WO2019243348A1

WO2019243348A1 - Polyethylene cast films

Info

Publication number: WO2019243348A1
Application number: PCT/EP2019/066057
Authority: WO
Inventors: Lucio Baccaro; Attilio SCALA; Bart VAN DEN ESSCHERT
Original assignee: Sabic Global Technologies B.V.
Priority date: 2018-06-21
Filing date: 2019-06-18
Publication date: 2019-12-26
Also published as: EP3810420A1

Abstract

The present invention relates to a multi-layer film comprising: (a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a) comprising moieties derived from ethylene and 1-octene or 1-hexene, having a density of ≥ 900 and ≤ 925 kg/m³, and an MFR₂ of ≥ 0.5 and ≤ 1.5 g/10 min; and (b) at least one layer comprising an LLDPE (b) comprising moieties derived from ethylene and 1-hexene, having a density of ≥ 900 and ≤ 925 kg/m³ and an MFR₂ of ≥ 2.0 and ≤ 4.0 g/10 min; wherein the density is determined in accordance with ASTM D1505 (2010) and the MFR₂ is the melt mass flow rate determined in accordance with ASTM D1238 (2013) at 190°C under a load of 2.16 kg, and wherein the film is produced by cast extrusion moulding. Such multi-layer film demonstrates a desirable balance of impact resistance, slow penetration puncture resistance, tear resistance and tensile properties.

Description

Polyethylene cast films.

[0001 ] The present invention relates to polyethylene films produced by cast technology. The invention also relates to a process for production of such films.

[0002] A suitable preparation method for polyethylene films is casting or cast film extrusion. The preparation of a films by casting is well-known in the art. In general, casting is a continuous operation of melting and conveying a polymer in a heated screw-and-barrel assembly, also referred to as a melt extruder. The molten polymer may then be extruded through a slit die onto a roll, which preferably is a chilled, highly polished turning roll, where it may be quenched from one side, which results in the extruded polymeric material to be cooled to form a film, which may be sent to a second roller for further cooling on the other side. Alternatively, an extruded polymer web may be passed through a quench tank for cooling. The film then may pass through a system of rollers, which have different purposes, and may finally be wound onto a roll for storage.

[0003] Cast films have particular desirable properties, including desirable optical properties such as transparency, haze and gloss, barrier properties and certain desirable mechanical properties, which render them particularly suitable for a variety of purposes, in particular where puncture resistance, barrier resistance and transparency are applicable. Furthermore, the casting process allows for production of films at very high speeds, allowing for economically attractive production of films, and films of a wide variety in thickness can be produced.

Furthermore, casting of films allows for the production of multi-layer film structures. Such multi layer film structures allow for the use of different material formulations in the different layers, as a result of which one can tailor the properties of the multi-layer structure by choosing layers each having their particular properties.

[0004] Such multi-layer polyethylene cast film structures are well known and widely used.

However, there remains a need to further develop the properties of such films, in particular the mechanical properties. Improvement of the mechanical properties of such films can be used in two different regards. One the one hand, better mechanical properties of a film of otherwise the same dimensions properties as the films of the art allows for use of such films in applications where such properties are in demand, for which the films of the art are not suitable. On the other hand, better mechanical properties allow for the production of a film of reduced thickness, i.e. a down-gauged film, having the same properties as the films of the art. This may result in a reduction of the quantity of film material used to achieve the same purpose, in other words to reduce the weight of the packaging, which is a tendency that is continuously strived for by those in the field.

[0005] One particular property that is in demand for improvement to be able to achieve such down-gauging is the slow puncture resistance. This reflects the tendency of the film, when for example used in a package, to tear or show defects when exposed to an object of certain sharpness, for example an object with a sharp corner.

[0006] The inventors now have achieved such improvement by a multi-layer film comprising:

(a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a)

comprising moieties derived from ethylene and 1 -octene or 1 -hexene, having a density of > 900 and < 925 kg/m³, and an MFR₂ of > 0.5 and < 1 .5 g/10 min; and

(b) at least one layer comprising an LLDPE (b) comprising moieties derived from

ethylene and 1 -hexene, having a density of > 900 and < 925 kg/m³ and an MFR₂ of > 2.0 and < 4.0 g/10 min;

wherein the density is determined in accordance with ASTM D1505 (2010) and the MFR₂ is the melt mass flow rate determined in accordance with ASTM D1238 (2013) at 190°C under a load of 2.16 kg, and wherein the film is produced by cast extrusion moulding.

Such multi-layer film demonstrates a desirable balance of impact resistance, slow penetration puncture resistance, tear resistance and tensile properties, in particular an improved slow penetration puncture resistance.

