All-polyethylene blown film produced by the double bubble process

Abstract

Provided herein are substantially full polyethylene films, and specifically blown biaxially oriented full polyethylene films. The films can be multilayer films and can be produced using a double bubble film process. A specific multilayer film includes at least two skin layers and at least one core layer arranged directly or indirectly between the at least two skin layers. The film comprises: a metallocene linear low density polyethylene with a narrow composition distribution (narrow-CD mLLDPE), a long chain branched metallocene linear low density polyethylene (LCB mLLDPE), and optionally either or both of a low density polyethylene (LDPE) and a high density polyethylene (HDPE).

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Provisional Application 63 / 202,734, filed June 22, 2021, entitled “FULL POLYETHYLENE BLOWN FILMTHROUGH DOUBLE BUBBLE PROCESS,” the entire contents of which are incorporated herein by reference.

[0003] field

[0004] This disclosure relates to polyethylene compositions and films made therefrom, as well as systems and methods for forming such films.

[0005] background

[0006] Orientation films, especially biaxially oriented films, are desirable for many applications.

[0007] Historically, such films have been made using blends of materials, specifically characterized by propylene-based polymers in biaxially oriented polypropylene (BOPP) films. For example, over 60% of the biaxially oriented film market is represented by polypropylene and obtained using a sequential tenter frame process. The strength and success of biaxially oriented polypropylene films are due to their excellent processability (wide stretching temperature profile, low crystallinity), good overall properties, attractive cost (high production speed), and good yield (low density).

[0008] However, there has been a recent increase in interest in developing simplified membrane solutions using polyethylene, preferably in which polymers other than polyethylene or polyethylene-based polymers are substantially absent from the membrane layer (meaning that for each polymer used in the membrane, the majority, preferably 75% or more, 90% or more, or even 98% or 99% or more, of the polymer used in the membrane is polyethylene or a polyethylene-based copolymer). However, polyethylene tends to have a higher degree of crystallinity than polypropylene, making it more difficult to reduce thickness and maintain a proper balance of stiffness and toughness properties.

[0009] One way to achieve biaxially oriented films is through the so-called double-bubble method. Polypropylene, however, is a typical polymer used in this method. In the double-bubble method, a polymer film is extruded, blown into a first bubble, flattened into a tube, and then blown again at a higher temperature into a second bubble, wherein the second bubble is stretched in a direction perpendicular to the stretching / blowing direction of the first bubble. In this way, biaxial orientation is imparted to the film.

[0010] This method would be complex to operate and require high precision; this problem is amplified when using all-polyethylene films, especially when using polyethylene-based films that provide acceptable properties to the end-use film (such as mechanical and optical properties, such as tensile strength at break; elongation at break; tear strength; 1% secant modulus; and breaking energy), resulting in the lack of an overall acceptable all-PE film for the dual-bubble method to date, leaving a considerable gap in the supply of all-PE films.

[0011] Some potentially interesting references in this field include: U.S. Patent Publication Nos. 2006 / 0131778; 2012 / 0164421; 2014 / 0147646 and U.S. Patent Nos. 3,456,044, 5,888,660 and 6,423,420, WIPO Publication WO2020 / 190507, and Bobovitch, AL et al., “Mechanical Properties Stress-Relaxation, and Orientation of Double Bubble Biaxially Oriented Polyethylene Films,” J. Appl. Poly. Sci., Vol. 100(5), pp. 3545-3553 (2006).

[0012] Overview

[0013] In some embodiments, this disclosure provides polyethylene films, particularly biaxially oriented polyethylene films. The film may include at least two surface layers and at least one core layer disposed directly or indirectly between the at least two surface layers. In various embodiments, the film comprises: narrow-composition linear low-density polyethylene with a narrow distribution (narrow-CD mLLDPE), long-chain branched linear low-density polyethylene with a long distribution (LCB mLLDPE), and optionally any or both of low-density polyethylene (LDPE) and high-density polyethylene (HDPE). In various embodiments, the narrow-CD mLLDPE comprises 85 to 95% by weight of ethylene-derived units and the balance derived from C3-C. 12 The α-olefin (wt% based on the total mass of the polymer in the narrow-CD mLLDPE) further comprises at least 50% compositional width index (CDBI), a melt index (I2, ASTM D1238 at 190°C, 2.16 kg load) in the range of 0.1–3.0 g / 10 min, a molecular weight distribution (MWD, Mw / Mn) in the range of 1.5–4, a peak melting temperature in the range of 105–120°C, and a Vicat softening temperature in the range of 70–130°C. In various embodiments, the LCB mLLDPE comprises 80–99 wt% units derived from ethylene and the balance derived from C3–C4.12 The membrane contains α-olefins and further comprises at least 50% CDBI, I2 in the range of 0.1-0.7 g / 10 min (190 °C, 2.16 kg load), g'(vis) in the range of 0.85-0.95, and MWD in the range of 2.5-5.5. The membrane may optionally also include low-density polyethylene (LDPE) and / or high-density polyethylene (HDPE).

[0014] In several embodiments, the membrane comprises all or substantially all of its polymer content as polyethylene (homopolymer polyethylene and / or polyethylene copolymer). Furthermore, the membrane can be manufactured by a blown film method, preferably a double-bubble blown film method.

[0015] Formulations for preparing multilayer polymer films are also provided. The formulations may include a surface formulation and a core formulation; one of the surface and core formulations may contain a narrow-CD mLLDPE (e.g., those described above), and the other of the surface and core formulations may contain a first LCB mLLDPE (e.g., those described above). Optionally, the formulation containing the narrow-CD mLLDPE may also contain a second LCB mLLDPE having one or more of the following properties different from the first LCB mLLDPE: density, peak melting temperature, and Vicat softening temperature.

[0016] Even further embodiments include a method for preparing a biaxially oriented multilayer polymer film. Such a method includes (a) extruding two or more polymer formulations at an extrusion temperature to form an extrudate; (b) inflating the extrudate to form a first film bubble; (c) flattening the first film bubble to form a flattened tube; (d) heating the flattened tube; (e) inflating or expanding the flattened tube to form a second film bubble; and (f) flattening the second film bubble to obtain a biaxially oriented multilayer polymer film. The polymer formulation in (a) may comprise a surface formulation and a core formulation. One of the surface and core formulations comprises narrow-CD mLLDPE (e.g., narrow-CD mLLDPE as described above), and the other of the surface and core formulations comprises LCB mLLDPE (e.g., according to the general description of LCB mLLDPE above). Furthermore, extrusion (a) may include heating or preheating the polymer formulations (one or more), for example causing the formulations (one or more) to soften or melt, thereby aiding in the formation of the first film bubble. Heating (d) can be applied to the temperature of the second membrane bubble, which can be higher than the temperature of the first membrane bubble.

[0017] A membrane prepared by the aforementioned method is also provided.

[0018] Brief description of the attached diagram

[0019] Figure 1 This is an illustration of an exemplary double-bubble blown film forming system.

[0020] Detailed Explanation

[0021] This disclosure relates to polyethylene compositions and formulations thereof, and more particularly to formulations of polyethylene compositions that can be used to prepare biaxially oriented films, especially by a two-film bubble method. This disclosure also includes methods for preparing such formulations, forming the formulations into films, and the associated films themselves. Thus, various embodiments include blends of two or more formulations, each formulation being suitable for preparing a specific layer of a multilayer film; similarly, corresponding multilayer films (comprising two or more layers corresponding to the aforementioned formulations) are also covered.

[0022] The membrane is preferably “essentially all polyethylene,” meaning that there is essentially no polymer other than polyethylene (making the total polymer content of the membrane at least 90% by weight, preferably at least 95, 96, or 97% by weight, more preferably at least 99% by weight, for example at least 99.9% by weight or even 100% by weight of the polymer content is polyethylene). Typically, when the polymer content is less than 100% by weight of polyethylene, it can be due to small amounts of polymer binders and / or polymer processing aids (PPA), which may include polymer compounds (e.g., oils, fluoropolymers, etc., as described below with respect to PPA), or the use of other polymer materials commonly used in such membranes; and / or due to the presence of small amounts of impurities. In some cases, membranes optionally described as having a conventional amount of PPA (e.g., 1 to 5 parts by weight of resin (phr)) can be made such that the polymer compound of the membrane is essentially composed of polyethylene (while still allowing trace amounts of compounds (impurities, catalyst residues, etc.) typically expected in polymer membranes).

[0023] Further details describe polyethylene formulations, films, and methods of film formation, and various definitions used in reading this document are listed below.

