) ratio greater than about 1.5, or greater than about 1.7, or greater than about 2.0. In some embodiments, this ratio is from about 1.7 to about 3.5, from about 2.0 to about 3.0, or from about 2.2 to about 3.0.

[0047] The polyethylene polymers may have a melt index (MI) or (I2.16) as measured by ASTM D-1238-E (190°C/2.16 kg) of about 0.1 to about 300 g/10 min, about 0.1 to about 100 g/10 min, about 0.1 to about 50 g/10 min, about 0.1 g/10 min to about 5.0 g/10 min, about 0.1 g/10 min to about 3.0 g/10 min, about 0.1 g/10 min to about 2.0 g/10 min, about 0.1 g/10 min to about 1.2 g/10 min, about 0.2 g/10 min to about 1.5 g/10 min, about 0.2 g/10 min to about 1.1 g/10 min, about 0.3 g/10 min to about 1.0 g/10 min, about 0.4 g/10 min to about 1.0 g/10 min, about 0.5 g/10 min to about 1.0 g/10 min, about 0.6 g/10 min to about 1.0 g/10 min, about 0.7 g/10 min to about 1.0 g/10 min, or about 0.75 g/10 min to about 0.95 g/10 min.

[0048] The polyethylene polymers may have a melt index ratio (MIR) (I21.6 (190°C, 21.6 kg)/l2. i6 (190°C, 2.16 kg)) of from about 10 to about 50, from about 15 to about 45, from about 20 to about 40, from about 20 to about 35, from about 22 to about 38, from about 20 to about 32, from about 25 to about 31, or from about 28 to about 30.

[0049] In a class of embodiments, the polyethylene polymers may contain less than 5.0 ppm hafnium, less than 2.0 ppm haihium, less than 1.5 ppm hafnium, or less than 1.0 ppm hafnium. In other embodiments, the polyethylene polymers may contain from about 0.01 ppm to about 2 ppm haihium, from about 0.01 ppm to about 1.5 ppm hafnium, or from about 0.01 ppm to about 1.0 ppm hafnium.

[0050] Typically, the amount of hafnium is greater than the amount of zirconium in the polyethylene polymer. In a particular class of embodiments, the ratio of hafnium to zirconium (ppm/ppm) is at least about 2.0, at least about 10.0, at least about 15, at least about 17.0, at least about 20.0, at least about 25.0, at least about 50.0, at least about 100.0, at least about 200.0, or at least about 500.0 or more. While zirconium generally is present as an impurity in hafnium, it will be realized in some embodiments where particularly pure hafnium-containing catalysts are used, the amount of zirconium may be extremely low, resulting in a virtually undetectable or undetectable amount of zirconium in the polyethylene polymer. Thus, the upper limit on the ratio of hafnium to zirconium in the polymer may be quite large. [0051] In several classes of embodiments, the polyethylene polymers may have at least a first peak and a second peak in a comonomer distribution analysis, wherein the first peak has a maximum at a log(M_w) value of 4.0 to 5.4, 4.3 to 5.0, or 4.5 to 4.7; and a TREF elution temperature of 70.0°C to 100.0°C, 80.0°C to 95.0°C, or 85.0°C to 90.0°C. The second peak in the comonomer distribution analysis has a maximum at a log(M_w) value of 5.0 to 6.0, 5.3 to 5.7, or 5.4 to 5.6; and a TREF elution temperature of 40.0°C to 60.0°C, 45.0°C to 60.0°C, or 48.0°C to 54.0°C.

[0052] In several of the classes of embodiments described above, the polyethylene polymer may have a Broad Orthogonal Comonomer Distribution or "BOCD." "BOCD" refers to a Broad Orthogonal Composition Distribution in which the comonomer of a copolymer is incorporated predominantly in the high molecular weight chains or species of a polyolefin polymer or composition. The distribution of the short chain branches can be measured, for example, using Temperature Raising Elution Fractionation (TREF) in connection with a Light Scattering (LS) detector to determine the weight average molecular weight of the molecules eluted from the TREF column at a given temperature. The combination of TREF and LS (TREF-LS) yields information about the breadth of the composition distribution and whether the comonomer content increases, decreases, or is uniform across the chains of different molecular weights of polymer chains. BOCD has been described, for example, in U.S. Patent Nos. 8,378,043, Col. 3, line 34, bridging Col. 4, linel9, and 8,476,392, line 43, bridging Col. 16, line 54.

[0053] The TREF-LS data reported herein were measured using an analytical size TREF instrument (Polymerchar, Spain), with a column of the following dimension: inner diameter (ID) 7.8 mm and outer diameter (OD) 9.53 mm and a column length of 150 mm. The column was filled with steel beads. 0.5 mL of a 6.4% (w/v) polymer solution in orthodichlorobenzene (ODCB) containing 6 g BHT/4 L were charged onto the column and cooled from 140°C to 25°C at a constant cooling rate of 1.0°C/min. Subsequently, the ODCB was pumped through the column at a flow rate of 1.0 ml/min and the column temperature was increased at a constant heating rate of 2°C/min to elute the polymer. The polymer concentration in the eluted liquid was detected by means of measuring the absorption at a wavenumber of 2857 cm^"1 using an infrared detector. The concentration of the ethylene-a-olefin copolymer in the eluted liquid was calculated from the absorption and plotted as a function of temperature. The molecular weight of the ethylene-a-olefin copolymer in the eluted liquid was measured by light scattering using a Minidawn Tristar light scattering detector (Wyatt, Calif., USA). The molecular weight was also plotted as a function of temperature.

[0054] The breadth of the composition distribution is characterized by the T75- T25 value, wherein T25 is the temperature at which 25% of the eluted polymer is obtained and T75 is the temperature at which 75% of the eluted polymer is obtained in a TREF experiment as described herein. The composition distribution is further characterized by the Fso value, which is the fraction of polymer that elutes below 80°C in a TREF-LS experiment as described herein. A higher Fso value indicates a higher fraction of comonomer in the polymer molecule. An orthogonal composition distribution is defined by a M60/M90 value that is greater than 1 , wherein Μβο is the molecular weight of the polymer fraction that elutes at 60°C in a TREF-LS experiment and M90 is the molecular weight of the polymer fraction that elutes at 90°C in a TREF-LS experiment as described herein.