[0007] The LLDPE (b) may for example have an MFR₂ of > 2.0 and < 4.0 g/10 min, for example > 2.5 and < 3.2 g/10 min. The LLDPE (b) may for example have an MFR₂ of > 2.0 and < 3.9 or < 3.8 or < 3.7 or < 3.6 or < 3.5 or < 3.4 or < 3.3 or < 3.2 or < 3.1 or < 3.0 g/10 min. The LLDPE(b) may for example have an MFR₂ of > 2.1 or > 2.2 or > 2.3 or > 2.4 or > 2.5 and < 4.0 g/10 min. The LLDPE(b) may for example have an MFR₂ of > 2.1 or > 2.2 or > 2.3 or > 2.4 or > 2.5 and < 3.4 g/10 min.

[0008] The LDPE(a) may for example have an MFR₂ of > 0.5 and < 1 .4 or < 1 .3 or <1 .2 or < 1 .1 or < 1 .0 g/10 min. The LLDPE(a) may for example have an MFR₂ of > 0.6 or > 0.7 or > 0.8 and < 1.5 g/10 min. The LLDPE(a) may for example have an MFR₂ of > 0.6 or > 0.7 or > 0.8 and < 1.4 g/10 min.

[0009] For example, the LLDPE(a) may have an MFR₂ of > 0.6 and < 1.4 g/10 min, and/or the LLDPE(b) may have an MFR₂ of > 2.5 and < 3.2 g/10 min.

[0010] The LLDPE (a) preferably comprise moieties derived from ethylene and 1 -octene. For example, the LLDPE (a) may comprise > 90.0 wt%, preferably > 95.0 wt%, even more preferably > 98.0 wt%, of moieties derived from ethylene, with regard to the total weight of the LLDPE (a), and moieties derived from 1 -octene. For example, the LLDPE (a) may comprise > 90.0 wt% of moieties derived from ethylene and < 10.0 wt% of moieties derived from 1 -octene, with regard to the total weight of the LLDPE (a), preferably > 95.0 wt% of moieties derived from ethylene and < 5.0 wt% of moieties derived from 1 -octene. For example, the LLDPE (a) may consist of moieties derived from ethylene and 1 -octene. For example, the LLDPE (a) may consist of > 90.0 wt% of moieties derived from ethylene and < 10.0 wt% of moieties derived from 1 -octene, with regard to the total weight of the LLDPE (a), preferably > 95.0 wt% of moieties derived from ethylene and < 5.0 wt% of moieties derived from 1 -octene.

[001 1] The LLDPE (b) preferably comprise moieties derived from ethylene and 1 -hexene. For example, the LLDPE (b) may comprise > 80.0 wt%, preferably > 90.0 wt%, more preferably > 95.0 wt%, even more preferably > 98.0 wt%, of moieties derived from ethylene, with regard to the total weight of the LLDPE (b), and moieties derived from 1 -hexene. For example, the LLDPE (b) may comprise > 90.0 wt% of moieties derived from ethylene and < 10.0 wt% of moieties derived from 1 -hexene, with regard to the total weight of the LLDPE (b), preferably > 95.0 wt% of moieties derived from ethylene and < 5.0 wt% of moieties derived from 1 -hexene. For example, the LLDPE (b) may consist of moieties derived from ethylene and 1 -hexene. For example, the LLDPE (b) may consist of > 90.0 wt% of moieties derived from ethylene and <

10.0 wt% of moieties derived from 1 -hexene, with regard to the total weight of the LLDPE (b), preferably > 95.0 wt% of moieties derived from ethylene and < 5.0 wt% of moieties derived from 1 -hexene.

[0012] In a certain embodiment of the invention, the LLDPE (a) is produced using a single-site catalyst. In a certain further embodiment, the LLDPE (b) is produced using a single-site catalyst. Further, the LLDPE (a) or the LLDPE (b) may be produced using a single-site catalyst. Further, the LLDPE (a) and the LLDPE (b) may be produced using a single-site catalyst. [0013] A single-site catalyst may in the context of the present invention be understood to be a catalyst comprising a compound having one or more indenyl- or cyclopentadienyl-moieties, which may or may not bear substituents, and which are bound to a metal selected from Ti, Zr or Hf to form a complex with catalytic activity in olefin polymerisation. Such single-site catalyst may further comprise an activator compound.

