WO2018194740A1 - Multilayer films and methods of making the same - Google Patents

Abstract

Disclosed are multilayer films which can provide desired toughness performance for a laminate structure in a more efficient and cost-effective way.

Description

MULTILAYER FILMS AND METHODS OF MAKING THE SAME

PRIORITY CLAIM

[0001] This application claims the benefit of Serial No. 62/487,140, filed April 19, 2017 and is incorporated by reference in its entirety.

FIELD OF THE INVENTION

[0002] This invention relates to films, and in particular, to multilayer films comprising polyethylene, methods for making such films, and laminates made therefrom.

BACKGROUND OF THE INVENTION

[0003] Stand-up Pouches (SUPs) are commonly known as pouches capable of standing upright on shelves for display to consumers, which have been developed to replace traditional rigid packaging such as bottles and cans for use in flexible packaging industry. SUPs have long been popular with food, home or personal care markets, and are also widely used as convenient refill packs for bottles.

[0004] Laminate films are generally employed in the industry to prepare SUPs with sufficient stiffness-related and toughness-related properties to ensure package integrity without distortion and rupture, especially during packaging and transportation. Good sealing performance under common heat sealing conditions and, for some applications, barrier to moisture, light, and/or oxygen transmission are also desired.

[0005] Currently, most of the SUPs in the market are prepared from a flexible laminate film structure, comprising a polyethylene sealant film adhered to a substrate film commonly made of biaxially oriented polyester (PET), biaxially oriented polypropylene (BOPP), or biaxially oriented polyamide (BOPA). Particularly, a process including two steps of lamination is normally employed to prepare SUPs used for liquid, especially that weighing above 1.5 kg, which features laminating a sealant film to a first substrate commonly made of biaxially oriented polyamide, followed by adhering the so-formed structure to a second substrate made of biaxially oriented polyester. It has been difficult to reduce such two-step lamination to one step by skipping the polyamide substrate because the formed SUPs may not sustain impact force without adequate toughness provided by the polyamide substrate.

[0006] WO 2015/134721 discloses a coextruded multilayer blown film including a core layer including a blend of ethylene vinyl alcohol copolymer and an active oxygen barrier composition including a blend of a thermoplastic resin having carbon-carbon double bonds substantially in its main chain, a transition metal salt, and an oxygen barrier polymer; two intermediate layers each including polyamide; a first outer layer including high density polyethylene; a second outer layer including olefinic polymer; and two tie layers each adhering an intermediate layer to the first and second outer layers respectively; wherein from 20% to 65% by weight of the coextruded multilayer blown film is made up of high density polyethylene. A package includes a food product in a hermetic pouch made from the coextruded film, optionally adhered to a PET film, such as a printed, or trap-printed PET film, to form a laminate, the pouch having a longitudinal seal and transverse heat seals.

[0007] U.S. Patent No. 9,421,743 provides a film structure suitable for use in stand up pouches comprising all polyethylene material. The film structure can be a monolayer film or a multilayer film structure having specific requirements for each layer. The combination results in a film structure having adequate stiffness to function as a stand-up pouch while also providing acceptable water vapor transmission rates and good tear resistance.

[0008] That said, there remains a need in the art to simplify the conventional manufacture and structure for a laminate while maintaining its toughness performance up to standards required by SUPs used for liquid. Applicant has found that such objective can be achieved by applying in each of the two outer layers 100 wt% of a first polyethylene described herein, based on total weight of polymer in the outer layer, and in the core layer 100 wt% of a second polyethylene described herein, based on total weight of polymer in the core layer, to prepare a multilayer film. The multilayer film made of the above composition, when laminated to a single substrate of polyester, can demonstrate drop test performance at a level comparable to that of a conventional structure prepared by two-step lamination. Therefore, by removing the need for a polyamide substrate arranged between the sealant film and the polyester substrate in the conventional structure, a laminate structure with the inventive film can improve operation efficiency during production and provide cost saving benefits for SUP manufacturers.