[0055] In a class of embodiments, the polyethylene polymers as described herein may have a BOCD characterized in that the T75-T25 value is 1 or greater, 2.0 or greater, 2.5 or greater, 4.0 or greater, 5.0 or greater, 7.0 or greater, 10.0 or greater, 11.5 or greater, 15.0 or greater, 17.5 or greater, 20.0 or greater, or 25.0 or greater, wherein T25 is the temperature at which 25% of the eluted polymer is obtained and T75 is the temperature at which 75% of the eluted polymer is obtained in a TREF experiment as described herein.

[0056] The polyethylene polymers as described herein may further have a BOCD characterized in that M60/M90 value is 1.5 or greater, 2.0 or greater, 2.25 or greater, 2.50 or greater, 3.0 or greater, 3.5 or greater, 4.0 or greater, 4.5 or greater, or 5.0 or greater, wherein Μβο is the molecular weight of the polymer fraction that elutes at 60°C in a TREF-LS experiment and M90 is the molecular weight of the polymer fraction that elutes at 90°C in a TREF-LS experiment as described herein.

[0057] Additionally, the polyethylene polymers as described herein may further have a BOCD characterized in that Fso value is 1% or greater, 2% or greater, 3% or greater, 4% or greater, 5% or greater, 6% or greater, 7% or greater, 10% or greater, 1 1 % or greater, 12% or greater, or 15% or greater, wherein Fso is the fraction of polymer that elutes below 80°C.

[0058] Additionally, the melt strength of the polyethylene polymer at a particular temperature may be determined with a Gottfert Rheotens Melt Strength Apparatus. To determine the melt strength, unless otherwise stated, a polymer melt strand extruded from the capillary die is gripped between two counter-rotating wheels on the apparatus. The take-up speed is increased at a constant acceleration of 2.4 mm/sec². The maximum pulling force (in the unit of cN) achieved before the strand breaks or starts to show draw-resonance is determined as the melt strength. The temperature of the rheometer is set at 190°C. The capillary die has a length of 30 mm and a diameter of 2 mm. The polymer melt is extruded from the die at a speed of 10 mm/sec. The distance between the die exit and the wheel contact point should be 122 mm.

[0059] The melt strength of the polyethylene polymer may be in the range from about 1 to about 100 cN, about 1 to about 50 cN, about 1 to about 25 cN, about 3 to about 15 cN, about 4 to about 12 cN, or about 5 to about 10 cN.

[0060] Materials and processes for making the polyethylene polymer have been described in, for example, U.S. Pat. No. 6,956,088, particularly Example 1 ; U. S. Patent Application Publication No. 2009/0297810, particularly Example 1 ; U. S. Patent Application Publication No. 2015/0291748, particularly PE1 -PE5 in the Examples; and WO 2014/099356, particularly PE3 referenced on page 12 and in the Examples, including the use of a silica supported hafnium transition metal metallocene/methylalumoxane catalyst system described in, for example, U. S. Patent No. 6,242,545 and U. S. Patent No. 6,248,845, particularly Example 1.

[0061] The polyethylene polymer is commercially available from ExxonMobil Chemical Company, Houston, TX, and sold under Exceed XP™ Performance Polymer. Exceed XP™ Performance Polymer offers step-out performance with respect to, for example, dart drop impact strength, flex-crack resistance, and machine direction (MD) tear, as well as maintaining stiffness at lower densities. Exceed XP™ mPE also offers optimized solutions for a good balance of melt strength, toughness, stiffness, and sealing capabilities which makes this family of polymers well- suited for blown film/cast film solutions.

[0062] The first polyethylene present in the outer layer, the second polyethylene present in the core layer, and, preferably, the fourth polyethylene present in the inner layer of the multilayer film made according to the method described herein may be optionally in a blend with one or more other polymers, such as polyethylenes defined herein, which blend is referred to as polyethylene composition. In particular, the polyethylene compositions described herein may be physical blends or in situ blends of more than one type of polyethylene or compositions of polyethylenes with polymers other than polyethylenes where the polyethylene component is the majority component, e.g., greater than 50 wt% of the total weight of the composition. Preferably, the polyethylene composition is a blend of two polyethylenes with different densities. [0063] In one preferred embodiment, the outer layer of the multilayer film made according to the method described herein may further comprise at least one of an LDPE and an LLDPE. The LDPEs that are useful in the multilayer films described herein are ethylene based polymers produced by free radical initiation at high pressure in a tubular or autoclave reactor as well known in the art. The LDPEs have a medium to broad MWD determined according to the procedure disclosed herein of higher than 4, preferably from 5 to 40, and a high level of long chain branching as well as some short chain branching. The density is generally greater than 0.910 g/cm³ and is preferably from 0.920 to 0.940 g/cm³. The MI may be less than 0.55 or 0.45 g/10 min. The LLDPEs that are useful in the multilayer films described herein preferably have a density of from 0.915 to 0.935 g/cm³. The MI may range from 0.1 to 10 g/10 min and is determined by ASTM D-1238, preferably between 0.4 and 6 g/10 min, or between 0.8 and 3 g/10 min. The LLDPEs may have short chain branches formed by the incorporation of higher a-olefins such as C4 to Cs a-olefins including propylene, butene-1, 4-methylpentene-l, hexene- 1 and octene-1. The MIR may vary and be at least 5 or 10, and less than 100. mLLDPEs can be conveniently prepared by polymerization using a single site (often metallocene) catalyst in a gas phase, slurry or solution process. Using a series reactor combination, polyethylene polymers can be produced with broader molecular weight distribution or compositional distribution. mLLDPEs preferably have an MWD (M_w/M«) of from 1.5 to 4 as measured by DRI GPC, preferably at least 2.0, especially less than 3.5, and usually a CDBI in excess of 50%, preferably in excess of 60%. znLLDPE made using multi-site titanium based Ziegler-Natta catalysts are believed to have a narrow to medium molecular weight distribution defined herein as having an M_w/Mn as determined by GPC DRI of less than 5 combined with a broad CDBI of less than 50%. In the present invention, the outer layers may contain more than one type of LDPE or LLDPE.

