Multilayer film containing an ionomer of an ethylene acid polymer

Abstract

A multilayer film is provided that includes a zinc or sodium ionomer of an ethylene acid copolymer. The multilayer film can be fully compatible with the polyethylene recycling stream. The multilayer film includes a first outer layer, a second outer layer, and a core, and the core includes a first core layer that includes a zinc or sodium ionomer of an ethylene acid copolymer. The multilayer film of the present invention can exhibit improved, maintained, or desirable properties, such as high tear resistance, compared to existing multilayer film structures.

Description

Technical Field

[0001] Embodiments of the present disclosure generally relate to multilayer films, and more specifically, to multilayer films comprising a zinc or sodium ionomer of an ethylene acid copolymer.

[0002] Introduction An increasingly relevant problem in the packaging industry is the large amount of packaging waste and the lack of flexibility in packaging with a poor balance of rigidity and toughness. Multilayer films incorporating various materials, including polypropylene, polyamide, and polyethylene terephthalate, contribute to bulky packaging in industrial and consumer products. Such films used, for example, often require sufficient toughness and tear resistance to avoid film breakage during the film packaging process on a pallet. Combinations of layers and materials can enable good film performance, but such multilayer films may lack a balance between rigidity and toughness and can be difficult, if not impossible, to recycle together due to different types of materials that are not recyclable compatible with each other. There remains a need for multilayer films that are more easily recyclable and exhibit a balance of desired properties such as tear resistance, toughness, and / or rigidity, as the demand for less bulky, single-material, and recyclable materials continues to increase.

Summary of the Invention

[0003] Embodiments of the present disclosure meet one or more of the foregoing needs by providing a multilayer film comprising a recyclable compatible ethylene-based polymer comprising a zinc or sodium ionomer of an ethylene acid copolymer, which exhibits a desirable balance of tear resistance, toughness, and rigidity. The multilayer film can be fully recyclable compatible in the polyethylene recycling stream, and the tear resistance and toughness performance of the multilayer film of the present invention can be comparable to or better than those of other multilayer films.

[0004] Disclosed herein is a multilayer film. In one aspect, the multilayer film includes a first outer layer, a second outer layer, and a core, the core includes one or more core layers, the first core layer includes 5 to 45 wt% of a zinc or sodium ionomer of an ethylene acid copolymer based on the total weight of the first core layer, and 55 to 95 wt% of a polyethylene having a density of 0.950 to 0.970 g / cm 3 and a melt index (I2) of 0.3 to 10.0 g / 10 min, and the first core layer has a thickness of 5 to 40% of the total thickness of the multilayer film.

[0005] Also disclosed herein are articles. The articles can include a multilayer film according to the embodiments disclosed herein.

[0006] These and other embodiments are described in more detail in the "Detailed Description of the Invention".

Detailed Description of the Invention

[0007] The disclosed aspects of the multilayer film are described in more detail below. The multilayer film can have a wide variety of uses, for example, cast stretch film, inflation film, oriented film, stretch hood film, durable shipping bags, and the like. However, since the present disclosure is an exemplary implementation of the embodiments described herein, the present disclosure should not be construed as limiting the embodiments described below.

[0008] As used herein, the term "polymer" means a polymeric compound prepared by polymerizing monomers, whether of the same or different types. Thus, the general term "polymer" encompasses the term "homopolymer" (used to refer to a polymer prepared from only one type of monomer) and the term "copolymer". Trace amounts of impurities (e.g., catalyst residues) may be incorporated into and / or present within the polymer. The polymer can be a single polymer, a polymer blend, or a polymer mixture containing a mixture of polymers formed in situ during polymerization.

[0009] As used herein, the term "copolymer" means a polymer formed by the polymerization reaction of at least two structurally different monomers. The term "copolymer" includes terpolymers.

[0010] As used herein, the term "polyethylene" or "ethylene-based polymer" shall mean a polymer containing a majority (more than 50 wt%) of units derived from ethylene monomers. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers). Unless otherwise specified, the ethylene copolymers disclosed herein (e.g., the zinc or sodium ionomers of the ethylene acid copolymers described herein) are ethylene-based polymers.

[0011] Common forms of polyethylene well-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-site catalyst linear low density polyethylene (m-LLDPE) including both linear low density resin and substantially linear low density resin, ethylene plastomer (POP) and ethylene elastomer (POE), Medium Density Polyethylene (MDPE), and High Density Polyethylene (HDPE). These polyethylene materials are generally well-known in the art. However, the following description may be useful in understanding the differences among some of these different polyethylene resins.

[0012] The term "LDPE" may also be referred to as "high-pressure ethylene polymer" or "highly branched polyethylene", but is defined to mean that the polymer is homopolymerized or copolymerized, partially or completely, in an autoclave or tubular reactor at a pressure above 14,500 psi (100 MPa) using a free radical initiator such as peroxide (see, for example, U.S. Patent No. 4,599,392, which is incorporated herein by reference). LDPE resins typically have a density in the range of 0.916 - 0.935 g / cm 3 within the range.

