WO2023117419A1

WO2023117419A1 - Multi-layer film structure comprising multimodal ethylene copolymers and recycled ldpe for collation-shrink films

Info

Publication number: WO2023117419A1
Application number: PCT/EP2022/084726
Authority: WO
Inventors: Barbara Mandard; Luca Boragno; Tuan Anh TRAN
Original assignee: Borealis Ag
Priority date: 2021-12-23
Filing date: 2022-12-07
Publication date: 2023-06-29
Also published as: EP4452641A1

Abstract

A layered film structure comprising a core layer C and external layers E1 and E2, wherein core layer C comprises a multimodal ethylene copolymer (I) with at least one alpha-olefin comonomer having an MFR5 determined according to ISO 1133 of from 0.1 to 5 g/10 min and a density of 0.930 to 0.950 g/cm3 and a recycled LDPE having a MFR2 determined according to ISO 1133 of from 0.1 to 10 g/10 min and a density in the range from 910 to 940 kg/m3 and wherein external layer(s) E1 and/or E2 comprise(s) a multimodal ethylene terpolymer (II) having an MFR2 determined according to ISO 1133 of from 0.5 to 10 g/10 min and a density of 0.920 to 0.935 g/cm3.

Description

MULTI-LAYER FILM STRUCTURE COMPRISING MULTIMODAL ETHYLENE COPOLYMERS AND RECYCLED LDPE FOR COLLATION-SHRINK FILMS

The present invention relates to a layered film structure comprising a core layer and external layers, to a process for producing a layered film structure by coextrusion of the layers, to a collation shrink film comprising the layered film structure, and to the use of the collation shrink film for wrapping of articles.

Collation shrink films are films structures that are wrapped around an object to be packaged and shrunk to keep the units within the object together. The basic principle of collation shrink is to over-wrap a number of items in a loose film "sleeve" and then pass the wrapped goods through a heated shrink tunnel/oven to cause the collation shrink wrapping to occur. The film collapses around the multiple items and holds them in place. The most common use of these films is in the packaging of multiple containers (items), such as bottles or cans which might contain food, beverages and so on. The collation shrink film is wrapped around a number of the containers, for example a 6-pack of drinks or 24-pack of food cans, optionally held in a cardboard tray or pad, and shrunk around the containers.

Still today up to 5-10% of the merchandise is wasted during transportation. Improving the stability of the wrapped packs with improved collation-shrink film structures would allow the producers to have fewer losses. With today’s challenges and overall direction of reducing the film thickness, the pack stability is further compromised.

Thus, for being suitable for use as a collation shrink film, a film structure needs to have a specific combination of properties: First and foremost, the film structure must show a good shrinkage behaviour in order to hold the wrapped goods tightly. Furthermore, suitable film structures need to have good mechanical properties such as high stiffness, especially in view of down-gauge ability and pack stability, and good tensile properties.

Still further, puncture resistance and tear resistance are among the most important properties for collation shrink films in order to provide sufficient pack stability and to enable safe handling of the package.

Good optical appearance is also required at the same time for the pack stand out on the shelf, i.e. consumer perception at the selling points.

Low Density Polyethylene (LDPE) currently dominates the collation films market segment with its good shrink behaviour, especially in transverse direction (TD). It is known, however, that multimodal LLDPE exhibits significant benefits over LDPE when blended with other linear low density polyethylene and high density polyethylene components.

Thus, current collation shrink film solutions are film structures comprising LDPE and LLDPE and/or HDPE. The LDPE is necessary to give a high shrink rate and the LLDPE I HDPE component gives a combination of stiffness, toughness and bundling force (also known as cold shrink force).

For example, WO 2017/055174 discloses a collation shrink film which is based on a coextruded film structure comprising two layers A and B each made from specific ethylene copolymers.

Due to the latest regulations and market needs, industry is obliged to incorporate into packaging films certain amounts of polymer recyclate material. Due to the origin, previous use and difficult handling and sorting of the post consumer recycled (PCR) material, the recyclate normally has lower technical properties compared to virgin material, limiting or hindering its use in many applications.

