Patent Description:
The invention also relates to a process for the preparation of such a film and the use of such a film in packaging.

The use of machine directional oriented (MDO) films made from polyethylene is well known. These films are generally produced to down gauge existing blown film recipes. This means less polymer film is required to achieve a target end use. For example, <CIT> discloses a multilayer machine direction oriented film comprising at least a layer A and one layer B, whereby layer A comprises a multimodal linear low density polyethylene (LLDPE). A third layer C may be present. The films can be sealed to themself and are then peelable.

However, existing films can still be improved upon. A particular challenge with MDO film is to achieve a balance of a good sealing behaviour, especially a low seal initiation temperature (SIT) and/or a high seal strength and/or a low seal sealing time and/or a broad sealing window in combination with good optical properties, especially for example low haze and/or high gloss, as well as further in combination with suitable mechanical properties, especially a suitable stiffness and/or tensile modulus and/or tear strengths and/or dart drop impact resistance.

Films also need to be peelable. Many fresh food products are now sold in packaging in which a film seals the product for transport and sale but is peelable when the consumer wants to access the product. Products such as cold meats, cheese and the like are often sold in these sealable and peelable packages. It will be appreciated that seal strength is key in these sealable and peelable packages. In seal strength is too low then the seal does not protect the contents of the package during transport and storage. If the seal strength is too high then the film isn't peelable. The present inventors therefore sought a film which offers a targeted seal strength over a range of temperatures.

The present inventors therefore sought a solution to the problem of finding the balance above, in particular a solution for sealable and peelable films.

The present invention concerns a multilayer machine direction oriented film for sealing comprising at least one layer A and one layer B,.

Viewed from another aspect the invention provides a process for the preparation of a multilayer machine direction oriented film as hereinbefore defined comprising:.

In one embodiment of a machine direction oriented film according to invention said film may be a stretched film which is uniaxially oriented in the machine direction (MD) in a draw ratio of <NUM>:<NUM> to <NUM>:<NUM>, preferably <NUM>:<NUM> to <NUM>:<NUM> and having a film thickness of between <NUM> and <NUM> microns (after stretching) and/or whereby the ratio of the thickness of layer B to the thickness of layer A may be between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

The multimodal LLDPE of layer A is not a terpolymer, i.e. it does not comprise two or more comonomers. The multimodal LLDPE of layer A comprises one comonomer only.

It is preferred if both the HMW component and the LMW components of the LLDPE of layer A are copolymers of ethylene with the same C4-<NUM> alpha olefin, preferably copolymers of ethylene with <NUM>-butene.

In one embodiment of a film according to the invention, layer A may comprise <NUM> to <NUM> w%, preferably > <NUM> to < <NUM> w%, based on the total weight of polymer in the layer, of the multimodal LLDPE and <NUM> to <NUM> w%, preferably > <NUM> to < <NUM> w% of said plastomer.

In another embodiment of the film according to the invention, layer A may comprise <NUM> to <NUM> w%, preferably > <NUM> to < <NUM> w%, based on the total weight of polymer in the layer, of said plastomer and <NUM> to <NUM> w%, preferably > <NUM> to < <NUM> w% of the multimodal LLDPE.

In one embodiment of a film according to the invention, layer A may comprise <NUM> to <NUM> w%, preferably > <NUM> to < <NUM> w%, based on the total weight of the layer, of the multimodal LLDPE and <NUM> to <NUM> w%, preferably > <NUM> to < <NUM> w% of said plastomer.

In another embodiment of the film according to the invention, layer A may comprise <NUM> to <NUM> w%, preferably > <NUM> to < <NUM> w%, based on the total weight of the layer, of said plastomer and <NUM> to <NUM> w%, preferably > <NUM> to < <NUM> w% of the multimodal LLDPE.

In an embodiment of a film according to the invention, the multimodal LLDPE of layer A may have a density of between <NUM> and < <NUM>/m<NUM>, preferably between > <NUM> and < <NUM>/m<NUM>.

In an embodiment of a film according to the invention, the multimodal LLDPE of layer A may have a density of between <NUM> and <NUM>/m<NUM>, preferably between <NUM> and <NUM>/m<NUM>.

In another embodiment of a film according to the invention, the multimodal LLDPE of layer A may have a density of between <NUM> and <NUM>/m<NUM>, preferably between <NUM> and <NUM>/m<NUM>.

In an embodiment of a film according to the invention, the multimodal LLDPE of layer A may have an MFR<NUM> of between <NUM> and <NUM>/<NUM>, preferably <NUM> to <NUM>/<NUM>, e.g. > <NUM> and < <NUM>/<NUM>.

