WO2016094281A1 - Stretch wrapping film - Google Patents

Abstract

Disclosed is a stretch wrapping multilayer film for pallet or multipack applications comprising at least one ionomer-containing layer; and at least one additional layer comprising a polyolefin, wherein the ionomer comprises from 5 to 40 weight % of the polymeric material of the film, and the film shows strain hardening behavior, and high yield stress in particular in the machine direction of the film. Also disclosed are uses and methods to stretch wrap the film around objects.

Description

Title

STRETCH WRAPPING FILM

Field Of The Invention

This invention relates to a stretch wrapping film, such as for pallet packaging.

Background

Many relatively small items are shipped on pallets, that is, platforms that are easily moved by forklifts or small cranes. Pallets provide convenience in loading and unloading goods from shipping containers, and in moving smaller amounts of goods over shorter distances, such as within warehouses, or to deliver a retail quantity. The small items may be unpackaged or packaged, for example in bags or boxes, when they are placed on the pallets.

A loaded pallet preferably has integrity and stability, so that the goods are not damaged or lost during shipping. To provide the necessary integrity and stability, the pallet and its load have been typically wrapped together in film, for example overlapping layers of polyethylene stretch wrap that may be applied by machine or by hand. See, e.g., US RE38429. Other generally practiced methods for providing integrity and stability to loaded pallets include containing the goods in a single carton or box, wrapping the pallet and its load in heat shrinkable film, and encasing the loaded pallet in a sheath or "hood" which may be heat shrinkable or stretchable. These methods are sometimes referred to, individually or collectively, as "pallet unitizing".

Stretch wrapping concerns the bundling of items together using a film that is wrapped around the pallet while simultaneously stretching it (or prestretching the film and then wrapping). Stretch wrapping is used for a very wide variety of applications and notably for the tertiary packaging of food or drinks providing stability to load on pallets. This can apply to loads such as bottles, cans, but also to containers, heavy duty bags and the like.

The process of applying a stretch wrapping film consists of wrapping the film around the pallet from the bottom to the top or from the top to the bottom applying a varying stretch tension at room temperature or, on an automatic machine, applying a pre-stretch ratio and a chosen lay-on tension during wrapping.

Suitable performance characteristics of the stretch wrapping film include sufficient stretchability and holding force allowing the film to be tightly wrapped around the items being packaged and a low enough Coefficient of Friction (COF) for machinability and package handling. Films that are used in the stretch wrapping process require high holding force according to ASTM D4649 and associated with a high yield strength and tensile strength at low deformation ratios like 50% (referred to as load retention resistance), and puncture resistance to withstand handling and abuse during transportation.

Conventionally the films used in these applications are multilayer films with a defined stretchability and holding force in particular in the cold state. Many stretch wrapping films comprise combinations of low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and/or high density polyethylene (HDPE) or Ultra Low Density Polyethylene (ULDPE) for improved cling of the film. See for example EP1529633, EP2653392 and references therein. Multilayer stretch wrap films comprising various polyethylene layers are disclosed in U.S. Patents 4,518,654, 5,516,475, 5,907,942 and 6,361,875. Additional disclosures of interest include U.S. Patents 3,355319, 6,492,010 and 6,572979, U.S. Statutory Invention Registration H2073, U.S. Patent Application Publications US2009/061061, US2009/230595, PCT Publications WO95/00333 and WO2010/022066, and European Patent Applications EP0597502, EP0974452, and EP1857270.

However, a problem during the production of the finished stretch- wrapped goods (pallet or multipack) is that many of these films have to be pre-stretched or pre-oriented which represents an additional production step and increases therefore the cost. Furthermore many of the commercial films have insufficient holding force, or yield point mostly but not exclusively associated with poor strain hardening behavior, which results in insufficient pallet stability during transportation.

Furthermore during transportation a deformation or elongation or straining of the film will result in non-uniform deformation as soon as the yield point is surpassed, which is due to the missing "strain hardening" effect of the films used in this application. Strain hardening is the continuous increase of stress as a function of displacement in the stress train curve when undertaking a monoaxial tensile test according to ASTM 882 for example. Strain hardening means that upon deformation of the film, the force necessary for further deformation rises as the deformation and strain increases.

Therefore, it is desired that the films used for stretch wrapping show strain hardening.

For this purpose many films are pre-stretched for several 100% or actually oriented in a mono orientation process prior to being applied as stretch wrapping film.

Accordingly, it is desirable to find films that can overcome this problem and show superior strain hardening properties associated with a high yield stress in the stress strain curve, even at low stretching ratio (e.g. 50 % or less) for use in stretch wrapping.

Summary of the Invention

This invention relates to a stretch wrapping multilayer film comprising

(a) at least one layer comprising an ionomer comprising a copolymer comprising copolymerized units of ethylene and between 1 and 25 weight % of copolymerized units of methacrylic acid or acrylic acid wherein from 1 to 99 % of the carboxylic acid groups are neutralized to carboxylate salts comprising metal ions; and

(b) at least one additional layer comprising a polyolefin and not comprising an ionomer;

(c) optionally at least one adhesion layer; and

(d) optionally at least one layer comprising an ethylene copolymer other than an ionomer comprising copolymerized units of ethylene and copolymerized units of an ester of unsaturated carboxylic acids or an ester of vinyl alcohol;

wherein the total amount of the ionomer comprises from 5 to 40 weight % of the polymeric material of the multilayer film; and the ionomer-comprising composition of (a), the polyole fin-comprising composition of (b) and the compositions of the optional (c) and (d) layers, when present, comprise 100 % of the polymeric materials of the film; and wherein the yield stress of the film in the machine direction (MD) is at least 12 MPa, or is 25% higher than the yield stress of a corresponding film without ionomer when stretched by 50%; the strain hardening regime from 100 to 200% of elongation of the film is characterized by a continuous increase of stress of at least 2 MPa in the machine direction; and the film shrinks by less than 10 % in both the machine direction and the transverse direction when exposed to a temperature of 90 °C for at least 2 seconds.

The invention also provides a method for stretch wrapping an object, such as an object comprising a plurality of individual product containers, comprising:

(i) obtaining a stretch wrapping film described above; and

(ii) wrapping the object in the stretch wrapping film.

The invention also provides for use of a stretch wrapping film as described above to stretch wrap an object, such as an object comprising a plurality of individual products or an irregularly shaped object such as machinery or furniture.

The invention also provides a stretch wrapped product comprising the film described above wrapped around an object, such as an object comprising a plurality of individual products or an irregulary shaped object such as machinery or furniture.

Detailed Description of the Invention

All references disclosed herein are incorporated by reference.

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). As used herein, the terms "a" and "an" include the concepts of "at least one" and "one or more than one". The word(s) following the verb "is" can be a definition of the subject.

The transitional phrase "consisting of excludes any element, step, or ingredient not specified in the claim, closing the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith.

The transitional phrase "consisting essentially of limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) of the claimed invention. Optional additives as defined herein, at levels that are appropriate for such additives, and minor impurities are not excluded from a composition by the term "consisting essentially of. Moreover, such additives may possibly be added via a masterbatch that may include other polymers as carriers, so that minor amounts (less than 5 or less than 1 weight %) of polymers other than those recited may be present. Therefore, the term "consisting essentially of in relation to polymeric compositions is to indicate that substantially (greater than 95 weight % or greater than 99 weight %) the only polymer(s) present in a component is the polymer(s) recited.

Unless stated otherwise, all percentages, parts, ratios, etc., are by weight. Further, when an amount, concentration, or other value or parameter is given as either a range, preferred range or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range. When a component is indicated as present in a range starting from 0, such component is an optional component (i.e., it may or may not be present). When present an optional component may be at least 0.1 weight % of the composition or copolymer.

When materials, methods, or machinery are described herein with the term "known to those of skill in the art", "conventional" or a synonymous word or phrase, the term signifies that materials, methods, and machinery that are conventional at the time of filing the present application are encompassed by this description. Also encompassed are materials, methods, and machinery that are not presently conventional, but that may have become recognized in the art as suitable for a similar purpose.

The term "plurality" as used herein means two or more, including up to that needed for e.g. describing the number of individual items to be collated by wrapping in the stretch film, or the number of layers in a microlayer or nanolayer structure.

The term "machine direction" refers to the direction of travel of the polymers and resulting film through the film-forming machine. "Transverse direction" refers to the direction perpendicular to the machine direction across the width of the film.

As used herein, the term "copolymer" refers to polymers comprising copolymerized units resulting from copolymerization of two or more comonomers and may be described with reference to its constituent comonomers or to the amounts of its constituent comonomers such as, for example "a copolymer comprising ethylene and 15 weight % of acrylic acid". A description of a copolymer with reference to its constituent comonomers or to the amounts of its constituent comonomers means that the copolymer contains copolymerized units (in the specified amounts when specified) of the specified comonomers. Polymers having more than two types of monomers, such as terpolymers, are also included within the term "copolymer" as used herein. A dipolymer consists of two copolymerized comonomers and a terpolymer consists of three copolymerized comonomers. The term "consisting essentially of in reference to copolymerized comonomers allows for the presence of minor amounts (i.e. no more than 0.2 weight %) of non- recited copolymerized units, for example arising from impurities present in the commoner feedstock or from decomposition of comonomers during polymerization.

"(Meth)acrylic acid" includes methacrylic acid and/or acrylic acid and "(meth)acrylate" includes methacrylate and/or acrylate. The term "when exposed to a temperature of refers to the temperature of the environment around the film such as the temperature of the oven in which the film is placed or the temperature of an oil or water bath in which the film is placed. It will be appreciated that if the film is present in an oven for a short period of time, the film itself may not heat to the oven temperature. For ease of measurement however, "when exposed to a temperature" refers to the temperature of the environment rather than the actual film temperature.

