ES2993746A1 - MULTILAYER FILMS WITH IMPROVED CREEP, TEAR AND DART (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

A multilayer film may comprise a first skin layer, a second skin layer, and a core positioned between the first skin layer and the second skin layer. The first skin layer and the second skin layer may independently comprise linear low-density polyethylene (LLDPE) resin. The core may comprise a first core layer, a second core layer, and a third core layer. The first core layer and the third core layer may independently comprise high-density polyethylene (HDPE), LLDPE, or a combination thereof. The second core layer may comprise an ethylene-based copolymer selected from the group consisting of ethylene/propylene copolymer, ethylene/butyl acrylate copolymer, ethylene/ethyl acrylate copolymer, ethylene/methyl acrylate copolymer, and ethylene/vinyl acetate copolymer. The thickness of the second core layer may be less than 15% of a thickness of the multilayer film. At least one of the core layers may comprise HDPE. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

Multilayer films with improved creep, tear and dart

Technical field

Embodiments described herein generally relate to multilayer films and, more specifically, to multilayer films used for Heavy Duty Shipping Sacks (HDSS).

Background

In an interest of improving sustainability and reducing cost, it is desirable to reduce the thickness of films used to make heavy duty shipping sacks (“HDSS”). Reducing the thickness reduces the amount of material used and therefore overall emissions. However, this thickness reduction (also called “thinning”) must be achieved without sacrificing impact strength, tear strength, and creep resistance. It has become progressively more difficult to meet these specifications as the film is reduced in thickness, especially below 100 μm.

Regarding creep, it is well known that creep is inversely proportional to the cube of the thickness when the thickness is close to 100 μm. Creep can be improved by adding more HDPE and increasing the overall stiffness of the film. However, this worsens other mechanical properties, such as impact resistance.

Brief compendium

Accordingly, thinner films that can still meet impact resistance, tear resistance, and creep resistance are desired. Embodiments of the present disclosure meet this need by providing a multilayer film comprising a core layer comprising ethylene acrylate copolymer, ethylene propylene copolymer, or combinations thereof. Additional embodiments of the present disclosure meet this need by providing a core layer comprising ethylene acrylate copolymer, ethylene propylene copolymer, or combinations thereof and that is relatively thin, such as less than 20% of the thickness of the multilayer film.

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

Additional features and advantages will be presented in the detailed description that follows, and in part will be readily apparent to those skilled in the art from that description or will be recognized by practicing the embodiments described herein, including the detailed description that follows and the claims.

It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide a general description or framework for understanding the nature and character of the claimed subject matter.

Brief description of the various views of the drawings

To readily identify the discussion of any particular element or act, the most significant digit or digits in a reference numeral refer to the figure number in which that element is first presented. Where two embodiments include the same component, like numerals will be used to describe like components (e.g. first layer 204 in FIG. 2 will correspond to first layer 104 in FIG. 1).

FIG. 1 illustrates a side view of one embodiment of the present multilayer film. FIG. 2 illustrates a side view of one embodiment of the present multilayer film.

Detailed description

Specific embodiments of the present application will now be described. The disclosure may be embodied in a variety of forms and should not be construed as limited to the embodiments presented in this disclosure. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art.

As discussed above, thinner films that can still meet impact resistance, tear resistance, and creep resistance are desired for use in HDSS. Embodiments of the present disclosure meet this need by providing a multilayer film comprising a second core layer comprising ethylene-based copolymer selected from the group consisting of ethylene/propylene copolymer, ethylene/butyl acrylate copolymer, ethylene/ethyl acrylate copolymer, ethylene/methyl acrylate copolymer, and ethylene/vinyl acetate copolymer; and that is relatively thin, such as less than 15% of the thickness of the multilayer film.

Definitions

"Ethylene-acrylate copolymer" refers to ethylene-based polymers with acrylate comonomers. The ethylene-acrylate copolymers of the present disclosure may comprise a majority (greater than 50% w/w) of the ethylene monomer residues, based on the total polymer weight of the ethylene acrylate copolymer. The remainder of the polymer weight of the ethylene-acrylate copolymer may comprise the acrylate monomer residues.

"Ethylene-propylene copolymer" refers to ethylene-based polymers with propylene comonomers. The ethylene-propylene copolymers of the present disclosure may comprise a majority (greater than 50% w/w) of the ethylene monomer residues, based on the total polymer weight of the ethylene-propylene copolymer. The remainder of the polymer weight of the ethylene-propylene copolymer may comprise the propylene monomer residues.

“Residue” refers to the portion of a polymer derived from a specific monomer. “gf/gm” refers to grams force per micrometer.

"Severe Duty Shipping Sacks", also referred to herein as "HDSS", refer to packaging designed to hold large quantities of granular commodities such as polymer resins, solid chemicals, cement, animal feed, rice, and similar commodities. HDSS described herein may be suitable for holding more than 20 kg of granular commodities.

"Multilayer film" refers to any structure that has more than one layer. For example, the multilayer structure may have five or more layers, such as 6, 7, 89, 10, or 11 layers. In embodiments, the multilayer film may have an odd number of layers, such as 5, 6, 9, or 11 layers.

“Polyethylene” as used herein, and “ethylene-based polymer” shall mean polymers comprising greater than 50% by weight of units that have been derived from ethylene monomer. This includes homopolymers or copolymers of polyethylene (meaning units derived from two or more comonomers). Common forms of polyethylene known in the art include Low Density Polyethylene (LDPE); Linear Low Density Polyethylene (LLDPE); Ultra Low Density Polyethylene (ULDPE); Very Low Density Polyethylene (VLDPE); Unilocally catalyzed Linear Low Density Polyethylene, which includes both linear and substantially linear low density resins (m-LLDPE); Medium Density Polyethylene (MDPE); and High Density Polyethylene (HDPE).

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

The term “LDPE” may also be referred to as “high pressure ethylene polymer” or “highly branched polyethylene” and is defined to mean that the polymer is partially or fully homopolymerized or copolymerized in autoclaves or tubular reactors at pressures above 100 MPa (14,500 psi) with the use of free radical initiators, such as peroxides (see for example U.S. Pat. No. 4,599,392, incorporated herein by reference).

The term “LLDPE” includes resins made using traditional Ziegler-Natta catalyst systems as well as single site catalysts such as metallocenes (sometimes referred to as “m-LLDPE”). LLDPEs contain shorter chain branches than LDPEs and include the substantially linear ethylene polymers further defined in U.S. Pat. No. 5,272,236; U.S. Pat. No. 5,278,272; U.S. Pat. No. 5,582,923; and U.S. Pat. No. 5,733,155; homogeneously branched linear ethylene polymer compositions such as those of U.S. Pat. No. 3,645,992; heterogeneously branched ethylene polymers such as those prepared according to the process described in U.S. Pat. No. 4,076,698; and/or mixtures thereof (such as those described in U.S. Pat. No. 3,914,342 or U.S. Pat. No. 5,854,045). LLDPE can be made by gas-phase, solution-phase, or slurry polymerization or any combination thereof, using any type of reactor or reactor configuration known in the art, including, but not limited to, gas-phase and solution-phase reactors.

The term “C6 LLDPE” refers to ethylene-based polymers produced from ethylene monomer and hexene comonomer. Similarly, “C4 LLDPE” refers to ethylene-based polymers produced from ethylene monomer and butene comonomer, and “C8 LLDPE” refers to ethylene-based polymers produced from ethylene monomer and octene comonomer.

The term “HDPE” generally refers to polyethylenes having densities greater than about 0.935 g/cm3 and up to about 0.980 g/cm3, which are generally prepared with Ziegler-Natta catalysts, chromium catalysts, or single-site catalysts including, but not limited to, mono- or bis-substituted cyclopentadienyl catalysts (typically referred to as metallocene), constrained geometry catalysts, phosphinimine catalysts, and polyvalent aryloxyether catalysts (typically referred to as bisphenyl phenoxy).