[0064] In another preferred embodiment, the multilayer film made according to the method described herein may further comprise in the core layer at least one of an LLDPE as described above and a third polyethylene (as a polyethylene defined herein) derived from ethylene and one or more C3 to C20 a-olefin comonomers, said polyethylene having a density of about 0.910 to about 0.945 g/cm³, an MI, I2.16, of about 0.1 to about 15 g/10 min, an MWD of about 2.5 to about 5.5, and an MIR, I21.6/I2.16, of about 25 to about 100. In various embodiments, the third polyethylene may have one or more of the following properties: (a) a density (sample prepared according to ASTM D-4703, and the measurement according to ASTM D-1505) of about 0.910 to about 0.945 g/cm³, or about 0.915 to about 0.940 g/cm³;

(b) an MI (h.ie, ASTM D-1238, 2.16 kg, 190°C) of about 0.1 to about 15 g/10 min, or about 0.1 to about 10 g/10 min, or about 0.1 to about 5 g/10 min;

(c) an MIR (I21.6 (190°C, 21.6 kg)/I₂.i6 (190°C, 2.16 kg)) of greater than 25 to about 100, or greater than 30 to about 90, or greater than 35 to about 80;

(d) a CDBI (determined according to the procedure disclosed herein) of greater than about 50%, or greater than about 60%, or greater than 75%, or greater than 85%;

(e) an MWD of about 2.5 to about 5.5; MWD is measured according to the procedure disclosed herein; and/or

(f) a branching index ("g", determined according to the procedure described herein) of about 0.5 to about 0.97, or about 0.7 to about 0.95.

The third polyethylene is not limited by any particular method of preparation and may be formed using any process known in the art. For example, the third polyethylene may be formed using gas phase, solution, or slurry processes.

[0065] In one embodiment, the third polyethylene is formed in the presence of a Ziegler- Natta catalyst. In another embodiment, the third polyethylene is formed in the presence of a single-site catalyst, such as a metallocene catalyst (such as any of those described herein). Particularly useful catalyst systems include supported dimethylsilyl bis(tetrahydroindenyl) zirconium dichloride. Polyethylenes useful as the third polyethylene in this invention include those disclosed in U.S. Patent No. 6,476,171, which is hereby incorporated by reference for this purpose, and include those commercially available from ExxonMobil Chemical Company in Houston, Texas, such as those sold under the trade designation ENABLE™.

[0066] In another preferred embodiment, the multilayer film made according to the method described herein may comprise in the inner layer an ethylene-based plastomer (as a polyethylene defined herein) in a blend with the fourth polyethylene described herein, having about 15 to about 35 wt% units derived from C4-C10 a-olefins, based on total weight of the ethylene-based plastomer, which may have an: ethylene content of 50 to 90 wt% (preferably 60 to 85 wt%, or 65 to 80 wt%, or 65 to 75 wt%); ethylene content of 80 to 96 mol% (preferably 82 to 92 mol%, or 82 to 88 mol%, or 84 to 86 mol%); butene-1 content of 15 wt% or more (preferably 20 wt% or more, or 25 wt% or more); hexene-1 content of 20 wt% or more (preferably 25 wt% or more, or 30 wt% or more); and/or octene-1 content of 25 wt% or more (preferably 30 wt% or more, or 35 wt% or more).

[0067] Useful ethylene-based plastomers may have one or more of the following properties: density of 0.91 g/cm³ or less (preferably 0.905 g/cm³ or less, or 0.902 g/cm³ or less, or 0.85 g/cm³ or more, or 0.86 g/cm³ or more, or 0.87 g/cm³ or more, or 0.88 g/cm³ or 25 more, or 0.885 g/cm³ or more, or 0.85 to 0.91 g/cm³, or 0.86 to 0.91 g/cm³, or 0.87 to 0.91 g/cm³, or 0.88 to 0.905 g/cm³, or 0.88 to 0.902 g/cm³, or 0.885 to 0.902 g/cm³); heat of fusion (Hf) of 90 J/g or less (preferably 70 J/g or less, or 50 J/g or less, or 30 J/g or less, or 10 to 70 J/g, or 10 to 50 J/g, or 10 to 30 J/g); crystallinity of 40% or less (preferably 30% or less, or 20% or less, preferably at least 5%, or in the range of from 5 to 30%, or from 5 to 20%); melting point (T_m, peak first melt) of 100°C or less (preferably 95°C or less, or 90°C or less, or 80°C or less, or 70°C or less, or 60°C or less, or 50°C or less); crystallization temperature (T_c, peak) of 90°C or less (preferably 80°C or less, or 70°C or less, or 60°C or less, or 50°C or less, or 40°C or less); glass transition temperature (Tg) of -20°C or less (preferably -30°C or less, or -40°C or less); M_w of 30 to 2,000 kg/mol (preferably 50 to 1,000 kg/mol, or 90 to 500 kg/mol); M_w/M„ of 1 to 40 (preferably 1.4 to 20, or 1.6 to 10, or 1.8 to 3.5, or 1.8 to 2.5); branching index (g') of 1.4 to 20 (preferably 1.6 to 10, or 1.8 to 10); melt index (MI, 2.16 kg at 190°C) of 0.1 to 100 g/10 min (preferably 0.3 to 60 g/10 min, or 0.5 to 40 g/10 min, or 0.7 to 20 g/10 min); and/or CDBI of at least 60 wt% (preferably 5 at least 70 wt%, or at least 80 wt%, or at least 90 wt%, or at least 95 wt%).

[0068] The method of making the ethylene-based plastomer can be slurry, solution, gas- phase, high-pressure, or other suitable processes, through the use of catalyst systems appropriate for the polymerization of polyolefins, such as Ziegler-Natta catalysts, metallocene catalysts, other appropriate catalyst systems, or combinations thereof.