In an embodiment of a film according to the invention, the plastomer of layer A may have a density of between > <NUM> and < <NUM>/m<NUM>, preferably between <NUM> and < <NUM>/m<NUM>, further preferred > <NUM> and < <NUM>/m<NUM> and/or an MFR<NUM> of between <NUM> and <NUM>/<NUM>, preferably <NUM> and <NUM>/<NUM>, further preferred <NUM> and <NUM>/<NUM>.

According to another embodiment the plastomer of layer A may have a MFR<NUM> of between <NUM> and <NUM>/<NUM>, preferably <NUM> to <NUM>/<NUM> and more preferably from <NUM> to <NUM>/<NUM>.

In an embodiment of a film according to the invention, the multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefins of layer B may have a density either of > <NUM> to <NUM>/m<NUM>, preferably > <NUM> to <NUM>/m<NUM> or > <NUM> to < <NUM>/m<NUM>.

In an embodiment of a film according to the invention, the multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefins of layer B may have an MFR<NUM> of <NUM> and <NUM>/<NUM>, preferably > <NUM> and < <NUM>/<NUM>.

In an embodiment of a film according to the invention, the multimodal copolymer of ethylene of layer B may comprise a high molecular weight (HMW) component and a low molecular weight (LMW) component, whereby the HMW component may be a terpolymer, preferably a terpolymer of ethylene, <NUM>-butene and <NUM>-hexene or whereby both the HMW component and the LMW components of multimodal copolymer of ethylene of layer B are copolymers of ethylene with one C4-<NUM> alpha olefins, preferably copolymers of ethylene with <NUM>-butene.

In an embodiment of a film according to the invention, layer B may comprise > <NUM> wt%, such as > <NUM> to <NUM> w% or < <NUM> w%, preferably > <NUM> w% to <NUM> w% or < <NUM> w% of the multimodal ethylene copolymer and/or may comprise > <NUM> to < <NUM> w% , further preferred > <NUM> to < <NUM> w% of a further multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefins having a density of <NUM> to <NUM>/m<NUM>, preferably > <NUM> to < <NUM>/m<NUM> and/or MFR<NUM> of <NUM> and <NUM>/<NUM>, preferably > <NUM> and < <NUM>/<NUM>.

In an embodiment of a film according to the invention, layer B may comprise <NUM> to <NUM> w% or < <NUM> w%, preferably <NUM> w% to <NUM> w% or < <NUM> w% of the multimodal ethylene copolymer and/or may comprise <NUM> to <NUM> w% , further preferred <NUM> to <NUM> w% of a further multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefins having a density of <NUM> to <NUM>/m<NUM>, preferably <NUM> to <NUM>/m<NUM> and/or MFR<NUM> of <NUM> and <NUM>/<NUM>, preferably <NUM> and <NUM>/<NUM>.

The further multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefin of layer B may be a multimodal linear low density polyethylene (LLDPE) as described above for layer A.

According to the invention, the film comprises three layers with layer B located between layer A and a third layer C.

According to the invention, the third layer C comprises a multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefin, having a density of <NUM> to <NUM>/m<NUM> such as < <NUM> to <NUM>/m<NUM> and an MFR<NUM> of <NUM> to <NUM>/<NUM>.

The multimodal copolymer of ethylene of layer C may be the same as described above for layer A or B, preferably Layer C consists of only one multimodal copolymer of ethylene, e.g. one multimodal LLDPE copolymer.

According to the invention as described here above, the third layer C is different from layer B and/or wherein the film is asymmetric with respect to the outer layers, this means layer A is different from C.

The term LLDPE means linear low density polyethylene herein. The LLDPE of use in this invention is multimodal. The term "multimodal" means multimodal with respect to molecular weight distribution and includes also therefore bimodal polymers. The term "multimodal" may also mean multimodality with respect to the "comonomer distribution".

Usually, a LLDPE composition, comprising at least two polyethylene fractions, which have been produced under different polymerisation conditions resulting in different (weight average) molecular weights and molecular weight distributions for the fractions, is referred to as "multimodal". The prefix "multi" relates to the number of different polymer fractions present in the polymer. Thus, for example, the term multimodal polymer includes so called "bimodal" polymers consisting of two fractions. The form of the molecular weight distribution curve, i.e. the appearance of the graph of the polymer weight fraction as a function of its molecular weight, of a multimodal polymer, e.g. LLDPE, will show two or more maxima or at least be distinctly broadened in comparison with the curves for the individual fractions.

Ideally, the molecular weight distribution curve for multimodal polymers of the invention will show two distinction maxima.

For example, if a polymer is produced in a sequential multistage process, utilising reactors coupled in series and using different conditions in each reactor, the polymer fractions produced in the different reactors will each have their own molecular weight distribution and weight average molecular weight. When the molecular weight distribution curve of such a polymer is recorded, the individual curves from these fractions are superimposed into the molecular weight distribution curve for the total resulting polymer product, usually yielding a curve with two or more distinct maxima.