"Polymer" refers to a polymeric compound prepared by polymerizing monomers, whether of the same or different types. The term polymer thus encompasses the term homopolymer (used to refer to polymers prepared from only one type of monomer, with the understanding that trace amounts of impurities may be incorporated into the polymer structure), and the term copolymer or interpolymer. Trace amounts of impurities (e.g., catalyst residues) may be incorporated into and/or within the polymer. A polymer may be a single polymer or a combination of polymers.

As used herein, the term “copolymer” means a polymer formed by the polymerization reaction of at least two structurally different monomers. The term “copolymer” is inclusive of terpolymers. For example, ethylene copolymers, such as ethylene-propylene copolymers, include at least two structurally different monomers (e.g., ethylene-propylene copolymer includes copolymerized units of at least ethylene monomer and propylene monomer) and may optionally include additional monomers or functional or modifying materials, such as acid, acrylate, or anhydride functional groups. Stated another way, the copolymers described herein comprise at least two structurally different monomers, and although the copolymers may consist of only two structurally different monomers, they do not necessarily consist of only two structurally different monomers and may include additional monomers or functional or modifying materials.

"% w/w." means percentage by weight.

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

“g/cm3” also written “g/cc” means grams per cubic centimeter.

Achievements

As depicted in FIG. 1, a multilayer film 100 may comprise a first skin layer 102, a second skin layer 104, and a core 106. The core 106 may be positioned between the first skin layer 102 and the second skin layer 104. The core 106 may comprise a first core layer 108, a second core layer 110, and a third core layer 112.

Second core layer

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

The second core layer 110 may comprise an ethylene-acrylate copolymer (such as ethylene/butyl acrylate copolymer, ethylene/ethyl acrylate copolymer, ethylene/methyl acrylate copolymer, and/or ethylene/vinyl acetate copolymer). The ethylene-acrylate copolymer may comprise residues of an acrylate monomer, such as a C<2>-C-<6> acrylate monomer or a C<2> to C<5> monomer. In embodiments, the ethylene-acrylate copolymer may comprise 1% w/w to 49% w/w, such as 5% w/w to 49% w/w, 10% w/w to 49% w/w, 20% w/w to 49% w/w, 30% w/w. at 49% w/w, from 40% w/w to 49% w/w, from 1% w/w to 40% w/w, from 1% w/w to 30% w/w, from 1% w/w to 20% w/w, from 1% w/w to 10% w/w, from 10% w/w to 40% w/w, from 20% w/w to 30% w/w, from 15% w/w to 30% w/w, or any subset thereof of the acrylate monomer, based on the total polymer weight of the ethylene-acrylate copolymer. It should be understood that at least 80% w/w, at least 90% w/w, at least 99% w/w, or even at least 99.9% w/w of the ethylene-acrylate copolymer may comprise the combination of ethylene residues and acrylate residues, based on the total polymer weight of the ethylene-acrylate copolymer. Suitable ethylene-acrylate copolymers may include the ELVALOY™ line of polymers, available from Dow Inc., Midland, MI.

The ethylene-acrylate copolymer can have a melt index (I<2>) of 0.5 g/10 min to 8 g/10 min. In embodiments, the ethylene-acrylate copolymer can have a melt index (I<2>) of from 0.5 g/10 min to 8 g/10 min, from 0.5 g/10 min to 6 g/10 min, from 0.5 g/10 min to 4 g/10 min, from 0.5 g/10 min to 2 g/10 min, from 1 g/10 min to 10 g/10 min, from 2 g/10 min to 10 g/10 min, from 4 g/10 min to 10 g/10 min, from 6 g/10 min to 10 g/10 min, from 8 g/10 min to 10 g/10 min, from 2 g/10 min to 8 g/10 min, from 4 g/10 min to 6 g/10 min, or any subset thereof.

The second core layer 110 may comprise an ethylene-propylene copolymer. The ethylene-propylene copolymer may comprise residues of a propylene monomer. In embodiments, the ethylene-propylene copolymer may comprise 1% w/w to 49% w/w, such as 5% w/w to 49% w/w, 10% w/w to 49% w/w, 20% w/w to 49% w/w, 30% w/w to 49% w/w, 40% w/w to 49% w/w, 1% w/w to 40% w/w, 1% w/w to 30% w/w, 1% w/w to 20% w/w, 1% w/w. at 10% w/w, 10% w/w to 40% w/w, 20% w/w to 30% w/w, or any subset thereof of the propylene monomer, based on the total polymer weight of the ethylene-propylene copolymer. In embodiments, the ethylene-propylene copolymer may comprise from 60% w/w to 95% w/w of the ethylene monomer and from 5% w/w to 40% w/w of the propylene comonomer, based on the total polymer weight of the ethylene-propylene copolymer. It should be understood that at least 80% w/w, at least 90% w/w, at least 99% w/w, or even at least 99% w/w. The ethylene-propylene copolymer may comprise the combination of ethylene residues and propylene residues, based on the total polymer weight of the ethylene-propylene copolymer. Suitable ethylene-propylene copolymers may include the experimental resin XUS 39003.00, available from Dow Inc., Midland, MI. Additional suitable ethylene-propylene copolymers are described in PCT/US23/061210, which is incorporated by reference herein. Comonomer content may be measured using any suitable technique, such as techniques based on nuclear magnetic resonance ("NMR") spectroscopy, and, for example, by C NMR analysis as described in U.S. Pat.

7,498,282, which is incorporated herein by reference.

In some embodiments, the ethylene-propylene copolymer may have a density in the range of 0.865 to 0.920 g/cc. All individual values and subranges of 0.865 to 0.920 g/cc are described and included herein. For example, the ethylene-propylene copolymer may have a density in the range of 0.870 to 0.920 g/cc, 0.880 to 0.910 g/cc, 0.895 to 0.905 g/cc, or 0.895 to 0.910 g/cc. In some embodiments, the ethylene-propylene copolymer may have a melt index (I<2>) of at least 0.5 g/10 min. All individual values and subranges of at least 0.5 g/10 min are described and included herein. For example, the ethylene-propylene copolymer may have a melt index (I<2>) of at least 0.5 g/10 min, at least 0.6 g/10 min, at least 0.7 g/10 min, at least 0.8 g/10 min, at least 0.9 g/10 min, or at least 1.0 g/10 min, or it may have a melt index (I2) in the range of 0.5 g/10 min to 500 g/10 min, 0.5 g/10 min to 200 g/10 min, 0.5 g/10 min to 100 g/10 min, 0.5 g/10 min to 50 g/10 min, 0.5 g/10 min to 10 g/10 min, or 0.5 g/10 min to 8 g/10 min.

In some embodiments, the ethylene-propylene copolymer may have a single peak in an Improved Comonomer Composition Distribution (ICCD) elution profile between a temperature range of 40 °C to 100 °C. The improved comonomer composition distribution (ICCD) profile of the ethylene-propylene copolymer may be obtained by the test method described below.

In some embodiments, the ethylene-propylene copolymer may have a molecular weight distribution (Mw/Mn) in the range of 1.5 to 5.0. Any individual values and subranges from 1.5 to 5.0 are described and included herein. For example, the ethylene-propylene copolymer may have a molecular weight distribution (Mw/Mn) in the range of 1.5 to 5.0, 1.6 to 5.0, 1.8 to 5.0, 2.0 to 5.0, 1.5 to 4.0, 1.6 to 4.0, 1.8 to 4.0, 2.0 to 4.0, 1.5 to 3.0, 1.8 to 3.0, 2.0 to 3.0, 1.5 to 2.5, 1.8 to 2.5, or 2.0 to 2.5. The molecular weight distribution (Mw/Mn) may be measured according to the GPC test method described below. In some embodiments, the ethylene-propylene copolymer may be further characterized by having a melt flow ratio (I<10>/I<2>) of from 5 to 14. All individual values and subranges from 5 to 14 are described and included herein. For example, the ethylene-propylene copolymer may have a melt flow ratio (I<10>/I<2>) of from 5 to 14, from 6 to 12, from 6 to 10, or from 5 to 10.

