Multilayer film with enhanced creep, tear and dart drop

Abstract

The multilayer film (100) may include a first skin layer (102), a second skin layer (104), and a core (106) between the first skin layer (104) and the second skin layer (102). The first skin layer (102) and / or the second skin layer (104) may independently comprise a linear low density polyethylene (LLDPE) resin. The core 106 may include a first core layer (108), a second core layer (110), and a third core layer (112). The first core layer (108) and the third core layer (112) may independently comprise high density polyethylene (HDPE), LLDPE, or a combination of these. The second core layer (110) may include an ethylene-based copolymer selected from the group consisting of an ethylene / propylene copolymer, an ethylene / butyl acrylate copolymer, an ethylene / ethyl acrylate copolymer, an ethylene / methyl acrylate copolymer, and an ethylene / vinyl acetate copolymer. The thickness of the second core layer (110) may be less than 15% of the thickness of the multilayer film (100). At least one of the core layers (108, 110, 112) may comprise HDPE.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Spanish patent application No. P202330544, filed on June 28, 2023, the contents of which are incorporated herein by reference. Technical Field

[0003] The implementation schemes described herein generally relate to multilayer films, and more specifically, to multilayer films for heavy-duty transport bags (HDSS). Background Technology

[0004] To improve sustainability and reduce costs, it is desirable to reduce the thickness of the membranes used in the manufacture of heavy-duty transport bags (“HDSS”). Reducing the thickness decreases the amount of material used, thereby reducing overall emissions. However, this reduction in thickness (also known as “downgauging”) must be achieved without sacrificing impact resistance, tear resistance, and creep resistance. As membranes become thinner, meeting these specifications becomes increasingly difficult, especially below 100 μm.

[0005] Regarding creep, it is well known that when the thickness approaches 100 μm, creep is inversely proportional to the cube of the thickness. Creep can be improved by adding more HDPE and increasing the overall membrane stiffness. However, this degrades other mechanical properties, such as impact resistance. Summary of the Invention

[0006] Therefore, there is a need for thinner films that still meet the requirements for impact resistance, tear resistance, and creep resistance. Embodiments of this disclosure meet this need by providing a multilayer film comprising a core layer containing an ethylene-acrylate copolymer, an ethylene-propylene copolymer, or a combination thereof. Further embodiments of this disclosure meet this need by providing a core layer comprising an ethylene-acrylate copolymer, an ethylene-propylene copolymer, or a combination thereof, and which is relatively thin, such as less than 20% of the thickness of the multilayer film.

[0007] According to one embodiment of the present disclosure, a multilayer film can include a first skin layer, a second skin layer, and a core between the first skin layer and the second skin layer. The first skin layer and the second skin layer can independently comprise a linear low density polyethylene (LLDPE) resin. The core can include a first core layer, a second core layer, and a third core layer. The first core layer and the third core layer can independently comprise a high density polyethylene (HDPE), a linear low density polyethylene (LLDPE), or a combination of these. The second core layer can comprise an ethylene-based copolymer selected from the group consisting of an ethylene / propylene copolymer, an ethylene / butyl acrylate copolymer, an ethylene / ethyl acrylate copolymer, an ethylene / methyl acrylate copolymer, and an ethylene / vinyl acetate copolymer. The thickness of the second core layer can be less than 15% of the thickness of the multilayer film. At least one of the core layers can comprise HDPE.

[0008] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art who practice the embodiments described herein, including the detailed description which follows, and the claims which follow. It is intended that all such additional features and advantages be included within the scope of the subject matter of the present disclosure.

[0009] It should be understood that both the foregoing general description and the following detailed description are intended to provide an overview or framework for understanding the nature and character of the subject matter of the claimed subject matter. As such, the foregoing general description and the following detailed description are not intended to be taken as limiting upon the claimed subject matter. BRIEF DESCRIPTION OF DRAWINGS

[0010] To facilitate review of the various embodiments of the disclosure, the following descriptions of the drawings and description of the figures are provided. As will be realized, the various embodiments of the present disclosure are capable of conclusion in various alternative designs and settings, and are severable both as individual applications as well as being combinable into other designs and applications. The various aspects of the Figure 2 The first layer 204 in FIG. 1 will correspond to the first layer 104 in FIG. Figure 1 The first layer 204 in FIG. 1 will correspond to the first layer 104 in FIG.

[0011] Figure 1 A side view of one embodiment of a multilayer film of the present disclosure is shown.

[0012] Figure 2 A side view of one embodiment of a multilayer film of the present disclosure is shown. DETAILED DESCRIPTION

[0013] Specific embodiments of the application will now be described. The present disclosure can be embodied in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the subject matter to those skilled in the art.

[0014] As discussed above, there is a need for thinner membranes that still meet the requirements for impact resistance, tear resistance, and creep resistance for use in HDSS. Embodiments of this disclosure meet this need by providing a multilayer membrane comprising a second core layer containing an ethylene-based copolymer selected from the group consisting of ethylene / propylene copolymers, ethylene / butyl acrylate copolymers, ethylene / ethyl acrylate copolymers, ethylene / methyl acrylate copolymers, and ethylene / vinyl acetate copolymers; and which is relatively thin, such as less than 15% of the thickness of the multilayer membrane.

[0015] Definitions

[0016] "Ethylene-acrylate copolymer" refers to an ethylene-based polymer having acrylate comonomers. Based on the total polymer weight of the ethylene-acrylate copolymer, the ethylene-acrylate copolymer of this disclosure may contain a majority (greater than 50% by weight) of ethylene monomer residues. The remainder of the polymer weight of the ethylene-acrylate copolymer may contain acrylate monomer residues.

[0017] "Ethylene-propylene copolymer" refers to an ethylene-based polymer having a propylene comonomer. Based on the total polymer weight of the ethylene-propylene copolymer, the ethylene-propylene copolymer of this disclosure may contain a majority (greater than 50% by weight) of ethylene monomer residues. The remainder of the polymer weight of the ethylene-propylene copolymer may contain propylene monomer residues.

[0018] "Residue" refers to a polymer fraction derived from a specific monomer.

[0019] “gf / μm” refers to grams per micrometer.

[0020] "Heavyweight transport bags" (also referred to herein as "HDSS") are packages designed to hold large quantities of granular cargo, such as polymer resins, solid chemicals, cement, animal feed, rice, and similar goods. The HDSS disclosed herein is suitable for holding granular cargo exceeding 20 kg.

[0021] "Multilayer film" refers to any structure having more than one layer. For example, a multilayer structure can have five or more layers, such as 6, 7, 8, 9, 10 or 11 layers. In embodiments, the multilayer film may have an odd number of layers, such as 5, 6, 9 or 11 layers.

[0022] As used herein, “polyethylene” or “ethylene-based polymer” means a polymer comprising more than 50% by weight of units derived from ethylene monomers. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers). Common forms of polyethylene known in the art include low-density polyethylene (LDPE); linear low-density polyethylene (LLDPE); ultra-low-density polyethylene (ULDPE); very low-density polyethylene (VLDPE); single-point catalytic linear low-density polyethylene, including both linear and substantially linear low-density resins (m-LLDPE); medium-density polyethylene (MDPE); and high-density polyethylene (HDPE).

[0023] The term “ULDPE” is defined as a polyethylene-based copolymer having a density in the range of 0.895 g / cc to 0.915 g / cc.

[0024] The term “LDPE” can also be referred to as “high-pressure ethylene polymer” or “highly branched polyethylene”, and is defined to mean that the polymer is partially or fully homopolymerized or copolymerized in an autoclave or tubular reactor at pressures above 14,500 psi (100 MPa) using a free radical initiator (e.g., peroxide (see, for example, U.S. Patent No. 4,599,392, which is incorporated herein by reference)).

[0025] The term "LLDPE" includes resins made using conventional Ziegler-Natta catalyst systems as well as resins made using single-center catalysts (such as metallocenes) (sometimes referred to as "m-LLDPE"). LLDPE contains fewer long-chain branches than LDPE and includes: substantially linear ethylene polymers, further defined in U.S. Patent Nos. 5,272,236, 5,278,272, 5,582,923, and 5,733,155; homogeneous branched linear ethylene polymer compositions, such as those in U.S. Patent No. 3,645,992; heterogeneous branched ethylene polymers, such as those prepared according to the method disclosed in U.S. Patent No. 4,076,698; and blends thereof (such as those disclosed in U.S. Patent Nos. 3,914,342 or 5,854,045). LLDPE can be prepared by gas-phase, solution-phase, or slurry polymerization or any combination thereof using any type of reactor or reactor configuration known in the art (including, but not limited to, gas-phase and solution-phase reactors).

[0026] The term "C6 LLDPE" refers to an ethylene-based polymer produced from ethylene monomers and hexene comonomers. Similarly, "C4 LLDPE" refers to an ethylene-based polymer produced from ethylene monomers and butene comonomers, and "C8 LLDPE" refers to an ethylene-based polymer produced from ethylene monomers and octene comonomers.

[0027] The term "HDPE" typically refers to a density greater than approximately 0.935 g / cm³. 3 And at most about 0.980 g / cm 3 Polyethylene is generally prepared using Ziegler-Natta catalysts, chromium catalysts, or single-point catalysts (including but not limited to substituted mono- or di-cyclopentadienyl catalysts (commonly known as metallocenes), confined geometry catalysts, phosphine imine catalysts, and polyvalent aryloxy ether catalysts (commonly known as bisphenylphenoxy).

