WO2012106025A1 - Coextruded films and processes for making such films - Google Patents

Coextruded films and processes for making such films Download PDF

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Publication number
WO2012106025A1
WO2012106025A1 PCT/US2011/062994 US2011062994W WO2012106025A1 WO 2012106025 A1 WO2012106025 A1 WO 2012106025A1 US 2011062994 W US2011062994 W US 2011062994W WO 2012106025 A1 WO2012106025 A1 WO 2012106025A1
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equal
greater
film
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μιη
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PCT/US2011/062994
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French (fr)
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Mario Bastiaens
Michael J. VINCK
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Exxonmobil Chemical Patents Inc.
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Priority to US61/437,986 priority
Application filed by Exxonmobil Chemical Patents Inc. filed Critical Exxonmobil Chemical Patents Inc.
Publication of WO2012106025A1 publication Critical patent/WO2012106025A1/en

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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00Layered products comprising a layer of synthetic resin
    • B32B27/32Layered products comprising a layer of synthetic resin comprising polyolefins
    • B32B27/327Layered products comprising a layer of synthetic resin comprising polyolefins comprising polyolefins obtained by a metallocene or single-site catalyst
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2439/00Containers; Receptacles
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2605/00Vehicles
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2605/00Vehicles
    • B32B2605/003Interior finishings
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00Layered products comprising a layer of synthetic resin
    • B32B27/32Layered products comprising a layer of synthetic resin comprising polyolefins

Abstract

A multilayer blown film having at least one outer layer comprising a linear polyethylene having a density greater than or equal to 0.921 g/cm3; and a core layer having a metallocene linear polyethylene having a density greater than or equal to 0.927 g/cm3, a melt index ratio between 35 and 60 and a melt index of 0.4 g/10 min or less and a high density polyethylene; wherein the core layer has a density greater than the density of the at least one outer layer. Such a film having a high-throughput, high-clarity "HTC effect" is also disclosed. A process for making such films in a high throughput environment is also disclosed.

Description

COEXTRUDED FILMS AND PROCESSES FOR MAKING SUCH FILMS

PRIORITY CLAIM TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application Serial No. 61/437,986 filed January 31, 201 1, the disclosure of which is fully incorporated herein by reference.

FIELD OF INVENTION

[0002] This invention relates to coextruded films, blown film processes for making them and uses of such films in various applications.

BACKGROUND OF INVENTION

[0003] It is desirable for many applications to use transparent films. The acceptability of the transparency can be measured by a haze determination. Films must also extrude well and process well on a fast moving continuous production line.

[0004] Polyethylene is available in many forms. Some forms are capable of providing transparent films having reduced strength and other properties at high production line speeds. Multi-layer films have been developed where the skin layers provide various properties and core layers which meet other requirements such as stiffness and the like.

[0005] However, multi-layer films may have undesirable optical properties which include a high haze level. Numerous attempts have been made to improve the optical properties of such films, yet room for improvement remains. Improvement in the haze or clarity of a film may result in a reduction of properties directed to the processability of the film and/or properties important to a particular end use. Thus, there exists a need in the art for multi-layer films having improved haze characteristics in combination with other film properties.

SUMMARY OF THE INVENTION

[0006] In a first aspect according to the present disclosure, an embodiment of a multilayer blown film comprises at least one outer layer comprising a linear low density polyethylene having a density greater than or equal to 0.921 g/cm3; and a core layer comprising at least about 10 wt% of a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR i .ie @ 190°C) of greater than or equal to about 35 and less than or equal to about 60, and a melt index of less than or equal to about 0.4 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg, and a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3; wherein the core layer has a density greater than the density of the at least one outer layer. [0007] In another aspect according to the present disclosure, an embodiment of a multilayer blown film comprises two "A" skin layers arranged on opposite sides of a "B" core layer in an A/B/A configuration; wherein each of the A layers comprise a linear metallocene polyethylene comprising a copolymer derived from ethylene and one or more C3 to C20 a- olefin comonomers having a density greater than or equal to 0.927 g/cm3, a melt index of less than or equal to 2.2 as determined according to ASTM D1238 at 190°C/2.16 kg and a MIR, I21.6 / I2.i6@ 190°C of less than or equal to about 16; wherein the B layer comprises at least about 10 wt% of a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR, I21.6 / I2.i6@ 190°C) of greater than or equal to 46 and less than or equal to 58 and a melt index of less than or equal to 0.3 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg, and a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3; wherein the B layer has a density greater than the density of the A layer.

[0008] In another aspect according to the present disclosure, an embodiment of a process for producing a multilayer blown film comprises the steps of selecting a first polyethylene comprising a linear low density polyethylene having a density greater than or equal to 0.921 g/cm3; selecting a second polyethylene comprising a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR l21.eJh.i6 @ 190°C) of greater than or equal to about 35 and less than or equal to about 60, and a melt index of less than or equal to about 0.4 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg; selecting a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3; combining the second polyethylene with the high density polyethylene to produce a blend having a density greater than the density of the first polyethylene, wherein the blend comprises at least 10 wt% of the second polyethylene by weight of the blend; extruding the first polyethylene and the blend from a die at a strain rate of greater than or equal to about 0.6 s"1 wherein the first polyethylene forms first and second skin layers, and wherein the blend forms a core layer disposed between the first and second skin layers.

Brief Description of the Drawings

[0009] Figure 1 is a Haze-Thickness plot of selected examples of an embodiment of the present disclosure and examples of an alternative embodiment according to the present disclosure. Detailed Description

[0010] For the purposes of this disclosure, the following definitions will be generally applicable.

[0011] Melt index (MI, I2.i6), reported in grams per 10 minutes (g/lOmin), refers to the melt flow rate measured according to ASTM D-1238, condition E using 2.16 kg @ 190°C.

[0012] High load melt index (I21.6), reported in grams per 10 minutes (g/lOmin), refers to the melt flow rate measured according to ASTM D-1238, condition F using 21.6 kg @ 190°C.

[0013] Melt index ratio (MIR), which is a measure of shear sensitivity, is expressed as a ratio of the high load melt index to the melt index of the polymer (I21.6/I2.16), as determined according to ASTM D-1238, condition F, 21.6 kg @190°C divided by the melt index (MI) of the polymer determined according to ASTM D-1238, condition E, 2.16 kg @190°C. The melt index ratio may be referred to herein as MIR I21.6 / I2.16 @ 190°C, or simply as MIR. The densities are determined herein in the specification and claims according to ASTM D2839/D1505 (LDPE) or ASTM D4703/D1505 (LLDPE, HDPE) or IS01133 (VLDPE).

[0014] As used herein, polyethylene refers to ethylene homopolymers and/or ethylene a- olefin copolymers. By "copolymers" is meant combinations of ethylene and one or more a- olefins. In general, the a-olefin comonomers can be selected from those having 3 to 20 carbon atoms, such as C3-C20 a-olefins or C3-C12 a-olefins. Suitable a-olefin comonomers can be linear or branched or may include two unsaturated carbon-carbon bonds (dienes). Two or more comonomers may be used, if desired. Examples of suitable comonomers include linear C3-C12 a-olefins and a-olefins having one or more C1-C3 alkyl branches or an aryl group. Particularly preferred comonomers are 1-butene, 1-hexene, and 1-octene. Specific comonomer examples include propylene; 1-butene; 3 -methyl- 1-butene; 3, 3 -dimethyl- 1-butene; 1-pentene; 1-pentene with one or more methyl, ethyl, or propyl substituents; 1-hexene; 1-hexene with one or more methyl, ethyl, or propyl substituents; 1-heptene; 1-heptene with one or more methyl, ethyl, or propyl substituents; 1-octene; 1-octene with one or more methyl, ethyl, or propyl substituents; 1-nonene; 1-nonene with one or more methyl, ethyl, or propyl substituents; ethyl, methyl, or dimethyl-substituted 1-decene; 1-dodecene; and styrene. Specifically, the combinations of ethylene with a comonomer may include: ethylene 1-butene; ethylene 1- pentene; ethylene 4-methyl-l-pentene; ethylene 1-hexene; ethylene 1-octene; ethylene decene; ethylene dodecene; ethylene 1-butene 1-hexene; ethylene 1-butene 1-pentene; ethylene 1- butene 4-methyl-l-pentene; ethylene 1-butene 1-octene; ethylene 1-hexene 1-pentene; ethylene 1-hexene 4-methyl-l-pentene; ethylene 1-hexene 1-octene; ethylene 1-hexene decene; ethylene 1-hexene dodecene; ethylene propylene 1-octene; ethylene 1-octene 1-butene; ethylene 1- octene 1-pentene; ethylene 1-octene 4-methyl-l-pentene; ethylene 1-octene 1-hexene; ethylene 1-octene decene; ethylene 1-octene dodecene; combinations thereof and like permutations. It should be appreciated that the foregoing list of comonomers and comonomer combinations are merely exemplary and are not intended to be limiting.

[0015] If a comonomer(s) is used, the ethylene monomer is generally polymerized in a proportion of from 50.0 to 99.9 wt% of monomer, preferably, from 70 to 99 wt% of monomer, and more preferably, from 80 to 98 wt% of monomer, with from 0.1 to 50 wt% of comonomer(s), preferably, from 1 to 30 wt% of comonomer(s), and more preferably, from 2 to 20 wt% of comonomer(s), by total weight of the monomer and comonomer(s). For linear polyethylenes, the actual amount of comonomer(s), comonomer distribution along the polymer backbone, and comonomer branch length will generally define the density range.

[0016] Ethylene based polymers referred to herein include highly branched low density polyethylene (LDPE), which is distinct from linear low density polyethylene (LLDPE) consistent with the understanding of one skilled in the art.

[0017] LDPE may be obtained from ethylene by polymerization using free-radical initiators under high pressure conditions. Accordingly, LDPE may also be referred to in the art as high pressure polyethylene (HPPE). The free radicals trigger the incorporation of chain lengths along the length of a main chain so forming long chain branches, usually by what is known as a back-biting mechanism. The branches vary in length and configuration. LDPE can be described as heterogeneously branched. The polymer chains formed differ significantly and the molecular weight distribution as determined by gel permeation chromatography (GPC) is broad. The average molecular weight can be controlled with a variety of telogens or transfer agents which may incorporate at the chain ends or along the chain. Comonomers may be used such as olefins other than ethylene or minor amounts of olefinically copolymerizable monomers containing polar moieties such as a carbonyl group.