SUMMARY OF THE INVENTION

[0009] Provided are multilayer films comprising polyethylene, methods for making such films, and laminates and SUPs made therefrom.

[0010] In one embodiment, the present invention encompasses a multilayer film comprising: (a) two outer layers, each comprising about 100 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, wherein the first polyethylene is a metallocene polyethylene (mPE) having a density of about 0.910 to about 0.940 g/cm³, a melt index (MI), I2.16, of about 0.1 to about 15 g/10 min, a molecular weight distribution (MWD) of about 1.5 to about 5.5, and a melt index ratio (MIR), I21.6/I2.16, of about 10 to about 25; and (b) a core layer between the two outer layers, the core layer comprising about 100 wt% of a second polyethylene derived from ethylene and one or more C3 to C20 α-olefin comonomers, based on total weight of polymer in the core layer, wherein the second polyethylene is an mPE having a density of about 0.910 to about 0.945 g/cm³, an MI, I₂.ie, 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.

[0011] In another embodiment, the present invention relates to a method for making a multilayer film, comprising the steps of: (a) preparing two outer layers, each comprising about 100 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, wherein the first polyethylene is an mPE having a density of about 0.910 to about 0.940 g/cm³, an MI, I2.16, of about 0.1 to about 15 g/10 min, an MWD of about 1.5 to about 5.5, and an MIR, I21.6/I2.16, of about 10 to about 25; (b) preparing a core layer, the core layer comprising about 100 wt% of a second polyethylene derived from ethylene and one or more C3 to C20 α-olefin comonomers, based on total weight of polymer in the core layer, wherein the second polyethylene is an mPE 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 (c) forming a film comprising the layers in steps (a) and (b), wherein the core layer is between the two outer layers. Preferably, the method further comprises after step (c) a step of laminating the film in step (c) to a substrate film.

[0012] The multilayer film described herein or made according to any method disclosed herein has an average breakage rate (EMC method) of about 0% to about 20% at 5°C and 24°C, when laminated to a polyester substrate film. Preferably, the multilayer film further has at least one of the following properties: (i) a dart impact of at least about 4% higher; (ii) an Elmendorf tear of at least about 12% higher in Machine Direction (MD); and (iii) a maximum puncture force of at least about 4% higher, compared to that of a multilayer film having no more than about 80 wt% of the first polyethylene present in each of the outer layers but otherwise identical in terms of thickness, layer distribution, and total polyethylene amount of the film. Preferably, the multilayer film further comprising a substrate film comprising one or more of biaxially oriented polyester, biaxially oriented polypropylene, and biaxially oriented polyamide. More preferably, the substrate film does not comprise polyamide.

[0013] Also provided are laminates comprising any of the multilayer films described herein or made according to any method disclosed herein, and SUPs made therefrom.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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 0.930 g/cm³, typically from 0.910 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 g' vis 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).

[0019] As used herein, "core" layer and "outer" 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.

[0020] As used herein, "first" polyethylene and "second" 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.

[0021] As used herein, "drop test performance" refers to the capability of a loaded stand- up pouch to withstand the sudden shock resulting from a free fall in accordance with ASTM D 5276-98 which is incorporated by reference. The test is conducted in three batches under 5°C and then in three batches under 24°C, vertically with respect to the ground at a height of one meter (1^st batch) and, if passed, horizontally with respect to the ground at a height of one meter (2^nd batch), and, if passed again, then vertically with respect to the ground at a height of 1.5 meters (3^rd batch). Five samples each loaded with 2.1 L water are tested for each formulation in each batch. The drop test performance is represented by an average breakage rate under such, as a function of the breakage rate (percentage of broken bags in each batch) and a predetermined coefficient of each batch, calculated according to the following formula, which method is specifically developed by Applicant and is herein referred to as the "EMC method":

R= (Ri xc l +R2XC2+R3 xc₃)/(c 1 +C2+C3) ;

wherein R is average breakage rate; Ri, R2, and R₃ are breakage rate in the 1^st, 2^nd, and 3^rd batch, respectively; ci, c₂, and c₃ are predetermined coefficient of the 1^st, 2^nd, and 3^rd batch, respectively, wherein ci is 1, C2 is 2, and c₃ is 3. If the 1^st batch is failed, then R2 and R₃ will automatically become 100%; if the 1^st batch is passed but the 2^nd batch is failed, then R₃ will become 100%.