[0013] The term "LLDPE" includes both resins made using single-site catalysts including, but not limited to, traditional Ziegler-Natta catalyst systems and chromium-based catalysts, as well as mono- or bis-cyclopentadienyl catalysts (typically referred to as metallocenes), geometrically constrained catalysts, phosphine imine catalysts, and polyvalent aryloxy ether catalysts (typically referred to as bisphenol phenoxy), and includes linear, substantially linear, or heterogeneous polyethylene copolymers or homopolymers. LLDPE contains fewer long-chain branches than LDPE and is 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 as substantially linear ethylene polymers, homogeneous branched linear ethylene polymer compositions such as those of U.S. Patent No. 3,645,992, heterogeneous branched ethylene polymers prepared according to the process disclosed in U.S. Patent No. 4,076,698, and / or blends thereof (such as those disclosed in U.S. Patent No. 3,914,342 or U.S. Patent No. 5,854,045). LLDPE 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.

[0014] The term "MDPE" refers to polyethylene having a density of 0.926 to 0.935 g / cm 3 . "MDPE" is typically produced using a chromium or Ziegler-Natta catalyst or using a single-site catalyst including, but not limited to, substituted mono- or bis-cyclopentadienyl catalysts (typically referred to as metallocenes), geometrically constrained catalysts, phosphine imine catalysts, and polyvalent aryloxy ether catalysts (typically referred to as bisphenol phenoxy) and typically has a molecular weight distribution ("MWD") greater than 2.5.

[0015] The term "HDPE" refers to polyethylene having a density of about 0.935 g / cm 3 to a maximum of about 0.980 g / cm 3 prepared using single-site catalysts including, but not limited to, Ziegler-Natta catalysts, chromium catalysts, or substituted mono- or bis-cyclopentadienyl catalysts (typically referred to as metallocenes), geometrically constrained catalysts, phosphine imine catalysts, and polyvalent aryloxy ether catalysts (typically referred to as bisphenol phenoxy).

[0016] The term "ULDPE" refers to polyethylene having a density of 0.855 to 0.912 g / cm 3 prepared using single-site catalysts including, but not limited to, Ziegler-Natta catalysts, chromium catalysts, or substituted mono- or bis-cyclopentadienyl catalysts (typically referred to as metallocenes), geometrically constrained catalysts, phosphine imine catalysts, and polyvalent aryloxy ether catalysts (typically referred to as bisphenol phenoxy). ULDPE includes, but is not limited to, polyethylene (ethylene-based) plastomers and polyethylene (ethylene-based) elastomers.

[0017] As used herein, the term "zinc or sodium ionomer of ethylene acid copolymer" means an ionomer comprising an ethylene acid copolymer having carboxylic acid groups neutralized as carboxylates containing zinc or sodium cations, wherein the ethylene acid copolymer is a polymerization reaction product of more than 50 wt% ethylene monomer and more than 2 wt% monocarboxylic acid monomer based on the total weight of the monomers present in the ethylene acid copolymer.

[0018] As used herein, the term "core layer" refers to the non-skin or non-outer layer of a multilayer film. The core layer is the inner layer of the multilayer film, i.e., the layer positioned between two outer layers. In one embodiment, the first core layer is the non-outer layer of a three-layer film including a first outer layer and a second outer layer. The entirety of the core layer of the multilayer film of the present invention, i.e., one or more, constitutes the "core" of the film.

[0019] The terms "comprising", "including", "having" and their derivatives are not intended to exclude the presence of any additional constituent, step, or procedure, whether or not specifically disclosed. To avoid any doubt, all compositions claimed through the use of the term "comprising" may include any additional additive, adjuvant, or compound, whether polymeric or otherwise, unless there is a contradictory description. In contrast, the term "consisting essentially of" excludes any other component, step, or procedure from the scope of any subsequent description, except those that are not operationally essential. The term "consisting of" excludes any constituent, step, or procedure not specifically depicted or listed.

[0020] Disclosed herein is a multilayer film. In some embodiments, the multilayer film can be an oriented film oriented in the machine direction and / or the transverse direction. In some embodiments, the multilayer film is an inflation film. In other embodiments, the multilayer film is a cast stretch film. In further embodiments, the multilayer film is a stretch hood film.

[0021] The multilayer film according to the embodiments disclosed in this specification includes a first outer layer, a second outer layer, and a core, and the core includes one or more core layers. The core is disposed between the first outer layer and the second outer layer. The core includes a first core layer containing a zinc or sodium ionomer of an ethylene acid copolymer and polyethylene.

[0022] The first outer layer and the second outer layer of the multilayer film The first outer layer and the second outer layer of the multilayer film are not particularly limited. The first outer layer and the second outer layer can have the same polymer composition or different polymer compositions. In some embodiments, each of the first outer layer and the second outer layer has a thickness that is 5-35% of the total thickness of the multilayer film.

[0023] In some embodiments, each of the first outer layer and the second outer layer contains polyethylene. In some embodiments, the first outer layer and / or the second outer layer contains an ethylene-based polymer such as ULDPE, LLDPE, LDPE, MDPE, or HDPE. For example, in some embodiments, the first outer layer and / or the second outer layer contains ULDPE, LLDPE, LDPE, or a blend thereof.

[0024] In embodiments where the first outer layer and / or the second outer layer contains polyethylene, the polyethylene can have the following density. 0.940 g / cm 3 The following density can be had. 0.940 g / cm 3 All of the following individual values and subranges are included and disclosed herein. For example, the density of polyethylene can be from 0.870, 0.880, 0.890, 0.910, or 0.920 g / cm 3 as the lower limit to 0.940, 0.935, 0.930, or 0.925 g / cm 3 as the upper limit. All individual values and subranges of 0.870 - 0.940 g / cm 3 are included and disclosed herein.

