ES2993746B2 - MULTILAYER FILMS WITH IMPROVED FLOW, TEAR AND DART - Google Patents

Description

DESCRIPTION

Multilayer films with improved creep, tear, and dart resistance

Technical field

The achievements described in this report are generally related to multilayer films and, more specifically, to multilayer films used for heavy duty shipping sacks (HDSS).

Background

In an effort to improve sustainability and reduce costs, it is desirable to reduce the thickness of films used to make heavy-duty shipping bags (HDSS). Reducing the thickness reduces the amount of material used and therefore overall emissions. However, this reduction in thickness (also called “thinning”) must be achieved without sacrificing impact strength, tear resistance, and creep resistance. Meeting these specifications has become progressively more difficult as film thickness decreases, 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 summary

Therefore, thinner films that still possess 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.

Further realizations of the present disclosure meet this need by providing a core layer comprising ethylene-acrylate copolymer, ethylene-propylene copolymer, or combinations thereof, and which is relatively thin, such as less than 20% of the thickness of the multilayer film.

According to one embodiment of this disclosure, a multilayer film may comprise a first coating layer, a second coating layer, and a core positioned between the first coating layer and the second coating layer. The first coating layer and the second coating 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 the thickness of the multilayer film. At least one of the core layers may comprise HDPE.

Additional features and advantages will be set out in the detailed description that follows, and some will be readily apparent to those skilled in the art from that description or will be recognized by putting into practice the embodiments described herein, including the detailed description that follows and the claims.

It must be understood that both the above general description and the following detailed description describe various realizations and are intended to provide a general description or structure for understanding the nature and character of the claimed subject matter.

Brief description of the various views of the drawings

To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element first appears. Where two realizations include the same component, similar numerals will be used to describe similar 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 an embodiment of the present multilayer film.

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

Detailed description

Specific embodiments of this application will now be described. Disclosure may take various forms and should not be construed as being limited to the embodiments presented in this disclosure. Rather, these embodiments are provided so that this disclosure is 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 the impact strength, tear strength, and creep resistance requirements for use in HDSS are desired. Embodiments of the present disclosure meet this need by providing a multilayer film comprising a second core layer comprising 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; and which 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 this disclosure may comprise a majority (more than 50% w/w) of 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 acrylate monomer residues.

"Ethylene-propylene copolymer" refers to ethylene-based polymers with propylene comonomers. The ethylene-propylene copolymers of this disclosure may comprise a majority (more than 50% w/w) of 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 propylene monomer residues.

"Residues" refers to the part of a polymer derived from a specific monomer.

"gf/^m" refers to grams force per micrometer.

"Heavy Duty Shipping Bags," also referred to in this document as "HDSS," refers to packaging designed to contain large quantities of granular goods, such as polymer resins, solid chemicals, cement, animal feed, rice, and similar products. The HDSS described in this document may be suitable for containing more than 20 kg of granular goods.

"Multilayer film" refers to any structure that has more than one layer. For example, a multilayer structure can have five or more layers, such as 6, 7, 8, 9, 10, or 11 layers. In some implementations, multilayer film can have an odd number of layers, such as 5, 6, 9, or 11 layers.

"Polyethylene," as used herein, refers to "ethylene-based polymer" and means polymers comprising more than 50% by weight of units derived from ethylene monomers. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers). Common forms of polyethylene known in the art include Low-Density Polyethylene (LDPE); Linear Low-Density Polyethylene (LLDPE); Ultra-Low-Density Polyethylene (ULDPE); Very Low-Density Polyethylene (VLDPE); One-Place 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 that has 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 as meaning that the polymer is partially or totally homopolymerized or copolymerized in autoclave 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 substantially linear ethylene polymers further defined in U.S. Patent Nos. 5,272,236, 5,278,272, 5,582,923, and 5,733,155; homogeneously branched linear ethylene polymer compositions such as those of U.S. Patent No. 3,645,992; and heterogeneously branched ethylene polymers such as those prepared according to the process described in U.S. Patent No. 3,645,992. U.S. Patent No. 4,076,698; and/or mixtures thereof (such as those described in U.S. Patent No. 3,914,342 or U.S. Patent No. 5,854,045). LLDPE may 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 approximately 0.935 g/cm3 and up to approximately 0.980 g/cm3, which are generally prepared with Ziegler-Natta catalysts, chromium catalysts, or single-site catalysts which include, but are not limited to, substituted mono- or bis-cyclopentadienyl catalysts (typically referred to as metallocene), constrained geometry catalysts, phosphinimine catalysts, and polyvalent aryloxy ether 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 (for example, 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 in this dissertation, 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 and propylene monomers) and may optionally include additional monomers or functional or modifying materials, such as acid, acrylate, or anhydride functional groups. In other words, the copolymers described in this dissertation comprise at least two structurally different monomers, and although 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 coating layer 102, a second coating layer 104, and a core 106. The core 106 may be positioned between the first coating layer 102 and the second coating 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, depending 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 C2-C-6 acrylate monomer or a C2a-C5 monomer. In embodiments, the ethylene-acrylate copolymer may comprise from 1% w/w to 49% w/w, such as from 5% w/w to 49% w/w, from 10% w/w to 49% w/w, from 20% w/w to 49% w/w, from 30% w/w to 49% w/w, or 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, on the basis of the total polymer weight of the ethylene-acrylate copolymer. It is 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. The ethylene-acrylate copolymer may comprise a combination of ethylene residues and acrylate residues, depending 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 (I2) of 0.5 g/10 min to 8 g/10 min. In embodiments, the ethylene-acrylate copolymer can have a melt index (I2) of 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 from 1% w/w to 49% w/w, such as from 5% w/w to 49% w/w, from 10% w/w to 49% w/w, from 20% w/w to 49% w/w, from 30% w/w to 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, and from 1% w/w. to 10% w/w, from 10% w/w to 40% w/w, from 20% w/w to 30% w/w, or any subset thereof of the propylene monomer, on a total polymer weight basis 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, on a total polymer weight basis of the ethylene-propylene copolymer. It is 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 a combination of ethylene and propylene residues, depending 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 in this specification.