[0024] definition

[0025] The term "polyethylene" refers to a polymer having at least 50% by weight ethylene-derived units, such as at least 70% by weight ethylene-derived units, such as at least 80% by weight ethylene-derived units, such as at least 85% by weight or at least 90% by weight ethylene-derived units, or at least 95% or even 100% by weight ethylene-derived units. Polyethylene can therefore be a homopolymer or a copolymer having one or more other monomer units, including terpolymers. The polyethylene described herein may, for example, include at least one or more other olefins and / or comonomers.

[0026] "Olefin" or "alkene" is a linear, branched, or cyclic compound of carbon and hydrogen having at least one double bond. For the purposes of this specification and the appended claims, when a polymer or copolymer is referred to as containing an olefin, the olefin present in such a polymer or copolymer is in its polymerized form. For example, when a copolymer is claimed to have 50% to 55% by weight of "ethylene," it should be understood that the monomer units in the copolymer are derived from ethylene in the polymerization reaction, and said derived units are present at 50% to 55% by weight based on the weight of the copolymer. A "polymer" has two or more identical or different monomer units. A "homopolymer" is a polymer having identical monomer units. A "copolymer" is a polymer having two or more monomer units that are different from each other. A "terpolymer" is a polymer having three monomer units that are different from each other. Thus, as used herein, the definition of a copolymer includes terpolymers, etc. The term "different" used to refer to monomer units means that the monomer units differ from each other by at least one atom or are isomerically different.

[0027] The term "α-olefin" or "α-olefin" refers to an olefin R that has a terminal carbon-carbon double bond in its structure. 1 R 2 C = CH2, where R 1 and R 2 It can be hydrogen or any hydrocarbon group independently; for example, R 1 It is hydrogen and R 2 It is an alkyl group. "Linear α-olefin" is an α-olefin, where R... 1 It is hydrogen, and R 2 It is a hydrogen or linear alkyl group.

[0028] For the purposes of this disclosure, ethylene should be considered an α-olefin.

[0029] When a polymer or copolymer is referred to herein as containing an α-olefin (or α-olefin) including, but not limited to, ethylene, 1-butene, and 1-hexene, the olefin present in such a polymer or copolymer is in the polymerized form of that olefin. For example, when a polymer is said to have 80 to 99.9% by weight of “ethylene content,” “ethylene-derived content,” or “ethylene monomer content,” or to contain 80 to 99.9% by weight of “ethylene-derived units,” it should be understood that the monomer units in the copolymer are derived from ethylene in the polymerization reaction, and that the derived units are present at 80 to 99.9% by weight, based on the weight of the ethylene content plus the comonomer content.

[0030] As used herein, and unless otherwise specified, the term "C" refers to... n "This refers to hydrocarbons (one or more) whose each molecule has n carbon atoms, where n is a positive integer."

[0031] Multilayer membrane structure

[0032] In various embodiments, this disclosure describes multilayer membranes. The membranes described herein comprise at least two layers of a common type (each described in more detail below): a core layer B, formed of a core formulation as described herein; and a surface layer A, formed of a surface formulation as described herein. The membrane may be referred to, for example, A / B / A, meaning that the membrane structure is a three-layer membrane such that the core layer B is disposed between two surface layers A. Similarly, five-layer membranes may be mentioned, wherein the structure may be A / B / A / B / A, or A / A / B / A / A, or A / B / B / B / A, etc. Six, seven, and more layers are also covered.

[0033] Therefore, in general, multilayer membranes according to the various embodiments described herein can comprise any combination of surface layers A and core layers B as described herein, and in any order, provided that surface layers A form each outer layer of the membrane (e.g., the membrane has an A / … / A structure), and further provided that at least one core layer B is disposed between the outer surface layers A. Furthermore, unless the context otherwise specifies, each surface layer A of the multilayer membrane can be identical (e.g., formed from the same or identical surface formulation) or different (e.g., different surface layers such that each surface layer is individually described as surface layer A as provided herein), and the same applies to core layers B in membrane structures comprising multiple core layers B. In some specific cases, when specifically referring to different surface layers A, references may be made to A' (for a second different surface layer A), A' (for a third surface layer A different from each of the first two), etc., and similarly with respect to core layers B, references may be made to B', B'', etc. Furthermore, although surface layers A form outer layers, they can also be used in inner layers (e.g., employing an A / B / A / B / A structure).

[0034] A particularly preferred embodiment includes a three-layer membrane A / B / A, such that the membrane includes a core layer disposed between two surface layers. The surface layers can be identical (A / B / A, where A is identical) or different (A / B / A'). Other preferred embodiments include a five-layer membrane (e.g., A / B / A / B / A, A / B / B / B / A, A / B / A / A / A, etc., wherein the outer layer is surface layer A and at least one inner layer is core layer B; and any A layer can be identical or different compared to the other A layers; and the B layers can also be identical or different compared to the other B layers); however, membranes with more than 5 layers are also covered, wherein the outer layer is surface layer A (which can be identical or different) and at least one inner layer is core layer B.

[0035] The following describes in more detail the polyethylene (and its formulations) suitable for forming the various layers. Polyethylene may be suitably arranged in either the outer layer A or the core layer B, although in some cases, as noted below, certain polyethylene may preferably be arranged in a particular layer A or B. Following the polyethylene and optional additives, the components suitable for each layer (and / or the formulations for preparing each layer) are described. Furthermore, as noted above, the membranes described herein (and the corresponding formulations forming them) are advantageously “substantially all-polyethylene membranes,” having the meaning described above. Therefore, the membranes may sometimes be referred to as “all-PE membranes” and their formulations accordingly as “all-PE formulations.”

[0036] Narrow-CD mLLDPE

[0037] Polyethylenes particularly suitable for surface layer A and / or core layer B (or the respective surface layer and / or core formulation) include linear low-density polyethylene (LLDPE), and especially metallocene-catalyzed LLDPE (mLLDPE) with a flat composition distribution, comprising 80 to 99.9% by weight ethylene-derived units with the balance being derived from one or more C3-C4 compounds. 12 A copolymer of units of α-olefin comonomers (and particularly one or more of butene, hexene, octene, preferably one of those, and more preferably hexene). % by weight is based on the total mass of ethylene-derived units plus comonomer-derived units in the polyethylene. Such polyethylene is referred to as having a “flat compositional distribution,” acknowledging the introduction of comonomers in relatively equal amounts (in % by weight) into both shorter and longer molecular chains within the polymer. These may also be referred to as “narrow-CD” or “narrow compositional distribution” polyethylene; or equivalently, high-CDBI mLLDPE. Compositional distribution refers to the distribution of comonomers in polymer chains of different lengths (different molecular weights), and CDBI refers to the compositional distribution width index, defined as the weight percentage of copolymer molecules (chains) having a median total molar comonomer content of 50%, and it is described in U.S. Patent 5,382,630, which is incorporated herein by reference. The CDBI of a copolymer can be readily determined using known techniques for separating copolymer samples into single fractions. One such technique is the Temperature Rising Elution Fraction (TREF) described in Wild et al., J. Poly. Sci., Poly. Phys. Ed., Vol. 20, p. 441 (1982) and U.S. Patent No. 5,008,204, which is incorporated herein by reference. Thus, a higher CDBI value indicates a narrow compositional distribution (meaning a relatively even distribution of comonomers across polymer chains of different molecular weights).

[0038] Narrow-CD polyethylene may have a CDBI of at least 50%, more preferably at least 60%, for example in the range of 50-90% or 60-80%.

[0039] Narrow-CD polyethylene may more particularly have an ethylene derivative content ranging from a low of any one of 80, 85, 86, 87, 87.5, 88, 90, 91, 92, 93, 94, or 95 wt% to a high of any one of 88, 90, 93, 94, 95, 96, 97, 98, 99, or 99.9 wt%; wherein the range from any of the aforementioned low to any of the aforementioned high is covered, provided that the upper end is greater than the lower end (e.g., 85 to 95 wt%, e.g., 86 to 92 wt% ethylene derivative units, or 94 to 99 wt% ethylene derivative units). The balance is from C3-C. 12 Composition of α-olefin comonomer-derived units (e.g., hexene).