The term "stretch wrapped" as used herein does not relate to wrapping a product formed from a large number of small identical units such as rice, sweets or pasta but is based on a plurality of items such as containers that are combined into a single object wrapped in a film with certain stretch characteristics.

When the terms "stretched" or "elongated" and similar terms are with a percentage, the percentage of stretching is the amount of stretch beyond the original dimension of the film. For example, a film elongated by 100% is stretched to twice the original dimension of the film in the direction indicated. Likewise the percentage of "shrink" and the like is the amount of decrease in dimension compared to the pre-shrink dimension.

The term "an object comprising a plurality of individual product containers" means that the object being wrapped is itself formed from a plurality of preferably identical containers such as bags, cans, tins, bottles, jars, plastic liquid dispensers (e.g. shower gel, shampoo, and soap containers), boxes, vials, tubes and so on. The number of such containers making up the object might vary, e.g. from 2 to 64 containers. The skilled person will be familiar with objects that can be wrapped such as a 6-pack of beverage cans, 24-pack of food cans and so on.

Optionally the multiple containers might be carried on a tray, such as a cardboard tray. In that case, the tray forms part of the object being wrapped.

The containers typically may be arranged in a regular pattern such as a square or rectangle. Containers can have any cross-section such as circular (like bottles and cans), oval, square, rectangular or irregular. The smallest cross-sectional dimension of any container is preferably at least 1 cm. The maximum cross-sectional dimension is preferably 200 cm (the diagonal dimension for rectangular objects such as boxes) in the case of pallet unitizing. In consumer multipacks, containers may not be stacked before wrapping; therefore there may be a single layer of containers to be wrapped. Alternatively, containers may be stacked to provide a plurality of layers of containers, such as in pallet unitizing. For example, a pallet load may comprise from 1 to 20 layers of containers high arranged in arrays of 1 to 10 by 2 to 10 containers, depending on the size and shape of the containers.

A "pallet" as used herein is a low platform constructed of wood, plastic and/or metal on which items are placed for shipping and/or storage.

The films of the invention are multilayer films. In its simplest embodiment, this invention covers a multilayer stretch wrapping film comprising at least one ionomer containing layer and at least one additional layer comprising a polyolefin as the major component. Other optional layers include adhesion layers and/or layers comprising an ethylene copolymer other than an ionomer comprising copolymerized units of ethylene and copolymerized units of an ester of unsaturated carboxylic acids or an ester of vinyl alcohol. Multilayer films are preferably formed from at least three layers, such as 3 layers, 5 layers or 6 layers, or up to as many as 13 layers or more. Notably, the film structure does not include polyamides (nylons), polyesters such as polyethylene terephthalate (PET), ethylene vinyl alcohol (EVOH), polyvinylide chloride (PVDC) or other polymers except ionomers, polyolefins and other ethylene copolymers as defined herein.

An overall or total content of 5 to 40 of ionomer present in the film will provide strain hardening of the film. The strain hardening may be defined by a steady and uniform increase of the stress of at least 2 MPa, such as at least 3MPa, over the yield stress when elongating the film from 100% to 200% beyond its initial dimension in MD. This reduces the effect of non-uniform deformation of the film and leads to a tighter fitting package.

Furthermore it was surprisingly found that even though the ionomer content comprises less than 40 % of the entire film, the film exhibits a superior yield strength compared to a comparison film not containing an ionomer. The yield strength is at least 12 MPa, preferably 15 MPa; or at least 25% higher than the yield stress of a corresponding film without ionomer, when stretched by 50%.

This unique combination of yield strength and strain hardening effect will lead to superior performance in pallet and individual pack film packages and will keep the packs tight during production and transportation.

Depending on the level of its orientation, the film also shows shrinkage of less than 10 % in addition to its strain hardening behavior when exposed to elevated temperatures above 80 °C.

At least one layer of the multilayer film comprises, or consists essentially of, or consists of, an ionomeric composition comprising an ionomer, such that the total of the ionomer comprises from 5 to 40 weight %, such as from 5, 10, 15 or 20 % to 30, 35, or 40 %, of the polymeric components of the multilayer film. Ionomers are ionic copolymers of an olefin such as ethylene (E) with a metal salt of an unsaturated carboxylic acid, such as acrylic acid (AA), methacrylic acid (MAA), and/or other acids, and optionally softening comonomers such alkyl acrylates or alkyl methacrylates. At least one alkali metal, transition metal, or alkaline earth metal cation, such as lithium, sodium, potassium, magnesium, calcium, or zinc, or a combination of such cations, is used to neutralize some portion of the acidic groups in the copolymer resulting in a thermoplastic resin exhibiting enhanced properties. Preferred α,β-ethylenically unsaturated monocarboxylic acids include acrylic acid and methacrylic acid, present in the copolymer in 1 weight % to 25 weight %. Dipolymers preferably include from 8 to 20 weight % of α,β-ethylenically unsaturated monocarboxylic acid. For example, a dipolymer of ethylene and methacrylic acid can then be at least partially neutralized to salts comprising one or more alkali metal, transition metal, or alkaline earth metal cations to form an ionomer.

As indicated above, comonomers such as alkyl (meth)acrylates can be included in the ethylene acid copolymer to form a terpolymer that can be neutralized to provide carboxylate salts with alkali metal, alkaline earth metal or transition metal cations. Preferred are comonomers selected from alkyl acrylate and alkyl methacrylate wherein the alkyl groups have from 1 to 8 carbon atoms, and more preferred are comonomers selected from methyl acrylate, ethyl acrylate, z^'so-butyl acrylate (iBA), and «-butyl acrylate (nBA). The alkyl (meth) acrylate s are optionally included in amounts from 0 to 30 weight % alkyl (meth)acrylate such as from 1 to 30 weight % and preferably from 5 to 25 weight % of the copolymer when present.

The ethylene acid terpolymer comprises one or more E/X/Y terpolymers where E represents copolymerized units of ethylene, X represents copolymerized units of at least one C₃-C₈ α,β-ethylenically unsaturated carboxylic acid, Y represents copolymerized units of a softening comonomer (softening means that the polymer is made less crystalline).

Examples of X include acrylic acid or methacrylic acid and X can be from 3 to 35, 4 to 25, or 5 to 20, weight % of the E/X/Y copolymer and ethylene can make up the rest. Examples of Y include alkyl acrylate, alkyl methacrylate, or combinations thereof wherein the alkyl groups have from 1 to 8, or 1 to 4, carbon atoms. E/X/Y copolymers wherein Y is present in at least 1 weight %, or 2 to 35 weight % of the E/X/Y copolymer are notable. Ethylene can make up the rest of the E/X/Y terpolymer.

Specific terpolymers include ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/n-butyl methacrylate, ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylic acid/iso- butyl methacrylate, ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl methacrylate, ethylene/acrylic acid/ethyl acrylate and ethylene/methacrylic acid/ethyl methacrylate terpolymers, or combinations of two or more thereof.

The acid copolymers used herein are preferably "direct" or "random" acid copolymers. Direct or random copolymers are polymers polymerized by adding all monomers simultaneously, as distinct from a graft copolymer, where another monomer is grafted onto an existing polymer, often by a subsequent free radical reaction. Ethylene acid copolymers may be produced by any methods known to one skilled in the art such as use of "co-solvent technology" disclosed in U.S. Patent 5,028,674.

Ionomers are obtained by neutralization of an acid copolymer. Neutralization of the ethylene acid copolymer can be effected by first making the ethylene acid copolymer and treating the copolymer with inorganic base(s) with alkali metal, alkaline earth metal or transition metal cation(s). The copolymer can be from 1 to 99 % neutralized to form salts with at least one metal ion selected from lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum; or combinations of such cations. Neutralization may be from 10 to 70 %. Preferably the copolymer has from 20 %, alternatively from 35 %, to 70 % of the available carboxylic acid groups ionized by neutralization with at least one metal ion selected from sodium, zinc, lithium, magnesium, and calcium; and more preferably zinc or sodium. Particularly notable is an ionomer comprising zinc cations.

The amount of basic metal compound capable of neutralizing acidic groups may be provided by adding the stoichiometric amount of the basic compound calculated to neutralize a target amount of acid moieties in the acid copolymer (herein referred to as "% nominal neutralization" or "nominally neutralized"). Thus, sufficient basic compound is made available in the blend so that, in aggregate, the indicated level of nominal neutralization could be achieved. Metal compounds of note include formates, acetates, nitrates, carbonates,

hydrogencarbonates, oxides, hydroxides or alkoxides of the ions of alkali metals, especially sodium and potassium, and formates, acetates, nitrates, oxides, hydroxides or alkoxides of the ions of alkaline earth metals and transition metals. Of note are sodium hydroxide, potassium hydroxide, sodium acetate, potassium acetate, sodium carbonate and potassium carbonate.

Unmodified ionomers are prepared from the acid copolymers such as those disclosed in U.S. Patent 3,264,272. "Unmodified" refers to ionomers that are not blended with any material that has an effect on the properties of the unblended ionomer, except the additives described below. Notably, ionomers used in the stretch wrap films of the invention comprise less than one weight % of C₆-C₃6 monocarboxylic acids or salts thereof.

Ionomers are commercially available under the trademark SURLYN^® from DuPont.

A single ionomer may be present in the ionomeric composition, or the ionomeric composition may include two or more different ionomers, such as for example, ionomers with different cations, or ionomers with different polymeric structures, such as a blend of a dipolymeric ionomer and a terpolymeric ionomer.

The ionomeric composition(s) used in ionomer- containing layer(s) present in the stretch wrap film may consist essentially of the ionomers described above. Alternatively, the ionomer in the ionomer- containing layer(s) may be blended with less than 50 weight %, such as 5 to 25 weight % of a polyolefin or a second ethylene copolymer other than an ionomer as described below. Preferably, when the ionomer is blended with a polyolefin, the copolymer used in the ionomer contains from 1 to 15 weight % of copolymerized units of carboxylic acid comonomers.