Comonomer content can be measured using any suitable technique, such as techniques based on nuclear magnetic resonance (“NMR”) spectroscopy, and, for example, by 13C NMR analysis as described in U.S. Patent 7,498,282, which is incorporated herein by reference.

In some embodiments, the ethylene-propylene copolymer can have a density in the range of 0.865 to 0.920 g/cc. All individual values and sub-ranges from 0.865 to 0.920 g/cc are described and included in this specification. For example, the ethylene-propylene copolymer can 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 can have a melt index (I2) of at least 0.5 g/10 min. All individual values and sub-intervals of at least 0.5 g/10 min are described and included in this specification. For example, the ethylene-propylene copolymer may have a melt index (I2) of at least 0.5 g/10 min, at least 0.6 g/10 min, at least 0.7 g/10 min, at least 0.8 g/10 min, at least 0.9 g/10 min, or at least 1.0 g/10 min, or it may have a melt index (I2) in the range of 0.5 g/10 min to 500 g/10 min, from 0.5 g/10 min to 200 g/10 min, from 0.5 g/10 min to 100 g/10 min, from 0.5 g/10 min to 50 g/10 min, from 0.5 g/10 min to 10 g/10 min, or from 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 and 100°C. The improved comonomer composition distribution (ICCD) profile of the ethylene-propylene copolymer can be obtained using the test method described below.

In some embodiments, the ethylene-propylene copolymer can have a molecular weight distribution (Mw/Mn) in the range of 1.5 to 5.0. Every individual value and sub-range from 1.5 to 5.0 is described and included in this specification. For example, the ethylene-propylene copolymer can have a molecular weight (Mw/Mn) distribution 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 (Mw/Mn) distribution can be measured according to the GPC test method described below.

In some embodiments, the ethylene-propylene copolymer can be further characterized by having a melt flow ratio (I10/I2) of 5 to 14. All individual values and sub-intervals from 5 to 14 are described and included in this specification. For example, the ethylene-propylene copolymer can have a melt flow ratio (I10/I2) of 5 to 14, 6 to 12, 6 to 10, or 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 sub-ranges from 40 to 150 J/g are described and included in this specification. 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, and 90 to 10⁸ J/g, where the heat of fusion is measured according to the DSC test method described later.

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, depending on the total polymer weight of the ethylene/vinyl acetate copolymer. All individual values and sub-ranges from 9 to 28 w/w are described and included in this specification. 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, depending on the total weight of the ethylene/vinyl acetate copolymer. Examples of suitable commercially available ethylene/vinyl acetate copolymers include polymers marketed as ELVAX™, available from Dow Inc., Midland, MI.

The second core layer 110 may further comprise a filler, such as calcium carbonate (CaCO3), from 20 to 80% w/w. While not intended to be limited by theory, a synergy has been found between calcium carbonate fillers and ethylene-acrylate copolymers, resulting in improved mechanical properties. However, a variety of fillers (including CaCO3s) 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, or from 40% w/w. to 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, depending on the total weight of the second core layer 110.

As depicted in FIG. 1, the second core layer 110 can 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 can be the middle layer of the multilayer film 100, the middle layer of the core 106, or both. Alternative embodiments are conceived where the second core layer is not the middle layer of the multilayer film and core, provided that the second core layer is positioned between the first cladding layer and the second cladding layer. Without being limited by theory, it is believed that while the second core layer will improve the mechanical strength of any inner layer between the first cladding layer and the second cladding layer, there will be a significant improvement in performance when the second core layer 110 is the middle layer. The middle layer can be the layer that includes the 50% point within the multilayer film 100.