[0040] Narrow-CD mLLDPE provides a reduced softening point relative to the molding method, and further imparts excellent sealing, optical, and mechanical properties to the films thus produced. Narrow-CD mLLDPE preferably also possesses one or more, preferably all of the following additional properties:

[0041] The peak melting temperature is in the range of 105-120°C, preferably 110°C or 111°C to 115°C or 116°C. The peak melting temperature (also referred to herein as the “melting point”) is determined using a differential scanning calorimeter (DSC). DSC measurements can be performed using a TA DSC8000 instrument under a N2 atmosphere at a heating / cooling rate of 10 K / min. The sample is heated from -50°C to 300°C, held for 5 minutes to remove previous thermal history, then cooled to -50°C and then reheated to 300°C.

[0042] • The Vicat softening temperature (ASTM D1525) is within the softening point range of 70°C to 130°C, preferably 90°C to 110°C, for example, from the low of any one of 70, 75, 80, 85, 90, 95, 96, 97, 98, 99 or 100°C to the high of any one of 100, 101, 102, 103, 104, 105, 110, 115, 120, 125 or 130°C (wherein it covers the range from any of the aforementioned low points to any of the aforementioned high points, provided that the high point is greater than the low point, for example, 90°C to 110°C or 97°C to 103°C).

[0043] Melt index (MI, also known as I2 or I) 2.16The load used in the test is 2.16 kg, within the range of 0.1-5.0 g / 10 min (ASTM D1238, 190°C, 2.16 kg load), for example, from the low of any one of 0.1, 0.2, 0.3, 0.4, 0.5, 0.7 or 0.8 g / 10 min to the high of any one of 1.0, 1.1, 1.2, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0 g / 10 min; this also covers the range from any of the aforementioned lower ends to any of the aforementioned upper ends.

[0044] • The long chain branching index (LCB index, also referred to as g'(vis) or g' index in this paper) is greater than 0.95, preferably greater than or equal to 0.96 or 0.97.

[0045] Narrow-CD mLLDPE may also have one or more of the following, preferably all of them:

[0046] • Weight-average molecular weight (Mw) is in the range of 45,000-120,000 g / mol, for example 50,000-115,000 g / mol or 60,000 to 110,000 g / mol (which also covers the range from any of the lower end to any of the upper end of the above range, for example 45,000 to 110,000 g / mol);

[0047] • Number-average molecular weight (Mn) in the range of 20,000-55,000 g / mol, for example in the range from 25,000, 30,000, 35,000 or 40,000 to the high point of 30,000, 35,000, 40,000, 45,000, 50,000 or 55,000 g / mol, which also covers the range from any of the lower end to any of the upper end (provided that the upper end is greater than the lower end), for example 35,000-55,000 g / mol;

[0048] • Molecular weight distribution (MWD) in the range of 1.5 or 2.0 to 3.5 or 4;

[0049] • Density (ASTM D1505) is between 0.905 and 0.940 g / cm³. 3 Within the range, for example, from 0.905, 0.910, 0.911, 0.912 or 0.915 g / cm³. 3 The lower end of any one of them is 0.913, 0.914, 0.915, 0.920, 0.925, 0.926, 0.928, 0.930, 0.935 or 0.940 g / cm³ 3 Within the range of the upper end of any one of them, which includes the range from any of the aforementioned lower ends to any of the aforementioned upper ends (provided that the upper end is greater than the lower end), for example 0.910-0.915 g / cm³.3 ;

[0050] Suitable examples of polyethylene for narrow-CD mLLDPE include Exceed, which is available from ExxonMobil Chemical Company. TM Performance polyethylene and other commercially available mLLDPEs, such as Evolue from Prime Polymer Co., Ltd. TM SP1510.

[0051] For the polyethylene described above, and any other polyethylene described herein, the moments and distributions of molecular weight (Mw, Mn, Mz, Mw / Mn, Mz / Mn, etc.) and monomer / comonomer contents (C2, C4, C6 and / or C8 and / or others, etc.) and (g') were determined by high-temperature gel permeation chromatography (Polymer Char GPC-IR) using an infrared detector IR5 based on a multi-channel bandpass filter, an 18-angle light scattering detector, and a viscometer. vis Polymer separation was achieved using three Agilent PLgel 10 μm Mix-B LS columns. Detailed analytical principles and methods for molecular weight determination and g'(vis) are described in paragraphs

[0044] –

[0051] of PCT Publication WO2019 / 246069A1, which are incorporated herein by reference (note that the equation c = / / / mentioned in paragraph

[0044] regarding the concentration (c) at each point in the chromatogram is c = βI, where β is the mass constant and I is the IR5 broadband signal intensity (I) minus the baseline). Unless specifically mentioned, all molecular weight moments used or mentioned in this disclosure are determined according to conventional molecular weight (IR molecular weight) determination methods (e.g., those mentioned in paragraphs

[0044] –

[0045] of the aforementioned disclosure text), noting that for the equations in such paragraph

[0044] , a = 0.695 and K = 0.000579 (1-0.75Wt) are used, where Wt is the weight fraction of the comonomer, and further noting that the comonomer composition is determined by the ratio of the IR5 detector intensities corresponding to the CH2 and CH3 channels calibrated with a series of PE and PP homopolymer / copolymer standards, the nominal values ​​of which are predetermined by NMR or FTIR as indicated in paragraph

[0045] of the aforementioned PCT disclosure text (providing methyl number / 1000 total carbons (CH3 / 1000TC)). Other required parameters can be found in the paragraphs mentioned in the WO2019 / 246069A1 publication, but for convenience, some are included here: TCB at 145°C n = 1.500; I = 665nm; dn / dc = 0.1048ml / mg.

[0052] Narrow-CD mLLDPEs, as described above, are believed to provide excellent sealing, toughness, and puncture resistance when used in membranes. Additionally, they offer benefits for orientation methods such as dual-bubble formation methods, provided they impart a relatively low melting and softening point to the composition, aiding in bubble formation and stability (particularly in conjunction with one or more other polyethylenes, as discussed below).

[0053] In certain embodiments, narrow-CD mLLDPE may be used in the surface layer (or a corresponding surface layer formulation), where imparting the aforementioned properties may be particularly suitable. However, narrow-CD mLLDPE may also be used in the core layer in various embodiments, and in some cases, it may be present in at least one core layer and at least one surface layer of the membrane according to various embodiments herein.

[0054] Long-chain branched mLLDPE

[0055] Core formulations according to the various embodiments described herein are particularly suitable for forming one or more core layers B in multilayer films of this disclosure.

[0056] The core formulation typically includes one or more polyethylenes; preferably, the core formulation contains substantially no polymers other than polyethylene. One or more of the polyethylenes described below are particularly suitable for the core formulation.

[0057] Other suitable polyethylenes for use in the membrane formulations described herein include those that impart high bubble stability (e.g., in blown film processes such as two-bubble processes), preferably while still imparting suitable membrane performance properties. For example, the core or surface layer formulations (or both) may comprise one or more long-chain branched (LCB) mLLDPEs. (Note that these mLLDPEs are considered long-chain branched compared to other linear low-density polyethylenes, and particularly compared to other metallocene LLDPEs; however, their total long-chain branching will still be less than that of LDPEs with a very high degree of long-chain branching.) It is believed that such LCB mLLDPEs can contribute to high bubble stability, possibly even when the melting point is not significantly different from that of the polyethylene in the other layers, which is surprising in the case of two-bubble processes, which are often considered to rely on the melting point difference between polypropylene and the other layers in conventional formulations. Nevertheless, in some cases, melting point differences and LCBs can be present in certain LCB mLLDPEs.

[0058] LCB mLLDPE may, for example, have an LCB index or g'(vis) in the range of 0.80 to less than 0.97, such as in the range of 0.85-0.95.

[0059] LCB mLLDPE, such as the narrow-CD mLLDPE described above, is preferably having 80 to 99.9% by weight ethylene-derived units, with the balance derived from one or more C3-C... 12 A copolymer of α-olefins (and particularly one or more of butene, hexene, and octene, preferably one of those, and more preferably hexene). % by weight is based on the total mass of ethylene-derived units plus comonomer-derived units in polyethylene.

[0060] LCB mLLDPE preferably has a CDBI greater than or equal to 50%, more preferably greater than or equal to 70%, for example, in the range from a low point of any one of 50, 60, or 70% to a high point of any one of 80, 85, 90, 95, or 99%, wherein the range is from any of the aforementioned lower end to any of the aforementioned upper end. LCB mLLDPE may also have an MWD (Mw / Mn) in the range of 2.5-5.5, for example, in the range of 3 or 3.5 to 4.5 or 5.