[0025] In embodiments where the first outer layer and / or the second outer layer comprises polyethylene, the polyethylene can 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 from 0.1 g / 10 min to 50 g / 10 min are disclosed and included herein. For example, the polyethylene can 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.

[0026] Commercially available examples of polyethylene that can be used for the first outer layer and / or the second outer layer include, for example, those sold under the name ATTANE™, including ATTANE™ 4404G from The Dow Chemical Company, and those sold under the name INNATE™, including INNATE™ ST50.

[0027] In some embodiments, the first outer layer and the second outer layer comprise ULDPE. In embodiments where the first outer layer and / or the second outer layer comprises ULDPE, the ULDPE can have the following density. 0.912 g / cm 3 It can have the following. 0.912 g / cm 3 All individual values and sub-ranges below are included and disclosed herein. For example, the density of the ULDPE can be from 0.855, 0.860, 0.870, 0.880, or 0.890 g / cm as the lower limit 3 to 0.912, 0.910, 0.908, or 0.906 g / cm as the upper limit. 3 It can be up to. All individual values and sub-ranges from 0.855 to 0.912 g / cm 3 are included and disclosed herein.

[0028] In embodiments where the first outer layer and / or the second outer layer comprises ULDPE, the ULDPE can 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 from 0.1 g / 10 min to 50 g / 10 min are disclosed and included herein. For example, the ULDPE can 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.

[0029] Core of the multilayer film The multilayer film includes a core. The core includes one or more core layers. In some embodiments, the core comprises 100% by weight of an ethylene-based polymer, including a zinc or sodium ionomer of an ethylene acid copolymer (described below), based on the total weight of the core. The core is disposed between the first outer layer and the second outer layer. The core includes a first core layer. In some embodiments, the multilayer film disclosed herein is a three-layer film including a first outer layer, a second outer layer, and a core, and the core includes a first core layer. In other embodiments, the multilayer film includes at least five layers. For example, in some embodiments, the core comprises a first core layer, a second core layer, and a third core layer, the first core layer is disposed between the first outer layer and the third core layer, the second core layer is disposed between the third core layer and the second outer layer, and the third core layer is disposed between the first core layer and the second core layer (i.e., first outer layer / first core layer / third core layer / second core layer / second outer layer). In embodiments where the core includes a first core layer, a second core layer, and a third core layer, the multilayer film includes at least five layers.

[0030] The core includes a first core layer. The first core layer is 5 to 45% by weight of a zinc or sodium ionomer of an ethylene acid copolymer and 55 to 95% by weight of polyethylene, based on the total weight of the first core layer, and has a density of 0.950 to 0.970 g / cm 3It includes polyethylene having a density of and a melt index (I2) of 0.3 to 10.0 g / 10 min. The first core layer has a thickness of 5 to 40% of the total thickness of the multilayer film.

[0031] The first core layer contains 5 to 45% by weight of a zinc or sodium ionomer of an ethylene acid copolymer based on the total weight of the first core layer. All individual values and subranges of 5 to 45% by weight are disclosed and included herein. For example, the first core layer may contain 5, 10, 15, 20, or 22% by weight as the lower limit to 27, 30, 35, 40, or 45% by weight as the upper limit of a zinc or sodium ionomer of an ethylene acid copolymer based on the total weight of the first core layer.

[0032] In some embodiments, the first core layer contains a zinc ionomer of an ethylene acid copolymer. In other embodiments, the first core layer contains a sodium ionomer of an ethylene acid copolymer. In some embodiments, the zinc or sodium ionomer of the ethylene acid copolymer has a density in the range of 0.940 to 0.960 g / cm 3 or 0.945 to 0.955 g / cm 3 In some embodiments, the zinc or sodium ionomer of the ethylene acid copolymer has a melt index (I2) of less than 3.0 g / 10 min, or less than 2.0 g / 10 min, or less than 1.0 g / 10 min.

[0033] Commercially available examples of the sodium ionomer of the ethylene acid copolymer that can be used in the first core layer and / or the second core layer include SURLYN (trademark) 1707. Commercially available examples of the zinc ionomer of the ethylene acid copolymer that can be used in the first core layer and / or the second core layer include SURLYN (trademark) 1706.

[0034] The first core layer is 55 to 95% by weight of polyethylene based on the total weight of the first core layer, with a density of 0.950 to 0.970 g / cm 3It includes polyethylene having a density of and a melt index (I2) of 0.3 to 10.0 g / 10 min. All individual values from 55 to 95 wt% are disclosed and included herein. For example, the first core layer may include from 60, 65, 70, 72, or 73 wt% as a lower limit to 78, 80, 85, 90, or 95 wt% as an upper limit of polyethylene based on the total weight of the first core layer.

[0035] The polyethylene of the first core layer has a density of 0.950 to 0.970 g / cm 3 In one or more embodiments, the polyethylene of the first core layer is high density polyethylene (HDPE). All individual values and subranges are disclosed and included herein. For example, the polyethylene of the first core layer has a density from 0.950, 0.952, 0.954, 0.956, 0.958, or 0.960 g / cm 3 to 0.970, 0.968, 0.966, 0.965, or 0.964 g / cm 3 as an upper limit. The polyethylene of the first core layer has a melt index (I2) of 0.3 to 10.0 g / 10 min. All individual values and subranges are disclosed and included herein. For example, the polyethylene of the first core layer has a melt index (I2) from 0.3, 0.4, 0.5, 0.6, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, or 7.0 g / 10 min as a lower limit to 10.0, 9.0, 8.5, 7.0, 6.0, 5.0, 4.0, 3.0, 2.0, or 1.0 g / 10 min as an upper limit.