In any multimodal LLDPE, there may be by definition a lower molecular weight component (LMW) and a higher molecular weight component (HMW). The LMW component has a lower molecular weight than the higher molecular weight component. This difference is preferably at least <NUM>/mol.

The multimodal LLDPE of use in the invention comprises one comonomer only. It is possible that one of the LMW or HMW components is a homopolymer, preferably the LMW component. In that scenario, the other component is an ethylene copolymer. However, preferably both the LMW and HMW components are ethylene copolymers with the same comonomer.

The overall comonomer content in the multimodal LLDPE may be for example <NUM> to <NUM> % by mol, preferably <NUM> to <NUM> % by mol, more preferably <NUM> to <NUM> % by mol and most preferably <NUM> to <NUM> % by mol.

<NUM>-Butene may be present in an amount of <NUM> to <NUM> % by mol, such as <NUM> to <NUM> % by mol, more preferably <NUM> to <NUM> % by mol and most preferably <NUM> to <NUM> % by mol.

A C6 to C12 alpha olefin may be present in an amount of <NUM> to <NUM> % by mol, preferably <NUM> to <NUM> % by mol, more preferably <NUM> to <NUM>. % by mol and most preferably <NUM> to <NUM> % by mol, especially <NUM> to <NUM> % by mol.

In another embodiment of the present invention in the multimodal LLDPE of use, the HMW component as well as the lower molecular weight (LMW) component are ethylene copolymers with one C4-<NUM> alpha olefin, preferably copolymers of ethylene with <NUM>-butene.

The LMW component of the multimodal LLDPE copolymer may for example have a MFR<NUM> of at least <NUM>, preferably <NUM> to <NUM>/<NUM>, more preferably at least <NUM>/<NUM> up to <NUM>/<NUM>. The molecular weight of the low molecular weight component should preferably range from <NUM>,<NUM> to <NUM>,<NUM>, e.g. <NUM>,<NUM> to <NUM>,<NUM>.

The HMW component of the multimodal LLDPE may for example have preferably an MFR<NUM> of less than <NUM>/<NUM>, preferably less than <NUM>/<NUM>, especially less than <NUM>/<NUM>, and a density of less than <NUM>/m<NUM>, e.g. less than <NUM>/m<NUM>, preferably less than <NUM>/m<NUM>. The Mw of the higher molecular weight component may range from <NUM>,<NUM> to <NUM>,<NUM>,<NUM>, preferably <NUM>,<NUM> to <NUM>,<NUM>.

The multimodal LLDPE may be formed using single site catalysis or a Ziegler Natta catalyst. Both these types of catalyst are well known in the art.

In one embodiment, the multimodal LLDPE is made by single site catalysis and is therefore a metallocene catalyzed linear low density polyethylene (mLLDPE).

Metallocene catalyzed linear low density polyethylenes (mLLDPE) are known in the art and as such not subject of the invention. Reference is made in this regard for Example to <CIT>, example IE1 of <CIT> or <CIT>, or <CIT>, Example <NUM>.

In another embodiment, the multimodal LLDPE copolymer may comprise two ethylene butene copolymer components and is, ideally made by a Ziegler Natta catalyst and is therefore a Ziegler Natta catalyzed linear low density polyethylene (znLLDPE).

Such Ziegler Natta catalyzed linear low density polyethylene (znLLDPE) are also known in the art and as such not subject of the invention. They are for example produced using a ZN catalysts as disclosed in <CIT>, <CIT>, <CIT>, <CIT> or <CIT>.

The multimodal (e.g. bimodal) polymers can in general be made by mechanical blending two or more, separately prepared polymer components or, preferably, by in-situ blending in a multistage polymerisation process during the preparation process of the polymer components. Both mechanical and in-situ blending are well known in the field.

Accordingly, preferred multimodal LLDPEs, are prepared by in-situ blending in a multistage, i.e. two or more stage, polymerization or by the use of two or more different polymerization catalysts, including multi- or dual site catalysts, in a one stage polymerization.

Preferably the multimodal LLDPE, is produced in at least two-stage polymerization using the same catalyst, e.g. a single site or Ziegler-Natta catalyst. Thus, for example two slurry reactors or two gas phase reactors, or any combinations thereof, in any order can be employed. Preferably however, the multimodal polymer, e.g. LLDPE, is made using a slurry polymerization in a loop reactor followed by a gas phase polymerization in a gas phase reactor.

A loop reactor - gas phase reactor system is marketed by Borealis as a BORSTAR reactor system. Any multimodal polymer, e.g. LLDPE, present is thus preferably formed in a two stage process comprising a first slurry loop polymerisation followed by gas phase polymerisation.