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

The ethylene-based copolymer may be an ethylene/vinyl acetate (EVA) copolymer. The EVA copolymer may comprise 9 to 28% w/w vinyl acetate comonomer, based on the total polymer weight of the ethylene/vinyl acetate copolymer. All individual values and subranges from 9 to 28% w/w are described and included herein. In embodiments, the ethylene/vinyl acetate copolymer may comprise 10 to 25% w/w, 12 to 23% w/w, or 15 to 20% w/w vinyl acetate comonomer, based on the total weight of the ethylene/vinyl acetate copolymer. Examples of suitable commercially available ethylene/vinyl acetate copolymers include polymers under the name ELVAX™, available from Dow Inc., Midland, MI.

The second core layer 110 may further comprise a filler, such as calcium carbonate (CaCO<3>). From 20 to 80% w/w calcium carbonate (CaCO<3>). Without intending to be limited by theory, it has been found that a synergy exists between calcium carbonate fillers and ethylene-acrylate copolymers resulting in improved mechanical properties. However, a variety of fillers (including CaCO<3>) may optionally be used with both ethylene acrylate copolymers and ethylene-propylene copolymers to provide color and reduce cost. In embodiments, the second core layer 110 may comprise from 0% w/w to 80% w/w, such as from 10% w/w to 80% w/w, from 20% w/w to 80% w/w, from 40% w/w to 80% w/w. at 80% w/w, from 0% w/w to 60% w/w, from 0% w/w to 40% w/w, from 0% w/w to 20% w/w, from 10% w/w to 70% w/w, from 20% w/w to 60% w/w, from 30% w/w to 70% w/w, or any subset thereof of the fillings, based on the total weight of the second core layer 110.

As depicted in FIG. 1, the second core layer 110 may be positioned within the core 106 between the first core layer 108 and the third core layer 112. As such, the second core layer 110 may be the core layer of the multilayer film 100, the core layer of the core 106, or both. Alternative embodiments are envisioned where the second core layer is not the core layer of the multilayer film and the core, so long as the second core layer is positioned between the first skin layer and the second skin layer. Without being limited by theory, it is believed that while the second core layer will improve mechanical strength in any inner layer between the first skin layer and the second skin layer, there will be a significant improvement in performance when the second core layer 110 is the core layer. The core layer may be the layer that includes the 50% point within the multilayer film 100.

First, third, fourth and fifth core layers

Still referring to FIG. 1, the core 106 may comprise a first core layer 108 and a third core layer 112. The first core layer 108 may be positioned between the first cladding layer 102 and the second core layer 110. The third core layer 112 may be positioned between the second core layer 110 and the second cladding layer. Referring now to FIG.

2, a multilayer film 200 may comprise a first skin layer 202, a second skin layer 204, and a core 206. The core 206 may be positioned between the first skin layer 202 and the second skin layer 204. The core 206 may comprise a first core layer 208, a third core layer 212, and a second core layer 210. The core 206 may further comprise a fourth core layer 214 and a fifth core layer 216.

The core layers 206 may be arranged in any order. In embodiments, the fourth core layer 214 may be positioned between the first skin layer 202 and the first core layer 208. In embodiments, the fifth core layer 216 may be positioned between the second skin layer 204 and the third core layer 212. In embodiments, the second core layer 210 may be positioned between the first core layer 208 and the third core layer 212. Accordingly, the second core layer 210 may be the core layer. As previously mentioned, it is believed that while the second core layer will add performance to any inner layers between the first skin layer and the second skin layer, there will be a significant improvement in performance when the second core layer is the core layer.

Referring now to FIG. 1 and FIG. 2, the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and the fifth core layer 216 can each independently comprise HDPE, LLDPE, or combinations thereof. In embodiments, the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and the fifth core layer 216 can each independently comprise at least 70% w/w, such as at least 80% w/w, at least 90% w/w, at least 99% w/w, or even at least 99.9% w/w of HDPE, LLDPE, or combinations thereof, based on the total polymer weight of the layer.

At least one of the core layers 106, 206 may comprise high-density polyethylene (HDPE). In embodiments, at least two of the core layers 106, 206 may comprise HDPE. In embodiments, at least one layer comprising HDPE may be disposed on each side of the second core layer.

In embodiments, the multilayer film 100, 200 may comprise at least 30% w/w of the HDPE, based on the total weight of the multilayer film 100, 200. Use of a minimum percentage of HDPE may help meet density and flow requirements. In embodiments, the multilayer film 100, 200 may comprise at least 35% w/w, at least 40% w/w, at least 45% w/w, 30% w/w to 45% w/w, 35% w/w to 45% w/w, 40% w/w to 45% w/w, 35% w/w to 40% w/w, or any subset thereof of HDPE, based on the total weight of the multilayer film 100, 200.

In embodiments where the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and/or the fifth core layer 216 comprise HDPE, the HDPE may have a density greater than 0.940 g/cc, such as greater than 0.945 g/cc, greater than 0.950 g/cc, greater than 0.955 g/cc, greater than 0.960 g/cc, from 0.940 g/cc to 0.965 g/cc, from 0.940 g/cc to 0.960 g/cc, from 0.940 g/cc to 0.955 g/cc, 0.945 g/cc to 0.965 g/cc, or any subset thereof. Without being limited by theory, it is believed that increasing the density of HDPE results in better creep resistance properties.

In embodiments where the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and/or the fifth core layer 216 comprise an HDPE, the HDPE may have a melt index (I<2>) in the range of 0.1 g/10 min to 1.5 g/10 min. All individual values and subranges from 0.1 g/10 min to 1.5 g/10 min are described and included herein. For example, HDPE may have a melt index (I2) in the range of 0.1 g/10 min to 1.3 g/10 min, 0.1 g/10 min to 1.1 g/10 min, 0.1 g/10 min to 0.9 g/10 min, 0.1 g/10 min to 0.7 g/10 min, 0.1 g/10 min to 0.5 g/10 min, 0.3 g/10 min to 1.5 g/10 min, 0.5 g/10 min to 1.5 g/10 min, 0.7 g/10 min to 1.5 g/10 min, 0.9 g/10 min to 1.5 g/10 min, 0.3 g/10 min to 1.3 g/10 min, 0.5 g/10 min to 1.1 g/10 min, or any subset thereof.

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

In embodiments where the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and/or the fifth core layer 216 comprise an LLDPE, the LLDPE may have a density less than or equal to 0.930 g/cm3. All individual values and subranges less than or equal to 0.930 g/cm3 are included and described herein; for example, the density of the linear low density polyethylene may be from a lower limit of 0.870 g/cm3 to an upper limit of 0.928, 0.925, 0.920, or 0.915 g/cm3. All individual values and subranges between 0.870 and 0.930 g/cm3 are included and described herein.

In embodiments where the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214, and/or the fifth core layer 216 comprises an LLDPE, the LLDPE may have a melt index (I2) in the range of 0.1 g/10 min to 1.5 g/10 min. All individual values and subranges of 0.1 g/10 min to 1.5 g/10 min are described and included herein. For example, the LLDPE may have a melt index (I<2>) in the range of 0.1 g/10 min to 1.3 g/10 min, 0.1 g/10 min to 1.1 g/10 min, 0.1 g/10 min to 0.9 g/10 min, 0.1 g/10 min to 0.7 g/10 min, 0.3 g/10 min to 1.5 g/10 min, 0.5 g/10 min to 1.5 g/10 min, 0.7 g/10 min to 1.5 g/10 min, 0.3 g/10 min to 1.3 g/10 min, 0.5 g/10 min to 1.1 g/10 min, or any subset thereof.

Commercially available examples of LLDPE that can be used in the first core layer 108, 208, the third core layer 112, 212, the fourth core layer 214 and/or the fifth core layer 216 include those commercially available from Dow Inc. under the name ELITE™ including, for example, ELITE™ 5400.

Coating layers

The first skin layer 102, 202 and the second skin layer 104, 204 may independently comprise a linear low density polyethylene (hereinafter “LLDPE”). In embodiments, the multilayer film 200 may comprise at least 50% w/w, such as at least 60% w/w, at least 70% w/w, at least 80% w/w, at least 90% w/w, or even at least 99% w/w LLDPE, based on the total polymer weight of the layer.