When more than one ionomer- containing layer is present, the compositions of each ionomer-containing layer may be the same as, or different from, other ionomer-containing layer(s). For example, two different ionomer compositions may be used when at least two ionomer- containing layers are present in the multilayer structure, including two different ionomers, or an ionomer and an ionomer blended with a polyolefin.

The stretch wrap film also includes at least one layer comprising a polyolefin, preferably polyethylene (PE) homopolymers or copolymers of ethylene and other a-olefins. Other a-olefins include propylene, 1-butene, 1-hexene, 4-methyl-l-pentene, 1-octene, 1-decene, 1-tetradecene, l-octadecene,vinylacetate, alkyl (meth)acrylate or in combinations of two or more. It should be appreciated that the list of comonomers above is merely exemplary, and is not intended to be limiting. Various types of polyethylenes are known in the art. PE homopolymers and copolymers may be prepared by a variety of methods, for example, the well-known Ziegler-Natta catalyst polymerization (e.g., U.S. Patents 4,076,698 and 3,645,992), metallocene catalyzed

polymerization, Versipol^® catalyzed polymerization and by free radical polymerization. The polymerization may be conducted as solution phase processes, gas phase processes, and the like. Examples of PE polymers may include high density PE (HDPE), linear low density PE (LLDPE), low density PE (LDPE), very low or ultralow density PEs (VLDPE or ULDPE), lower density PE made with metallocene having high flexibility and low crystallinity (mPE). The density of PE may range from 0.865 g/cc to 0.970 g/cc. Linear PE may incorporate a-olefin comonomers such as butene, hexene or octene to decrease density to within the density range so described. For example, a copolymer may comprise a major portion (by weight) of ethylene that is copolymerized with another a-olefin having 3 to 20 carbon atoms and up to 20% by weight of the copolymer.

Low density polyethylene ("LDPE") can be prepared at high pressure using free radical initiators and typically has a density in the range of 0.916 to 0.940 g/cm³, preferably 0.924 to 0.940 g/cm³. LDPE is also known as "branched" or "heterogeneously branched" polyethylene because of the relatively large number of long chain branches extending from the main polymer backbone. Polyethylene in the same density range, 0.916 to 0.940 g/cm³, which is linear and does not contain large quantities of long chain branching is also known; this "linear low density polyethylene" ("LLDPE") can be produced with conventional Ziegler-Natta catalysts or with single site catalysts such as metallocene catalysts. Relatively higher density LDPE or LLDPE, typically in the range of 0.928 to 0.940 g/cm³ are sometimes referred to as medium density polyethylene ("MDPE") or Linear Medium Density Polyethylene (LMDPE). Polyethylenes having still greater density are the high density polyethylenes ("HDPEs"), i.e., polyethylenes having densities greater than 0.940 g/cm³, and are generally prepared with Ziegler-Natta catalysts, chrome catalysts or even single site catalysts such as metallocene catalysts. Very low density polyethylene ("VLDPE") is also known. VLDPEs can be produced by a number of different processes yielding polymers with different properties, but can be generally described as polyethylenes having a density less than 0.916 g/cm³, such as 0.890 to 0.915 g/cm³ or 0.900 to 0.915 g/cm³.

A "metallocene polyethylene" as used herein means a polyethylene produced by a metallocene catalyst, defined to be at least one metallocene catalyst component containing one or more substituted or unsubstituted cyclopentadienyl moiety (Cp) in combination with a Group 4, 5, or 6 transition metal (M). The metallocene catalyst precursors generally require activation with a suitable co-catalyst, or activator, in order to yield an "active metallocene catalyst", i.e., an organometallic complex with a vacant coordination site that can coordinate, insert, and polymerize olefins. Non-limiting examples of metallocene catalysts and catalyst systems useful in preparing metallocene polyethylenes include W096/11961; W096/11960 and WO01/98409; U.S. Patents 4,808,561; 5,017,714; 5,055,438; 5,064,802; 5,124,418; 5,153,157; 5,240,894; 5,272,236;

5,264,405; 5,278,272; 5,324,800; 5,507,475, 6,380,122; and 6,376,410; and references cited therein. Of note are metallocene polyethylenes comprising ethylene/octene copolymers or ethylene/hexene copolymers.

The PE copolymer may also be an ethylene propylene elastomer containing a small amount of unsaturated compounds having a double bond. Ethylene copolymers having small amounts of a diolefin component such as butadiene, norbornadiene, hexadiene and isoprene are also generally suitable. Terpolymers such as ethylene/propylene/diene monomer (EPDM) are also suitable. Blends of two or more of any of the polyethylene are also contemplated for use in this invention. For example, blends of LLDPE and LDPE or blends of LDPE and HDPE or blends of LDPE, LLDPE and HDPE may be used in at least one layer of the multilayer film.

As used herein, the terms "polyethylene" and "PE" are used generically to refer to any or all of the non-ionomeric polymers comprising ethylene described above, including any of the above-described materials and blends.

The ionomer may also be blended with a second ethylene copolymer other than an ionomer comprising consisting essentially of, or consisting of, copolymerized units of ethylene and copolymerized units of a polar comonomer such as esters of unsaturated carboxylic acids or esters of vinyl alcohol (e.g. vinyl acetate). The second ethylene copolymer may also comprise optional layer(s) in the multilayer structure.

Esters of unsaturated carboxylic acids include alkyl (meth)acrylates. Examples of alkyl acrylates include methyl acrylate, ethyl acrylate and butyl acrylate. For example, "ethylene/methyl acrylate (EMA)" means a copolymer of ethylene and methyl acrylate (MA); "ethylene/ethyl acrylate (EEA)" means a copolymer of ethylene and ethyl acrylate (EA); "ethylene/butyl acrylate (EBA)" means a copolymer of ethylene and butyl acrylate (BA); and includes both n-butyl acrylate and iso-butyl acrylate unless specified; and combinations of two or more thereof.

The alkyl (me th) acrylate comonomer incorporated into the ethylene copolymer can vary from 0.01 or 5 up to as high as 40 weight % of the total copolymer or even higher, such as from 5 to 30, or 10 to 25, weight %. The second ethylene copolymer may contain 15 to 40, or 18 to 35, weight % of (meth) acrylate comonomer.

The second ethylene copolymer can comprise, consist essentially of, or consists of, repeat units derived from ethylene and an ester of vinyl alcohol (e.g. vinyl acetate) such as that disclosed above wherein the second ethylene copolymer does not contain an epoxy (e.g. glycidyl) or anhydride moiety. Vinyl acetate comonomer incorporated into the ethylene copolymer can vary from 0.01 or 5 up to as high as 40 weight % of the total copolymer or even higher, such as from 5 to 30, or 10 to 25, weight %. The second ethylene copolymer may contain 15 to 40, or 18 to 35, weight % of vinyl acetate.

Increasing (meth) acrylate comonomer or vinyl acetate commoner content may improve the elastomeric properties and increase the tackiness of the copolymer. The second ethylene copolymer may have a melt index (MI) of from 0.1 to 100, or 0.5 to 20, or 0.5 to 10, g/lOmin, measured with ASTM D1238, condition E (190°C, 2160 gram weight).

The composition of each layer in the multilayer film may additionally comprise from 0.01 to 15, 0.01 to 10, or 0.01 to 5, weight %, based on the total composition weight, of additives including plasticizers, stabilizers including viscosity stabilizers and hydrolytic stabilizers, primary and secondary antioxidants, ultraviolet ray absorbers, UV stabilizers, anti-static agents, acid scavengers, nucleating agents, dyes, pigments or other coloring agents, frre-retardants, lubricants, reinforcing agents such as glass fiber and flakes, synthetic (for example, aramid) fiber or pulp, foaming or blowing agents, processing aids, slip additives, antiblock agents such as silica or talc, release agents, tackifying resins, cling agents, other polymer processing agents and so on, or combinations of two or more thereof. The additives may be incorporated into the composition by any known process such as by dry blending, extruding a mixture of the various constituents, the conventional masterbatch technique, or the like.

For some applications, such as pallet unitizing, the composition of the film layer(s) can further comprise a fire retardant such as a chemical additive including, but not limited to, phosphorous compounds, antimony oxides, and halogen compounds, particularly bromine compounds, and others well known in the art. A loading of such additives can be between 20 to 30, or 25 % (of the final air-dried composition or air-dried film weight). The amount of such non- polymeric materials in the film is not included when calculating the amount of polymeric material in the film.

In this invention, a stretch wrap film structure is provided having at least two layers, at least one layer comprising an ionomer in pure or blended form and at least one layer comprising polyolefm.

Preferably, the stretch wrap film comprises 3 or more layers.

As used herein, the term "skin layer" means that the layer is an outer or surface layer of the structure. Thus, in a three-layer structure there are two skin layers and a core layer, sandwiched by the skin layers. This structure will be denoted A/B/A, wherein the A layer denotes a skin layer, and the B layer denotes the core layer. It will be recognized that the A layers do not need to be identical, however. The final film comprising the A/B/A structure may be symmetrical or it may be unsymmetrical. In some embodiments the skin layer(s) may preferably comprise slip or antiblock additives, while inner or core layers may not.

For example, a 3-layer film comprises an inner core layer of ionomer and two surface layers comprising polyethylene, such that the inner core layer comprises from 5 to 40 % of the total film and each surface layer independently comprises from 20 to 50 % of the total film. A specific embodiment is a 3-layer film comprising surface layers comprising a blend of LDPE and LLDPE, such as a blend comprising 70 to 95 weight % of LLDPE and 5 to 30 weight % of LDPE.

Additional film layers are contemplated, for example tie layers as described below may be positioned between one or both of the A/B layers to improve interlayer adhesion.