[0028] "Polymer" refers to a polymeric compound prepared by polymerizing monomers, whether of the same or different types. Therefore, the term polymer encompasses the term homopolymer (used to refer to a polymer prepared from only one type of monomer, where it should be understood that trace impurities may be incorporated into the polymer structure) and the terms copolymer and interpolymer. Trace impurities (e.g., catalyst residues) may be incorporated into and / or within the polymer. A polymer can be a single polymer or a polymer blend.

[0029] As used herein, the term "copolymer" refers to a polymer formed by the polymerization of at least two monomers with different structures. The term "copolymer" includes terpolymers. For example, ethylene copolymers (such as ethylene-propylene copolymers) comprise at least two structurally different monomers (e.g., an ethylene-propylene copolymer comprises copolymer units of at least ethylene monomers and propylene monomers) and may optionally include additional monomers or functional materials or modifiers, such as acid, acrylate, or anhydride functional groups. In other words, the copolymers described herein contain at least two structurally different monomers, and although copolymers may consist of only two structurally different monomers, they are not necessarily composed of only two structurally different monomers and may contain additional monomers or functional materials or modifiers.

[0030] "Weight%" means weight percentage.

[0031] “g / 10min” means grams per ten minutes.

[0032] “gg / cm 3 (Also written as g / cc) means grams per cubic centimeter.

[0033] Embodiments

[0034] like Figure 1As depicted, the multilayer film 100 may include a first surface layer 102, a second surface layer 104, and a core 106. The core 106 may be located between the first surface layer 102 and the second surface layer 104. The core 106 may include a first core layer 108, a second core layer 110, and a third core layer 112.

[0035] Second core layer

[0036] The second core layer 110 may comprise an ethylene-based copolymer selected from the group consisting of ethylene / propylene copolymers, ethylene / butyl acrylate copolymers, ethylene / ethyl acrylate copolymers, ethylene / methyl acrylate copolymers, and ethylene / vinyl acetate copolymers. In an embodiment, based on the total polymer weight of the second core layer 110, the second core layer 110 may comprise at least 50% by weight, such as at least 60% by weight, at least 70% by weight, at least 80% by weight, at least 90% by weight, at least 95% by weight, at least 99% by weight, or even at least 99.9% by weight, of an ethylene-based copolymer.

[0037] The second core layer 110 may comprise an ethylene-acrylate copolymer (such as an ethylene / butyl acrylate copolymer, an ethylene / ethyl acrylate copolymer, an ethylene / methyl acrylate copolymer, and / or an ethylene / vinyl acetate copolymer). The ethylene-acrylate copolymer may comprise residues of acrylate monomers, such as C2-C-6 acrylate monomers or C2 to C5 monomers. In embodiments, based on the total polymer weight of the ethylene-acrylate copolymer, the ethylene-acrylate copolymer may comprise 1% to 49% by weight, such as 5% to 49% by weight, 10% to 49% by weight, 20% to 49% by weight, 30% to 49% by weight, 40% to 49% by weight, 1% to 40% by weight, 1% to 30% by weight, 1% to 20% by weight, 1% to 10% by weight, 10% to 40% by weight, 20% to 30% by weight, 15% to 30% by weight, or any subset thereof, of acrylate monomers. It should be understood that, based on the total polymer weight of the ethylene-acrylate copolymer, at least 80% by weight, at least 90% by weight, at least 99% by weight, or even at least 99.9% by weight of the ethylene-acrylate copolymer may comprise a combination of ethylene residues and acrylate residues. Suitable ethylene-acrylate copolymers may include ELVALOY, commercially available from Dow Chemical Company, Midland, Michigan. ™ Series of polymers.

[0038] The ethylene-acrylate copolymer may have a melt index (I2) of 0.5 g / 10 min to 8 g / 10 min. In embodiments, the ethylene-acrylate copolymer may have a melt index (I2) of 0.5 g / 10 min to 8 g / 10 min, 0.5 g / 10 min to 6 g / 10 min, 0.5 g / 10 min to 4 g / 10 min, 0.5 g / 10 min to 2 g / 10 min, 1 g / 10 min to 10 g / 10 min, 2 g / 10 min to 10 g / 10 min, 4 g / 10 min to 10 g / 10 min, 6 g / 10 min to 10 g / 10 min, 8 g / 10 min to 10 g / 10 min, 2 g / 10 min to 8 g / 10 min, 4 g / 10 min to 6 g / 10 min, or any subset thereof.

[0039] The second core layer 110 may comprise an ethylene-propylene copolymer. The ethylene-propylene copolymer may comprise residues of propylene monomers. In an embodiment, based on the total polymer weight of the ethylene-propylene copolymer, the ethylene-propylene copolymer may comprise 1% to 49% by weight, such as 5% to 49% by weight, 10% to 49% by weight, 20% to 49% by weight, 30% to 49% by weight, 40% to 49% by weight, 1% to 40% by weight, 1% to 30% by weight, 1% to 20% by weight, 1% to 10% by weight, 10% to 40% by weight, 20% to 30% by weight, or any subset thereof, of propylene monomers. In an embodiment, based on the total polymer weight of the ethylene-propylene copolymer, the ethylene-propylene copolymer may comprise 60% to 95% by weight of ethylene monomers and 5% to 40% by weight of propylene comonomers. It should be understood that, based on the total polymer weight of the ethylene-propylene copolymer, at least 80% by weight, at least 90% by weight, at least 99% by weight, or even at least 99% by weight of the ethylene-propylene copolymer may comprise a combination of ethylene residues and propylene residues. Suitable ethylene-propylene copolymers may include XUS 39003.00 experimental resin, commercially available from Dow Chemical Company, Midland, Michigan. Other suitable ethylene-propylene copolymers are described in PCT / US23 / 061210, which is incorporated herein by reference.

[0040] The comonomer content can be measured using any suitable technique, such as nuclear magnetic resonance (“NMR” spectroscopy, and, for example, by means of the method described in U.S. Patent 7,498,282. 13 The patent is incorporated herein by reference and is measured by C NMR analysis.

[0041] In some embodiments, the ethylene-propylene copolymer may have a density in the range of 0.865 g / cc to 0.920 g / cc. All individual values ​​and sub-ranges of 0.865 g / cc to 0.920 g / cc are disclosed and included herein. For example, the ethylene-propylene copolymer may have a density in the range of 0.870 g / cc to 0.920 g / cc, 0.880 g / cc to 0.910 g / cc, 0.895 g / cc to 0.905 g / cc, or 0.895 g / cc to 0.910 g / cc.

[0042] In some embodiments, the ethylene-propylene copolymer may have a melt index (I2) of at least 0.5 g / 10 min. This document discloses and includes all individual values ​​and sub-ranges of at least 0.5 g / 10 min. For example, the ethylene-propylene copolymer may have a melt index (I2) of at least 0.5 g / 10 min, at least 0.6 g / 10 min, at least 0.7 g / 10 min, at least 0.8 g / 10 min, at least 0.9 g / 10 min, or at least 1.0 g / 10 min, or may have a melt index (I2) in the range of 0.5 g / 10 min to 500 g / 10 min, 0.5 g / 10 min to 200 g / 10 min, 0.5 g / 10 min to 100 g / 10 min, 0.5 g / 10 min to 50 g / 10 min, 0.5 g / 10 min to 10 g / 10 min, or 0.5 g / 10 min to 8 g / 10 min.

[0043] In some embodiments, the ethylene-propylene copolymer may exhibit a single peak in the modified comonomer composition distribution (ICCD) elution profile within a temperature range of 40°C to 100°C. The modified comonomer composition distribution (ICCD) profile of the ethylene-propylene copolymer can be obtained via the test methods described below.

[0044] In some embodiments, the ethylene-propylene copolymer may have a molecular weight distribution (M0.0) in the range of 1.5 to 5.0. w / M n This document discloses and includes all individual values ​​and sub-ranges from 1.5 to 5.0. For example, ethylene-propylene copolymers may have molecular weight distributions (M0) in the ranges of 1.5 to 5.0, 1.6 to 5.0, 1.8 to 5.0, 2.0 to 5.0, 1.5 to 4.0, 1.6 to 4.0, 1.8 to 4.0, 2.0 to 4.0, 1.5 to 3.0, 1.8 to 3.0, 2.0 to 3.0, 1.5 to 2.5, 1.8 to 2.5, or 2.0 to 2.5. w / M n Molecular weight distribution (M) w / M nIt can be measured according to the GPC test method described below.

[0045] In some embodiments, the ethylene-propylene copolymer is further characterized by having a melt flow ratio of 5 to 14 (I 10 / I2). This document discloses and includes all individual values ​​and sub-ranges of 5 to 14. For example, ethylene-propylene copolymers may have melt flow ratios of 5 to 14, 6 to 12, 6 to 10, or 5 to 10 (I 10 / I2).

[0046] In some embodiments, the ethylene-propylene copolymer may have a heat of fusion in the range of 40 J / g to 150 J / g. All individual values ​​and sub-ranges of 40 J / g to 150 J / g are disclosed and included herein. For example, the ethylene-propylene copolymer may have a heat of fusion in the ranges of 40 J / g to 108 J / g to 150 J / g, 45 J / g to 130 J / g, 50 J / g to 120 J / g, 60 J / g to 108 J / g, 70 J / g to 108 J / g, 80 J / g to 108 J / g, and 90 J / g to 108 J / g, wherein the heat of fusion is measured according to the DSC test method described below.