[0061] In addition, LCB mLLDPE may have a melt index (I2, determined according to ASTM D1238 at 190°C and 2.16 kg load) in the range of 0.1-0.7 g / 10 min, for example, in the range from the low point of any one of 0.1, 0.15, 0.2 or 0.22 to the high point of any one of 0.22, 0.25, 0.26, 0.27, 0.30, 0.40, 0.45, 0.50, 0.60 or 0.70 g / 10 min, which also covers the range from any of the above lower end to any of the above upper end (provided that the upper end is greater than the lower end), for example 0.15-0.30 g / 10 min, or 0.15 to 0.27 g / 10 min.

[0062] In addition, this article covers some variants of LCB mLLDPE. First LCB mLLDPE variants exhibit high stiffness and excellent processability, but lower toughness. Besides the properties mentioned above (common to these LCB mLLDPE variants), such first LCB mLLDPE variants may possess one or more of the following properties, preferably all of them:

[0063] • The peak melting temperature (determined by DSC as described above) is in the range of 115°C-135°C, preferably 120°C, 121°C, 123°C or 125°C to 130°C or 133°C;

[0064] • The Vicat softening temperature is in the range of 110-130°C, for example, 115°C to 125°C, or from the lower of any one of 110, 115, 118, 119, or 120°C to the higher of any one of 123, 124, 125, 127, 130, or 135°C, wherein the range is from any of the aforementioned lower to any of the aforementioned higher (e.g., 115°C to 125°C); and

[0065] • Density between 0.930 and 0.950 g / cm³ 3 Within the range, for example from 0.935, 0.936, 0.937 or 0.938 g / cm³ 3 The lowest point of any one of them is 0.942, 0.943, 0.944, 0.945 or 0.950 g / cm³. 3 The high point of any of the above, wherein this article covers the range from any of the above low points to any of the above high points (e.g., 0.935 to 0.945 g / cm). 3 ).

[0066] Examples of commercially available LCB mLLDPEs of this variant include Enable from ExxonMobil Chemical Company. TM Trademarked polyethylene, such as Enable TM 4002 performance polyethylene.

[0067] The second LCB mLLDPE variant exhibits a superior balance of toughness and stiffness while still providing excellent processability and a lower density than the first LCB mLLDPE variant. Such a second LCB mLLDPE variant may possess one or more of the following properties, preferably all of them:

[0068] • The peak melting temperature (determined by DCS as described above) is in the range of 100°C to 115°C, for example, from 105°C to 115°C, or in the range from a low point of any of 100, 105, 106 or 107°C to a high point of any of 110, 111, 112, 113, 114 or 115°C (wherein the range from any of the aforementioned low points to any of the aforementioned high points is covered, for example, from 106°C to 112°C);

[0069] • The Vicat softening temperature is in the range of 95°C to 110°C, for example, from the lowest of any one of 95, 97, 98, 99, or 100°C to the highest of any one of 105, 106, 107, 108, 109, or 110°C, wherein it covers the range from any of the aforementioned lower to any of the aforementioned higher (e.g., 100 to 105°C); and

[0070] • Density in the range of 0.910-0.929, for example from 0.910, 0.911, 0.912 or 0.913 g / cm³ 3 The lowest point of any one of them is 0.919, 0.920, 0.921, 0.922, 0.923, 0.925, 0.927 or 0.929 g / cm³. 3 The highest point of any one of them, which covers the range from any of the aforementioned low points to any of the aforementioned high points (e.g., 0.910 to 0.925 g / cm³). 3 For example, 0.913 to 0.919 g / cm³ 3 ).

[0071] Examples of commercially available LCB mLLDPEs according to the second variant (e.g., second LCB mLLDPE) include Exceed from ExxonMobil Chemical Company. TM XP 6000 series performance polyethylene, such as Exceed TM XP6026 performance polyethylene.

[0072] LDPE

[0073] In various embodiments, any one or both of the surface formulation A and the core formulation B (and the corresponding surface (one or more) A and / or core (one or more) B) may comprise LDPE, and in particular LDPE homopolymers, together with any of the more than one mLLDPE discussed, for example for contributing to the stability of the film bubble in blown film processes.

[0074] In many embodiments, there are no particular limitations on LDPE. As those skilled in the art will appreciate, LDPE is typically formed by free radical polymerization (e.g., high-pressure polymerization in a tube and / or autoclave reactor) and has a high degree of long-chain branching (preferably where g' < 0.70, < 0.60, or even < 0.55). Furthermore, according to some embodiments, LDPE may have a density in the range of 0.915-0.930; and / or a melt index (MI, 2.16 kg at 190°C) in the range of 0.1-4.0, for example, 0.1 g / 10 min to 1.0 g / 10 min, or 0.1 to 0.5 g / 10 min (wherein covering the range from any of the aforementioned low to any of the aforementioned high points). In some embodiments, MI may be fractional, for example less than 1.0, such as less than any of 0.9, 0.8, 0.7, 0.6, or 0.5 g / 10 min.

[0075] HDPE

[0076] In various embodiments, one or more HDPEs may be used in surface layer A and / or core layer B (and / or in the respective surface / core formulations). Various HDPEs will be suitable, and in many embodiments using HDPEs, there are no particular limitations on the properties of the HDPEs other than density, which is greater than or equal to 0.935 g / cm³. 3 Preferably, it is greater than or equal to 0.940 g / cm³. 3 0.945g / cm 3 0.950g / cm 3 Or even 0.955g / cm 3 For example, at concentrations of 0.935, 0.940, 0.945, 0.950, or 0.955 g / cm³. 3 The lowest point of any one of them is 0.956, 0.960, 0.962, 0.965, 0.967 or 0.970 g / cm³. 3 Within the range of any of the above high points, which includes the range from any of the above low points to any of the above high points (e.g., 0.955 to 0.970 g / 10 min).

[0077] However, some implementations of HDPE may additionally possess one or more of the following properties: melt index (I0). 2.16 (190℃, 2.16kg load) within the range of 0.1-1.5g / 10min, preferably 0.5 to 1.0g / 10min; melt index ratio (high load melt index or I 21.6 (Measured at 190℃ and under a 21.6kg load) and I 2.16 The ratio of g / 10 min is in the range of 35 or 40 to 50 or 60 g / 10 min; and the Vicat softening temperature is in the range of 120°C to 150°C, for example, in the range of 125°C to 135°C or 140°C. HDPE may have two of these additional properties. Incorporating HDPE into either the surface layer (or formulation) or the core layer (or formulation) can help provide a softening temperature gap between the core layer and the surface layer, which can facilitate film formation methods as already noted.

[0078] Suitable HDPEs include PE homopolymers and ethylene-α-olefin copolymers (wherein the α-olefin can be any of those discussed above along with mLLDPE), and they can be produced by any suitable method known to those skilled in the art, such as gas-phase fluidized bed polymerization or slurry polymerization, or a combination thereof (e.g., in the case of reactors or other bimodal HDPE compositions, they can be produced in two or more reactors in series).

[0079] Polymer processing additives

[0080] In addition to the polyethylene in each layer / formulation, polymer processing additives or polymer processing aids (PPA) may optionally be included in any one or more formulations / layers in a typical amount. For example, any layer may contain 0 to 5 phr (parts / hundred parts of resin) of PPA, such as in the range from 0, 1 or 2 phr to 3, 4 or 5 phr, which covers the range from any of the aforementioned low points to any of the aforementioned high points.

[0081] Suitable PPAs include any known PPAs, such as fluoropolymers, oils, other lubricating compounds, etc., including DYNAMAR from 3M. TM PPA is a specific instance, although other PPAs can be used or substituted for it.

[0082] Layer formulation and layer composition

[0083] As previously noted, the multilayer film according to the various embodiments herein comprises at least one surface layer A and at least one core layer B; preferably at least two surface layers and at least one core layer (e.g., A / B / A or A / … / A, wherein at least one intermediate layer is the core layer B).

[0084] Multilayer membranes typically comprise (1) narrow-CD mLLDPE in one or more layers, and (2) LCB mLLDPE in one or more layers. Optionally, the membrane also comprises LDPE and / or HDPE in one or more layers; and optionally, the membrane also comprises PPA in one or more layers.

[0085] According to several embodiments, the membrane uses narrow-CD mLLDPE in the surface layer (one or more) and LCB mLLDPE (one or more) in the core layer (one or more) (and the corresponding surface and core formulations, respectively). Any layer / formulation may also include either or both of LDPE and HDPE; and likewise, any layer / formulation may include PPA.

