CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 63/235,883 filed August 23, 2021, the entire disclosure of which is incorporated by reference herein.

TECHNICAL FIELD

[0002] The present disclosure relates to multilayer structures and more specifically, to multilayer structures comprising a machine direction oriented film.

BACKGROUND

[0003] While there is interest in the marketplace in machine direction oriented (MDO) polyethylene films, one limitation on the use of MDO polyethylene films is the significant loss of sealing performance following orientation relative to other films. A 20 °C to 25 °C increase in sealing temperatures is typical for MDO polyethylene films, relative to other films. MDO polyethylene films are also understood to have reduced temperature resistance relative to laminated films. This combination of factors results in a very narrow sealing window, and can make it challenging to manufacture articles from such MDO films where a heat sealing step is needed.

[0004] Accordingly, new structures are desired which can broaden of the range between sealing and shrinkage in the multilayer structure in a cost effective manner.

SUMMARY

[0005] Sealant layers should generally be capable of sealing at temperatures below the degradation temperatures of the other portions of a multilayer structure that is being sealed. For example, in some production lines, in which two films are sealed together by seal bars, the sealant layers of both films are in contact with each other, the seal bars contact and heat the outer layers of the films. The heat is transferred through the outer layers of the films to the inner sealant layers which seal to one another. Reduced sealing temperatures are desirable, since they enable reduced degradation (e.g., burning) of the other layers of the multilayer structure. Additionally, reduced sealing temperatures allow for more consistent sealing, since the sealing procedure can be run in a broader window between the degradation temperature of the fdm and a sealant layer’s seal initiation temperature. Embodiments of the present disclosure meet this need by providing an MDO multilayer fdm with a metal layer, a first layer extruded onto the metal layer, and a sealant layer in adhering contact with the first layer as described further herein.

[0006] According to the one embodiment of the present disclosure, a multilayer structure may comprise a machine direction oriented (MDO) multilayer film, a first layer, and a sealant layer. The MDO multilayer film may comprise (i) a metal layer and (ii) an inner layer in adhering contact with the metal layer. The inner layer may comprise ethylene vinyl alcohol; polyvinyl alcohol; or a blend of polyethylene, and an interpolymer of ethylene and methyl acrylate, ethyl acrylate, or carboxylic acid. The first layer may be extruded onto the metal layer of the MDO multilayer film. The first layer may comprise an interpolymer of ethylene and acrylic acid or methacrylic acid. The interpolymer may have a melt index (I2) of 5 to 20 g/10 minutes, an acid content of 1 to 10 weight percent and a melting temperature of 90 °C to 100 °C. The sealant layer may be in adhering contact with the first layer. The sealant layer may comprise a polyethylene having a melt index (I2) of 3 to 30 g/10 minutes and a heat seal initiation temperature of 95 °C or less.

[0007] Although the concepts of the present disclosure are described herein with primary reference to machine direction oriented films with metal layers, it is contemplated that the concepts will enjoy applicability to any multilayer films.

DETAILED DESCRIPTION

[0008] Reference will now be made in greater detail to various embodiments, which are examples of the claimed subject matter. It should be understood that the features of the multilayered structures described in the detailed description should not be understood as limiting on the claimed embodiments unless explicitly described as such.

[0009] According to some embodiments of the present disclosure, a multilayer structure may comprise a machine direction oriented (MDO) multilayer film, a first layer, and a sealant layer. The machine direction oriented (MDO) multilayer film may comprise (i) a metal layer and (ii) an inner layer in adhering contact with the metal layer. In some embodiments, the metal layer is a metallized layer. The inner layer may comprise ethylene vinyl alcohol; polyvinyl alcohol; or a blend of polyethylene and an interpolymer of ethylene and methyl acrylate, ethyl acrylate, or carboxylic acid. The first layer may be extruded onto the metal layer of the machine direction oriented multilayer film. The first layer may comprise an interpolymer of ethylene and acrylic acid or methacrylic acid. The interpolymer may have a melt index (I2) of 5 to 20 g/10 minutes, an acid content of 1 to 10 weight percent and a melting temperature of 90 °C to 100 °C. The sealant layer may be in adhering contact with the first layer. The sealant layer may comprise a polyethylene having a melt index (I2) of 3 to 30 g/10 minutes and a heat seal initiation temperature of 95 °C or less.

[0010] According to one or more embodiments, a multilayer structure may comprise a machine direction oriented film. As described herein, “machine direction oriented” films are those that are formed by uniaxially stretching of the film in the machine direction to improve physical and barrier properties. For example, the film may be heated and uniaxially stretched in the machine direction over a series of rollers. As used herein, the term “machine direction” means the length of a film in the direction in which it is produced. Machine direction oriented films may exhibit improved tensile properties as compared with those not subjected to the machine direction orientation procedure.

[0011] A “film,” as described herein, generally includes any continuous layer of polyolefin-including material, which generally has a large length to thickness ratio and width to thickness ratio. In one or more embodiments, a film may comprise one or more olefin-based polymers. The terms, “olefin- based polymer,” “olefinic polymer,” and “polyolefin,” as used herein, refer to a polymer that comprises, in polymerized form, a majority amount of olefin monomer, for example, ethylene or propylene (based on the weight of the polymer) and, optionally, may comprise one or more comonomers. The term "polymer" refers to a polymeric compound prepared by polymerizing monomers, whether of the same or a different type. The generic term polymer thus embraces the term "homopolymer," usually employed to refer to polymers prepared from only one type of monomer as well as "copolymer" which refers to polymers prepared from two or more different monomers. The films described herein may be a multilayer film, which contains more than one layer. [0012] As used herein, an “interpolymer” may refer to a polymer derived from more than one species of monomer. For example, an interpolymer may comprise 2, 3, 4, or more than 4 species of monomer. As used herein, a “terpolymer” may refer to a polymer derived from three species of monomer. The terpolymer may be characterized as a random interpolymer, a periodic interpolymer, a statistical interpolymer, or a block interpolymer. As used herein, a “random interpolymer” may refer to an interpolymer comprising multiple species of monomeric units distributed in a random sequence. As used herein, a “periodic interpolymer” may refer to an interpolymer comprising three or more species of monomeric units arranged in a repeating pattern. As used herein, a “statistical interpolymer” may refer to an interpolymer comprising two or more monomeric units with a distribution which follows a statistical rule. As used herein, a “block interpolymer” may refer to an interpolymer comprising two or more monomeric units and where the monomeric units cluster with similar monomeric units. For example, a block interpolymer may have a structure of the form AAAABBBCCC.