Other embodiments include 5-layer structures, such as A/B/C/B/A structures, preferably in which the A skin layers comprise polyethylene, B inner layers comprise an ionomer and C core layers comprise polyethylene. Notable embodiments include structures wherein the skin layer(s) comprise LLDPE, LDPE or a blend of LLDPE and LDPE, such as a blend comprising 70 to 95 weight % of LLDPE and 5 to 30 weight % of LDPE. Embodiments also include those wherein the core layer comprises a blend of LLDPE and LDPE, such as a blend of 5 to 30 weight % of LLDPE and 70 to 95 weight % of LDPE; or wherein the core layer comprises a blend of 70 to 90 weight % of LDPE and 10 to 30 weight % of HDPE; or wherein the core layer comprises 30 to 80 weight % of LLDPE, 10 to 50 weight % of LDPE and 10 to 30 weight % of HDPE. The core layer may also comprise an ionomer as part of a blend. For example, the core layer may be used to recycle edge trimmings, etc. Preferably, the core layer is thicker than the other layers. Further embodiments may include microlayer or nanolayer substructures such as produced by a nanolayer feedblock technology disclosed in U.S. Patent 6,905,324. This allows the design of film substructures of repeating polymer sequences such as D/E/F/E/F/E/F/E/F/E/F/D and the like. For example, each nanolayer substructure may comprise a plurality of nanolayers, each nanolayer comprising up to 1 % of the total film thickness, with the nanolayer substructure comprising from 5 to 10 weight % of the total film thickness. For the purpose of defining layers as used herein, a nanolayer substructure is treated as a single layer. A notable embodiment of the stretch wrap film comprises two nanolayer substructures, each 5 to 10 weight % of the total film thickness. A notable stretch wrap film comprises at least one ionomer-containing layer comprising alternating nanolayers comprising ionomer-comprising nanolayers and nanolayers not comprising ionomer, or alternating nanolayers of an ionomer and nanolayers of a different ionomer.

Additional layers may be contemplated in the stretch wrap film of this invention such as cling and/or slip layers such as described in U.S. Patents 4,518,654 and 5,907,942. For example, the stretch wrap film may comprise an outer high cling layer which may be located on or near the inner surface of the stretch film. The inner surface is the surface that is closest to the materials to be wrapped and is typically the surface on the inside of a tubular blown film used as the stretch wrap film. Cling layers may be useful to provide better hold on the articles to be shrink wrapped.

Some examples of high cling resins are resins such as ethylene alkyl acrylate copolymers having an alkyl acrylate, such as methyl, ethyl or butyl acrylate, content of 2 to 40 weight % of the copolymer and very low density polyethylenes (VLDPE). The VLDPE resins typically have a density of from 0.88 to 0.910 g/cm³ and a melt index of from 1 to 10 g/ 10 min, preferably from 2 to 5 g/10 min.

Alternatively the inside skin layer may contain cling additives such as polisobutylenes, amorphous atactic polypropylenes or ethylene-vinyl acetate copolymers having 5 to 15 weight % copolymerized vinyl acetate.

It may be desirable that the stretch wrap film may also comprise an outer slip layer which may be constructed of various resin materials suitable for such purposes. Slip layers are useful to allow wrapped pallets to move past each other without clinging or dragging, to minimize damage caused by pallets moving against each other. The outer slip layer may be located on an outer surface of the first layer or on an outer surface of the second layer. Examples of such resins include polyolefm resins and copolymers of polyolefins such as polyethylene, polypropylene, and combinations thereof. Suitable polymer resins additionally include copolymers of polyethylene with minor amounts of other C₄_i₀ olefins, particularly C₆-8 polyolefins. Preferred polyethylenes include HDPE resins having a density of from 0.92 to 0.94 g/cm³, and a melt index of from 1.0 to 4.0 g/10 min., and LLDPE resins having a density of from 0.925 to 0.945 g/cm³, and a melt index of from 2.0 to 5.0 g/10 min. Preferred polymers include polypropylenes, preferably isotactic, having a density of from 0.89 to 0.91 g/cm³, and a melt index of from 5 to 25 g/10 min. as determined by ASTM D1238.

The outer slip layer may include any of several anticling, slip or antiblock additives to improve the slip characteristics of the layer. Such additives include silicas, talcs, diatomaceous earth, silicates, lubricants, etc. These additives are generally blended with the resin material in an amount of from 100 to 20,000 ppm. When an outer slip layer is present in the stretch wrap film, a high cling layer may be preferably be included as a layer in the stretch wrap film.

Other additional layers may include adhesion or "tie" layers to provide improved interlayer adhesion between layers, such as between ionomer- containing layers and polyolefin layers.

The adhesion layer(s) will be compositionally distinct from the other layers; that is the number of components, the ratio of components or the chemical structure (for example, monomer ratio of polymeric components having the same monomers) of the components comprising the adhesion layer, will differ from the other layers. For example, adhesion compositions described in U.S. Patents 6,545,091, 5,217,812, 5,053,457, 6,166,142, 6,210,765 and U.S. Patent Application Publication 2007/0172614 are useful in this invention.

A preferred adhesion composition useful in the multilayer film is a multicomponent composition comprising 1) a functionalized polymer, 2) an ethylene polymer or copolymer, and optionally 3) a tackifier.

The functionalized polymers useful as component 1) of the preferred multicomponent adhesion composition comprise anhydride- or epoxide -modified polymers or copolymers comprising copolymerized units of ethylene and a cyclic anhydride or monoester of C₄-C₈ unsaturated acids having at least two carboxylic acid groups or an epoxide-containing moiety. The ethylene polymers or copolymers useful as component 2) of the adhesion composition comprise at least one ethylene polymer or copolymer, chemically distinct from the functionalized polymer; that is the component 1) polymer composition. "Chemically distinct" means that a) the ethylene copolymer of the second component of the adhesion comprises at least one species of copolymerized monomer that is not present as a comonomer in the functionalized polymer component or b) the functionalized polymer component of the adhesion comprises at least one species of copolymerized monomer or grafted moiety that is not present in the ethylene copolymer of the second component of the adhesion. Thus, the first and second polymers are different in chemical structure and are distinct polymer species.

The functionalized polymer may be a modified copolymer, meaning that the copolymer is grafted and/or copolymerized with organic functionalities such as with anhydride and/or epoxide functionalities. Examples of anhydrides used to modify polymers are maleic acid, maleic acid monoethylester, itaconic anhydride, maleic anhydride and substituted maleic anhydride, maleic anhydride being preferred.

When anhydride-modified polymer is used, it may contain from 0.03 to 10 weight %, 0.05 to 5 weight %, or 0.05 to 3 % of an anhydride, the weight percentage being based on the total weight of the modified polymer. These include polymers that have been grafted with from 0.1 to 10 weight % of an unsaturated dicarboxylic acid anhydride, preferably maleic anhydride.

Generally, they will be grafted olefin polymers, for example grafted polyethylene, grafted EVA copolymers, grafted ethylene alkyl acrylate copolymers and grafted ethylene alkyl methacrylate copolymers, each grafted with from 0.1 to 10 weight % of an unsaturated dicarboxylic acid anhydride. Specific examples of suitable anhydride -modified polymers are disclosed in U.S. Patent Application Publication 2007/0172614.

The functionalized polymer may also be an ethylene copolymer comprising

copolymerized units of ethylene and a comonomer selected from the group consisting of C₄-C₈ unsaturated anhydrides, monoesters of G Cg unsaturated acids having at least two carboxylic acid groups, diesters of C₄-C₈ unsaturated acids having at least two carboxylic acid groups and mixtures of such copolymers. The ethylene copolymer may comprise from 3 to 25 weight % of copolymerized units of the comonomer. The copolymer may be a dipolymer or a higher order copolymer, such as a terpolymer or tetrapolymer. The copolymers are preferably random copolymers. Examples of suitable comonomers of the ethylene copolymer include unsaturated anhydrides such as maleic anhydride and itaconic anhydride; or Q-C₂₀ alkyl monoesters of butenedioic acids (e.g. maleic acid, fumaric acid, itaconic acid and citraconic acid), including methyl hydrogen maleate, ethyl hydrogen maleate, or propyl hydrogen fumarate. These functionalized polymer components of the adhesion composition are ethylene copolymers obtained by a process of high-pressure free radical random copolymerization, rather than graft copolymers. The monomer units are incorporated into the polymer backbone or chain and are not incorporated to an appreciable extent as pendant groups onto a previously formed polymer backbone.

Examples of epoxides used to modify polymers are unsaturated epoxides comprising from four to eleven carbon atoms, such as glycidyl (meth)acrylate, allyl glycidyl ether, vinyl glycidyl ether and glycidyl itaconate, glycidyl (meth)acrylates being particularly preferred.

Epoxide -modified ethylene copolymers preferably contain from 0.03 to 15 weight %, 0.03 to 10 weight %, 0.05 to 5 weight %, or 0.05 to 3 % of an epoxide, the weight percentage being based on the total weight of the modified ethylene copolymer. Preferably, epoxides used to modify ethylene copolymers are glycidyl (meth)acrylates. The ethylene/glycidyl (meth)acrylate copolymer may further contain copolymerized units of an alkyl (meth)acrylate having from one to six carbon atoms Representative alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate, or combinations of two or more thereof. Of note are ethyl acrylate and butyl acrylate. Preferably, modified ethylene copolymers comprised in the tie layer are modified with acid, anhydride and/or glycidyl (meth) acrylate functionalities.

The second component of the preferred adhesion composition is at least one ethylene polymer or copolymer compositionally distinct from the first functionalized polymer component, including the polyolefins or ethylene copolymers with polar comonomers described above.

The adhesion composition may also include a tackifier. The tackifier may be any suitable tackifier known generally in the art. For example, the tackifier may include types listed in U.S. Patent 3,484,405. Suitable tackifiers include a variety of natural and synthetic resins and rosin materials. Tackifier resins that can be employed are liquid, semi-solid to solid, complex amorphous materials generally in the form of mixtures of organic compounds having no definite melting point and no tendency to crystallize. Compositions comprising olefin polymers and modified polymers thereof are commercially available under the trademarks APPEEL^®, BYNEL^®, ELVALOY^®AC, and EL VAX^® from DuPont.