Furthermore, it is desired to have as high as possible PCR content in the flexible packaging without increasing the film thickness while keeping the performance as described above for final targeted applications.

WO 2020/207940 discloses a multilayer collation shrink film consisting of a core layer B) sandwiched by two outer layers A), wherein both outer layers A) consist of a1 ) 12 to 18 wt.-% of a multimodal polymer of ethylene with at least two different comonomers selected from alpha-olefins having from 4 to 10 carbon atoms, a2) which multimodal polymer of ethylene has a density in the range from 910 to 935 kg/m³, and a Mw/Mn of 2 to 8, a3) 12 to 18 wt.-% of a multimodal terpolymer of ethylene and at least two alpha olefin comonomers wherein the multimodal terpolymer has a density in the range from 930 to 940 kg/m³; and 64 to 76 wt.-% of a LDPE homopolymer being a virgin polymer having a density in the range from 905 to 940 kg/m³ and an MFR2 in the range from 0.1 to 20 g/10 min; and core layer B) consisting of b1 ) 65 to 75 wt.-% of recycled LDPE having a MFR2 in the range from 0.1 to 10 g/10 min and a density in the range from 910 to 940 kg/m³; and 35 to 25 wt.-% of a multimodal terpolymer of ethylene and at least two alpha olefin comonomers wherein the multimodal terpolymer has a density in the range from 930 to 940 kg/m³ However, the amount of recycled LDPE could still be increased. Therefore, it is an object of the present invention to provide a film structure suitable for use as a collation shrink film which fulfils the above requirements, especially a film structure which has an increased amount of post consumer recycled (PCR) material, good shrinkage behaviour and, at the same time, excellent stiffness and toughness.

The present invention is based on the finding that such a film structure for a collation shrinkage film can be provided by a layered film structure comprising a core and two external layers which comprise specifically selected ethylene co and/or terpolymers in the core and at least one of the external layers.

The present invention therefore provides a layered film structure comprising, or consisting of, a core layer C and external layers E1 and E2 wherein core layer C comprises, or consists of, a multimodal ethylene copolymer (I) with at least one alpha-olefin comonomer having an MFRs of from 0.5 to 5 g/10 min and a density of 0.930 to 0.950 g/cm³ and a recycled LDPE having a MFR2 determined according to ISO 1 133 of from 0.1 to 10 g/10 min and a density in the range from 910 to 940 kg/m³ and wherein external layer(s) E1 and/or E2 comprise(s) a multimodal ethylene terpolymer (II) having an MFR2 of from 0.5 to 10 g/10 min and a density of 0.920 to 0.935 g/cm³.

The present invention further relates to a process for producing a layered film structure as defined above. Furthermore, the present invention relates to a collation shrink film comprising or consisting of a layered film structure as defined above. Finally, the present invention relates to the use of a collation shrink film as defined above for wrapping of articles.

Specifically, the present invention relates to a polyethylene based multilayer collation shrink film comprising recycled LDPE in an amount of 40 wt.-% to 65 wt.-%, preferably 45 wt.-% to 62 wt.-%, more preferably 50 wt.-% to 60 wt.-% with respect to the total amount of polyethylene in the film having a dart drop impact (DDI) determined according to ASTM D1709 on a 45 pm film of more than 60 g.

The combination of a core layer C and external layers E1 and E2 as characterized above solve the above described objects. In particular, this combination allows for a maintained contraction force, stiffness and toughness of the film structure even with high amounts of recycled LDPE so that in use as collation shrink film pack the CO2 footprint is reduced, but the performance of the film is not affected. Usually, multimodal ethylene copolymer (I) is different from multimodal ethylene terpolymer (II).

Preferably, in the layered film structure the multimodal ethylene copolymer (I) is trimodal and/or is a terpolymer.

More preferably, in the layered film structure the multimodal ethylene copolymer (I) is a trimodal copolymer comprising, or consisting of a) 10 to 30 wt% of a first ethylene homopolymer; b) 15 to 35 wt% a second ethylene homopolymer having an MFR2 which is at least 50 g/10 min higher than the MFR2 of component a); and c) 40 to 65 wt% of a third ethylene copolymer with at least one alpha-olefin comonomer.