[0013] As described herein, "polyethylene" or an "ethylene-based polymer" shall mean polymers comprising greater than 50% by mole of units derived from ethylene monomer. This includes ethylene-based homopolymers, ethylene copolymers (meaning units derived from ethylene and an additional monomer), and ethylene interpolymer (meaning units derived from ethylene and at least one additional comonomer). These comonomers may include C3-C12 a-olefin comonomers, or may include polar comonomers. These polar comonomers may include but are not limited to those with carboxylic acid, acrylate, or acetate functionality, for example, methacrylic acid, acrylic acid, vinyl acetate, methyl acrylate, ethyl acrylate, isobutylacrylate, n-butylacrylate, glycidyl methacrylate, and monoethyl ester of maleic acid. Forms of polyethylene include, but are not limited to, Low Density Polyethylene (LDPE); Linear Low Density Polyethylene (LLDPE); Ultra Low Density Polyethylene (ULDPE); Very Low Density Polyethylene (VLDPE); single-site catalyzed Linear Low Density Polyethylene, including both linear and substantially linear low density resins (m-LLDPE); Medium Density Polyethylene (MDPE); and High Density Polyethylene (HDPE).

[0014] Additionally, as described herein, the term "LDPE" may also be referred to as "high pressure ethylene polymer" or "highly branched polyethylene" and is defined to mean that the polymer is partly or entirely homopolymerized or copolymerized in autoclave or tubular reactors at pressures above 14,500 psi (100 MPa) with the use of free-radical initiators, such as peroxides (see, for example, U.S. 4,599,392, which is hereby incorporated by reference). LDPE resins typically have a density in the range of 0.916 to 0.940 g/cm.

[0015] The term "LLDPE", as described herein, may include resins made using Ziegler-Natta catalyst systems as well as resin made using single-site catalysts, including, but not limited to, bis-metallocene catalysts (sometimes referred to as "m-LLDPE"), phosphinimine, and constrained geometry catalysts; and resin made using post-metallocene, molecular catalysts, including, but not limited to, bis(biphenylphenoxy) catalysts (also referred to as polyvalent aryloxyether catalysts). LLDPE includes linear, substantially linear, or heterogeneous ethylene-based copolymers or homopolymers. LLDPEs contain less long chain branching than LDPEs and include the substantially linear ethylene polymers, which are further defined in U.S. Patent No. 5,272,236; U.S. Patent No. 5,278,272; U.S. Patent No. 5,582,923; and U.S. Patent No. 5,733,155; the homogeneously branched ethylene polymers such as those in U.S. Patent No. 3,645,992; the heterogeneously branched ethylene polymers such as those prepared according to the process disclosed in U.S. Patent No. 4,076,698; and blends thereof (such as those disclosed in U.S. Patent No. 3,914,342 or U.S. Patent No. 5,854,045). The LLDPE resins can be made via gas-phase, solution-phase or slurry polymerization or any combination thereof, using any type of reactor or reactor configuration known in the art. The LLDPE resins can be made via gas-phase, solution-phase, or slurry polymerization or any combination thereof, using any type of reactor or reactor configuration known in the art.

[0016] The term “ULDPE” is defined as a polyethylene-based copolymer having a density in the range of 0.895 to 0.915 g/cc.

[0017] The term "MDPE" refers to polyethylenes having densities from 0.926 to 0.935 g/cc. "MDPE" is typically made using chromium or Ziegler-Natta catalysts or using single-site catalysts including, but not limited to, bis-metallocene catalysts and constrained geometry catalysts.

[0018] Additionally, as described herein, the term "HDPE" refers to polyethylenes having densities of about 0.940 g/cm or greater, which are generally prepared with Ziegler-Natta catalysts, chrome catalysts or even metallocene catalysts. [0019] A multilayer structure may comprise a MDO multilayer film, a first layer, and a sealant layer. As described herein, a “multilayer structure” means any structure having more than one layer. For example, the multilayer structure (for example, a film) may have two, three, four, five or more layers. A multilayer structure may be described as having the layers designated with letters. For example, a three layer structure having a core layer B, and two external layers A and C may be designated as A/B/C. Likewise, a structure having two core layers B and C and two external layers A and D would be designated A/B/C/D.

[0020] The MDO multilayer film may have a thickness of from 10 pm to 100 pm. For example, the MDO multilayer film may have a thickness of from 10 pm to 90 pm, from 10 pm to 75 pm, from 10 pm to 60 pm, from 10 pm to 45 pm, from 10 pm to 30 pm, from 20 pm to 100 pm, from 20 pm to 90 pm, from 20 pm to 75 pm, from 20 pm to 60 pm _a from 20 pm to 45 pm, from 20 pm to 30 pm, or any subset thereof.

[0021] According to one or more embodiments, the machine direction oriented film may have a melting point of less than or equal to 150 °C, such as less than or equal to 145 °C, or even less than or equal to 140 °C. This is in contrast to other films, which may have greater melting points. For example, polypropylene films may have melting points of greater than 150 °C, and polyethylene terephthalate films may have melting points of greater than 250 °C.

[0022] The MDO multilayer film may comprise (i) a metal layer and (ii) an inner layer in adhering contact with the metal layer. The term “in adhering contact” and like terms mean that one facial surface of one layer and one facial surface of another layer are in touching and binding contact to one another such that one layer cannot be removed from the other layer without damage to the interlayer surfaces (i.e., the in-contact facial surfaces) of both layers.