The multilayer film may be prepared according to well-known film preparation techniques, including cast film coextrusion (including the above mentioned nanofeedblock technology), and blown film coextrusion.

A multilayer film can be prepared by coextrusion as follows: granulates or pellets of the various components for each layer are melted in suitable extruders and converted into a film using a converting technique. For coextrusion, the molten polymers are passed through a die or set of dies to form layers of molten polymers that are processed as a layered flow and then cooled to form a layered structure. The film may be further oriented beyond the immediate quenching or casting of the film. In general terms the process comprises the steps of coextruding a multilayer flow of molten polymers, quenching the coextrudate and orienting the quenched coextrudate in at least one direction. The film may be uniaxially oriented, or it may be mono- or biaxially oriented by drawing in two mutually perpendicular directions in the plane of the film to achieve a satisfactory combination of mechanical and physical properties.

Cast films are prepared by passing the extrudate through a slot die and passing it through nip rollers. In a preferred embodiment of the cast film or extrusion coating film production the polymer flow of at least 2 extruders may be passed through a nanofeedblock as described in U.S. Patent 6,905,324 creating an alternating nanolayer film structure.

A preferred film is a blown film obtained through blown film extrusion. Generally, the compositions of the various layers are fed from extruders to an annular die and blown by blown extrusion to form a bubble that is converted into a tubular film. Blown films are to some extent biaxially oriented depending on the blow up ratio. Orientation in the transverse direction is due to the increase in diameter of the bubble as the polymeric material exits the annular die and orientation in the machine direction is due to stretching of the bubble during blowing. Blow extrusion and stretching techniques are well known in the art; see for example EP299750.

Orientation and stretching apparatus to uniaxially or biaxially stretch film are known in the art and may be adapted by those skilled in the art to produce the films of this invention. Examples of such apparatus and processes include e.g. those disclosed in U.S. Patents 3,278,663; 3,337,665; 3,456,044; 4,590,106; 4,760,116; 4,769,421; 4,797,235 and 4,886,634.

Orientation of multilayer films is generally carried out on a commercial scale using MDO, tenterframe or double bubble tubular processes conducted at temperatures below the melting point of at least one of the polymers present in the multilayer film. Machine manufacturers employing the double bubble tubular process technology include Kuhne

Anlagenbau, Macro Engineering & Technology, and Plamex Maschinenbau. Machine manufacturers employing the tenterframe include Briickner Group GmbH. Machine manufacturers employing the MDO process include Windmoller &Holscher KG.

In a preferred embodiment, the multilayer film is oriented through a double bubble extrusion process, where simultaneous biaxial orientation may be effected by extruding a primary multilayer film tube which is subsequently quenched, reheated and then expanded by internal gas pressure to induce transverse orientation, and drawn by differential speed nip or conveying rollers at a rate which will induce longitudinal or machine orientation. More particularly, a primary tube is melt extruded from an annular die. This extruded primary tube is cooled quickly to minimize crystallization and then collapsed. It is then again heated to its orientation temperature (e.g. by means of a water bath). In the orientation zone a secondary tube is formed by inflation, thereby radially expanding the film in the transverse direction, and the tube is pulled or stretched in the machine direction at a temperature such that expansion occurs in both directions, preferably simultaneously; the expansion of the tube being accompanied by a sharp, sudden reduction of thickness at the draw point. The tubular film can then again be flattened through nip rolls. Flat films can be prepared by splitting the tubular film along its length and opened up into flat sheets that can be rolled and/or further processed.

In some embodiments, the final characteristics may be obtained using triple bubble processes, which are similar to the double bubble process described except a third heating and blowing operation is conducted.

The films may also be optionally oriented uniaxially in the machine direction by stretching but not oriented further in the transverse direction. That means that they are stretched in a single direction, the machine direction after the actual blown film extrusion. The preparation of a uniaxially oriented multilayer film of the invention can comprise at least the steps of forming a layered film structure in a blown film process with a blow up ratio of at least 1.5, preferably at least 2.0 or higher and stretching the obtained multilayer film in a draw ratio of at least 1:3.

Typically the compositions providing the layers of the film will be blown i.e.

(co)extruded at a temperature in the range 160 °C to 240 °C, and cooled by blowing gas (generally air) at a temperature of 10 to 50 °C to provide a frost line height of 1 or 2 to 8 times the diameter of the die. The blow up ratio should generally be in the range 1.2 to 6, preferably 1.5 to 4.

Alternatively for ABCCBA type film structures, the film can advantageously be prepared first by coextruding compositions forming the layers A, B and C through an annular die, and blowing by blown extrusion into a tubular film to form a bubble. The formed bubble is then collapsed e.g. in nip rolls to form a film where the C layers are contacted inside/inside, i.e.

ABC/CBA. Alternatively, the coextruded bubble may be collapsed and split into two films. The two films can then be stretched separately in a winding machine (2 x ABC films).

The film may be stretched only in the machine direction to be essentially uniaxial. The effect of stretching in only one direction is to uniaxially orient the film. Stretching is preferably carried out at a temperature in the range 70 to 90 °C, e.g. 80 °C. Any conventional stretching rate may be used, e.g. 2 to 40 % per second.

The film may be stretched at least 2 times, preferably 3 to 10 times, its original length in the machine direction. This is stated herein as a draw ratio of at least 1:3, i.e. "1" represents the original length of the film and "3" denotes that it has been stretched to 3 times that original length. Films may be stretched in a draw ratio of at least 1:4, more preferably between 1:5 and 1:8, such as between 1 :5 and 1 :7. An effect of stretching (or drawing) is that the thickness of the film is similarly reduced. Thus a draw ratio of at least 1:3 preferably also means that the thickness of the film is at least three times less than the original thickness.

The films of the invention may have a starting (or original) thickness of 400 μηι or less, preferably 30 to 300 μηι, more preferably 40 to 250 μηι, prior to the stretching step. After stretching, the final thickness of the oriented films of the invention is typically 50 μηι or less, preferably 10 to 50 μηι, more preferably 15 to 40 μηι, still more preferably 20 to 38 μηι, e.g. 23 to 38 μηι, especially 25 to 32 μηι.

The processing parameters of the stretching may be adjusted individually or in parallel to achieve a coextruded multilayer film structure exhibiting shrink performance of less than 10 percent, such as from 1 to 10 percent, more preferably of less than 5 percent or from 1 to 5 percent, when measured after exposure to a temperature of 120°C for 10 seconds in dry hot air, using a sample of 10 x 10 cm, in the machine/axial direction (MD) and/or the transverse/radial direction (TD). A shrink performance of 10% in machine/axial direction (MD) and/or transverse/radial direction (TD) means that the sample has shrunk to 90% of its original dimensions in

machine/axial direction (MD) and/or transverse/radial direction (TD).

The films of the invention preferably have high stiffness before processing. Higher stiffness allows the stretch wrap film to be easily handled. Film stiffness may be 100 to 1000 MPa, preferably 100 to 500MPa. The material may have high penetration energy to withstand sharp objects. Penetration resistance values maybe of the order of 80 to 150 millijoules (mJ)/mm measured according to DIN EN ISO 6603-2 or equivalent standards.

Bundling force is preferably above 2 N in the machine direction. The films of the invention preferably have a haze value according to ASTM D1003-13 of less than 20%.

Embodiments of the multilayer film include:

The multilayer film which shows shrinkage of at least 10% when exposed to a temperature of at least 110 °C.

The multilayer film wherein the film is oriented in a draw ratio of at least 1:3.

The multilayer film wherein the polyolefin comprises high density polyethylene, linear low density polyethylene, low density polyethylene, very low or ultralow density polyethylene, or metallocene low density polyethylene or combinations thereof.

The multilayer film comprising at least three layers.

The multilayer film comprising an inner core layer comprising polyethylene and two surface layers comprising an ionomer, wherein the inner layer comprises from 60 to 95 % of the total film and the ionomer surface layers each independently comprise 2 to 20 % of the film.

The multilayer film comprising an inner core layer comprising a blend of LDPE and HDPE. The multilayer film comprising an inner core layer comprising a blend of LDPE and LLDPE. The multilayer film wherein the core layer comprises a blend of LLDPE, HDPE and LDPE.

The multilayer film comprising an inner core layer of ionomer and two surface layers comprising polyethylene, such that the inner core layer comprises from 5 to 40 % of the total film and each surface layer independently comprises from 20 to 50 % of the total film.

The multilayer film comprising surface layers comprising a blend of LDPE and LLDPE. The multilayer film comprising at least five layers.

The multilayer film having an A/B/C/B/A structure in which the A skin layers comprise polyethylene, B inner layers consist essentially of the ionomer and C core layers comprise polyethylene.

The multilayer film wherein at least one A layer comprises LLDPE, LDPE or a blend of LLDPE and LDPE.

The multilayer film wherein at least one A layer comprises a blend comprising 70 to 95 weight % of LLDPE and 5 to 30 weight % of LDPE.

The multilayer film wherein the core layer comprises a blend comprising LLDPE and LDPE. The multilayer film wherein the core layer comprises a blend comprising LLDPE and HDPE. The multilayer film wherein the core layer comprises a blend comprising LLDPE, HDPE and LDPE.

The multilayer film wherein the core layer comprises a blend comprising 5 to 30 weight % of LLDPE and 70 to 95 weight % of LDPE.

The multilayer film wherein the core layer comprises a blend comprising 70 to 90 weight % of LDPE and 10 to 30 weight % of HDPE.

The multilayer film wherein the core layer comprises a blend comprising 30 to 80 weight % of LLDPE, 10 to 50 weight % of LDPE and 10 to 30 weight % of HDPE.

The multilayer film wherein the core layer is thicker than the other layers.