In an even more preferred embodiment of the invention, in the layered film structure the multimodal ethylene copolymer (I) is a trimodal terpolymer comprising, or consisting of a) 10 to 30 wt% of a first ethylene homopolymer; b) 15 to 35 wt% a second ethylene homopolymer having an MFR2 which is at least 50 g/10 min higher than the MFR2 of component a); and c) 40 to 65 wt% of a third ethylene terpolymer with at least two alpha-olefin comonomers.

Preferably, copolymer (I) has a density of equal to or more than 0.934 g/cm³, more preferably of equal to or more than 0.937 g/cm³. Preferably, the copolymer (I) has a density of equal to or less than 945 g/cm³.

Also preferably, copolymer (I) has a MFR2 measured according to ISO 1133 of 0.2 to 0.5 g/10 min.

Also preferably, copolymer (I) has a MFRs measured according to ISO 1133 of 0.5 to 3.0, more preferably 1.0 to 2.5 g/10 min, even more preferably 1.1 to 1.9 g/10 min and still more preferably 1.2 to 1.8.

Also preferably, copolymer (I) has a MFR21 measured according to ISO 1133 of 20 to 45, more preferably 25 to 37 g/10 min.

The FRR21/5 of copolymer (I) is preferably in the range from 18 to 28. Preferably, the third fraction c) of copolymer (I) is an ethylene 1 -hexene copolymer or a terpolymer of ethylene and at least two alpha-olefin comonomers, such as 1 -butene and 1 -hexene.

The copolymer (I) is present in the core layer composition in an amount of more than 10 wt.-%, preferably in an amount of 15 to 35 wt.-%, more preferably 20 to 30 wt.-%, based on the total weight of the core layer composition.

In the present disclosure, the term “recycled low density ethylene polymer” refers to a recycled polymer material that comprises at least 80 wt.-%, preferably at least 75 wt.-%, more preferably at least 90 wt.-% and most preferably at least 95 wt.-% of LDPE, based on the total weight of the recycled low density ethylene polymer, which has been recycled. Accordingly, the “recycled low density ethylene polymer” may comprise up to 20 wt.-%, preferably up to 15 wt.-%, more preferably up to 10 wt.-% and most preferably up to 5 wt.-%, based on the total weight of the recycled low density ethylene polymer, of other (preferably recycled) polymer components such as for example LLDPE, MDPE and HDPE.

Recycled polymer material is a polymer material that is recovered from postconsumer waste and/or industrial waste. Post-consumer waste refers to objects having completed at least a first use cycle (or life cycle), i.e. having already served their first purpose; while industrial waste refers to the manufacturing scrap which does normally not reach a consumer.

As the opposite, the term “virgin” refers to freshly produced materials and/or objects prior to first use and not being recycled. In case that the origin of the polymer is not explicitly mentioned, the polymer is a “virgin” polymer.

In one embodiment of the present invention, the recycled LDPE originates from post-consumer waste.

Preferably, the recycled LDPE has an MFR2 of from 0.1 to 10 g/10 min, more preferably from 0.2 to 5 g/10 min, still more preferably from 0.25 to 1 .0 g/10 min and most preferably from 0.3 to 0.8 g/10 min, determined according to ISO 1133.

The recycled LDPE preferably has a density of from 910 to 945 kg/m³, preferably from 910 to 940 kg/m³, more preferably from 915 to 935 kg/m³ and most preferably from 918 to 930 kg/m³, determined according to ISO 1183.

The recycled LDPE preferably has a melting point (second melting) in the range of from 100 to 140 °C, preferably in the range from 105 to 130°C and more preferably in the range from 108 to 125 °C, determined according to ISO 1 1357. As the recycled LDPE, the products NAV 101 and/or CWT 100 LG as supplied by Ecoplast and Borealis may be used.

In another embodiment of the invention, the recycled LDPE may be a mixture of recycled LDPEs, such as a mixture from NAV 101 and CWT 100 LG.

The recycled LDPE is present in the core layer composition in an amount of equal to or more than 65 wt.-%, preferably in an amount of 70 to 90 wt.-%, more preferably 70 to 85 wt.-%, based on the total weight of the core layer composition.