[0086] In such an embodiment, surface layer A may comprise 50-100% by weight of narrow-CD mLLDPE (or a blend of two or more narrow-CD mLLDPEs), based on the mass of the total polymer in the formulation or layer (if applicable). More specifically, surface layer formulation A and / or the corresponding surface layer A comprise narrow-CD mLLDPE (or a blend of two or more narrow-CD mLLDPEs) in the range from a low of any one of 50, 55, 60, 65, 68, and 70% by weight to a high of any one of 72, 75, 80, 85, 90, 95, and 100% by weight, wherein this document covers the range from any of the aforementioned lower ends to any of the aforementioned upper ends (e.g., 65 to 75% by weight). In a particular embodiment, the remainder of the material in surface formulation A and / or surface layer A (other than PPA discussed below) may consist of LDPE and / or HDPE, such that the surface formulation / layer contains from 50, 60, or 65 wt% to 75, 80, or 85 wt% narrow-CD mLLDPE and from 15, 20, or 25 wt% to 35, 40, or 50 wt% LDPE and / or HDPE (such wt% represents the sum of the two when LDPE and HDPE are used).

[0087] Furthermore, if applicable, the core layer B and / or core formulation B of such embodiments may contain 50-100% by weight of LCB mLLDPE (or a blend of two or more LCB mLLDPEs) in the formulation or layer. More specifically, the core formulation B and / or the corresponding core layer B contain LCB mLLDPE (or a blend of two or more LCB mLLDPEs) in the range from a low of any one of 50, 55, 60, 65, 68, and 70% by weight to a high of any one of 72, 75, 80, 85, 90, 95, and 100% by weight, wherein this document covers the range from any of the aforementioned lower ends to any of the aforementioned upper ends (e.g., 60 to 85% by weight, e.g., 65 to 75% by weight, or 75 to 85% by weight). In a particular embodiment, the balance of material in core formulation B and / or core layer B (other than PPA discussed below) may consist of LDPE and / or HDPE, such that the surface formulation / layer comprises from 50, 60, or 65 wt% to 75, 80, or 85 wt% of LCB mLLDPE (or a blend of two or more LCB mLLDPEs) and from 15, 20, or 25 wt% to 35, 40, or 50 wt% of LDPE and / or HDPE (such wt% represents the sum of both when LDPE and HDPE are used).

[0088] In certain embodiments in which a blend of two LCB mLLDPEs is used in core formulation B and / or the corresponding core layer B, the first LCB mLLDPE (e.g., the first LCB mLLDPE variant discussed above) may be present in an amount ranging from a low of any one of 10, 15, 18, or 20 wt% to a high of any one of 22, 24, 25, 30, 45, 50, or 55 wt%, which also covers the range from any of the aforementioned lower end to any of the aforementioned upper end; and the second LCB mLLDPE (e.g., the second LCB mLLDPE variant discussed above) mLLDPE variants may be present in amounts ranging from a low of any one of 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, or 80 wt% to a high of any one of 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or 90 wt%, encompassing the range from any of the aforementioned low to any of the aforementioned high, provided that the upper end is greater than the lower end (e.g., 10 to 45, for example, 15 to 25 wt% of the first LCB mLLDPE and 55 to 90, for example, 75 to 85 wt% of the second LCB mLLDPE). In some embodiments, a 50 / 50 blend of the two LCB mLLDPEs may be used; in other embodiments, a blend containing more second LCB mLLDPE than the first LCB mLLDPE may be used. In yet another embodiment, a blend of 25 to 35 wt% of the first LCB mLLDPE and 35 to 45 wt% of the second LCB mLLDPE may be used.

[0089] In subcategories of membranes (and / or formulations) according to these embodiments, LCB mLLDPE may also be included in the surface formulation A (and / or corresponding surface layer A) in addition to narrow-CD mLLDPE. In such embodiments, the surface layer / formulation comprises 20-50 wt% narrow-CD mLLDPE, 20-50 wt% LCB mLLDPE of the second variant discussed above (having a lower density and a greater stiffness / strength and processability balance), and the balance (if present) comprises optional LDPE and / or HDPE. In some of these embodiments, more LCB mLLDPE than narrow-CD mLLDPE is included in the surface layer / formulation A. Furthermore, in such embodiments, the LCB mLLDPE used in the core layer / formulation B may be any type of LCB mLLDPE, but is preferably the first variant of the LCB mLLDPE discussed above (having a higher density than the second variant of the LCB mLLDPE).

[0090] Another membrane and / or formulation embodiment includes narrow-CD mLLDPE (one or more) in the core layer / formulation B and LCB mLLDPE (one or more) in the surface layer / formulation A. The amount of each type of polyethylene in each layer is within the range discussed above, except that the LCB mLLDPE is in the surface layer / formulation A instead of the core layer / formulation B; and the narrow-CD mLLDPE (one or more) is in the core layer / formulation B instead of the surface layer / formulation A. Similarly, any layer type may include the amounts of LDPE and / or HDPE as discussed above. Furthermore, according to the above, subclasses of these embodiments may include blends of narrow-CD mLLDPE and a second variant of LCB mLLDPE in the same layer or formulation (in these embodiments, in the core layer / formulation B), said blend comprising 20-50 wt% narrow-CD mLLDPE, 20-50 wt% LCB mLLDPE of the second variant discussed above (having a lower density and a greater stiffness / strength and processability balance), and the balance (if present) comprising optional LDPE and / or HDPE. Moreover, the core layer / formulation of such embodiments may include more LCB mLLDPE than narrow-CD mLLDPE.

[0091] Additionally, in all embodiments discussed above, either or both of the surface formulation A and / or core formulation B (and / or the corresponding surface and core layers) may include 5 phr of PPA or less, for example, 4 phr or less, 3 phr or less, 2 phr or less, or 1 phr or less. Some embodiments have no PPA in the surface or core layer; others have PPA only in the surface layer; and still others have PPA in each of the surface and core layers. The amount of PPA described herein in phr (parts per hundred parts of resin) is based on the amount (by mass) of non-PPA polymeric material (polyethylene) (e.g., LLDPE plus LDPE plus HDPE) in the formulation / layer. Furthermore, all weight percent described above for polyethylene in the various layers and / or formulations are based on the amount (by mass) of polyethylene in the layer / formulation and do not include PPA. Preferably, apart from optional PPA, no polymeric material other than polyethylene is included in each layer / formulation. And in any case, excluding PPA, such that there is no polymer material other than polyethylene in the layer / formulation (and therefore in the film made therefrom).

[0092] Furthermore, this article covers various layer distributions. For example, the surface layer may each constitute 5, 10, 15, 25 to 20, 25, 30, 35, 40 or 45% by weight of the membrane (wherein covering the range from any of the aforementioned low points to any of the aforementioned high points, provided that the upper end is greater than the lower end), with the balance formed by the core layer (one or more). As a specific example, in a 3-layer A / B / A membrane, the surface layer A may each constitute 10-35% by weight of the membrane, for example 10-20% or 25-35% by weight, with the balance formed by the core layer B. Thus, 15 / 70 / 15 membranes and 30 / 40 / 30 membranes are covered in the foregoing.

[0093] Double membrane blister

[0094] In various embodiments, the substantially all-PE polymer formulation described above is formed into an oriented multilayer film, preferably a biaxially oriented multilayer film.

[0095] In a particularly preferred embodiment, the substantially all-PE polymer formulation described above is co-extruded together to form a co-extrusion, and then the co-extrusion is oriented. Preferably, the co-extrusion is biaxially oriented, and most preferably it is oriented by a two-film blown film method to obtain a biaxially oriented film.

[0096] Using the surface and core formulations described above, excellent biaxially oriented polyethylene (BOPE) films can be produced via the double-bubble method. It is believed that selecting the core and surface formulations as described above achieves a desired balance between melt strength and melt / softening point differences, thereby maintaining the stability of the bubbles formed during the double-bubble orientation process. Therefore, using the formulations described herein, those skilled in the art can achieve biaxially oriented films with acceptable or even excellent properties, while simultaneously achieving a substantially all-PE solution.

[0097] The following describes exemplary double-bubble methods for obtaining biaxially oriented films according to various embodiments. As indicated, this method can be applied to each of a variety of polymer film formulations (e.g., each of several layers) for subsequent combination; or it can be applied to co-extrusions (e.g., when each of multiple layers is co-extruded, and then proceeds through biaxial orientation). The following description is written in the latter case (e.g., assuming all layers are co-extruded to form a multilayer co-extrusion for biaxial orientation).