[0023] The metal layer may be a metallized layer applied to the outer layer of the MDO multilayer film using vacuum metallization. Vacuum metallization is a well-known technique for depositing metals in which a metal source is evaporated in a vacuum environment, and the metal vapor condenses on the surface of the film to form a thin layer as the film passes through the vacuum chamber. [0024] The metals that can be deposited to form the metallized layer include Al, Zn, Au, Ag, Cu, Ni, Cr, Ge, Se, Ti, Sn, or oxides thereof. In some embodiments, the metallized layer is formed from aluminum or aluminum oxide (AI2O3). The metallized layer may also include the metalloid silicon or oxides thereof. According to some embodiments, the metallized layer may comprise aluminum, silicon, or oxides thereof

[0025] The metallized layer may advantageously provide a good barrier to oxygen and water vapor. The combination of MDO multilayer fdm with the metallized layer deposited on the specified outer surface can provide a synergistic combination of both mechanical and barrier properties.

[0026] In some embodiments, the metallized layer may be a decorative layer included to add gloss to a flexible package. The skilled person would be familiar with multiple applicable metallization techniques. These may include but are not limited to physical vapor deposition or vacuum metallization. While various thicknesses are contemplated, the metallized layer may in one or more embodiments have a thickness of less than 100 nanometers, or from 10 to 80 nanometers, or from 20 to 60 nanometers.

[0027] In some embodiments, the metal layer may be a foil layer adhered to the rest of the MDO multilayer fdm with a tie layer. In embodiments where the metal layer is a foil layer, the foil layer may have a thickness of from 6 to 15 pm, from 6 to 12 pm, from 10 to 15 pm, from 8 to 12 pm, or any subset thereof.

[0028] In embodiments where a tie layer is present, he tie layer may comprise a maleated polyethylene, a copolymer of ethylene and carboxylic acid, or a combination thereof. As used herein, a “maleated” substance is one which comprises a salt or ester of maleic acid.

[0029] Referring again to the MDO multilayer fdm, the MDO multilayer fdm may have five layers and the structure A/B/C/D/E where layer A is the inner layer and the metallized layer is on the surface of layer A. Layer A may have a thickness of from 10 % to 20 % of the total thickness of the MDO multilayer fdm. Layer B may have a thickness of from 10 % to 20 % of the total thickness of the MDO multilayer fdm. Layer C may have a thickness of from 20 % to 40 % of the total thickness of the MDO multilayer fdm. Layer D may have a thickness of from 10 % to 30 % of the total thickness of the MDO multilayer film. Layer E may have a thickness of from 10 % to 30 % of the total thickness of the MDO multilayer film. The layers may be extruded one atop the other. The MDO multilayer film may have one or more polyethylene layers. For example, the MDO multilayer film may have 2, 3, 4, or 5 polyethylene layers.

[0030] As stated previously, Layer A, which is the inner layer, comprises at least one polymer having at least one polar monomer. For example, the inner layer (Layer A) may comprise one or more of ethylene vinyl-alcohol (EVOH), polyvinyl-alcohol (PVOH), polyethylene resin, a mixture of a polyethylene resin and an interpolymer of ethylene and acrylate, or a mixture of a polyethylene resin and an interpolymer of ethylene and a carboxylic acid.

[0031] For inner layer embodiments including EVOH, the EVOH may have a density from 0.90 g/cm ³ to 1.40 g/cm ³ , or from 0.95 g/cm ³ to 1.20 g/cm ³ , or any subset thereof. Layer A may have a melt index of from 0.70 g/10 min to 1.9 g/10 min. The EVOH may have a melt index of from 1.00 g/10 min to 3.00 g/10 min, or from 1.00 g/10 min to 2.50 g/10 min, or from 1.50 g/10 min to 2.00 g/10 min, or any subset thereof. The EVOH may have a melting temperature of from 120 °C to 250 °C, or 150 °C to 200, or any subset thereof. Suitable commercial examples of the EVOH may include the Eval E171B, F171B, and J171B commercial grades available from EVAL Europe NV.

[0032] For inner layer embodiments including polyethylene resin, the polyethylene may be an ethylene-a-olefin copolymer having a density from 0.940 g/cm ³ to 0.975 g/cm ³ , or from 0.945 g/cm ³ to 0.970 g/cm ³ , or from 0.950 g/cm ³ to 0.965 g/cm ³ , or any subset thereof. The ethylene-a-olefin copolymer may have a melt index of from 0.5 g/10 min to 3.00 g/10 min, or from 0.75 g/10 min to 2.00 g/10 min, or any subset thereof. The ethylene-a-olefin copolymer may be an LLDPE. Suitable commercial LLDPE resins may include DOWLEX™ 2750ST from Dow Inc., Midland, ML Additionally, suitable commercial examples may include the ELITE™ 5960G1 enhanced polyethylene from Dow Inc., Midland, ML

[0033] For inner layer embodiments including interpolymer of ethylene and acrylate, the acrylate may comprise any suitable C2-C12 acrylate, for example, methyl acrylate, ethyl acrylate, isobutylacrylate, n-butyl acrylate, and glycidyl methacrylate. In one embodiment, the acrylate comprises n-butyl acrylate. In terms of monomer amount, the ethylene-acrylate comonomer may comprise 10 to 40% by wt. of acrylate, or from 15 to 35 wt.%, or from 20 to 30 wt.% acrylate with the balance comprising ethylene monomer. The interpolymer of ethylene and acrylate may have a density from 0.910 g/cm ³ to 0.955 g/cm ³ , or from 0.920 g/cm ³ to 0.950 g/cm ³ , or from 0.925 g/cm ³ to 0.945 g/cm ³ , or any subset thereof. The interpolymer of ethylene and acrylate may have a melt index of from 0.5 g/10 min to 5.00 g/10 min, or from 1.00 g/10 min to 4.50 g/10 min, or from 1.50 g/10 min to 4.00 g/10 min, or any subset thereof. Suitable commercial examples may include ELVALOY™ AC grades 1224, 3117, and 3427 from Dow Inc., Midland, MI.

[0034] Layer B may also comprise one or more polyethylenes. The polyethylene(s) may have a density of from 0.910 g/cm ³ to 0.950 g/cm ³ , or from 0.915 to 0.945 g/cm ³ . In some embodiments, there may be a mixture of lesser density polyethylene (from 0.910 g/cm ³ to 0.920 g/cm ³ ) and greater density polyethylene (from 0.930 g/cm ³ to 0.945 g/cm ³ ). The polyethylene(s) may have a melt index of from 0.25 g/10 min to 2.0 g/10 min, or from 0.50 g/10 min to 1.5 g/10 min, or from 0.75 g/10 min to 1.25 g/10 min, or any subset thereof. The polyethylene(s) in Layer B may have a melting temperature of from 100 °C to 140 °C, or from 110 °C to 130 °C, or from 115 °C to 130 °C, or any subset thereof. Suitable commercial examples may include the ELITE™ 5400GS and 5940ST enhanced polyethylenes from Dow Inc., Midland, MI, which may be used individually or in a blend.