Multimodal ethylene terpolymer (II) of the layered film structure of the invention preferably comprises, or consists of, a multimodal polymer of ethylene with at least two different comonomers selected from alpha-olefins having from 4 to 10 carbon atoms, which has a ratio MFR21/MFR2 of 13 to 30 and a MWD of 5 or less.

Such multimodal ethylene terpolymers are disclosed, for example, in WO 2016/083208. As far as definitions (such as for the “modality” of a polymer) and production methods for these ethylene terpolymers are concerned it is referred to WO 2016/083208. Furthermore, all embodiments and preferred embodiments of such ethylene terpolymers as described in WO 2016/083208 which have a density in the range a density of 0.910 to 0.935 g/cm³ are also preferred embodiments of ethylene terpolymer (II) in the present application, whether or not explicitly described herein.

Multimodal ethylene terpolymer (II) preferably has a MFR2 in the range of from 0.5 to 2 g/10 min, more preferably from 0.8 to 1 .6 g/10 min.

Preferably, multimodal ethylene terpolymer (II) has a density of 0.920 to 0.933 g/cm³, more preferably of 0.923 to 0.930 g/cm³.

Multimodal ethylene terpolymer (II) preferably has a ratio MFR21/MFR2 of 15 to 30, more preferably of 15 to 25.

The at least two alpha-olefin comonomers having from 4 to 10 carbon atoms of multimodal ethylene terpolymer (II) are preferably 1 -butene and 1 -hexene.

Preferably, the total amount of comonomers present in the multimodal ethylene terpolymer (II) is of 0.5 to 10 mol%, preferably of 1 .0 to 8 mol%, more preferably of 1 .0 to 5 mol%, more preferably of 1 .5 to 5.0 mol%. Multimodal ethylene terpolymer (II), which preferably is a bimodal terpolymer, preferably comprises, or consists of, an ethylene polymer component (A) and an ethylene polymer component (B), wherein the ethylene polymer component (A) has higher MFR2 than ethylene polymer component (B).

More preferably, the ethylene polymer component (A) has MFR2 of 1 to 50 g/10 min, preferably of 1 to 40 g/10 min, more preferably of 1 to 30 g/10 min, more preferably of 2 to 20 g/10 min, more preferably of 2 to 15 g/10 min, and even more preferably of 2 to 10 g/10 min.

The ratio of the MFR2 of ethylene polymer component (A) to the MFR2 of the final multimodal ethylene terpolymer (II) is 2 to 50, preferably 5 to 40, more preferably 10 to 30, more preferably 10 to 25, and still more preferably 15 to 25.

Preferably, ethylene polymer component (A) comprises a different comonomer than the ethylene polymer (B).

Preferably, ethylene polymer component (A) has lower amount (mol%) of comonomer than ethylene polymer component (B), more preferably, the ratio of [the amount (mol%) of alpha-olefin comonomer having from 4 to 10 carbon atoms comonomer present in ethylene polymer component (A)] to [the amount (mol%) of at least two alpha-olefin comonomers having from 4 to 10 carbon atoms of the final multimodal polymer of ethylene (a)] is of 0.2 to 0.6, preferably of 0.25 to 0.5.

Preferably, the alpha-olefin comonomer having from 4 to 10 carbon atoms of ethylene polymer component (A) is 1 -butene and the alpha-olefin comonomer having from 4 to 10 carbon atoms of ethylene polymer component (B) is 1 - hexene.

Preferably, ethylene polymer component (A) has different, preferably higher, density than the density of the ethylene polymer component (B).

The density of the ethylene polymer component (A) is preferably 0.925 to 0.950 g/cm³, more preferably 0.930 to 0.945 g/cm³.