In embodiments where the first skin layer 102, 202 and/or the second skin layer 104, 204 comprise an LLDPE, the LLDPE may have a density less than or equal to 0.940 g/cm3. All individual values and subranges less than or equal to 0.940 g/cm3 are included and described herein; for example, the density of the LLDPE may be from a lower limit of 0.870 g/cm3, 0.880 g/cm3, 0.890 g/cm3, 0.910 g/cm3, 0.920 g/cm3 to an upper limit of 0.940 g/cm3, 0.938 g/cm3, 0.936 g/cm3, or 0.935 g/cm3. All individual values and subranges between 0.870 g/cm3 and 0.940 g/cm3 are included and described in this specification.

In embodiments where the first skin layer 102, 202 and/or the second skin layer 104, 204 comprise an LLDPE, the LLDPE may have a melt index (I<2>) in the range of 0.1 g/10 min to 50 g/10 min. All individual values and subranges from 0.1 g/10 min to 50 g/10 min are described and included herein. For example, the LLDPE may have a melt index (I<2>) 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.

Commercially available examples of LLDPE that can be used in Multilayer Film 200 and/or Multilayer Film 200 include those commercially available from Dow Inc., under the name ELITE™ and under the name DOWLEX™.

In some embodiments, the first skin layer 102, 202 and/or the second skin layer 104, 204 may comprise a fourth low density layer (LDPE). It should be understood that the first skin layer 102, 202 and the second skin layer 104, 204 may comprise LDPE in addition to LLDPE. In embodiments where the multilayer film 200 and/or the multilayer film 200 comprise an LDPE, the LDPE may have a density in the range 0.916 g/cm3 to 0.935 g/cm3. All individual values and subranges of 0.916 g/cm3 to 0.935 g/cm3 are included and described herein; For example, the density of LDPE can be from a lower limit of 0.916 g/cm3, 0.918 g/cm3, 0.920 g/cm3, or 0.922 g/cm3 to an upper limit of 0.935 g/cm3, 0.933 g/cm3, 0.931 g/cm3 or 0.929 g/cm3.

In embodiments where the first skin layer 102, 202 and/or the second skin layer 104, 204 comprise an LDPE, the LDPE may have a melt index (I<2>) in the range of 0.1 g/10 min to 50 g/10 min. All individual values and subranges from 0.1 g/10 min to 50 g/10 min are described and included herein. For example, the LDPE may have a melt index (I<2>) 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.

In some embodiments the first skin layer 102, 202 and/or the second skin layer 104, 204 may independently comprise from 0% w/w to 30% w/w of the LDPE, based on the total weight of the respective layer. All individual values of 0% w/w to 30% w/w are described and included herein. For example, the multilayer film 200 and/or the multilayer film 200 may comprise from 0% w/w to 25% w/w, from 0% w/w to 20% w/w, from 0% w/w to 10% w/w, from 0% w/w to 5% w/w, from 5% w/w to 30% w/w, from 5% w/w to 30% w/w, from 5% w/w to 40% w/w, from 5% w/w to 50% w/w, from 5% w/w to 60% w/w, from 60% w/w to 70% w/w, from 70% w/w to 80% w/w, from 80% w/w to 90% w/w, from 90% w/w to 10 ... at 20% w/w, or any subset thereof, based on the total polymer weight of the respective layer.

Commercially available examples of LDPE that can be used in Multilayer Film 200 and/or Multilayer Film 200 include those commercially available from Dow Inc. under the name AGILITY™.

Multilayer film

The multilayer film 100, 200 may have a thickness of less than 180 gm. As previously described, it is desired to create multilayer films, which can meet the required mechanical properties while minimizing the film thickness. In embodiments, the multilayer film 100, 200 may have a thickness of less than 160 gm, less than 140 gm, less than 120 gm, less than 100 gm, less than 90 gm, 70 gm to 180 gm, 70 gm to 150 gm, 70 gm to 125 gm, 70 gm to 115 gm, 70 gm to 105 gm, 70 gm to 100 gm, 70 gm to 95 gm, 70 gm to 90 gm, 80 gm to 180 gm, 80 gm to 150 gm, 80 gm to 125 gm, 80 gm to 115 gm, 80 gm to 105 gm, 80 gm to 100 gm, 80 gm to 95 gm, 80 gm to 90 gm, 80 gm to 180 gm, 80 gm to 150 gm, 80 gm to 125 gm, 80 gm to 115 gm, 80 gm to 105 ... gm, 80 gm to 100 gm, 80 gm to 90 gm, 90 gm to 180 gm, 90 gm to 150 gm, 90 gm to 115 gm, 90 gm to 105 gm, 90 gm to 100 gm, or any subset thereof.

Still referring to FIG. 1 and FIG. 2, the first coating layer 102, 202 and/or the second coating layer 104, 204 can independently have a thickness of 10% to 30% of a thickness of the multilayer film 100, 200. In embodiments, the first coating layer 102, 202 and/or the second coating layer 104, 204 can independently have a thickness of 10% to 25%, 10% to 20%, 10% to 15%, 15% to 30%, 20% to 30%, 15% to 25%, or any subset thereof of a thickness of the multilayer film 100, 200.

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

The second core layer 110, 210 may have a thickness of less than 15% of a thickness of the multilayer film 100, 200. Without being limited by theory, it is believed that the performance of the multilayer film 100, 200 may be optimized when the second core layer 110, 210 is as thin as possible. However, due to manufacturing challenges and variability in layer thickness, it may not be possible to create a second core layer of less than 3% of the thickness of the multilayer film 110, 210. In embodiments, the second core layer 110, 210 may have a thickness of less than or equal to 10%, less than or equal to 5%, 3% to 20%, 3% to 15%, 3% to 10%, 3% to 7%, 3% to 5%, 1% to 20%, 5% to 20%, or any subset thereof of the thickness of the multilayer film 100, 200. In embodiments, the second core layer 110, 210 may have a thickness of 3% to 7% of a thickness of the multilayer film 100, 200.

Referring now to FIG. 2, the fourth core layer 214 and the fifth core layer 216 may independently have a thickness of 3% to 45%, 3% to 40%, 3% to 35%, 3% to 30%, 3% to 25%, 3% to 20%, 3% to 15%, 3% to 10%, 5% to 45%, 10% to 45%, 15% to 45%, 20% to 45%, 30% to 45%, 5% to 40%, 10% to 35%, 15% to 30%, or any subset thereof of a thickness of the multilayer film 100, 200. Referring again to FIG. 1 and FIG. 2, the multilayer film 100, 200 may have a density of 0.929 g/cc to 0.942 g/cc. In embodiments, the multilayer film 100, 200 may have a density of 0.929 g/cc to 0.940 g/cc, 0.929 g/cc to 0.935 g/cc, 0.930 g/cc to 0.942 g/cc, 0.935 g/cc to 0.942 g/cc, 0.930 g/cc to 0.940 g/cc, 0.932 g/cc to 0.938 g/cc, or any subset thereof.

The multilayer film 100, 200 may have a normalized Type A Dart Drop Impact of at least 4.0 g/μm. In embodiments, the multilayer film 100, 200 may have a Type A Dart Drop Impact of at least 4.4 g/μm, at least 4.6 g/μm, at least 4.8 g/μm, at least 5.0 g/μm, from 4.0 g/μm to 6.0 g/μm, from 4.2 g/μm to 6.0 g/μm, from 4.4 g/μm to 6.0 g/μm, or any subset thereof.

The multilayer film 100, 200 may have a Type A Dart Drop Impact of at least 400 g/μm, such as at least 425 g/μm, at least 450 g/μm, at least 500 g/μm, at least 600 g/μm, or any subset thereof.

The multilayer film 100, 200 may have a normalized Elmendorf Cross Direction Tear Strength of at least 16.6 gf/μm. In embodiments, the multilayer film 100, 200 may have a Elmendorf Cross Direction Tear Strength of at least 16.8 gf/μm, at least 17.0 gf/μm, at least 17.2 gf/μm, at least 17.4 gf/μm, at least 17.6 gf/μm, at least 17.8 gf/μm, at least 18.0 gf/μm, from 16.6 gf/μm to 20 gf/μm, or any subset thereof.