[0047] Ethylene-based copolymers can be ethylene / vinyl acetate (EVA) copolymers. Based on the total polymer weight of the ethylene / vinyl acetate copolymer, the EVA copolymer may contain 9% to 28% by weight of vinyl acetate comonomer. All individual values ​​and sub-ranges of 9% to 28% by weight are disclosed and included herein. In embodiments, based on the total weight of the ethylene / vinyl acetate copolymer, the ethylene / vinyl acetate copolymer may contain 10% to 25%, 12% to 23%, or 15% to 20% by weight of vinyl acetate comonomer. Examples of suitable commercially available ethylene / vinyl acetate copolymers include those named ELVAX. ™ The polymer was purchased from Dow Chemical Company in Midland, Michigan.

[0048] The second core layer 110 may also contain fillers such as calcium carbonate (CaCO3). 20% to 80% by weight of calcium carbonate (CaCO3). Not wishing to be limited by theory, a synergistic effect has been found between calcium carbonate fillers and ethylene-acrylate copolymers, resulting in improved mechanical properties. However, various fillers, including CaCO3, may optionally be used with ethylene-acrylate copolymers and ethylene-propylene copolymers to provide color and reduce cost. In embodiments, based on the total weight of the second core layer 110, the second core layer 110 may contain 0% to 80% by weight of fillers such as 10% to 80% by weight, 20% to 80% by weight, 40% to 80% by weight, 0% to 60% by weight, 0% to 40% by weight, 0% to 20% by weight, 10% to 70% by weight, 20% to 60% by weight, 30% to 70% by weight, or any subset thereof.

[0049] like Figure 1 As depicted, the second core layer 110 may be located within the core 106 between the first core layer 108 and the third core layer 112. Therefore, the second core layer 110 may be the central layer of the multilayer film 100, the central layer of the core 106, or both. Alternative embodiments are envisioned where the second core layer is not the central layer of the multilayer film and the core, as long as the second core layer is located between the first and second surface layers. Without being theoretically limited, it is believed that while the second core layer will improve the mechanical strength of any inner layer between the first and second surface layers, performance will be significantly improved when the second core layer 110 is the central layer. The central layer may be a layer comprising 50% of the points within the multilayer film 100.

[0050] First, third, fourth, and fifth core layers

[0051] Still referencing Figure 1 Core 106 may include a first core layer 108 and a third core layer 112. The first core layer 108 may be located between the first surface layer 102 and the second core layer 110. The third core layer 112 may be located between the second core layer 110 and the second surface layer. Now refer to Figure 2 The multilayer film 200 may include a first surface layer 202, a second surface layer 204, and a core 206. The core 206 may be located between the first surface layer 202 and the second surface layer 204. The core 206 may include a first core layer 208, a third core layer 212, and a second core layer 210. The core 206 may also include a fourth core layer 214 and a fifth core layer 216.

[0052] The core layers 206 can be arranged in any order. In one embodiment, a fourth core layer 214 may be located between the first surface layer 202 and the first core layer 208. In another embodiment, a fifth core layer 216 may be located between the second surface layer 204 and the third core layer 212. In yet another embodiment, a second core layer 210 may be located between the first core layer 208 and the third core layer 212. Therefore, the second core layer 210 may be the center layer. As previously mentioned, it is believed that while the second core layer will enhance the performance of any inner layer between the first and second surface layers, performance will be significantly improved when the second core layer is the center layer.

[0053] Now for reference Figure 1 and Figure 2 The first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and the fifth core layer 216 may each independently contain HDPE, LLDPE, or combinations thereof. In an embodiment, based on the total polymer weight of the layers, the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and the fifth core layer 216 may each independently contain at least 70% by weight, such as at least 80% by weight, at least 90% by weight, at least 99% by weight, or even at least 99.9% by weight, of HDPE, LLDPE, or combinations thereof.

[0054] At least one of the core layers 106 and 206 may contain high-density polyethylene (HDPE). In an embodiment, at least two of the core layers 106 and 206 may contain HDPE. In an embodiment, at least one layer containing HDPE may be disposed on each side of the second core layer.

[0055] In an embodiment, based on the total weight of the multilayer films 100 and 200, the multilayer films 100 and 200 may contain at least 30% by weight of HDPE. Using a minimum percentage of HDPE helps to meet density and creep requirements. In an embodiment, based on the total weight of the multilayer films 100 and 200, the multilayer films 100 and 200 may contain at least 35% by weight, at least 40% by weight, at least 45% by weight, 30% to 45% by weight, 35% to 45% by weight, 40% to 45% by weight, 35% to 40% by weight, or any subset thereof of HDPE.

[0056] In embodiments where the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and / or the fifth core layer 216 comprises HDPE, the HDPE may have a density greater than 0.940 g / cc, such as greater than 0.945 g / cc, greater than 0.950 g / cc, greater than 0.955 g / cc, greater than 0.960 g / cc, 0.940 g / cc to 0.965 g / cc, 0.940 g / cc to 0.960 g / cc, 0.940 g / cc to 0.955 g / cc, 0.945 g / cc to 0.965 g / cc, or any subset thereof. Without being theoretically limited, it is believed that increasing the density of HDPE leads to improved creep resistance properties.

[0057] In embodiments in which the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and / or the fifth core layer 216 comprise HDPE, the HDPE may have a melt index (I2) in the range of 0.1 g / 10 min to 1.5 g / 10 min. All individual values ​​and sub-ranges of 0.1 g / 10 min to 1.5 g / 10 min are disclosed and included herein. For example, HDPE may have a melt index (I2) in the range of 0.1 g / 10 min to 1.3 g / 10 min, 0.1 g / 10 min to 1.1 g / 10 min, 0.1 g / 10 min to 0.9 g / 10 min, 0.1 g / 10 min to 0.7 g / 10 min, 0.1 g / 10 min to 0.5 g / 10 min, 0.3 g / 10 min to 1.5 g / 10 min, 0.5 g / 10 min to 1.5 g / 10 min, 0.7 g / 10 min to 1.5 g / 10 min, 0.9 g / 10 min to 1.5 g / 10 min, 0.3 g / 10 min to 1.3 g / 10 min, 0.5 g / 10 min to 1.1 g / 10 min, or any subset thereof.

[0058] Commercially available examples of HDPE that can be used in the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and / or the fifth core layer 216 include those that can be marketed under the name UNIVAL. ™ Those purchased from Dow, including, for example, UNIVAL ™ DMDA 6400.

[0059] In embodiments in which the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and / or the fifth core layer 216 comprise LLDPE, the LLDPE may have a content of less than or equal to 0.930 g / cm³. 3 The density of the sample is included and disclosed herein. This document includes and discloses samples with a density less than or equal to 0.930 g / cm³. 3All individual values ​​and sub-ranges; for example, the density of linear low-density polyethylene can be between 0.870 g / cm³. 3 The lower limit is 0.928 g / cm³. 3 0.925g / cm 3 0.920g / cm 3 Or 0.915g / cm 3 The upper limit. This article includes and discloses 0.870 g / cm. 3 With 0.930 g / cm 3 All individual values ​​and subranges between.

[0060] In embodiments in which the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and / or the fifth core layer 216 comprise LLDPE, the LLDPE may have a melt index (I2) in the range of 0.1 g / 10 min to 1.5 g / 10 min. All individual values ​​and sub-ranges of 0.1 g / 10 min to 1.5 g / 10 min are disclosed and included herein. For example, LLDPE may have a melt index (I2) in the range of 0.1 g / 10 min to 1.3 g / 10 min, 0.1 g / 10 min to 1.1 g / 10 min, 0.1 g / 10 min to 0.9 g / 10 min, 0.1 g / 10 min to 0.7 g / 10 min, 0.3 g / 10 min to 1.5 g / 10 min, 0.5 g / 10 min to 1.5 g / 10 min, 0.7 g / 10 min to 1.5 g / 10 min, 0.3 g / 10 min to 1.3 g / 10 min, 0.5 g / 10 min to 1.1 g / 10 min, or any subset thereof.

[0061] Commercially available examples of LLDPEs that can be used in the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and / or the fifth core layer 216 include those that can be marketed under the name ELITE. ™ Those purchased from Dow, including, for example, ELITE ™ 5400.

[0062] Skin layer

[0063] The first outer layers 102, 202 and the second outer layers 104, 204 may independently comprise linear low-density polyethylene (hereinafter referred to as "LLDPE"). In an embodiment, based on the total polymer weight of the layers, the multilayer film 200 may comprise at least 50% by weight, such as at least 60% by weight, at least 70% by weight, at least 80% by weight, at least 90% by weight, or even at least 99% by weight, of LLDPE.

[0064] In embodiments in which the first surface layer 102, 202 and / or the second surface layer 104, 204 comprises LLDPE, the LLDPE may have a content of less than or equal to 0.940 g / cm³. 3 The density of the sample is included and disclosed herein. This document includes and discloses samples with a density less than or equal to 0.940 g / cm³. 3 All individual values ​​and sub-ranges; for example, the density of LLDPE can be between 0.870 g / cm³. 3 0.880 g / cm 3 0.890 g / cm 3 0.910 g / cm 3 0.920g / cm 3 The lower limit is 0.940 g / cm³. 3 0.938g / cm 3 0.936 g / cm 3 Or 0.935g / cm 3 The upper limit. This article includes and discloses 0.870 g / cm³. 3 With 0.940 g / cm 3 All individual values ​​and subranges between.