[0098] A biaxially oriented membrane method may generally include: (a) extruding or co-extruding one or more polymer formulations to form an extrudate; (b) blowing or expanding the extrudate to form a first membrane bubble; (c) flattening the first membrane bubble to form a flattened tube; (d) heating the flattened tube; (e) blowing or expanding the flattened tube to form a second membrane bubble; and (f) flattening the second membrane bubble to obtain a biaxially oriented membrane. MD and TD orientations preferably occur in both membrane bubbles, but typically the second membrane bubble includes a larger blow-up ratio than the first membrane bubble, resulting in a membrane with the desired degree of biaxial orientation.

[0099] For reference Figure 1 The two-membrane bubble method is described in more detail according to various implementation schemes. Figure 1 This is a schematic diagram illustrating an exemplary dual-film bubble extrusion system 3000. As shown with respect to (a) extruding or co-extruding one or more polymer formulations to form an extrudate: formulations (e.g., surface formulations or core formulations as described above) are individually fed into extruder 3010 through feed line 3005 to form an extrudate. Alternatively, multiple formulations (e.g., surface formulations and core formulations, or, in a particular embodiment, two surface formulations and core formulations) may be fed into extruder 3010 through multiple feed lines (not shown), or they may be combined and fed through feed line 3005. Arrangements other than feed lines for feeding one or more formulations are also covered, such as any arrangement known in the art. For example, it also covers a gravity feeding system in which the extruder may be equipped with one or more feed hoppers; in addition, when multiple hoppers are used, extruder blending may occur in a mixing hopper installed below the feed hopper, from which the blend is discharged into the extruder 3010.

[0100] The extrudate (whether formed from a formulation fed into the extruder 3010 or a blend of formulations) is forced through a die assembly 3015 (which may include, for example, a die, a screen changer, and a connector, wherein the extruder is connected to the die via the screen changer and the connector). The melt flow of the extrudate is shaped within the die through one or more annular gaps and forced out, causing the extrudate to exit as an extrudate tube 3020. For simplicity, in... Figure 1 The image shows a single extruder and die assembly; however, multiple extruders can be connected to a single die, for example, such that each extruder is connected to the die via a screen changer and a connector, allowing the die to take in the extruded stream from one or more connected extruders and discharge the combined extrudate (or co-extrudate).

[0101] The extrusion tube 3020 will preferably have the basic composition of the film to be formed in the method; thus, for a method of forming a multilayer film, multiple formulations (each preferably corresponding to one layer of the film) can be (a) fed into a single extruder and co-extruded into and through a die assembly; or (b) each can be fed through its respective extruder and then fed into a common die and co-extruded into the extrusion tube 3020. For example, to prepare a three-layer film comprising a core layer sandwiched between two surface layers, it is preferable to feed the core formulation and two surface layer formulations (each as described above) – whether by co-extruded all of these through a single extruder 3010, or by extruding the surface layer through one extruder and the core layer through a second extruder – to form a co-extrusion in a common die, and then discharge the co-extrusion as the extrusion tube 3020. All these and other forms of forming co-extrusions are covered herein, and the resulting composition (made of multiple formulations) used for feeding into the remainder of the film-forming method is referred to herein as a “co-extrusion”, however, has been formed. Furthermore, unless the context clearly indicates otherwise, the term “extrusion” as used herein is intended to refer generally to both single-formulation extrusions and multi-formulation extrusions or “co-extrusions”.

[0102] Furthermore, regarding extrusion, the formulation (one or more) may be preheated and / or heated within the extruder (one or more) to a temperature suitable for causing softening or melting of the polymer in the formulation (one or more) (e.g., a temperature in the range of 120°C to 230°C, such as from a low point of any one of 120, 130, 140, 150, or 160°C to a high point of any one of 200, 220, 250, or 280°C, wherein this document covers the range from any upper end to any lower end). This heating temperature may be referred to as the first bubble temperature, for example, to indicate the desired temperature for the formation of the first bubble. Heat may be provided using any known technology or equipment; and the extruder may have a constant temperature or may have a temperature gradient (e.g., multiple zones defined along the length of the extruder, each zone having an associated temperature).

[0103] For (b) blowing or expanding the extrudate to form the first membrane bubble: as in Figure 1In the embodiments shown, the extruder tube 3020 is cooled or quenched (e.g., using a water ring 3030, which provides temperature-controlled (e.g., quenched) water on the outer surface of the extruder feed line 3020). Air is then introduced into the interior of the extruder tube 3020 to form a downwardly extending first film bubble 3035. For example, air can be injected through the die orifice in an amount sufficient to cause the extruder to expand into a film bubble with a desired diameter. As described in U.S. Patent Publication No. 2014 / 0147646, the film thickness is controlled by the blow-up ratio (BUR), extraction speed, and output. The BUR of the blown film can range from a low of any one of 1, 1.5, 1.8, 2.0, or 2.2 to a high of any one of 3, 3.5, 5, 8, or 10. The die clearance can range from a low of any one of 0.5, 0.8, or 1.0 mm to a high of any one of 2, 3, 5, or 9 mm. Furthermore, it should be noted that although the first film bubble 3035 is in Figure 1 The bubble is shown as downward-facing, but in other embodiments, the first bubble 3035 can be blown upward-facing.

[0104] Then, (c) flatten the first membrane bubble 3035 (e.g.) Figure 1 As shown, the flattened tube 3055 is formed by using rollers 3040 and 3045. Although Figure 1 The specifications describe two sets of rollers, 3040 and 3045, but multiple rollers can be used in various assemblies. Furthermore, they can be used as… Figure 1 The rollers 3040 and 3045 described herein may be used in conjunction with or as an alternative to any method suitable for cooling and flattening the membrane bubble. For example, the membrane bubble may be quenched by using water, for example, in the form of a waterfall spray and / or immersion, and / or one or more rollers may be used to flatten the membrane bubble. Alternatively, cooling air may be blown over the flattened / flattened membrane bubble while warm air is exhausted via an exhaust pipe. Furthermore or alternatively, the tube 3035, which is flattened into a flattened tube 3055, may be simultaneously cooled on the outside by a double-lip air ring. This air ring provides primary cooling and sets the frost line. The cooling air may be cooled in a heat exchanger connected to the quench water circuit of the site. The membrane bubble 3035 may be stabilized in a sizing sleeve, where it then enters the flattening stage.

[0105] Then, (d) the flattened tube 3055 is reheated to soften it, preferably by heating it to a higher temperature than that reached in extrusion (a). This can be referred to as heating to a second film bubble temperature, which is higher than the temperature reached in extrusion (a).

[0106] Along with or immediately after heating (d), the flattened tube (e) is re-inflated or re-expanded to form a second film bubble. The second film bubble may be larger than the first film bubble (e.g., with a higher diameter) and may also be biaxially stretched (e.g., at the same draw ratio in both the machine direction and the transverse (or cross) direction). However, in other cases, the second film bubble may have different dimensions compared to the first film bubble. Furthermore, the orientation of the film obtained from this method can be defined by a combination of the extruder output, the coiling speed of the second film bubble relative to the first film bubble, and its width.

[0107] like Figure 1 The description states that heating (d) and re-inflation (e) occur simultaneously. Air is blown into the expanding, flattening tube 3055, causing it to inflate downwards again into a second membrane bubble 3065 (larger than the first membrane bubble 3035), while simultaneously heating it. Figure 1 The embodiments show the use of a series of multiple heaters (heaters 3060 and 3068) capable of uniform heating or heating by varying temperatures, thereby establishing a heating gradient along the second bubble 3065. For example, the oven temperature can vary in very small increments, such as about + / -10°C, or about + / -5°C, or about + / -2°C (comparing one pair of ovens to the next pair, such as pair 3060 to pair 3068). Additional pairs of ovens or a single oven can be used. In many cases, the oven is an infrared heater and can define a hollow cylinder surrounding most of the vertical distance of the flattened tube 3055 as it expands into the bubble 3065.

[0108] Then (f) the film bubble is flattened. As part of the flattening process, a cooling film bubble is preferred (e.g., using an air ring, such as air ring 3075, in...). Figure 1 (Illustrated with a simplified cross-section); then it is flattened, for example, using a clamping roller 3080. Optionally, one or more thickness scanners 3070 can be used to monitor the thickness of the second membrane bubble 3065 (e.g., for method control). Multiple sets of clamping rollers 3080 can be used (not shown in the diagram). Figure 1 (See the instructions). The resulting film is then wound onto roller 3099.

[0109] In various embodiments, the double-film bubble method may also include one or more of the following: (i) annealing the film; (ii) cutting the film to form multiple films (e.g., before winding onto roller 3099).