[0018] LDPE is defined for use herein to include a polymer comprising at least 85 mol% of units derived from ethylene which is heterogeneously branched and contains less than 7.5 mol% of units derived from comonomers containing polar moieties such as a carbonyl group, including ethylenically unsaturated esters, e.g., ethylene vinyl acetate, ethylene methyl acrylate, ethylene methacrylic acid, n-butacrylate (EBA) or ethylene acrylic acid.

[0019] Linear ethylene based polymers, which include linear low density polyethylene (LLDPE), are produced using catalytic polymerization mechanisms. Polymerization may be performed with Ziegler-Natta catalysts comprising generally a transition metal component and in most cases an activator or cocatalyst. Monomers, such as ethylene or other olefin comonomers, incorporate principally at the end of the polymer chain. Backbiting mechanisms are substantially absent. The molecular weight distribution (MWD) as measured by GPC Mw/Mn is relatively narrow, which is defined herein as less than 10. Such polymers tend to be more linear and have zero, or low levels of long chain branches. As used herein in the description and claims, references to non-branched linear polyethylene refer to polymers having a melt index ratio (MIR) of less than 30, wherein the MIR is defined as the melt index ratio as determined at 190°C according to ASTM D1238, i.e., I21.6 /I2.i6 @190°C.

[0020] If long chain branches are present in measurable amounts, their length and structure is assumed to be similar and linear. They may be referred to as homogeneously branched linear polyethylene. This term as used herein in the description and claims refers to polymers having an MIR of greater than 35. The molecular weight distribution (MWD, Mw/Mn) for a long chain branched linear polyethylene is less than 6, typically less than 5, with less than 4 indicating a higher level of long chain branching, which is narrow relative to that prevalent for LDPE. Because of the sensitivity of the catalysts to poisoning by polar groups, monomers having polar groups cannot be used. The main comonomers are alpha-olefins.

[0021] Linear polyethylene is defined for use herein to include a polymer comprising at least 65 mol% of ethylene derived units and a balance of units derived from an alpha-olefin having from 3 to 12 carbon atoms which is not branched or, if branched, is homogeneously branched. Generally these polymers have an Mw/Mn as determined by GPC differential refractive index (DRI) as described herein of less than 5.5.

[0022] Linear polyethylene may be sub-divided into different types depending on their density. The main groups are very low density polyethylene (VLDPE), linear low density polyethylene (LLDPE) and high density polyethylene (HDPE). In the general literature the stated density ranges for these polymers may vary. In the specification and claims, VLDPE is defined as a linear polyethylene having a density of less than 0.91 g/cm3; LLDPE is defined as a linear polyethylene having a density of from 0.91 up to 0.94 g/cm3; and HDPE is defined as a linear polymer having a density of above 0.94 g/cm3.

[0023] Linear polyethylene may also be subdivided having regard to the nature of the catalysts system used which influences homogeneity and so the overall properties in processing and properties of the film produced. The prefix "zn" is used in the specification and claims, as in "znLLDPE", to indicate that the catalyst system used titanium as the transition metal component and an aluminum alkyl as cocatalyst. The prefix "m" is used in the specification and claims, as in mLLDPE, to indicate that the transition metal component used was a single site catalyst, which may include a metallocene or other single site catalyst, activated by methods well known for such components, such as alumoxane or a non-coordinating anion; "zn" linear polyethylene types tend to have a greater heterogeneity in terms of molecular weight distribution and composition distribution as compared to "m" linear polyethylene types, as may be determined by suitable fractionation techniques appropriate to the density concerned, such as a measurement of the compositional distribution breadth index (CDBI) or a Crystaf measurement as is known to one of minimal skill in the art.

[0024] As used herein in the description and claims, "zn" linear polyethylene types refer to polyethylenes, analyzable by elution fractionation, having a CDBI of less than 45%, whereas "m" linear polyethylene types refer to polyethylene having a CDBI of greater than 50%, the CDBI being determined as described in WO93/03093 (US5206075). At low densities other fractionation techniques can be used to separate "zn" and "m" types of linear polyethylene.

[0025] In the case of the mLLDPE as described above, preferably hexane extractables are less than 1.5 wt%, preferably less than 1 wt%, especially less than 0.6 wt%. The FDA hexane extractable test is from the version current to 07 July 2003. The test may be performed according to 21 CFR 177.1520 (d)(3)(ii)(e) using a film for extraction and weighing the dried film after extraction and drying to measure the weight loss.

[0026] Catalytic polymerization mechanisms are also used to produce linear polymers based on other olefins, mostly propylene. Examples include propylene based polymers such as polypropylene homopolymer, random propylene copolymer (RCP) as well as propylene based elastomers (PBE), including those described in WO99/07788 and WO2003/040201 having varying degrees of randomness or blockiness. The term "other linear polyolefin polymers" is used in the specification and claims to refer to other linear polymers generally using a catalytic polymerization mechanism with units derived from one or more olefin monomers, that may or may not be branched, but which exclude linear polyethylene as defined above.

[0027] In describing the compositions in the description and claims, all percentages by weight are based on the total weight of polymer in the compositions, excluding any other non- polymeric additives, unless otherwise mentioned.

[0028] Generally preferred ethylene polymers and copolymers that are useful in this invention include those sold by ExxonMobil Chemical Company in Houston Texas, including those sold as ExxonMobil™ HDPE, ExxonMobil™ LLDPE, and ExxonMobil™ LDPE; and those sold under the EXACT™, EXCEED™, ESCORENE™, ESCORENE ULTRA™, EXXCO™, ESCOR™, ENABLE™, NTX™, PAXON™ and OPTEMA™ tradenames. Coextrusion processes

[0029] Films can be extruded by cast extrusion or blown film extrusion. The present disclosure is concerned with blown film extrusion and especially coextrusion. The term coextrusion in the specification and claims refers to an extrusion process where at least two molten polymer compositions are extruded and bonded together in a molten condition through a die exit forming a bubble inflated by a gas. 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.

[0030] In blown film extrusion the film is pulled upwards by, for example, pinch rollers after exiting from the die and is simultaneously inflated and stretched transversely or 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. The location at which further MD or TD orientation stops is generally referred to as the "frost line" because of the development of haze at that location.

[0031] Variables in this process that determine the ultimate film properties include the die gap, the BUR, the TD stretch, the take up speed, the MD stretch, and the frost line height. Certain defects tend to limit production speed and are largely determined by the polymer rheology including the shear sensitivity which is related to the maximum output, the melt tension, the bubble stability, BUR, and take up speed.

[0032] Film producers have to balance the processability of a film with the physical properties of a film. Processability is generally regarded as the ease in which a particular film can be produced and which determines the maximum achievable output of a film on a film extrusion machine. The physical properties of a film are related to a particular end use, but include the mechanical strength of a film at a particular thickness. Important to physical properties for purposes herein are the optical properties including haze, uniformity, clarity, and the like. For purposes herein, the optical properties are expressed in term of the haze of the film as determined according to ASTM D1003, with a % haze of less than about 10% being acceptable (e.g., a "good" haze value for a film), with a % haze of less than or equal to about 8% being preferred and a % haze of less than or equal to about 5% as determined according to ASTM D1003 being more preferred.

[0033] The processability of a particular film is necessarily related to the physical properties of the film. However, the processability of a film may also be related to the equipment on which the film is produced. However, three fundamental processing parameters have been discovered which are useful in describing the processability of a film which are independent of the equipment used to produce the film, so long as the equipment is generally dimensioned and arranged to produce a blown film.

[0034] As disclosed in WO 2007/141036, which is fully incorporated herein by reference, process time, draw down ratio and average stretch (strain) rate or deformation rate provide a unifying basis for describing the production of films. Process time and strain rate give an accurate model for the amount of orientation which is built-in during film blowing and the time in which this orientation is taking place. These values unify the traditionally used process parameters. For purposes herein, process time is defined as the total time a polymer spends between the die lip exit and the frost line, and is expressed in seconds (s).

[0035] Process time is calculated as follows:

t = (FLH / (Vf - Vo)) * Ln (Vf/V0)

wherein

FLH : Frost line height in m

Vo : Melt velocity at the die exit in m/s

Vf : Film velocity in m/s

t : Process time in s.

The melt velocity at the die exit Vo is calculated from the total extruder output, the die gap area and the melt density. The film velocity Vf is equal to the take-off speed of the nip rolls or can be calculated from the die diameter, output, BUR, resin density and thickness by one of skill in the art.

[0036] For purposes herein, drawdown ratio (DDR) is the ratio Vf/Vo. The draw ratio is an index of the deformation in MD.

[0037] Also for purposes herein, the average stretch (strain) rate, also referred to herein as the deformation rate (e(t)), is the average stretch rate of the polymer melt and is expressed in reciprocal seconds (s 1). Long process time means low stretch rate and short process time means high stretch rate. The deformation rate is calculated as follows :

e(t) = (Vf Vo) / FLH.

[0038] The fundamental processing parameters can be calculated starting from the die diameter, die gap, melt density, output, resin density, BUR, thickness and FLH, thus, a meaningful comparison may be made as to the processability of a particular blown film independent of the equipment used to produce the blown film. [0039] The location of the frost line can be determined visually in ambient light. Generally the haze of the film shows at this location as crystallites diffract the light. The frost line may also be detected by optical apparatus, including infra-red inspection, especially where the haze of the solid film approaches that of the molten extrudate and visual detection becomes difficult, generally at a haze level of less than 3.

[0040] To be clear, the height of the frost line (FLH) is the distance between the die exit and the frost line. Generally a sufficient accuracy can be obtained by determining the FLH in one position. The precise position may drift or undulate around the bubble. For greater accuracy the FLH may be measured at a number of locations and/or averaged over time from a number of successive measurements. Where more than one frost line is present, the location of the last frost line (furthest from the die exit) is to be taken for the purpose of the FLH determination.

[0041] To calculate the speed Vo with which the coextruded polymer mass passes through the die exit, first the cross-sectional area of the annular die exit is determined using the length of the die circumference and die exit gap. The speed of the polymer mass passing through the die exit can be accurately determined by converting the weight of raw polymer consumed (using a weighing cell in an extruder hopper conventionally installed for such a purpose) into volume by using the general standard density value of 0.77 g/cm3 at 190°C, which value is generally accepted for molten polyethylene type polymers in the literature. The die exit area and volume information can be combined to provide a linear speed at the die exit Vo.

