WO2020167929A1

WO2020167929A1 - Methods for making films and films made thereby

Info

Publication number: WO2020167929A1
Application number: PCT/US2020/017905
Authority: WO
Inventors: Chiao Kiat PEY
Original assignee: Exxonmobil Chemical Patents Inc.
Priority date: 2019-02-13
Filing date: 2020-02-12
Publication date: 2020-08-20

Abstract

Disclosed herein are methods for making a machine direction oriented film by a blown film coextrusion line and films produced thereby.

Description

METHODS FOR MAKING FILMS AND FILMS MADE THEREBY

FIELD OF THE INVENTION

This application claims the benefit of U.S. Provisional Application No. 62/805,075, filed 13 February 2019 and entitled“Methods for Making Films and Films Made Thereby,” the disclosure of which is incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to methods for making a machine direction oriented (MDO) film, films produced thereby, and laminates made therefrom.

BACKGROUND OF THE INVENTION

Coextruded blown films are widely used in a variety of packaging as well as other applications. Film properties are often subject to the combined effect of the coextrusion process conditions and polymer compositions selected for the different layers. In order to address requirements of particular end-uses, film producers have to accordingly highlight certain film properties while balancing between mechanical properties such as stiffness and impact strength, to ensure package integrity without distortion and rupture, and optical properties such as clarity and haze, which impact the attractiveness of the packaging and visual inspection of the goods at the point of sale. Good sealing performance under common heat sealing conditions and, for some applications, barrier to moisture, light and/or oxygen transmission are also desired.

Laminates, prepared from a flexible film structure comprising a polyethylene sealant film adhered to a substrate film commonly made of polyamide, polyester (PET), biaxially oriented polypropylene (BOPP), or biaxially oriented polyamide (BOP A), are commonly employed to provide good oxygen and aroma barrier as well as favored mechanical properties including both toughness and stiffness. However, these materials have been found difficult to be effectively recycled, thus giving rise to a growing trend to seek“pure” polyethylene solutions, i.e. by laminating a polyethylene sealant to a substrate also made of polyethylene. Based on a single class of resins, such laminates can be conveniently recycled to improve sustainability and can deliver material cost-effectiveness by virtue of the more inexpensive polyethylene polymers. However, the polyethylene substrates usually have limited use due to failure to deliver other properties desired by specific applications, such as stiffness and elongation, at a level comparable to that provided by the non-recyclable substrates. Therefore, film manufacturers have long been challenged to develop a convenient and flexible approach to improve currently underperforming properties of polyethylene substrates with the available selection of ethylene polymers. WO 2018/071250 relates to oriented films comprising linear low density polyethylene polymer and having improved balance of properties including improved machine direction tear strength. This oriented polymer film has at least one layer comprising 50 to 100 wt% of an ethylene-based polymer. This MDO polymer film has a normalized MD Elmendorf Tear (ASTM D-1922) of at least 40 g/pm. In certain embodiments, this MDO polymer film does not tear when MD Elmendorf Tear is measured according to ASTM D- 1922.

WO 2016/135213 provides laminated film structures comprising one first film being laminated to a second film and whereby this laminated film structures are based on polyethylene only, i.e. polymers other than polyethylene are substantially absent and wherein the first film is an MDO film, which can be down-gauged to a film thickness below 30 pm, preferably to 25pm and below, e.g. to a film thickness of 20pm.

WO 2016/097951 discloses a multilayer film having Machine Direction Orientation (MDO) prepared by first co-extruding a multilayer film, then stretching the multilayer film in the machine direction at a temperature lower than the melting point of the polyethylene resin that is used to prepare the film. At least one layer of this film is a first polyethylene composition having a density of from about 0.94 to about 0.97 g/cc and at least one second layer is prepared from a polyethylene composition having a lower density than the first polyethylene composition.

European Patent No. 2,875,948 relates to a multilayer machine direction oriented film comprising at least an (A) layer and (B) layer, at least one of said (A) layer or (B) layer comprising at least 50 wt% of a multimodal linear low density polyethylene (LLDPE) having a density of 905 to 940 kg/m³ and an MFR 2 of 0.01 to 20 g/10 min and comprising a lower molecular weight (LMW) component and a higher molecular weight (HMW) component; wherein said LMW component is an ethylene homopolymer and said HMW component is an ethylene polymer of ethylene with at least two C4-12 alpha olefins; wherein said film is a stretched film which is uniaxially oriented in the machine direction (MD) in a draw ratio of at least 1:3 and has a film thickness of at least 40 microns (after stretching) and wherein said film does not comprise a layer in which more than 50 wt% of said layer comprises a polymer component having a melting point (T_m) of 100°C or less.

That said, exploring alternative laminate substrate design with increased recyclability while maintaining other properties at a desired level remains an area of ongoing and intense effort. Applicant has discovered that, during a blown coextrusion process, introduction of at least about 50 wt% of a polyethylene as described herein (based on total weight of polymer in the layer) into each layer of a tubular film followed by machine direction orientation can make the two inner surfaces of the blown bubble inseparable. As a result, the tubular film remains a single film when exiting the MDO unit with the two layers in contact with each other by the two inner surfaces combined into one serving as the core layer of the so-obtained MDO film. The inventive MDO film, in addition to mitigated cost pressure and enhanced production sustainability, can particularly benefit film manufacturers with improved tensile properties superior to that achievable with the conventional non-recyclable substrates.

SUMMARY OF THE INVENTION

Provided are methods for making a machine direction oriented (MDO) film by a coextrusion line, and films made thereby.

In one embodiment, the present invention is directed to a method for making a machine direction oriented (MDO) film by a blown extrusion line comprising three extruders, comprising the steps of: (a) extruding a core layer from a first extruder; (b) extruding two outer layers from a second extruder, wherein the core layer is between the two outer layers; (c) extruding two inner layers from a third extruder, wherein each inner layer is between the core layer and each outer layer; (d) forming a film comprising the layers in steps (a), (b), and (c); (e) subjecting the film in step (d) to machine direction orientation; and (1) forming an MDO film without a slitting step prior to winding; wherein each layer comprises at least about 50 wt% of a polyethylene, based on total weight of polymer in the layer, the polyethylene having a density of about 0.910 to about 0.945 g/cm³, a melt index (MI), I2_.16, of about 0.1 to about 15 g/10 min, a molecular weight distribution (MWD) of about 1.5 to about 5.5, and a melt index ratio (MIR), I21_.6/I2_.16, of about 10 to about 100.

In another embodiment, the present invention encompasses a machine direction oriented (MDO) film, comprising two outer layers, a core layer between the two outer layers, and two inner layers each between the core layer and each outer layer, wherein each layer comprises at least about 50 wt% of a polyethylene, based on total weight of polymer in the layer, the polyethylene having a density of about 0.910 to about 0.945 g/cm³, a melt index (MI), I2_.16, of about 0.1 to about 15 g/10 min, a molecular weight distribution (MWD) of about 1.5 to about 5.5, and a melt index ratio (MIR), I21_.6/I2_.16, of about 10 to about 100; wherein the MDO film is prepared by a blown extrusion line comprising three extruders, comprising the steps of: (a) extruding the core layer from a first extruder; (b) extruding the two outer layers from a second extruder; (c) extruding the two inner layers from a third extruder; (d) forming a film comprising the layers in steps (a), (b), and (c); (e) subjecting the film in step (d) to machine direction orientation; and (1) forming the MDO film without a slitting step prior to winding. Often, the MDO film described herein or made according to any method disclosed herein may have at least one of the following properties: (i) an average elongation at break of at most about 40%; and (ii) an average absolute modulus of at least about 70 N/mm.