[0022] Drop test performance is tested herein under 5°C and 24°C, respectively. Bag samples are prepared by laminate films formed with either a single polyester substrate film or two substrate films, one made of polyamide and the other made of polyester. As used herein, a polyester substrate film refers to a 12 μιη substrate film of neat biaxially oriented polyester, while a polyamide substrate film refers to a 15 μιη substrate film of neat biaxially oriented polyamide between the sealant film and the polyester substrate film in laminate films formed with two substrate films. [0023] As used herein, film layers that are the same in composition and in thickness are referred to as "identical" layers.

Polyethylene

[0024] In one aspect of the invention, the polyethylene that can be used for the multilayer film 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 PCT Publication Nos. 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 Mulhaupt 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 tradenames 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).

[0026] 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 g/mol, preferably 40,000 to 200,000 g/mol, preferably 50,000 to 750,000 g/mol, as measured by using a gel permeation chromatograph ("GPC") according to the procedure disclosed herein; and/or

2. a T_m 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) x 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. 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, 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. 9,956,088.

[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, greater than 10,000 g/mol in another embodiment, greater than 12,000 g/mol in yet another embodiment, greater than 20,000 g/mol in yet another embodiment, 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 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- 1-pentene, 3 -methyl- 1 -pentene, 3, 5, 5-trimethyl- 1-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 diolefin 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, 1,11- 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 norbornene, 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. Several commercial products produced with such catalyst/activator combinations are commercially available from ExxonMobil Chemical Company in Houston, Texas under the tradename EXCEED™ Polyethylene or ENABLE™ Polyethylene.

[0036] In a class of embodiments, the multilayer film of the present invention comprises in each of the two outer layers 100 wt% of a first polyethylene (as a polyethylene defined herein) derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the outer layer, wherein the first polyethylene is an mPE having a density of about 0.910 to about 0.940 g/cm³, an MI, I₂.i6, of about 0.1 to about 15 g/10 min, an MWD of about 1.5 to about 5.5, and an MIR, I21.6/I2.16, of about 10 to about 25. In various embodiments, the first 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 0.940 g/cm³, or about 0.912 to about 0.927 g/cm³, or about 0.912 to about 0.918 g/cm³;

(b) an MI (I2.16, ASTM D-1238, 2.16 kg, 190°C) of about 0.1 to about 15 g/10 min, or about 0.3 to about 10 g/10 min, or about 0.5 to about 5 g/10 min;

(c) an MIR (I21.6 (190°C, 21.6 kg)/I₂.i₆ (190°C, 2.16 kg)) of about 10 to about 25, or about 12 to about 20, or about 15 to about 18;

(d) a Composition Distribution Breadth Index ("CDBI") of up to about 85%, or up to about 75%, or about 5% to about 85%, or 10% to 75%. 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;

(e) an MWD of about 1.5 to about 5.5; 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. Mw/Mn 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 M_w is the value reported using the LALLS detector and M_n is the value reported using the DRI detector described above; and/or

(f) a branching index of about 0.9 to about 1.0, or about 0.96 to about 1.0, or about

0.97 to about 1.0. Branching Index is an indication of the amount of branching of the polymer and is defined as

"Rg" stands for Radius of Gyration, and is measured using a Waters 150 gel permeation chromatograph equipped with a Multi- Angle Laser Light

Scattering ("MALLS") detector, a viscosity detector, and a differential refractive index detector.

"[Rglfcr" is the Radius of Gyration for the branched polymer sample and "[Rg]/,„" is the Radius of Gyration for a linear polymer sample.