[0014] The LLDPE (a) may for example have a number-average molecular weight (M_n) of >

25.0, preferably > 30.0 kg/mol, for example > 25.0 and < 45.0, preferably > 30.0 and < 40.0 kg/mol. For example, the LLDPE (a) may have a z-average molecular weight (M_z) of < 500, preferably < 400 kg/mol, for example > 200 and < 500 kg/mol, preferably > 250 and < 400 kg/mol. The LLDPE (a) may for example have an M_w/M_n ratio of > 2.0 and < 4.0. The LLDPE (a) may for example have an M_z/M_n ratio of < 25.0, preferably < 20.0, for example > 5.0 and < 25.0, preferably > 5.0 and < 20.0, more preferably > 5.0 and <15.0. Herein M_n is the number average molecular weight, M_w is the weight average molecular weight, and M_z is the z-average molecular weight, as determined in accordance with ASTM D6474 (2012).

[0015] The LLDPE materials used in the multi-layer film according to the present invention may for example be produced in a gas-phase polymerisation process, a slurry polymerisation process, or in a solution polymerisation process. For example, the LLDPE (a) may be produced in a gas-phase polymerisation process, a slurry polymerisation process, or in a solution polymerisation process. The LLDPE (a) may for example be produced in a gas-phase polymerisation process. The LLDPE (a) may be produced in a solution polymerisation process. For example, the LLDPE (b) may be produced in a gas-phase polymerisation process, a slurry polymerisation process, or in a solution polymerisation process. The LLDPE (b) may be produced in a gas-phase polymerisation process. The LLDPE (b) may be produced in a solution polymerisation process. In a certain embodiment of the invention, the LLDPE (a) is produced in a gas-phase polymerisation process and the LLDPE (b) is produced in a gas-phase

polymerisation process. Alternatively, the LLDPE (a) may be produced in a solution

polymerisation process and the LLDPE (b) may be produced in a solution polymerisation process. Alternatively, the LLDPE (a) may be produced in a gas-phase polymerisation process and the LLDPE (b) may be produced in a solution polymerisation process. Alternatively, the LLDPE (a) may be produced in a solution polymerisation process and the LLDPE (b) may be produced in a gas-phase polymerisation process. [0016] Such gas-phase polymerisation process may comprise a single polymerisation reactor in which the LLDPE is produced. Alternatively, such gas-phase polymerisation process may comprise multiple polymerisation reactors positioned in series wherein the reaction product from a preceding reactor is introduced into a subsequently positioned reactor, together with further monomer(s). The further monomer(s) may be ethylene and/or a comonomer. In the production of LLDPE (a), the comonomer is 1 -octene. In the production of LLDPE (b), the comonomer is 1 - hexene.

[0017] Such solution polymerisation process may comprise a single polymerisation reactor in which the LLDPE is produced. Alternatively, such solution polymerisation process may comprise multiple polymerisation reactors positioned in series wherein the reaction product from a preceding reactor is introduced into a subsequently positioned reactor, together with further monomer(s). The further monomer(s) may be ethylene and/or a comonomer. In the production of LLDPE (a), the comonomer is 1 -octene. In the production of LLDPE (b), the comonomer is 1 - hexene.

[0018] Each of the LLDPE materials used in the multi-layer film according to the present invention may for example comprise > 80.0 wt%, preferably > 90.0 wt%, more preferably > 95.0 wt%, even more preferably > 98.0 wt%, of moieties derived from ethylene, with regard to the total weight of the LLDPE. For example, LLDPE (a) may comprise > 80.0 wt%, preferably > 90.0 wt%, more preferably > 95.0 wt%, even more preferably > 98.0 wt%, of moieties derived from ethylene, with regard to the total weight of the LLDPE (a). For example, LLDPE (b) may comprise > 80.0 wt%, preferably > 90.0 wt%, more preferably > 95.0 wt%, even more preferably > 98.0 wt%, of moieties derived from ethylene, with regard to the total weight of the LLDPE (b).

[0019] For example, the multi-layer film according to the invention involves a certain

embodiment wherein:

• the LLDPE (a) comprises > 80.0 wt% of moieties derived from ethylene and/or > 2.0 and < 20.0 wt% of moieties derived from 1 -octene or 1 -hexene, with regard to the total weight of the LLDPE (a); and/or

• the LLDPE (b) comprises > 80.0 wt% of moieties derived from ethylene and/or > 2.0 and < 20.0 wt% of moieties derived from 1 -hexene, with regard to the total weight of the LLDPE (b). [0020] The multi-layer film of the invention may in certain embodiments comprise two outer layers and at least one inner layer. For example, the multi-layer film may comprise two outer layers and at least one inner layer, wherein at least one inner layer is a layer (a) comprising the LLDPE (a).