[0069] Useful ethylene plastomers may be produced using a metallocene catalyst system, i.e., a mono- or bis-cyclopentadienyl transition metal catalysts in combination with an activator of alumoxane and/or a non-coordinating anion in solution, slurry, high-pressure, or gas-phase.

The catalyst and activator may be supported or unsupported and the cyclopentadienyl rings by may substituted or unsubstituted. Information on the methods and catalysts/activators to produce such mPE homopolymers and copolymers is available in WO 94/26816; WO 94/03506; EPA 277,003; EPA 277,004; U.S. Patent No. 5,153,157; U.S. Patent No. 5,198,401; U.S. Patent No.

5,240,894; U.S. Patent No. 5,017,714; CA 1,268,753; U.S. Patent No. 5,324,800; EPA 129,368;

U.S. Patent No. 5,264,405; EPA 520,732; WO 92/00333; U.S. Patent No. 5,096,867; U.S. Patent No. 5,507,475; EPA 426 637; EPA 573 403; EPA 520 732; EPA 495 375; EPA 500 944; EPA 570 982; WO91/09882; WO94/03506; and U.S. Patent No. 5,055,438. More generally, preferred plastomers are produced using a single-site catalyst, whether a metallocene catalyst or not, and have an Mw/Mn of 1.5 to 3 (preferably 1.8 to 2.5) and a CDBI of 70% or more (preferably 80% or more, or 90% or more).

[0070] Plastomers that are useful in this invention include those commercially available under the trade names EXACT™ (ExxonMobil Chemical Company), AFFINITY™, ENGAGE™, FLEXOMER™ (The Dow Chemical Company), QUEO™ (Borealis AG, Austria), and TAFMER™ (Mitsui Company).

[0071] In yet another preferred embodiment, the multilayer film made according to the method described herein may comprise in the inner layer an ethylene- vinyl acetate (EVA) (as a polyethylene defined herein). The EVA suitable for the multilayer film made according to the method described herein may be a copolymer of ethylene and vinyl acetate, having a MI, I2.16, of from about 0.2 to about 20 g/10 min, from about 0.2 to about 9 g/10 min, from about 0.2 to about 3 g/10 min, or from about 0.2 to about 1 g/10 min. The EVA may have a vinyl acetate content (VA%) of from about 5 to about 30 wt%, from about 5 to about 20 wt%, or from about 5 to about 10 wt%. EVA copolymers useful in the present invention may include those commercially available from ExxonMobil Chemical Company as Escorene™ Ultra FL series resins.

[0072] In one embodiment, the first polyethylene can be present in an amount of at least about 50 wt%, for example, about 50 wt%, about 55 wt%, about 60 wt%, about 65 wt%, about 70 wt%, about 75 wt%, about 80 wt%, about 85 wt%, about 90 wt%, about 95 wt%, or about 100 wt%, based on total weight of polymer in the outer layer. In another embodiment, the second polyethylene can be present in an amount of at least about 40 wt%, for example, anywhere between 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, or 70 wt%, and 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, or 100 wt%, based on total weight of polymer in the core layer. In a preferred embodiment where the inner comprises the fourth polyethylene in a blend with the ethylene-based plastomer described herein, the fourth polyethylene is present in an amount of from about 20 to about 50 wt%, for example, from about 20 wt%, 25 wt%, or 30 wt%, to about 35 wt%, 40 wt%, 45 wt%, or 50 wt%, or vary in the range of any combination of the values recited herein, based on total weight of polymer in the inner layer. [0073] In a class of embodiments, in addition to polyethylene as described above, the multilayer film made according to the present invention may further comprise other polymers, including without limitation other polyolefins, polar polymers, and cationic polymers, in any of the outer layer, the outer sub-layer, the core layer, the inner sub-layer, and the inner layer.

[0074] It has been surprisingly discovered that, as the die gap on the extruder for preparing a multilayer film increases, particularly to a width of more than 2 mm, use of the first polyethylene described herein in the outer layer and the second polyethylene described herein in the core layer can lead to improved balance between MD tear strength and LCB content of the formed film. Thus, the longstanding difficulty in satisfying both at the same time rather than highlighting one at the expense of the other has been well solved with MD tear strength maintained or even enhanced in LCB presence, which effect is reflected more significantly at a die gap above 2 mm. This opens the potential for the inventive film as promising alternative for packaging applications highly demanding in terms of MD tear strength.

Additives

[0075] The multilayer film made according to the method described herein may also contain in at least one layer various additives as generally known in the art. Examples of such additives include a slip agent, an antiblock, a filler, an antioxidant, an ultraviolet light stabilizer, a thermal stabilizer, a pigment, a processing aid, a crosslinking catalyst, a flame retardant, and a foaming agent, etc., and combinations thereof. Especially, the multilayer film made according to the present invention may further comprise functional additives suitable for particular packaging applications, for example, a tackifier, an antifungal agent, and an ultraviolet absorber for silage films. Preferably, the additives may each individually present in an amount of about 0.01 wt% to about 50 wt%, or about 0.1 wt% to about 15 wt%, or from 1 wt% to 10 wt%, based on total weight of the film layer.

[0076] In a preferred embodiment, at least one of the core layer and the inner layer of the multilayer film made according to the method described herein comprises a tackifier in an amount of from about 5 to about 10 wt%, for example, about 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%, based on total weight of the layer. Suitable tackifiers useful in the multilayer film made according to the method described herein include polybutenes, terpene resins, alkali metal glycerol stearates and oleates, and hydrogenated resins and esters.

[0077] Any additive useful for the multilayer film may be provided separately or together with other additive(s) of the same or a different type in a pre-blended masterbatch, where the target concentration of the additive is reached by combining each neat additive component in an appropriate amount to make the final composition.