The multilayer film wherein the yield stress of the film in the machine direction (MD) is at least 12 MPa, or is at least 25% higher than the yield stress of a corresponding film without ionomer when stretched by 50%; and the strain hardening regime from 100 to 200% of elongation of the film is characterized by a continuous increase of stress of at least 2 MPa in the machine direction.

The multilayer film wherein the holding stress at 200% deformation at 23 °C is at least 25 % higher, or at least 33 % higher, than a corresponding film without ionomer.

The multilayer film having a distinct yield point and wherein strain hardening is retained at higher temperature when ionomer is present in the structure compared to a corresponding film without ionomer.

The multilayer film wherein at elevated temperatures the tensile strength or hold stress is higher than that of a corresponding film without ionomer at the corresponding temperature.

The multilayer film wherein the holding stress at 200% deformation at 40 °C and 50 °C of Example 3 is at least 40 % higher than that of a corresponding film without ionomer at the corresponding temperature.

The multilayer film wherein the holding stress at 200% deformation at 50 °C is higher than that of a corresponding film without ionomer at 40 °C.

The mechanical properties and ease of processing of the stretch film composition render stretch wrapping films applicable for covering, containing or enclosing articles or objects during transport and storage to provide protection and unitizing. Articles for this use include (1) films or sheets of material comprising the stretch wrap film structure that may be wrapped around or draped over the objects being packaged such as pallet stretch wrap films and the like to conform tightly around the objects;

(2) tubes or sleeves comprising the stretch film structure described herein that may be wrapped around the objects to conform tightly around the objects;

(3) lidding material comprising the stretch film structure. The lidding material may be used in combination with rigid or semi-rigid or flexible structures such as tubs, boxes, bins and the like to prepare a package comprising the stretch film structure.

Stretch Wrap Process

The stretch wrap process is generally described below in its most common form, in which the stretch wrap film is in the form of continuous rolls that allows for the film to be dispensed from a spool and wrapped around the objects to be wrapped in a continuous sequence. Other variations of this process using different forms of the film can be envisioned. Films comprising slip layers are preferably dispensed from the roll so that the slip layer is positioned away from the wrapped object, and films comprising cling layers are preferably dispensed from the roll so that the cling layer is positioned so that it contacts the wrapped object.

For pallet unitizing, film may be dispensed from a roll or spool and wrapped around the sides and optionally the top of the pallet in overlapping fashion to sufficiently cover and contain the objects to be unitized. In some cases the film may be carried around a stationary pallet to wrap it. Alternatively, the pallet may be placed on a rotating platform and turned as the film is dispensed from a stationary dispensing station.

The stretchable wrapping films of the invention are preferably used in the wrapping of household, food, healthcare or beverage products, in particular products that are packaged in containers such as bags, bottles, cans, jars, boxes, tubs and the like. Wherever a product is shipped in numerous essentially identical containers, the use of stretch film is useful to prevent damage to the products and keep the product secure during transport. The most common application is therefore in the beverage or food transportation market.

It will be appreciated that the stretchable wrapping film might also be used to wrap nonfood products such as chemicals, cleaning products, construction materials, agricultural products and the like.

When used for pallet unitizing, films of the invention may be used to collate a wide variety of objects, including a plurality of containers including boxes, cans, buckets, barrels or the like, or it may be used to cover and protect at least one irregularly shaped object such as machinery, furniture and the like.

It is noted that stretch wrap films may be prestretched up to 200 or more % in the machine direction, well above the elastic limit of the film in order to reach the strain hardening regime in the stress strain curve of the film as well as a relatively high stress or holding force. The holding force is necessary in order to represent a resistance to deformation to the wrapped pallet so that the pallet cannot deform or the collated objects cannot move on the pallet. It is important to note however that films containing between 5 and 40 weight % of ionomers as described herein reach the strain hardening regime associated with a yield point after only a few % of elongation. This ensures that the resistance against further deformation is higher than the force needed for the previous deformation, as expressed by an increase in force in the stress strain curve of the polymer film. Notably, such ionomer-containing films may be prestretched to a lesser degree, in order to serve as stretch wrap films.

The films in the Examples are characterized by a strain hardening regime that starts at least after 50% elongation and thereafter is characterized by a continuous increase of the stress by at least 2 MPa over elongation/deformation from 100 to 200% in MD. Another characteristic of the film composition is a high holding stress of at least 12, including greater than 15 MPa, after

50% deformation in MD, or which is at least 25% higher than the yield stress of a comparable film structure without ionomers.

The following Examples are presented to demonstrate and illustrate, but are not meant to unduly limit the scope of the invention.

EXAMPLES

Materials Used

ION-1: Ionomer comprising a dipolymer comprising ethylene and methacrylic acid (12 weight percent), 37 % neutralized to carboxylate salts with zinc cations, with MI of 1.8 g/10 minutes. LLDPE-1: A butene-linear low density polyethylene with density of 0.918 g/cm³, melting point of 121 °C and MI of 1.0 g/10 minutes, commercially available under the designation 118NE from Saudi Basic Industries (SABIC) Europe.

LLDPE-2: linear low density polyethylene with density of 0.918 g/cm³, melting point of 121 °C and MI of 2.8 g/10 minutes, commercially available under the designation 318BE from Saudi Basic Industries (SABIC) Europe.

LDPE: A low density polyethylene with density of 0.922 g/cm³, melting point of 121 °C and MI of 0.85 g/10 minutes, commercially available under the designation 2201TH00 from Saudi Basic Industries (SABIC) Europe.

HDPE: a high density polyethylene homopolymer with density of 0.961 g/cm³ and MI of 0.7 g/10 minutes, commercially available under the designation HTA108 from ExxonMobil™.

MPE1 : a medium density ethylene-hexene copolymer with density of 0.935 g/cm³ and MI of 0.5 g/10 minutes, commercially available under the designation Enable^® 35-05HH from

ExxonMobil™.

Melt Index (MI), the mass rate of flow of a polymer through a specified capillary under controlled conditions of temperature and pressure, was determined and/or reported according to ASTM 1238 at 190°C using a 2160 g weight, in g/10 minutes.

Penetration resistance was measured according to DIN EN ISO 6603-2. Tensile properties were measured according to ASTM 882 using a tensile testing machine made by Zwick, Model 1465. The tests at elevated temperatures were done using a tensile testing machine made by Zwick, model Z 2.5 according to the same standard. Haze was tested according to ASTM D1003-13 with a Hazemeter M57 manufactured by Diffusion systems Ltd. Five-layer blown films with ABCBA structure were prepared using the conditions summarized in Tables 1 to 7. In the Tables, Layer 1 was the outside surface layer of the tubular bubble, layer 5 was the inside surface layer of the bubble and layers 2, 3 and 4 were interior layers. The layers in the Comparative Example films all comprised only polyethylene compositions. When adjacent interior layers have the same composition, the combined layers form a single core layer. Comparative Example C4 replaced the LLDPE-2/LDPE blend in the B layers with MPEl. The Example films replaced a fraction of the total interior layers of the Comparative films with ionomer B layers.

Table 1 Comparative Example C 1

Gauge Extruder Melt Barrel Temperature Settings [°C]

Layer Layer Composition [μπι] RPM I [%1 Kg/hr T [°C] P [bar] Zl Z2 Z3 Z4 MCF BR1

1 LLDPE-l/LDPE 80/20 6 30.4 50 12.3 222 192 179 200 209 220 220 220

2 LLDPE-l/LDPE 20/80 6 30.7 35 11.3 217 197 179 199 209 220 220 219

3 LLDPE-l/LDPE 20/80 16 77.7 48 29.5 226 279 180 200 210 220 220 220

4 LLDPE-l/LDPE 20/80 6 30.4 34 10.7 217 212 179 199 209 219 220 220

5 LLDPE-l/LDPE 80/20 6 30.8 50 11.9 224 240 180 200 210 219 219 220

Nominal Total gauge [μηι] 40 Total 81.8 Line Speed [m/min] 16.6 Blow Up Ratio 2.8

Table 2 Example 1

Gauge Extruder Melt Barrel Temperature Settings [°C]

Layer Layer Composition [μιη] RPM I [%1 Kg/hr T [°C] P [bar] Zl Z2 Z3 Z4 MCF BR1

1 LLDPE-l/LDPE 80/20 6 30.6 49 12.4 223 185 179 200 209 220 220 220

2 ION-1 6 30.7 41 14.4 216 131 179 199 209 220 220 219

3 LLDPE-l/LDPE 20/80 16 77.7 48 29.9 226 273 180 200 210 220 220 220

4 ION-1 6 30.4 41 13.2 215 137 179 199 209 219 220 220

5 LLDPE-l/LDPE 80/20 6 30.8 50 11.9 224 229 180 200 210 219 219 220

Nominal Total gauge [μηι] 40 Total 81.8 Line Speed [m/min] 16.6 Blow Up Ratio 2.8

Table 3 Comparative Example C2

Gauge Extruder Melt Barrel Temperature Settings [°C]

Layer Layer Composition [μπι] RPM I [%] Kg/hr T [°C] P [bar] Zl Z2 Z3 Z4 MCF BR1

1 LLDPE-l/LDPE 95/5 6 28 48 11.4 222 192 179 230 240 250 250 249

2 LDPE-l/HDPE 80/20 6 30.2 32 11.2 217 197 179 200 210 220 220 220

3 LDPE-l/HDPE 80/20 16 79.2 45 29.3 226 279 180 199 210 220 219 220

4 LDPE-l/HDPE 80/20 6 30.2 31 10.5 217 212 180 200 209 219 219 220

5 LLDPE-l/LDPE 80/20 6 29.4 45 11.2 224 240 179 229 240 250 250 249

Nominal Total gauge [μηι] 40 Total 73.6 Line Speed [m/min] 16.6 Blow Up Ratio 2.8

Table 4 Example 2

Gauge Extruder Melt Barrel Temperature Settings [°C]