Core layers one, three, four and five

Referring again to FIG. 1, the core 106 can comprise a first core layer 108 and a third core layer 112. The first core layer 108 can be positioned between the first cladding layer 102 and the second core layer 110. The third core layer 112 can 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 coating layer 202, a second coating layer 204, and a core 206. The core 206 may be positioned between the first coating layer 202 and the second coating 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 can be arranged in any order. In embodiments, the fourth core layer 214 can be positioned between the first cladding layer 202 and the first core layer 208. In embodiments, the fifth core layer 216 can be positioned between the second cladding layer 204 and the third core layer 212. In embodiments, the second core layer 210 can be positioned between the first core layer 208 and the third core layer 212. Consequently, the second core layer 210 can be the middle layer. As mentioned previously, it is believed that while the second core layer will add performance to any inner layer between the first cladding layer and the second cladding layer, there will be a significant performance improvement when the second core layer is the middle 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 may 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 may 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, depending 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 arranged on each side of the second core layer.

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

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 HDPE, the HDPE may have a melt index (I2) in the range of 0.1 g/10 min to 1.5 g/10 min. All individual values and sub-ranges from 0.1 g/10 min to 1.5 g/10 min are described and included in this specification. For example, HDPE can have a melting 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™ which includes, 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 LLDPE, the LLDPE may have a density less than or equal to 0.930 g/cm³. All individual values and sub-intervals less than or equal to 0.930 g/cm³ are included and described herein; for example, the density of linear low-density polyethylene may range 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 sub-intervals 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 comprise an LLDPE, the LLDPE may have a melting index (I2) in the range of 0.1 g/10 min to 1.5 g/10 min. All individual values and sub-intervals from 0.1 g/10 min to 1.5 g/10 min are described and included in this specification. For example, LLDPE may have a melting index (I2) in the range of 0.1 g/10 min to 1.3 g/10 min, 0.1 g/10 min to 1.1 g/10 min, 0.1 g/10 min to 0.9 g/10 min, 0.1 g/10 min to 0.7 g/10 min, 0.3 g/10 min to 1.5 g/10 min, 0.5 g/10 min to 1.5 g/10 min, 0.7 g/10 min to 1.5 g/10 min, 0.3 g/10 min to 1.3 g/10 min, 0.5 g/10 min to 1.1 g/10 min, or any subset thereof.

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™ which includes, for example, ELITE™ 5400.

Coating layers

The first coating layer 102, 202 and the second coating layer 104, 204 may independently comprise linear low-density polyethylene (hereafter referred to as "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 of LLDPE, depending on the total polymer weight of the layer.

In embodiments where the first coating layer 102, 202 and/or the second coating layer 104, 204 comprise LLDPE, the LLDPE may have a density less than or equal to 0.940 g/cm3. All individual values and sub-intervals less than or equal to 0.940 g/cm3 are included and described in this specification; 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 subintervals between 0.870 g/cm3 and 0.940 g/cm3 are included and described in this report.

In embodiments where the first coating layer 102, 202 and/or the second coating layer 104, 204 comprise LLDPE, the LLDPE may have a melt index (I2) in the range of 0.1 g/10 min to 50 g/10 min. All individual values and sub-ranges from 0.1 g/10 min to 50 g/10 min are described and included in this specification. For example, the LLDPE may have a melt index (I2) in the range of 0.1 g/10 min to 40 g/10 min, 0.1 g/10 min to 30 g/10 min, 0.1 g/10 min to 20 g/10 min, 0.1 g/10 min to 10 g/10 min, or 0.1 g/10 min to 5 g/10 min.

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 names ELITE™ and DOWLEX™.

In some embodiments, the first coating layer 102, 202 and/or the second coating layer 104, 204 may comprise a fourth low-density polyethylene (LDPE) layer. It should be understood that the first coating layer 102, 202 and the second coating layer 104, 204 may comprise LDPE in addition to LLDPE. In embodiments where the multilayer film 200 and/or the multilayer film 200 comprise LDPE, the LDPE may have a density in the range of 0.916 g/cm³ to 0.935 g/cm³. All individual values and sub-ranges from 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 coating layer 102, 202 and/or the second coating layer 104, 204 comprise LDPE, the LDPE may have a melt index (I2) in the range of 0.1 g/10 min to 50 g/10 min. All individual values and sub-ranges from 0.1 g/10 min to 50 g/10 min are described and included in this specification. For example, the LDPE may have a melt index (I2) in the range of 0.1 g/10 min to 40 g/10 min, 0.1 g/10 min to 30 g/10 min, 0.1 g/10 min to 20 g/10 min, 0.1 g/10 min to 10 g/10 min, or 0.1 g/10 min to 5 g/10 min.

In some embodiments, the first coating layer 102, 202 and/or the second coating layer 104, 204 may independently comprise from 0% w/w to 30% w/w of LDPE, depending on the total weight of the respective layer. All individual values from 0% w/w to 30% w/w are described and included in this specification. 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, or from 5% w/w. at 20% w/w, or any subset thereof, depending on the total polymer weight of the respective layer.