The multilayer film 100, 200 may have an Elmendorf Cross Direction Tear Strength of at least 1500 grams force (gf). In embodiments, the multilayer film 100, 200 may have an Elmendorf Cross Direction Tear Strength of at least 1600 gf, at least 1700 gf, at least 1800 gf, at least 1900 gf, at least 2000 gf, from 1500 gf to 3000 gf, from 1600 gf to 3000 gf, from 1700 gf to 3000 gf, from 1800 gf to 3000 gf, from 1900 gf to 3000 gf, from 2000 gf to 3000 gf, or any subset thereof.

The multilayer film 100, 200 may have a normalized Elmendorf Machine Direction Tear Strength of at least 8.8 gf/gm. In embodiments, the multilayer film 100, 200 may have an Elmendorf Machine Direction Tear Strength of at least 9.0 gf/gm, at least 9.2 gf/gm, at least 9.4 gf/gm, at least 9.6 gf/gm, at least 9.8 gf/gm, at least 10.0 gf/gm, from 8.8 gf/gm to 12 gf/gm, from 9.0 gf/gm to 12 gf/gm, from 9.2 gf/gm to 12 gf/gm, from 9.4 gf/gm to 12 gf/gm, or any subset thereof.

The multilayer film 100, 200 may have an Elmendorf Machine Direction Tear Strength of at least 800 gf, such as at least 825 gf, at least 850 gf, at least 900 gf, at least 1000 gf, at least 1100 gf, from 800 gf to 1500 gf, from 850 gf to 1500 gf, from 900 gf to 1500 gf, from 1000 gf to 1500 gf, or any subset thereof.

The multilayer film 100, 200 may have a high performance creep of less than 50%. In embodiments, the multilayer film 100, 200 may have a high performance creep of less than 45%, less than 40%, less than 35%, less than 30%, less than 25%, less than 20%, less than 15%, less than 10%, less than 5%, 1% to 50%, 1% to 40%, 1% to 30%, 1% to 25%, or any subset thereof.

It should be understood that the multilayer film 100 may comprise 5 or more layers. In embodiments, the multilayer film 100 may comprise more than 5 layers, such as 7, 9, or 11 layers.

Multilayer films 100 described herein can be produced using techniques known to those skilled in the art based on the teachings herein. For example, the multilayer film can be produced by film lamination and/or coextrusion. The formation of coextruded multilayer films 100 is known in the art and is applicable to the present disclosure. Coextrusion systems for making multilayer films 100 employ at least two extruders feeding a common die assembly. The number of extruders depends on the number of different materials or polymers. For example, a five-layer coextrusion may require up to five extruders although fewer may be used if two or more of the layers are made from the same materials or polymers.

In some embodiments, the multilayer film is a machine direction oriented film. In other embodiments, the multilayer film is a cast stretch film. In additional embodiments, the multilayer is a stretch hood film.

Additives

It is to be understood that any of the above layers may further comprise one or more additives known to those skilled in the art such as, for example, antioxidants, ultraviolet light stabilizers, thermal stabilizers, slip agents, anti-blocking agents, anti-static agents, pigments or dyes, processing aids, cross-linking catalysts, flame retardants, fillers and foaming agents. The layer may contain any amount of such additives, such as 0% w/w to 10% w/w, 0% w/w to 5% w/w, 0% w/w to 1% w/w, 0% w/w to 0.1% w/w, 0% w/w to 0.001% w/w, or any subset thereof, based on a weight of the layer.

Articles

Embodiments of the present disclosure also provide articles that include any of the inventive multilayer films described herein. Examples of such articles may include wrappers, packages, flexible packages, pouches, and sachets. Articles of the present disclosure may be formed from the multilayer films described herein using techniques known to those skilled in the art in view of the teachings herein. Articles of the present disclosure may include a heavy duty shipping bag comprising one or more multilayer films 100, 200.

Test methods

Density

Density is measured according to ASTM D792, and is expressed in grams/cm3 (g/cm3).

Melt indices (I2, I10, and I21)

Melt index (I<2>) is measured according to ASTM D 1238-10 at 190 Celsius and 2.16 kg, Method B, and is expressed in grams eluate/10 minutes (g/10 min).

Melt index (I<10>) is measured according to ASTM D 1238-10 at 190 Celsius and 10 kg, Method B, and is expressed in grams eluted/10 minutes (g/10 min).

Melt index (I<21>) is measured according to ASTM D 1238-10 at 190 Celsius and 21.6 kg, Method B, and is expressed in grams eluted/10 minutes (g/10 min).

Improved Comonomer Composition Distribution (ICCD)

In 2015, an improved method for comonomer content analysis (iCCD) was developed (Cong and Parrott et al., WO2017040127A1). The iCCD test was performed with Crystallization Elution Fractionation (CEF) instrumentation (PolimerChar, Spain) equipped with IR-5 detector (PolimerChar, Spain) and a dual-angle light scattering detector Model 2040 (Precision Detectors, now Agilent Technologies). A guard column packed with 20-27 micron glass (MoSCi Corporation, USA) in a 5 cm or 10 cm X1/4” (ID) stainless steel was installed just before the IR-5 detector in the detector oven. Ortho-dichlorobenzene (ODCB, 99% anhydrous grade or technical grade) was used. Silica gel 40 (particle size 0.2~0.5 mm, cat. no. 10181-3) was obtained from EMD Chemicals (can be used to dry ODCB solvent before). The dried silica was packed into three HT-GPC emptied columns to further purify ODCB as eluent. The CEF instrument is equipped with an autosampler with N<2> purge capability. ODCB is sparged with dry nitrogen (N<2>) for one hour before use. Sample preparation was performed with autosampler at 4 mg/mL (unless otherwise specified) with shaking at 160 °C for 1 hour. The injection volume was 300 μl. The iCCD temperature profile was: crystallization at 3 °C/min from 105 °C to 30 °C, thermal equilibration at 30 °C for 2 minutes (including Soluble Fraction Elution Time set to 2 minutes), elution at 3 °C/min from 30 °C to 140 °C. The flow rate during crystallization is 0.0 mL/min. The flow rate during elution is 0.50 mL/min. Data were collected at one data point/second.

The iCCD column was packed with gold-coated nickel particles (Bright7GNM8-NiS, Nippon Chemical Industrial Co.) in a 15 cm (length) X 1/4” (ID) stainless steel tube. Column packing and conditioning was with a slurry method according to reference (Cong, R.; Parrott, A.N.; Hollis, C.; Cheatham, M. WO2017040127A1). The final pressure with TCB slurry packing was 150 Bar.

Column temperature calibration was performed using a mixture of the Linear Homopolymer Polyethylene Reference Material (zero comonomer content, Melt Index (I<2>) of 1.0, Mw/Mn polydispersity approximately 2.6 by conventional ge permeation chromatography, 1.0 mg/ml) and Eicosane (2 mg/ml) in ODCB. The iCCD temperature calibration consisted of four steps: (1) Calculate the delay volume defined as the temperature offset between the measured peak elution temperature of Eicosane minus 30.00 °C; (2) subtract the temperature offset from the elution temperature of the raw iCCD temperature data. It should be noted that this temperature offset is a function of experimental conditions, such as elution temperature, elution flow rate, etc.; (3) Create a linear calibration line that transforms the elution temperature into a range of 30.00 °C and 140.00 °C such that the linear homopolymer polyethylene reference had a peak temperature at 101.0 °C, and Eicosane had a peak temperature of 30.0 °C; (4) For the soluble fraction measured isothermally at 30°C, the elution temperature below 30.0 °C is linearly extrapolated using the elution heating rate of 3°C/min according to the reference (Cerk and Cong et al., US9,688,795).

The comonomer content versus iCCD elution temperature was constructed using 12 reference materials (ethylene homopolymer and ethylene-octene random copolymer made with one-site metallocene catalyst, having ethylene equivalent weight average molecular weight ranging from 35,000 to 128,000). All of these reference materials were analyzed in the same manner as previously specified at 4 mg/mL. The reported elution temperature peaks followed the figure of octene mol % versus iCCD elution temperature at R2 of 0.978.