[0021 ] The multi-layer film of the present invention may in certain embodiments comprise two outer layers, wherein at least one outer layer is a layer (b) comprising the LLDPE (b).

Preferably, both outer layers are each a layer (b) comprising LLDPE (b).

[0022] It is preferred that at least one outer layer is arranged to contact an inner layer (a) comprising LLDPE (a).

[0023] Each layer (a) comprising LLDPE (a) may for example comprise an individually selected quantity of the LLDPE (a) with regard to the total weight of that layer (a), preferably an individually selected quantity of at least 80.0 wt% of the LLDPE (a), more preferably at least 90.0 wt%, even more preferably that layer may consist of the LLDPE (a) and optionally up to 2.0 wt% of additives, with regard to the total weight of that layer.

[0024] Each layer (b) comprising LLDPE (b) may for example comprise an individually selected quantity of the LLDPE (b) with regard to the total weight of that layer (b), preferably an individually selected quantity of at least 80.0 wt% of the LLDPE (b), more preferably at least 90.0 wt%, even more preferably that layer may consist of the LLDPE (b) and optionally up to 2.0 wt% of additives, with regard to the total weight of that layer.

[0025] Preferably, each layer (a) comprising LLDPE (a) may for example comprise an individually selected quantity of the LLDPE (a) with regard to the total weight of that layer (a), preferably an individually selected quantity of at least 80.0 wt% of the LLDPE (a), more preferably at least 90.0 wt%, even more preferably that layer may consist of the LLDPE (a) and optionally up to 2.0 wt% of additives, with regard to the total weight of that layer, and each layer (b) comprising LLDPE (b) may for example comprise an individually selected quantity of the LLDPE (b) with regard to the total weight of that layer (b), preferably an individually selected quantity of at least 80.0 wt% of the LLDPE (b), more preferably at least 90.0 wt%, even more preferably that layer may consist of the LLDPE (b) and optionally up to 2.0 wt% of additives, with regard to the total weight of that layer. [0001 ] In a particular embodiment, the LLDPE (b) demonstrates a stress-strain relationship such that in the whole region of strain of 100-300% the derivative of the stress-strain curve do/de is > 5.0 kPa/%, stress and strain being determined in accordance with ISO 527-3 (1995). For example, the LLDE (b) may demonstrate a stress-strain relationship such that in the whole region of strain of 100-300% the derivative of the stress-strain curve do/de is > 5.0 kPa/%, preferably > 7.5 kPa/%, more preferably > 10.0 kPa/%, even more preferably > 15.0 kPa/%, even further preferably > 20.0 kPa. For example, LLDPE (b) may demonstrate a stress-strain relationship such that in the whole region of strain of 100-300% the derivative of the stress- strain curve do/de is > 5.0 kPa/% and < 500 kPa/%, preferably > 5.0 kPa/% and < 200kPa/%, more preferably > 7.5 kPa/% and < 200 kPa/%, even more preferably > 10.0 kPa/% and < 200 kPa/%, even further preferably > 15.0 kPa/% and < 20.0 kPa/%.

[0026] The multi-layer film according to the invention may for example comprise or consist of 3, 5, 7, 9, or 1 1 layers. For example, the multi-layer film of the invention may comprise or consist of 3, 5 or 7 layers. The multi-layer film according to the invention may for example consist of 3,

5, 7, 9, or 1 1 layers. For example, the multi-layer film of the invention may consist of 3, 5 or 7 layers.

[0027] The multi-layer film according to the invention may for example be a 3-layer film wherein each outer layer is a layer (b) comprising LLDPE (b) and the inner layer is a layer (a) comprising LLDPE (a). Alternatively, the multi-layer film may be a 5-layer film wherein each outer is a layer (b) comprising LLDPE (b), further comprising two intermediate layers each arranged to contact one of the outer layers, and a core layer, wherein at least one of the intermediate layers or the core layer comprises or consists of LLDPE (a). For example, the multi-layer film may be a 5- layer film wherein each outer is a layer (b) comprising LLDPE (b), further comprising two intermediate layers each arranged to contact one of the outer layers, and a core layer, wherein each of the intermediate layers and the core layer may individually be selected to comprise LLDPE (a) or LLDPE (b), wherein at least one of the intermediate layers or the core layer comprises or consists of LLDPE (a).

[0028] For example, the multi-layer film may be a 5-layer film wherein each outer is a layer (b) comprising LLDPE (b), further comprising two intermediate layers each arranged to contact one of the outer layers, and a core layer, wherein each of the intermediate layers and the core layer may individually be selected to comprise LLDPE (a) or LLDPE (b), wherein at least one of the intermediate layers or the core layer comprises or consists of LLDPE (a), wherein the LLDPE(a) has an MFR₂ of > 0.6 and < 1 .4 g/10 min, and/or wherein the LLDPE(b) has an MFR₂ of > 2.5 and < 3.2 g/10 min.