[0037] The first polyethylene is not limited by any particular method of preparation and may be formed using any process known in the art. For example, the first polyethylene may be formed using gas phase, solution, or slurry processes.

[0038] In one embodiment, the first polyethylene is formed in the presence of a metallocene catalyst. For example, the first polyethylene may be an mPE 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. mPEs useful as the first polyethylene include those commercially available from ExxonMobil Chemical Company in Houston, Texas, such as those sold under the trade designation EXCEED™.

[0039] In accordance with another embodiment, the multilayer film described herein comprises in the core layer 100 wt% of a second polyethylene (as a polyethylene defined herein) derived from ethylene and one or more C3 to C20 a-olefin comonomers, based on total weight of polymer in the core layer, wherein the second polyethylene is an mPE having a density of about 0.910 to about 0.945 g/cm³, an MI, I₂.ie 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 second 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 (I₂.i₆, 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 80, or greater than 35 to about 60;

(d) a Composition Distribution Breadth Index ("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.

[0040] The second polyethylene is not limited by any particular method of preparation and may be formed using any process known in the art. For example, the second polyethylene may be formed using gas phase, solution, or slurry processes.

[0041] In one embodiment, the second polyethylene is formed in the presence of a single- site catalyst, such as a metallocene catalyst (such as any of those described herein). Polyethylenes useful as the second polyethylene in this invention include those disclosed in U.S. Patent No. 6,255,426, entitled "Easy Processing Linear Low Density Polyethylene" (Lue), 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™.

[0042] In one embodiment, the first and the second polyethylenes described herein can each be neat polymer of one polyethylene or 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.

Film Structures

[0043] The multilayer film of 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 polyolefins include homopolymers or copolymers of C2 to C40 olefins, preferably C2 to C20 olefins, preferably a copolymer of an a-olefin and another olefin or α-olefin (ethylene is defined to be an α-olefin for purposes of this invention). Preferably, homopolyethylene, 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 a-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.

[0044] In particular, a multilayer film can also include layers comprising materials such as ethylene vinyl alcohol (EVOH), poly amide (PA), polyvinylidene chloride (PVDC), or aluminium, so as to obtain barrier performance for the film where appropriate.

[0045] In one aspect of the invention, the multilayer film 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.

[0046] In one preferred embodiment, the multilayer film further comprises a substrate film comprising one or more of biaxially oriented polyester, biaxially oriented polypropylene, and biaxially oriented polyamide. In a more preferred embodiment, the substrate film does not comprise polyamide. These multilayer films can optionally include additional barrier layers such as aluminium barrier.

[0047] The thickness of the multilayer films may range from 10 to 200 μιη in general and is mainly determined by the intended use and properties of the film. Conveniently, the film has a thickness of from 10 to 200 μιη, from 50 to 200 μιη, or from 80 to 180 μιη. Preferably, the thickness ratio between one of the outer layers and the core layer is about 1 : 1 to about 1 :4, for example, about 1: 1, about 1: 1.5, about 1 :2, about 1:2.5, about 1:3, about 1 :3.5, or about 1:4.

[0048] The multilayer film described herein may have an A/Y/A structure, wherein A is an outer layer and Y is the core layer in contact with the outer layer. Suitably, one or both outer 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). The composition of the A layers may be the same or different, but conform to the limitations set out herein. Preferably, the A layers are identical.

Film Properties and Applications

[0049] The multilayer films of the present invention may be adapted to form flexible packaging laminate films, including stand-up pouches, as well as a wide variety of other applications, such as cling film, low stretch film, non-stretch wrapping film, pallet shrink, overwrap, agricultural, and collation shrink film. 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.

[0050] The inventive multilayer film described herein may have has an average breakage rate (EMC method) of about 0% to about 20% at 5°C and 24°C, when laminated to a polyester substrate film. Preferably, the multilayer film has an average breakage rate (EMC method) of about 0% at 5°C and 24°C, when laminated to a polyester substrate film.