Also provided are laminates comprising any of the MDO films described herein or made according to any method disclosed herein.

BRIEF DESCRIPTION OF THE DRAWING

The FIG. depicts a schematic representation of film structure for Sample 1 in Example

1

DETAILED DESCRIPTION OF THE INVENTION

Various specific embodiments, versions of the present invention will now be described, including exemplary embodiments and definitions that are adopted herein. While the following detailed description gives specific exemplary embodiments, those skilled in the art will appreciate that these embodiments are exemplary only, and that the present invention can be practiced in other ways. Any reference to the“invention” may refer to one or more, but not necessarily all, of the present inventions defined by the claims. The use of headings is for purposes of convenience only and does not limit the scope of the present invention.

As used herein, a“polymer” may be used to refer to homopolymers, copolymers, interpolymers, terpolymers, etc. A“polymer” has two or more of the same or different monomer units. A“homopolymer” is a polymer having monomer units that are the same. A “copolymer” is a polymer having two or more monomer units that are different from each other. A“terpolymer” is a polymer having three monomer units that are different from each other. The term“different” as used to refer to monomer units indicates that the monomer units differ from each other by at least one atom or are different isomerically. Accordingly, the definition of copolymer, as used herein, includes terpolymers and the like. Likewise, the definition of polymer, as used herein, includes copolymers and the like. Thus, as used herein, the terms “polyethylene,”“ethylene polymer,”“ethylene copolymer,” and“ethylene based polymer” mean a polymer or copolymer comprising at least 50 mol% ethylene units (preferably at least 70 mol% ethylene units, more preferably at least 80 mol% ethylene units, even more preferably at least 90 mol% ethylene units, even more preferably at least 95 mol% ethylene units or 100 mol% ethylene units (in the case of a homopolymer)). Furthermore, the term“polyethylene composition” means a composition containing one or more polyethylene components.

As used herein, when a polymer is referred to as comprising a monomer, the monomer is present in the polymer in the polymerized form of the monomer or in the derivative form of the monomer. As used herein, when a polymer is said to comprise a certain percentage, wt%, of a monomer, that percentage of monomer is based on the total amount of monomer units in the polymer.

For purposes of this invention and the claims thereto, an ethylene polymer having a density of 0.910 to 0.940 g/cm³ is referred to as a“low density polyethylene” (LDPE); an ethylene polymer having a density of 0.890 to 0.930 g/cm³, typically from 0.910 to 0.930 g/cm³, that is linear and does not contain a substantial amount of long-chain branching is referred to as“linear low density polyethylene” (LLDPE) and can be produced with conventional Ziegler- Natta catalysts, vanadium catalysts, or with metallocene catalysts in gas phase reactors, high pressure tubular reactors, and/or in slurry reactors and/or with any of the disclosed catalysts in solution reactors (“linear” means that the polyethylene has no or only a few long-chain branches, typically referred to as a g' vis of 0.97 or above, preferably 0.98 or above); and an ethylene polymer having a density of more than 0.940 g/cm³ is referred to as a“high density polyethylene” (HDPE).

As used herein,“core” layer,“outer” layer, and“inner” layer are merely identifiers used for convenience, and shall not be construed as limitation on individual layers, their relative positions, or the laminated structure, unless otherwise specified herein.

As used herein,“first” polyethylene,“second” polyethylene,“third” polyethylene, and “fourth” polyethylene are merely identifiers used for convenience, and shall not be construed as limitation on individual polyethylene, their relative order, or the number of polyethylene polymers used, unless otherwise specified herein.

As used herein, stretch ratio through a machine direction (MD) orientation unit is the ratio of film length before MD orientation to the film length after MD orientation. This is stated, for example, as a stretch ratio of 4, where 4 represents the film length after MD orientation relative to a film of unit length before MD orientation, i.e., the film has been stretched to 4 times the original length. Orientation refers to the alignment of polymer chains in the film.

As used herein, when a film is referred to as“symmetrical”, it contains layers on one side of the core layer that are mirror images of those on the other side relative to the core layer.

As used herein, film layers that are the same in composition and in thickness are referred to as“identical” layers.

As used herein, a“laminate” refers to a multilayer structure comprising a sealant and a substrate attached to each other by lamination.

Polyethylene Polymer In one aspect of the invention, the MDO film described herein or made according to the method described herein may comprise two outer layers, a core layer between the two outer layers, and two inner layers each between the core layer and each outer layer, each comprising a polyethylene having a density of about 0.910 to about 0.945 g/cm³, an MI, h.ie, of about 0.1 to about 15 g/10 min, an MWD of about 1.5 to about 5.5, and an MIR, I21_.6/I2_.16, of about 10 to about 100. The polyethylene that can be used for the MDO film made according to the method described herein are selected from ethylene homopolymers, ethylene copolymers, and compositions thereof. Useful copolymers comprise one or more comonomers in addition to ethylene and can be a random copolymer, a statistical copolymer, a block copolymer, and/or compositions thereof. The method of making the polyethylene is not critical, as it can be made by slurry, solution, gas phase, high pressure or other suitable processes, and by using catalyst systems appropriate for the polymerization of polyethylene polymers, such as Ziegler-Natta- type catalysts, chromium catalysts, metallocene-type catalysts, other appropriate catalyst systems or combinations thereof, or by free-radical polymerization. In an exemplary embodiment, the polyethylene polymers are made by the catalysts, activators and processes described in U.S. Patent Nos. 6,342,566; 6,384,142; and 5,741,563; and WO 03/040201 and WO 97/19991. Such catalysts are well known in the art, and are described in, for example, ZIEGLER CATALYSTS (Gerhard Fink, Rolf Miilhaupt and Hans H. Brintzinger, eds., Springer-Verlag 1995); Resconi et al; and I, II METALLOCENE-BASED POLYOLEFINS (Wiley & Sons 2000).

Polyethylene polymers that are useful in this invention include those sold under the tradenames ENABLE™, EXACT™, EXCEED™, ESCORENE™, EXXCO™, ESCOR™, PAXON™, and OPTEMA™ (ExxonMobil Chemical Company, Houston, Texas, USA); DOW™, DOWLEX™, ELITE™, AFFINITY™, ENGAGE™, and FLEXOMER™ (The Dow Chemical Company, Midland, Michigan, USA); BORSTAR™ and QUEO™ (Borealis AG, Vienna, Austria); and TAFMER™ (Mitsui Chemicals Inc., Tokyo, Japan).