The conditions used in such a process are well known. For slurry reactors, the reaction temperature will generally be in the range <NUM> to <NUM> (e.g. <NUM>-<NUM>), the reactor pressure will generally be in the range <NUM> to <NUM> bar (e.g. <NUM>-<NUM> bar), and the residence time will generally be in the range <NUM> to <NUM> hours (e.g. <NUM> to <NUM> hours). The diluent used will generally be an aliphatic hydrocarbon having a boiling point in the range -<NUM> to +<NUM>. In such reactors, polymerization may if desired be effected under supercritical conditions. Slurry polymerisation may also be carried out in bulk where the reaction medium is formed from the monomer being polymerised.

For gas phase reactors, the reaction temperature used will generally be in the range <NUM> to <NUM> (e.g. <NUM> to <NUM>), the reactor pressure will generally be in the range <NUM> to <NUM> bar, and the residence time will generally be <NUM> to <NUM> hours. The gas used will commonly be a non-reactive gas such as nitrogen or low boiling point hydrocarbons such as propane together with monomer (e.g. ethylene).

Preferably, the lower molecular weight polymer fraction is produced in a continuously operating loop reactor where ethylene is polymerised in the presence of a polymerization catalyst as stated above and a chain transfer agent such as hydrogen. The diluent is typically an inert aliphatic hydrocarbon, preferably isobutane or propane.

The higher molecular weight component can then be formed in a gas phase reactor using the same catalyst.

Where the higher molecular weight component is made second in a multistage polymerisation it is not possible to measure its properties directly. However, the skilled man is able to determine the density, MFR<NUM> etc of the higher molecular weight component using Kim McAuley's equations. Thus, both density and MFR<NUM> can be found using <NPL>.

The density is calculated from McAuley's equation <NUM>, where final density and density after the first reactor is known.

MFR<NUM> is calculated from McAuley's equation <NUM>, where final MFR<NUM> and MFR<NUM> after the first reactor is calculated. The use of these equations to calculate polymer properties in multimodal polymers is common place.

The polymers of use on the invention are however commercially available materials. An Example for a Ziegler Natta catalysed linear low density polyethylene (znLLDPE) is FB2230, which is a bimodal ethylene/<NUM>-butene copolymer with a density of <NUM>/m3 and an MFR<NUM> of <NUM>/<NUM> commercially available from Borealis.

Layer A furthermore comprises a plastomer. The plastomer may be a copolymer of ethylene and <NUM>-butene, <NUM>-hexene or <NUM>-octene in which the ethylene forms the major component. Preferred plastomers are copolymers of ethylene and <NUM>-butene or ethylene and <NUM>-octene, more preferably ethylene and <NUM>-octene. The content of comonomer, such as <NUM>-octene in a plastomer, such as an ethylene <NUM>- octene plastomer may be <NUM> to <NUM> wt%, such as <NUM> to <NUM> wt% in the copolymer.

In an embodiment, as mentioned above the plastomer of layer A may have a density of between > <NUM> and < <NUM>/m<NUM>, preferably between <NUM> and < <NUM>/m<NUM>, further preferred > <NUM> and < <NUM>/m<NUM> or <NUM> to <NUM>/m<NUM>. The MFR<NUM> may be between <NUM> and <NUM>/<NUM>, preferably <NUM> and <NUM>/<NUM>, further preferred <NUM> and <NUM>/<NUM>.

The molecular mass distribution Mw/Mn of suitable ethylene based plastomers is most often below <NUM>, such as <NUM> or below, but is at least <NUM>. It is preferably between <NUM> and <NUM>.

Suitable ethylene based plastomers can be any copolymer of ethylene and propylene or ethylene and C4 - C10 alpha olefin having the above defined properties, which are commercial available, i. from Borealis under the tradename Queo, from DOW Chemical Corp (USA) under the tradename Engage or Affinity, or from Mitsui under the tradename Tafmer.

Alternately these ethylene based plastomers can be prepared by known processes, in a one stage or two stage polymerization process, comprising solution polymerization, slurry polymerization, gas phase polymerization or combinations therefrom, in the presence of suitable catalysts, like vanadium oxide catalysts or single-site catalysts, e.g. metallocene or constrained geometry catalysts, known to the art skilled persons.

Preferably, these ethylene based plastomers are prepared by a one stage or two stage solution polymerization process, especially by high temperature solution polymerization process at temperatures higher than <NUM>.

Such process is essentially based on polymerizing the monomer and a suitable comonomer in a liquid hydrocarbon solvent in which the resulting polymer is soluble. The polymerization is carried out at a temperature above the melting point of the polymer, as a result of which a polymer solution is obtained. This solution is flashed in order to separate the polymer from the unreacted monomer and the solvent. The solvent is then recovered and recycled in the process.

Preferably the solution polymerization process is a high temperature solution polymerization process, using a polymerization temperature of higher than <NUM>. Preferably the polymerization temperature is at least <NUM>°, more preferably at least <NUM>. The polymerization temperature can be up to <NUM>.