[0065] In embodiments in which the first surface layer 102, 202 and / or the second surface layer 104, 204 comprises LLDPE, the LLDPE may have a melt index (I2) in the range of 0.1 g / 10 min to 50 g / 10 min. All individual values ​​and sub-ranges of 0.1 g / 10 min to 50 g / 10 min are disclosed and included herein. For example, the LLDPE may have a melt index (I2) in the range of 0.1 g / 10 min to 40 g / 10 min, 0.1 g / 10 min to 30 g / 10 min, 0.1 g / 10 min to 20 g / 10 min, 0.1 g / 10 min to 10 g / 10 min, or 0.1 g / 10 min to 5 g / 10 min.

[0066] Commercially available examples of LLDPE that can be used in multilayer film 200 and / or multilayer film 200 include those under the name ELITE. ™ And named DOWLEX ™ Those were purchased from Dow Chemical.

[0067] In some embodiments, the first surface layers 102, 202 and / or the second surface layers 104, 204 may comprise low-density polyethylene (LDPE). It should be understood that, in addition to LLDPE, the first surface layers 102, 202 and the second surface layers 104, 204 may also comprise LDPE. In embodiments where the multilayer film 200 and / or the multilayer film 200 comprises LDPE, the LDPE may have a content of 0.916 g / cm³. 3Up to 0.935 g / cm 3 The density is within the range specified in this document. This document includes and discloses 0.916 g / cm³. 3 Up to 0.935 g / cm 3 All individual values ​​and sub-ranges; for example, the density of LDPE can be between 0.916 g / cm³. 3 0.918 g / cm 3 0.920g / cm 3 Or 0.922g / cm 3 The lower limit is 0.935 g / cm³. 3 0.933g / cm 3 0.931 g / cm 3 Or 0.929 g / cm 3 The upper limit.

[0068] In embodiments in which the first surface layer 102, 202 and / or the second surface layer 104, 204 comprises LDPE, the LDPE may have a melt index (I2) in the range of 0.1 g / 10 min to 50 g / 10 min. All individual values ​​and sub-ranges of 0.1 g / 10 min to 50 g / 10 min are disclosed and included herein. For example, LDPE may have a melt index (I2) in the range of 0.1 g / 10 min to 40 g / 10 min, 0.1 g / 10 min to 30 g / 10 min, 0.1 g / 10 min to 20 g / 10 min, 0.1 g / 10 min to 10 g / 10 min, or 0.1 g / 10 min to 5 g / 10 min.

[0069] In some embodiments, based on the total weight of the respective layers, the first surface layer 102, 202 and / or the second surface layer 104, 204 may independently contain 0 wt% to 30 wt% of LDPE. All individual values ​​from 0 wt% to 30 wt% are disclosed and included herein. For example, based on the total polymer weight of the respective layers, multilayer film 200 and / or multilayer film 200 may contain 0 wt% to 25 wt%, 0 wt% to 20 wt%, 0 wt% to 10 wt%, 0 wt% to 5 wt%, 5 wt% to 30 wt%, 5 wt% to 20 wt%, or any subset thereof.

[0070] Commercially available examples of LDPE that can be used in multilayer film 200 and / or multilayer film 200 include those available from Dow Chemical Company under the name AGILITY. ™ Those obtained through commercial purchases.

[0071] Multilayer film

[0072] The multilayer films 100 and 200 may have a thickness of less than 180 µm. As previously described, it is desirable to produce multilayer films that satisfy desired mechanical properties while minimizing film thickness. In embodiments, the multilayer films 100 and 200 may have thicknesses of less than 160 µm, less than 140 µm, less than 120 µm, less than 100 µm, less than 90 µm, 70 µm to 180 µm, 70 µm to 150 µm, 70 µm to 125 µm, 70 µm to 115 µm, 70 µm to 105 µm, 70 µm to 100 µm, 70 µm to 95 µm, and 70 µm to 90 µm. Thickness of m, 80µm to 180µm, 80µm to 150µm, 80µm to 125µm, 80µm to 115µm, 80µm to 105µm, 80µm to 100µm, 80µm to 90µm, 90µm to 180µm, 90µm to 150µm, 90µm to 115µm, 90µm to 105µm, 90µm to 100µm, or any subset thereof.

[0073] Still referencing Figure 1 and Figure 2 The first surface layer 102, 202 and / or the second surface layer 104, 204 may independently have a thickness of 10% to 30% of the thickness of the multilayer film 100, 200. In embodiments, the first surface layer 102, 202 and / or the second surface layer 104, 204 may independently have a thickness of 10% to 25%, 10% to 20%, 10% to 15%, 15% to 30%, 20% to 30%, 15% to 25%, or any subset thereof of the thickness of the multilayer film 100, 200.

[0074] The first core layers 108, 208 and the third core layers 112, 212 may independently have a thickness of 3% to 45%, 3% to 40%, 3% to 35%, 3% to 30%, 3% to 25%, 3% to 20%, 3% to 15%, 3% to 10%, 5% to 45%, 10% to 45%, 15% to 45%, 20% to 45%, 30% to 45%, 5% to 40%, 10% to 35%, 15% to 30%, or any subset thereof, of the thickness of the multilayer films 100, 200.

[0075] The second core layers 110 and 210 may have a thickness less than 15% of the thickness of the multilayer films 100 and 200. Without being theoretically limited, it is believed that the performance of the multilayer films 100 and 200 can be optimized when the second core layers 110 and 210 are at their thinnest. However, due to manufacturing limitations and variations in layer thickness, it may not be possible to manufacture a second core layer with a thickness less than 3% of the thickness of the multilayer films 110 and 210. In embodiments, the second core layers 110 and 210 may have a thickness less than or equal to 10%, less than or equal to 5%, 3% to 20%, 3% to 15%, 3% to 10%, 3% to 7%, 3% to 5%, 1% to 20%, 5% to 20%, or any subset thereof of the thickness of the multilayer films 100 and 200. In embodiments, the second core layers 110 and 210 may have a thickness of 3% to 7% of the thickness of the multilayer films 100 and 200.

[0076] Now for reference Figure 2 The fourth core layer 214 and the fifth core layer 216 may independently have a thickness of 3% to 45%, 3% to 40%, 3% to 35%, 3% to 30%, 3% to 25%, 3% to 20%, 3% to 15%, 3% to 10%, 5% to 45%, 10% to 45%, 15% to 45%, 20% to 45%, 30% to 45%, 5% to 40%, 10% to 35%, 15% to 30%, or any subset thereof of the thickness of the multilayer films 100 and 200.

[0077] Refer again Figure 1 and Figure 2 The multilayer films 100 and 200 may have a density of 0.929 g / cc to 0.942 g / cc. In embodiments, the multilayer films 100 and 200 may have densities of 0.929 g / cc to 0.940 g / cc, 0.929 g / cc to 0.935 g / cc, 0.930 g / cc to 0.942 g / cc, 0.935 g / cc to 0.942 g / cc, 0.930 g / cc to 0.940 g / cc, 0.932 g / cc to 0.938 g / cc, or any subset thereof.

[0078] Multilayer membranes 100 and 200 may have a normalized dart impact type A of at least 4.0 g / µm. In embodiments, multilayer membranes 100 and 200 may have a dart impact type A of at least 4.4 g / µm, at least 4.6 g / µm, at least 4.8 g / µm, at least 5.0 g / µm, 4.0 g / µm to 6.0 g / µm, 4.2 g / µm to 6.0 g / µm, 4.4 g / µm to 6.0 g / µm, or any subset thereof.

[0079] Multilayer films 100 and 200 may have a dart impact type A of at least 400 g / µm, such as at least 425 g / µm, at least 450 g / µm, at least 500 g / µm, at least 600 g / µm, or any subset thereof.

[0080] Multilayer films 100 and 200 may have a normalized Elmendorf transverse tear resistance of at least 16.6 gf / µm. In embodiments, multilayer films 100 and 200 may have Elmendorf transverse tear resistance of at least 16.8 gf / µm, at least 17.0 gf / µm, at least 17.2 gf / µm, at least 17.4 gf / µm, at least 17.6 gf / µm, at least 17.8 gf / µm, at least 18.0 gf / µm, 16.6 gf / µm to 20 gf / µm, or any subset thereof.

[0081] Multilayer films 100 and 200 may have an Elmendorf transverse tear resistance of at least 1500 gf. In embodiments, multilayer films 100 and 200 may have an Elmendorf transverse tear resistance of at least 1600 gf, at least 1700 gf, at least 1800 gf, at least 1900 gf, at least 2000 gf, 1500 gf to 3000 gf, 1600 gf to 3000 gf, 1700 gf to 3000 gf, 1800 gf to 3000 gf, 1900 gf to 3000 gf, 2000 gf to 3000 gf, or any subset thereof.

[0082] Multilayer films 100 and 200 may have a normalized Elmendorf longitudinal tear resistance of at least 8.8 gf / µm. In embodiments, multilayer films 100 and 200 may have an Elmendorf longitudinal tear resistance of at least 9.0 gf / µm, at least 9.2 gf / µm, at least 9.4 gf / µm, at least 9.6 gf / µm, at least 9.8 gf / µm, at least 10.0 gf / µm, 8.8 gf / µm to 12 gf / µm, 9.0 gf / µm to 12 gf / µm, 9.2 gf / µm to 12 gf / µm, 9.4 gf / µm to 12 gf / µm, or any subset thereof.