Preferred ethylene homopolymers and copolymers useful in this invention typically have one or more of the following properties:

1. an M_w of 20,000 g/mol or more, 20,000 to 2,000,000 g/mol, preferably 30,000 to 1,000,000, preferably 40,000 to 200,000, preferably 50,000 to 750,000, using a gel permeation chromatograph (“GPC”) according to the procedure disclosed herein; and/or

2. a T_m of 30°C to 150°C, preferably 30°C to 140°C, preferably 50°C to 140°C, more preferably 60°C to 135°C, as determined by second melting curve based on ASTM D3418; and/or 3. a crystallinity of 5% to 80%, preferably 10% to 70%, more preferably 20% to 60%, preferably at least 30%, or at least 40%, or at least 50%, as determined by enthalpy of crystallization curve based on ASTM D3418 and calculated by the following formula:

Crystallinity % = Enthalpy (J/g)/ 298 (J/g) ^c 100%,

wherein 298 (J/g) is enthalpy of 100% crystallinity polyethylene; and/or

4. a heat of fusion of 300 J/g or less, preferably 1 to 260 J/g, preferably 5 to 240 J/g, preferably 10 to 200 J/g, as determined based on ASTM D3418-03; and/or

5. a crystallization temperature (T_c) of 15°C to 130°C, preferably 20°C to 120°C, more preferably 25°C to 110°C, preferably 60°C to 125°C, as determined based on ASTM D3418-03; and/or

6. aheat deflection temperature of 30°C to 120°C, preferably 40°C to 100°C, more preferably 50°C to 80°C as measured based on ASTM D648 on injection molded flexure bars, at 66 psi load (455 kPa); and/or

7. a Shore hardness (D scale) of 10 or more, preferably 20 or more, preferably 30 or more, preferably 40 or more, preferably 100 or less, preferably from 25 to 75 (as measured based on ASTM D 2240); and/or

8. a percent amorphous content of at least 50%, preferably at least 60%, preferably at least 70%, more preferably between 50% and 95%, or 70% or less, preferably 60% or less, preferably 50% or less as determined by subtracting the percent crystallinity from 100.

The polyethylene may be an ethylene homopolymer, such as HDPE. In one embodiment, the ethylene homopolymer has a molecular weight distribution (M_w/M_n) or (MWD) of up to 40, preferably ranging from 1.5 to 20, or from 1.8 to 10, or from 1.9 to 5, or from 2.0 to 4. In another embodiment, the 1% secant flexural modulus (determined based on ASTM D790A, where test specimen geometry is as specified under the ASTM D790 section “Molding Materials (Thermoplastics and Thermosets),” and the support span is 2 inches (5.08 cm)) of the polyethylene falls in a range of 200 to 1000 MPa, and from 300 to 800 MPa in another embodiment, and from 400 to 750 MPa in yet another embodiment, wherein a desirable polymer may exhibit any combination of any upper flexural modulus limit with any lower flexural modulus limit. The MI of preferred ethylene homopolymers range from 0.05 to 800 dg/min in one embodiment, and from 0.1 to 100 dg/min in another embodiment, as measured based on ASTM D1238 (190°C, 2.16 kg).

In an exemplary embodiment, the polyethylene comprises less than 20 mol% propylene units (preferably less than 15 mol%, preferably less than 10 mol%, preferably less than 5 mol%, and preferably 0 mol% propylene units). In another embodiment of the invention, the polyethylene useful herein is produced by polymerization of ethylene and, optionally, an alpha-olefin with a catalyst having, as a transition metal component, a bis (n-C34 alkyl cyclopentadienyl) hafnium compound, wherein the transition metal component preferably comprises from about 95 mol% to about 99 mol% of the hafnium compound as further described in U.S. Patent No. 9,956,088.

In another embodiment of the invention, the polyethylene is an ethylene copolymer, either random or block, of ethylene and one or more comonomers selected from C3 to C20 a- olefins, typically from C3 to C10 a-olefms. Preferably, the comonomers are present from 0.1 wt% to 50 wt% of the copolymer in one embodiment, and from 0.5 wt% to 30 wt% in another embodiment, and from 1 wt% to 15 wt% in yet another embodiment, and from 0.1 wt% to 5 wt% in yet another embodiment, wherein a desirable copolymer comprises ethylene and C3 to C20 a-olefm derived units in any combination of any upper wt% limit with any lower wt% limit described herein. Preferably the ethylene copolymer will have a weight average molecular weight of from greater than 8,000 g/mol in one embodiment, and greater than 10,000 g/mol in another embodiment, and greater than 12,000 g/mol in yet another embodiment, and greater than 20,000 g/mol in yet another embodiment, and less than 1,000,000 g/mol in yet another embodiment, and less than 800,000 g/mol in yet another embodiment, wherein a desirable copolymer may comprise any upper molecular weight limit with any lower molecular weight limit described herein.

In another embodiment, the ethylene copolymer comprises ethylene and one or more other monomers selected from the group consisting of C3 to C20 linear, branched or cyclic monomers, and in some embodiments is a C3 to C12 linear or branched alpha-olefin, preferably butene, pentene, hexene, heptene, octene, nonene, decene, dodecene, 4-methyl-pentene- 1,3- methyl pentene-l,3,5,5-trimethyl-hexene-l, and the like. The monomers may be present at up to 50 wt%, preferably from up to 40 wt%, more preferably from 0.5 wt% to 30 wt%, more preferably from 2 wt% to 30 wt%, more preferably from 5 wt% to 20 wt%, based on the total weight of the ethylene copolymer.

Preferred linear alpha-olefins useful as comonomers for the ethylene copolymers useful in this invention include C3 to Cx alpha-olefins, more preferably 1 -butene, 1 -hexene, and 1- octene, even more preferably 1 -hexene. Preferred branched alpha-olefins include 4-methyl- 1- pentene, 3-methyl- 1 -pentene, 3,5,5 -trimethyl- 1 -hexene, and 5 -ethyl- 1 -nonene. Preferred aromatic-group-containing monomers contain up to 30 carbon atoms. Suitable aromatic-group- containing monomers comprise at least one aromatic structure, preferably from one to three, more preferably a phenyl, indenyl, fluorenyl, or naphthyl moiety. The aromatic-group- containing monomer further comprises at least one polymerizable double bond such that after polymerization, the aromatic structure will be pendant from the polymer backbone. The aromatic-group containing monomer may further be substituted with one or more hydrocarbyl groups including but not limited to Ci to Cio alkyl groups. Additionally, two adjacent substitutions may be joined to form a ring structure. Preferred aromatic-group-containing monomers contain at least one aromatic structure appended to a polymerizable olefmic moiety. Particularly, preferred aromatic monomers include styrene, alpha-methylstyrene, para- alkylstyrenes, vinyltoluenes, vinylnaphthalene, allyl benzene, and indene, especially styrene, paramethyl styrene, 4-phenyl- 1 -butene and allyl benzene.

Preferred diolefm monomers useful in this invention include any hydrocarbon structure, preferably C4 to C30, having at least two unsaturated bonds, wherein at least two of the unsaturated bonds are readily incorporated into a polymer by either a stereospecific or a non- stereospecific catalyst(s). It is further preferred that the diolefm monomers be selected from alpha, omega-diene monomers (i.e., di -vinyl monomers). More preferably, the diolefm monomers are linear di-vinyl monomers, most preferably those containing from 4 to 30 carbon atoms. Examples of preferred dienes include butadiene, pentadiene, hexadiene, heptadiene, octadiene, nonadiene, decadiene, undecadiene, dodecadiene, tridecadiene, tetradecadiene, pentadecadiene, hexadecadiene, heptadecadiene, octadecadiene, nonadecadiene, icosadiene, heneicosadiene, docosadiene, tricosadiene, tetracosadiene, pentacosadiene, hexacosadiene, heptacosadiene, octacosadiene, nonacosadiene, triacontadiene, particularly preferred dienes include 1,6-heptadiene, 1,7-octadiene, 1,8-nonadiene, 1,9-decadiene, 1,10-undecadiene, 1,11- dodecadiene, 1 , 12-tri decadiene, 1 , 13-tetradecadiene, and low molecular weight poly butadienes (Mw less than 1000 g/mol). Preferred cyclic dienes include cyclopentadiene, vinylnorbomene, norbomadiene, ethybdene norbomene, divinylbenzene, dicyclopentadiene, or higher ring containing diolefms with or without substituents at various ring positions.