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

Multilayer film

Multilayer film 100, 200 can have a thickness of less than 180 µm. As previously described, the goal is to create multilayer films that can meet the required mechanical properties while minimizing film thickness. In implementations, the 100, 200 multilayer film can have a thickness of less than 160 µm, less than 140 µm, less than 120 µm, less than 100 µm, less than 90 µm, from 70 µm to 180 µm, from 70 µm to 150 µm, from 70 µm to 125 µm, from 70 µm to 115 µm, from 70 µm to 105 µm, from 70 µm to 100 µm, from 70 µm to 95 µm, from 70 µm to 90 µm, from 80 µm to 180 µm, from 80 µm to 150 µm, from 80 µm to 125 µm, from 80 µm to 115 µm, from 80 µm to 105 µm, from 80 µm to 100 µm, from 80 µm to 90 µm, from 90 µm to 180 pm, from 90 pm to 150 pm, from 90 pm to 115 pm, from 90 pm to 105 pm, from 90 pm to 100 pm, 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 multilayer film thickness 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 multilayer film thickness 100, 200.

The first core layer 108, 208 and the third core layer 112, 212 can 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 multilayer film thickness 100, 200.

The second core layer 110, 210 can have a thickness of less than 15% of the thickness of the multilayer film 100, 200. Not being limited by theory, it is believed that the performance of the multilayer film 100, 200 can 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 less than 3% of the thickness of the 110, 210 multilayer film. In embodiments, the second 110, 210 core layer 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 100, 200 multilayer film. In embodiments, the second 110, 210 core layer may have a thickness of 3% to 7% of the thickness of the 100, 200 multilayer film.

Referring now to FIG. 2, the fourth core layer 214 and the fifth core layer 216 can 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 multilayer film thickness of 100, 200. Referring again to FIG. 1 and FIG. 2. The 100, 200 multilayer film may have a density of 0.929 g/cc to 0.942 g/cc. In embodiments, the 100, 200 multilayer film 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 100, 200 multilayer film may have a standardized Type A Dart Drop Impact of at least 4.0 g/pm. In embodiments, the 100, 200 multilayer film may have a Type A Dart Drop Impact of at least 4.4 g/pm, at least 4.6 g/pm, at least 4.8 g/pm, at least 5.0 g/pm, from 4.0 g/pm to 6.0 g/pm, from 4.2 g/pm to 6.0 g/pm, from 4.4 g/pm to 6.0 g/pm, or any subset thereof.

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

The 100, 200 multilayer film may have a standardized Elmendorf transverse tear strength of at least 16.6 gf/pm. In embodiments, the 100, 200 multilayer film may have an Elmendorf transverse tear strength of at least 16.8 gf/pm, at least 17.0 gf/pm, at least 17.2 gf/pm, at least 17.4 gf/pm, at least 17.6 gf/pm, at least 17.8 gf/pm, at least 18.0 gf/pm, from 16.6 gf/pm to 20 gf/pm, or any subset thereof.

The 100, 200 multilayer film may have an Elmendorf transverse tear strength of at least 1500 grams-force (gf). In embodiments, the 100, 200 multilayer film may have an Elmendorf transverse 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 100, 200 multilayer film may have a standardized Elmendorf machine-direction tear strength of at least 8.8 gf/pm. In embodiments, the 100, 200 multilayer film may have an Elmendorf machine-direction tear strength of at least 9.0 gf/pm, at least 9.2 gf/pm, at least 9.4 gf/pm, at least 9.6 gf/pm, at least 9.8 gf/pm, at least 10.0 gf/pm, from 8.8 gf/pm to 12 gf/pm, from 9.0 gf/pm to 12 gf/pm, from 9.2 gf/pm to 12 gf/pm, from 9.4 gf/pm to 12 gf/pm, or any subset thereof.

The 100, 200 multilayer film 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.

Multilayer film 100, 200 may have a high-performance fluence of less than 50%. In embodiments, multilayer film 100, 200 may have a high-performance fluence 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%, from 1% to 50%, from 1% to 40%, from 1% to 30%, from 1% to 25%, or any subset thereof.

It should be understood that Multilayer Film 100 may comprise 5 or more layers. In some embodiments, Multilayer Film 100 may comprise more than 5 layers, such as 7, 9, or 11 layers.

Multilayer films described herein can be produced using techniques known to those skilled in the art, based on the teachings in this document. For example, multilayer film can be produced by lamination and/or coextrusion of films. The formation of coextruded multilayer films is known in the art and is applicable to this disclosure. Coextrusion systems for making multilayer films 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 can be used if two or more of the layers are made of the same materials or polymers.

In some embodiments, the multilayer film is machine-oriented film. In other embodiments, the multilayer film is cast stretch film. In further embodiments, the multilayer film is hood stretch film.