[0083] The multilayer films 100 and 200 may have an Elmendorf longitudinal tear resistance of at least 800 gf, such as at least 825 gf, at least 850 gf, at least 900 gf, at least 1000 gf, at least 1100 gf, 800 gf to 1500 gf, 850 gf to 1500 gf, 900 gf to 1500 gf, 1000 gf to 1500 gf, or any subset thereof.

[0084] The multilayer membranes 100 and 200 may have high-flux creep of less than 50%. In embodiments, the multilayer membranes 100 and 200 may have high-flux creep of less than 45%, less than 40%, less than 35%, less than 30%, less than 25%, less than 20%, less than 15%, less than 10%, less than 5%, 1% to 50%, 1% to 40%, 1% to 30%, 1% to 25%, or any subset thereof.

[0085] It should be understood that the multilayer film 100 may include five or more layers. In an embodiment, the multilayer film 100 may include more than five layers, such as seven, nine, or eleven layers.

[0086] The multilayer film 100 disclosed herein can be produced using techniques known to those skilled in the art based on the teachings herein. For example, the multilayer film can be produced by film lamination and / or co-extrusion. The formation of the co-extruded multilayer film 100 is known in the art and is applicable to this disclosure. A co-extrusion system for manufacturing the multilayer film 100 employs at least two extruders feeding a common die assembly. The number of extruders depends on the number of different materials or polymers. For example, a five-layer co-extrusion may require up to five extruders, but if two or more layers are made of the same material or polymer, fewer extruders can be used.

[0087] In some embodiments, the multilayer film is a longitudinally oriented film. In other embodiments, the multilayer film is a cast and stretched film. In still other embodiments, the multilayer film is a stretch cap film.

[0088] Additives

[0089] It should be understood that any of the aforementioned layers may also include one or more additives known to those skilled in the art, such as antioxidants, UV stabilizers, heat stabilizers, slip agents, antiblocking agents, antistatic agents, pigments or colorants, processing aids, crosslinking catalysts, flame retardants, fillers, and foaming agents. The layer may contain any amount of such additives, such as 0% to 10% by weight, 0% to 5% by weight, 0% to 1% by weight, 0% to 0.1% by weight, 0% to 0.001% by weight, or any subset thereof, based on the weight of the layer.

[0090] Article

[0091] Embodiments of this disclosure also provide articles comprising any of the multilayer films of the present invention described herein. Examples of such articles may include wraps, packages, flexible packaging, bags, and pouches. In view of the teachings herein, articles of this disclosure can be formed from the multilayer films disclosed herein using techniques known to those skilled in the art. Articles of this disclosure may include heavy-duty transport bags comprising one or more multilayer films 100, 200.

[0092] Test methods

[0093] Density

[0094] Density was measured according to ASTM D792 and expressed in grams per cubic centimeter. 3 (g / cm) 3 )express.

[0095] Melt index (I2, I 10 and I 21 )

[0096] Melt flow index (I2) is measured according to ASTM D 1238-10 at 190 degrees Celsius and 2.16 kg using Method B, and is expressed as grams eluted per 10 minutes (g / 10min).

[0097] Melt index (I) 10 )Measured according to ASTM D 1238-10 at 190 degrees Celsius and 10 kg in Method B, and expressed as grams eluted per 10 minutes (g / 10min).

[0098] Melt index (I) 21 )Measured according to ASTM D 1238-10 at 190 degrees Celsius and 21.6 kg by Method B, and expressed as grams eluted per 10 minutes (g / 10min).

[0099] Improved comonomer composition distribution (ICCD)

[0100] An improved method for comonomer content analysis (iCCD) was developed in 2015 (Cong and Parrott et al., WO2017040127A1). iCCD tests were performed using a Crystallization Elution Fractionation (CEF) instrument (Perimocha, Spain) equipped with an IR-5 detector (PolymerChar, Spain) and a two-corner light scattering detector model 2040 (Precision Detectors, now Agilent Technologies). A guard column filled with 20-27 micron glass (MoSCi Corporation, USA) was installed just before the IR-5 detector in the detector oven. o-Dichlorobenzene (ODCB, 99% anhydrous or industrial grade) was used. The results were obtained from the EMD. Chemicals obtained silica gel 40 (particle size 0.2–0.5 mm, catalog number 10181-3) (previously used as a solvent for drying ODCB). The dried silica was packed into three empty HT-GPC columns to further purify ODCB as the eluent. The CEF instrument was equipped with an autosampler with N2 purging capability. ODCB was bubbled with dry nitrogen (N2) for one hour before use. Sample preparation was performed at 160 °C with shaking at a concentration of 4 mg / ml (unless otherwise specified) using the autosampler for 1 hour. The injection volume was 300 μl. The iCCD temperature profile was as follows: crystallization from 105 °C to 30 °C at 3 °C / min, thermal equilibration at 30 °C for 2 minutes (including elution time for the soluble fraction set to 2 minutes), and elution from 30 °C to 140 °C at 3 °C / min. The flow rate during crystallization was 0.0 ml / min. The flow rate during elution was 0.50 ml / min. Data was collected at a rate of one data point per second.

[0101] An iCCD column was filled with gold-plated nickel particles (Bright7GNM8-NiS, Nippon Chemical Industrial Co.) in a 15cm (length) x 1 / 4” (ID) stainless steel tube. Column filling and conditioning were performed according to references (Cong, R.; Parrott, A.; Hollis, C.; Cheatham, M. WO2017040127A1). The final pressure for TCB slurry filling was 150 bar.

[0102] By using a reference material, linear homopolymer polyethylene (with zero comonomer content, melt index (I2) of 1.0, and polydispersity M... w / M nColumn temperature calibration was performed using a mixture of ODCB containing eicosane (2 mg / ml) and approximately 2.6 mg / ml via conventional gel permeation chromatography. The iCCD temperature calibration consisted of four steps: (1) calculating the delay volume, which was defined as the temperature shift between the measured peak elution temperature of eicosane and 30.00 °C; and (2) subtracting the temperature shift of the elution temperature from the raw iCCD temperature data. It should be noted that the temperature shift is a function of experimental conditions, such as elution temperature, elution flow rate, etc.; (3) A linear calibration line for switching elution temperatures in the range of 30.00 °C and 140.00 °C is established such that the linear homopolymer polyethylene reference has a peak temperature at 101.0 °C and the eicosane has a peak temperature at 30.0 °C; (4) For the soluble fraction measured isothermally at 30 °C, the elution temperature below 30.0 °C is linearly extrapolated by using an elution heating rate of 3 °C / min, according to the reference (Cerk and Cong et al., US9,688,795).

[0103] A relationship between comonomer content and elution temperature of iCCD was constructed using 12 reference materials (ethylene homopolymers and ethylene-octene random copolymers prepared with unit-point metallocene catalysts, with ethylene equivalent weight-average molecular weights ranging from 35,000 to 128,000). All these reference materials were analyzed in the same manner as previously specified at 4 mg / mL. The reported elution peak temperatures follow the relationship between octene mol% and R in the figure. 2 The elution temperature of the iCCD is 0.978.

[0104] By assuming a shape factor of 1 and all virial coefficients equal to zero, the molecular weights of the polymer and polymer fractions were determined directly from the LS detector (90-degree angle) and the concentration detector (IR-5) according to the Rayleigh-Gans-Debys approximation (Striegel and Yau, Modern Size Exclusion Liquid Chromatogram, pp. 242 and 263). An integration window was set to integrate all chromatograms over an elution temperature range of 23.0 °C to 120 °C (temperature calibration specified above).

[0105] Calculating molecular weight (Mw) from iCCD involves the following steps: (1) Measuring the inter-detector offset. The offset is defined as the geometric volume offset between the LS detector and the concentration detector. It is calculated as the difference in elution volume (mL) of the polymer peak between the concentration detector and the LS chromatogram. This is converted to a temperature offset using the elution heat rate and elution flow rate. Using linear high-density polyethylene (comonomer content of zero, melt index (I2) of 1.0), the polydispersity Mw was obtained by conventional gel permeation chromatography. w / Mn Approximately 2.6). The same experimental conditions as the normal iCCD method described above were used, except for the following parameters: crystallization from 140°C to 137°C at 10°C / min, thermal equilibration at 137°C for 1 minute as the elution time for the soluble fraction, elution time for the soluble fraction (SF) of 7 minutes, and elution from 137°C to 142°C at 3°C / min. The flow rate during crystallization was 0.0 ml / min. The flow rate during elution was 0.80 ml / min. The sample concentration was 1.0 mg / ml. (2) Before integration, each LS data point in the LS chromatogram was shifted to correct for detector offset. (3) The baseline of step (1) was subtracted from the LS and concentration chromatograms over the entire elution temperature range. The MW detector constant was calculated using known MW HDPE samples in the range of 100,000 to 140,000 Mw and the area ratio of the LS and concentration integrated signals. (4) The Mw of the polymer was calculated by using the ratio of the integrated light scattering detector (90-degree angle) to the concentration detector and the MW detector constant.