In an exemplary embodiment, one or more dienes are present in the polyethylene at up to 10 wt%, preferably at 0.00001 wt% to 2 wt%, preferably 0.002 wt% to 1 wt%, even more preferably 0.003 wt% to 0.5 wt%, based upon the total weight of the polyethylene. In some embodiments, diene is added to the polymerization in an amount of from an upper limit of 500 ppm, 400 ppm, or 300 ppm to a lower limit of 50 ppm, 100 ppm, or 150 ppm.

Preferred ethylene copolymers useful herein are preferably a copolymer comprising at least 50 wt% ethylene and having up to 50 wt%, preferably 1 wt% to 35 wt%, even more preferably 1 wt% to 6 wt% of a C3 to C20 comonomer, preferably a C4 to Cx comonomer, preferably hexene or octene, based upon the weight of the copolymer. Preferably these polymers are metallocene polyethylenes (mPEs).

Useful mPE homopolymers or copolymers may be produced using mono- or bis- cyclopentadienyl transition metal catalysts in combination with an activator of alumoxane and/or a non-coordinating anion in solution, slurry, high pressure or gas phase. The catalyst and activator may be supported or unsupported and the cyclopentadienyl rings may be substituted or unsubstituted.

In a class of embodiments, the polyethylene in at least one of the inner layers of the MDO film made according to the method described herein may comprise at least one of a first polyethylene and a second polyethylene, both as a polyethylene defined herein, the first polyethylene having a density of about 0.910 to about 0.945 g/cm³, an MI, I2_.16, of about 0.1 to about 15 g/10 min, an MWD of about 2.5 to about 5.5, and an MIR, I21_.6/I2_.16, of about 25 to about 100; the second polyethylene having a density of about 0.910 to about 0.940 g/cm³, an MI, I2_.16, of about 0.1 to about 15 g/10 min, an MWD of about 1.5 to about 5.5, and an MIR, I21_.6/I2_.16, of about 10 to about 25.

In various embodiments, the first polyethylene may have one or more of the following properties:

(a) a density (sample prepared according to ASTM D-4703, and the measurement according to ASTM D-1505) of about 0.910 to about 0.945 g/cm³, or about 0.920 to about 0.940 g/cm³;

(b) an MI (U_.ie, ASTM D-1238, 2.16 kg, 190°C) of about 0.1 to about 15 g/10 min, or about 0.1 to about 10 g/10 min, or about 0.1 to about 5 g/10 min;

(c) an MIR (I21.6 (190°C, 21.6 kg)/l2_.i6 (190°C, 2.16 kg)) of greater than 25 to about 100, or greater than 30 to about 90, or greater than 35 to about 80;

(d) a composition distribution breadth index (CDBI) of greater than about 50%, or greater than about 60%, or greater than 75%, or greater than 85%; the CDBI may be determined using techniques for isolating individual fractions of a sample of the resin. The preferred technique is Temperature Rising Elution Fraction (“TREF”), as described in Wild, et al, J. Poly. Sci., Poly. Phys. Ed., Vol. 20, p. 441 (1982), which is incorporated herein for purposes of U.S. practice;

(e) a molecular weight distribution (MWD) or (M_w/M_n) of about 2.5 to about 5.5;

MWD is measured using a gel permeation chromatograph (“GPC”) on a Waters 150 gel permeation chromatograph equipped with a differential refractive index (“DRI”) detector and a Chromatix KMX-6 on line light scattering photometer. The system is used at 135°C with 1, 2, 4-tri chlorobenzene as the mobile phase using Shodex (Showa Denko America, Inc.) polystyrene gel columns 802, 803, 804, and 805. This technique is discussed in“Liquid Chromatography of Polymers and Related Materials III,” J. Cazes editor, Marcel Dekker, 1981, p. 207, which is incorporated herein by reference. Polystyrene is used for calibration. No corrections for column spreading are employed; however, data on generally accepted standards, e.g., National Bureau of Standards Polyethylene 1484 and anionically produced hydrogenated polyisoprenes (alternating ethylene-propylene copolymers) demonstrate that such corrections on MWD are less than 0.05 units. M_w/M_n is calculated from elution times. The numerical analyses are performed using the commercially available Beckman/CIS customized LALLS software in conjunction with the standard Gel Permeation package. Reference to M_w/M_n implies that the M_w is the value reported using the LALLS detector and M_n is the value reported using the DRI detector described above; and/or

(1) a branching index (“g”) of about 0.5 to about 0.97, or about 0.7 to about 0.95. Branching Index is an indication of the amount of branching of the polymer and is defined as g'=[Rg]¾r/[Rg]²/m.“Rg” stands for Radius of Gyration, and is measured using a Waters 150 gel permeation chromatograph equipped with a Multi-Angle Laser Light Scattering (“MALLS”) detector, a viscosity detector and a differential refractive index detector. | Rg |/„ is the Radius of Gyration for the branched polymer sample and | Rg|_/„,” is the Radius of Gyration for a linear polymer sample.

The first polyethylene is not limited by any particular method of preparation and may be formed using any process known in the art. For example, the first polyethylene may be formed using gas phase, solution, or slurry processes.

In one embodiment, the first polyethylene is formed in the presence of a Ziegler-Natta catalyst. In another embodiment, the first polyethylene is formed in the presence of a single site catalyst, such as a metallocene catalyst (such as any of those described herein). Particularly useful catalyst systems include supported dimethylsilyl bis(tetrahydroindenyl) zirconium dichloride. Polyethylene polymers useful as the first polyethylene in this invention include those disclosed in U.S. Patent No. 6,476,171, which is hereby incorporated by reference for this purpose, and include those commercially available from ExxonMobil Chemical Company in Houston, Texas, such as those sold under the trade designation ENABLE™.

In various embodiments, the second polyethylene may have one or more of the following properties: (a) a density (sample prepared according to ASTM D-4703, and the measurement according to ASTM D-1505) of about 0.910 to 0.940 g/cm³, or about 0.912 to about 0.935 g/cm³;

(b) an MI (I2_.16, ASTM D-1238, 2.16 kg, 190°C) of about 0.1 to about 15 g/10 min, or about 0.5 to about 10 g/10 min, or about 1 to about 5 g/10 min;

(c) an MIR (I21.6 (190°C, 21.6 kg)/l2_.i6 (190°C, 2.16 kg)) of about 10 to about 25, or about 15 to about 20;

(d) an CDBI (measured according to the procedure disclosed herein) of up to about 85%, or up to about 75%, or about 5 to about 85%, or 10 to 75%. The CDBI may be determined using techniques for isolating individual fractions of a sample of the resin. The preferred technique is Temperature Rising Elution Fraction (“TREF”), as described in Wild, et al, J. Poly. Sci., Poly. Phys. Ed., Vol. 20, p. 441 (1982), which is incorporated herein for purposes of U.S. practice;

(e) an MWD (measured according to the procedure disclosed herein) of about 1.5 to about 5.5; and/or

(1) a branching index (“g”, determined according to the procedure described herein) of about 0.9 to about 1.0, or about 0.96 to about 1.0, or about 0.97 to about 1.0.