[0036] Examples of commercially available polyethylenes that can be used in the first core layer and / or the second core layer include, for example, those commercially available under the names ELITE (trademark) 5960G1 and DOW (trademark) DMDA-8007 NT 7 from The Dow Chemical Company.

[0037] In some embodiments, the first core layer has a Raman measured percent crystallinity of 50% to 63%. The Raman crystallinity can be measured according to the test method described below.

[0038] In some embodiments, the multilayer film includes a second core layer. In some embodiments, the second core layer has the same polymer composition as the first core layer. In other embodiments, the second core layer has a polymer composition different from that of the first core layer. In some embodiments, the second core layer comprises, based on the total weight of the second core layer, 5 to 45 wt% of a zinc or sodium ionomer of an ethylene acid copolymer and 55 to 95 wt% of a polyethylene having a density of 0.950 to 0.970 g / cm 3 The polyethylene and the zinc or sodium ionomer of the ethylene acid copolymer of the second core layer can have the same density and melt index (I2) parameters as the polyethylene and ionomer of the first core layer.

[0039] In some embodiments, the multilayer film includes a third core layer. In such embodiments, the third core layer is disposed between the first core layer and the second core layer and comprises a polyethylene having a melt index of less than 7.0 g / 10 min and a density of less than 0.940 g / cm 3 The polyethylene of the third core layer can have a melt index of less than 7.0 g / 10 min, less than 6.0 g / 10 min, or less than 5.0 g / 10 min. The polyethylene of the third core layer can have a density of less than 0.940 g / cm 3 less than, less than 0.930 g / cm 3 less than, or less than 0.925 g / cm 3 less than.

[0040] Additive Any of the aforementioned layers may further include one or more additives known to those skilled in the art, such as antioxidants, UV stabilizers, heat stabilizers, slip agents, anti-blocking agents, antistatic agents, pigments or colorants, processing aids, crosslinking catalysts, flame retardants, fillers, and foaming agents. For example, in some embodiments, the first outer layer and the second outer layer each include an anti-blocking agent.

[0041] Multilayer film The multilayer films disclosed herein can be manufactured using techniques known to those skilled in the art based on the teachings herein. For example, the multilayer film can be manufactured by coextrusion. The formation of coextruded multilayer films is known in the art and applicable to the present disclosure. A coextrusion system for making a multilayer film uses at least two extruders that feed into a common die assembly. The number of extruders depends on the number of different materials or polymers that make up the coextruded film. For example, five-layer coextrusion may require up to five extruders, but the number of extruders can be reduced if two or more layers are made of the same material or polymer.

[0042] In various embodiments, the multilayer films of the present invention can have several desirable properties. Without being bound by any theory, the particular structure of the multilayer film, including the inclusion of specific zinc or sodium ionomers of polyethylene and ethylene acid copolymers in the core, can create a particular layer morphology in the multilayer film that promotes higher absorption of energy when the structure is mechanically required, resulting in a multilayer film having the desired tear resistance, toughness, and / or stiffness properties.

[0043] In some embodiments, the multilayer film has a thickness of 6 to 150 microns, 6 to 100 microns, or 6 to 50 microns.

[0044] In some embodiments, the multilayer film of the present invention comprises at least 90% by weight of an ethylene-based polymer, or at least 95% by weight of an ethylene-based polymer, or at least 99% by weight of an ethylene-based polymer, or at least 99.5% by weight of an ethylene-based polymer, or at least 99.9% by weight of an ethylene-based polymer, based on the total weight of the multilayer film. Since the multilayer films in some embodiments contain at least 90% by weight of an ethylene-based polymer, they can be compatible with polyethylene recycle streams. In some embodiments, the multilayer film consists essentially of 100% by weight of an ethylene-based polymer, based on the total weight of the multilayer film.

[0045] In some embodiments, the multilayer film is an oriented film in the machine direction. In some embodiments, the multilayer film is a cast stretch film. In further embodiments, the multilayer film is an inflation film.

[0046] Cast stretch film and inflation film In one embodiment, the multilayer film of the present invention is a cast stretch film. A cast stretch film is a high transparency film used to protect and integrate manufactured articles or items for transportation and storage. It is highly desirable for a cast stretch film to have high transverse tear strength to minimize catastrophic breakage during wrapping on a pallet. A cast stretch film can be distinguished from an inflation stretch film by the manufacturing method. The main differences between a cast film and an inflation film are related to the cooling method, film orientation, line speed, and gauge control. Cast films typically exhibit better optical properties and a very high degree of machine direction orientation compared to inflation films. A cast stretch film can be manufactured using techniques known to those skilled in the art based on the teachings herein.

[0047] In an embodiment where the multilayer film is a cast stretch film, the cast stretch film can have an ESTL tear of greater than 0.4 seconds / micron. The ESTL tear can be measured according to the test method described below. By dividing the ESTL tear measurement value of the propagation time in seconds (s) by the film thickness in microns, a measurement value in seconds / micron can be obtained.