[0035] In other embodiments, layer B may include a tie layer comprising ethylene and acid copolymers. In one or more embodiments, the tie layers may include an anhydride-grafted ethylene/alpha-olefm interpolymer. The term, “anhydride-grafted ethylene/alpha-olefm interpolymer,” as used herein, refers to an ethylene/alpha-olefm interpolymer that comprises at least one anhydride group linked by a covalent bond. The anhydride-grafted ethylene/alpha-olefm interpolymer may be an ethylene-based polymer with an anhydride grafting monomer grafted thereto. Suitable ethylene-based polymers for the low-melt viscosity maleic anhydride-grafted polyolefin include, without limitation, polyethylene homopolymers and copolymers with a-olefins, copolymers of ethylene and vinyl acetate, and copolymers of ethylene and one or more alkyl (meth) acrylates. In specific embodiments, the anhydride-grafted ethylene/alpha-olefm interpolymer may comprise a maleic anhydride-grafted linear low density polyethylene (LLDPE). [0036] In one or more embodiments, the anhydride-grafted ethylene/alpha-olefm interpolymer comprises up to 10 wt.%, up to 5 wt.%, or from 0.1 to 4 wt.% of the maleic anhydride grafting monomer, based on the total weight of the anhydride-grafted ethylene/alpha-olefm interpolymer.

[0037] Examples of anhydride grafting moieties may include but are not limited to, maleic anhydride, citraconic anhydride, 2-methyl maleic anhydride, 2-chloromaleic anhydride, 2,3 -dimethylmaleic anhydride, bicyclo[2,2,l]-5-heptene-2,3-dicarboxylic anhydride and 4-methyl-4-cyclohexene-l,2- dicarboxylic anhydride, bicyclo(2.2.2)oct-5-ene-2,3-dicarboxylic acid anhydride, lo- octahydronaphthalene-2,3-dicarboxylic acid anhydride, 2-oxa-l,3-diketospiro(4.4)non-7-ene, bicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride, tetrahydrophtalic anhydride, norbom-5- ene-2, 3 -dicarboxylic acid anhydride, nadic anhydride, methyl nadic anhydride, himic anhydride, methyl himic anhydride, and x-methyl-bi-cyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride. In one embodiment, the anhydride grafting moiety comprises maleic anhydride.

[0038] In further embodiments, the anhydride-grafted ethylene/alpha-olefm interpolymer has a density from 0.890 g/cm ³ to 0.940 g/cm ³ , as measured according to ASTM Method No. D792-91. Other density ranges may be from 0.900 g/cm ³ to 0.930 g/cm ³ , or from 0.905 g/cm ³ to 0.915 g/cm ³ . In one or more embodiments, the anhydride-grafted ethylene/alpha-olefm interpolymer may have a melt index (I2) of 0.5 g/ 10 min to 3 g/ 10 min, or from 1 g/ 10 min to 2 g/ 10 min, or from 1.5 g/ 10 min to 2.0 g/10 min as determined in accordance with ASTM method D1238 at 190°C and 2.16 kg. Suitable commercial examples of the anhydride-grafted ethylene/alpha-olefm interpolymer may include BYNEL™ 41E687B from Dow Inc., Midland, MI.

[0039] Layers C and D may also comprise one or more polyethylenes. Like layer B, the polyethylene(s) may have a density of from 0.910 g/cm ³ to 0.950 g/cm ³ , or from 0.915 to 0.945 g/cm ³ . In some embodiments, there may be a mixture of lesser density polyethylene (from 0.910 g/cm ³ to 0.920 g/cm ³ ) and greater density polyethylene (from 0.930 g/cm ³ to 0.945 g/cm ³ ). The polyethylene(s) may have a melt index of from 0.25 g/10 min to 2.0 g/10 min, or from 0.50 g/10 min to 1.5 g/10 min, or from 0.75 g/10 min to 1.25 g/10 min, or any subset thereof. The polyethylene(s) in Layer B may have a melting temperature of from 100 °C to 140 °C, or from 110 °C to 130 °C, or from 115 °C to 130 °C, or any subset thereof. Suitable commercial examples may include the ELITE™ 5400GS and 5940ST enhanced polyethylenes from Dow Inc., Midland, MI, which may be used individually or in a blend.

[0040] Layer E may also comprise one or more polyethylene resins. The polyethylene(s) may be an ethylene-a-olefin copolymer having a density from 0.940 g/cm ³ to 0.975 g/cm ³ , or from 0.945 g/cm ³ to 0.970 g/cm ³ , or from 0.950 g/cm ³ to 0.965 g/cm ³ , or any subset thereof. The ethylene-a-olefin copolymer may have a melt index of from 0.5 g/10 min to 3.00 g/10 min, from 0.75 g/10 min to 2.00 g/10 min, or any subset thereof. The ethylene-a-olefin copolymer may be an LLDPE. Suitable commercial LLDPE resins may include DOWLEX™ 2750ST from Dow Inc., Midland, ML Additionally, suitable commercial examples may include the ELITE™ 5960G1 enhanced polyethylene from Dow Inc., Midland, ML

[0041] Referring again to the first layer as described above, the first layer may be extrusion coated onto the metallized layer of the machine direction oriented multilayer film. As described herein, extruding a first layer may include forming the first layer through a die to form the desired layer thickness and other physical characteristics. Polymer blends of the disclosure can be prepared by melt blending the prescribed amounts of the components with a twin screw extruder before feeding into an extrusion coater (or other equipment) for film fabrication. Such polymer blends can also be prepared by tumble blending the prescribed amounts of the components before feeding into the extrusion coater (or other equipment) for film fabrication. In some embodiments, polymer blends can be in the form of pellets. For example, the individual components can be melt blended and then formed into pellets using a twin screw extruder or other techniques known to those of skill in the art based on the teachings herein. In some embodiments, a polymer blend can include the combination of a compounded pellet and additional polymer that is tumble blended before feeding into the extrusion coater.