[0051] In another preferred embodiment, the multilayer film described herein further has at least one of the following properties: (i) a dart impact of at least about 4% higher; (ii) an Elmendorf tear of at least about 12% higher in Machine Direction (MD); and (iii) a maximum puncture force of at least about 4% higher, compared to that of a multilayer film having no more than about 80 wt% of the first polyethylene present in each of the outer layers but otherwise identical in terms of thickness, layer distribution, and total polyethylene amount of the film. These highlighted toughness-related properties of the multilayer film may contribute to counterbalancing loss of toughness in the laminate structure by removal of the polyamide substrate.

[0052] It has been surprisingly discovered that use of the multilayer film described herein as the sealant film of a laminate structure may release manufacturers of SUPs for liquid from the longstanding dependency on a polyamide substrate in addition to a polyester substrate without significantly compromising due toughness. Specifically, when a multilayer film prepared by two outer layers each comprising 100 wt% of the first polyethylene described herein (based on total weight of polymer in the outer layer) and a core layer comprising 100 wt% of the second polyethylene described herein (based on total weight of polymer in the core layer) is introduced into a laminate structure as a sealant film, drop test performance at a level similar or comparable to that obtained with the conventional laminate structure including two substrates, i.e., a polyester substrate and a polyamide substrate between the sealant film and the polyester substrate, can be achieved with only a single substrate of polyester. As a result, the inventive film can serve as a promising solution to help increase production efficiency and cost-effectiveness that have been long restricted by the currently available laminate structure for the SUP industry.

Methods for Making the Multilayer Film

[0053] 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 two outer layers, each comprising about 100 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, wherein the first polyethylene is an mPE having a density of about 0.910 to about 0.940 g/cm³, an MI, I2.16 of about 0.1 to about 15 g/10 min, an MWD of about 1.5 to about 5.5, and an MIR, I21.6 I2.16 of about 10 to about 25; (b) preparing a core layer between the two outer layers, the core layer comprising about 100 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 the second polyethylene is an mPE 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 (c) forming a film comprising the layers in steps (a) and (b). Preferably, the method further comprises after step (c) a step of laminating the film in step (c) to a substrate film. More preferably, the substrate film comprises one or more of biaxially oriented polyester, biaxially oriented polypropylene, and biaxially oriented polyamide. More preferably, the substrate film does not comprise polyamide.

[0054] 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.

[0055] 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 Jinming die with a 1.4 mm die gap, along with a Jinming 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.

[0056] 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 1.6 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 μιη 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.

[0057] 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.

[0058] 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. 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.

[0059] The 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 as previously described herein using any process known in the art, including solvent based adhesive lamination, solvent less adhesive lamination, extrusion lamination, heat lamination, etc.

EXAMPLES

[0060] The present invention, while not meant to be limited by, may be better understood by reference to the following examples and tables.

Example 1

[0061] Example 1 illustrates mechanical properties demonstrated by two inventive film samples (Samples 1 and la) in comparison with six comparative samples (Samples 2-4 and 2a- 4a) differing from the inventive samples in formulation of outer layers and one comparative sample (Samples 5) of commercially available film used for preparing SUPs. Polyethylene and additive products used in the samples include: EXCEED™ 1018LA mPE resin (density: 0.918 g/cm³, MI: 1.0 g/lOmin) (ExxonMobil Chemical Company, Houston, Texas, USA), ENABLE™ 20-05HE mPE resin (density: 0.920 g/cm³, MI: 0.5 g/lOmin) (ExxonMobil Chemical Company, Houston, Texas, USA), and ENABLE™ 35-05HH mPE resin (density: 0.935 g/cm³, MI: 0.5 g/lOmin) (ExxonMobil Chemical Company, Houston, Texas, USA); the POLYBATCH™ CE 505E slip agent (A. Schulman, Fairlawn, Ohio, USA), and the POLYWHITE™ B8750 masterbatch (A. Schulman, Fairlawn, Ohio, USA). Samples 1-4 and la-4a were prepared on Jinming coextrusion blown film line with a BUR of 2.5 with an A/Y/A structure at a layer thickness ratio of 1:2:1, all having a core layer formulated with 91.5 wt% of ENABLE™ 35-05HH mPE resin and 8.5 wt% of POLYWHITE™ B8750 masterbatch, based on total weight of the core layer. Outer layer formulations (based on total weight of the outer layer) and thickness of the film samples, accompanied by test results therefor, are depicted in Table 1.