[0048] In one embodiment, the multilayer film of the present invention is an inflation film. The inflation film can be produced by methods known in the art. In an embodiment where the multilayer film is an inflation film, the inflation film can have at least one of the following properties: a machine direction Elmendorf tear strength of greater than 0.13 N / micron and / or a Dart drop impact B of greater than 0.031 N / micron. The machine direction Elmendorf tear strength and the Dart drop impact B can be measured according to the test methods described below.

[0049] Article Embodiments of the present invention also provide articles comprising any of the multilayer films of the present invention described herein. Examples of such articles can include wraps, packages, flexible packages, pouches, and sachets. The articles of the present invention can be formed from the multilayer films disclosed herein using techniques known to those skilled in the art in view of the teachings herein.

[0050] Test Method Density Density is measured according to ASTM D792 and expressed in grams / cm 3 (g / cm 3 )

[0051] Melt Index (I2) The melt index (I2) is measured at 2.16 kg and 190 °C according to ASTM D - 1238. The value is reported in g / 10 min corresponding to the number of grams eluted per 10 minutes.

[0052] Raman microscopy Using Raman microscopy and multivariate calibration, the crystallinity % of individual layers of a multilayer film is measured. Raman microscopy, a type of vibrational spectroscopy, is sensitive to the vibrations of the polymer backbone and can provide information about both the amorphous and crystalline phases of polymers and polyethylene compositions. Raman can use visible or near-infrared radiation and, when combined with an optical microscope, provides a lateral spatial resolution of approximately 0.8 - 1.2 micrometers (depending on the excitation laser and microscope objective lens used).

[0053] A Partial Least Square (PLS) model is constructed to correlate the percent crystallinity (%) calculated from the annealed polyethylene density with the Raman data. This model is then used to predict the percent crystallinity of each layer in the multilayer film. The anneal density is measured according to ASTM D792. The percent crystallinity (%) is calculated from the measured anneal density using the following equation (Equation 1).

[0054]

Equation

[0055] The polarized Raman spectra are acquired using an equivalent Thermo Scientific DXR2 micro-Raman instrument. The Raman spectra are acquired using a 900 groove / mm grating. The spectral range is from 50 to 3500 cm with a data interval of 0.964 cm -1 and -1covered the Raman shift. Other data acquisition parameters are as follows. Acquisition time: 3 to 10 seconds, number of acquisitions: 3 to 6, dark current subtraction, cosmic ray filter, and white light correction: turned on. Calibration data was recorded using a 50 micrometer pinhole and a 100x (0.90NA) objective lens of Olympus M PlanN.

[0056] 0.859~0.964g / cm 3 Twenty-eight polyethylene composition resins in the density range of are used for calibration and cross-validation of the PLS model. The PLS model is validated using an independent set of density plaques and then used to measure the resin crystallinity of the resins used in the individual layers of the multilayer film. The PLS model has the following parameters: spectral region: 1571cm 1 ~971cm -1 , normalization: integral area 1356~1227cm -1 - of the same reference point, total number of samples: 28, # calibration reference numbers: 26, # independent cross-validation sample numbers: 2, # independent validation sample numbers: 6, data preprocessing: annealed base resin density model and calculated percent crystallinity model - mean centering, second derivative, SG smoothing (15 points, cubic polynomial), number of factors used for calibration of both models (annealed base resin density and calculated percent crystallinity) = 4, and is constructed with TQ Analyst (trademark) software.

[0057] After validation of the PLS model, cross-sections of the multilayer film are prepared by cryosectioning. Depolarized Raman spectra are acquired at five different positions within each layer using a 100x (0.9NA) objective lens and a 25 micrometer pinhole. The Raman spectra obtained from each layer are averaged, and the percent crystallinity of the layer is measured using the PLS model with the average spectrum.

[0058] Ultimate stretch Ultimate stretch is measured using the Highlight Stretch Film Test Standard (Highlight Industries, Wyoming, Michigan, U.S.A.). The film roll is placed on the Highlight unwind roller and wound through the equipment rollers following the instructions of the Highlight test procedure. The ultimate stretch test is selected from the test menu and a method is selected (Standard, Heavy, Light). The initial setting is Standard and should be used for most films. Heavy is for films thicker than 1 mil (25.4 μm), while the Light method should be used for films less than 50 gauge (approx. 12 μm) or films with a width less than 15 inches. Depending on the selected method, the test lamp speed is changed. Once the method is selected, the test is started and the film is stretched between two pre-stretch rollers. The stretch is achieved by the speed difference between the pre-stretch rollers. The film is stretched between the two pre-stretch rollers until a uniform cut is observed. If the cut in the film is not straight or if the film breaks anywhere other than between the pre-stretch rollers, the break is considered a bad cut and is not included in the data. However, the data reported on the graph represents the failure point. The stretch force data point is selected when the stretch passes 200% stretch. The test is repeated at least three times and the average ultimate stretch (US) and average stretch force (SF) are reported.