Layer Layer Composition [μιη] RPM I [%] Kg/hr T [°C] P [bar] Zl Z2 Z3 Z4 MCF BR1

1 LLDPE-l/LDPE 95/5 6 28.8 54 11.9 231 173 179 200 220 229 230 230

2 ION-1 6 26.8 40 12.8 215 125 179 200 210 220 220 230

3 LDPE-l/HDPE 80/20 16 77.6 44 29.1 223 242 179 200 209 219 220 220

4 ION-1 6 27.3 40 12 214 130 180 200 210 220 220 220

5 LLDPE-l/LDPE 95/5 6 29.9 45 12.7 251 202 178 229 240 250 250 249

Nominal Total gauge [μηι] 40 Total 78.5 Line Speed [m/min] 16.6 Blow Up Ratio 2.8

Table 5 Comparative Example C3

Gauge Extruder Melt Barrel Temperature Settings [°C]

Layer Layer Composition [μπι] RPM I [%] Kg/hr T [°C] P [bar] Zl Z2 Z3 Z4 MCF BR1

1 LLDPE-2/LDPE/HDPE 60/10/30 6 31.6 38 12.8 220 127 180 199 210 220 220 220

2 LLDPE-2/LDPE 80/20 6 31.3 37 12.7 217 148 179 199 209 220 220 220

3 LLDPE-2/LDPE/HDPE 30/50/20 16 85.2 53 32.6 227 258 179 200 209 219 220 220

4 LLDPE-2/LDPE 80/20 6 31.3 35 12.2 218 155 179 199 209 219 219 219

5 LLDPE-2/LDPE/HDPE 60/10/30 6 30.8 38 12.2 221 150 180 200 210 220 220 219

Nominal Total gauge [μηι] 40 Total 82.5 Blow Up Ratio 2.0

Table 6 Example 3

Gauge Extruder Melt Barrel Temperature Settings [°C]

Layer Layer Composition [μιη] RPM I [%] Kg/hr T [°C] P [bar] Zl Z2 Z3 Z4 MCF BR1

1 LLDPE-2/LDPE/HDPE 60/10/30 6 31.3 38 12.7 220 126 180 199 210 219 220 219

2 ION-1 6 30.0 39 14.8 216 114 175 201 209 218 220 220

3 LLDPE-2/LDPE/HDPE 30/50/20 16 83.1 53 32.6 226 254 179 197 212 223 219 220

4 ION-1 6 30.9 37 14.1 217 117 178 201 208 218 220 220

5 LLDPE-2/LDPE/HDPE 60/10/30 6 30.8 37 12.1 221 147 179 200 210 219 220 219

Nominal Total gauge [μηι] 40 Total 86.3 Blow Up Ratio 2.0

Table 7 Comparative Example C4

Gauge Extruder Melt Barrel Temperature Settings [°C]

Layer Layer Composition [μπι] RPM I [%] Kg/hr T [°C] P [bar] Zl Z2 Z3 Z4 MCF BR1

1 LLDPE-2/LDPE/HDPE 60/10/30 6 31.3 38 12.6 220 121 179 200 210 219 219 220

2 MPE1 6 30.0 51 12.4 218 211 176 200 206 215 220 219

3 LLDPE-2/LDPE/HDPE 30/50/20 16 85.6 53 33.3 226 253 182 199 199 222 220 220

4 MPE1 6 30.4 49 11.6 221 229 177 200 206 216 220 219

5 LLDPE-2/LDPE/HDPE 60/10/30 6 30.9 37 12.2 221 148 180 200 209 220 220 219

Nominal Total gauge [μηι] 40 Total 82.1 Blow Up Ratio 2.0

Table 8

Comparative Example C5 Gauge Example 5 Gauge

Layer Layer Composition [μιη] Layer Composition [μιη]

1 LLDPE-2/LDPE/HDPE 60/10/30 6 LLDPE-2/LDPE/HDPE 60/10/30 6

2 LLDPE-2/LDPE 80/20 6 ION1 6

3 LLDPE-2/LDPE/HDPE 60/10/30 16 LLDPE-2/LDPE/HDPE 60/10/30 16

4 LLDPE-2/LDPE 80/20 6 ION1 6

5 LLDPE-2/LDPE/HDPE 60/10/30 6 LLDPE-2/LDPE/HDPE 60/10/30 6

Nominal Total gauge [μηι] 40 Nominal Total gauge [μηι] 40

The properties of the films including penetration testing, tensile properties and haze are summarized in Table 9. The Example films exhibited strain hardening and no yield point compared to the Comparative Example films. Higher penetration resistance, higher tensile strength and stiffness and lower haze were also exhibited by the Example films compared to the Comparative Example films without ionomer layers.

Table 9 also summarizes the shrink performance of the films under various heat and time conditions. Shrinkage was 0 % with short duration heating temperatures below 90 °C for all samples. At higher temperature and longer exposure times, shrinkage in MD was still very low.

Importantly, Table 9 summarizes the holding stress and strain hardening conditions of the Example films and clearly illustrates that they show a high strain hardening behavior and a high holding stress after minimum deformation of 50% in both MD and TD compared to Comparative Example films. It can be seen from the results in Table 9 that the introduction of MPE1 in the B layers provides a strain hardening behavior in the stress-strain curve but maintains or even reduces the low yield point and yield stress at 50% deformation, which is associated with a low holding force. On the other hand, introducing ION-1 in the B layers significantly increases the yield stress at 50% deformation and maintains the strain hardening behavior in the stress strain regime.

As shown in Table 10, Example 3 shows improved tensile properties at elevated temperatures (23 °C, 40 °C and 50 °C) compared to a structure not containing ionomer (C3). As can be seen, strain hardening is retained even at higher temperature when ionomer is present in the structure. At 23 °C the holding stress at 200% deformation of Example 3 is at least 25 % higher, or at least 33 % higher, than C3. What is more interesting is that even at elevated temperatures the tensile strength or hold stress of the ionomer- containing structure Example 3 is higher than the corresponding comparative example C3 at the corresponding temperature. At 40 °C and 50 °C the holding stress at 200% deformation of Example 3 is at least 40 % higher than C3. Even more surprising is that the holding stress at 200% deformation of Example 3 at 50 °C is higher than the one of C3 at 40 °C. This is a surprising result, given that the melt point of ionomers like ION-1 is

20 °C lower compared to polyethylene known from the literature. Therefore the structure in Example 3 is in a better position to more tightly hold together a package or a pallet of several articles than the film C3, in particular at elevated temperatures such as 40 °C or 50 °C, which are common in the interior of a truck when standing in traffic.

Table 9

Table 10 Tests at Elevated Temperatures

Example Temperature C3 3

23 °C 15-16 20-23

Holding Stress (MPa)

TD 40 °C 11-12 17-18 at 200%o deformation

50 °C 8-9 12-14

Yield Point TD 23, 40 and 50 °C Yes No Strain Hardening TD 23, 40 and 50 °C No Yes

The invention includes the following embodiments.

1. A stretch wrapping multilayer film comprising

(a) at least one layer comprising an ionomer comprising a copolymer comprising copolymerized units of ethylene and between 1 and 25 weight % of copolymerized units of methacrylic acid or acrylic acid wherein from 1 to 99 % of the carboxylic acid groups are neutralized to carboxylate salts comprising metal ions; and

(b) at least one additional layer comprising a polyolefin and not comprising an ionomer;

(c) optionally at least one adhesion layer; and

(d) optionally at least one layer comprising an ethylene copolymer other than an ionomer, comprising copolymerized units of ethylene and copolymerized units of an ester of unsaturated carboxylic acids or an ester of vinyl alcohol;

wherein the total amount of the ionomer comprises from 5 to 40 weight % of the polymeric material of the multilayer film; and the ionomer-comprising composition of (a), the polyole fin-comprising composition of (b) and the compositions of the optional (c) and (d) layers, when present, comprise 100 % of the polymeric materials of the film; and

wherein the yield stress of the film in the machine direction (MD) is at least 12 MPa, or is at least 25% higher than the yield stress of a corresponding film without ionomer when stretched by 50%; the strain hardening regime from 100 to 200% of elongation of the film is characterized by a continuous increase of stress of at least 2 MPa in the machine direction; and the film shrinks by less than 10 % in both the machine direction and the transverse direction when exposed to a temperature of 90 °C for at least 2 seconds.

2. The multilayer film according to embodiment 1 wherein the polyolefin comprises high density polyethylene, linear low density polyethylene, low density polyethylene, very low or ultralow density polyethylene, metallocene polyethylene, ethylene propylene copolymer or blends thereof.

3. The multilayer film according to embodiment 1 or 2 wherein at least one ionomer- containing layer comprises an ionomer comprising a copolymer comprising copolymerized units of ethylene and between 1 and 15 weight % copolymerized units of methacrylic acid or acrylic acid and further comprises high density polyethylene, linear low density polyethylene, low density polyethylene, very low or ultralow density polyethylene, metallocene polyethylene or ethylene propylene copolymer, or EVA or EMA, EEA, EBA.

4. The multilayer film according to embodiment 1, 2 or 3 wherein at least one ionomer- containing layer comprises alternating nanolayers comprising ionomer-comprising nanolayers and nanolayers not comprising ionomer, or alternating nanolayers of an ionomer and nanolayers of a different ionomer.

5. The multilayer film according to embodiment 1, 2, 3 or 4 comprising at least three layers.

6. The multilayer film according to embodiment 1, 2, 3, 4 or 5 comprising an inner core layer comprising the ionomer and two surface layers comprising polyethylene not comprising an ionomer, such that the ionomer of the inner core layer comprises from 5 to 40 % of the polymeric material of the total film.