Preferably, the multimodal ethylene terpolymer (II) comprises the ethylene polymer component (A) in an amount of 30 to 70 wt.-%, preferably of 40 to 60 wt.- %, more preferably of 35 to 50 wt.-%, more preferably 40 to 50 wt.-% and the ethylene polymer component (B) in an amount of 70 to 30 wt.-%, preferably of 60 to 40 wt.-%, more preferably of 50 to 65 wt.-%, more preferably 50 to 60 wt.- %, based on the total amount (100 wt.-%) of the multimodal terpolymer (II). Most preferably, multimodal ethylene terpolymer (II) consists of the ethylene polymer components (A) and (B) as the sole polymer components. Accordingly, the split between ethylene polymer component (A) to ethylene polymer component (B) is of (30 to 70):(70 to 30) preferably of (40 to 60):(60 to 40), more preferably of (35 to 50):(65 to 50), more preferably of (40 to 50):(50 to 60).

Preferred as multimodal ethylene terpolymers (II) are also such commercially available as Anteo™ from Borealis or Borouge having the properties as required herein, especially Anteo™ FK 2715.

Preferably, in the layered film structure according to the invention core layer C comprises 20 wt.-% or more of said multimodal ethylene copolymer (I).

In one embodiment core layer C consists of multimodal ethylene copolymer (I) and a recycled LDPE or a mixture of recycled LDPEs as defined herein.

Thus, in one preferred embodiment core layer C consists of 15 wt.-% to 35 wt.- %, preferably 20 wt.-% to 30 wt.-% of the multimodal ethylene copolymer (I) and 65 wt.-% to 85 wt.-%, preferably 70 wt.-% to 20 wt.-% of a recycled LDPE or a mixture of recycled LDPEs as defined herein.

External layer(s) E1 and E2 of the layered film structure of the invention may be made of the same polymer composition or of different polymer compositions in any one of the embodiments described herein for the polymer composition usable for layer E1 and/or E2. Preferably, E1 and E2 are made of the same polymer composition.

Preferably, external layer(s) E1 and/or E2 comprise(s) 60 wt.-% or more, more preferably comprise 65 wt.-% or more, and even more preferably 70 wt.-% or more of said multimodal ethylene terpolymer (II).

In addition to multimodal ethylene terpolymer (II) external layer E1 and/or E2 may comprise a low density polyethylene (LDPE), which is a virgin LDPE as defined above.

Preferably, if an LDPE is present in external layer(s) E1 and/or E2, it is used in an amount of 5 to 40 wt.-%, more preferably in an amount of from 10 to 35 wt.- %, and still more preferably in an amount of from 15 to 30 wt.-%.

The LDPE used in layer(s) E1 and/or E2 preferably has a density of 0.905 to 0.945 g/cm³, more preferably of 0.915 to 0.935 g/cm³, and most preferably of 0.918 to 0.927 g/cm³. Preferably, the LDPE used in layer(s) E1 and/or E2 has a MFR2 of 0.05 to 10 g/10 min, more preferably of 0.1 to 5 g/10 min, still more preferably 0.2 to 3 g/10 min, and most preferably 0.4 to 1 .5 g/10 min.

In one embodiment external layer(s) E1 and/or E2 consist(s) of multimodal ethylene terpolymer (II) and a LDPE as defined herein.

The layered film structure according to the invention may consist of core layer C and external layers E1 and E2.

The layered film structure of the invention according to any one of the embodiments described herein preferably has a thickness of 100 micrometer or lower, more preferably 60 micrometer or lower, even more preferably 50 micrometer or lower.

Furthermore, the layered film structure of the invention according to any one of the embodiments described herein preferably has a thickness of 30 micrometer or higher, more preferably 35 micrometer or higher, and most preferably 40 micrometer or higher.

If the film structure of the invention consists of layers E1 , C and E2 preferably core layer C has a thickness of 45 to 75% of the total film structure thickness, more preferably of 50 to 70% of the total film thickness.

External layer(s) E1 and/or E2 has/have each preferably a thickness of 5 to 25% of the total film structure thickness.

If the film structure of the invention consists of layers E1 , C and E2 preferably external layer(s) E1 and/or E2 has/have each a thickness of 10 to 25% of the total film structure thickness, more preferably of 15 to 25% of the total film thickness.

In a preferred embodiment of the present invention, the core layer has a thickness of from 25 to 35 pm, preferably from 27 to 32 pm. Furthermore, preferably, the outer layers each have a thickness of from 5 to 10 pm, preferably from 6 to 9 pm.