[0029] The multi-layer film according to the invention may for example have a thickness of 5.0- 100.0 pm, preferably 5.0-75.0 pm, more preferably 5.0-50.0 pm, even more preferably 15.0-50.0 pm, even more preferably 20.0-40.0 pm, or 50.0-100.0 pm, preferably 70.0-100.0 pm, or 50.0- 75.0 pm.

[0030] The invention also relates to a process for manufacturing a multi-layer film according to the invention, wherein the process involves at least two melt extruders comprising slit dies for extrusion of film, and optionally further melt extruder(s) each comprising slit dies, and a setup for capturing the molten film layers obtained from the melt extruders, combining the molten film layers to form a multi-layer film and cooling the obtained film, the process comprising the steps of:

(i) providing a quantity of the LLDPE (a) or a composition comprising the LLDPE (a) to a first melt extruder comprising a slit die, and extruding to form a first film layer ;

(ii) providing a quantity of the LLDPE (b) or a composition comprising the LLDPE (b) to a second melt extruder comprising a slit die, and extruding to form a second film layer;

(iii) optionally providing further film layer(s) produced using the further melt extruder(s)

(iv) combining the layers to form a multi-layer film; and

(v) subjecting the multi-layer film to cooling equipment to solidify the multi-layer film.

[0031 ] Preferably, the first film layer is combined with the second film layer and at least one further film layer such that the first film layer forms an inner layer and the second film layer forms an outer layer of the multi-layer film.

[0032] Further preferably, at least one of the further film layer(s) is produced of a material equal to the second film layer, preferably wherein that further film layer forms an outer layer of the multi-layer film.

[0033] It is particularly preferred that the process according to the invention is a continuously operated process. [0034] In a certain particular embodiment, the invention relates to a multi-layer film comprising:

(a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a)

comprising moieties derived from ethylene and 1 -octene or 1 -hexene, having a density of > 900 and < 925 kg/m³, an MFR₂ of > 0.5 and < 1.5 g/10 min, and an M_w/M_n ratio of > 2.0 and < 4.0; and

(b) at least one layer comprising an LLDPE (b) comprising moieties derived from

ethylene and 1 -hexene, having a density of > 900 and < 925 kg/m³ and an MFR₂ of

> 2.0 and < 4.0 g/10 min;

wherein the density is determined in accordance with ASTM D1505 (2010) and the MFR₂ is the melt mass flow rate determined in accordance with ASTM D1238 (2013) at 190°C under a load of 2.16 kg, and wherein the film is produced by cast extrusion moulding; wherein M_n is the number average molecular weight and M_w is the weight average molecular weight, as determined in accordance with ASTM D6474 (2012).

[0035] In a further embodiment, the invention relates to a multi-layer film comprising:

(a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a)

comprising moieties derived from ethylene and 1 -octene or 1 -hexene, having a density of > 900 and < 925 kg/m³, an MFR₂ of > 0.5 and < 1.5 g/10 min, an M_w/M_n ratio of > 2.0 and < 4.0, and an M_z/M_w ratio of > 5.0 and < 25.0; and

(b) at least one layer comprising an LLDPE (b) comprising moieties derived from

> 2.0 and < 4.0 g/10 min;

wherein the density is determined in accordance with ASTM D1505 (2010) and the MFR₂ is the melt mass flow rate determined in accordance with ASTM D1238 (2013) at 190°C under a load of 2.16 kg, and wherein the film is produced by cast extrusion moulding; wherein M_n is the number average molecular weight, M_w is the weight average molecular weight, and M_z is the z-average molecular weight, as determined in accordance with ASTM D6474 (2012).

[0036] In yet a further embodiment, the invention also relates to to a multi-layer film comprising:

(a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a)

(b) at least one layer comprising an LLDPE (b) comprising moieties derived from

> 2.0 and < 4.0 g/10 min;

wherein the density is determined in accordance with ASTM D1505 (2010) and the MFR₂ is the melt mass flow rate determined in accordance with ASTM D1238 (2013) at 190°C under a load of 2.16 kg, and wherein the film is produced by cast extrusion moulding; wherein M_n is the number average molecular weight, M_w is the weight average molecular weight, and M_z is the z-average molecular weight, as determined in accordance with ASTM D6474 (2012); wherein the film comprises two outer layers and at least one inner layer, wherein at least one of the inner layer(s) is a layer (a) comprising the LLDPE (a).