The second polyethylene is not limited by any particular method of preparation and may be formed using any process known in the art. For example, the second polyethylene may be formed using gas phase, solution, or slurry processes.

In one embodiment, the second polyethylene is formed in the presence of a metallocene catalyst. For example, the second polyethylene may be an mPE produced using mono- or bis- cyclopentadienyl transition metal catalysts in combination with an activator of alumoxane and/or a non-coordinating anion in solution, slurry, high pressure or gas phase. The catalyst and activator may be supported or unsupported and the cyclopentadienyl rings may be substituted or unsubstituted. mPEs useful as the second polyethylene include those commercially available from ExxonMobil Chemical Company in Houston, Texas, such as those sold under the trade designation EXCEED™.

In an exemplary embodiment, at least one of the inner layers of the MDO film made according to the method described herein may further comprise a third polyethylene (as a polyethylene defined herein) having a density of at least about 0.945 g/cm³, preferably about 0.945 g/cm³ to about 0.965 g/cm³. The third polyethylene is typically prepared with either Ziegler-Natta or chromium-based catalysts in slurry reactors, gas phase reactors, or solution reactors. Polyethylene polymers useful as the third polyethylene in this invention include those commercially available from ExxonMobil Chemical Company in Houston, Texas, such as HDPE.

In another class of embodiments, the polyethylene in at least one of the core layer and the two outer layers of the MDO film made according to the method described herein may comprise a fourth polyethylene, the fourth polyethylene having a density of about 0.910 to about 0.945 g/cm³, an MI, I2_.16, of about 0.1 to about 15 g/10 min, an MWD of about 2.5 to about 5.5, and an MIR, I21_.6/I2_.16, of about 25 to about 100. In various embodiments, the fourth polyethylene may conform to characteristics as set out above for the first polyethylene. The fourth polyethylene may be the same as or different from the first polyethylene. Preferably, the fourth polyethylene is the same as the first polyethylene.

The first, the second, and the third polyethylene polymers, if present in at least one of the inner layers, and the fourth polyethylene, if present in at least one of the core layer and the two outer layers of the MDO film made according to the method described herein, may each be optionally in a blend with one or more other polymers, such as polyethylenes defined herein, which blend is referred to as polyethylene composition. In particular, the polyethylene compositions described herein may be physical blends or in situ blends of more than one type of polyethylene or compositions of polyethylenes with polymers other than polyethylenes where the polyethylene component is the majority component, e.g., greater than 50 wt% of the total weight of the composition.

In one embodiment, the two outer layers, the core layer, and the two inner layers of the MDO film made according to the method described herein may each comprise at least about 50 wt% of a polyethylene having a density of about 0.910 to about 0.945 g/cm³, a melt index (MI), I2_.16, of about 0.1 to about 15 g/10 min, a molecular weight distribution (MWD) of about 1.5 to about 5.5, and a melt index ratio (MIR), I21_.6/I2_.16, of about 10 to about 100. The polyethylene may be present in each of the above layers in an amount of, for example, about 50 wt%, about 55 wt%, about 60 wt%, about 65 wt%, about 70 wt%, about 75 wt%, about 80 wt%, about 85 wt%, about 90 wt%, about 95 wt%, or about 100 wt%, or in the range of any combination of the values recited herein, based on total weight of polymer in the layer. In an exemplary embodiment where the polyethylene in at least one of the inner layers comprises at least one of the first polyethylene described herein and the second polyethylene described herein, the first polyethylene and the second polyethylene are present in a total amount of at least about 50 wt%, for example, about 50 wt%, about 55 wt%, about 60 wt%, about 65 wt%, about 70 wt%, about 75 wt%, about 80 wt%, about 85 wt%, about 90 wt%, about 95 wt%, about 100 wt%, or in the range of any combination of the values recited herein, based on total weight of polymer in the core layer. In another exemplary embodiment, the polyethylene in at least one of the core layer and the two outer layers is present in an amount of from about 80 to about 100 wt%, for example, about 80 wt%, about 82 wt%, about 84 wt%, about 86 wt%, about 90 wt%, about 92 wt%, about 94 wt%, about 96 wt%, about 98 wt%, about 100 wt%, or anywhere between any combination of the values recited herein, based on total weight of polymer in the layer.

In a class of embodiments, in addition to polyethylene as described above, the MDO film of the present invention may further comprise other polymers, including without limitation other polyolefins, polar polymers, and cationic polymers, in any layer of the MDO film.

Film Structures

The MDO film of the present invention may further comprise additional layer(s), which may be any layer typically included in multilayer film constructions. For example, the additional layer(s) may be made from:

1. Polyolefins. Preferred polyolefins include homopolymers or copolymers of C2 to C40 olefins, preferably C2 to C20 olefins, preferably a copolymer of an a-olefm and another olefin or a-olefm (ethylene is defined to be an a-olefm for purposes of this invention). Preferably homopolyethylene, homopolypropylene, propylene copolymerized with ethylene and/or butene, ethylene copolymerized with one or more of propylene, butene or hexene, and optional dienes. Preferred examples include thermoplastic polymers such as ultra-low density polyethylene, very low density polyethylene, linear low density polyethylene, low density polyethylene, medium density polyethylene, high density polyethylene, polypropylene, isotactic polypropylene, highly isotactic polypropylene, syndiotactic polypropylene, random copolymer of propylene and ethylene and/or butene and/or hexene, elastomers such as ethylene propylene rubber, ethylene propylene diene monomer rubber, neoprene, and compositions of thermoplastic polymers and elastomers, such as, for example, thermoplastic elastomers and rubber toughened plastics.

2. Polar polymers. Preferred polar polymers include homopolymers and copolymers of esters, amides, acetates, anhydrides, copolymers of a C2 to C20 olefin, such as ethylene and/or propylene and/or butene with one or more polar monomers, such as acetates, anhydrides, esters, alcohol, and/or acrylics. Preferred examples include polyesters, polyamides, ethylene vinyl acetate copolymers, and polyvinyl chloride.

3. Cationic polymers. Preferred cationic polymers include polymers or copolymers of geminally disubstituted olefins, a-heteroatom olefins and/or styrenic monomers.

Preferred geminally disubstituted olefins include isobutylene, isopentene, isoheptene, isohexane, isooctene, isodecene, and isododecene. Preferred a-heteroatom olefins include vinyl ether and vinyl carbazole, preferred styrenic monomers include styrene, alkyl styrene, para-alkyl styrene, a-methyl styrene, chloro-styrene, and bromo-para-methyl styrene. Preferred examples of cationic polymers include butyl rubber, isobutylene copolymerized with para methyl styrene, polystyrene, and poly-a-methyl styrene.

4. Miscellaneous. Other preferred layers can be paper, wood, cardboard, metal, metal foils (such as aluminum foil and tin foil), metallized surfaces, glass (including silicon oxide (SiOx) coatings applied by evaporating silicon oxide onto a film surface), fabric, spunbond fibers, and non-wovens (particularly polypropylene spunbond fibers or non-wovens), and substrates coated with inks, dyes, pigments, and the like.

In particular, the MDO film made according to the method described herein can also include layers comprising materials such as ethylene vinyl alcohol (EVOH), polyamide (PA), polyvinylidene chloride (PVDC), or aluminium, so as to obtain barrier performance for the film where appropriate.