Film Structures

[0078] The multilayer film made according to the present invention may further comprise additional layer(s), which may be any layer typically included in multilayer film constructions. For example, the additional layer(s) may be made from:

1. Poly olefins. Preferred poly olefins include homopolymers or copolymers of d to C40 olefins, preferably C2 to C20 olefins, preferably a copolymer of an a-olefin and another olefin or a-olefin (ethylene is defined to be an a-olefin for purposes of this invention). Preferably homopoly ethylene, homopolypropylene, propylene copolymerized with ethylene and/or butene, ethylene copolymerized with one or more of propylene, butene or hexene, and optional dienes. Preferred examples include thermoplastic polymers such as ultra-low density polyethylene, very low density polyethylene, linear low density polyethylene, low density polyethylene, medium density polyethylene, high density polyethylene, polypropylene, isotactic polypropylene, highly isotactic polypropylene, syndiotactic polypropylene, random copolymer of propylene and ethylene and/or butene and/or hexene, elastomers such as ethylene propylene rubber, ethylene propylene diene monomer rubber, neoprene, and compositions of thermoplastic polymers and elastomers, such as, for example, thermoplastic elastomers and rubber toughened plastics.

2. Polar polymers. Preferred polar polymers include homopolymers and copolymers of esters, amides, acetates, anhydrides, copolymers of a C2 to C20 olefin, such as ethylene and/or propylene and/or butene with one or more polar monomers, such as acetates, anhydrides, esters, alcohol, and/or acrylics. Preferred examples include polyesters, polyamides, ethylene vinyl acetate copolymers, and polyvinyl chloride.

3. Cationic polymers. Preferred cationic polymers include polymers or copolymers of geminally disubstituted olefins, a-heteroatom olefins and/or styrenic monomers. Preferred geminally disubstituted olefins include isobutylene, isopentene, isoheptene, isohexane, isooctene, isodecene, and isododecene. Preferred α-heteroatom olefins include vinyl ether and vinyl carbazole, preferred styrenic monomers include styrene, alkyl styrene, para-alkyl styrene, a-methyl styrene, chloro-styrene, and bromo-para-methyl styrene. Preferred examples of cationic polymers include butyl rubber, isobutylene copolymerized with para methyl styrene, polystyrene, and poly-a-methyl styrene. 4. Miscellaneous. Other preferred layers can be paper, wood, cardboard, metal, metal foils (such as aluminum foil and tin foil), metallized surfaces, glass (including silicon oxide (SiOx) coatings applied by evaporating silicon oxide onto a film surface), fabric, spunbond fibers, and non-wovens (particularly polypropylene spunbond fibers or non-wovens), and substrates coated with inks, dyes, pigments, and the like.

[0079] In particular, a multilayer film can also include layers comprising materials such as ethylene vinyl alcohol (EVOH), polyamide (PA), polyvinylidene chloride (PVDC), or aluminium, so as to obtain barrier performance for the film where appropriate.

[0080] In one aspect of the invention, the multilayer film made according to the method described herein may be produced in a stiff oriented form (often referred to as "pre-stretched" by persons skilled in the art) and may be useful for laminating to inelastic materials, such as polyethylene films, biaxially oriented polyester (e.g., polyethylene terephthalate (PET)) films, biaxially oriented polypropylene (BOPP) films, biaxially oriented polyamide films, foil, paper, board, or fabric substrates, or may further comprise one of the above substrate films to form a laminate structure.

[0081] The thickness of the multilayer films may range from 5 to 200 μπι in general and is mainly determined by the intended use and properties of the film. Conveniently, the film has a thickness of from 5 to 200 μπι, from 10 to 150 μπι, from 15 to 90 μπι, or from 20 to 60 μπι. Preferably, the thickness ratio between the outer layer, the core layer, and the inner layer can be from about 1 :2: 1 to about 1 : 10: 1 , for example, about 1 :2: 1, about 1 :3 : 1, about 1 :4: 1 , about 1 :5: 1 , about 1 :6: 1, about 1 :7: 1 , about 1 : 8: 1, about 1 :9: 1, about 1 : 10: 1 , or vary in the range of any combination of the values recited herein.

[0082] The multilayer film made according to the method described herein may have an A/Y/B structure, wherein A is the outer layer, B the inner layer, and Y the core layer in between. Suitably one or both of the outer and the inner layers are a skin layer forming one or both sealant surfaces and can serve as a lamination skin (the surface to be adhered to the substrate) or a sealable skin (the surface to form a seal). For silage applications, the inner layer preferably may comprise a tackifier to provide cling required for film wrapping around a bale. The composition of the A, Y, and B layers all conform to the limitations set out herein.

[0083] In one embodiment, the multilayer film has a A/Y/B structure, comprising an outer layer, an inner layer, a core layer between the outer layer and the inner layer, wherein (a) the outer layer comprises (i) at least about 60 wt% of an polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the outer layer, and (ii) an LLDPE; (b) the core layer comprises (i) from about 40 to about 60 wt% of the polyethylene in (a), (ii) a blend of an LLDPE and a polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, said polyethylene having a density of about 0.910 to about 0.945 g/cm³, an MI, Γ2.16, of about 0.1 to about 15 g/10 min, an MWD of about 2.5 to about 5.5, and an MIR, I21.6/I2.16, of about 25 to about 100; and (iii) from about 5 to about 10 wt% of a tackifier, based on total weight of the core layer; and (c) the inner layer comprises from about 5 to about 10 wt% of a tackifier, based on total weight of the inner layer. In one preferred embodiment, the inner layer further comprises at least about 90 wt% of an EVA, based on total weight of polymer in the inner layer. In another preferred embodiment, the inner layer further comprises (i) an ethylene-based plastomer, having about 15 to about 35 wt% units derived from C4-C10 a-olefins, based on total weight of the ethylene-based plastomer; and (ii) from about 20 to about 50 wt% of the polyethylene in (a). Preferably, the polyethylene has one or more of the following: (i) up to about 5 mol% units derived from an α-olefin comonomer; (ii) an MI, I2.16, of from about 0.1 g/10 min to about 300 g/10 min; (iii) an MIR, I21.6/I2.16, of from about 15 to about 45; (iv) an M_w of from about 20,000 to about 200,000; (v) an MWD of from about 2.0 to about 4.5; (vi) an Mz/M_w ratio of from about 1.7 to about 3.5; and (vii) a CDBI of from 20% to 35%. Preferably, the polyethylene in (a) has a density of from about 0.918 to about 0.921 g/cm³. Preferably, the thickness ratio between the outer layer, the core layer, and the inner layer is from about 1 :6: 1.