[0042] The first layer may have been extruded onto the MDO multilayer film at a loading of from 2 grams per square meter (gsm) to 16 gsm. For example, the first layer may have a loading of from 2 gsm to 12 gsm, 2 gsm to 8 gsm, 2 gsm to 6 gsm, 4 gsm to 16 gsm, 4 gsm to 12 gsm, 4 gsm to 8 gsm, or any subset thereof. [0043] The interpolymer of the first layer may comprise from 50 wt. % to 98 wt. % ethylene monomer. For example, the interpolymer of the first layer may comprise from 60 wt. % to 98 wt. %, from 70 wt. % to 98 wt. %, from 80 wt. % to 98 wt. %, from 90 wt. % to 98 wt. %, from 50 wt. % to 90 wt. %, from 50 wt. % to 80 wt. %, 50 wt. % to 70 wt. %, from 50 wt. % to 60 wt. %, from 60 wt. % to 90 wt. %, from 70 wt. % to 80 wt. %, or any subset thereof, of ethylene.

[0044] The first layer may comprise an interpolymer of ethylene and acrylic acid or methacrylic acid.

[0045] The interpolymer of the first layer may have a melt index (I2) of 5 to 20 g/10 minutes. For example, the interpolymer of the first layer may have an I2 of 5 to 18 g/10 minutes, 8 to 20 g/10 minutes, 8 to 18 g/10 minutes, 5 to 15 g/10 minutes, 12 to 20 g/10 minutes, 12 to 15 g/10 minutes, or any subset thereof. As used herein, “melt index” (I2) is a measure of melt flow rate of a polymer as measured by ASTM DI 238 at a temperature of 190 °C and a 2.16 kg load. “Melt index” may also be referred to herein as “I2” and “melt flow rate.”

[0046] The interpolymer of the first layer may have an acid content of from 1 to 10 weight percent (wt. %). As used herein, the “acid content” refers to the quantity of acrylic acid relative to the total weight of the interpolymer. For example, the interpolymer of the first layer may have an acid content of from 1 wt. % to 9 wt. %, from 1 wt. % to 8 wt. %, from 1 wt. % to 6 wt. %, from 2 wt. % to 10 wt. %, from 3 wt. % to 10 wt. %, from 4 wt. % to 10 wt. %, from 2 wt. % to 8 wt. %, from 3 wt. % to 7 wt. %, from 4 wt. % to 6 wt. %, or any subset thereof.

[0047] The interpolymer of the first layer may have a melting temperature of from 90 °C to 100 °C. For example, the interpolymer of the first layer may have a melting temperature of from 90 °C to 98 °C, from 90 °C to 96 °C, from 90 °C to 94 °C, from 90 °C to 92 °C, from 92 °C to 98 °C, from 92 °C to 96 °C, from 92 °C to 94 °C, from 94 °C to 98 °C, from 94 °C to 96 °C, from 96 °C to 98 °C, or any subset thereof.

[0048] The interpolymer of the first layer may be a terpolymer of ethylene; acrylic acid or methacrylic acid; and alkyl acrylate. For example, the interpolymer of the first layer may be a terpolymer of ethylene, acryclic acid, and alkyl acrylate or the interpolymer of the first layer may be a terpolymer of ethylene, methacrylic acid, and alkyl acrylate. In one or more embodiments of the present disclosure, the interpolymer may be a member of the NUCREL™ line available from Dow Inc, Midland, MI.

[0049] The multilayer structure may comprise a sealant layer. The sealant layer may generally be heated and pressed to seal two multilayer structures to one another by their sealant layers. The sealant layer may be in adhering contact with the first layer.

[0050] In one or more embodiments, the sealant layer may be in adhering contact with the first layer. In one or more embodiments, the sealant layer may be extruded onto the first layer. As described herein, extruding a sealant layer may include forming the sealant layer through a die to form the desired layer thickness and other physical characteristics.

[0051] The sealant layer may have been extruded onto the first layer at a loading of from 10 grams gsm to 30 gsm. For example, the sealant layer may have a loading of from 10 gsm to 26 gsm, 10 gsm to 24 gsm, 10 gsm to 21 gsm, 14 gsm to 30 gsm, 14 gsm to 26 gsm, 14 gsm to 24 gsm, 14 gsm to 21 gsm, 18 gsm to 30 gsm, 18 gsm to 24 gsm, 18 gsm to 21 gsm, 18 gsm to 20 gsm, or any subset thereof.

[0052] The sealant layer may comprise 60 wt. % to 85 wt. % of at least one polyethylene. For example, the sealant layer may comprise from 60 wt. % to 80 wt. %, from 60 wt. % to 75 wt. %, from 60 wt. % to 70 wt. %, from 65 wt. % to 85 wt. %, from 70 wt. %, to 85 wt. %, from 75 wt. % to 85 wt. %, from 65 wt. % to 80 wt. %, from 70 wt. % to 75 wt. %, or any subset thereof, of at least one polyethylene.

[0053] The sealant layer may comprise a polyethylene having a density of from 0.870 grams per cubic centimeter (g/cc) to 0.911 g/cc. For example, the sealant layer may comprise a polyethylene having a density of from 0.870 g/cc to 0.901 g/cc, from 0.870 g/cc to 0.891 g/cc, from 0.870 g/cc to 0.881 g/cc, from 0.880 g/cc to 0.911 g/cc, from 0.890 g/cc to 0.911 g/cc, from 0.901 g/cc to 0.911 g/cc, from 0.880 g/cc to 0.901 g/cc, or any subset thereof.

[0054] The sealant layer may comprise a polyethylene having a melt index (I2) of at least 3 g/10 minutes. For example, the sealant layer may comprise a polyethylene having an I2 of at least 4 g/10 minutes, at least 5 g/10 minutes, at least 7.5 g/10 minutes, at least 10 g/10 minutes, at least 15 g/10 minutes, at least 20 g/10 minutes, at least 25 g/10 minutes, or even at least 30 g/10 minutes.