[0042] To calculate the speed Vf with which the coextruded polymer mass passes through the frost line, the die diameter, blow up ratio (BUR) and one or a series of measurements of the film thickness (using a conventional micrometer apparatus) are combined to determine the cross-sectional area of the film bubble at the frost line. The density used in the calculation is the average of the densities of the polymer components and other materials used for the solid polymers. The thickness of the film will be attenuated considerably compared with the die gap as the film accelerates towards the frost line. The Vf calculated will generally be the same as the haul-off or take up speed if that measurement is correctly calibrated.

[0043] A combination of the aforementioned deformation rate control and other process controls in combination with selection of certain polymers and arrangements have been discovered, which may be used to produce films having low haze at high production rates for a wide variety of end use applications by influencing polymer chain relaxation and shrinkage.

[0044] A higher take up speed will increase Vf and increase the deformation rate and the machine direction orientation. Accordingly, a thinner film indicates a higher strain rate. It has been discovered that the speed with which the film is deformed after exiting the die influences the manner in which the crystallization and orientation of the core layer impacts on the crystallization of the outer skin layer in contact with the core layer, which in turn has an effect on the optical properties of the film.

[0045] In blown film extrusion, deformation rates (also referred to herein as strain rates) may vary with the thickness of the film. Conventionally this might be as low as 0.01 s"1 for a 200 micrometer (micron, μιη) film with a BUR of 4, and a die gap of 1 mm taken up at a low output at one end, and up to 8 s"1 for a thin 10 μιη film from a die gap of 2.5 mm, a low BUR of 2 taken up at high speed.

[0046] Optical properties of light transmission and scattering include: haze measured through the bulk of the film, clarity measured through the bulk of the film, gloss at an angle of 45° measured on the outside surface of the film and gloss at an angle of 45° measured on the inside surface of the film.

[0047] Haze, as determined according to ASTM D1003, and as used herein in the specification and claims, represents the scattering in transmission of light at an angle >2.5° from the incident angle and reduces the contrast of objects viewed through the film. It involves scattering on the surface, referred to as surface haze, and in the interior of the film, referred to as internal haze and depending largely on the crystallites formed as the film cools after extrusion. References herein to haze are references to the overall haze and represent the ratio of diffused light to the total light transmitted by the film. Clarity refers to the proportion of light transmitted at an angle < 0.1° from the incident angle and is determined according to ASTM D-1746. The gloss is a measure of the light that is reflected at the same angle as the incident beam but in opposite direction and is determined according to ASTM D-2457.

[0048] In an embodiment, the inventive film is produced with a strain rate of greater than or equal to about 0.6 s"1, preferably greater than or equal to about 0.8 s"1. It has been unexpectedly discovered that particular multilayer blown films may have improved optical properties when produced at a relatively high strain rate (i.e., greater than or equal to about 0.6 s"1). Furthermore, it has been unexpectedly discovered that particular multilayer blown films may have improved optical properties including a % haze less than or equal to about 10%, when produced at a strain rate of greater than or equal to about 0.6 s"1, which include an outer "skin" layer having a density of greater than or equal to about 0.921 g/cm3, which represents a significant improvement in the art.

[0049] The ability to include a polyethylene having a density of greater than 0.921 g/cm3 in the outer layer of a multilayer blown film according to an embodiment of the present disclosure provides for a film having improved properties for a number of end uses, and/or a thinner overall film thickness, due to the increase in the overall stiffness of the film provided by the higher density material in the outer skin layer.

[0050] In an embodiment, the outer layer of the multilayer blown film comprises a linear low density polyethylene having a density greater than or equal to 0.921 g/cm3, as determined according to ASTM D4703/1505, preferably greater than or equal to about 0.925 g/cm3, preferably having a density of not greater than or equal to about 0.940 g/cm3 as determined according to ASTM D4703/1505 being still more preferred.

[0051] In an embodiment, the outer layer of the multilayer blown film is a "low MIR linear polyethylene." The low MIR linear polyethylenes may be of the znPE and mPE types. For purposes herein, a low MIR linear polyethylene has a MIR (I21.6 /I2.16 @190°C) of less than 35, preferably less than 30, preferably less than 25, preferably less than 20, preferably less than or equal to about 16. The low MIR indicates essentially zero or a low level of long chain branches as well as a narrow molecular weight distribution which may be expressed as an Mw/Mn value determined by GPC of less than about 10, preferably less than about 6, preferably less than about 5.5, preferably less than about 5, preferably less than about 4.5, preferably less than about 4. The C13 NMR spectrum characteristics are shared with those of linear polyethylenes because any long chain branching is at too low a level to influence the C13 NMR spectrum.

[0052] In an embodiment, the outer layer comprises a linear low density polyethylene (LLDPE), preferably produced with a single site catalyst such as a metallocene catalyst. Accordingly, the outer layer preferably comprises an mLLDPE. In an embodiment, the outer layer comprises an LLDPE having a MI (I2.16 @190°C) of less than or equal to about 2.2 g/lOmin, preferably less than or equal to about 1.7 g/lOmin, preferably less than or equal to about 1.3 g/lOmin, as determined according to ASTM D-1238, condition E.

[0053] In an embodiment, the outer layer may consist of, or consist essentially of LLDPE, preferably mLLDPE. In another embodiment, the outer skin layer in the multi-layer film structures of the invention may contain, in admixture with the LLDPE, high density polyethylene (HDPE), high pressure polyethylene (HPPE), low density polyethylene (LDPE), polypropylene, or a combination thereof. The LLDPE is preferably present in the outer skin layer at a concentration of at least 1 wt%, preferably at least about 10 wt%, preferably at least about 20 wt%, preferably at least about 30 wt%, preferably at least about 40 wt%, preferably at least about 50 wt%, preferably at least about 60 wt%, preferably at least about 70 wt%, preferably at least about 80 wt%, preferably at least about 90 wt%, preferably at least about 95 wt%, based on the total weight of the outer skin layer of the multi-layer film structure.

[0054] The outer skin layer may further comprise other additives well known in the art, which may include, for example: fillers; antioxidants (e.g., hindered phenolics such as IRGANOX™ 1010 or IRGANOX™ 1076 available from Ciba-Geigy); phosphites (e.g., IRGAFOS™ 168 available from Ciba-Geigy); anti-cling additives; tackifiers, such as polybutenes, terpene resins, aliphatic and aromatic hydrocarbon resins, alkali metal and glycerol stearates and hydrogenated rosins; UV stabilizers; heat stabilizers; antiblocking agents; release agents; anti-static agents; pigments; colorants; dyes; waxes; silica; fillers; talc and the like.

[0055] When employed, the anti-block use is generally minimized to maintain film clarity. Preferably the skin layer contains less than 2000 ppm of particulate. Particle sizes of talc or silica anti-block useful for anti-block in films may vary as is well known in the art. Slip agents and the like may be added to modify the surface properties such as coefficient of friction (COF).

[0056] In an embodiment, the outer skin layer of the multilayer blown film comprises: an mLLDPE having a density of greater than or equal to about 0.927 g/cm3, and/or a MIR of less than or equal to about 34, and/or an MI of less than or equal to about 2.2; a znLLDPE having a MIR of less than or equal to about 30; an LDPE, or a combination thereof, wherein the haze of the multilayer blown film is less than about 10%.

Core layer

[0057] In an embodiment, the core layer of the inventive multilayer blown film comprises at least about 10 wt% of a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, preferably not greater than 0.940 g/cm2, a melt index ratio (MIR I21.6/I2.16 @ 190°C) of greater than or equal to about 35 and less than or equal to about 60, and a melt index of less than or equal to about 0.4 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg, in combination with a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3, preferably not greater than 0.975 g/cm2, such that the core layer has a density greater than the density of the outer skin layer(s).

[0058] In an embodiment, the mLLDPE of the core layer has a MIR of greater than or equal to about 40, preferably greater than or equal to about 45, preferably greater than or equal to about 48 and less than or equal to about 60, preferably less than or equal to about 58. In an embodiment, the mLLDPE of the core layer has an MI of less than or equal to about 0.4 g/10 min, preferably less than or equal to about 0.3 g/10 min. [0059] In an embodiment, the mLLDPE exhibits a relationship between melt index and density according to the following formula:

ln(MIR-CX) = -18.20 - 0.26341n(MI, I2.16) + 23.58 x [density, g/cm3] where MIR-CX is a calculated value approximating the MIR obtained by measuring the melt index and high load melt index, preferably MIR-CX is between 35 and 60, more preferably between 48 and 58. In an embodiment, the MIR is preferably between 35 and 60, more preferably between 48 and 58. In an embodiment MIR-CX is within ±10% of the MIR. Accordingly, in an embodiment, the mLLDPE of the core layer has a density and melt index which conform to the following formula:

22.3 > 23.58 x [density, g/cm3]- 0.26341n(MI, I2.16) > 21.7.

[0060] Likewise, in an embodiment, the mLLDPE preferably has a density and melt index which conform to the following formula:

22.26 > 23.58 x [density, g/cm3]- 0.26341n(MI, I2.16) > 22.07.

[0061] In an embodiment, the core layer comprises greater than or equal to about 10 wt% of the mLLDPE, based on the total weight of the core layer, preferably greater than or equal to about 20 wt%, preferably greater than or equal to about 30 wt%, preferably greater than or equal to about 40 wt%, preferably greater than or equal to about 50 wt%, preferably greater than or equal to about 60 wt%, preferably greater than or equal to about 70 wt%, preferably greater than or equal to about 80 wt%, preferably greater than or equal to about 90 wt%, based on the total weight of the core layer.

[0062] In an embodiment, the core layer comprises greater than or equal to about 0.5 wt% of the HDPE, based on the total weight of the core layer, preferably greater than or equal to about 5 wt%, preferably greater than or equal to about 10 wt%, preferably greater than or equal to about 15 wt%, preferably greater than or equal to about 20 wt%, preferably greater than or equal to about 25 wt%, preferably greater than or equal to about 30 wt%, preferably greater than or equal to about 40 wt%, preferably greater than or equal to about 50 wt%, based on the total weight of the core layer.

[0063] In an embodiment, the core layer has a density greater than or equal to the density of the skin layer. In an embodiment, the density of the core layer is at least 0.002 g/cm3 greater than the density of the skin layer, preferably at least 0.004 g/cm3 greater, preferably at least 0.006 g/cm3 greater, preferably at least 0.008 g/cm3 greater, preferably at least 0.01 g/cm3 greater than the density of the skin layer.