The polymer molecular weight and molecular weight of polymer fractions were determined directly from the LS detector (90 degree angle) and the concentration detector (IR-5) according to Rayleigh-Gans-Debys approximation (Striegel and Yau, Modern Size Exclusion Liquid Chromatograms, page 242 and page 263) assuming a shape factor of 1 and all virial coefficients equal to zero. Integration windows are set to integrate all chromatograms at the elution temperature (temperature calibration is specified above) ranging from 23.0 to 120 °C. The iCCD Molecular Weight (Mw) calculation includes the following steps: (1) Measure the interdetector drift. The drift is defined as the geometric volume deviation between LS with respect to the concentration detector. It is calculated as the difference in elution volume (mL) of polymer peak between concentration detector and LS chromatograms. It is converted to temperature deviation using thermal elution rate and elution flow rate. A linear high-density polyethylene (having zero comonomer content, Melt index (I<2>) of 1.0, polydispersity Mw/Mn about 2.6 by conventional gel permeation chromatography) is used. The same experimental conditions as the normal iCCD method above are used except the following parameters: crystallization at 10 °C/min from 140 °C to 137 °C, thermal equilibration at 137 °C for 1 minute as Soluble Fraction Elution Time, soluble fraction (SF) time of 7 minutes, elution at 3 °C/min from 137 °C to 142 °C. The flow rate during crystallization is 0.0 mL/min. The flow rate during elution is 0.80 mL/min. The sample concentration is 1.0 mg/ml. (2) Each LS data point in the LS chromatogram is shifted to correct for interdetector drift prior to integration. (3) The baseline-subtracted LS and concentration chromatograms are integrated over the elution temperature range from Step (1). The detector MW constant is calculated using a known MW HDPE sample in the range of 100,000 to 140,000Mw and the area ratio of the LS and integrated concentration signals. (4) The Mw of the polymer is calculated using the ratio of the integrated light scattering detector (90 degree angle) to the concentration detector and using the detector MW constant.

Conventional GPC (Mw, Mn, Mw/Mn)

The chromatographic system consisted of a high temperature GPC chromatograph GPC-IR from PolimerChar (Valencia, Spain) equipped with an internal IR5 infrared detector (IR5) coupled to a 2-angle laser light scattering (LS) detector Model 2040 from Precision Detectors (now Agilent Technologies). For all light scattering measurements, the 15 degree angle was used for measurement. The oven compartment of the autosampler was set to 160° Celsius and the column compartment was set to 150° Celsius. The columns used were 4 x 20 micron “Mixed A” 30 cm linear mixed bed columns from Agilent. The chromatographic solvent used was 1,2,4-trichlorobenzene containing 200 pμm butylated hydroxytoluene (BHT). The solvent source was splashed nitrogen. The injection volume used was 200 microliters and the flow rate was 1.0 milliliter/minute. Calibration of the GPC column set was performed with 21 narrow molecular weight distribution polystyrene standards with molecular weights ranging from 580 to 8,400,000 and arranged in 6 “cocktail” mixtures with at least a decade separation between individual molecular weights. Standards were purchased from Agilent Technologies. Polystyrene standards were prepared at 0.025 grams in 50 milliliters of solvent for molecular weights equal to or greater than 1,000,000, and 0.05 grams in 50 milliliters of solvent for molecular weights less than 1,000,000. Polystyrene standards were dissolved at 80 degrees Celsius with gentle shaking for 30 minutes. Standard peak molecular weights of polystyrene were converted to polyethylene molecular weights using Equation 1 (as described in Williams Ward, J. Polym. Sci., Polym. Let., 6, 621 (1968)).:

where M is the molecular weight, A has a value of 0.4315 and B equals 1.0

A fifth order polynomial was used to fit the respective polyethylene equivalent calibration points. A small adjustment to A (from approximately 0.415 to 0.44) was made to correct for column resolution and band broadening effects so that NIST standard NBS 1475 is obtained at 52,000 Mw.

Total plate count on the established GPC column was performed with Eicosane (prepared at 0.04 g in 50 milliliters of TCB and dissolved for 20 minutes with gentle shaking.) Plate count (Equation 2) and symmetry (Equation 3) were measured in a 200 microliter injection according to the following equations:

where RV is the retention volume in millimeters, peak width is in millimeters, peak max is the maximum peak height, and /height is <1/2>peak maximum height.

where RV is the retention volume in millimeters and peak width is in millimeters, Peak max is the maximum peak position, one-tenth of peak height is 1/10 of the peak maximum height, and where, Peak trailing refers to the peak tail at retention volumes later than Peak max and where Peak leading refers to the peak leading at retention volumes earlier than Peak max. The plate count for the chromatographic system should be greater than 24,000 and the symmetry should be between 0.98 and 1.22.

Samples were prepared semi-automatically using PolimerChar’s Instrument Control Software, where samples had a target weight of 2 mg/ml, and solvent (containing 200 ppm BHT) was added to a stoppered septa vial previously sparged with nitrogen, by means of PolimerChar’s high temperature autosampler. Samples were dissolved for 2 hours at 160° Celsius with “low speed” stirring.

Calculations of Mn(GPC), M<w>(<gpc>), and M<z>(<gpc>) were based on GPC results using the internal IR5 detector (measurement channel) of the PolimerChar GPC-IR chromatograph according to Equations 4-6, using PolimerChar's GPCone™ software, the baseline-subtracted IR chromatogram at each equally spaced data collection point (i), and the polyethylene equivalent molecular weight obtained from the standard calibration curve for point (i) of Equation 1.

In order to monitor drifts over time, a flow marker (decane) was introduced into each sample via a micropump controlled with the PolimerChar GPC-IR system. This flow marker (FM) was used to linearly correct the pump flow rate (flow rate (nominal)) for each sample by RV alignment of the respective decane peak within the sample (RV(Sample FM)) to that of the decane peak within the narrow standard calibration (RV(FM Calibrated)). The changes over time of the decane marker peak are then assumed to be related to a linear shift in flow rate (flow rate (effective)) throughout the run. To facilitate the highest accuracy of an RV measurement of the flow marker peak, a least squares fitting routine is used to fit the peak of the flow marker concentration chromatograms to a quadratic equation. The first derivative of the quadratic equation is then used to solve for the true peak position. After calibrating the system against a marker peak flow, the effective flow rate (relative to the narrow standard calibration) is calculated as Equation 7. The marker peak flow processing was performed using PolimerChar's GPCoNe™ Software. An acceptable flow correction is such that the effective flow rate is within ±2% of the nominal flow rate.

Flow rate (effective) = Flow rate (nominal) * (RV(calibrated FM) / RV(sample FM)) (EC7) The Systematic Approach for determining multi-detector offsets is done in a manner consistent with that published by Balke, Mourey, et. al. (Mourey and Balke, Chromatography Polym. Chpt 12, (1992)) (Balke, Thitiratsakul, Lew, Cheung, Mourey, Chromatography Polym. Chpt 13, (1992)), recording triple detector optimization (MW and IV) results of a broad homopolymer polyethylene standard (Mw/Mn > 3) to the narrow standard column calibration results from the narrow standard calibration curve using PolimerChar’s GPCOne™ Software.

Absolute molecular weight data were obtained in a manner consistent with those published by Zimm (Zimm, B.H., J. Chem. Phys., 16, 1099 (1948)) and Kratochvil (Kratochvil, P., Classical Light Scattering from Polymer Solutions, Elsevier, Oxford, NY (1987)) using PolimerChar's GPPCone™ software. The overall injected concentration used in the molecular weight determination was obtained from the mass detector area and the mass detector constant derived from a suitable linear polyethylene homopolymer or one of the polyethylene standards of known weight average molecular weight. Calculated molecular weights (using GPPCone™) were obtained using a light scattering constant derived from one or more of the polyethylene standards listed below and a refractive index concentration coefficient, dn/dc, of 0.104. Generally, the detector mass response (IR5) and the light scattering constant (determined using GPCoNe™) should be determined from a linear standard with an excess molecular weight of approximately 50,000 g/mol. Other respective moments, Mn(Abs) and Mz(Abs) are to be calculated according to the following equations 8-9:

DSC method - Heat of fusion

Differential scanning calorimetry is a common technique that can be used to examine the melting and crystallization of semicrystalline polymers. The general principles of DSC measurements and applications of DSC to study semicrystalline polymers are described in standard texts (e.g., E. A. Turi, ed., Thermal Characterization of Polymeric Materials, Academic Press, 1981).