Additives

It should 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, antiblocking agents, antistatic agents, pigments or colorants, processing aids, crosslinking catalysts, flame retardants, fillers, and foaming agents. The layer may contain any quantity of such additives, such as from 0% w/w to 10% w/w, from 0% w/w to 5% w/w, from 0% w/w to 1% w/w, from 0% w/w to 0.1% w/w, from 0% w/w to 0.001% w/w, or any subset thereof, depending on the layer's weight.

Articles

Implementations of this disclosure also provide articles that include any of the inventive multilayer films described herein. Examples of such articles may include wraps, packages, flexible packaging, sachets, and pouches. Articles of this 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 this disclosure may include a heavy-duty shipping bag comprising one or more multilayer films 100, 200.

Testing methods

Density

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

Merger indices (I2, I10, and I21)

The melting index (I2) 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).

The melting index (110) 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).

The melting index (I21) 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).

Enhanced 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 using Crystallization Elution Fractionation (CEF) instrumentation (PolimerChar, Spain) equipped with an IR-5 detector (PolimerChar, Spain) and a Model 2040 dual-angle light scatter detector (Precision Detectors, now Agilent Technologies). A protective column packed with 20–27 µm glass (MoSCi Corporation, USA) in a 5 cm (length) or 10 cm x 1/4” (ID) stainless steel tube was installed just upstream of the IR-5 detector in the detector oven. Ortho-dichlorobenzene (ODCB, 99% anhydrous or technical grade) was used. Silica gel 40 (particle size 0.2–0.5 mm, catalog number 10181-3) was obtained from EMD Chemicals (it can be used to dry the ODCB solvent beforehand). The dried silica was packed into three HT-GPC emptied columns for further purification, in addition to ODCB as the eluent. The CEF instrument is equipped with an autosampler with N2 purge capability. ODCB is sputtered with dry nitrogen (N2) for one hour prior to use. Sample preparation was performed using an autosampler at 4 mg/mL (unless otherwise specified). (other mode) with stirring at 160°C for 1 hour. The injection volume was 300 pl. The iCCD temperature profile was: crystallization at 3°C/min from 105°C to 30°C, thermal equilibrium 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 was 0.0 ml/min. The flow rate during elution was 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 were performed using a slurry method as described in reference (Cong, R.; Parrott, UN.; Hollis, C.; Cheatham, M. WO2017040127A1). The final pressure with TCB slurry packing was 150 bar.

Column temperature calibration was performed using a mixture of Linear Reference Material homopolymer polyethylene (with zero comonomer content, melting index (I2) of 1.0, polydispersity Mw/Mn approximately 2.6 by conventional ge permeability chromatography, 1.0 mg/ml) and eicosane (2 mg/ml) in an ODCB. The iCCD temperature calibration consisted of four steps: (1) Calculating the lag volume, defined as the temperature deviation between the measured peak elution temperature of eicosane and 30.00°C; (2) subtracting the temperature deviation from the elution temperature of the raw iCCD temperature data. It should be noted that this temperature deviation 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 the 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 extrapolated linearly using the elution heating rate of 3°C/min per the reference (Cerk and Cong et al., US9,688,795).

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

The molecular weight of the polymer and the molecular weight of the polymer fractions were determined directly from the LS detector (90-degree angle) and the concentration detector (IR-5) according to the Rayleigh-Gans-Debys approximation (Striegel and Yau, Modern Size Exclusion Liquid Chromatograms, Page 242 and Page 263) assuming a shape factor of 1 and all virial coefficients equal to zero. Integration windows were established for integrating all chromatograms at the elution temperature (temperature calibration specified above), ranging from 23.0 to 120°C.

The Molecular Weight (Mw) calculation for iCCD includes the following steps: (1) Measure the interdetector deviation. The deviation is defined as the geometric volume deviation between the LS and the concentration detector. It is calculated as the difference in the elution volume (mL) of polymer peak between the concentration detector and the LS chromatograms. This is converted to the temperature deviation using the thermal elution rate and elution flow rate. A linear high-density polyethylene (HDPE) is used (which has zero comonomer content, a melting index (I2) of 1.0, and a polydispersity Mw/Mn of approximately 2.6 by conventional gel permeability chromatography). The same experimental conditions as the standard iCCD method above are used, except for the following parameters: crystallization at 10°C/min from 140°C to 137°C, thermal equilibrium at 137°C for 1 minute as the Soluble Fraction Elution Time, soluble fraction (SF) time of 7 minutes, and 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 on the LS chromatogram is shifted for interdetector offset correction before integration. (3) The baseline subtracted LS and concentration chromatograms are integrated over the entire elution temperature range of Step (1). The MW detector constant is calculated using a known MW HDPE sample in the range of 100,000 to 140,000 Mw and the ratio of the LS and integrated concentration signal areas. (4) The Mw of the polymer was calculated using the ratio of the integrated light scattering detector (90 degree angle) to the concentration detector and using the MW detector constant.