Film Properties and Applications

[0084] The multilayer films of the present invention may be adapted to form flexible packaging films for a wide variety of other applications, such as, cling film, low stretch film, non-stretch wrapping film, pallet shrink, over-wrap, agricultural, and collation shrink film and laminate films, including silage films. The film structures that may be used for bags are prepared such as sacks, trash bags and liners, industrial liners, produce bags, and heavy duty bags. The film may be used in flexible packaging, food packaging, e.g., fresh cut produce packaging, frozen food packaging, bundling, packaging and unitizing a variety of products. Conveniently, the multilayer film made according to the method described herein is suitable for use in silage applications.

[0085] The inventive multilayer film made according to the method described herein or made according to any method disclosed herein may have a normalized Elmendorf tear of at least about 10.8 g/μηι in MD at a die gap of at least 2.25 mm. The inventive film design can benefit a multilayer film prepared at a die gap over 2 mm with unexpected improvement on MD tear strength regardless of a considerable level of LCB content, indicating desirable potential for use in packaging applications substantially favoring MD tear performance.

Methods for Making the Multilayer Film

[0086] Also provided are methods for making multilayer films of the present invention. A method for making a multilayer film may comprise the step of: (a) preparing an outer layer comprising at least about 50 wt% of a first polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the outer layer; (b) preparing an inner layer and a core layer between the outer layer and the inner layer, wherein the core layer comprises at least about 40 wt% of a second polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the core layer; and (c) forming a multilayer film comprising the layers in steps (a) and (b).

[0087] The multilayer films described herein may be formed by any of the conventional techniques known in the art including blown extrusion, cast extrusion, coextrusion, blow molding, casting, and extrusion blow molding.

[0088] In one embodiment of the invention, the multilayer films of the present invention are formed by using blown techniques, i.e., to form a blown film. For example, the composition described herein can be extruded in a molten state through an annular die and then blown and cooled to form a tubular, blown film, which can then be axially slit and unfolded to form a flat film. As a specific example, blown films can be prepared as follows. The polymer composition is introduced into the feed hopper of an extruder, such as a 50 mm extruder that is water-cooled, resistance heated, and has an L/D ratio of 30: 1. The film can be produced using a 28 cm die with a die gap with a width from 1.4 mm to 2.5 mm, along with a dual air ring and internal bubble cooling. The film is extruded through the die into a film cooled by blowing air onto the surface of the film. The film is drawn from the die typically forming a cylindrical film that is cooled, collapsed and, optionally, subjected to a desired auxiliary process, such as slitting, treating, sealing, or printing. Typical melt temperatures are from about 180°C to about 230°C. Blown film rates are generally from about 3 to about 25 kilograms per hour per inch (about 4.35 to about 26.11 kilograms per hour per centimeter) of die circumference. The finished film can be wound into rolls for later processing. A particular blown film process and apparatus suitable for forming films according to embodiments of the present invention is described in U. S. Patent No. 5,569,693. Of course, other blown film forming methods can also be used.

[0089] The compositions prepared as described herein are also suited for the manufacture of blown film in a high-stalk extrusion process. In this process, a polyethylene melt is fed through a gap (typically 0.5 to 2.5 mm) in an annular die attached to an extruder and forms a tube of molten polymer which is moved vertically upward. The initial diameter of the molten tube is approximately the same as that of the annular die. Pressurized air is fed to the interior of the tube to maintain a constant air volume inside the bubble. This air pressure results in a rapid 3-to-9-fold increase of the tube diameter which occurs at a height of approximately 5 to 10 times the die diameter above the exit point of the tube from the die. The increase in the tube diameter is accompanied by a reduction of its wall thickness to a final value ranging from approximately 10 to 50 μιτι and by a development of biaxial orientation in the melt. The expanded molten tube is rapidly cooled (which induces crystallization of the polymer), collapsed between a pair of nip rolls and wound onto a film roll.

[0090] In blown film extrusion, the film may be pulled upwards by, for example, pinch rollers after exiting from the die and is simultaneously inflated and stretched transversely sideways to an extent that can be quantified by the blow up ratio (BUR). The inflation provides the transverse direction (TD) stretch, while the upwards pull by the pinch rollers provides a machine direction (MD) stretch. As the polymer cools after exiting the die and inflation, it crystallizes and a point is reached where crystallization in the film is sufficient to prevent further MD or TD orientation. The location at which further MD or TD orientation stops is generally referred to as the "frost line" because of the development of haze at that location.

[0091] Variables in this process that determine the ultimate film properties include the die gap, the BUR and TD stretch, the take up speed and MD stretch and the frost line height (FLH). Certain factors tend to limit production speed and are largely determined by the polymer rheology including the shear sensitivity which determines the maximum output and the melt tension which limits the bubble stability, BUR and take up speed. Desirably, the multilayer film made according to the method described herein react more positively to a die gap above 2 mm in terms of highlighted MD tear performance.

[0092] A laminate structure with the inventive multilayer film prepared as described herein can be formed by laminating respective lamination skins of the sealant to the substrate using any process known in the art, including solvent based adhesive lamination, solvent less adhesive lamination, extrusion lamination, heat lamination, etc.

EXAMPLES

[0093] The present invention, while not meant to be limited by, may be better understood by reference to the following examples and tables.

Example 1

[0094] Example 1 illustrates MD tear strength demonstrated by an inventive film sample (Sample 1) in comparison with four comparative samples (Samples 2-5), all of which were prepared with a 25 μιτι A/Y/B structure at a layer thickness ratio of 1 : 6: 1 on a coextrusion blown film line with processing variables including a die gap of 2.5 mm, a BUR of 2.4, an FLH of 850 mm, an output of 150 lb (about 68 kg) /h, and a strain rate of 1.1 s^"1.