The Heat of Fusion is determined using DSC from TA Instruments, Inc. The test is performed in reference to ASTM D3428. Calibration is accomplished by preparing 2-3 mg of indium and placing it in a T-zero aluminum pan. The pan is then loaded into the DSC instrument and subjected to the following heating program cycle: 1) equilibrate the test chamber at 180 °C, 2) hold the temperature at 180 °C for 1 min., 3) raise the temperature to 130 °C at 10 °C/min., 4) hold the temperature at 130 °C for 3 min., and 5) raise the temperature at 10 °C/min. to 180 °C. Once complete, the last heat curve performed in step 5 is analyzed to determine the melting temperature of the indium sample. The DSC is considered to be operating compliantly if the melting temperature is within a tolerance of 0.5°C of 156.6°C.

For sample testing, polymer samples are first pressed to a thin film at a temperature of 190 °C. Approximately 4 to 5 mg of sample is weighed and placed in the DSC pan. The lid is crimped onto the pan to ensure a closed atmosphere. The sample pan is placed in the DSC cell and equilibrated at 180 °C. The sample is held at this temperature for 5 min. The sample is then cooled at a rate of 10 °C/min to -90 °C and held isothermally at that temperature for 5 min. The sample is subsequently heated at a rate of 10 °C/min to 150 °C (to ensure complete melting); this stage is designated the 2nd heating curve. The resulting enthalpy curves are analyzed for peak melting temperature, onset and peak crystallization temperatures, and the heat of fusion (also known as heat of melting), AHf. The heat of fusion, in Joules/gram, is measured from the 2nd heating curve by performing a linear integration of the fusion endotherm along the baseline

Dart

The Dart Drop test follows ASTM D1709 Method A and provides a measure of the energy required to cause a plastic film to fail under specified conditions by impact of a freely falling dart. The test result is the energy, expressed in terms of the weight of the missile dropped a specified height, that would result in the failure of 50% of the specimens tested. The film sample is conditioned for at least 40 hours at 23°C (±2°C) and 50% R.H. (±10%) prior to testing which is performed at 23°C (±2°C) and 50% RH (±10%). For current film samples Method-A is used, which uses a 3.81 cm (1.5”) diameter dart head and 66 cm (26”) drop height. The dart head material of construction is aluminum. The specimen thickness is measured at the center of the specimen and the specimen is then clamped with a 12.7 cm (5”) inner diameter ring specimen holder. The dart is loaded above the center of the specimen and released by either a pneumatic or electromagnetic mechanism. The dart is loaded with an initial weight which is subsequently increased or decreased by a chosen weight depending on the pass/fail rate of each drop. Typically approximately 20-25 specimens are used for drop experiments. Finally, a staircase method per ASTM D1709 is employed to calculate the ‘Dart’ value based on the collected pass/fail data, initial weight, and weight increment.

Elmendorf tear resistance

Average Elmendorf tear strength is measured in machine direction (MD) and cross machine direction (CD) according to ASTM D1922.

High performance fluency

High performance flow is determined according to ISO 899.

ASPECTS

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

According to a second aspect, in conjunction with the first aspect, the second core layer may be positioned between the first core layer and the third core layer. According to a third aspect, in conjunction with the first or second aspects, the second core layer may further comprise calcium carbonate.

According to a fourth aspect, in conjunction with any of aspects 1-3, the multilayer film may comprise at least 30% w/w HDPE, based on the total polymer weight of the multilayer film.

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

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

According to a seventh aspect, in conjunction with any of aspects 1-6, the core may further comprise: a fourth core layer positioned between the first skin layer and the first core layer, and a fifth core layer positioned between the third core layer and the second skin layer. According to an eighth aspect, in conjunction with any of aspects 1-7, the fourth core layer and the fifth core layer may each independently comprise HDPE, LLDPE, or combinations thereof.

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

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

According to an eleventh aspect, in conjunction with any of aspects 1-10, the multilayer film may have a normalized Type A Dart Drop Impact of at least 4.4 g/μm.

According to a twelfth aspect, in conjunction with any of aspects 1-11, the multilayer film may have a normalized Elmendorf Cross Direction Tear Strength of at least 16.6 gf/μm.

According to a thirteenth aspect, in conjunction with any of aspects 1-12, the multilayer film may have a normalized Elmendorf Machine Direction Tear Strength of at least 8.8 gf/μm.

According to a fourteenth aspect, in conjunction with any of aspects 1-13, the multilayer film can have a high-performance creep of less than 50%. According to a fifteenth aspect, in conjunction with any of aspects 1-14, the second core layer may be the central layer, the second core layer may be positioned between the first core layer and the third core layer, the multilayer film may have a density of 0.929 g/cc to 0.942 g/cc, the first skin layer, the second skin layer, or both may further comprise low density polyethylene (LDPE), the second core layer may have a thickness less than or equal to 10% of a thickness of the multilayer film, the multilayer film may have a thickness less than or equal to 110 μm, the multilayer film may have a Type A Dart Drop Impact of at least 4.4 g/μm, the multilayer film may have an Elmendorf Cross Direction Tear Strength of at least 16.6 gf/μm, and the multilayer film may have an Elmendorf Machine Direction Tear Strength of at least 8.8 gf/μm.

EXAMPLES

The following examples are provided to illustrate embodiments described in this disclosure and are not intended to limit the scope of this disclosure or its appended claims.

Materials

INNATE™ ST50 (also referred to herein as “ST50”), a linear low density polyethylene having a density of 0.918 g/cm3 and melt index (I<2>) of 0.85 g/10 min and commercially available from Dow Inc., (Midland, MI). INNATE™ ST50 is an ethylene-based polymer as that term is defined herein.

INNATE™ ST70 (also referred to herein as “ST70”), a linear low density polyethylene having a density of 0.926 g/cm3 and melt index (I<2>) of 0.85 g/10 min and commercially available from Dow Inc., (Midland, MI). INNATE™ ST70 is an ethylene-based polymer as that term is defined herein.

INNATE™ ST100 (also referred to herein as “ST100”), a linear low density polyethylene having a density of 0.928 g/cm3 and melt index (I<2>) of 0.85 g/10 min and commercially available from Dow Inc., (Midland, MI). INNATE™ ST100 is an ethylene-based polymer as that term is defined herein. ELITE™ 5400, a linear low density polyethylene having a density of 0.916 g/cm3 and melt index (I<2>) of 1.0 g/10 min and commercially available from Dow Inc., (Midland, MI). ELITE™ 5400 is an ethylene-based polymer as that term is defined herein.

DOWLEX™ GM 8090 (also referred to herein as “GM 8090”) is a low-density polyethylene commercially available from Dow Inc. (Midland, MI). DOWLEX™ GM 8090 has a density of 0.916 g/cm3 and melt index (I<2>) of 1.0 g/10 min. DOWLEX™ GM 8090 is an ethylene-based polymer as that term is defined herein.

AGILITY™ EN 1604 is a low density polyethylene having a density of 0.921 g/cm3 and melt index (I<2>) of 0.25 g/10 min and is commercially available from Dow Inc., (Midland, MI). AGILITY™ EN 1604 is an ethylene-based polymer as that term is defined herein.

UNIVAL™ DMDA 6400 (also referred to herein as “DMDA 6400”) is a high density polyethylene having a density of 0.961 g/cm3, a melt flow index (I<2>) of 0.80 g/10 min, and a melt index (I<21>) of 57 g/10 min and is commercially available from Dow Inc., (Midland, MI). UNIVAL™ DMDA 6400 is an ethylene-based polymer as that term is defined herein.