The pressure in such a solution polymerization process is preferably in a range of <NUM> to <NUM> bar, preferably <NUM> to <NUM> bar and more preferably <NUM> to <NUM> bar.

The liquid hydrocarbon solvent used is preferably a C5-<NUM>-hydrocarbon which may be unsubstituted or substituted by C1-<NUM> alkyl group such as pentane, methyl pentane, hexane, heptane, octane, cyclohexane, methylcyclohexane and hydrogenated naphtha. More preferably unsubstituted C6-<NUM>-hydrocarbon solvents are used.

A known solution technology suitable for the process according to the invention is the Borceed technology. Plastomers of the invention are ideally formed using metallocene type catalysts. Plastomers of use in the invention are commercially available and can be bought from polymer suppliers and aid the sealing of the claimed films.

Layer B comprises at least one multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefin and having a density of > <NUM> to <NUM>/m<NUM> and an MFR<NUM> of <NUM> to <NUM>/<NUM>. The polymer is preferably a multimodal linear low density polyethylene (LLDPE) with at least one C4-<NUM> alpha olefin which comprises a lower molecular weight (LMW) component and a higher molecular weight (HMW) component. Layer B should be different to layer A.

In one embodiment the at least one multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefin may be a Ziegler Natta catalysed LLDPE copolymer. In another embodiment, the multimodal LLDPE copolymer may comprise two ethylene butene copolymer components and is, ideally made by a Ziegler Natta catalyst and is therefore a Ziegler Natta catalyzed linear low density polyethylene (znLLDPE).

In another embodiment of the present invention, in the multimodal LLDPE of use in layer B), the HMW component as well as the lower molecular weight (LMW) component are ethylene copolymers of ethylene with one C4-<NUM> alpha olefins, preferably copolymers of ethylene with <NUM>-butene. In this case, the multimodal LLDPE is a multimodal LLDPE copolymer.

An example for a Ziegler Natta catalysed linear low density polyethylene (znLLDPE) is FB2230, which is a bimodal ethylene/<NUM>-butene copolymer with a density of <NUM>/m<NUM> and an MFR<NUM> of <NUM>/<NUM> commercially available from Borealis.

In another embodiment the at least one multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefins may be an ethylene terpolymer, such as a Ziegler Natta catalysed ethylene terpolymer.

The multimodal ethylene terpolymer may comprise at least two C4-<NUM> alpha-olefin comonomers. Ideally, the multimodal ethylene terpolymer contains <NUM> comonomers only. The comonomers are especially selected from <NUM>-butene, <NUM>-hexene or <NUM>-octene. The amount of comonomers present in the multimodal ethylene terpolymer is preferably <NUM> to <NUM> mol%, e.g. <NUM> to <NUM>% mole, especially <NUM> to <NUM>% mole.

The multimodal ethylene terpolymer suitable for use in films of the present invention can comprise a lower molecular weight fraction being a polyethylene homopolymer and a higher molecular weight fraction being a terpolymer of ethylene and at least two alpha olefin comonomers having <NUM> - <NUM> carbon atoms.

Thus, the multimodal ethylene terpolymer suitable for use in the films of the present invention can preferably comprise:.

Preferably, the comonomer of the higher molecular weight component is a C6-C10-alpha-olefin selected from the group of <NUM>-hexene, <NUM>-methyl-<NUM>-pentene, <NUM>-octene and <NUM>-decene, especially <NUM>-hexene or <NUM>-octene.

The multimodal ethylene terpolymer preferably has a density of e.g. > <NUM>- < <NUM>/m<NUM>. Ideally, the multimodal terpolymer has a density of > <NUM> - <NUM>/m<NUM>. Alternatively the density may be from <NUM> - <NUM>/m<NUM>.

The multimodal ethylene terpolymer may be produced by polymerisation using conditions which create a multimodal (e.g. bimodal) polymer product ideally using a Ziegler Natta catalyst system. Typically, a two or more stage, i.e. multistage, polymerisation process is used with different process conditions in the different stages or zones (e.g. different temperatures, pressures, polymerisation media, hydrogen partial pressures, etc). Preferably, the multimodal (e.g. bimodal) composition is produced by a multistage polymerisation, e.g. using a series of reactors, with optional comonomer addition preferably in only the reactor(s) used for production of the higher/highest molecular weight component(s). A multistage process is defined to be a polymerisation process in which a polymer comprising two or more fractions is produced by producing each or at least two polymer fraction(s) in a separate reaction stage, usually with different reaction conditions in each stage, in the presence of the reaction product of the previous stage which comprises a polymerisation catalyst. The polymerisation reactions used in each stage may involve conventional ethylene homopolymerisation or copolymerisation reactions, e.g. gas-phase, slurry phase, liquid phase polymerisations, using conventional reactors, e.g. loop reactors, gas phase reactors, batch reactors etc. (see for example <CIT> and <CIT>). Terpolymers meeting the requirements of the invention are known and can be bought from suppliers such as Borealis, e.g. FX1002.