[0064] The core layer may further include very low density polyethylene (VLDPE), an LDPE, an LLDPE, or a combination thereof. In an embodiment, the LDPE or the LLDPE has a MI I2.i6@190°C of less than or equal to about 2.0 g/10 min, preferably less than or equal to about 1.5 g/10 min, preferably less than or equal to about 1.2 g/10 min. The LDPE may be HPPE or the like. The LLDPE may be a znLLDPE, and/or an mLLDPE. The core layer may further include polypropylene.

Multilayer blown film

[0065] In an embodiment, the multilayer blown film comprises at least one outer layer and a core layer, preferably two outer layers with a core layer disposed between the two outer layers, wherein the outer layer comprises a metallocene linear low density polyethylene comprising a copolymer derived from ethylene and one or more C3 to C20 a-olefin comonomers having a density greater than or equal to 0.921 g/cm3, preferably greater than or equal to about 0.927 g/cm3; a melt index of less than or equal to about 2.2 g/10 min, preferably less than or equal to about 1.7 g/lOmin as determined according to ASTM D 1238 at 190°C/2.16 kg; a MIR, I21 6 / 12 16 @ 190°C of less than or equal to about 20, preferably less than or equal to about 16; and a core layer comprising at least about 10 wt% of a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR hi.dh.ie @ 190°C) of greater than or equal to about 48, and less than or equal to about 58, and a melt index of less than or equal to about 0.3 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg; and a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3; wherein the core layer has a density greater than the density of the at least one outer layer; and wherein the film comprises a haze of less than about 10% according to ASTM D1003, preferably a haze of less than about 8%, more preferably a haze of less than about 5% according to ASTM D1003 wherein the film has been extruded at a strain rate of greater than or equal to about 0.6 s"1, preferably a strain rate of greater than or equal to about 0.8 s"1.

[0066] In an embodiment, the multilayer blown film disclosed herein has a haze determined according to ASTM D1003 which is less than the haze of each of the components of the film (e.g., the individual components of the skin layer and the individual components of the core layer) when determined individually according to ASTM D1003 at the same thickness as the multilayer blown film.

[0067] In an embodiment, layers may be interposed between the core and skin layers, part of the purpose may be to limit the amount of the more expensive polymers for the skin and/or core layers.

[0068] In an embodiment, the core layer comprises a blend of the mLLDPE/HDPE. In an embodiment, the core layer comprises at least two distinct layers, one comprising the mLLDPE in contact with a layer comprising the HDPE wherein the average density of the two combined layers is greater than the density of the outer skin layers of the multilayer blown film. For example, the core layer may comprise a layer of the mLLDPE sandwiched between two of the HDPE layers, or a layer of the HDPE sandwiched between two of the mLLDPE layers.

[0069] In an embodiment, the multilayer blown film comprises two "A" skin layers arranged on opposite sides of a "B" core layer in an A/B/A configuration; wherein the A layers comprise a linear metallocene polyethylene comprising a copolymer derived from ethylene and one or more C3 to C20 a-olefin comonomers having a density greater than or equal to 0.921 g/cm3; and a melt index of less than or equal to about 1.3 as determined according to ASTM D1238 at 190°C/2.16 kg; and a MIR, I21.6 / I2.16 of less than or equal to about 16; and a core layer comprising at least about 10 wt% of a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR I21.6/I2.16 @ 190°C) of greater than or equal to about 35 and less than or equal to about 60, and a melt index of less than or equal to about 0.3 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg; and a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3; wherein the core layer has a density greater than the density of the at least one outer layer; and wherein the film comprises a haze of less than about 10% according to ASTM D1003.

[0070] The thickness of each layer of the film, and of the overall film is not particularly limited, but is determined according to the desired properties of the film. Typical film layers have a thickness of from about 1 to about 1000 μιη, more typically from about 5 to about 200 μιη, and typical films have an overall thickness of from about 10 to about 100 μιη, with a thickness of about 15 to about 70 μιη being preferred for particular end uses.

Stretch Films

[0071] The multilayer blown films according to an embodiment of the instant disclosure may be utilized to prepare stretch films. Stretch films are widely used in a variety of bundling and packaging applications. The term "stretch film" indicates films capable of stretching and applying a bundling force, and includes films stretched at the time of application as well as "pre-stretched" films, i.e., films which are provided in a pre-stretched form for use without additional stretching. Stretch films may include conventional additives, such as cling- enhancing additives such as tackifiers, and non-cling or slip additives, to tailor the slip/cling properties of the film.

[0072] It is desirable to maximize the degree to which a stretch film is stretched, as expressed by the percent of elongation of the stretched film relative to the unstretched film, and termed the "stretch ratio." At relatively larger stretch ratios, stretch films impart greater holding force. Further, films which can be used at larger stretch ratios with adequate holding force and film strength offer economic advantages, since less film is required for packaging or bundling.

[0073] As stretch film is stretched, a small decrease in the film thickness due to small fluctuations in thickness uniformity can result in a large fluctuation in elongation, giving rise to bands of weaker and more elongated film transverse to the direction of stretching, a defect known as "tiger striping". Thus, it is desirable to have a yield plateau slope large enough to avoid tiger striping over typical thickness variations of, for example, ± 5%. For robust operation over a wide range of elongation, and using a wide variety of stretching apparatus, it is desirable to have a broad yield plateau region. In addition, since the extent of elongation correlates inversely with the amount of film that must be used to bundle an article, it is desirable for the film to be stretchable to a large elongation. While in principle the elongation at break is the maximum possible elongation, in practice, the natural draw ratio is a better measure of maximum elongation. Thus, it is desirable to have a large natural draw ratio. Other desirable properties, not illustrated in a stress-elongation curve, include high cling force and good puncture resistance.

[0074] The multilayer blown films according to an embodiment of the instant disclosure are particularly suitable for stretch film applications. It has been surprisingly found that films of the invention exhibit improved properties, such as applicability over a wide range of stretch ratios without suffering from local deformation leading to break, hole formation, tiger striping, or other defects. Films prepared according to an embodiment of the instant disclosure show higher holding force than conventional films of the same film thickness.

[0075] Stretch films can be provided so that an end user stretches the film upon application to provide a holding force, or can be provided in a pre-stretched condition. Such pre-stretched films, also included within the term "stretch film," are stretched and rolled after extrusion and cooling, and are provided to the end user in a pre-stretched condition, so that the film upon application provides a holding force by applying tension without the need for the end user to further stretch the film.

[0076] Additives can be provided in the various film layers, as is well-known in the art. For stretch film applications, an additive such as a tackifier can be used in one or more layers to provide a cling force. Suitable tackifiers and other additives are well-known. Suitable tackifiers include any known tackifier effective in providing cling force, such as, for example, polybutenes, low molecular weight polyisobutylenes (PIB), polyterpenes, amorphous polypropylene, ethylene vinyl acetate copolymers, microcrystalline wax, alkali metal sulfosuccinates, and mono- and di-glycerides of fatty acids, such as glycerol monostearate, glycerol monooleate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate and sorbitan monooleate. The tackifier, if used, can be used in any concentration which will impact the desired cling force, typically from 0.1 to 20 wt% and more typically from 0.25 to 6.0 wt%. Tackifiers can be used in monolayer films or in multiple layer films. In multiple layer films, a tackifier can be added to both outer layers to provide a stretch film having two- sided cling, or in only one outer layer, to provide a stretch film having one-sided cling.

[0077] Some resins and blends described herein may also be suited for use in stretch handwrap films. Stretch film handwrap requires a combination of excellent film toughness, especially puncture, MD tear performance, dart drop performance, and a very stiff, i.e., difficult to stretch, film. Film 'stiffness' minimizes the stretch required to provide adequate load holding force to a wrapped load and to prevent further stretching of the film. The film toughness is required because handwrap loads (being wrapped) are typically more irregular and frequently contain greater puncture requirements than typical machine stretch loads.

Shrink Films

[0078] The multilayer blown films disclosed herein may be utilized to prepare shrink films. Shrink films, also referred to as heat-shrinkable films, are widely used in both industrial and retail bundling and packaging applications. Such films are capable of shrinking upon application of heat to release stress imparted to the film during or subsequent to extrusion. The shrinkage can occur in one direction or in both longitudinal and transverse directions. Conventional shrink films are described, for example, in International Patent Publication WO 2004/022646, which is herein incorporated by reference in its entirety.

[0079] Industrial shrink films are commonly used for bundling articles on pallets. Typical industrial shrink films are formed in a single bubble blown extrusion process to a thickness of about 80 to 200 μιη, and provide shrinkage in two directions, typically at a machine direction (MD) to transverse direction (TD) ratio of about 60:40.

[0080] Retail films are commonly used for packaging and/or bundling articles for consumer use, such as, for example, in supermarket goods. Such films are typically formed in a single bubble blown extrusion process to a thickness of about 35 to 80, μιη, with a typical MD:TD shrink ratio of about 80:20.

[0081] One use for films made from the polymers and/or blends described herein is in "shrink-on-shrink" applications. "Shrink-on-shrink," as used herein, refers to the process of applying an outer shrink wrap layer around one or more items that have already been individually shrink wrapped (herein, the "inner layer" of wrapping). In these processes, it is desired that the films used for wrapping the individual items have a higher melting (or shrinking) point than the film used for the outside layer. When such a configuration is used, it is possible to achieve the desired level of shrinking in the outer layer, while preventing the inner layer from melting, further shrinking, or otherwise distorting during shrinking of the outer layer.

Greenhouse Films

[0082] The multilayer blown films disclosed herein may be utilized to prepare greenhouse films. Greenhouse films described herein include those greenhouse film structures known to those skilled in the art. Greenhouse films are generally heat retention films that, depending on climate requirements, retain different amounts of heat. Less demanding heat retention films are used in warmer regions or for spring time applications. More demanding heat retention films are used in the winter months and in colder regions.

Bags

[0083] Bags include those bag structures and bag applications known to those skilled in the art. Exemplary bags include shipping sacks, trash bags and liners, industrial liners, produce bags, and heavy duty bags.

[0084] In some embodiments, the multilayer blown film described herein may be utilized to prepare heavy duty bags. Heavy duty bags are prepared by techniques known to those skilled in the art, such as, for example, vertical form fill and seal equipment. Exemplary conventional heavy duty bags and the apparatus utilized to prepare them are disclosed in U.S.

Patent Application Publication 2006/0188678 and U.S. Patent Nos. 4,571,926; 4,532,753;

4,532,752; 4,589,247; 4,506,494; and 4,103,473, each of which is herein incorporated by reference in its entirety.