Conventional GPC (Mw, Mn, Mw/Mn)

The chromatographic system consisted of a PolimerChar (Valencia, Spain) high-temperature GPCIR chromatograph equipped with an internal IR5 infrared detector coupled to a Precision Detectors (now Agilent Technologies) Model 2040 two-angle laser light scattering (LS) detector. All light scattering measurements were taken at a 15-degree angle. The autosampler's oven compartment was set to 160° Celsius, and the column compartment to 150° Celsius. The columns used were four 20-micrometer, 30-cm linear "Mixed A" columns from Agilent. The chromatographic solvent was 1,2,4-trichlorobenzene containing 200 ppm butylated hydroxytoluene (BHT). The solvent source was splashed nitrogen. The injection volume used was 200 microliters and the flow rate was 1.0 milliliters/minute.

The GPC column set was calibrated using 21 narrowly distributed molecular weight polystyrene standards ranging from 580 to 8,400,000. These standards were arranged in six "cocktail" mixtures with at least a decade's separation between individual molecular weights. The standards were purchased from Agilent Technologies. Polystyrene standards were prepared as 0.025 grams in 50 milliliters of solvent for molecular weights of 1,000,000 or greater, and 0.05 grams in 50 milliliters of solvent for molecular weights less than 1,000,000. The polystyrene standards were dissolved at 80 degrees Celsius with gentle stirring for 30 minutes. Standard peak molecular weights of polystyrene were converted to molecular weights of polyethylene 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 is equal to 1.0

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

The total plaque count of the established GPC column was performed using Eicosane (prepared at 0.04 g in 50 milliliters of TCB and dissolved for 20 minutes with gentle stirring). The plaque 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 % of the maximum peak 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 height is 1/10 of the maximum peak height, and where trailing peak refers to the peak tail in retention volumes later than peak max and where leading peak refers to the leading peak in retention volumes prior to peak max. The plate count for the chromatographic system must be greater than 24,000 and the symmetry must be between 0.98 and 1.22.

Samples were prepared semi-automatically using PolimerChar's Instrument Control software. The samples had a target weight of 2 mg/ml, and the solvent (containing 200 ppm BHT) was added to a capped septa vial previously sprayed with nitrogen using PolimerChar's high-temperature autosampler. The samples were dissolved for 2 hours at 160° Celsius with low-speed stirring.

The calculations of Mn (<gpc>), Mw (<gpc>), and Mz (<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 IR chromatogram subtracted at each equally spaced data collection point (i), and the equivalent molecular weight of polyethylene obtained from the standard calibration curve for point (i) of Equation 1.

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

The systematic approach for the determination of multidetector deviations 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)), triple detector recording results of optimization (MW and IV) of a wide homopolymer polyethylene standard (Mw/Mn > 3) to 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 that 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 GPCOne™ 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 average molecular weight polyethylene standards of known weight. The calculated molecular weights (using GPCOne™) were obtained using a light scattering constant, derived from one or more of the polyethylene standards mentioned below, and a refractive index concentration coefficient, dn/dc, of 0.104. Generally, the mass detector response (IR5) and the light scattering constant (determined using GPCOne™) should be determined from a linear standard with a molecular weight in excess 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 standards texts (e.g., E. A. Turi, ed., Thermal Characterization of Polymeric Materials, Academic Press, 1981).

The heat of fusion was determined using a DSC instrument from TA Instruments, Inc. The test was performed in accordance with ASTM D3428. Calibration was performed by preparing 2–3 mg of indium and placing it in a temperature-zero aluminum pan. The pan was then loaded into the DSC instrument and subjected to the following heating program cycle: 1) equilibrate the test chamber to 180°C, 2) maintain the temperature at 180°C for 1 min., 3) increase the temperature to 130°C at a rate of 10°C/min., 4) maintain the temperature at 130°C for 3 min., and 5) increase the temperature to 180°C at a rate of 10°C/min. Once completed, the final heat curve generated in step 5 was analyzed to determine the melting point of the indium sample. The DSC is considered to be functioning compatiblely if the melting temperature is within a tolerance of 0.5°C from 156.6°C.