[0095] Polymer and additive products used in the sample films include the following polymers. PE-1 polymer sample was prepared with a bis (n-propylcyclopentadienyl) hafnium dichloride metallocene catalyst as further described in U.S. Patent No. 6,956,088. PE-1 had density of 0.918 g/cm³; MI of 0.50 g/10 min; Ce content of 3 mol%; MIR of 29.6; Mw of 156,768; MWD of 3.3; M_z/M_w of 2.4; and a T75-T25 of 21.9°C. The PE-1 polymer meets the descriptions of the first, the second, and the fourth poly ethylenes defined herein. PE-2 polymer was prepared the same type of catalyst and method as PE-1 polymer except that PE-2 was prepared to have density of 0.916 g/cm³; MI of 0.50 g/10 min; Ce content of 3.4 mol%; MIR of 30.1; M_w of 156,120; MWD of 3.6; Mz/M_w of 2.4; and T75-T25 of 24.5°C. Polymer samples PE-3 and PE-4 were produced using bis (l-methyl,3-n-butylcyclopentadienyl) zirconium dichloride metallocene catalyst as further described in U.S. Patent No. 6,090,740. PE-3 polymer had density of 0.918 g/cm³; MI of 1.0 g/10 min; Ce content of 2.5 mol%; MIR of 15.8; M_w of 114,004; MWD of 2.4; and M_z/M_w of 1.8. PE-4 polymer had density of 0.918 g/cm³; MI of 2.0 g/10 min; MIR of 16.1 ; M_w of 102,922; MWD of 2.4; and M_z/M_w of 1.8. PE-5 polymer was prepared using supported dimethylsilyl-bis (tetrahydroindenyl) zirconium dichloride metallocene catalyst as further described in U.S. Patent No. 6,476,171. PE-5 polymer samples had density of 0.927 g/cm³; MI of 0.30 g/10 min; MIR of 59; M_w of 119,253; MWD of 3.8; and M_z/M_w of 2.3. PE-5 polymer meets the description of the third polyethylene defined herein. EXXONMOBIL™ LDPE LD 150BW LDPE resin (density: 0.923 g/cm³, MI: 0.75 g/10 min) is commercially available from ExxonMobil Chemical Company, Houston, Texas, USA. EXXONMOBIL™ LLDPE LL 1001XV LLDPE resin (density: 0.918 g/cm³, MI: 1.0 g/10 min) is commercially available from ExxonMobil Chemical Company, Houston, Texas, USA. ESCORENE™ Ultra FL 00218 EVA copolymer resin (density: 0.940 g/cm³, MI: 1.7 g/10 min, VA%: 18.0) also commercially available from ExxonMobil Chemical Company, Houston, Texas, USA. DOWLEX™ 2045G LLDPE resin (density: 0.920 g/cm³, MI: 1.0 g/10 min) is commercially available from The Dow Chemical Company, Midland, Michigan, USA. QUEO™ 8201 ethylene-based octene-1 plastomer resin (density: 0.883 g/cm³, MI: 1.1 g/10 min, ethylene content: 71 wt%) is commercially available from Borealis AG, Vienna, Austria. PIB Compound PT-60 polyisobutylene tackifier (polyisobutylene content: 57-60 wt%) is commercially available from Polyfill Technologies, India.

[0096] Elmendorf tear strength was measured in MD based on ASTM D 1922-06a using the Tear Tester 83-11-01 from TMI Group of Companies and measures the energy required to continue a pre-cut tear in the test sample, presented as normalized tearing force in grarn^m. Samples were conditioned at 23°C ± 2°C and 50% ± 10% relative humidity for at least 40 hours prior to test. Samples were cut across the web using the constant radius tear die and were free of any visible defects (e.g., die lines, gels, etc.).

[0097] Structure-wise formulations (based on total weight of the layer) of the films samples and corresponding test results of normalized MD tear strength are listed below in Table 1.

[0098] As shown in Table 1, when a die gap as wide as 2.5 mm is applied, the inventive multilayer film featuring layer composition as described herein can outperform the comparative samples in terms of MD tear strength, in presence of some LCB introduced by PE-3 type resin, which suggests the inventive film has superior MD tear strength.

Table 1 : Structure-wise formulations (wt%) and normalized MD tear strength (g/μηϊ) of

Samples 1-5

Example 2

[0099] Another four inventive samples (Samples 6-9) differing in the inner layer but otherwise identical with Sample 1 in Example 1 in terms of layers' composition were prepared with varying processing variables to respectively compare MD tear strength with four comparative samples (Samples 6a-9a), all of which were prepared with a 25 μηι A/Y/B structure at a layer thickness ratio of 1 :6: 1 on a coextrusion blown film line. Structure-wise formulations (based on total weight of the layer), processing variables, and test results of normalized MD tear strength for all samples are shown below in Table 2.

[00100] According to the data in Table 2, when EVA is used in the inner layer in place of the ethylene-based plastomer in Example 1 to introduce more LCB to the multilayer film, the inventive film formulation can display a reliably higher tolerance for LCB addition at a die gap above 2 mm, if not as outstanding at a narrower die gap, to better balance between MD tear strength and LCB addition. Therefore, without being bound by theory, it can be concluded that use of the first and the second polyethylene polymers in a multilayer film as set out herein plays a critical role in securing MD tear strength in presence of LCB, thus leading to favored convenience and flexibility in film design for packaging applications focusing on MD tear performance.

[00101] All documents described herein are incorporated by reference herein, including any priority documents and/or testing procedures. When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated. As is apparent from the foregoing general description and the specific embodiments, while forms of the invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited thereby.

Table 2: Structure-wise formulations (wt%). processing variables, and normalized MP tear strength of Samples 6-9 and 6a-9a

Claims

CLAIMS What is claimed is:

1. A method for making a multilayer film, comprising the steps of:

(a) preparing an outer layer comprising at least about 50 wt% of a first polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the outer layer;

(b) preparing an inner layer and a core layer between the outer layer and the inner layer, wherein the core layer comprises at least about 40 wt% of a second polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the core layer; and

(c) forming a multilayer film comprising the layers in steps (a) and (b);

wherein at least one of the first and the second polyethylenes has a density of from about 0.918 to about 0.921 g/cm³; wherein the multilayer film has a normalized Elmendorf tear of at least about 10.8 g/μπι in MD at a die gap of at least 2.25 mm.