The thickness of the MDO films may range from 10 to 200 pm in general and is mainly determined by the intended use and properties of the film. Conveniently, the MDO film can have a thickness ranging from 10 to 110 pm. The lower limit of the thickness after MD orientation can be 10, 15, 20, 25, 30, 40, 50, 60, 70, or 80 pm. The upper limit of the thickness after MD orientation can be 110, 100, 80, 70, 60, 50, 40, 30, 25, or 20 pm. Any combination of lower and upper limits, where upper limit is > lower limit, should be considered to be disclosed by the above limits, e.g., 10 to 100 pm, 10 to 50 pm, 15 to 40 pm, 20 to 30 pm, 30 to 90 pm, 40 to 110 pm, 40 to 100 pm, etc. In certain exemplary embodiments, the MDO film has a thickness of no more than about 60 pm, preferably 40 to 60 pm.

Preferably, the thickness ratio between one of the outer layers and the inner layer at the same side of the core layer of the MDO film made according to the method described herein is from about 1:2 to about 1:6, for example, about 1 :2, about 1 :3, about 1:4, about 1:5, about 1 :6, or in the range of any combination of the values recited herein.

In an exemplary embodiment, the MDO film made according to the method described herein may have an A/B/X/C/D structure, wherein A and D layers are the two outer layers, respectively, and X represents the core layer, and B and C layers are the two inner layers between the core layer and each outer layer, respectively. Suitably one or both the outer layers are a skin layer forming one or both film surfaces and can serve as a lamination skin (the surface to be adhered to a sealant film or a substrate film) or a sealable skin (the surface to form a seal).

Preferably, one of the outer layers serves as the lamination skin to be attached to a sealant film. Preferably, the MDO film made according to the method described herein is symmetrical. More preferably, the layers that are mirror images to each other relative to the core layer are extruded from a single extruder. The composition of A and D layers may be the same or different, but conform to the limitations set out herein for the sealant. Preferably, the A and D layers are identical. The composition of B and C layers may be the same or different, but conform to the limitations set out herein for the sealant. Preferably, the B and C layers are identical.

Film Properties and Applications

The MDO films of the present invention may be adapted to form flexible packaging laminate films, including stand-up pouches, as well as a wide variety of other applications, such as cling film, low stretch film, non-stretch wrapping film, pallet shrink, over-wrap, agricultural, and collation shrink film. The film structures that may be used for bags are prepared such as sacks, trash bags and liners, industrial liners, produce bags, and medium duty bags. The film may be used in flexible packaging, food packaging, e.g., fresh cut produce packaging, frozen food packaging, bundling, packaging and unitizing a variety of products.

Desirably, the MDO film made according to the method described herein may have at least one of the following properties: (i) an average elongation at break of at most about 40%; and (ii) an average absolute modulus of at least about 70 N/mm.

Coextrusion Processes

The present invention generally relates to blown film extrusion and especially coextrusion methods. Generally, the term coextrusion refers to an extrusion process where at least two same or different molten polymer compositions are extruded and bonded together in a molten condition in the die exit. A bubble is blown up by internal air supply. Films are formed, while cooling progressively, after a complex interplay of stretching, orientation and crystallization until the film reaches a take-up device enclosing the top of the bubble, such as a pair of pinch rollers, and the bubble is split into two parts followed by being edge trimmed and wound around two winders.

In one embodiment of the invention, the MDO film made according to the method described herein is formed by a blown extrusion line. For example, the polymer composition formulated as described herein can be extruded in a molten state through an annular die and then blown and cooled to form a tubular, blown film, which can then be axially slit and unfolded to form a flat film. As a specific example, blown films can be prepared as follows. The polymer composition is introduced into the feed hopper of an extruder, such as a 50 mm extruder that is water-cooled, resistance heated, and has an L/D ratio of 30: 1. The film can be produced using a 28 cm die with a 1.4 mm die gap, along with a dual air ring and internal bubble cooling. The film is extruded through the die into a film cooled by blowing air onto the surface of the film. The film is drawn from the die typically forming a cylindrical film that is cooled, collapsed and, optionally, subjected to a desired auxiliary process, such as slitting, treating, sealing, or printing. Typical melt temperatures are from about 180°C to about 230°C. Blown film rates are generally from about 3 to about 25 kilograms per hour per inch (about 4.35 to about 26.11 kilograms per hour per centimeter) of die circumference. The finished film can be wound into rolls for later processing. A particular blown film process and apparatus suitable for forming films according to embodiments of the present invention is described in U.S. Patent No. 5,569,693. Of course, other blown film forming methods can also be used.

In blown film extrusion, the film may be pulled upwards by, for example, pinch rollers after exiting from the die and is simultaneously inflated and stretched transversely sideways to an extent that can be quantified by the blow up ratio (BUR). The inflation provides the transverse direction (TD) stretch, while the upwards pull by the pinch rollers provides a machine direction (MD) stretch. As the polymer cools after exiting the die and inflation, it crystallizes and a point is reached where crystallization in the film is sufficient to prevent further MD or TD orientation.

Variables in this process that determine the ultimate film properties include the die gap, the BUR, the take up speed and the frost line height. Certain factors tend to limit production speed and are largely determined by the polymer rheology including the shear sensitivity which determines the maximum output and the melt tension which limits the bubble stability, BUR and take up speed.

In an exemplary embodiment, the MDO film made according to the method described herein is subject to machine direction orientation (MD orientation). Some methods of producing a polymer film suitable for MD orientation subsequent to the film making may be blown and cast film methods. Particular blown film methods include extruding the polyethylene composition through an annular die to form an extruded tube of molten material to provide the tube with a tube diameter which is substantially the annular die diameter. At the same time, continuously extruding the tube, expanding the tube, downstream of said annular die, to attenuate the walls thereof to form the tube of molten material into a bubble of a bubble diameter which exceeds (i) the annular die diameter and (ii) the tube diameter. The bubble has a frost line which comprises a demarcation line between the molten material and crystalline film. Increased stretch ratio reduces final film thickness. The film may then be then sent to a second roller for cooling on the other side. Typically, although not necessarily, the film passes through a system of rollers and is wound onto a roll. Most flat dies are of T-slot or coat hanger designs, which contain a manifold to spread the flowing polymer across the width of the die, followed downstream by alternating narrow and open slits to create the desired flow distribution and pressure drop.

Films suitable for MD orientation have a gauge (or thickness as defined above) before MD orientation ranging from 10 to 130 pm. The lower limit of film gauge before MD orientation can be 10, 15, 20, 25, 30, 40, 45, 50, 60, 70, 80, or 90 pm. The upper limit on gauge before MD orientation can be 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 35, 30, 25, or 20 pm. Any combination of lower and upper limits (where upper limit > lower limit) should be considered to be disclosed by the above limits, e.g., 10 to 130 pm, 20 to 130 pm, 30 to 130 pm, 40 to 130 pm, 50 to 130 pm, etc. In certain exemplary embodiments, the film before MD orientation has a gauge of 50 to 130 pm.

This application is directed to orientation of polymer films formed by blown processes after the film polymer is no longer in its molten state and has solidified having a crystalline structure. MD orientation can be achieved by any known MD orientation process either in-line or off-line with the extrusion on blown films. That is, the film produced by blown process can either be temporarily stored (off-line) before MD orientation or can be fed directly (in-line) to the MD orientation equipment.

Orientation methods may be with or without heat added. Cold drawing or stretching are suitable methods. When the film is heated, no case will the polymer be heated above its melting temperature.