Layer B) may also comprise a further multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefin different from the multimodal copolymer already present in the B) layer. The further multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefin of layer B may be a multimodal linear low density polyethylene (LLDPE) as described above for layer A, preferably a multimodal LLDPE terpolymer as described for Layer B). The further multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefin of layer B) may have a density of <NUM> to <NUM>/m<NUM>, preferably > <NUM> to < <NUM>/m<NUM> and/or MFR<NUM> of <NUM> and <NUM>/<NUM>, preferably > <NUM> and < <NUM>/<NUM>.

According to the invention, the third layer C comprises a multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefins, having a density of <NUM> to <NUM>/m<NUM>, preferably > <NUM> to <NUM>/m<NUM> and an MFR<NUM> of <NUM> to <NUM>/<NUM>. Layer C) may comprise at least <NUM> wt% of said multimodal copolymer of ethylene.

The multimodal copolymer of ethylene of layer C may be the same as described above for layer A or B, preferably Layer C consists of only one multimodal copolymer of ethylene as described for Layer B, e.g. a multimodal LLDPE terpolymer.

Thus the multimodal copolymer of ethylene of layer C is preferably either the multimodal ethylene terpolymer as described for layer B or the multimodal ethylene copolymer as described for Layer A.

Films are produced by extrusion through an annular die with a pressure difference applied to blow the extruded cylinder into a film and achieve the desired orientation within the film, i.e. to build a stress into the cooled film.

For film formation using polymer mixtures the different polymer components (e.g. within layers (A), (B) and (C)) are typically intimately mixed prior to extrusion and blowing of the film as is well known in the art. It is especially preferred to thoroughly blend the components, for example using a twin screw extruder or a single screw extruder, preferably a counter-rotating extruder prior to extrusion and film blowing.

The films of the invention are uniaxially oriented. That means that they are stretched in a single direction, the machine direction. They are therefore no biaxially oriented films.

The preparation of a uniaxially oriented multilayer film of the invention comprises at least the steps of forming a layered film structure and stretching the obtained multilayer film in a draw ratio of at least <NUM>:<NUM>, preferably <NUM>:<NUM>, more preferably at least <NUM>:<NUM>, and still more preferably <NUM>:<NUM>. The upper limit for the draw ratio is <NUM>:<NUM>.

Typically the compositions providing the layers of the film will be blown i.e. (co)extruded at a temperature in the range <NUM> to <NUM>, and cooled by blowing gas (generally air) at a temperature of <NUM> to <NUM> to provide a frost line height of <NUM> or <NUM> to <NUM> times the diameter of the die. The blow up ratio should generally be in the range <NUM> to <NUM>, preferably <NUM> to <NUM>.

The obtained film is subjected to a subsequent stretching step, wherein the film is stretched in the machine direction. Stretching may be carried out by any conventional technique using any conventional stretching devices which are well known to those skilled in the art. Preferably a stretching device suited for stretching at temperatures ><NUM> is used.

The films of the invention may not be made by a process in which the formed bubble is then collapsed e.g. in nip rolls to form said film where layers (A) are contacted inside/inside, i.e. ABA/ABA.

In the present invention, the coextruded bubble may be collapsed and split into two films. The two films can then be stretched separately in a winding machine. For ABC films the coextrude bubble may be cut into one film of <NUM>*lay flat width.

Stretching is preferably carried out at a temperature in the range <NUM> - <NUM> e.g. about <NUM>. Any conventional stretching rate may be used, e.g. <NUM> to <NUM> %/second.

The film is stretched only in the machine direction to be uniaxial. The effect of stretching in only one direction is to uniaxially orient the film.

An effect of stretching (or drawing) is that the thickness of the film is similarly reduced. Thus a draw ratio of at least <NUM>:<NUM> preferably also means that the thickness of the film is at least three times less than the original thickness.

Blow extrusion and stretching techniques are well known in the art, e.g. in <CIT>.

The film preparation process steps of the invention are known and may be carried out in one film line in a manner known in the art. Such film lines are commercially available.

The films of the invention have an original thickness of <NUM> to <NUM> before stretching, preferably <NUM> to <NUM> and more preferably <NUM> to <NUM>.

After stretching, the final thickness of the uniaxially oriented films according to this invention is typically in the range <NUM> to <NUM>, preferably <NUM> to <NUM> and more preferably of <NUM> to <NUM>.