[0055] The sealant layer may comprise a polyethylene having a melt index (I2) of 3 to 30 g/10 minutes. For example, the sealant layer may comprise a polyethylene having a melt index (I2) of 3 to 25 g/10 minutes, 3 to 15 g/10 minutes, 3 to 10 g/10 minutes, 8 to 30 g/10 minutes, 8 to 20 g/10 minutes, 16 to 30 g/10 minutes, 16 to 25 g/10 minutes, or any subset thereof. As used herein, melt index (I2) is a measure of melt flow rate of a polymer as measured by ASTM DI 238 at a temperature of 190 °C and a 2.16 kg load.

[0056] The sealant layer may comprise a polyethylene having a heat seal initiation temperature of 95 °C or less. For example, the sealant layer may comprise a polyethylene having a heat seal initiation temperature of 92.5 °C or less, 90 °C or less, 87.5 °C or less, 85 °C or less, 82.5 °C or less, 80 °C or less, 75 °C or less, or even 70 °C or less.

[0057] In one or more embodiments, the sealant layer may comprise a low density polyethylene.

[0058] According to one or more embodiments, the sealant layer may comprise from 15 to 40 percent by weight (wt. %) of a low density polyethylene based on the total weight of the sealant layer. For example, the sealant layer may comprise from 15 wt. % to 20 wt. %, from 20 wt. % to 25 wt. %, from 25 wt. % to 30 wt. %, from 30 wt. % to 35 wt. %, from 35 wt. % to 40 wt. %, or combinations of any of these ranges, of a low density polyethylene based on the total weight of the sealant layer. In additional embodiments, the sealant layer may comprise from 15 wt. % to 30 wt. % of a low density polyethylene based on the total weight of the sealant layer.

[0059] In one or more embodiments, the low density polyethylene of the sealant layer may have a melt index (I2) of from 0.9 g/10 minutes to 3.5 g/10 minutes. For example, the low density polyethylene of the sealant layer may have a melt index of from 0.9 g/10 minutes to 3.0 g/10 minutes, from 0.9 g/10 minutes to 2.8 g/10 minutes, from 0.9 g/10 minutes to 2.5 g/10 minutes, from 1.1 g/10 minutes to 3.5 g/10 minutes, from 1.4 g/10 minutes to 3.5 g/10 minutes, from 1.1 g/10 minutes to 3.0 g/10 minutes, from 1.3 g/10 minutes to 2.5 g/10 minutes, or any subset thereof. [0060] In one or more embodiments, the low density polyethylene of the sealant layer may be chosen from DOW™ LDPE 770G (commercially available from Dow Inc, Midland, MI), which has a density of 0.918 g/cm ³ , a melt index of 2.3 g/10 minutes, and a melting point of 110 °C, or AGILITY™ EC 7220 Performance LDPE (commercially available from Dow Inc, Midland, MI), which has a density of 0.918 g/cm ³ and a melt index of 1.5 g/10 minutes. However, other LDPE’s are contemplated for use in the sealant layer, and embodiments described herein are not limited to those including these polymers.

[0061] The sealant layer may also comprise a propylene-based plastomer. As described herein, a “propylene-based plastomer” refers to a plastomer that includes greater than 50% by mole of units derived from propylene monomer. This includes propylene-based homopolymers or interpolymers (meaning units derived from two or more monomers). Plastomer s may generally be understood as polymeric materials which combine qualities of elastomers and thermoplastics.

[0062] According to one or more embodiments, the sealant layer may comprise from 60 wt. % to 85 wt. % of a propylene-based plastomer based on the total weight of the sealant layer. For example, the sealant layer may comprise from 60 wt. % to 65 wt. %, from 65 wt. % to 70 wt. %, from 70 wt. % to 75 wt. %, from 75 wt. % to 80 wt. %, from 80 wt. % to 85 wt. %, or any combination of these ranges, of a propylene-based plastomer based on the total weight of the sealant layer.

[0063] According to one or more embodiments, the propylene-based plastomer may have a density of 0.890 g/cm ³ or less. For example, the propylene-based plastomer may have a density of from 0.860 g/cm ³ to 0.890 g/cm ³ , such as from 0.860 g/cm ³ to 0.865 g/cm ³ , from 0.865 g/cm ³ to 0.870 g/cm ³ , from 0.870 g/cm ³ to 0.875 g/cm ³ , from 0.875 g/cm ³ to 0.880 g/cm ³ , from 0.880 g/cm ³ to 0.885 g/cm ³ , from 0.885 g/cm ³ to 0.890 g/cm ³ , or any combination of these ranges.

[0064] In one or more embodiments, the propylene-based plastomer may have a melt index (I2) (at 230 °C and 2.16 kg) of at least 8 g/10 minutes. For example, the propylene-based plastomer may have a melt flow rate (at 230 °C and 2.16 kg) of from 8 g/10 minutes to 35 g/10 minutes, such as from 8 g/10 minutes to 15 g/10 minutes, from 15 g/10 minutes to 20 g/10 minutes, from 20 g/10 minutes to 25 g/10 minutes, from 25 g/10 minutes to 30 g/10 minutes, from 30 g/10 minutes to 35 g/10 minutes, or any combination of these ranges. Unless otherwise specified, as described herein, the melt index (I2) is measured in accordance with ASTM D 1238-10, Condition 230 °C/2.16 kg, and is reported in grams eluted per 10 minutes.

[0065] In one or more embodiments, the propylene-based plastomer may have a melting point of from 70 °C to 100 °C. For example, the propylene-based plastomer may have a melting point of from 70 °C to 80 °C, from 80 °C to 90 °C, from 90 °C to 100 °C, or any combination of these ranges.

[0066] In one or more embodiments, the propylene-based plastomer may be an interpolymer comprising units of propylene and ethylene. According to one or more embodiments, the propylene- based plastomer may have an ethylene content of from 2 mol. % to 12 mol. %. For example, the propylene-based plastomer may have an ethylene content of from 2 mol. % to 4 mol. %, from 4 mol. % to 6 mol. %, from 6 mol. % to 8 mol. %, from 8 mol. % to 10 mol. %, from 10 mol. % to 12 mol. %, or any combination of these ranges.