Packaging

[0085] Packaging is prepared with, or incorporates the multilayer blown films described herein. Packaging includes those packaging structures and packaging applications known to those skilled in the art. Exemplary packaging includes flexible packaging, food packaging, e.g., fresh cut produce packaging, frozen food packaging, bundling, packaging and unitizing a variety of products. Applications for such packaging include various foodstuffs, rolls of carpet, liquid containers and various like goods normally containerized and/or palletized for shipping, storage, and/or display.

[0086] Further end-use product applications may also include surface protection applications, with or without stretching, such as in the temporary protection of surfaces during manufacturing, transportation, etc. There are many potential applications of articles and films produced according to an embodiment of the instant disclosure.

[0087] The multilayer blown films disclosed herein are also suited for the manufacture of blown film in a high-stalk extrusion process. In this process, a polyethylene melt is fed through a gap (typically 0.8mm to 1.2 mm) in an annular die attached to an extruder and forms a tube of molten polymer which is moved vertically upward. The initial diameter of the molten tube is approximately the same as that of the annular die. Pressurized air is fed to the interior of the tube to maintain a constant air volume inside the bubble. This air pressure results in a rapid 3- to-9-fold increase of the tube diameter which occurs at a height of approximately 5 to 14 times the die diameter above the exit point of the tube from the die. The increase in the tube diameter is accompanied by a reduction of its wall thickness to a final value ranging from approximately 0.5 to 2 mils and by a development of biaxial orientation in the film. The expanded tube is rapidly cooled (which induces crystallization of the polymer), collapsed between a pair of nip rolls and wound onto a film roll.

[0088] Two factors are useful to determine the suitability of a particular polyethylene resin or blend for high stalk extrusion: the maximum attainable rate of film manufacture and mechanical properties of the formed film. Adequate processing stability is desired at throughput rates of up to 15 lb/hr/inch (2.675 kilograms per hour per centimeter) die and high linespeeds (>609.6 ft/min (200 m/min)) for thin gauge manufacture on modern extrusion equipment. The resins and blends described herein have molecular characteristics which allow them to be processed successfully at these high speeds. Mechanical strength of the film is different in two film directions, along the film roll (machine direction, MD) and in the perpendicular direction (transverse direction, TD). Typically, the TD strength in such films is significantly higher than their MD strength. The films manufactured from the resins prepared in the processes and the catalysts described herein have a favorable balance of the MD and TD strengths.

[0089] The multilayer blown films described herein show improved performance in mechanical and optical properties when compared to films previously known in the art. For example, films described herein have improved shrink properties, better clarity, good seal strength and hot tack performance, increased toughness, and lower coefficient of friction. In addition, such films may also exhibit higher ultimate stretch and typically have better processability when compared with other films known in the art, in combination with a haze of less than about 10% according to ASTM D1003 at a thickness of less than or equal to about 50 μιη. [0090] In an embodiment, the multilayer blown films described herein have a puncture resistance of greater than or equal to about 2.35 Ν/μιη, preferably greater than or equal to about 2.4 Ν/μιη, preferably greater than or equal to about 2.5 Ν/μιη, preferably greater than or equal to about 2.6 Ν/μιη, preferably greater than or equal to about 2.7 Ν/μιη, preferably greater than or equal to about 2.8 Ν/μιη at a thickness of greater than or equal to about 40 μιη as determined according to the method described below. Puncture resistance determines the low speed puncture properties of plastic film samples. The method is designed to provide load versus deformation response under multi-axial deformation conditions at a fixed relatively low test speed. According to the method, a piston with a standard probe fixed to the load cell is pushed through a film sample in a circular sample holder up to break. The load is measured on the load cell and the deformation is measured by the travel of the cross-head. Puncture resistance enables measurement of the degree of capability of films in wrapping sharp articles. According to the method, Travel at Fmax relates to the measured deformation in the film sample at maximum load and is expressed in (mm). Travel at Break refers to the measured deformation in the film sample at break point and is expressed in (mm). Maximum puncture force refers to the maximum (nominal) load sustained by the film sample before the break point. It is normalized for the film thickness and expressed in (Ν/μιη). Puncture force at break refers to the load at the break point which is normalized for the film thickness and is expressed in ( /μιη). Puncture energy at Fmax refers to the total energy absorbed by the film sample at the maximum load. It is the integration of the area up to maximum force under the load- deflection curve normalized for the film sample thickness. It is expressed in (mJ/μιη). Puncture energy at break refers to the total energy absorbed by the film sample at the moment of break point. It is the integration of the area up to the breaking point under the load- deflection curve. It is normalized for the film sample thickness and expressed in (mJ/μιη). Strain refers to the travel distance of the cross-head and so the puncture probe and the deflection of the film sample. It is expressed in (mm). Standard force refers to the load measured at the load cell. It is expressed in (N). Samples are held for at least 40 hours at 23°C + 2°C and at 50% + 5% relative humidity prior to testing. The testing is conducted on a Zwick 1445 NR2 (Zwick GmbH & Co. KG, Germany) according to the manufacturer's instructions.

HTC Effect

[0091] It has been discovered that embodiments of the multilayer blown films described herein demonstrate an improvement in optical properties, i.e., a reduction in haze, when produced under relatively high strain rates of greater than or equal to about 0.6 s"1. [0092] This unexpected property of the films disclosed herein is referred to herein as the "high throughput-high clarity" effect, and is referred to herein at the "HTC" effect. The HTC effect provides for an improvement on the optical properties in concert with faster production rates and/or the ability to utilize a thinner film in place of what would have been a thicker film when the thicker film was previously used to obtain a particular optical property. In addition, this unexpected property is further enhanced by the ability of the films disclosed herein to include a polyethylene having a density of greater than or equal to 0.921 g/cm3 in the outer skin layer. This presence of this relatively higher density material in the outer skin layer imparts an overall stiffness to the film which translates into improved processing and handling characteristics for particular end uses, as well as the ability to utilize a thinner film in place of a thicker film, wherein the added thickness of the film being replaced was utilized to obtain particular properties required by an end use.

[0093] It has been discovered that the HTC effect is observed in embodiments of multilayer blown films which include at least one outer layer comprising a linear low density polyethylene having a density greater than or equal to 0.921 g/cm3; and a core layer comprising at least about 10 wt% of a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR

Figure imgf000022_0001
@ 190°C) of greater than or equal to about 35 and less than or equal to about 60, and a melt index of less than or equal to about 0.4 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg; and a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3; wherein the core layer has a density greater than the density of the at least one outer layer, such that a film may be produced at strain rates of greater than or equal to about 0.6 s"1. In an embodiment, the film is produced having a haze of less than about 10% according to ASTM D1003 at a thickness of less than or equal to about 50 μιη.

[0094] The HTC effect may be observed in a plot beginning at the origin (0,0) and having increasing haze according to ASTM D 1003 on the y-axis in %, vs the increasing film thickness on the x-axis in microns (μιη), which is referred to herein as a Haze-Thickness plot. When the HTC effect is present, the slope of a linear line fit (i.e., least squares fitting) to the data for films having thicknesses between about 45 microns and 80 microns and the same layer thickness ratios (e.g., A/B/A = 1/3/1), has a positive slope greater than or equal to about 0.2 %haze/micron, preferably greater than or equal to about 0.25% haze/micron, preferably greater than or equal to about 0.3% haze/micron, and a y-intercept of less than or equal to about -2, preferably less than or equal to about -5, preferably less than or equal to about -8, when the y- intercept is obtained according the slope-intercept equation for the fitted line: (% haze )Y= m (%haze/micron) * X(thickness in microns) + b wherein m is the slope of the line; and

b is the y-intercept.

In an embodiment, the data have a goodness of fit "R2" value of at least 0.95, preferably at least 0.97, with a value of at least 0.99 being still more preferred. For purposes herein, the goodness of fit R2 value is determined according to a least-squares fitting process known to one of skill in the art, and is defined herein as the square of the residuals of the data after the fit, which is an indication of what fraction of the variance of the data are explained by the fitted line.

[0095] Accordingly, in an embodiment, the HTC effect is observed in a film when extrapolation of a fitted line of a Haze-Thickness plot results in a zero (0) haze (the X-axis intercept) at a thickness greater than or equal to about 5 microns. In an embodiment, an extrapolated zero haze value as described above will be obtained for a fitted line at a film thickness of at least about 10 microns, preferably at a film thickness of at least about 20 microns.

[0096] Since a Haze-Thickness plot of multilayer blown film according to an embodiment of the instant disclosure does not have an essentially zero y-intercept similar to films which do not show the HTC effect, it is reasonable to conclude that the Haze-Thickness plot of a film which shows the HTC effect is not a linear relationship. This is indeed what has been discovered about the films produced according to one embodiment of the instant disclosure. In fact, the inventive films of one embodiment herein typically show a "power" or logarithmic relationship when the trend line is forced through a point having zero haze at zero thickness (the origin of the plot).

[0097] The HTC effect may also be observed in a plot of increasing haze (%) on the y-axis vs. increasing strain rate (s 1) on the x-axis, referred to herein as a Haze vs. Strain Rate plot. The HTC effect presents itself as a power or logarithmic relationship wherein an increase in strain rate produces a decrease in haze, wherein increasing incremental changes in strain rate produce ever larger reductions in haze at meaningful strain rates between 0.2 and 1.2 s"1.

Process to produce multilayer blown films

[0098] The films according to various embodiments of the instant disclosure may be produced on any combination of equipment designed and arranged to produce multilayer blown films by coextrusion. In an embodiment, a process for producing a multilayer blown film, comprises the steps of selecting a first polyethylene comprising a linear low density polyethylene having a density greater than or equal to 0.921 g/cm3; selecting a second polyethylene comprising a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR I21.6 I2.16 @ 190°C) of greater than or equal to about 35 and less than or equal to about 60, and a melt index of less than or equal to about 0.4 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg; selecting a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3; combining at least 10 wt% of the second polyethylene with the high density polyethylene to produce a blend having a density greater than the density of the first polyethylene; and extruding the first polyethylene and the blend from a die wherein the first polyethylene forms a first and second skin layer, wherein the blend forms a core layer disposed between the first and second skin layer, when extruded at a strain rate of greater than or equal to about 0.6 s"1, preferably at a strain rate of greater than or equal to about 0.8 s"1. In an embodiment, the film comprises a haze of less than about 10% according to ASTM D1003 at a thickness of less than or equal to about 50 μιη.