[0059] Pallet Penetration - Type A Load (OPP - A) This test uses the Bruceton staircase method to determine the maximum load force at which the film can pass over a test probe for three wraps without breaking. Insert the test probe into the test stand at the desired overhang distance. The overhang distance is determined by the film thickness. Thick films are typically tested with a 12-inch overhang and thin films are tested with a 5-inch overhang. Position the film so that the test probe is aligned with the center of the film. Attach the film to the test stand and start the wrapper. When the wrapper reaches 250% pre-stretch, the film should be able to pass over the probe for up to three wraps. Start with a low F2 force of 7 pounds and wrap the film three times. If the film is not punctured by the probe, repeat the test with an increasing F2 force in 0.5-pound increments until it breaks. For each 0.5-pound increment, manually press the film against the probe and test a new set of films. If the film breaks during any of the wraps, the load setting at that force is considered a failure. Depending on the film's performance (i.e., pass or break) at the load setting, adjust the load force up or down and repeat the test with a new load setting. Continue this until the maximum force that does not result in failure. The broken F2 force represents the puncture value on the film pallet, and generally, the standard deviation is not reported unless the test is repeated more than twice starting from 7 pounds. The significance of the data is considered to be ±1 pound, and the highest passing F2 force is reported. The Type A load test is commonly used in pallet packing, and those skilled in the art will understand its meaning as used herein. Table 8 shows the equipment and settings used in this method.

[0060]

Table 1

[0061] Puncture on Pallet - Type B (OPP - B) When the unitized pallet is not uniform in shape and has limited irregularities, it is defined as type "B - load". This test uses the Bruceton staircase method to determine the maximum load force at which the film can pass over the test probe for three - layer winding without breaking. Insert the test probe into the test bench at the desired protrusion distance. All films were tested with a 2 - inch × 2 - inch non - pointed metal probe extending 6 inches outside. Place the film so that the test probe is aligned with the center of the film. Attach the film to the test bench and start the wrapper. When the wrapper reaches 250% pre - stretch, the film becomes capable of passing over the probe for up to three - layer winding. Starting from the film tension / load force (F2) of 7 pounds after stretch, wind the film three times. If the film is not punctured by the probe, repeat the test with an increasing F2 force in 0.5 - pound increments until it breaks. If the film breaks during any of the windings, the load setting at that force is considered a failure. When the F2 force reaches the point where breakage begins, six tests are repeated at one force setting. If the film passes four out of six tests, the F2 force of the film is increased. If the film breaks four out of six tests, the test is stopped and this is considered the breakage point of the film. Depending on the performance of the film (i.e., pass or break) at the load setting, increase / decrease the load force and repeat the test with the new load setting. This continues until the maximum force at which no breakage is observed. The highest passing F2 force is reported as the On Pallet Puncture (OPP) value. The standard variation of this test is observed to be ±1 pound. The type B load test is commonly used in pallet packing, and those skilled in the art should understand its meaning as used herein. Table 9 below shows the equipment and settings used in this method.

[0062]

Table 2

[0063] Tear on pallet This test uses the Bluston staircase method to determine the maximum load force at which the film can pass through a test probe fixed to a blade to initiate puncture. Insert the test probe into the test bench at the desired protrusion distance. Place the film so that the test probe is aligned with the center of the film. Attach the film to the test bench and start the wrapper. When the wrapper reaches 250% pre-stretch, pass the film through the probe, and in this test, a single layer of the film is tested. The film tension (F2 force) increases from an initial low value of about 7 pounds in 0.5-pound increments until the film is completely torn across the entire transverse direction (CD) or cross direction (TD). The tear value on the pallet is recorded as the maximum F2 force at which the first puncture does not propagate across the width of the film and cause damage. Table 10 shows the equipment and settings used in this method.

[0064] [Table 3]

[0065] ESTL Tear ESTL tear is measured using an ESTL Film Performance Tester (ESTL, Deerlijk, Belgium) - FPT - 750 Film Property Tester. Select "Tear Propagation" from the test menu and then select the W-wrap method. The following table shows the parameters selected on the instrument to measure the break time (ESTL tear). Stretch the film sample to a pre-stretched state and then clamp the film. Use a small "gun-shaped knife" to make a small vertical cut in the film. After making this cut, the canvas releases the film clamp. One second later, the take-up spindle starts pulling the film at a constant speed. The other shafts are blocked. This creates a tensile force on the film after the first cut. The FPT - 750 Film Property Tester monitors the time and force required to cut through the entire height of the film. Repeat the test three times and report the average break time in seconds (s).

[0066]

Table 4

[0067] 2% Secant Modulus of ASTM's D882 - CD and MD The 2% secant modulus in the transverse direction (CD) and the machine direction (MD) is measured in accordance with ASTM's D882. This test involves the determination of the tensile or elongation properties of plastics in the form of thin sheets, including films with a thickness of less than 1 mm (0.04 inches). Films are arbitrarily defined as having a nominal thickness of 0.25 mm (0.010 inches) or less. Tensile properties can vary depending on sample preparation, separation speed, and test environment. Therefore, for the most rigorous comparison of two or more materials, all test specimens should be prepared and tested in exactly the same way. Modulus measurement is a special case of this test. After compensation is applied, the modulus is calculated by dividing the tensile stress by the corresponding strain for the straight - line portion of the curve or the extension of the straight line. If there is no linear behavior, a tangent is drawn at the inflection point, and a toe - compensation is provided by using the intersection of the tangent and the strain axis as zero strain. Next, the secant modulus can be calculated as the ratio of stress to corrected strain at any point on the curve. The values of the secant modulus are reported at 1, 2% strain in both the machine direction (MD) and the machine transverse direction (CD).

[0068] ASTM's D1709: Dart Drop Impact Dart drop impact B is measured in accordance with ASTM's D1709. The film dart drop test determines the energy required to break a plastic film under specified conditions of impact by free - falling darts. The test result is the energy expressed as the weight of the striker falling from a specified height that will cause 50% breakage of the test specimens being tested.