For the three-layer structure the outer layers (layer A and C) and core layer (layer B) may all be of equal thickness or alternatively the core layer (layer B) may be thicker than each outer layer. A convenient film comprises two outer layers which each form <NUM> to <NUM>%, preferably <NUM> to <NUM>% of the total final thickness of the <NUM>-layered film, the core layer forming the remaining thickness, e.g. <NUM> to <NUM>%, preferably <NUM> to <NUM>% of the total final thickness of the <NUM>-layered film.

The total thickness of the film is <NUM>%, thus the some of the individual layers has to be <NUM>%.

In a preferred embodiment of the invention, films according to the invention, comprise as multimodal linear low density polyethylene (LLDPE) in layer A, a Ziegler Natta catalyzed linear low density polyethylene (znLLDPE).

Such films can be used as peelable heat sealable films, i.e. as sealable and peelable films. Some goods are now packed in films that are heat sealed but, when the package is opened the film is peelable. Many fresh food products are packaged in this way.

Films of the invention therefore need to provide a good seal to protect the packaged goods. In addition, films must be peelable, i.e. they should have the ability to provide an easily openable seal on a package. Peelability generally refers to the ability to separate two materials or substrates in the course of opening a package without compromising the integrity of either of the two. The force required to pull a seal apart is called "seal strength" or "heat seal strength" or "peel strength", which is determined as described in the experimental part for the sealing initiation temperature (SIT) measured on a <NUM> MDO blown film.

Such films according to the present invention have a seal strength from <NUM> to <NUM> N/<NUM> over an unusually broad interval of sealing temperatures, i.e. over an interval of at least <NUM>, preferably at least <NUM>, such as <NUM> to <NUM>. The interval starting point can be as low as <NUM>.

Viewed from another aspect the invention provides a sealable and peelable package comprising a multilayer machine direction oriented film according to the invention, sealed to a substrate; wherein said film can be peeled away from the substrate.

The substrate to which the film is sealed is typically a polyolefin substrate or cardboard. Suitable substrates include polyethylenes such as LDPE or polypropylene.

The comparative examples herein have relatively high seal strengths at higher seal initiation temperatures. These films are not therefore suitable for peelable applications. The seal strength is too high and the film cannot be peeled away from the surface below. In contrast, the films of the invention exhibit comparatively low seal strengths over a range of seal initiation temperatures making them ideal for seal and peel applications.

The invention will now be described with reference to the following non-limited examples and figures.

<FIG> illustrates the heat seal curve for CE1. <FIG> illustrates the heat seal curve for CE2. <FIG> illustrates the heat seal curve for IE1. <FIG> illustrates the heat seal curve for IE2.

Density of the materials is measured according to ISO <NUM>:<NUM> (E), method D, with isopropanol-water as gradient liquid. The cooling rate of the plaques when crystallising the samples was <NUM>/min. Conditioning time was <NUM> hours.

The melt flow rate (MFR) is determined according to ISO <NUM> and is indicated in g/<NUM>. The MFR is an indication of the melt viscosity of the polymer. The MFR is determined at <NUM> for PE and at <NUM> for PP. The load under which the melt flow rate is determined is usually indicated as a subscript, for instance MFR<NUM> is measured under <NUM> load, MFR<NUM> is measured under <NUM> load or MFR<NUM> is measured under <NUM> load.

The weight average molecular weight Mw and the molecular weight distribution (MWD = Mw/Mn wherein Mn is the number average molecular weight and Mw is the weight average molecular weight) is measured by a method based on ISO <NUM>-<NUM>:<NUM>. A Waters 150CV plus instrument, equipped with refractive index detector and online viscosimeter was used with <NUM> x HT6E styragel columns from Waters (styrene-divinylbenzene) and <NUM>,<NUM>,<NUM>-trichlorobenzene (TCB, stabilized with <NUM>/L <NUM>,<NUM>-Di tert butyl-<NUM>-methyl-phenol) as solvent at <NUM> and at a constant flow rate of <NUM>/min. <NUM>µL of sample solution were injected per analysis. The column set was calibrated using universal calibration (according to ISO <NUM>-<NUM>:<NUM>) with <NUM> narrow MWD polystyrene (PS) standards in the range of <NUM>/mol to <NUM><NUM>/mol. Mark Houwink constants were used for polystyrene and polyethylene (K: <NUM> x10-<NUM> dL/g and a: <NUM> for PS, and K: <NUM> x10-<NUM> dL/g and a: <NUM> for PE). All samples were prepared by dissolving <NUM> - <NUM> of polymer in <NUM> (at <NUM>) of stabilized TCB (same as mobile phase) and keeping for <NUM> hours at <NUM> and for another <NUM> hours at <NUM> with occasional shaking prior sampling in into the GPC instrument.

Comonomer Content (%wt and %mol) was determined by using <NUM>C-NMR. The <NUM>C-NMR spectra were recorded on Bruker <NUM> spectrometer at <NUM> from samples dissolved in <NUM>,<NUM>,<NUM>-trichlorobenzene/benzene-d<NUM> (<NUM>/<NUM> w/w). Conversion between %wt and %mol can be carried out by calculation.