[0099] In an embodiment, the first polyethylene, the second polyethylene, and the high density polyethylene are selected such that a fitted line of a haze-thickness plot over film thicknesses from about 45 μιη to about 80 μιη at the same layer thickness ratios, has a positive slope of greater than or equal to about 0.2% haze/μιη and a y-intercept value of less than or equal to about -2. In an embodiment, the fitted line of the haze-thickness plot has a positive slope of greater than or equal to about 0.25% haze/μιη, a y-intercept value of less than or equal to about -5, or a combination thereof. In another embodiment, the fitted line of the haze- thickness plot has a positive slope of greater than or equal to about 0.3% haze/μιη, a y- intercept value of less than or equal to about -8, or a combination thereof.

[00100] In an embodiment, the first polyethylene, the second polyethylene, and the high density polyethylene are selected such that a fitted line of a haze-thickness plot over film thicknesses from about 45 μιη to about 80 μιη at the same layer thickness ratios, has an extrapolated zero haze value at a thickness of greater than or equal to about 5 μιη, preferably greater than or equal to about 10 μιη, with greater than or equal to about 20 μιη being still more preferred.

[00101] Accordingly, the instant disclosure provides the following embodiments:

A. A multilayer blown film comprising:

at least one outer layer comprising a linear low density polyethylene having a density greater than or equal to 0.921 g/cm3;

a core layer comprising at least about 10 wt% of a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR I21.6 I2.16 @ 190°C) of greater than or equal to about 35 and less than or equal to about 60, and a melt index of less than or equal to about 0.4 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg; and a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3; and wherein the core layer has a density greater than the density of the at least one outer layer.

B. The multilayer blown film of Embodiment A, wherein the at least one outer layer comprises a metallocene linear low density polyethylene (mLLDPE).

C. The multilayer blown film of Embodiment A or Embodiment B, wherein the at least one outer layer comprises: a metallocene linear low density polyethylene having a MIR, I21.6 / 12.16 @ 190°C of less than or equal to about 34; a Ziegler-Natta linear low density polyethylene having a MIR, I21.6 / I2.16 @ 190°C of less than or equal to about 30; or a combination thereof.

D. The multilayer blown film of any one of Embodiments A, B or C, wherein the core layer further comprises a linear low density polyethylene (LLDPE) having an MI of less than or equal to about 2.2 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg.

E. The multilayer blown film of any one of Embodiments A, B, C or D, wherein the core layer comprises greater than or equal to about 10 wt% and less than or equal to about 90 wt% of the metallocene linear low density polyethylene based on the total weight of the core layer.

F. The multilayer blown film of any one of Embodiments A, B, C, D or E, wherein the core layer comprises a blend comprising the metallocene linear low density polyethylene and the high density polyethylene.

G. The multilayer blown film of any one of Embodiments A, B, C, D, E or F comprising two outer layers, wherein the core layer is disposed between the two outer layers.

H. The multilayer blown film of Embodiment G, wherein the two outer layers have the same composition.

I. The multilayer blown film of any one of Embodiments A, B, C, D, E, F, G or H, wherein the outer layer comprises: a metallocene linear low density polyethylene comprising a copolymer derived from ethylene and one or more C3 to C20 a-olefin comonomers having a density greater than or equal to 0.927 g/cm3; a melt index of less than or equal to about 1.3 as determined according to ASTM D1238 at 190°C/2.16 kg; and a MIR, I21.6 / 12.16 @ 190°C of less than or equal to about 16.

J. The multilayer blown film of any one of Embodiments A, B, C, D, E, F, G, H or I, wherein the film has a haze of less than or equal to about 10% as determined according to ASTM D 1003.

K. The multilayer blown film of any one of Embodiments A, B, C, D, E, F, G, H, I or J, wherein the film has a haze of less than or equal to about 8% as determined according to ASTM D1003 and a thickness of less than or equal to about 50 μιη.

L. The multilayer blown film of any one of Embodiments A, B, C, D, E, F, G, H, I, J, or K, wherein the film is produced at a strain rate of greater than or equal to about 0.6 s"

1

M. The multilayer blown film of any one of Embodiments A, B, C, D, E, F, G, H, I, J, K, or L, wherein the metallocene linear low density polyethylene present in the core layer has a density and a melt index relationship according to the formula:

22.3 > 23.58 x [density, g/cm3] - 0.2634 ln(MI, I2.i6@190°C, g/10 min) > 21.7.

N. The multilayer blown film of any one of Embodiments A, B, C, D, E, F, G, H, I, J, K, L, or M, wherein the MIR l21.eJh.i6 @ 190°C of the metallocene linear low density polyethylene present in the core layer is greater than or equal to about 46 and less than or equal to about 58.

O. The multilayer blown film of any one of Embodiments A, B, C, D, E, F, G, H, I, J, K, L, M, or N, where a film has a dart impact of greater than or equal to about 2.5 Ν/μιη as determined according to ASTM D 1709-04.

P. The multilayer blown film of any one of Embodiments A, B, C, D, E, F, G, H, I, J, K, L, M, N, or O, wherein a fitted line of a haze-thickness plot over film thicknesses from about 45 μιη to about 80 μιη at the same layer thickness ratios, has a positive slope of greater than or equal to about 0.2 %haze^m and a y-intercept value of less than or equal to about -2.

Q. The multilayer blown film of any one of Embodiment P, wherein the fitted line of the haze-thickness plot has a positive slope of greater than or equal to about 0.3 %haze^m, a y-intercept value of less than or equal to about -8, or a combination thereof. R. The multilayer blown film of any one of Embodiments A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, or Q, wherein a fitted line of a haze-thickness plot over film thicknesses from about 45 μιη to about 80 μιη at the same layer thickness ratios, has an extrapolated zero haze value at a thickness of greater than or equal to about 5 μιη. S. A multilayer blown film comprising:

two "A" skin layers arranged on opposite sides of a "B" core layer in an A/B/A configuration;

wherein each of the A layers comprise a linear metallocene polyethylene comprising a copolymer derived from ethylene and one or more C3 to C20 a-olefin comonomers having a density greater than or equal to 0.921 g/cm3; and a melt index of less than or equal to about 1.3 as determined according to ASTM D1238 at 190°C/2.16 kg; and a MIR, I21.6 / I2.i6@ 190°C of less than or equal to about 16;

wherein the B layer comprises at least about 10 wt% of a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR, I21.6 / L.i6@ 190°C) of greater than or equal to about 46 and less than or equal to about 58, and a melt index of less than or equal to about 0.3 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg, and a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3; and

wherein the B layer has a density greater than the density of the A layers.

T. The multilayer blown film of Embodiment S, wherein a fitted line of a haze- thickness plot over film thicknesses from about 45 μιη to about 80 μιη at the same layer thickness ratios, has a positive slope of greater than or equal to about 0.2% haze/μιη and a y-intercept value of less than or equal to about -2.

U. A process for producing a multilayer blown film, comprising:

selecting a first polyethylene comprising a linear low density polyethylene having a density greater than or equal to 0.921 g/cm3;

selecting a second polyethylene comprising a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR I21.6 I2.16 @ 190°C) of greater than or equal to about 35 and less than or equal to about 60, and a melt index of less than or equal to about 0.4 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg;

selecting a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3; combining the second polyethylene with the high density polyethylene to produce a blend having a density greater than the density of the first polyethylene, wherein the blend comprises at least 10 wt% of second polyethylene by weight of the blend; and extruding the first polyethylene and the blend from a die wherein the first polyethylene forms first and second skin layers, wherein the blend forms a core layer disposed between the first and second skin layers, and wherein the film is extruded at a strain rate of greater than or equal to about 0.6 s"1.

V. The process of Embodiment U, wherein the film is produced at a strain rate of greater than or equal to about 0.8 s"1.

W. The process of Embodiment U or V, wherein the first polyethylene, the second polyethylene, and the high density polyethylene are selected such that a fitted line of a haze-thickness plot over film thicknesses from about 45 μιη to about 80 μιη at the same layer thickness ratios, has a positive slope of greater than or equal to about 0.2 %haze^m and a y-intercept value of less than or equal to about -2.

X. The process of Embodiment W, wherein the fitted line of the haze-thickness plot has a positive slope of greater than or equal to about 0.3% haze/μιη, a y-intercept value of less than or equal to about -8, or a combination thereof.

Y. The process of any one of Embodiments U, V, W, or X, wherein the first polyethylene, the second polyethylene, and the high density polyethylene are selected such that a fitted line of a haze-thickness plot over film thicknesses from about 45 μιη to about 80 μιη at the same layer thickness ratios, has an extrapolated zero haze value at a thickness of greater than or equal to about 5 μιη.

Examples

The polyethylenes used to produce the examples are listed in Table 1.

Table 1

PE Designation ExxonMobil Name Density MI MIR Mw/Mn

LDPE, HPPE, hetero geneously branched.

ExxonMobil™ LDPE 0.922 0.33 88 6.8

LD165BW1

ExxonMobil™ LDPE 0.9225 2 50 5.4

LD100BW

Low MIR mLLDPE (no Long Chain Branching),

Exceed™ El 327 mPE 0.927 1.3 16 2.1

High MIR mLLDPE (Long Chain Branching), homogeneously branched

Enable™ 27-03CH 0.927 0.3 46-58 3.4 mPE

Enable™ 35-05CH 0.935 0.5 46-58 3.4 mPE

HDPE

ExxonMobil™ HDPE 0.961 0.7 66 9.4

HTA108

[00103] The various properties of the polymers and the examples were determined according to the following tests and procedures.

[00104] Melt Index, I 2.16, reported in grams per 10 minutes (g/10 min), refers to the melt flow rate measured according to ASTM D-1238, condition E using a load of 2.16 kg at 190°C. The Melt Index Ratio (MIR) expressed in Ι21.β / I2.i6 is determined following the above ASTM tests methods, with I21.6 representing a measurement using a load of 21.6 kg at 190°C. It is a dimensionless number representing the ratio of the high load melt index to the low load melt index.

[00105] The densities are determined herein in the specification and claims according to ASTM D2839/D1505 (LDPE) or ASTM D4703/D1505 (LLDPE, HDPE) or IS01133 (VLDPE).

[00106] The melting point and heat of fusion referred to in the description and claims were determined by differential scanning calorimetry (DSC) according to ASTM-3418.