[0106] Conventional GPC (M w , M n , M w / M n )

[0107] The chromatographic system consisted of a PolymerChar GPC-IR (Valencia, Spain) high-temperature GPC chromatograph equipped with an internal IR5 infrared detector (IR5) connected to a Precision Detector (now an Agilent Technologies 2040 2-angle laser scattering (LS) detector. A 15-degree angle was used for all light scattering measurements. The autosampler oven chamber was set to 160°C, and the column chamber to 150°C. Four Agilent "Mixed A" 30 cm 20 μm linear mixed-bed columns were used. The chromatographic solvent used was 1,2,4-trichlorobenzene containing 200 ppm butylated hydroxytoluene (BHT). The solvent source was nitrogen injection. The injection volume was 200 μL, and the flow rate was 1.0 mL / min.

[0108] GPC column calibration was performed using 21 polystyrene standards with narrow molecular weight distributions, ranging from 580 to 8,400,000, arranged in a six-cocktail mixture, with individual molecular weights spaced at least tenfold apart. The standards were purchased from Agilent Technologies. For molecular weights equal to or greater than 1,000,000, 0.025 g of polystyrene standard was prepared in 50 mL of solvent; for molecular weights less than 1,000,000, 0.05 g of polystyrene standard was prepared in 50 mL of solvent. The polystyrene standards were dissolved at 80°C and gently stirred for 30 min. The peak molecular weights of the polystyrene standards were converted to polyethylene molecular weights using Equation 1 (as described in Williams and Ward, *Journal of Polymer Science, Polymer Letters*, 6, 621 (1968)).

[0109] (Equation 1)

[0110] Where M is the molecular weight, A has a value of 0.4315, and B equals 1.0.

[0111] A fifth-order polynomial was used to fit the calibration point for the corresponding polyethylene equivalent. Small adjustments were made to A (from approximately 0.415 to 0.44) to correct for column resolution and band broadening effects, resulting in NIST standard NBS 1475 at 52,000 Mw.

[0112] Plate counting was performed on the GPC column assembly using eicosane (prepared in 50 mL of TCB at 0.04 g and dissolved under slow stirring for 20 min). Plate counts (Equation 2) and symmetry (Equation 3) were measured at 200 μL injections according to the following equations:

[0113] (Equation 2)

[0114] Where RV is the retention volume in milliliters, peak width is in milliliters, peak maximum is the maximum height of the peak, and ½ height is half the height of the peak maximum.

[0115] (Equation 3)

[0116] Where RV is the retention volume in milliliters, and peak width is in milliliters, peak maximum is the position of the peak value, one-tenth height is 1 / 10 of the height of the peak maximum, and a subsequent peak refers to the tail of a peak whose retention volume is later than the peak maximum, while a preceding peak refers to the front of a peak whose retention volume is earlier than the peak maximum. The plate count of the chromatographic system should be greater than 24,000, and the symmetry should be between 0.98 and 1.22.

[0117] Samples were prepared semi-automatically using PolymerChar "Instrument Control" software, with a target sample weight of 2 mg / ml. Solvent (containing 200 ppm BHT) was added to a pre-bubbled, diaphragm-capped vial via a PolymerChar high-temperature autosampler. The sample was then dissolved at 160°C for 2 hours with "low-speed" shaking.

[0118] Based on the GPC results, using the internal IR5 detector (measurement channel) of the PolymerChar GPC-IR chromatograph, according to Equations 4-6, the PolymerChar GPCOne was used. ™ The software calculates the Mn content based on the baseline-subtracted IR chromatograms at each equidistant data collection point (i) and the polyethylene equivalent molecular weight obtained from the narrow standard calibration curve at point (i) according to Equation 1. (GPC) Mw (GPC) and Mz (GPC) The calculation.

[0119] (Equation 4)

[0120] (Equation 5)

[0121] (Equation 6)

[0122] To monitor deviations over time, a flow rate marker (decane) was introduced into each sample via a micropump controlled by a PolymerChar GPC-IR system. This flow rate marker (FM) was used to linearly correct the pump flow rate (nominal flow rate) for each sample by comparing the RV (RV(FM sample)) of the corresponding decane peak within the sample with the RV (RV(FM calibrated)) of the decane peak within the narrow standard calibration. It was then assumed that any variation in the decane marker peak time was linearly related to the flow rate (effective flow rate) over the entire run. To facilitate the highest accuracy in RV measurement of the flow marker peak, a least-squares fitting procedure was used to fit the peak values ​​of the flow marker concentration chromatogram to a quadratic equation. The first derivative of the quadratic equation was then used to solve for the true peak position. After calibration based on the flow marker peak, the effective flow rate (relative to the narrow standard calibration) was calculated according to Equation 7. (via PolymerChar GPCOne) ™ The software processes the flow marker peaks. Acceptable flow rate correction ensures that the effective flow rate is within + / - 2% of the nominal flow rate.

[0123] Flow rate (effective) = Flow rate (nominal) * (RV (FM calibrated) / RV (FM sample)) (Equation 7)

[0124] A systematic method for determining multi-detector offset was developed in conjunction with Balke, Mourey et al. (Mourey and Balke, Chromatography Polym., Chapter 12, (1992)) (Balke, Thitiratsakul, Lew, Cheung, Mouurey, Chromatography Polym., Chapter 13, (1992)), thereby using PolymerChar GPCOne. ™ The software optimizes the triple detector logarithmic (MW and IV) results from wide homopolymer polyethylene standards (Mw / Mn>3) with the narrow standard column calibration results from the narrow standard calibration curve.

[0125] Absolute molecular weight data were obtained using PolymerChar GPCOne. ™The software was obtained in a manner consistent with the following publications: Zimm (Zimm, BH, *Chem. Phys.*, 16, 1099 (1948)) and Kratochvil (Kratochvil, P., *Classical Light Scattering from Polymer Solutions*, Elsevier, Oxford, NY (1987)). The total injection concentration used for determining the molecular weight was obtained from the mass detector area and the mass detector constant, which was derived from either a suitable linear polyethylene homopolymer or a polyethylene standard with a known weight-average molecular weight. The calculated molecular weight (using GPCOne) was... ™ The light scattering constant and refractive index concentration coefficient dn / dc of 0.104 are obtained using one or more polyethylene standards mentioned below. Typically, the mass detector response (IR5) and light scattering constant (using GPCOne) are also used. ™ The determination should be performed using linear standards with a molecular weight exceeding approximately 50,000 g / mol. Other corresponding torques Mn (Abs) and Mz (Abs) The calculation is based on equation 8-9 as follows:

[0126] (Equation 8)

[0127] (Equation 9)

[0128] DSC method - heat of fusion

[0129] Differential scanning calorimetry (DSC) is a common technique used to examine the melting and crystallization of semi-crystalline polymers. The general principles of DSC measurements and its applications in the study of semi-crystalline polymers are described in standard texts (e.g., E.A. Turi, ed., *Thermal Characterization of Polymeric Materials*, Academic Press, 1981).

[0130] The heat of fusion was determined using a DSC from TA Instruments, Inc. The test was performed according to ASTM standard D3428. Calibration was performed by preparing 2-3 mg of indium and placing it in a T-zero aluminum pan. The pan was then loaded into the DSC instrument and the following heating program was cycled: 1) equilibrate the test chamber at 180°C, 2) hold the temperature at 180°C for 1 minute, 3) gradually decrease the temperature to 130°C at a rate of 10°C / min, 4) hold the temperature at 130°C for 3 minutes, and 5) gradually increase the temperature back to 180°C at a rate of 10°C / min. Once completed, the final heating profile from step 5 was analyzed to determine the melting temperature of the indium sample. If the melting temperature was within a 0.5°C tolerance of 156.6°C, the DSC was considered to be operating compliantly.

[0131] For sample testing, the polymer sample was first pressed into a film at 190°C. Approximately 4 to 5 mg of sample was weighed and placed in a DSC pan. The lid was screwed on tightly to ensure a sealed atmosphere. The sample pan was placed in the DSC cell and equilibrated at 180°C. The sample was held at this temperature for 5 minutes. The sample was then cooled to -90°C at a rate of 10°C / min and held isothermally at this temperature for 5 minutes. Subsequently, the sample was heated to 150°C at a rate of 10°C / min (to ensure complete melting); this step was designated as the second heating curve. The peak melt temperature, the onset and peak crystallization temperatures, and the heat of fusion (also known as the heat of melting) ΔHf of the resulting enthalpy curve were analyzed. The heat of fusion, in Joules per gram, was measured from the second heating curve by linear integration of the endothermic melting from the baseline.

[0132] Dart drop

[0133] The dart test follows ASTM D1709 Method A and provides a measure of the energy required to cause failure of a plastic film under specific conditions of impact by a freely falling dart. The test result is expressed as the energy of a projectile dropped from a specified height (which will cause failure in 50% of the tested specimens). The film samples are conditioned at 23°C (±2°C) and 50% RH (±10%) for at least 40 hours prior to testing. Method A with a 1.5" diameter dart head and a 26" drop height will be used for the current film samples. The dart head is constructed of aluminum. The sample thickness at the center is measured, and the sample is then clamped using a ring-shaped specimen holder with an inner diameter of 5". A dart is loaded above the center of the sample and released via a pneumatic or electromagnetic mechanism. The dart is loaded with an initial weight, which is subsequently increased or decreased based on the pass / fail of each drop. Drop tests typically use approximately 20-25 specimens. Finally, the "dart" value is calculated using the step method according to ASTM D1709, based on the collected pass / fail data, initial weight, and weight increments.

[0134] Elmendorf tear resistance

[0135] The average Elmendorf tear resistance was measured in the longitudinal (MD) and transverse (CD) directions according to ASTM D1922.