[0037] In yet a further embodiment, the invention also relates to a multi-layer film comprising:

(a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a)

(b) at least one layer comprising an LLDPE (b) comprising moieties derived from

> 2.0 and < 4.0 g/10 min;

wherein the density is determined in accordance with ASTM D1505 (2010) and the MFR₂ is the melt mass flow rate determined in accordance with ASTM D1238 (2013) at 190°C under a load of 2.16 kg, and wherein the film is produced by cast extrusion moulding; wherein M_n is the number average molecular weight, M_w is the weight average molecular weight, and M_z is the z-average molecular weight, as determined in accordance with ASTM D6474 (2012); wherein the film comprises two outer layers and at least one inner layer, wherein at least one of the inner layer(s) is a layer (a) comprising the LLDPE (a), wherein the film consist of 5 layers.

[0038] In yet a further embodiment, the invention also relates to a multi-layer film comprising:

(a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a)

(b) at least one layer comprising an LLDPE (b) comprising moieties derived from

> 2.0 and < 4.0 g/10 min;

wherein the density is determined in accordance with ASTM D1505 (2010) and the MFR₂ is the melt mass flow rate determined in accordance with ASTM D1238 (2013) at 190°C under a load of 2.16 kg, and wherein the film is produced by cast extrusion moulding; wherein M_n is the number average molecular weight, M_w is the weight average molecular weight, and M_z is the z-average molecular weight, as determined in accordance with ASTM D6474 (2012); wherein the film comprises two outer layers and at least one inner layer, wherein at least one of the inner layer(s) is a layer (a) comprising the LLDPE (a), wherein the film consist of 5 layers; wherein the two outer layers each comprise the LLDPE (b) and wherein each of the layers comprises LLDPE (a) or LLDPE (b).

[0039] In a certain embodiment, the invention also relates to a multi-layer film comprising:

(a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a)

comprising moieties derived from ethylene and 1 -octene or 1 -hexene, having a density of > 900 and < 925 kg/m³, and an MFR₂ of > 0.5 and < 1.5 g/10 min; and

(b) at least one layer comprising an LLDPE (b) comprising moieties derived from

> 2.0 and < 4.0 g/10 min;

wherein the density is determined in accordance with ASTM D1505 (2010) and the MFR₂ is the melt mass flow rate determined in accordance with ASTM D1238 (2013) at 190°C under a load of 2.16 kg, and wherein the film is produced by cast extrusion moulding;

and wherein the film exhibits, in the machine direction:

• a stress at 200% strain of > 1 1.0 MPa, preferably > 12.0 MPa; and/or

• a stress at 300% strain of > 14.0 MPa, preferably > 16.0 MPa; and/or

• a stress at 400% strain of > 20.0 MPa, preferably > 28.0 MPa; and/or

• a stress at 500% strain of > 35.0 MPa, preferably > 46.0 MPa,

wherein stress and strain are determined in accordance with ISO 527-3 (1995).

[0040] In a certain further embodiment, the invention also relates to a multi-layer film comprising: (a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a) comprising moieties derived from ethylene and 1 -octene or 1 -hexene, having a density of > 900 and < 925 kg/m³, and an MFR₂ of > 0.5 and < 1.5 g/10 min; and

(b) at least one layer comprising an LLDPE (b) comprising moieties derived from

> 2.0 and < 4.0 g/10 min;

and wherein the film exhibits, in the machine direction:

• a stress at 200% strain of > 1 1.0 MPa, preferably > 12.0 MPa

wherein stress and strain are determined in accordance with ISO 527-3 (1995).

[0041 ] In a yet further embodiment, the invention also relates to a multi-layer film comprising:

(a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a)

(b) at least one layer comprising an LLDPE (b) comprising moieties derived from

> 2.0 and < 4.0 g/10 min;

and wherein the film exhibits, in the machine direction:

• a stress at 300% strain of > 14.0 MPa, preferably > 16.0 MPa

wherein stress and strain are determined in accordance with ISO 527-3 (1995).

[0042] In a yet further embodiment, the invention also relates to a multi-layer film comprising:

(a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a)

(b) at least one layer comprising an LLDPE (b) comprising moieties derived from

> 2.0 and < 4.0 g/10 min; wherein the density is determined in accordance with ASTM D1505 (2010) and the MFR₂ is the melt mass flow rate determined in accordance with ASTM D1238 (2013) at 190°C under a load of 2.16 kg, and wherein the film is produced by cast extrusion moulding;

and wherein the film exhibits, in the machine direction:

• a stress at 400% strain of > 20.0 MPa, preferably > 28.0 MPa

wherein stress and strain are determined in accordance with ISO 527-3 (1995).