[00107] Weight average molecular weight (Mw), number average molecular weight (Mn) and molecular weight distribution as Mw/Mn were measured using a high temperature size exclusion chromatograph (SEC) (Waters Alliance 2000), equipped with a differential refractive index detector (DRI). Three Polymer Laboratories PLgel 10mm Mixed-B columns were used. The nominal flow rate was 1.0 cm3 /min, and the nominal injection volume was 300 μί^. The various transfer lines, columns, and differential refractometer (the DRI detector) were contained in an oven maintained at 145°C. [00108] Polymer solutions were prepared in filtered 1,2,4-trichlorobenzene (TCB) containing -1000 ppm of butylated hydroxy toluene (BHT). The same solvent was used as the SEC eluent. Polymer solutions were prepared by dissolving the desired amount of dry polymer in the appropriate volume of SEC eluent to yield concentrations ranging from 0.5 to 1.5 mg/mL. The sample mixtures were heated at 160°C with continuous agitation for about 2 to 2.5 hours. Sample solution will be filtered off-line before injecting to GPC with 2 μιη filter using the Polymer Labs SP260 Sample Prep Station.

[00109] The separation efficiency of the column set was calibrated using a series of narrow MWD polystyrene standards, which reflects the expected MW range for samples and the exclusion limits of the column set. Seventeen individual polystyrene standards, ranging from Mp -580 to 10,000,000, were used to generate the calibration curve. The polystyrene standards are obtained from Polymer Laboratories (Amherst, MA). To assure internal consistency, the flow rate is corrected for each calibrant run to give a common peak position for the flow rate marker (taken to be the positive inject peak) before determining the retention volume for each polystyrene standard. The flow marker peak position thus assigned was also used to correct the flow rate when analyzing samples; therefore, it is an essential part of the calibration procedure. A calibration curve (logMp vs. retention volume) is generated by recording the retention volume at the peak in the DRI signal for each PS standard, and fitting this data set to a 2nd -order polynomial. The equivalent polyethylene molecular weights are determined by using the following Mark-Houwink coefficients:

Figure imgf000030_0001

The DRI detector generated elution profiles which were converted using known software to generate Mw and Mn values.

Film properties

[00110] Thickness was measured using a micrometer and is measured also during the haze measurement. The thickness of the constituent layers is determined by the loss of weight feeders of the coextrusion line. The relative output multiplied by the density of the extruded material determines the layer distribution. It can be confirmed afterwards if necessary by using a microtomed sample of the film cut in cross section and examined by optical microscopy using polarized light so the individual layers become visible and can be measured relative to each other and relative to the total thickness of the film in question.

[00111] Haze was measured according to a procedure based on ASTM D-1003 using a Hunterlab Ultrascan XE spectrophotometer. The haze is the ratio in % of the diffused light relative to the total light transmitted by the sample film. The haze (total haze) is measured in total transmittance mode, illuminant C, 2° observer, scale XYZ as standard.

Illuminant C: overcast skylight, 6740K

2° observer: 2° field of view, focus on the fovea 1931 CIE standard observer

Scale XYZ: X=red light related/red/green coder

Y=green light related/black white coder

Z=blue light related/blue-yellow coder

Only the Y value is relevant for haze and represents the total light transmitted through the sample.

[00112] The tensile properties of the films are tested on a method which is based on ASTM D882-02 with static weighing and a constant rate of grip separation using a Zwick 1445 tensile tester with a 200N or 500N load cell. The deformation is measured by means of the cross-head position. Since a rectangular shaped test specimen is used, no additional extensometer is 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. A pre-load of 0.1 N was used to compensate for the so called TOE region at the origin of 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), 500 mm/min to measure yield point and break point. The film samples may be tested in machine direction (MD) and transverse direction (TD). While the standard permits number of performance aspects related to the tensile properties to be determined, in this specification the following were measured.

[00113] Puncture resistance determines the low speed puncture properties of plastic film samples. The method is designed to provide load versus deformation response under multiaxial deformation conditions at a fixed relatively low test speed. According to the method, a piston with a standard probe fixed to the load cell is pushed through a film sample in a circular sample holder up to break. The load is measured on the load cell and the deformation is measured by the travel of the cross-head. Puncture resistance enables measurement of the degree of capability of films in wrapping sharp articles. According to the method, Travel at Fmax relates to the measured deformation in the film sample at maximum load and is expressed in (mm). Travel at Break refers to the measured deformation in the film sample at break point and is expressed in (mm). Maximum puncture force: This is the maximum (nominal) load sustained by the film sample before the break point. It is normalised for the film thickness and expressed in (Ν/μιη). Puncture force at break refers to the load at the break point which is normalised for the film thickness and is expressed in ( /μιη). Puncture energy at Fmax refers to the total energy absorbed by the film sample at the maximum load. It is the integration of the area up to maximum force under the load-deflection curve normalised for the film sample thickness. It is expressed in (mJ/μιη). Puncture energy at break refers to the total energy absorbed by the film sample at the moment of break point. It is the integration of the area up to the breaking point under the load-deflection curve. It is normalised for the film sample thickness and expressed in (mJ/μιη). Strain refers to the travel distance of the cross-head and so the puncture probe and the deflection of the film sample. It is expressed in (mm). Standard force refers to the load measured at the load cell. It is expressed in (N). Samples are held for at least 40 hours at 23°C + 2°C and at 50% + 5% relative humidity prior to testing. The testing is conducted on a Zwick 1445 NR.2 (Zwick GmbH & Co. KG) according to the manufacturer's instructions.

[00114] Dart Impact was measured by a method following ASTM D-1709-04 on a Dart Impact Tester Model C from Davenport Lloyd Instruments in which a pneumatically operated annular clamp is used to obtain a uniform flat specimen and the dart is automatically released by an electro-magnet as soon a sufficient air pressure is reached on the annular clamp. The test measures energy in terms of the weight (mass) of the dart falling from a specified height, which would result in 50% failure of specimens tested. Method A used darts head made of Tuflon™ (a phenolic resin) with a diameter of 38mm dropped from a height of 660 mm for films whose impact resistance requires masses of 50 g or less to 2 kg to fracture them. Method B employs a dart with a diameter of 51 mm dropped from a height of 1524 mm with an internal diameter of the specimen holder of 127 mm for both method A and B. The values given are acquired by the standard Staircase Testing Technique. The samples have a minimum width of 20 cm and a recommended length of 10 m and should be free of pinholes, wrinkles, folds, or other obvious imperfections.

[00115] The Elmendorf tear strength is based on ASTM D-1922-03a using the Protear Tearing Tester 2600 and measures the energy required to continue a pre-cut tear in the test sample. The potential energy of the raised pendulum is converted into kinetic energy during the swing. The total work done in tearing the film sample is the difference between the initial potential energy of the raised pendulum and the remaining potential energy at the completion of the tear. Two pendulums and appropriate augmenting weights may be used: 400 and 800 g weights for the 200 g pendulum system and 3200 and 6400 g weights for the 1600 g pendulum system. The Protear equipment reports average tearing resistance for a 43 mm tearing distance. The augmenting weights: may be 400, 800, 1600, 3200, and 6400 g. A minimum of 6 samples each in MD and TD direction with a sharp knife and the dedicated mould. The thickness of each sample is measured at the tear area at a minimum 3 points; the average is recorded as the sample thickness. The pendulum base weight is selected by estimating the test range. At 200 g - 800 g test range, a, 200 g pendulum is used and at 1600 g to 6400 g, a 1600 g pendulum is used. The test weight is selected, so that the test results will be between 20% and 80% of the pendulum scale. The line of tear should fall within 60° at either side of the vertical for valid data points.

[00116] Shrink (Betex shrink), reported as a percentage, was measured by cutting circular specimens from a film using a 50 mm die. The samples were then put on a copper foil and embedded in a layer of silicon oil. This assembly was heated by putting it on a 150°C hot plate (model Betex) until the dimensional change ceased. An average of four specimens is reported. A negative shrinkage number indicates expansion of a dimension after heating when compared to its preheating dimension.

[00117] All multilayer films were made on a Windm511er & H51scher 3-layer coextrusion blown film line with following features:

• Extruder A (internal layer): 60 mm diameter, grooved feed

· Extruder B (middle layer): 90 mm diameter, grooved feed

• Extruder C (external layer): 60 mm diameter, smooth bore

• 250 mm die diameter

• 1.4 mm die gap

• IBC and Optifil P2 thickness profile control

[00118] A group of exemplary films was produced in an A/B/A arrangement with a relative thickness of 1/3/1. The films were produced at different strain rates to produce films having targeted thicknesses between 40 μιη and 80 μιη to evaluate the presence of the HTC effect in an embodiment of the films. Examples of an embodiment of alternative films were also produced in this same way. These alternative embodiment examples do not show the HTC effect. The data are shown in Table 2, wherein the alternative embodiment examples are marked with the letter "A" prior to the Example No.

Figure imgf000034_0001

[00119] A Haze-Thickness plot of the data in Table 2 is shown graphically in Figure 1. The equation for the fitted line (the trendline) for the data of the embodiment having the HTC effect y = 0.323 lx - 8.0923 with a goodness of fit R2 = 0.9947.

The equation for the fitted line (the trendline) for the alternative embodiment data is:

y = 0.1785x - 0.6456 with a goodness of fit R2 = 0.9937.

As the data in these examples show, the HTC embodiment films have a higher slope than the alternative embodiment data which is greater than or equal to 0.2. The fitted line for the HTC embodiment data between a thickness of 40 μιη and 80 μιη results in a y intercept which is less than -2 (i.e., -8.0923). Extrapolation of the fitted line for the inventive data produces a 0% haze (X-axis intercept) at a thickness of - 25 μιη.

[00120] In contrast, the alternative embodiment examples show a slope of less than 0.2 (i.e., 0.1785) and a y intercept of greater than -1 (i.e., -0.6456). Extrapolation of the fitted line for the alternative embodiment data produces a 0% haze (X-axis intercept) at a thickness of ~ 3.6 μιη.

[00121] The unexpected benefit of the HTC effect is seen in the HTC embodiment data and not in the alternative embodiment data, even though the only difference between the two films is the presence of ENABLE 27-03 in the core layer of the HTC embodiment examples, as compared to ENABLE 35-05 in the alternative embodiment examples.

[00122] Other properties of the HTC embodiment examples and the alternative embodiment examples were measured. The data are shown in Table 3.