Impact Strength is determined on Dart-drop (g/<NUM>%). Dart-drop is measured using ISO <NUM>-<NUM>, method "A". A dart with a <NUM> diameter hemispherical head is dropped from a height of <NUM> onto a film sample clamped over a hole. If the specimen fails, the weight of the dart is reduced and if it does not fail the weight is increased. At least <NUM> specimens are tested. The weight resulting in failure of <NUM>% of the specimens is calculated and this provides the dart drop impact (DDI) value (g). The relative DDI (g/µm) is then calculated by dividing the DDI by the thickness of the film.

Tensile modulus (secant modulus, <NUM>-<NUM>% ) is measured according to ASTM D <NUM>-A on film samples prepared as described under below "Film Sample preparation". The speed of testing is <NUM>/min. The test temperature is <NUM>. Width of the film was <NUM>.

Haze was determined according to ASTM D <NUM>-<NUM> on films as produced indicated below.

Gloss was determined according to ASTM D2457 measured outside, lengthwise, at an angle of <NUM>° (in MD) on films as produced indicated below.

The method determines the sealing temperature range (sealing range) of polyethylene films, in particular blown films or cast films. The sealing temperature range is the temperature range, in which the films can be sealed according to conditions given below.

The lower limit (heat sealing initiation temperature (SIT)) is the sealing temperature at which a sealing strength of > <NUM> N is achieved. The upper limit (sealing end temperature (SET)) is reached, when the films stick to the sealing device.

The sealing range is determined on a J&B Hot Tack Testerwith a film of <NUM> thickness with the following further parameters:.

Specimen is sealed A to A at each sealbar temperature and seal strength (force) is determined at each step. The seal initiation temperature is determined at which the seal strength reaches <NUM> N.

Three layer blown films were produced on a Dr. Colin <NUM> Layer Blown film line. The melt temperature of the sealing layer (A) was <NUM> to <NUM>, the melt temperature of the core layer (B) was in the range of <NUM> to <NUM> and for the outer layer (C) <NUM>. The throughput of the extruders was in sum <NUM>/h. Layer thickness has been determined by Scanning Electron Microscopy. The compositions used for the layers are indicated in the table <NUM>.

Further parameters for the blown film line were:.

The formed films had a total thickness of <NUM>.

Stretching was carried out using a monodirectional stretching machine manufactured by Hosokawa Alpine AG in Augsburg/Germany. The unit consists of preheating, drawing, annealing, and cooling sections, with each set at specific temperatures to optimize the performance of the unit and produce films with the desired properties.

The film obtained from blown film extrusion was pulled into the orientation machine then stretched between two sets of nip rollers where the second pair runs at higher speed than the first pair resulting in the desired draw ratio. Stretching is carried out with the respective draw ratios to reach the desired thickness. (draw ratios and final thickness of MDO films are given in Table <NUM>) After exiting the stretching machine the film is fed into a conventional film winder where the film is slit to its desired width and wound to form reels.

The properties of the multilayer films after stretching are also indicated in table <NUM>.

In <FIG> the heat seal curves for determining SIT (10N/<NUM>) and the Seal Strength of IE1, IE2, CE1 and CE2 are shown. As can be easily seen from the figures and the table the inventive film structures show a seal strength suitable for peel seal films (in the range of <NUM> to <NUM> N/<NUM>) along an clearly broader interval of sealing temperatures starting at <NUM> compared to the comparative film structures.

Claim 1:
A multilayer machine direction oriented film for sealing comprising three layers with layer B located between layer A and a third layer C,
wherein layer A comprises <NUM> to <NUM> wt%, based on the total weight of the layer, of at least one multimodal linear low density polyethylene (LLDPE) copolymer with one C4-<NUM> alpha olefin having a density of <NUM> to <NUM>/m<NUM> and an MFR<NUM> of <NUM> to <NUM>/<NUM> which comprises a lower molecular weight (LMW) component and a higher molecular weight (HMW) component;
and <NUM> to <NUM> w%, based on the total weight of the layer, of at least one ethylene based plastomer with a density between <NUM> and <NUM>/m<NUM>, and
wherein layer B comprises <NUM> to <NUM> wt% based on the total weight of the layer, of at least one multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefin having a density of <NUM> to <NUM>/m<NUM> and an MFR<NUM> of <NUM> to <NUM>/<NUM>;
wherein the third layer C is different from layer B and layer A and wherein the third layer C comprises a multimodal copolymer of ethylene with at least one C4-<NUM> alpha olefin an having a density of > <NUM> to <NUM>/m3 and an MFR<NUM> of <NUM> to <NUM>/<NUM>..