[0136] High throughput creep

[0137] High-throughput creep was measured according to ISO 899 standard.

[0138] Aspects

[0139] According to a first aspect, the multilayer film may include a first surface layer, a second surface layer, and a core located between the first surface layer and the second surface layer, wherein: the first surface layer and the second surface layer independently comprise linear low-density polyethylene (LLDPE) resin; the core comprises a first core layer, a second core layer, and a third core layer; the first core layer and the third core layer may independently comprise high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), or a combination thereof; the second core layer may comprise an ethylene-based copolymer selected from the group consisting of: ethylene / propylene copolymer, ethylene / butyl acrylate copolymer, ethylene / ethyl acrylate copolymer, ethylene / methyl acrylate copolymer, and ethylene / vinyl acetate copolymer; the thickness of the second core layer may be less than 15% of the thickness of the multilayer film; and at least one of the core layers comprises high-density polyethylene (HDPE).

[0140] According to the second aspect, in conjunction with the first aspect, the second core layer may be located between the first core layer and the third core layer.

[0141] According to the third aspect, in conjunction with the first or second aspect, the second core layer may also contain calcium carbonate.

[0142] According to the fourth aspect, in conjunction with any one of aspects 1 to 3, the multilayer film may contain at least 30% by weight of HDPE based on the total polymer weight of the multilayer film.

[0143] According to the fifth aspect, in conjunction with any one of aspects 1 to 4, the second core layer may comprise an ethylene-based copolymer selected from the group consisting of: ethylene / butyl acrylate copolymer, ethylene / ethyl acrylate copolymer, and ethylene / methyl acrylate copolymer.

[0144] According to the sixth aspect, in conjunction with any one of aspects 1 to 5, the first surface layer, the second surface layer, or both may further comprise low-density polyethylene (LDPE).

[0145] According to the seventh aspect, in conjunction with any one of aspects 1 to 6, the core may further include: a fourth core layer located between the first surface layer and the first core layer; and a fifth core layer located between the third core layer and the second surface layer.

[0146] According to the eighth aspect, in conjunction with any one of aspects 1 to 7, the fourth core layer and the fifth core layer may each independently comprise HDPE, LLDPE, or a combination thereof.

[0147] According to the ninth aspect, in conjunction with any one of aspects 1 to 8, the second core layer may have a thickness less than or equal to 10% of the thickness of the multilayer film.

[0148] According to the tenth aspect, in conjunction with any one of aspects 1 to 8, 10, the multilayer film may have a thickness of less than 180 µm.

[0149] According to the eleventh aspect, in conjunction with any one of aspects 1 to 10, the multilayer film may have a normalized dart impact type A of at least 4.4 g / µm.

[0150] According to the twelfth aspect, in conjunction with any one of aspects 1 to 11, the multilayer film may have a normalized Elmendorf transverse tear resistance of at least 16.6 gf / µm.

[0151] According to aspect thirteen, in conjunction with any one of aspects 1 to 12, the multilayer film may have a normalized Elmendorf longitudinal tear resistance of at least 8.8 gf / µm.

[0152] According to aspect fourteen, in conjunction with any one of aspects 1 to 13, the multilayer membrane may have a high-flux creep of less than 50%.

[0153] According to aspect fifteen, in conjunction with any one of aspects 1 to 14, the second core layer may be a central layer, the second core layer may be located between the first core layer and the third core layer, the multilayer film may have a density of 0.929 g / cc to 0.942 g / cc, the first surface layer, the second surface layer, or both may further comprise low-density polyethylene (LDPE), the second core layer may have a thickness less than or equal to 10% of the thickness of the multilayer film, the multilayer film may have a thickness less than or equal to 110 µm, the multilayer film may have a dart impact A rating of at least 4.4 g / µm, the multilayer film may have an Elmendorf transverse tear resistance of at least 16.6 gf / µm, and the multilayer film may have an Elmendorf longitudinal tear resistance of at least 8.8 gf / µm.

[0154] Examples

[0155] The following examples are provided to illustrate the implementation schemes described in this disclosure, and these examples are not intended to limit the scope of this disclosure or its appended claims.

[0156] Materials

[0157] INNATE ™ ST50 (also referred to herein as "ST50") is a linear low-density polyethylene with a density of 0.918 g / cm³. 3 It has a melt index (I2) of 0.85 g / 10 min and is commercially available from Dow Chemical Company (Midland, Michigan). ™ ST50 is an ethylene-based polymer, as the term is defined herein.

[0158] INNATE ™ ST70 (also referred to herein as "ST70") is a linear low-density polyethylene with a density of 0.926 g / cm³. 3 It has a melt index (I2) of 0.85 g / 10 min and is commercially available from Dow Chemical Company (Midland, Michigan). ™ ST70 is an ethylene-based polymer, as the term is defined herein.

[0159] INNATE ™ ST100 (also referred to herein as "ST100") is a linear low-density polyethylene with a density of 0.928 g / cm³.3 It has a melt index (I2) of 0.85 g / 10 min and is commercially available from Dow Chemical Company (Midland, Michigan). ™ ST100 is an ethylene-based polymer, as the term is defined herein.

[0160] ELITE ™ 5400, a linear low-density polyethylene with a density of 0.916 g / cm³. 3 It has a melt index (I2) of 1.0 g / 10 min and is commercially available from Dow Chemical Company (Midland, Michigan). ELITE ™ 5400 is an ethylene-based polymer, as the term is defined herein.

[0161] DOWLEX ™ GM 8090 (also referred to herein as "GM 8090") is linear low-density polyethylene, commercially available from Dow Chemical Company (Midland, Michigan). ™ GM 8090 has a strength of 0.916 g / cm³. 3 Its density and melt index (I2) of 1.0 g / 10 min. DOWLEX ™ GM 8090 is an ethylene-based polymer, as the term is defined herein.

[0162] AGILITY ™ AT 1604 is low-density polyethylene with a density of 0.921 g / cm³. 3 Furthermore, it has a melt index (I2) of 0.25 g / 10 min and is commercially available from Dow Chemical Company (Midland, Michigan). ™ AT 1604 is an ethylene-based polymer, as the term is defined herein.

[0163] UNIVAL ™ DMDA 6400 (also referred to as "DMDA 6400" in this document) is high-density polyethylene with a density of 0.961 g / cm³. 3 And the melt index (I2) is 0.80 g / 10 min, and the melt index (I) is... 21 The concentration is 57 g / 10 min, and it is commercially available from Dow Chemical Company (Midland, Michigan). UNIVAL ™ DMDA 6400 is an ethylene-based polymer, as the term is defined herein.

[0164] ELVALOY ™AC 3117 (also referred to herein as "EA") is an ethylene-acrylate copolymer (83% ethylene and 17% butyl acrylate) with a density of 0.924 g / cm³. 3 It has a melt index (I2) of 1.5 g / 10 min and is commercially available from Dow Chemical Company (Midland, Michigan). ELVALOY ™ AC 3117 is an ethylene-acrylate copolymer, as the term is defined herein.

[0165] Some implementations use ELVALOY ™ A blend of AC 3117 and CaCO3 (also referred to herein as "EA+CaCO3"). Based on the total weight of the layers, the blend contains approximately 42% by weight of calcium carbonate, with the balance being an ethylene-acrylate copolymer.

[0166] XUS 39003.00 (also referred to herein as "EP") is an ethylene-propylene copolymer commercially available from Dow Corporation (Midland, Michigan). EP contains 27.1 wt% propylene comonomer and 72.9 wt% ethylene monomer and has a density of 0.867 g / cm³. 3 The melt index (I2) is 0.90 g / 10 min, I 10 The I2 ratio is 10.82, the heat of fusion is 50.24 J / g, and the Mw / Mn ratio is 3.98. EP has a proportion of 0.8 wt% of reverse-inserted propylene units based on 2,1 insertions, where the weight percentage is based on the total weight of EP. EP is an ethylene-based polymer, as the term is defined herein.

[0167] Some embodiments use a blend of XUS 39003.0 (“EP”) and calcium carbonate (also referred to herein as “EP+CaCO3”). Based on the total weight of the layers, the blend contains approximately 42% by weight of calcium carbonate, with the balance being an ethylene-propylene copolymer.

[0168] ELITE ™ 5960G1 (also referred to herein as "5960") is high-density polyethylene (HDPE) commercially available from Dow Chemical Company (Midland, Michigan). 5960 has a melt index (I2) of 8.5 g / 10 min and a melt flow rate of 0.962 g / cm³. 3 The density. 5960 is an ethylene-based polymer, as the term is defined herein.

[0169] 5-layer film

[0170] A series of five-layer multilayer films were prepared by co-extrusion on the Tarragona Collin co-extrusion line. Each layer was extruded on a separate extruder. Unless otherwise specified, the resulting films had a thickness of approximately 100 μm.

[0171] Table 1 shows the composition of some of the 5-layer multilayer films disclosed herein.

[0172]

[0173] Table 2 shows some of the mechanical properties of the five-layer membrane described in Table 1.

[0174]

[0175] As shown in Table 2, the comparison membrane CE-A exhibits sufficient dart resistance (size >400g) and creep resistance (size <50%). However, it falls short in both MD-tear and CD-tear resistance (sizes >800g and >1500g, respectively). It should be noted that CE-A is 60% by weight HDPE, while EX-1 through EX-11 each comprise 30% by weight HDPE.