Table 1: Outer layer formulations ( t%), thickness and mechanical properties for film samples of Example 1

Table 1 (continued)

[0062] Samples were conditioned at 23 °C + 2°C and 50% + 10% relative humidity for at least 40 hours prior to determination of all properties.

[0063] Dart impact was measured by a method following ASTM D1709 on a Dart Impact Tester Model C from Davenport Lloyd Instruments in which a pneumatically operated annular clamp is used to obtain a uniform flat specimen and the dart is automatically released by an electro-magnet as soon a sufficient air pressure is reached on the annular clamp. A dart with a 38.10 + 0.13mm diameter hemispherical head dropped from a height of 0.66 + 0.01 m was employed. Dart impact measures the energy causing a film to fail under specified conditions of impact of a freely-falling dart. This energy is expressed in terms of the weight (mass, g) of the dart falling from a specified height, which would result in 50% failure of tested samples. Samples have a minimum width of 20 cm and a recommended length of 10 m.

[0064] Elmendorf tear strength was measured in MD based on ASTM D1922-06a 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 tearing force in gram. 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.).

[0065] Puncture resistance was measured based on ASTM D5748, which is designed to provide load versus deformation response under biaxial deformation conditions at a constant relatively low test speed (change from 250 mm/min to 5 mm/min after reach pre-load (0.1N)).

Film samples were tested below the cross-head area with the 2.5kN load cell. The sample was about 550mm*900mm in size. Maximum Puncture force is the maximum load achieved by the film sample before the break point, expressed in (N).

[0066] As shown in Table 1, at a given or similar thickness, the inventive Samples 1 and la featuring layer compositions described herein can outperform the comparative samples in strengthening toughness-related properties, as demonstrated by dart impact, Elmendorf tear, and maximum puncture force, which may play a role in making up for toughness support for a laminate structure in absence of the polyamide substrate.

Example 2

[0067] Samples 1, la, 2, 2a, 4, and 4a in Example 1, along with another seven film samples, were laminated to either a single polyester substrate film or two substrate films made of polyamide and polyester in turn, to prepare laminate structures (Samples A-M) for comparison of drop test performance. In addition to those used in Example 1, polyethylene products used in the samples include: EXCEED™ 1012HA mPE resin (density: 0.912 g/cm³, MI: 1.0 g/lOmin) (ExxonMobil Chemical Company, Houston, Texas, USA), ExxonMobil™ LDPE LD 150BW LDPE resin (density: 0.923 g/cm³, MI: 0.75 g/lOmin) (ExxonMobil Chemical Company, Houston, Texas, USA), DOWLEX™ 2045.01G C₈-LLDPE resin (density: 0.922 g/cm³, MI: 1.0 g/lOmin, Ziegler-Natta catalyzed) (The Dow Chemical Company, Midland, Michigan, USA), and HANWHA™ LLDPE 4200 resin (density: 0.920 g/cm³, MI: 1.6 g/lOmin). Sealant films of all laminate samples except Sample E were prepared on Jinming coextrusion blown film line with a BUR of 2.5 with an A/Y/A structure at a layer thickness ratio of 1 :2: 1, all having a core layer formulated with 100 wt% of ENABLE™ 35-05HH mPE resin, based on total weight of polymer in the core layer. Drop test were conducted for all laminate samples per described herein. Outer layer (monolayer for Sample M) formulation (based on total weight of polymer in the outer layer), laminate structure including thickness of the sealant films, test results therefor, and average breakage rates calculated therefrom are demonstrated in Table 2.