Table 3

Sample

Number 1 2 3 4 5 A6 A7 A8 A9 A10 All

Layer

distribution 1/3/1 1/3/1 1/3/1 1/3/1 1/3/1 1/3/1 1/3/1 1/3/1 1/3/1 1/3/1 1/3/1

Thickness μιη 40 50 60 70 80 30 40 50 60 70 80 thickness μιη 44 52 62 72 80 33.5 41.5 51.5 62 71 81.5 measured

Optical

properties

Total Haze % 6.4 9.0 12.0 14.8 17.7 5.0 6.9 8.8 10.7 11.8 13.8

Gloss 45° % 77 74 77 62 56 84 80 76 73 70 67

Clarity % 72 70 59 60 56 69 68 67 66 66 56

Tensile

properties

10% offset yield MPa 15.7 15.8 15.7 15.8 16.2 17.4 17.4 16.9 17.2 17.1 17.2 stress in MD

10% offset yield

stress in TD MPa 16.3 16.1 16.5 16.5 16.3 16.5 17.3 17.1 17.6 17.4 16.6

Tensile @ break

MD MPa 46.3 50.4 47.0 48.1 50.4 47.0 44.7 44.4 45.5 42.4 42.2

Tensile @ break

TD MPa 48.0 51.6 51.7 49.5 50.4 40.4 43.8 40.6 41.1 40.8 40.2

Elongation @

break MD % 612 682 685 707 749 592 614 664 690 679 719

Elongation @

break TD % 755 790 797 793 812 678 731 714 717 739 752 mj/m

Energy MD m3 157 180 169 173 185 159 155 159 168 156 166 mj/m

Energy TD m3 164 181 189 181 185 136 155 142 147 152 157

1% secant mod

MD MPa 372 393 393 400 412 448 447 438 449 447 445

1% secant mod

TD MPa 435 446 445 447 407 525 516 480 494 480 448

Elmendorf tear

strength

MD g/μιη 3.1 3.9 4.1 5.0 5.4 1.7 1.9 3.2 3.8 3.2 3.5

TD g/μιη 16.9 16.4 15.5 13.9 14.0 16.4 16.7 16.1 15.6 13.7 12.9

MD g 131 195 255 367 438 52 82 129 230 224 298

TD g 743 818 962 977 1 137 505 705 806 954 979 1 101

Puncture

Resistance

Maximum force Ν/μιη 2.68 2.82 2.75 2.75 2.64 2.61 2.3 2.28 2.15 2.07 1.98

Maximum force N 1 18 145 169 197 21 1 87 95 1 17 133 147 161

Travel @ Fmax mm 125 137 135 140 140 109 107 1 10 107 108 109 mj/μ

Energy @ Fmax m 193 223 214 220 213 170 149 152 142 138 132

Shrink

properties

Betex shrink

MD % 75 73 71 70 69 79 79 75 71 73 70

TD % 13 20 19 20 20 14 13 13 14 21 18

Retramat

shrink @190°C

45sec

Shrinking force

MD N 0.048 0.047 0.048 0.044 0.046 0.030 0.035 0.044 0.039 0.034 0.039

Contracting N 1.21 1.55 1.79 2.32 2.46 0.842 1.31 1.69 1.79 2.11 2.46 force MD

Shrinkage ratio % 68 65 62 57 52 71 66 60.5 63.5 60 55

MD [00123] As the data for these examples show, the multilayer blown films produced according to an embodiment of the instant disclosure show the HTC effect in combination with improved optical and physical properties compared to the alternative embodiment films.

[00124] Although the present invention has been described in considerable detail with reference to certain aspects and embodiments thereof, other aspects and embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.

[00125] Certain features of the present invention are described in terms of a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges from any lower limit to any upper limit are within the scope of the invention unless otherwise indicated.

[00126] All patents, test procedures, and other documents cited in this application are fully incorporated herein by reference for all jurisdictions in which such incorporation is permitted.

Claims

A multilayer blown film comprising:
at least one outer layer comprising a linear low density polyethylene having a density greater than or equal to 0.921 g/cm3;
a core layer comprising at least about 10 wt% of a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR I21.6/I2.16 @ 190°C) of greater than or equal to about 35 and less than or equal to about 60, and a melt index of less than or equal to about 0.4 g/10 min as determined according to ASTM D 1238 at 190°C/2.16 kg, and a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3, wherein the core layer has a density greater than the density of the at least one outer layer.
The multilayer blown film of claim 1, wherein the at least one outer layer comprises a metallocene linear low density polyethylene (mLLDPE).
The multilayer blown film of claim 1, wherein the at least one outer layer comprises: a metallocene linear low density polyethylene having an MIR, I21.6/ 12.16 @ 190°C of less than or equal to about 34;
a Ziegler-Natta linear low density polyethylene having an MIR, I21.6 / 12.16 @ 190°C of less than or equal to about 30; or
a combination thereof.
The multilayer blown film of claim 1, wherein the core layer further comprises a linear low density polyethylene (LLDPE) having a MI of less than or equal to about 2.2 g/10 min as determined according to ASTM D 1238 at 190°C/2.16 kg.
The multilayer blown film of claim 1, wherein the core layer comprises greater than or equal to about 10 wt% and less than or equal to about 90 wt% of the metallocene linear low density polyethylene based on the total weight of the core layer.
The multilayer blown film of claim 1, wherein the core layer comprises a blend comprising the metallocene linear low density polyethylene and the high density polyethylene.
The multilayer blown film of claim 1 comprising two outer layers, wherein the core layer is disposed between the two outer layers. The multilayer blown film of claim 7, wherein the two outer layers have the same composition.
The multilayer blown film of claim 1, wherein the outer layer comprises:
a metallocene linear low density polyethylene comprising a copolymer derived from ethylene and one or more C3 to C20 a-olefin comonomers having a density greater than or equal to 0.927 g/cm3; a melt index of less than or equal to 1.3 as determined according to ASTM D1238 at 190°C/2.16 kg; and a MIR, I21.6 / 12.16 @ 190°C of less than or equal to about 16.
The multilayer blown film of claim 1, wherein the film has a haze of less than or equal to about 10% as determined according to ASTM D1003.
The multilayer blown film of claim 1, wherein the film has a haze of less than or equal to about 8% as determined according to ASTM D1003 and a thickness of less than or equal to about 50 μιη.
The multilayer blown film of claim 1 , wherein the film is produced at a strain rate of greater than or equal to about 0.6 s"1.
The multilayer blown film of claim 1, wherein the metallocene linear low density polyethylene present in the core layer has a density and a melt index relationship according to the formula:
22.3 > 23.58 x [density, g/cm3] - 0.2634 ln(MI, I2.16@190°C, g/10 min) > 21.7.
The multilayer blown film of claim 1, wherein the MIR I21.6 I2.16 @ 190°C of the metallocene linear low density polyethylene present in the core layer is greater than or equal to about 46 and less than or equal to about 58.
The multilayer blown film of claim 1 , where a film has a dart impact of greater than or equal to about 2.5 Ν/μιη as determined according to ASTM D1709-04.
The multilayer blown film of claim 1, wherein a fitted line of a haze-thickness plot from about 45 μιη to about 80 μιη, has a positive slope of greater than or equal to about
0.2% haze/μιη and a y-intercept value of less than or equal to about -2.
The multilayer blown film of claim 16, wherein the fitted line of the haze-thickness plot has a positive slope of greater than or equal to about 0.3% haze/μιη, a y-intercept value of less than or equal to about -5, or a combination thereof.
The multilayer blown film of claim 1 , wherein a fitted line of a haze-thickness plot from about 45 μιη to about 80 μιη, has an extrapolated zero haze value at a thickness of greater than or equal to about 5 μιη. A multilayer blown film comprising:
two "A" skin layers arranged on opposite sides of a "B" core layer in an A/B/A
configuration;
wherein each of the A layers comprise a linear metallocene polyethylene comprising a copolymer derived from ethylene and one or more C3 to C20 a-olefin comonomers having a density greater than or equal to 0.921 g/cm3; and a melt index of less than or equal to about 1.3 as determined according to ASTM D1238 at 190°C/2.16 kg; and a MIR, I21 6 / 12 16@ 190°C of less than or equal to about 16;
a core layer comprising at least about 10 wt% of a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR, I21.6 / L.i6@ 190°C) of greater than or equal to about 46 and less than or equal to about 58, and a melt index of less than or equal to about 0.3 g/ 10 min as determined according to ASTM D 1238 at 190°C/2.16 kg, and a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3, wherein the core layer has a density greater than the density of the at least one outer layer;
wherein the film comprises a haze of less than about 10% according to ASTM D 1003 at a thickness of less than or equal to about 50 μιη.
The multilayer blown film of claim 19, wherein a fitted line of a haze-thickness plot over film thicknesses from about 45 μιη to about 80 μιη at the same layer thickness ratios, has a positive slope of greater than or equal to about 0.2% haze/μιη and a y- intercept value of less than or equal to about -2.
A process for producing a multilayer blown film, comprising:
selecting a first polyethylene comprising a linear low density polyethylene having a density greater than or equal to 0.921 g/cm3;
selecting a second polyethylene comprising a metallocene linear low density polyethylene (mLLDPE) having a density greater than or equal to 0.927 g/cm3, a melt index ratio (MIR I21.6/I2.16 @ 190°C) of greater than or equal to about 35 and less than or equal to about 60, and a melt index of less than or equal to about 0.4 g/10 min as determined according to ASTM D1238 at 190°C/2.16 kg; selecting a high density polyethylene (HDPE) having a density of greater than 0.94 g/cm3; combining at least 10 wt% of the second polyethylene with the high density polyethylene to produce a blend having a density greater than the density of the first polyethylene; and
extruding the first polyethylene and the blend from a die wherein the first polyethylene forms a first and second skin layer, wherein the blend forms a core layer disposed between the first and second skin layer, and wherein the film is extruded at a strain rate of greater than or equal to about 0.6 s"1.
The process of claim 21, wherein the film is produced at a strain rate of greater than or equal to about 0.8 s"1.
The process of claim 21, wherein the first polyethylene, the second polyethylene, and the high density polyethylene are selected such that a fitted line of a haze -thickness plot over film thicknesses from about 45 μιη to about 80 μιη at the same layer thickness ratios, has a positive slope of greater than or equal to about 0.2% haze/μιη and a y- intercept value of less than or equal to about -2.
The process of claim 23, wherein the fitted line of the haze-thickness plot has a positive slope of greater than or equal to about 0.3% haze/μιη, a y-intercept value of less than or equal to about -8, or a combination thereof.
The process of claim 21, wherein the first polyethylene, the second polyethylene, and the high density polyethylene are selected such that a fitted line of a haze -thickness plot from over film thicknesses from about 45 μιη to about 80 μιη at the same layer thickness ratios, has an extrapolated zero haze value at a thickness of greater than or equal to about 5 μιη.
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