[0069] After generating the film, the film was conditioned at a temperature of 23°C (±2°C) and a relative humidity of 50% (±5) for at least 40 hours according to ASTM standards. The standard test conditions are a temperature of 23°C (±2°C) and a relative humidity of 50% (±5) according to ASTM specifications.

[0070] Test results can be reported by either Method A, which uses a 1.5-inch diameter dirt head and a 26-inch drop height, or Method B, which uses a 2.0-inch diameter dirt head and a 60-inch drop height. The thickness of the sample is measured at the center of the sample and then the sample is secured in an annular test specimen holder with a 5-inch inner diameter. Dirt is loaded above the center of the sample and released by either a pneumatic or electromagnetic mechanism.

[0071] The test is conducted according to the "staircase" method. If the sample breaks, a new sample with the dirt weight reduced by a known fixed amount is tested. If the sample does not break, a new sample with the dirt weight increased by a known amount is tested. After 20 specimens have been tested, the number of broken specimens is determined. If this number is 10, the test is completed. If this number is less than 10, the test is continued until 10 breaks are recorded. If the number is greater than 10, the test is continued until the total of those that did not break is 10. The dirt drop strength is determined from these data according to ASTM D1709 and expressed in grams as Type A dirt drop impact. All samples analyzed were 2 mils thick.

[0072] Puncture energy at break This test is based on ASTM D5748, the puncture resistance method by protrusions of stretch wrap film. While a probe moving at a low speed (10 inches / min) attempts to puncture the test specimen, the film test specimen is held by a pneumatic clamp having an opening with a diameter of 4 inches. This method applies biaxial stress representing the types of stress encountered in many end uses of packaging films. Two probes are available for the test. The Dow method probe is stainless steel with a round 1 / 2 - inch diameter head, while the ASTM probe is Teflon - coated stainless steel having a teardrop shape and a 0.75 - inch diameter as defined in ASTM D5748.

[0073] ASTM D1922: Elmendorf tear for CD and MD This test is carried out in accordance with ASTM D1922, and the force (grams) required to propagate a tear across the film test specimen is measured using an improved Pro - Tear Electronic Elmendorf Tear tester. Acting by gravity, the pendulum oscillates in an arc and tears the test specimen from a pre - cut slit. The tear propagates in the transverse direction. This test can be measured in both the machine direction (MD) and the machine cross - direction (CD).

Example

[0074] Table 1 below lists the materials included in the exemplary multilayer films described below. Except for Braskem DS6D82, all of the materials listed below are ethylene - based polymers and are commercially available from The Dow Chemical Company (Midland, MI).

[0075]

Table 5

[0076] Examples of Cast Films Two sets of multilayer films are formed on a Dr Collin simultaneous extrusion cast film line. For the first set, the Dr Collin coextrusion film line has the following parameters: target film thickness: 15 μm; extruders: 5 extruders; layer configuration: A / B / C / D / E; layer distribution (%): 10 / 20 / 20 / 20 / 30; throughput speed: 550 kg / h; chill roll temperature: 21 °C; die temperature: 280 °C; gap: 5 mm; the melting temperatures of extruders A, B, C, D, and E are 252 °C, 197 °C, 280 °C, 280 °C, and 280 °C, respectively.

[0077] For the second set, the Dr Collin coextrusion film line has the following parameters: target film thickness: 15 μm; extruders: 5 extruders; layer configuration: A / B / C / D / E; layer distribution (%): 10 / 15 / 30 / 15 / 30; throughput speed: 550 kg / h; chill roll temperature: 21 °C; die temperature: 280 °C; gap: 5 mm; the melting temperatures of extruders A, B, C, D, and E are 255 °C, 200 °C, 280 °C, 280 °C, and 280 °C, respectively.

[0078] For the first set, a 5-layer cast stretch film with a thickness of 15 microns is formed and designated as examples and comparative examples of the present invention. Each film of the examples has a structure of A / B / C / D / E, where A is the first outer layer, B is the first core layer, C is the third core layer, D is the second core layer, and E is the second outer layer. Table 2 reports the structure of the formed 5-layer multilayer film. For each of these examples, the first outer layer has a thickness of 10% of the total film thickness, the first core layer has a thickness of 20% of the film thickness, the third core layer has a thickness of 20% of the film thickness, the second core layer has a thickness of 20% of the film thickness, and the second outer layer has a thickness of 30% of the film thickness.

[0079] [Table 6]

[0080] For the second set, a 5-layer cast stretch film having a thickness of 15 microns is formed and designated as an example and a comparative example of the present invention. Each of the films of the examples has a structure of A / B / C / D / E, where A is the first outer layer, B is the first core layer, C is the third core layer, D is the second core layer, and E is the second outer layer. Table 3 reports the structure of the formed 5-layer multilayer film. For each of these examples, the first outer layer has a thickness of 10% of the total film thickness, the first core layer has a thickness of 15% of the film thickness, the third core layer has a thickness of 30% of the film thickness, the second core layer has a thickness of 15% of the film thickness, and the second outer layer has a thickness of 30% of the film thickness.