2. The method of claim 1, wherein the multilayer film in step (c) is formed by blown extrusion, cast extrusion, co-extrusion, blow molding, casting, or extrusion blow molding.

3. The method of claim 1 or 2, wherein at least one of the first and the second polyethylenes has one or more of the following: (i) up to about 5 mol% units derived from an a-olefin comonomer; (ii) a melt index (MI), I2.16, of from about 0.1 g/10 min to about 300 g/10 min; (iii) a melt index ratio (MIR), I21.6/I2.16, of from about 15 to about 45; (iv) a weight average molecular weight (M_w) of from about 20,000 to about 200,000; (v) a molecular weight distribution (MWD) of from about 2.0 to about 4.5; (vi) a z-average molecular weight (M_z) to weight average molecular weight (M_w) (M_z/M_w) ratio of from about 1.7 to about 3.5; and (vii) a composition distribution breadth index (CDBI) of from 20% to 35%.

4. The method of any of claims 1 to 3, wherein at least one of the first and the second polyethylenes is produced by gas-phase polymerization of ethylene with a catalyst having as a transition metal component a bis(n-C3-4 alkyl cyclopentadienyl) hafnium compound, wherein said transition metal component comprises from about 95 mol% to about 99 mol% of said hafnium compound.

5. The method of any of claims 1 to 4, wherein the first polyethylene is the same as the second polyethylene.

6. The method of any of claims 1 to 5, wherein the outer layer further comprises at least one of a low density polyethylene (LDPE) and a linear low density polyethylene (LLDPE).

7. The method of any of claims 1 to 6, wherein the core layer further comprises at least one of (i) LLDPE and (ii) a third polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, said polyethylene having a density of about 0.910 to about 0.945 g/cm³, an MI, I2.16, of about 0.1 to about 15 g/10 min, an MWD of about 2.5 to about 5.5, and an MIR, I21.6/I2.16, of about 25 to about 100.

8. The method of any of claims 1 to 7, wherein the inner layer comprises an ethylene- vinyl acetate (EVA).

9. The method of any of claims 1 to 8, wherein the inner layer comprises (i) an ethylene- based plastomer, having about 15 to about 35 wt% units derived from C4-C10 a-olefins, based on total weight of the ethylene-based plastomer; and (ii) from about 20 to about 50 wt% of a fourth polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the inner layer.

10. The method of claim 9, wherein the fourth polyethylene is the same as the first polyethylene or the second polyethylene.

11. The method of any of claims 1 to 10, wherein at least one of the core layer and the inner layer comprises from about 5 to about 10 wt% of a tackifier, based on total weight of the layer.

12. The method of any of claims 1 to 1 1 , wherein the thickness ratio between the outer layer, the core layer, and the inner layer is from about 1 :2: 1 to about 1 : 10: 1.

13. A multilayer film, comprising an outer layer, an inner layer, a core layer between the outer layer and the inner layer, wherein (a) the outer layer comprises at least about 50 wt% of a first polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the outer layer; and

(b) the core layer comprises at least about 40 wt% of a second polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the core layer;

wherein at least one of the first and the second polyethylenes has a density of from about 0.918 to about 0.921 g/cm³; wherein the multilayer film has a normalized Elmendorf tear of at least about 10.8 g/μιη in Machine Direction (MD) at a die gap of at least 2.25 mm.

14. A multilayer film, comprising an outer layer, an inner layer, a core layer between the outer layer and the inner layer, wherein

(a) the outer layer comprises (i) at least about 60 wt% of an polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the outer layer, and (ii) an LLDPE;

(b) the core layer comprises (i) from about 40 to about 60 wt% of the polyethylene in (a), (ii) a blend of an LLDPE and a polyethylene derived from ethylene and one or more C3 to C20 a-olefin comonomers, said polyethylene having a density of about 0.910 to about 0.945 g/cm³, an MI, I2.16, of about 0.1 to about 15 g/10 min, an MWD of about 2.5 to about 5.5, and an MIR, I21.6/I2.16, of about 25 to about 100; and (iii) from about 5 to about 10 wt% of a tackifier, based on total weight of the core layer; and

(c) the inner layer comprises from about 5 to about 10 wt% of a tackifier, based on total weight of the inner layer;

wherein the polyethylene in (a) has a density of from about 0.918 to about 0.921 g/cm³; wherein the multilayer film has a normalized Elmendorf tear of at least about 10.8 g/ μηι in MD at a die gap of at least 2.25 mm.

15. The multilayer film of claim 14, wherein the inner layer further comprises at least about 90 wt% of an EVA, based on total weight of polymer in the inner layer.

16. The multilayer film of claim 14 or 15, wherein the inner layer further comprises (i) an ethylene-based plastomer, having about 15 to about 35 wt% units derived from C4-C10 a-olefins, based on total weight of the ethylene-based plastomer; and (ii) from about 20 to about 50 wt% of the polyethylene in (a).

17. The multilayer film of any of claims 14 to 16, wherein the polyethylene in (a) has one or more of the following: (i) up to about 5 mol% units derived from an a-olefin comonomer;

(ii) an MI, I2.16, of from about 0.1 g/10 min to about 300 g/10 min; (iii) an MIR, I21.6/I2.16, of from about 15 to about 45; (iv) an M_w of from about 20,000 to about 200,000; (v) an MWD of from about 2.0 to about 4.5; (vi) an M_z/M_w ratio of from about 1.7 to about 3.5; and (vii) a CDBI of from 20% to 35%.

18. The multilayer film of any of claims 14 to 17, wherein the thickness ratio between the outer layer, the core layer, and the inner layer is from about 1 : 6: 1.

19. A silage film comprising the multilayer film of any of claims 13 to 18 or made according to the method of any of claims 1 to 12.