7. The multilayer film according to embodiment 1, 2, 3, 4, 5 or 6 comprising surface layers comprising metallocene polyethylene, linear low density polyethylene, low density polyethylene, or blends thereof. 8. The multilayer film according to embodiment 1, 2, 3, 4, 5, 6 or 7 comprising an inner core layer of ionomer and two surface layers comprising polyethylene, preferably comprising a blend comprising LDPE and LLDPE, such that the inner core layer comprises from 5 to 40 % of the total film and each surface layer independently comprises from 20 to 50 % of the total film. 9. The multilayer film according to embodiment 1, 2, 3, 4 or 5 comprising an inner core layer comprising polyethylene and optionally ionomer and two surface layers comprising ionomer.

10. The multilayer film according to embodiment 1, 2, 3, 4, 5 or 9 comprising an inner core layer comprising polyethylene, preferably a blend of LDPE and HDPE or a blend of LDPE and LLDPE, or a blend of LDPE, HDPE and LLDPE, and two surface layers comprising an ionomer, wherein the inner layer comprises from 60 to 95 % of the total film and the ionomer surface layers each independently comprise 2 to 20 % of the film.

11. The multilayer film according to embodiment 1, 2, 3, 4, 5, 9 or 10 comprising an inner core layer comprising a blend of LDPE and HDPE.

12. The multilayer film according to embodiment 1, 2, 3, 4, 5, 9 or 10 comprising an inner core layer comprising a blend of LDPE and LLDPE.

13. The multilayer film according to embodiment 1, 2, 3, 4, 5, 9 or 10 comprising an inner core layer comprising a blend of LDPE, LLDPE and HDPE.

14. The multilayer film according to embodiment 1, 2, 3, 4 or 5 having an A/B/C/B/A structure in which the A skin layers comprise polyethylene, B inner layers consist essentially of the ionomer and the C core layer comprises polyethylene.

15. The multilayer film according to embodiment 1, 2, 3, 4 or 5 having an A/B/C/B/A structure wherein the A skin layers comprise polyethylene not comprising an ionomer, B inner layers comprise the ionomer and the C core layer comprises polyethylene and optionally ionomer.

16. The multilayer film according to embodiment 14 or 15 wherein at least one A layer comprises LLDPE, LDPE or a blend of LLDPE and LDPE.

17. The multilayer film according to embodiment 14, 15 or 16 wherein at least one A layer comprises a blend comprising 70 to 95 weight % of LLDPE and 5 to 30 weight % of LDPE.

18. The multilayer film according to embodiment 14, 15, 16 or 17 wherein the C layer comprises a blend comprising LDPE and HDPE or a blend comprising LDPE and LLDPE, or a blend comprising LDPE, HDPE and LLDPE

19. The multilayer film according to embodiment 14, 15, 16, 17 or 18 wherein the C layer comprises a blend comprising 5 to 30 weight % of LLDPE and 70 to 95 weight % of LDPE or a blend comprising 70 to 90 weight % of LDPE and 10 to 30 weight % of HDPE or a blend comprising 30 to 80 weight % of LLDPE, 10 to 50 weight % of LDPE and 10 to 30 weight % of HDPE.

20. The multilayer film according to any of embodiments 1 to 19 wherein the core layer is thicker than any of the other layers.

21. A method for stretch wrapping an object, comprising:

(i) obtaining a stretch wrapping film according to any of claims 1 to 20; and

(ii) wrapping the object in the stretch wrapping film. 22. The method of embodiment 21 wherein the stretch wrapping film of (i) is supplied on a spool and (ii) comprises dispensing the stretch wrapping film from the spool, wrapping the film around at least a portion of a plurality of individual products and cutting the film to an appropriate length to wrap around the object comprising the plurality of individual products.

23. Use of a multilayer film structure according to any of embodiments 1 to 20 to stretch wrap an object comprising a plurality of individual products.

24. The use according to embodiment 23 wherein the multilayer film structure is in the form of a generally planar film or sheet; a bag, pouch, hood or sheath, tube or sleeve, or lidding material.

25. A stretch wrapped product comprising the film according to any of embodiments 1 to 20 wrapped around an object and optionally a pallet.

26. The stretch wrapped product of embodiment 25 comprising a pallet and a plurality of containers including bags, tubs, boxes, cans, buckets, bottles, tubes, or barrels.

27. The stretch wrapped product of embodiment 25 comprising a pallet and at least one irregularly shaped object, including machinery or furniture.

Claims

Claims

1. A stretch wrapping multilayer film comprising

(a) at least one layer comprising an ionomer comprising a copolymer comprising copolymerized units of ethylene and between 1 and 25 weight % of copolymerized units of methacrylic acid or acrylic acid wherein from 1 to 99 % of the carboxylic acid groups are neutralized to carboxylate salts comprising metal ions; and

(b) at least one additional layer comprising a polyolefin and not comprising an ionomer;

(c) optionally at least one adhesion layer; and

(d) optionally at least one layer comprising an ethylene copolymer other than an ionomer, comprising copolymerized units of ethylene and copolymerized units of an ester of unsaturated carboxylic acids or an ester of vinyl alcohol;

wherein the total amount of the ionomer comprises from 5 to 40 weight % of the polymeric material of the multilayer film; and the ionomer-comprising composition of (a), the polyole fin-comprising composition of (b) and the compositions of the optional (c) and (d) layers, when present, comprise 100 % of the polymeric materials of the film; and

wherein the yield stress of the film in the machine direction (MD) is at least 12 MPa, or is at least 25% higher than the yield stress of a corresponding film without ionomer when stretched by 50%; the strain hardening regime from 100 to 200% of elongation of the film is characterized by a continuous increase of stress of at least 2 MPa in the machine direction; and the film shrinks by less than 10 % in both the machine direction and the transverse direction when exposed to a temperature of 90 °C for at least 2 seconds.

2. The multilayer film according to claim 1 wherein the polyolefin comprises high density polyethylene, linear low density polyethylene, low density polyethylene, very low or ultralow density polyethylene, metallocene polyethylene, ethylene propylene copolymer or blends thereof.

3. The multilayer film according to claim 1 or 2 wherein at least one ionomer- containing layer comprises an ionomer comprising a copolymer comprising copolymerized units of ethylene and between 1 and 15 weight % copolymerized units of methacrylic acid or acrylic acid and further comprises high density polyethylene, linear low density polyethylene, low density polyethylene, very low or ultralow density polyethylene, metallocene polyethylene or ethylene propylene copolymer, an ethylene vinyl acetate copolymer or an ethylene alkyl acrylate copolymer, preferably ethylene methyl acrylate, ethylene ethyl acrylate, or ethylene butyl acrylate.

4. The multilayer film according to claim 1, 2 or 3 wherein at least one ionomer- containing layer comprises alternating nanolayers comprising ionomer-comprising nanolayers and nanolayers not comprising ionomer, or alternating nanolayers of an ionomer and nanolayers of a different ionomer.

5. The multilayer film according to any of claims 1, 2, 3, or 4 comprising an inner core layer comprising the ionomer and two surface layers comprising polyethylene, preferably comprising metallocene polyethylene, linear low density polyethylene, low density polyethylene, or blends thereof, more preferably comprising a blend comprising LDPE and LLDPE and not comprising an ionomer, such that the ionomer of the inner core layer comprises from 5 to 40 % of the polymeric material of the total film, preferably wherein and each surface layer independently comprises from 20 to 50 % of the total film.

6. The multilayer film according to any of claims 1, 2, 3, or 4 comprising an inner core layer comprising polyethylene, preferably a blend of LDPE and HDPE or a blend of LDPE and LLDPE, or a blend of LDPE, HDPE and LLDPE, and optionally the ionomer; and two surface layers comprising the ionomer, preferably wherein the inner layer comprises from 60 to 95 % of the total film and the ionomer surface layers each independently comprise 2 to 20 % of the film.

7. The multilayer film according to any of claims 1, 2, 3, or 4 having an A/B/C/B/A structure in which the A skin layers comprise polyethylene, preferably not comprising an ionomer, the B inner layers consist essentially of the ionomer and the C core layer comprises polyethylene and optionally the ionomer, preferably wherein at least one A layer comprises LLDPE, LDPE or a blend of LLDPE and LDPE, preferably a blend comprising 70 to 95 weight % of LLDPE and 5 to 30 weight % of LDPE.

8. The multilayer film according to claim 7 wherein the C layer comprises a blend comprising LDPE and HDPE, preferably a blend comprising 70 to 90 weight % of LDPE and 10 to 30 weight % of HDPE; or a blend comprising LDPE and LLDPE, preferably comprising 5 to 30 weight % of LLDPE and 70 to 95 weight % of LDPE; or a blend comprising LDPE, HDPE and LLDPE, preferably comprising 30 to 80 weight % of LLDPE, 10 to 50 weight % of LDPE and 10 to 30 weight % of HDPE.

9. The multilayer film according to claim any of claims 1 to 8 wherein the core layer is thicker than any of the other layers.

10. A method for stretch wrapping an object, comprising:

(i) obtaining a stretch wrapping film according to any of claims 1 to 9; and

(ii) wrapping the object in the stretch wrapping film.

11. The method of claim 10 wherein the stretch wrapping film of (i) is supplied on a spool and (ii) comprises dispensing the stretch wrapping film from the spool, wrapping the film around at least a portion of a plurality of individual products and cutting the film to an appropriate length to wrap around the object comprising the plurality of individual products.

12. Use of a multilayer film structure according to any of claims 1 to 9 to stretch wrap an object comprising a plurality of individual products.

13. The use according to claim 12 wherein the multilayer film structure is in the form of a generally planar film or sheet; a bag, pouch, hood or sheath, tube or sleeve, or lidding material.

14. A stretch wrapped product comprising the film according to any of claims 1 to 9 wrapped around an object and optionally a pallet.

15. The stretch wrapped product of claim 14 comprising a pallet and a plurality of containers including bags, tubs, boxes, cans, buckets, bottles, tubes, or barrels; or comprising a pallet and at least one irregularly shaped object, including machinery or furniture.