For sample testing, polymer samples are first pressed into a thin film at 190°C. Approximately 4 to 5 mg of sample are weighed and placed in the DSC pan. The lid is crimped onto the pan to ensure a sealed atmosphere. The sample pan is placed in the DSC cell and equilibrated to 180°C. The sample is held at this temperature for 5 minutes. The sample is then cooled at a rate of 10°C/min to -90°C and held isothermally at that temperature for 5 minutes. Subsequently, the sample is heated at a rate of 10°C/min to 150°C (to ensure complete melting); this stage is designated the 2a heating curve. The resulting enthalpy curves are analyzed for peak melting temperature, crystallization onset and peak temperatures, and heat of fusion (also known as heat to melt), AHf. The heat of fusion, in Joules/gram, is measured from the 2nd heating curve by performing a linear integration of the fusion endotherm according to 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 the impact of a free-falling dart. The test result is the energy, expressed in terms of the weight of the dart falling from a specified height, that would result in the failure of 50% of the tested specimens. The film sample is conditioned for at least 40 hours at 23°C (± 2°C) and 50% RH (± 10%) before the test, which is performed at 23°C (± 2°C) and 50% RH (± 10%). For the current film samples, Method A is used, employing a dart head 3.81 cm (1.5") in diameter and a drop height of 66 cm (26"). The dart head is made of aluminum. The sample thickness is measured at the center of the sample, and the sample is then clamped with an annular specimen holder with an inside diameter of 12.7 cm (5 in.). The dart is loaded above the center of the sample and released by a pneumatic or electromagnetic mechanism. The dart is loaded with an initial weight, which is subsequently increased or decreased by a weight chosen depending on whether it passes or fails on each drop. Typically, approximately 20–25 specimens are used for the drop experiments. Finally, a ladder method according to ASTM D1709 is used to calculate the ‘Dart’ value based on the collected pass/fail data, the initial weight, and the weight increment.

Tear resistance Elmendorf

The average Elmendorf tear strength is measured in the machine direction (MD) and cross-machine direction (CD) according to ASTM D1922.

High-performance fluency

High-performance creep is determined according to ISO 899.

ASPECTS

According to a first aspect, a multilayer film may comprise 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 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 can 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 can also 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 of HDPE, on the basis of 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 coating layer, the second coating 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 cladding layer and the first core layer, and a fifth core layer positioned between the third core layer and the second cladding 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 of aspects 1-8, the second core layer may have a thickness less than or equal to 10% of a multilayer film thickness.

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

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/pm.

According to a twelfth aspect, in conjunction with any of aspects 1-11, the multilayer film can have a standardized Elmendorf Transverse Tear Resistance of at least 16.6 gf/pm.

According to a thirteenth aspect, in conjunction with any of aspects 1-12, the multilayer film can have a standardized Elmendorf Machine Direction Tear Resistance of at least 8.8 gf/pm.

According to a fourteenth aspect, in conjunction with any of aspects 1-13, the multilayer film can have a high-performance fluence of less than 50%.

According to a fifteenth aspect, in conjunction with any of aspects 1-14, the second core layer may be the middle 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 coating layer, the second coating 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 pm, the multilayer film may have a Type A Dart Drop Impact of at least 4.4 g/pm, the multilayer film may have an Elmendorf Transverse Tear Strength of at least 16.6 gf/pm, and the multilayer film may have an Elmendorf Machine Tear Strength of at least 8.8 gf/pm.

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 accompanying claims.

Materials

INNATE™ ST50 (also referred to in this document as "ST50"), a linear low-density polyethylene having a density of 0.918 g/cm3 and a melt index (I2) of 0.85 g/10 min and commercially available from Dow Inc., (Midland, MI). INNATE™ ST50 is an ethylene-based polymer as the term is defined in this document.

INNATE™ ST70 (also referred to in this document as "ST70"), a linear low-density polyethylene having a density of 0.926 g/cm3 and a melt index (I2) of 0.85 g/10 min and commercially available from Dow Inc., (Midland, MI). INNATE™ ST70 is an ethylene-based polymer as the term is defined in this document.

INNATE™ ST100 (also referred to in this document as "ST100"), a linear low-density polyethylene having a density of 0.928 g/cm3 and a melt index (I2) of 0.85 g/10 min and commercially available from Dow Inc., (Midland, MI). INNATE™ ST100 is an ethylene-based polymer as the term is defined in this document.

ELITE™ 5400 is a linear low-density polyethylene with a density of 0.916 g/cm³ and a melt index (I²) of 1.0 g/10 min, commercially available from Dow Inc. (Midland, MI). ELITE™ 5400 is an ethylene-based polymer as defined herein. DOWLEX™ GM 8090 (also referred to herein as "GM 8090") is a commercially available low-density polyethylene from Dow Inc. (Midland, MI). DOWLEX™ GM 8090 has a density of 0.916 g/cm³ and a melt index (I²) of 1.0 g/10 min. DOWLEX™ GM 8090 is an ethylene-based polymer as defined herein.

AGILITY™ EN 1604 is a low-density polyethylene with a density of 0.921 g/cm³ and a melt index (I²) of 0.25 g/10 min, commercially available from Dow Inc., (Midland, MI). AGILITY™ EN 1604 is an ethylene-based polymer as defined herein. UNIVAL™ DMDA 6400 (also referred to herein as "DMDA 6400") is a high-density polyethylene with a density of 0.961 g/cm³, a melt index (I²) of 0.80 g/10 min, and a melt strength index (I²<1>) of 57 g/10 min, commercially available from Dow Inc., (Midland, MI). UNIVAL™ DMDA 6400 is an ethylene-based polymer as defined herein.