[0067] In one or more embodiments, the propylene-based plastomer may be VERSIFY™ 4200 Plastomer (commercially available from Dow Inc, Midland, MI), which has a density of 0.876 g/cm ³ , melt index of 25 g/10 minutes, and melting point of 84 °C. However, other propylene-based plastomers are contemplated for use in the sealant layer, and embodiments described herein are not limited to those including these polymers.

[0068] According to one or more embodiments, the sealant layer may comprise a combination of a low density polyethylene and a propylene-based plastomer. For example, the sealant layer may comprise from 15 wt. % to 40 wt. % of a low density polyethylene and from 60 wt. % to 85 wt. % of a propylene-based plastomer based on the total weight of the sealant layer.

[0069] Embodiments of the present disclosure also relate to articles, such as packages, formed from the multilayer structures of the present disclosure. Such packages can be formed from any of the multilayer structures of the present disclosure described herein. Examples of such articles can include flexible packages, pouches, stand-up pouches, and pre-made packages or pouches. According to specific embodiments of the present disclosure, the article may be a pouch. [0070] The pouch may have a length of at least 25 mm. For example, the pouch may have a length of at least 50 mm, at least 75 mm, at least 100 mm, at least 150 mm, or at least 200 mm. The pouch may have a width of at least 25 mm. For example, the pouch may have a width of at least 50 mm, at least 75 mm, at least 100 mm, at least 150 mm, or at least 200 mm.

[0071] The pouch may have a volume of at least 25 milliliters (ml). For example, the pouch may have a volume of at least 50 ml, at least 75 ml, at least 100 ml, at least 150 ml, at least 200 ml, at least 250 ml, at least 300 ml, at least 400 ml, at least 500 ml, at least 750 ml, at least 1000 ml, at least 1500 ml, at least 2000 ml, or at least 2500 ml.

[0072] The pouch may have a sealed layer. The sealed layer may be the spot where two layers of pouch were fused together under heat and pressure. The sealed layer may have a peel strength of at least 3 newtons per 15 mm width of seal (N/15 mm). For example, the sealed layer may have a peel strength of at least 4 N/15 mm, at least 5 N/15 mm, or at least 6 N/15 mm. The seal strength may be measured according to ASTM D903.

EXAMPLES

[0073] A sample pouch was prepared with from an MDO multilayer fdm, a first layer extruded onto the MDO multilayer film, and a sealant layer in adhering contact with the first layer.

[0074] The MDO multilayer film had a total thickness of 25 pm. The film was arranged in the order A/B/C/D/E. Each of the respective layers was 15 %/l 5 %/30 %/20 %/20 % of the thickness of the MDO multilayer film.

[0075] Table 1 : Compositions of the Multilayer Film

[0076] Layer A was 15 % of the total thickness of the MDO multilayer film and comprised EVOH Eval JI 71. Layer B was 15 % of the total thickness of the MDO multilayer film and comprised Bynel 41E687. Layer C was 30 % of the total thickness of the multilayer film and comprised 80% Elite 5940ST +20% ELITE™ 5400GS. Layer D was 20 % of the total thickness of the MDO multilayer film and comprised ELITE™ 5940ST. Layer E was 20 % of the total thickness of the MDO multilayer film and comprised ELITE™ 5960G1. [0077] The MDO film described above to be used as metallization substrate was prepared on a Hosokawa-Alpine 5-Layer blown film line with screw settings of 65/65/90/65/65 mm respectively, and a die head of 400 mm diameter. The primary film before MDO had a thickness of 130 pm. The take off speed was 16.1 meters per minute (m/min). The output was 370 kg/h. The Blow-Up Ratio (BUR) was 3.0.

[0078] The temperature profile for each extruder was as follows: A =225 °C in all zones; B = 200 °C in all zones; C = 200 °C in all zones; D = 220 °C in all zones; E = 225 °C in all zones; and die head = 228 °C in all zones.

[0079] The formed film was then subjected to MDO stretching to form the MDO film. The stretching step was carried out in a Hosokawa-Alpine MDO unit equipped with four preheaters and four annealing and cooling rollers. The speeds and ratios in relevant parts of the system are: intake speed of 16.1 m/min; exit speed of 87.2; and an overall stretching ratio of 5.43. The relevant temperatures are: preheat 1 = 105 °C; preheat 2 = 115 °C; stretching 1 = 115 °C; stretching 2 = 115 °C; annealing = 110 °C; and cooling = 75 °C.

[0080] The MDO substrate film was further metallized by vacuum deposition using a K5 Expert System by Bobst. The metallized layer, which had a thickness of 30 nm, was deposited on the surface of Layer A, opposite to the surface of Layer A which faces Layer B.

[0081] The MDO substrate film was placed in a vacuum chamber at pressure of 10' ⁴ Torr. An aluminum wire was placed in the vacuum chamber and heated to 1400 °C. The MDO substrate film was then passed through the vacuum chamber at a rate of 500 m/min. The final coated thickness of the aluminum layer was ca. 30nm.

[0082] The first layer was then extruded onto the MDO multilayer film and comprised 6 grams per square meter (gsm) NUCREL™ 3990. The polymer was coated using an ErWePa extrusion coating line using a melt temperature of 285 °C and a line speed of 100 m/min and an air gap of 250 mm. All other conditions were typical of this well-known processing technique. The first layer was in direct contact with layer E of the MDO film. [0083] The sealant layer was extruded onto the first layer and comprised 19 gsm of a blend comprising 80 wt. % of AFFINITY™ PL1280 (Dow Inc.) and 20 wt. % of AGILITY™ EC7220. Processing conditions and machine setup is the same of the layer described above. The total thickness of the first layer and the sealant layer was 25 pm.

EXAMPLE 1 : POUCHES

[0084] The multilayer structure, including the MDO multilayer film, first layer, and sealant layer, was formed into pouches. The pouches were heat sealed at a cross seal temperature of 110 °C, a long seal temperature of 120 °C, and a dwell time of 300 milliseconds (ms). The total thickness of the multilayer film was 50 pm. The pouches were sealed at a speed of 60 pouches per minute ppm and each had a length of 240 millimeters (mm). The pouches were shown to be hermetically sealed when tested on a Bosch VFF sealing line and was deemed to have a good visual appearance.