A preferred MD orientation process can consist of heating the film to an orientation temperature, preferably using a set of temperature controlled rollers. The orientation temperature may be up to the polymer’s melt temperature. Next the heated film is fed into a slow drawing roll with a nip roller, which has the same rolling speed as the heating rollers. The film then enters a fast drawing roller having a speed that is, for example, 1.5 to 12 times faster than the slow draw roll, which effectively orients (stretches) the film on a continuous basis. The oriented film then enters annealing thermal rollers, which allow stress relaxation by holding the film at an elevated temperature for a period of time. The annealing temperature is preferably within, or slightly below (e.g., 10 to 20°C below but not lower than room temperature, for purposes here room temperature is 23 °C), the same temperature range as used for stretching. Finally, the film is cooled through cooling rollers to an ambient temperature to produce a machine direction oriented (MDO) film.

In an exemplary embodiment, the MDO film made according to the method described herein is an MDO film formed with a stretch ratio of from about 4.0 to about 5.0, more preferably from about 4.2 to about 4.8.

The inventive method for making an MDO film is developed based on a discovery that machine direction orientation of a tubular film comprising in each layer at least 50 wt% of a polyethylene as described herein prepared by a blown coextrusion line can create inseparable inner surfaces of the blown bubble, thus leading to one single film structure exiting the MDO unit. This MDO film can be subsequently wound by a single winder after edge trimming without slitting, and the two layers in contact with each other by the two inner surfaces of the blown bubble turn into the core layer of the final MDO film. The inventive method can contribute to advantages of the so-obtained MDO film as substrate over the conventional non- recyclable substrates in tensile performance.

Suitably, the MDO film of the present invention can be used for a substrate film to form laminate structure. The laminate structure can be prepared by laminating a sealant to a substrate comprising the MDO film made according to the method described herein via respective lamination skins using any process known in the art, including solvent based adhesive lamination, solvent less adhesive lamination, extrusion lamination, heat lamination, etc.

In one preferred embodiment, a method for making an MDO film by a blown extrusion line comprising three extruders, comprising the steps of: (a) extruding a core layer from a first extruder; (b) extruding two outer layers from a second extruder, wherein the core layer is between the two outer layers; (c) extruding two inner layers from a third extruder, wherein each inner layer is between the core layer and each outer layer; (d) forming a film comprising the layers in steps (a), (b), and (c); (e) subjecting the film in step (d) to machine direction orientation; and (1) forming an MDO film without a slitting step prior to winding; wherein each of the inner layers comprises a first polyethylene, a second polyethylene, and a third polyethylene, the first polyethylene having a density of about 0.910 to about 0.945 g/cm³, an MI, I2_.16, of about 0.1 to about 15 g/10 min, an MWD of about 2.5 to about 5.5, and an MIR, I21_.6/I2_.16, of about 25 to about 100; the second polyethylene having a density of about 0.910 to about 0.940 g/cm³, an MI, I2_.16, of about 0.1 to about 15 g/10 min, an MWD of about 1.5 to about 5.5, and an MIR, I21_.6/I2_.16, of about 10 to about 25; the third polyethylene having a density of at least about 0.945 g/cm³; wherein the first polyethylene and the second polyethylene are present in a total amount of at least about 50 wt%, based on total weight of polymer in the core layer; wherein each of the core layer and the two outer layers comprises about 100 wt% of the first polyethylene, based on total weight of polymer in the layer; wherein the MDO film is formed at a stretch ratio of from about 4.0 to about 5.0 and the thickness ratio between the outer layer and the inner layer at the same side of the core layer is from about 1 :4; wherein the MDO film has at least one of the following properties: (i) an average elongation at break of at most about 40%; and (ii) an average absolute modulus of at least about 70 N/mm. In one desirable embodiment, the two outer layers are identical. In another desirable embodiment, the two inner layers are identical.

EXAMPLES

The present invention, while not meant to be limited by, may be better understood by reference to the following examples and table.

Example 1

An inventive MDO film of 54 pm with an A/B/X/C/D structure at a layer thickness ratio of 1 :4:2:4: 1, referred to as Sample 1, was prepared on a coextrusion blown film line according to the method described herein, including a step of MD orientation at a stretch ratio of 4.7. Polyethylene products used in the sample include: PE-1 polymer (as the first and the fourth polyethylene described herein) (density: 0.940 g/cm³; MI: 0.25 g/10 min; MIR: >60; MWD: ~4) (ExxonMobil Chemical Company, Houston, Texas, USA), PE-2 polymer (as the second polyethylene described herein) (density: 0.918 g/cm³; MI: 1.0 g/10 min; MIR: 16) (ExxonMobil Chemical Company, Houston, Texas, USA), and PE-3 polymer (as the third polyethylene described herein) (density: 0.961 g/cm³; MI: 0.70 g/10 min) (ExxonMobil Chemical Company, Houston, Texas, USA).

A schematic representation of film structures for Sample 1 is shown in the Figure. The outlined five-layer distribution of Sample 1 in the Figure indicates that, by applying MD orientation to a tubular film formulated as set out herein, the two inner surfaces of the blown bubble can be inseparable from each other to form one film structure.

Example 2

Example 2 illustrates the effect of MD orientation on tensile properties of the inventive MDO film of Sample 1, as reflected by elongation at break and 1% Secant modulus, in comparison with three comparative samples, Samples 2-4, of a single layer structure made of biaxially oriented polypropylene (BOPP), oriented polyamide (OP A), and oriented polyester (OPET), respectively.

Tensile properties of the film samples were measured by a method which is based on

ASTM D882 with static weighing and a constant rate of grip separation using a Zwick 1445 tensile tester with a 200N. Since rectangular shaped test samples were used, no additional extensometer was used to measure extension. The nominal width of the tested film sample is 15 mm and the initial distance between the grips is 50 mm. The film samples were conditioned for at least 40 hours at a temperature of 23 ± 2°C and a relative humidity of 50 ± 10% prior to the test. Elongation at break is defined as the strain at the corresponding break point, expressed as a change in length per unit of original length multiplied with a factor 100 (%). A pre-load of 0. IN was used to compensate for the so called toe region at the origin of the stress-strain curve. 1% Secant modulus is calculated by drawing a tangent through two well defined points on the stress-strain curve. The constant rate of separation of the grips is 5 mm/min upon reaching the pre-load, 5 mm/min to measure 1% Secant modulus (up to 1% strain). The reported value corresponds to the stress at 1% strain (with x correction). The result is expressed as load per unit area (MPa). The value is an indication of the film stiffness in tension. The 1% secant modulus is used for thin film and sheets as no clear proportionality of stress to strain exists in the initial part of the curve. The film samples were tested in both MD and TD for elongation at break and 1% Secant modulus and test results are expressed by values defined as follows with MD and TD readings:

Average Elongation at Break [%] = (elongation at break in MD + elongation at break in TD)/2;

Average Absolute Modulus (N/mm) = {(1% Secant modulus in MD + 1% Secant modulus in TD)/2}[MPa] x (film thickness/1000)[mm].

Structure-wise formulation (based on total weight of polymer the layer) and film thickness of the samples, accompanied by test results therefore, are depicted in the Table.