ELVALOY™ AC 3117 (also referred to in this document as "EA") is an ethylene acrylate copolymer (83% ethylene and 17% butyl acrylate) with a density of 0.924 g/cm³ and a melting index (I²) of 1.5 g/10 min, commercially available from Dow Inc., (Midland, MI). The term "ethylene-acrylate copolymer" is defined in this document.

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

XUS 39003.00 (also referred to in this specification as “EP”) is a commercially available ethylene-propylene copolymer 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 (I²) of 0.90 g/10 min, an I<10>/I² ratio of 10.82, a heat of fusion of 50.24 J/g, and an Mw/Mn ratio of 3.98. EP has an inversely inserted propylene unit ratio of 0.8% w/w, where the weight percent is based on the total weight of EP. EP is an ethylene-based polymer as the term is defined in this specification.

Some examples use a combination of XUS 39003.0 (“EP”) and Calcium Carbonate (also referred to in this document as “EP+CaCO3”). The combination comprises approximately 42% w/w calcium carbonate, with the ethylene-propylene copolymer in balance, based on the total layer weight.

ELITE™ 5960G1 (also referred to in this document as “5960”) is a commercially available high-density polyethylene (HDPE) from Dow Inc. (Midland, MI). 5960 has a melt index (I2) of 8.5 g/10 min and a density of 0.962 g/cm3. 5960 is an ethylene-based polymer as the term is defined in this document.

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 were approximately 100 µm thick.

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

Table 1: Compositions of 5-layer films

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 CE-A comparison film has sufficient dart strength (specification > 400g) and creep resistance (specification < 50%). However, both MD-Tear and CD-Tear are insufficient (specification > 800g and > 1500g, respectively). It should be noted that CE-A is 60% w/w HDPE, while EX-1 through EX-11 each contain 30% w/w HDPE.

The examples in this disclosure, which include the second core layer, show significant improvements in properties, especially when the density is above 0.934 g/cm³. The extremely high dart and tear strength would also allow for a higher HDPE content (which would improve creep performance at the expense of dart and tear strength). This is the approach used to optimize the 7-layer structures described later.

When considering different components for the second core layer, EA+CaCO3 provides the best mechanical properties due to the synergy between the ethylene acrylate copolymer and calcium carbonate. However, embodiments without calcium carbonate offer 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 resistance). Furthermore, there is an even greater improvement in creep when only one cladding layer comprises LDPE. Further optimization is possible by selecting the best cladding layers or by increasing the HDPE content through combinations 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 were approximately 100 µm thick. Film details are included below in Table 3.

Table 3

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

As can be seen in Table 4-A, the embodiments of this disclosure exhibit excellent mechanical properties. This is true for both ethylene-acrylate copolymer 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 is still significant, as can be seen by comparing EX-18.

Table 4-B provides the material properties of some 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 layer B. In EX-20, the second core layer is in layer C.

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 central 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 pm to 95 pm 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 pm

Table 4-C

When the EX-14 film is reduced in thickness from 100 pm to 95 pm, the resulting film still exceeds the parameters required for an HDSS film.

Although particular embodiments of this 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 (14)

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; at least one of the core layers comprises high-density polyethylene (HDPE); and where multilayer film comprises at least 30% w/w of HDPE, on a basis of the total polymer weight of the multilayer film. 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 second core layer comprises an ethylene-based copolymer selected from the group consisting of ethylene/butyl acrylate copolymer, ethylene/ethyl acrylate copolymer, and ethylene/methyl acrylate copolymer. 5. The multilayer film of any preceding claim, wherein the first coating layer, the second coating layer, or both further comprise low-density polyethylene (LDPE). 6. The multilayer film of any preceding claim, wherein the core further comprises: a fourth core layer positioned between the first cladding layer and the first core layer, and a fifth core layer positioned between the third core layer and the second cladding layer. 7. The multilayer film of claim 6, wherein the fourth core layer and the fifth core layer each independently comprise HDPE, LLDPE, or combinations thereof. 8. The multilayer film of any preceding claim, wherein the second core layer has a thickness less than or equal to 10% of a thickness of the multilayer film. 9. The multilayer film of any preceding claim, wherein the multilayer film has a thickness of less than 180 pm. 10. The multilayer film of any preceding claim, wherein the multilayer film has a Type A Dart Drop Impact of at least 4.4 g/pm. 11. The multilayer film of any preceding claim, wherein the multilayer film has an Elmendorf Transverse Tear Strength of at least 16.6 gf/pm. 12. The multilayer film of any preceding claim, wherein the multilayer film has an Elmendorf Transverse Tear Strength of at least 8.8 gf/pm. 13. The multilayer film of any preceding claim, wherein the multilayer film has a high creep performance of less than 50%. 14. 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 the thickness of the multilayer film, The multilayer film has a thickness of less than or equal to 110 pm, The multilayer film has a Type A Dart Drop Impact of at least 4.4 g/pm, the multilayer film has an Elmendorf Transverse Tear Resistance of at least 16.6 gf/pm, and The multilayer film has a machine-directed tear resistance of at least 8.8 gf/pm.