EXAMPLE 2: HOT TACK

[0085] Additionally, the multilayer film was tested for hot tack strength. The operating conditions were as follows: the seal pressure was 0.5 N/mm ² , the seal time was 0.5 sec., the cooling time was 0.2 sec., the peel speed was 200 mm/sec., and the sample width was 15 mm. The results are given as follows in Table 2. The hot tack present at lower temperatures, such as 100 °C demonstrates that the present multilayer film begins heat seal initiation at lower temperatures.

[0086] Table 2

TEST METHODS

[0087] Unless otherwise specified, the following testing methods are utilized to measure the respective properties shown below:

[0088] Density

[0089] Samples for density measurement should be prepared according to ASTM D4703. Measurements should be made, according to ASTM D792, Method B, within one hour of sample pressing.

[0090] Melting Point

[0091] Melting Point (Tm) should be measured using Differential Scanning Calorimetry (DSC). Differential Scanning Calorimetry (DSC) may be measured on a DSC, such as a TA Instruments QI 000 DSC equipped with an RCS cooling accessory and an auto sampler. The melting point (Tm) of the samples should be measured according to ASTM D3418.

[0092] Heat Seal Measurements

[0093] Heat seal measurements on the film should be performed on a commercial tensile testing machine according to ASTM F-88 (Technique A). The heat seal test is a gauge of the strength of seals (seal strength) in flexible barrier materials. It does this by measuring the force required to separate a test strip of material containing the seal and identifies the mode of specimen failure. Seal strength is relevant to the opening force and package integrity. Prior to cutting, the films are conditioned for a minimum of 40 hours at 23°C (+ 2°C) and 50% (+ 5%) R.H. (relative humidity) per ASTM D-618 (procedure A). Sheets are then cut from the three-layer coextruded laminated film in the machine direction to a length of approximately 11 inches and a width of approximately 8.5 inches. The sheets are heat sealed across the machine direction on a Brugger HSG-C sealer over a range of temperatures under the following conditions: Sealing Pressure, or dwell force: 0.138 N/mm ² (20 psi) and dwell times of 0.3 s and 0.5 s.

[0094] The seal may be performed in a Brugger HSG-C sealer with 0.5 seconds dwell time at 210N seal bar pressure. The sealed specimen may be tested in an Instron Tensiomer at 10 in/min (4.2 mm/sec or 250 mm/min).

[0095] Hot Tack

[0096] “Hot tack strength" and like terms mean the strength of heat seals formed between thermoplastic surfaces of flexible webs, immediately after a seal has been made and before it cools to ambient temperature. In form-fdl operations, sealed areas of packages are frequently subject to disruptive forces while still hot. If the hot seals have inadequate resistance to these forces, breakage can occur during the packaging process. Hot tack strength, also known as hot seal strength, is a measure to characterize and rank materials in their ability to perform in commercial applications where this quality is critical. Hot tack strength can be measured in accordance with ASTM Fl 921 as described below.

[0097] Hot tack initiation temperature refers to the temperature at which hot tack strength is at least a given threshold strength. For example, the hot tack initiation temperature may be determined at 1.0 N/15 mm.

[0098] Several aspects are described in the present disclosure. A first aspect may be a multilayer structure comprising: (a) a machine direction oriented (MDO) multilayer film comprising (i) a metal layer and (ii) an inner layer in adhering contact with the metal layer, wherein the inner layer comprises: ethylene vinyl alcohol, polyvinyl alcohol, or both; or a blend of polyethylene and an interpolymer of ethylene and methyl acrylate, ethyl acrylate, or carboxylic acid; (b) a first layer extruded onto the metal layer of the machine direction oriented multilayer film wherein the first layer comprises an interpolymer of ethylene and acrylic acid or methacrylic acid, wherein the interpolymer has a melt index (I2 of 5 to 20 g/10 minutes, an acid content of 1 to 10 weight percent and a melting temperature of 90 °C to 100 °C; and (c) a sealant layer in adhering contact with the first layer, wherein the sealant layer comprises a polyethylene having a melt index (I2) of 3 to 30 g/10 minutes and a heat seal initiation temperature of 95 °C or less.

[0099] Another aspect may include any other previously disclosed aspect, wherein the metal layer is a metallized layer comprising oxides of aluminum or silicon.

[00100] Another aspect may include any other previously disclosed aspect, wherein the interpolymer of the first layer is a terpolymer of ethylene; acrylic acid or methacrylic acid; and alkyl acrylate.

[00101] Another aspect may include any other previously disclosed aspect, wherein the interpolymer of the first layer comprises 50 to 98 wt. % ethylene.

[00102] Another aspect may include any other previously disclosed aspect, wherein the sealant layer comprises 15 to 40 percent by weight of a low density polyethylene based on the total weight of the sealant layer.

[00103] Another aspect may include any other previously disclosed aspect, wherein the sealant layer further comprises 60 to 85 percent by weight of a propylene-based plastomer having a density of 0.890 g/cc or less and a melt flow rate (at 230° C and 2.16 kg) of at least 8 g/10 minutes.

[00104] Another aspect may include any other previously disclosed aspect, wherein the sealant layer further comprises 60 to 85 percent by weight of at least one polyethylene having a density of 0.870 g/cc to 0.911 g/cc and a melt index (12) of at least 3 g/10 minutes.

[00105] Another aspect may include any other previously disclosed aspect, wherein the MDO multilayer film has one or more polyethylene layers.

[00106] Another aspect may include an article comprising the multilayer structure of any preceding disclosed aspect. In another aspect, the article is a pouch. [00107] It is also noted that recitations herein of “at least one” component, element, etc., should not be used to create an inference that the alternative use of the articles “a” or “an” should be limited to a single component, element, etc.

[00108] Having described the subject matter of the present disclosure in detail and by reference to specific embodiments thereof, it is noted that the various details disclosed herein should not be taken to imply that these details relate to elements that are essential components of the various embodiments described herein, even in cases where a particular element is illustrated in each of the drawings that accompany the present description. Further, it will be apparent that modifications and variations are possible without departing from the scope of the present disclosure, including, but not limited to, embodiments defined in the appended claims. More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these aspects.

[00109] It is noted that one or more of the following claims utilize the term “wherein” as a transitional phrase. For the purposes of defining the present invention, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term “comprising.”