[0176] Embodiments of this disclosure including a second core layer exhibit significant improvements in properties, particularly at densities above 0.934 g / c. The extremely high dart and tear resistance will also allow for increased HDPE content (which will improve creep properties at the expense of dart and tear resistance). This is the approach followed in optimizing the following 7-layer structure.

[0177] When observing the different components of the second core layer, EA+CaCO3 provided most of the optimal mechanical properties due to the synergistic effect between the ethylene-acrylate copolymer and calcium carbonate. However, the calcium carbonate-free implementation provided improved creep.

[0178] A comparison of EX-1 with EX-9 and EX-20 shows that using 5% high melt strength LDPE (such as AGILITY AT 1604) in the surface layer improves creep without negatively impacting other properties (dart and tear). Furthermore, creep is improved even more when only one surface layer contains LDPE. Further optimization is possible by selecting the optimal surface layer, or by increasing the HDPE content in the core layer blend.

[0179] 7-layer film

[0180] A series of 7-layer multilayer films were prepared by co-extrusion on the Tarragona Collin co-extrusion line. Each layer was extruded on a separate extruder. Unless otherwise specified, the resulting films had a thickness of approximately 100 μm. Details of the films are included in Table 3 below.

[0181]

[0182] Table 4-A provides material properties for some embodiments of the 7-layer membrane, in which a second core layer is provided at the center.

[0183]

[0184] As can be seen from Table 4-A, the embodiments of this disclosure exhibit excellent mechanical properties. This is true for both the ethylene-acrylate copolymer and ethylene-propylene copolymer embodiments. Furthermore, while the overall enhancement of properties is less than 5% when the thickness of the second core layer increases from 5% to 10%, it is still significant. This can be seen by comparing EX-18.

[0185] Table 4-B provides material properties for some embodiments of the 7-layer membrane, where the second core layer is not in the center. In EX-19, the second core layer is in layer B. In EX-20, the second core layer is in layer C.

[0186]

[0187] Comparing EX-19 and EX-20 with other embodiments reveals that the mechanical properties are better when the second core layer is the center layer, relative to when the second core layer is one of the other core layers. However, the mechanical properties are still significantly improved compared to the absence of a second core layer.

[0188] Table 4-C provides details of an implementation scheme for Example 14, which has been reduced from 100 μm thickness to 95 μm and is labeled EX-14(b). The relative thickness of each layer remains the same as shown in Table 3.

[0189] Table 3: 7L with thickness reduced to 95µm

[0190]

[0191] When the EX-14 membrane was thinned from 100 μm to 95 μm, the resulting membrane still exceeded the parameters required for the HDSS membrane.

[0192] While specific embodiments of this disclosure have been described and illustrated, it will be apparent to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of this disclosure. Therefore, it is intended that all such changes and modifications be covered within the scope of this disclosure in the appended claims. Claims (as amended under Article 19 of the Treaty) 1. A multilayer film, the multilayer film comprising a first surface layer, a second surface layer, and a core located between the first surface layer and the second surface layer, wherein: The first and second surface layers independently comprise linear low-density polyethylene (LLDPE) resin; The core includes a first core layer, a second core layer, and a third core layer; The first core layer and the third core layer independently comprise high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), or a combination thereof; The second core layer comprises an ethylene-based copolymer selected from the group consisting of: ethylene / propylene copolymer, ethylene / butyl acrylate copolymer, ethylene / ethyl acrylate copolymer, ethylene / methyl acrylate copolymer, and ethylene / vinyl acetate copolymer; The thickness of the second core layer is less than 15% of the thickness of the multilayer film; At least one of the core layers comprises high-density polyethylene (HDPE); and based on the total polymer weight of the multilayer film, the multilayer film comprises at least 30% by weight of HDPE. 2. The multilayer film according to claim 1, wherein the second core layer is located between the first core layer and the third core layer. 3. The multilayer film according to any of the preceding claims, wherein the second core layer further comprises calcium carbonate. 4. The multilayer film according to any of the preceding claims, wherein the second core layer comprises an ethylene-based copolymer selected from the group consisting of: ethylene / butyl acrylate copolymer, ethylene / ethyl acrylate copolymer, and ethylene / methyl acrylate copolymer. 5. The multilayer film according to any of the preceding claims, wherein the first surface layer, the second surface layer, or both further comprise low-density polyethylene (LDPE). 6. The multilayer film according to any preceding claim, wherein the core further comprises: The fourth core layer, located between the first surface layer and the first core layer, and The fifth core layer is located between the third core layer and the second surface layer. 7. The multilayer film according to claim 7, wherein the fourth core layer and the fifth core layer each independently comprise HDPE, LLDPE, or a combination thereof. 8. The multilayer film according to any of the preceding claims, wherein the second core layer has a thickness less than or equal to 10% of the thickness of the multilayer film. 9. The multilayer film according to any of the preceding claims, wherein the multilayer film has a thickness of less than 180 µm. 10. The multilayer film according to any of the preceding claims, wherein the multilayer film has a dart impact type A of at least 4.4 g / µm. 11. The multilayer film according to any of the preceding claims, wherein the multilayer film has an Elmendorf transverse tear resistance of at least 16.6 gf / µm. 12. The multilayer film according to any of the preceding claims, wherein the multilayer film has an Elmendorf longitudinal tear resistance of at least 8.8 gf / µm. 13. The multilayer membrane according to any of the preceding claims, wherein the multilayer membrane has a high-flux creep of less than 50%. 14. The multilayer film according to any of the preceding claims, wherein: The second core layer is the central layer. The second core layer is located between the first core layer and the third core layer. The multilayer film has a density of 0.929 g / cc to 0.942 g / cc. The first surface layer, the second surface layer, or both further comprise low-density polyethylene (LDPE). The second core layer has a thickness less than or equal to 10% of the thickness of the multilayer film. The multilayer film has a thickness of less than or equal to 110 µm, and the multilayer film has a dart impact type A of at least 4.4 g / µm. The multilayer film has an Elmendorf transverse tear resistance of at least 16.6 gf / µm, and The multilayer film has an Elmendorf longitudinal tear resistance of at least 8.8 gf / µm.

Claims

1. A multilayer film, the multilayer film comprising a first surface layer, a second surface layer, and a core located between the first surface layer and the second surface layer, wherein: The first and second surface layers independently comprise linear low-density polyethylene (LLDPE) resin; The core includes a first core layer, a second core layer, and a third core layer; The first core layer and the third core layer independently comprise high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), or a combination thereof; The second core layer comprises an ethylene-based copolymer selected from the group consisting of: ethylene / propylene copolymer, ethylene / butyl acrylate copolymer, ethylene / ethyl acrylate copolymer, ethylene / methyl acrylate copolymer, and ethylene / vinyl acetate copolymer; The thickness of the second core layer is less than 15% of the thickness of the multilayer film; and At least one of the core layers comprises high-density polyethylene (HDPE).

2. The multilayer film according to claim 1, wherein the second core layer is located between the first core layer and the third core layer.

3. The multilayer film according to any of the preceding claims, wherein the second core layer further comprises calcium carbonate.

4. The multilayer film according to any of the preceding claims, wherein the multilayer film comprises at least 30% by weight of HDPE based on the total polymer weight of the multilayer film.

5. The multilayer film according to any of the preceding claims, wherein the second core layer comprises an ethylene-based copolymer selected from the group consisting of: ethylene / butyl acrylate copolymer, ethylene / ethyl acrylate copolymer, and ethylene / methyl acrylate copolymer.

6. The multilayer film according to any of the preceding claims, wherein the first surface layer, the second surface layer, or both further comprise low-density polyethylene (LDPE).

7. The multilayer film according to any preceding claim, wherein the core further comprises: The fourth core layer, located between the first surface layer and the first core layer, and The fifth core layer is located between the third core layer and the second surface layer.

8. The multilayer film according to claim 7, wherein the fourth core layer and the fifth core layer each independently comprise HDPE, LLDPE, or a combination thereof.

9. The multilayer film according to any of the preceding claims, wherein the second core layer has a thickness less than or equal to 10% of the thickness of the multilayer film.

10. The multilayer film according to any of the preceding claims, wherein the multilayer film has a thickness of less than 180 µm.

11. The multilayer film according to any of the preceding claims, wherein the multilayer film has a dart impact type A of at least 4.4 g / µm.

12. The multilayer film according to any of the preceding claims, wherein the multilayer film has an Elmendorf transverse tear resistance of at least 16.6 gf / µm.

13. The multilayer film according to any of the preceding claims, wherein the multilayer film has an Elmendorf longitudinal tear resistance of at least 8.8 gf / µm.

14. The multilayer membrane according to any of the preceding claims, wherein the multilayer membrane has a high-flux creep of less than 50%.

15. The multilayer film according to any of the preceding claims, wherein: The second core layer is the central layer. The second core layer is located between the first core layer and the third core layer. The multilayer film has a density of 0.929 g / cc to 0.942 g / cc. The first surface layer, the second surface layer, or both further comprise low-density polyethylene (LDPE). The second core layer has a thickness less than or equal to 10% of the thickness of the multilayer film. The multilayer film has a thickness of less than or equal to 110 µm. The multilayer film has a dart impact type A of at least 4.4 g / µm. The multilayer film has an Elmendorf transverse tear resistance of at least 16.6 gf / µm, and The multilayer film has an Elmendorf longitudinal tear resistance of at least 8.8 gf / µm.

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