ELVALOY™ AC 3117 (also referred to herein as “EA”) is an ethylene-acrylate copolymer (83% ethylene and 17% butyl acrylate) having a density of 0.924 g/cm3 and a melt index (I<2>) of 1.5 g/10 min and is commercially available from Dow Inc., (Midland, MI). ELVALOY™ AC 3117 is an ethylene-acrylate copolymer as that term is defined herein.

Some examples use a blend of ELVALOY™ AC 3117 and CaCO3 (also referred to herein as "EA+CaCO3"). The blend comprises approximately 42% w/w calcium carbonate, with the balance ethylene-acrylate copolymer, based on total layer weight.

XUS 39003.00 (also referred to herein as “EP”) is an ethylene-propylene copolymer commercially available from Dow Inc. (Midland, MI). EP comprises 27.1% w/w propylene comonomer and 72.9% w/w ethylene monomer and has a density of 0.867 g/cm3, a melt index (I<2>) of 0.90 g/10 min, an I<10>/I<2>of 10.82, a heat of fusion of 50.24 J/g, and a Mw/Mn of 3.98. EP has a ratio of reversely inserted propylene units on a 2, 1 insertion basis of 0.8% w/w, where the weight percent is based on the total weight of EP. EP is an ethylene-based polymer as that term is defined herein.

Some examples use a blend of XUS 39003.0 (“EP”) and Calcium Carbonate (also referred to herein as “EP+CaCO<3>”). The blend comprises approximately 42% w/w calcium carbonate, with the balance ethylene-propylene copolymer, based on total layer weight.

ELITE™ 5960G1 (also referred to herein as “5960”) is a high-density polyethylene (HDPE) commercially available from Dow Inc. (Midland, MI). 5960 has a melt index (I<2>) of 8.5 g/10 min and a density of 0.962 g/cm3. 5960 is an ethylene-based polymer as that term is defined herein.

5 layer films

A series of 5-layer multilayer films were prepared by coextrusion on a Tarragona Collin coextrusion line. Each layer was extruded on a separate extruder. Unless otherwise specified, the resulting films had a thickness of approximately 100 gm.

Table 1 gives the compositions of some 5-layer multilayer films of the present disclosure.

Table 1: 5-layer film compositions

Table 2 shows some mechanical properties of the five-layer films described in Table 1.

Table 2: Properties of 5-layer films

As shown in Table 2, the comparative film CE-A has sufficient dart (specification is >400g) and creep (specification is <50%) performances. However, both MD-Tear and CD-Tear are insufficient (specification is >800g and >1500g respectively). It should be noted that CE-A is 60% w/w HDPE, while EX-1 to EX-11 each include 30% w/w HDPE.

The examples in the present disclosure that include the second core layer show significant improvements in properties, especially when the density is above 0.934 g/c. The extremely high dart and tear performance would also allow for higher HDPE content (which would improve creep performance at the expense of dart and tear). This is the approach followed to optimize the 7-layer structures described below.

When looking at different components for the second core layer, EA+CaCO<3> provides the majority of the best mechanics due to the synergy between the ethylene-acrylate copolymer and calcium carbonate. However, the calcium carbonate-free embodiments provide better creep.

As can be seen by comparing EX-1 with EX-9 and EX-20, the use of 5% high melt strength LDPE such as AGILITY EN 1604 in the cladding layers improves creep without negatively affecting other properties (dart and tear). Additionally, there is an even greater improvement in creep when only one cladding layer comprises LDPE. Further optimization is possible by choosing the best cladding layers, or increasing the HDPE content also through blends in the core layers.

7 layer films

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

Table 3

Table 4-A provides the material properties of some of the embodiments of the 7-layer films with the second core layer in the center.

Table 4-A

As can be seen in Table 4-A, the embodiments of the present disclosure exhibit excellent mechanical properties. This is true for both ethylene-acrylate copolymer embodiments and ethylene-propylene copolymer embodiments. Additionally, when the thickness of the second core layer is increased from 5% to 10%, the overall improvement in properties is less than 5% but still significant. As can be seen by comparing EX-18

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

Table 4-B

As can be seen by comparing EX-19 and EX-20 with the other examples the mechanical properties are better when the second core layer is the core layer, compared to when the second core layer is one of the other core layers. However, there is still a significant improvement in mechanical properties compared to the absence of a second core layer.

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

Table 3:7L thickness reduced to 95 μm

Table 4-C

When the EX-14 film is reduced in thickness from 100 gm to 95 gm, the resulting film still exceeds the parameters required for an HDSS film. While particular embodiments of the present disclosure have been illustrated and described, it will be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the disclosure. Therefore, the appended claims are intended to cover all such changes and modifications that are within the scope of this disclosure.

Claims (15)

1. A multilayer film comprising a first coating layer, a second coating layer and a core positioned between the first coating layer and the second coating layer, wherein: The first coating layer and the second coating layer independently comprise linear low-density polyethylene (LLDPE) resin; The core comprises a first core layer, a second core layer and a third core layer; The first core layer and the third core layer independently comprise high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), or a combination thereof; The second core layer comprises an ethylene-based copolymer selected from the group consisting of ethylene/propylene copolymer, ethylene/butyl acrylate copolymer, ethylene/ethyl acrylate copolymer, ethylene/methyl acrylate copolymer, and ethylene/vinyl acetate copolymer; the thickness of the second core layer is less than 15% of the thickness of the multilayer film; and at least one of the core layers comprises high-density polyethylene (HDPE). 2. The multilayer film of claim 1, wherein the second core layer is positioned between the first core layer and the third core layer. 3. The multilayer film of any preceding claim, wherein the second core layer further comprises calcium carbonate. 4. The multilayer film of any preceding claim, wherein the multilayer film comprises at least 30% w/w HDPE, based on the total polymer weight of the multilayer film. 5. The multilayer film of any preceding claim, wherein the second core layer comprises an ethylene-based copolymer selected from the group consisting of ethylene/butyl acrylate copolymer, ethylene/ethyl acrylate copolymer and ethylene/methyl acrylate copolymer. 6. The multilayer film of any preceding claim, wherein the first skin layer, the second skin layer, or both further comprise low-density polyethylene (LDPE). 7. The multilayer film of any preceding claim, wherein the core further comprises: a fourth core layer positioned between the first skin layer and the first core layer, and a fifth core layer positioned between the third core layer and the second cladding layer. 8. The multilayer film of claim 7, wherein the fourth core layer and the fifth core layer each independently comprise HDPE, LLDPE, or combinations thereof. 9. The multilayer film of any preceding claim, wherein the second core layer has a thickness of less than or equal to 10% of a thickness of the multilayer film. 10. The multilayer film of any preceding claim, wherein the multilayer film has a thickness of less than 180 µm. 11. The multilayer film of any preceding claim, wherein the multilayer film has a Type A Dart Drop Impact of at least 4.4 g/μm. 12. The multilayer film of any preceding claim, wherein the multilayer film has an Elmendorf Cross Direction Tear Strength of at least 16.6 gf/μm. 13. The multilayer film of any preceding claim, wherein the multilayer film has an Elmendorf Cross Direction Tear Strength of at least 8.8 gf/μm. 14. The multilayer film of any preceding claim, wherein the multilayer film has a high creep performance of less than 50%. 15. The multilayer film of any preceding claim, wherein: the second core layer is the central layer, The second core layer is positioned between the first core layer and the third core layer, the multilayer film has a density of 0.929 g/cc to 0.942 g/cc, the first coating layer, the second coating layer or both further comprise low-density polyethylene (LDPE), the second core layer has a thickness less than or equal to 10% of a thickness of the multilayer film, the multilayer film has a thickness of less than or equal to 110 μm, The multilayer film has a Type A Dart Drop Impact of at least 4.4 g/μm, The multilayer film has an Elmendorf Transverse Direction Tear Strength of at least 16.6 gf/μm, and The multilayer film has an Elmendorf Machine Direction Tear Strength of at least 8.8 gf/ktm.