[0110] For illustrative purposes, the methods described above are provided together with Figure 1 Other available dual-film bubble extrusion techniques are disclosed, for example, in U.S. Patent Nos. 3,456,044 and 6,423,420, and U.S. Patent Publications Nos. 2012 / 0164421 and 2014 / 0147646, which are incorporated herein by reference for this purpose.

[0111] Therefore, more generally, this disclosure includes a method for forming a multilayer polymer film, comprising: (a) extruding or co-extruding one or more polymer formulations (preferably two or more polymer formulations) at an extrusion temperature to form an extrudate, wherein the polymer formulations (one or more) are one or more of the surface formulations and core formulations described above; (b) inflating the extrudate to form a first film bubble; (c) flattening the first film bubble to form a flattened tube; (d) heating the flattened tube to a second film bubble temperature (preferably greater than the extrusion temperature and greater than the softening point of each polymer in the polymer formulations (one or more)); (e) inflating the flattened tube to form a second film bubble; and (f) flattening the second film bubble to obtain a multilayer polymer film. The second film bubble is preferably larger in diameter than the first film bubble, and the multilayer polymer film is preferably biaxially oriented (e.g., wherein biaxial stretching is used in the second film bubble forming).

[0112] Specifically, the polymer formulations (one or more) used in such a method may include two surface formulations A and a core formulation B, such that a three-layer polymer membrane with an A / B / A structure is formed after (f) flattening the second membrane bubble. The two surface formulations A may be identical or different in composition; when different, they may be referred to as surface formulations A and A', and the membrane may be specifically referred to as having an A / B / A' structure to describe two compositionally different surface formulations A and A'. However, the general structure A / B / A does not necessarily mean that the two surface formulations A are identical unless the context clearly indicates otherwise.

[0113] As noted, surface formulations A may be identical in composition. Thus, polymer formulations (one or more) may be more simply referred to as comprising a surface formulation A and a core formulation B, and co-extruded formulations such that a three-layer polymer film of an A / B / A structure (where the two A layers have the same composition) is formed after (f) flattening the second membrane bubble.

[0114] Two or more extruders can be used in such co-extrusion methods, and it is preferable to use two extruders (e.g., one extruder for surface formulation A and one for core formulation B) when both surface layers use the same surface formulation A. In other embodiments, three extruders (e.g., one extruder for the first surface formulation A and a second extruder for the second surface formulation A') or four extruders can be used (e.g., one extruder for each different formulation to be used when preparing different layers of the film).

[0115] In even other embodiments, a five-layer polymer film can be formed (e.g., by using one or more surface formulations and one or more core formulations for co-extrusion). The five-layer film can take the form of, for example, an A / B / A / B / A structure, or A / A / B / A / A, or A / B / B / B / A (again, where A is a surface layer and / or a layer made of a surface formulation as described herein, and the composition of any two A layers can be the same or different from each other; and B is a core layer and / or a layer made of a core formulation as described herein). The film structure will generally depend on the co-extrusion method used, which will be well understood by those skilled in the art to select based on the desired layer structure.

[0116] Similarly, this document also covers extensions to seven or more layers. Thus, in general, a multilayer film obtained by the method just described can have two or more layers, preferably three or more layers, and the layers can comprise any combination of surface layer A and core layer B as described herein, and in any order, provided that surface layer A forms each outer layer of the film (e.g., the film has an A / … / A structure), and further provided that at least one core layer B is disposed between the outer surface layers A. Each surface layer A can be identical (e.g., formed from the same or identical surface formulation) or different (e.g., different surface layers such that each surface layer is individually described as surface layer A as provided herein), and is also used for the core layer B.

[0117] application

[0118] Those skilled in the art will appreciate that formulations as described herein and membranes formed therefrom can be used in any suitable membrane application. These include, for example, extruded, co-extruded, cast, and / or laminated films. This document specifically covers packaging such as shrink wrap, manual or pallet wrapping, food and non-food packaging, particularly barrier packaging (whether moisture barrier, gas barrier, or both), and other similar articles that are highly suitable for films (and particularly oriented films). These and other usable articles include, for example, packaging materials for irradiated medical devices or food, including trays, and containers for storing liquids such as water, milk, or juice, including single-serving and large storage containers. Example

[0119] A three-layer membrane is prepared according to one of six formulations used in a double-membrane bubble production method. The membranes each have formulations according to Tables 1 to 6 below. As described above, in the membrane formulations, ENABLE... TM 4002MC and EXCEED TM XP 6026ML (available from ExxonMobil Chemical Company) is an example of LCB mLLDPE; EXCEED TM1012MA is an example of narrow-CDmLLDPE; HTA 108 (ExxonMobil) TM HTA 108 HDPE is an example of HDPE; and Lupolen TM 2420 DLDPE (available from LyondellBasell) is an example of LDPE. PPA is a polymer processing additive, specifically DYNAMAR from 3M. TM FX5929 Polymer Processing Additive. Note that the weight percent in Tables 1-6 are based on all components except PPA; while PPA is based on phr (parts / hundred parts of resin).

[0120] Table 1. Membrane formulations from Example 1

[0121]

[0122]

[0123] Table 2. Membrane formulations from Example 2

[0124]

[0125] Table 3. Membrane formulations from Example 3

[0126]

[0127] Table 4. Membrane formulations from Example 4

[0128]

[0129]

[0130] Table 5. Membrane formulations from Example 5

[0131]

[0132] Table 6. Membrane formulations from Example 6

[0133]

[0134] nature

[0135] Shrinkage (Betex shrinkage) was measured as a percentage by cutting circular specimens from the film using a 50mm die. The specimens were then placed on copper foil and embedded in a silicone oil layer. The assembly was heated by placing it on a 150°C heating plate (model Betex) until dimensional change ceased. The average of four specimens was reported. A negative shrinkage value indicates dimensional expansion after heating compared to its preheated size. Specimens 4, 5, and 6 were also tested in the same manner at 110°C and 130°C (except for 150°C). Furthermore, tensile properties (1% secant modulus, tensile strength, and elongation at break %) were measured for each example according to ASTM D-882 in MD and TD. Some specimens (Examples 1-3) were additionally tested for tear strength (Elmendorf tear, ASTM D1922-09), and others (Examples 4-6) were tested for holding force. Finally, the shrinkage was measured with two ternary copolymer polypropylenes (TF400 from Hanwha Total Petrochemical Company). TM The polyethylene-hexene core between the propylene-ethylene-butene (PP-Butene) outer layers (available from Dow Chemical Company) is called DOWLEX. TM These properties were compared with a commercially available sample (Comparative Example 1) of an existing double-bubble shrink film made of 2045 polyethylene with a thickness of 20 micrometers and a layer ratio of 3 / 4 / 3. The results of each property measurement are reported in Table 7 below. For each film tested for (1) shrinkage, (2) MD tensile properties, (3) TD tensile properties, (4) MD tear and (5) TD tear, the film thickness is reported.

[0136] Table 7 Properties of Examples 1-6

[0137]

[0138]

[0139] discuss

[0140] The data show that the all-PE film of the embodiments provides reasonable and acceptable properties of a double-bubble shrink film, while providing substantial advantages based on all-PE (except for a small amount of PPA).

[0141] Examples 2 and 3 (using narrow-CD mLLDPE in the core layer) achieve equivalent shrinkage, acceptable high tensile properties, and excellent tear resistance compared to existing control examples.

[0142] Even greater tear resistance can be achieved using Example 1, which uses a blend of narrow-CD mLLDPE and the second variant LCB mLLDPE in the surface layer and the first variant LCB mLLDPE in the core layer; although it is noted that these increases come at the cost of tensile properties, with Example 1 showing lower stiffness and tensile strength.

[0143] Examples 4, 5, and 6 (using LCB mLLDPE in the core layer instead of the surface layer, while maintaining narrow-CD mLLDPE in the surface layer) showed lower shrinkage values ​​but higher tensile properties on average (especially for Examples 5 and 6), particularly on TD.

[0144] For the sake of brevity, this document only explicitly discloses certain ranges. However, a range not explicitly stated can be described by combining any lower limit with any upper limit, and a range not explicitly stated can be described by combining any lower limit with any other lower limit; similarly, a range not explicitly stated can be described by combining any upper limit with any other upper limit. Furthermore, even if not explicitly stated, each point or individual value is included within a range between its endpoints. Thus, each point or individual value can serve as its own lower or upper limit, combined with any other point or individual value or any other lower or upper limit, to describe a range not explicitly stated.