It can be seen from the Table that the inventive sample prepared by the inventive method featuring MD orientation and introduction of the polyethylene described herein at a particular amount in each layer can outperform the comparative samples made of conventional non-recyclable materials by reduced elongation and increased stiffness. Therefore, without being bound by theory, by manipulating MD orientation and formulation of film layers with polyethylene resins, sustainability provided by recyclable substrates in step with property improvement for laminates as desired by the packaging industry can be expected.

Table: Structure-wise formulations (wt%), layer thickness, and test results of Samples

1-4 in Example 2

All documents described herein are incorporated by reference herein, including any priority documents and/or testing procedures. When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated. As is apparent from the foregoing general description and the specific embodiments, while forms of the invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited thereby.

Claims

CLAIMS What is claimed is:

1. A method for making a machine direction oriented (MDO) film by a blown extrusion line comprising three extruders, comprising the steps of:

(a) extruding a core layer from a first extruder;

(b) extruding two outer layers from a second extruder, wherein the core layer is between the two outer layers;

(c) extruding two inner layers from a third extruder, wherein each inner layer is between the core layer and each outer layer;

(d) forming a film comprising the layers in steps (a), (b), and (c);

(e) subjecting the film in step (d) to machine direction orientation; and

(1) forming an MDO film without a slitting step prior to winding;

wherein each layer comprises at least about 50 wt% of a polyethylene, based on total weight of polymer in the layer, the polyethylene having a density of about 0.910 to about 0.945 g/cm³, a melt index (MI), I2_.16, of about 0.1 to about 15 g/10 min, a molecular weight distribution (MWD) of about 1.5 to about 5.5, and a melt index ratio (MIR), I21_.6/I2_.16, of about 10 to about 100.

2. The method of claim 1, wherein the MDO film has at least one of the following properties: (i) an average elongation at break of at most about 40%; and (ii) an average absolute modulus of at least about 70 N/mm.

3. The method of claim 1 or claim 2, wherein the MDO film is formed at a stretch ratio of from about 4.0 to about 5.0.

4. The method of claim 1 or any one of claims 2-3, wherein the MDO film has a thickness of no more than about 60 pm.

5. The method of claim 1 or any one of claims 2-4, wherein the thickness ratio between the outer layer and the inner layer at the same side of the core layer is from about 1 :2 to about

1 :6.

6 The method of claim 1 or any one of claims 2-5, wherein the MDO film is symmetrical.

7. The method of claim 6, wherein the layers that are mirror images to each other relative to the core layer are extruded from a single extruder.

8. The method of claim 1 or any one of claims 2-7, wherein the polyethylene in at least one of the inner layers comprises at least one of a first polyethylene and a second polyethylene, the first polyethylene having a density of about 0.910 to about 0.945 g/cm³, an MI, I2_.16, of about 0.1 to about 15 g/10 min, an MWD of about 2.5 to about 5.5, and an MIR, I21_.6/I2_.16, of about 25 to about 100; the second polyethylene having a density of about 0.910 to about 0.940 g/cm³, an MI, I2_.16, of about 0.1 to about 15 g/10 min, an MWD of about 1.5 to about 5.5, and an MIR, I21_.6/I2_.16, of about 10 to about 25.

9. The method of claim 1 or any one of claims 2-8, wherein at least one of the inner layers further comprises a third polyethylene, the third polyethylene having a density of at least about 0.945 g/cm³.

10. The method of claim 1 or any one of claims 2-9, wherein the polyethylene in at least one of the core layer and the two outer layers is present in an amount of from about 80 to about 100 wt%, based on total weight of polymer in the layer.

11. The method of claim 1 or any one of claims 2-10, wherein the polyethylene in at least one of the core layer and the two outer layers comprises a fourth polyethylene, the fourth polyethylene having a density of about 0.910 to about 0.945 g/cm³, an MI, I2_.16, of about 0.1 to about 15 g/10 min, an MWD of about 2.5 to about 5.5, and an MIR, I21_.6/I2_.16, of about 25 to about 100.

12. The method of claim 11, wherein the fourth polyethylene is the same as the first polyethylene.

13. A method for making an MDO film by a blown extrusion line comprising three extruders, comprising the steps of:

(a) extruding a core layer from a first extruder;

(b) extruding two outer layers from a second extruder, wherein the core layer is between the two outer layers; (c) extruding two inner layers from a third extruder, wherein each inner layer is between the core layer and each outer layer;

(d) forming a film comprising the layers in steps (a), (b), and (c);

(e) subjecting the film in step (d) to machine direction orientation; and

(1) forming an MDO film without a slitting step prior to winding;

wherein each of the inner layers comprises a first polyethylene, a second polyethylene, and a third polyethylene, the first polyethylene having a density of about 0.910 to about 0.945 g/cm³, an MI, I2_.16, of about 0.1 to about 15 g/10 min, an MWD of about 2.5 to about 5.5, and an MIR, I21_.6/I2_.16, of about 25 to about 100; the second polyethylene having a density of about 0.910 to about 0.940 g/cm³, an MI, I2_.16, of about 0.1 to about 15 g/10 min, an MWD of about 1.5 to about 5.5, and an MIR, I21_.6/I2_.16, of about 10 to about 25; the third polyethylene having a density of at least about 0.945 g/cm³; wherein the first polyethylene and the second polyethylene are present in a total amount of at least about 50 wt%, based on total weight of polymer in the core layer;

wherein each of the core layer and the two outer layers comprises about 100 wt% of the first polyethylene, based on total weight of polymer in the layer;

wherein the MDO film is formed at a stretch ratio of from about 4.0 to about 5.0 and the thickness ratio between the outer layer and the inner layer at the same side of the core layer is from about 1 :4;

wherein the MDO film has at least one of the following properties: (i) an average elongation at break of at most about 40%; and (ii) an average absolute modulus of at least about 70 N/mm.

14. The method of claim 13, wherein the two outer layers are identical.

15. The method of claim 13 or claim 14, wherein the two inner layers are identical.

16. A machine direction oriented (MDO) film, comprising two outer layers, a core layer between the two outer layers, and two inner layers each between the core layer and each outer layer, wherein each layer comprises at least about 50 wt% of a polyethylene, based on total weight of polymer in the layer, the polyethylene having a density of about 0.910 to about 0.945 g/cm³, a melt index (MI), I2_.16, of about 0.1 to about 15 g/10 min, a molecular weight distribution (MWD) of about 1.5 to about 5.5, and a melt index ratio (MIR), I21_.6/I2_.16, of about 10 to about 100; wherein the MDO film is prepared by a blown extrusion line comprising three extruders, comprising the steps of:

(a) extruding the core layer from a first extruder;

(b) extruding the two outer layers from a second extruder;

(c) extruding the two inner layers from a third extruder;

(d) forming a film comprising the layers in steps (a), (b), and (c);

(e) subjecting the film in step (d) to machine direction orientation; and

(f) forming the MDO film without a slitting step prior to winding.

17. The MDO film of claim 16, wherein the MDO film has at least one of the following properties: (i) an average elongation at break of at most about 40%; and (ii) an average absolute modulus of at least about 70 N/mm.

18. The MDO film of claim 16 or claim 17, wherein the MDO film is formed at a stretch ratio of from about 4.0 to about 5.0.

19. The MDO film of claim 16, 17, or 18, wherein the MDO film has a thickness of no more than about 60 pm.

20. A laminate comprising a substrate and a sealant, wherein the substrate comprises the

MDO film of any one of claims 16 to 19 or made according to the method of any one of claims 1 to 15.