[0081]

Table 7

[0082] Thickness, ultimate stretch, ESTL tear (propagation time), on-pallet tear, on-pallet puncture type A load (OPP-A), and on-pallet puncture type B load (OPP-B) are measured for each of the comparative examples and the examples of the present invention. Table 4 below provides the results for the first set of film examples. Table 5 below provides the results for the second set of film examples. As can be seen from Table 4 below, Example 1 of the present invention, which contains 100% by weight of an ethylene polymer and can be compatible with the polyethylene recycle stream, has significantly better ESTL tear and on-pallet tear than Comparative Examples 1, 3, and 4. Comparative Example 2 has better ESTL tear and on-pallet tear, but Comparative Example 2 contains a mixture of polypropylene and polyethylene. Example 1 of the present invention has desirable ultimate stretch and on-pallet puncture. As can be seen from Table 5 below, Example 2 of the present invention, which contains 100% by weight of an ethylene polymer and can be compatible with the polyethylene recycle stream, has better ESTL tear than Comparative Examples 5, 7, and 8. Comparative Example 6 has a higher ESTL tear than Example 2 of the present invention and contains a mixture of polypropylene and polyethylene. Example 2 of the present invention has desirable ultimate stretch and on-pallet puncture.

[0083]

Table 8

[0084]

Table 9

[0085] Examples of Inflation Films The multilayer film is formed on a Dr Collin inflation film line equipped with five extruders. The Dr Collin inflation film line has the following parameters: layer distribution (%): 33 / 12 / 10 / 12 / 33 (for Comparative Example 14) and 30 / 15 / 10 / 15 / 30 (for the remaining examples); take-off: 4.5 m / min; blow-up ratio (BUR): 2.5; die gap: 1.8 mm; die temperature: 235 °C; the melting temperatures of extruders A, B, C, D, and E are 235 °C, 240 °C, 234 °C, 240 °C, and 235 °C, respectively.

[0086] A 5-layer inflation film is formed and referred to as the examples and comparative examples of the present invention. The inflation film of each example has a structure of A / B / C / D / E, where A is the first outer layer, B is the first core layer, C is the third core layer, D is the second core layer, and E is the second outer layer. Table 6 reports the structure of the formed multilayer film. (Except for Comparative Example 14) For each of these examples, the first outer layer has a thickness of 30% of the total film thickness; the first core layer has a thickness of 15% of the film thickness; the third core layer has a thickness of 10% of the film thickness; the second core layer has a thickness of 15% of the film thickness, and the second outer layer has a thickness of 30% of the film thickness. Comparative Example 14 is a technically 3-layer inflation film where the core contains the same polymer composition and the first outer layer has a thickness of 33% of the total film thickness. The first core layer has a thickness of 34% of the film thickness, and the second outer layer has a thickness of 33% of the film thickness.

[0087]

Table 10

[0088] Measure the 2% secant modulus in the transverse direction (CD), the 2% secant modulus in the machine direction (MD), Dart Drop Impact Type B, puncture energy at break, Elmendorf tear in CD, and Elmendorf tear in MD for each of the inflation films of the comparative examples and the examples of the present invention. Tables 7 and 8 below provide the results. As can be seen from Table 7, the examples of the present invention have significantly better puncture energy at break and Elmendorf tear in CD and MD than the comparative examples. The examples of the present invention also have a balance of other desirable properties.

[0089]

Table 11

[0090] Use Raman microscopy to measure the percent crystallinity of the first core layer of the multilayer inflation film of a particular example. Table 8 reports the results.

[0091]

Table 12

Claims

1. A core comprising a first outer layer, a second outer layer, and one or more core layers, wherein the first core layer comprises 5 to 45% by weight of zinc or sodium ionomer of ethylene acid copolymer based on the total weight of the first core layer, and 55 to 95% by weight of 0.950 to 0.970 g / cm³ based on the total weight of the first core layer. ３ The density, and the melt index (I) of 0.3 to 10.0 g / 10 min. ２ A core containing polyethylene having ) A multilayer film comprising the first core layer having a thickness of 5 to 40% of the total thickness of the multilayer film.

2. The multilayer film according to claim 1, wherein the first outer layer and the second outer layer each contain polyethylene.

3. The multilayer film according to claim 1, wherein the multilayer film contains more than 80% by weight of an ethylene-based polymer based on the total weight of the multilayer film.

4. The multilayer film according to claim 1, wherein the core comprises 100% by weight of an ethylene-based polymer based on the total weight of the core.

5. The multilayer film according to claim 1, wherein the first core layer has a Raman-measured percentage crystallinity of 50% to 63%.

6. The second core layer, based on the total weight of the second core layer, consists of 5 to 45% by weight of zinc or sodium ionomer of ethylene acid copolymer and 55 to 95% by weight of polyethylene, with a density of 0.950 to 0.970 g / cm³. ３ A multilayer film according to claim 1, comprising polyethylene having a density of .

7. The third core layer has a melt index of less than 7.0 g / 10 min and 0.940 g / cm³. ３ The multilayer film according to claim 6, comprising polyethylene having a density of less than 1, wherein the third core layer is disposed between the first core layer and the second core layer.

8. The multilayer film according to claim 1, wherein the multilayer film is a cast stretch film having an ESTL tear rate of more than 0.4 seconds / micron.

9. The multilayer film according to claim 1, wherein the multilayer film is an inflation film having at least one of the following characteristics: mechanical direction Elmendorf tear strength exceeding 0.13 N / micron and / or dirt drop impact B exceeding 0.031 N / micron.

10. An article comprising the multilayer film described in any one of claims 1 to 9.