[0145] All documents mentioned herein are incorporated herein by reference, including any priority documents and / or test procedures, provided they do not contradict this document. As will be apparent from the foregoing general description and specific embodiments, various changes may be made without departing from the spirit and scope of this disclosure, although the form of this disclosure has been set forth and described. Therefore, it is not intended to limit this disclosure. Similarly, for the purposes of U.S. law, the term “comprising” is considered synonymous with the term “including.” Likewise, whenever a component, element, or group of elements is preceded by the conjunction “comprising,” it should be understood that we also consider a group of the same components or elements preceded by the conjunctions “substantially constitutes…,” “consisting of…,” “selected from…,” or “is,” and vice versa.

[0146] While this disclosure has been described in relation to many embodiments and examples, those skilled in the art who benefit from this disclosure will appreciate that other embodiments can be designed without departing from the scope and spirit of this disclosure.

Claims

1. A multilayer film comprising at least two surface layers and at least one core layer disposed directly or indirectly between the at least two surface layers, wherein the multilayer film comprises: (a) Narrow-CD metallocene linear low-density polyethylene (narrow-CD mLLDPE) comprising 85 to 95% by weight units derived from ethylene and the balance derived from C3-C 12 α-Olefins, the weight percentage being based on the total mass of the polymer in narrow-CD mLLDPE, and also possessing: a compositional width index (CDBI) of at least 50%, a melt index in the range of 0.1–3.0 g / 10 min, determined according to ASTM D1238 at 190 °C and a 2.16 kg load, a molecular weight distribution (MWD, Mw / Mn) in the range of 1.5–4, a peak melting temperature in the range of 105 °C–120 °C, and a Vicat softening temperature in the range of 70 °C–130 °C; and (b) Long-chain branched metallocene linear low-density polyethylene (LCB mLLDPE) comprising 80 to 99% by weight units derived from ethylene and the balance derived from C3-C 12 α-olefin, the weight % is based on the total mass of the polymer in LCB mLLDPE, and also has: at least 50% CDBI, I2 in the range of 0.1-0.7 g / 10 min, which is determined at 190 °C under a 2.16 kg load, g'(vis) in the range of 0.85-0.95, and MWD in the range of 2.5-5.5; (c) Optionally, (c-1) has a density in the range of 0.915-0.930 g / cm³. 3 Low-density homopolymer polyethylene (LDPE) and (c-2) within the range have a density greater than or equal to 0.935 g / cm³. 3 Any or both of high-density polyethylene (HDPE); and (d) Optionally, polymer processing additives; These include narrow-CD mLLDPE (a) and LCB mLLDPE (b) in different layers relative to each other; The multilayer film is biaxially oriented; and Furthermore, of the total polymer content of the membrane, at least 95% by weight is composed of polyethylene. And the membrane satisfies one of requirements i) to iii): i) The LCB mLLDPE is a first LCB mLLDPE, and each of the surface layers contains the first LCB mLLDPE; and the core layer contains (i) a narrow-CD mLLDPE and (ii) a second LCB mLLDPE; ii) The LCB mLLDPE is a first LCB mLLDPE, and the core layer comprises the first LCB mLLDPE; and each of the surface layers comprises (i) a narrow-CD mLLDPE and (ii) a second LCB mLLDPE; or iii) The surface layer comprises narrow-CD mLLDPE and the core layer comprises LCB mLLDPE, wherein the LCB mLLDPE is the first LCB mLLDPE, the second LCB mLLDPE, or a combination thereof. The first LCB mLLDPE has a peak melting temperature in the range of 115℃-135℃, a Vicat softening temperature in the range of 110℃-130℃, and a melting point of 0.930-0.950 g / cm³. 3 Density within the range; and The second LCB mLLDPE has a peak melting temperature in the range of 100℃-114℃, a Vicat softening temperature in the range of 95℃-109℃, and a strength of 0.910-0.929 g / cm³. 3 Density within the range.

2. The membrane according to claim 1, wherein: The membrane meets requirement i) or ii).

3. The membrane according to claim 1, wherein the membrane satisfies requirement i), and Each layer also contains LDPE; and / or The surface layer also contains HDPE.

4. The membrane according to claim 1, wherein the membrane satisfies requirement iii) and the surface layer further comprises LDPE.

5. The membrane according to claim 1, wherein the membrane satisfies requirement iii) and the LCB mLLDPE is a first LCB mLLDPE, and further wherein the core layer comprises the first LCB mLLDPE and the second LCB mLLDPE.

6. The membrane according to any one of the preceding claims, wherein at least 97% by weight of the total polymer content of the membrane is composed of polyethylene.

7. The membrane according to claim 6, wherein the membrane comprises 1 to 4 phr of polymer processing additives.

8. The membrane according to claim 6, wherein the polymer content of the membrane is entirely composed of polyethylene.

9. A method for forming a biaxially oriented multilayer polymer film, the method comprising: (a) Extruding two or more polymer formulations at an extrusion temperature to form an extrudate, wherein the polymer formulation comprises: Surface formulation and core formulation; wherein the surface formulation or core formulation comprises narrow-CD metallocene linear low-density polyethylene (narrow-CD mLLDPE), and another of the surface formulation or core formulation comprises long-chain branched metallocene linear low-density polyethylene (LCB mLLDPE). Narrow-CD mLLDPE contains 85 to 95% by weight units derived from ethylene and the balance derived from C3-C. 12 α-Olefins, the weight percentage being based on the total mass of the polymer in narrow-CD mLLDPE, and also possessing: a compositional width index (CDBI) of at least 50%, a melt index in the range of 0.1–3.0 g / 10 min, determined according to ASTM D1238 at 190 °C and a 2.16 kg load, a molecular weight distribution (MWD, Mw / Mn) in the range of 1.5–4, a peak melting temperature in the range of 105 °C–120 °C, and a Vicat softening temperature in the range of 70 °C–130 °C; and Additionally, LCB mLLDPE contains 80 to 99% by weight units derived from ethylene and the balance derived from C3-C. 12 α-olefin, the weight % based on the total mass of the polymer in LCB mLLDPE, and also having: at least 50% CDBI, I2 in the range of 0.1-0.7 g / 10 min, determined at 190 °C under a 2.16 kg load, g'(vis) in the range of 0.85-0.95, and MWD in the range of 2.5-5.5; and Additionally, at least one of the surface formulation and the core formulation may optionally include stabilized polyethylene; (b) Inflate the extrudate to form the first membrane bubble; (c) Flatten the first membrane bubble to form a flattened tube; (d) Heating the flattened tube to the second membrane bubble temperature, wherein the second membrane bubble temperature is greater than the extrusion temperature and also greater than the softening point of the following materials: (i) narrow-CD mLLDPE, (ii) LCB mLLDPE, (iii) stabilized polyethylene and (iv) any other polymer in the polymer formulation; (e) The tube is inflated and flattened to form a second membrane bubble; and (f) Flattening the second membrane bubble to obtain a biaxially oriented multilayer polymer membrane, wherein at least 95% by weight of the polymer content of the multilayer polymer membrane is composed of polyethylene. The obtained biaxially oriented multilayer films satisfy one of requirements i) to iii): i) The LCB mLLDPE is a first LCB mLLDPE, and each of the surface layers contains the first LCB mLLDPE; and the core layer contains (i) a narrow-CD mLLDPE and (ii) a second LCB mLLDPE; ii) The LCB mLLDPE is a first LCB mLLDPE, and the core layer comprises the first LCB mLLDPE; and each of the surface layers comprises (i) a narrow-CD mLLDPE and (ii) a second LCB mLLDPE; or iii) The surface layer comprises narrow-CD mLLDPE and the core layer comprises LCB mLLDPE, wherein the LCB mLLDPE is the first LCB mLLDPE, the second LCB mLLDPE, or a combination thereof. The first LCB mLLDPE has a peak melting temperature in the range of 115℃-135℃, a Vicat softening temperature in the range of 110℃-130℃, and a melting point of 0.930-0.950 g / cm³. 3 Density within the range; and The second LCB mLLDPE has a peak melting temperature in the range of 100℃-114℃, a Vicat softening temperature in the range of 95℃-109℃, and a strength of 0.910-0.929 g / cm³. 3 Density within the range.

10. The method of claim 9, wherein the obtained biaxially oriented multilayer film is a film according to any one of claims 1-8.

11. The method of claim 9, wherein the membrane comprises 1 to 4 phr of polymer processing additives.

12. The method according to claim 9, wherein the polymer content of the membrane is entirely composed of polyethylene.

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