[0043] In a yet further embodiment, the invention also relates to a multi-layer film comprising:

(a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a)

(b) at least one layer comprising an LLDPE (b) comprising moieties derived from

and wherein the film exhibits, in the machine direction:

• a stress at 500% strain of > 35.0 MPa, preferably > 46.0 MPa,

wherein stress and strain are determined in accordance with ISO 527-3 (1995).

[0044] The invention in a certain embodiment also relates to a food package comprising the multi-layer film of the invention.

[0045] The invention will now be illustrated by the following non-limiting examples.

Materials.

• PE-A: LLDPE (a): SUPEER™ 81 12, an ethylene/1 -octene copolymer produced via

solution polymerisation using a single-site catalyst, obtainable from SABIC, having a density of 912 kg/m³, an MFR₂ of 1 .1 g/10 min.

• PE-B: LLDPE (b): SUPEER™ 7318, also referred to as VM002, an ethylene/1 -hexene copolymer produced via gas-phase polymerisation using a single-site catalyst, obtainable from SABIC, having a density of 918 kg/m³, and an MFR₂ of 3.0 g/10 min. • PE-C: Exceed 3518CB, an ethylene/1 -hexene copolymer produced using a single-site catalyst, obtainable from ExxonMobil, having a density of 918 kg/m³ and an MFR₂ of 3.5 g/10 min. [0046] The PE-B demonstrated a stress-strain relationship as presented in the below table, tested in accordance with ISO 527-3 (1995).

[0047] In this table, the strain (e) presents the elongation in % of the sample, the stress (s) presents the force to be applied to maintain the sample at that elongation in MPa, and do/de presents the derivative of the stress-strain curve at a given strain, in kPa/%, indicating the increase of force to be applied to maintain elongation at an increased elongation.

[0048] Using the above listed materials, a number of formulations were made, of which films were produced via cast moulding. The formulations of the experimental materials used for production of films are listed in the table below, wherein the numbers reflect parts by weight with regard to the weight of the film:

[0049] Example 3 represents the film of the present invention. Examples 1 , 2 and 4 are included for comparative purposes. [0050] Films were produced via cast moulding according to the following procedure.

[0051 ] For production of a 5-layer film, a film line was used having four melt extruders. The extruders were operated according to the below temperature conditions for each zone:

The material extruded from extruder A was processed to form film layer 1 , from extruder B to form layer 2, and from extruder D to form layer 5. The material that was extruded via extruder C was split into two 50/50 wt% streams each to form a separate layer (layers 3 and 4). Layers 1 through 5 were positioned on top of each other consecutively. The material as extruded was forced through a slit die to form a layered film. The extruded film was passed via a chill roll system comprising a chill roll having a temperature of 45°C, and three further rolls.

The extruders were operated according to the below conditions: Example 1 :

Example 2:

Example 3:

Example 4:

[0052] Wherein the output is to be understood to be the quantity of material exiting each extruder; the speed is the screw speed, in revolutions per minute; the die pressure is the pressure of the material in the last zone of the extruder before the material is extruded; and the melt temp is the temperature of the material in the last zone of the extruder before the material reaches the die.

[0053] The chill roll system was arranged so that layer 5 (one of the outer surface layers) of the extruded film contacted the surface of the chill roll, subsequently layer 1 (the other outer surface layer) contacted the surface of roll 2, again layer 5 contacted roll 3, again layer 1 contacted roll 4, and layer 5 was positioned as the surface layer contacting the winder roll. The speed of the rolls was set such that each roll was operated at a slightly higher speed than the preceding roll, to ensure a small force was exerted onto the film avoiding processing imbalances. [0054] The thus obtained films were subjected to a variety of analytical tests to determine the properties of the films. Results of those tests are presented in the table here below.

Wherein:

• The dart impact resistance property impact failure weight was determined in accordance with ASTM D1709 (2016), method A.

· The slow rate penetration resistance properties force to break, probe penetration and energy (or work to break) were determined in accordance with ASTM F1306-90 (2008).

• The tear resistance properties tearing force were determined in accordance with ASTM D1922 (2015), where MD indicates the machine direction, i.e. the direction in which the film is passed through the cast moulding process, and TD indicates the transverse direction, i.e. the direction perpendicular to the machine direction in the plane of the film.