[0068] It can be seen from Table 2 that the inventive Samples A and I formed with a single polyester substrate exceeded in drop test performance of a level close to or even equivalent to that achievable with the conventional laminate structure formed with two substrates, in contrast to those counterparts with the same single substrate but otherwise formulated in sealant films. By virtue of the particular sealant formulation specified herein, the inventive film allows for comparable toughness performance at a reduced manufacture cost.

[0069] 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: Outer layer (monolayer for Sample M) formulation (wt%), laminate structure with thickness, breakage rate for each batch, and average breakage rate calculated therefrom for laminate samples of Example 2

Table 2 (continued)

Claims

CLAIMS What is claimed is:

1. A multilayer film, comprising:

(a) two outer layers, each comprising about 100 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, wherein the first polyethylene is a metallocene polyethylene (mPE) having a density of about 0.910 to about 0.940 g/cm³, a melt index (MI), I2.16 of about 0.1 to about 15 g/10 min, a molecular weight distribution (MWD) of about 1.5 to about 5.5, and a melt index ratio (MIR), I21.6/I2.16 of about 10 to about 25; and

(b) a core layer between the two outer layers, the core layer comprising about 100 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 the second polyethylene is a metallocene polyethylene (mPE) 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;

wherein the multilayer film has an average breakage rate (EMC method) of about 0% to about 20% at 5°C and 24°C, when laminated to a polyester substrate film.

2. The multilayer film of claim 1, wherein the multilayer film has an average breakage rate (EMC method) of about 0% at 5°C and 24°C, when laminated to a polyester substrate film.

3. The multilayer film of claim 1 or 2, further comprising a substrate film comprising one or more of biaxially oriented polyester, biaxially oriented polypropylene, and biaxially oriented poly amide.

4. The multilayer film of claim 3, wherein the substrate film does not comprise polyamide.

5. The multilayer film of any of claims 1 to 4, wherein the multilayer film further has at least one of the following properties: (i) a dart impact of at least about 4% higher; (ii) an Elmendorf tear of at least about 12% higher in Machine Direction (MD); and (iii) a maximum puncture force of at least about 4% higher, compared to that of a multilayer film having no more than about 80 wt% of the first polyethylene present in each of the outer layers but otherwise identical in terms of thickness, layer distribution, and total polyethylene amount of the film.

6. The multilayer film of any of claims 1 to 5, wherein the two outer layers are identical.

7. The multilayer film of any of claims 1 to 6, wherein the thickness ratio between one of the outer layers and the core layer is about 1: 1 to about 1:4.

8. A laminate comprising the multilayer film of any of claims 1 to 7.

9. A stand-up pouch comprising the laminate of claim 8.

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

(a) preparing two outer layers, each comprising about 100 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, wherein the first polyethylene is a metallocene polyethylene (mPE) having a density of about 0.910 to about 0.940 g/cm³, a melt index (MI), I2.16 of about 0.1 to about 15 g/10 min, a molecular weight distribution (MWD) of about 1.5 to about 5.5, and a melt index ratio (MIR), I21.6/I2.16 of about 10 to about 25;

(b) preparing a core layer, the core layer comprising about 100 wt% of a second polyethylene derived from ethylene and one or more C₃ to C20 α-olefin comonomers, based on total weight of polymer in the core layer, wherein the second polyethylene is a metallocene polyethylene (mPE) 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

(c) forming a film comprising the layers in steps (a) and (b), wherein the core layer is between the two outer layers;

wherein the multilayer film has an average breakage rate (EMC method) of about 0% to about 20% at 5°C and 24°C, when laminated to a polyester substrate film.

11. The method of claim 10, further comprising after step (c) a step of laminating the film in step (c) to a substrate film.

12. The method of claim 11, wherein the substrate film comprises one or more of biaxially oriented polyester, biaxially oriented polypropylene, and biaxially oriented polyamide.

13. The method of claim 11, wherein the substrate film does not comprise polyamide.

14. The method of any of claims 10 to 13, wherein the multilayer film in step (c) is formed by blown extrusion, cast extrusion, co-extrusion, blow molding, casting, or extrusion blow molding.