• The tensile properties elastic modulus, yield strength at 0.1 % offset, tensile strength at break, percent elongation at break, percent elongation at yield, tensile energy to break and breaking factor were determined in accordance with ASTM D882 (2012). [0055] Of these films, stress-strain data determined in the machine direction of the films are presented in the below table, tested in accordance with ISO 527-3 (1995). In this table, the strain (e) presents the elongation in % of the sample, the stress (s) presents the force to be applied to maintain the sample at that elongation in MPa.

[0056] The above results demonstrate the films according to the invention to provide an improved slow puncture resistance where further properties are at least kept at par with solutions of the art.

Claims

1. Multi-layer film comprising:

(a) at least one layer comprising a linear low-density polyethylene (LLDPE) (a)

comprising moieties derived from ethylene and 1 -octene or 1 -hexene, having a density of > 900 and < 925 kg/m³, and an MFR₂ of > 0.5 and < 1.5 g/10 min, preferably of > 0.6 and < 1.4 g/10 min; and

(b) at least one layer comprising an LLDPE (b) comprising moieties derived from

ethylene and 1 -hexene, having a density of > 900 and < 925 kg/m³ and an MFR₂ of > 2.0 and < 4.0 g/10 min, preferably of > 2.5 and < 3.2 g/10 min;

2. Multi-layer film according to claim 1 , wherein the LLDPE (a) is produced using a single site catalyst and/or LLDPE (b) is produced using a single-site catalyst.

3. Multi-layer film according to any one of claims 1 -2, comprising two outer layers and at least one inner layer, wherein at least one of the inner layer(s) is a layer (a) comprising the LLDPE (a) or consisting of the LLDPE(a).

4. Multi-layer film according to any one of claims 1 -3, wherein the layer(s) (a) each comprise at least 80.0 wt% of the LLDPE (a), with regard to the total weight of each of the layer(s)

(a).

5. Multi-layer film according to any one of claims 3-4, wherein at least one outer layer is a layer (b) comprising the LLDPE (b) or wherein both outer layers each are a layer (b) comprising the LLDPE (b).

6. Multi-layer film according to any one of claims 1 -5, wherein the layers) (b) each comprise at least 80.0 wt% of the LLDPE (b), with regard to the total weight of each of the layer(s)

(b).

7. Multi-layer film according to any one of claims 1 -6, wherein the LLDPE (b) demonstrates a stress-strain relationship such that in the whole region of strain of 100-300% the derivative of the stress-strain curve da/de is > 5.0 kPa/%, stress and strain being determined in accordance with ISO 527-3 (1995).

8. Multi-layer film according to any one of claims 1 -7, wherein:

• the LLDPE (b) comprises > 80.0 wt% of moieties derived from ethylene and/or > 2.0 and < 20.0 wt% of moieties derived from 1 -hexene, with regard to the total weight of the LLDPE (b).

9. Multi-layer film according to any one of claims 1 -8, wherein the film exhibits, in the

machine direction:

• a stress at 200% strain of > 1 1.0 MPa, preferably > 12.0 MPa; and/or

• a stress at 300% strain of > 14.0 MPa, preferably > 16.0 MPa; and/or

• a stress at 400% strain of > 20.0 MPa, preferably > 28.0 MPa; and/or

• a stress at 500% strain of > 35.0 MPa, preferably > 46.0 MPa,

wherein stress and strain are determined in accordance with ISO 527-3 (1995).

10. Multi-layer film according to any one of claims 1 -9, wherein the film comprises or consists of 3, 5, 7 or 9 layers; and/or wherein the film has a thickness of 5.0-100.0 pm.

1 1 . Process for the production of a multi-layer film according to any one of claims 1 -10,

wherein the process involves at least two melt extruders comprising slit dies for extrusion of film, and optionally further melt extruder(s) each comprising slit dies, and a setup for capturing the molten film layers obtained from the melt extruders, combining the molten film layers to form a multi-layer film and cooling the obtained film, the process comprising the steps of:

(iii) optionally providing further film layer(s) produced using the further melt extruders

(iv) combining the layers to form a multi-layer film; and (v) subjecting the multi-layer film to cooling equipment to solidify the multi-layer film.

12. Process according to claim 1 1 , wherein the first film layer is combined with the second film layer and at least one further film layer such that the first film layer forms an inner layer and the second film layer forms an outer layer of the multi-layer film.

13. Process according to any one of claims 1 1 -12 wherein at least one of the further film

layer(s) is produced of a material equal to the second film layer, preferably wherein that further film layer forms an outer layer of the multi-layer film.

14. Process according to any one of claims 1 1 -13, wherein the process is a continuously operated process.

15. Food package comprising the multi-layer film according to any one of claims 1 -10.