In one even more preferred embodiment, the layered film structure of the present invention has a weight ratio of E/C/E of 15/70/15, wherein the thickness of the core layer is 31 .5 pm and thickness of the outer layer is 6.75 pm each. In another even more preferred embodiment, the layered film structure of the present invention has a weight ratio of E/C/E of 20/60/20, wherein the thickness of the core layer is 27 pm and thickness of the outer layer is 9 pm each.

The layered film structure of the invention preferably has a contracting force in machine direction measured on a 45 micrometer test film of 2.0 N or higher, more preferably of 2.1 N or higher.

Preferably, the layered film structure of the invention has a contracting force in machine direction measured on a 45 pm test film of 4.0 N or lower, more preferably of 3.5 N or lower and most preferably of 3.0 or lower.

Furthermore, preferably, the layered film structure of the invention has a Tear Elmendorf resistance in transverse direction measured on a 45 micrometer test film of 1 10 N/mm or higher, more preferably of 120 N/mm or higher and most preferably of 130 N/mm or higher.

Preferably, the layered film structure of the invention has a Tear Elmendorf resistance in transverse direction measured on a 45 pm test film of 350 N/mm or lower, more preferably of 300 N/mm or lower and most preferably of 200 N/mm or lower.

Furthermore, preferably, the layered film structure of the invention has a Tear Elmendorf resistance in machine direction measured on a 45 micrometer test film of 6 N/mm or higher, more preferably of 8 N/mm or higher and most preferably of 10 N/mm or higher.

Preferably, the layered film structure of the invention has a Tear Elmendorf resistance in machine direction measured on a 45 pm test film of 50 N/mm or lower, more preferably of 40 N/mm or lower and most preferably of 30 N/mm or lower.

Furthermore, preferably, the layered film structure of the invention has a tensile modulus in transverse direction measured on a 45 micrometer test film of 350 MPa or higher, more preferably of 400 MPa or higher and most preferably of 450 MPa or higher.

Preferably, the layered film structure of the invention has a tensile modulus in transverse direction measured on a 45 pm test film of 890 MPa or lower, more preferably of 700 MPa or lower and most preferably of 600 MPa or lower. Furthermore, preferably, the layered film structure of the invention has a tensile modulus in machine direction measured on a 45 micrometer test film of 200 MPa or higher, more preferably of 300 MPa or higher and most preferably of 340 MPa or higher.

Preferably, the layered film structure of the invention has a tensile modulus in machine direction measured on a 45 pm test film of 750 MPa or lower, more preferably of 500 MPa or lower and most preferably of 450 MPa or lower.

Preferably, the layered film structure of the invention has a dart drop impact (DDI) determined according to ASTM D1709 on a 45 micrometer test film of more than 60 g, preferably more than 70 g and most preferably more than 80 g.

Furthermore, preferably, the layered film structure of the invention has a dart drop impact (DDI) determined according to ASTM D1709 on a 45 pm test film of less than 290 g, preferably less than 200 g and most preferably less than 150 g.

Furthermore, preferably the layered film structure of the invention has a shrinkage in oil at 140 °C according to DIN 55543-4 in machine direction for a 45 micrometer test film of 75% or higher.

Preferably, the layered film structure of the invention has a shrinkage in oil at 140 °C according to DIN 55543-4 in machine direction measured on a 45 pm test film of 92% or lower, more preferably of 88% or lower.

Furthermore, preferably, the layered film structure of the invention has a shrinkage in oil at 140 °C according to DIN 55543-4 in transverse direction for a 45 micrometer test film of 10% or higher.

Preferably, the layered film structure of the invention has a shrinkage in oil at 140 °C according to DIN 55543-4 in transverse direction measured on a 45 pm test film of 40% or lower, preferably 25% or lower.

The present invention also relates to a process for producing a layered film structure according to any one of the above described embodiments wherein the layers of the film structure are co-extruded.

The different polymer components in any of layers of the film are typically intimately mixed prior to layer formation, for example using a twin screw extruder, preferably a counter-rotating extruder. Then, the blends are converted into a coextruded film structure. Preferably, the blends are converted into a coextruded film structure on a blown-film line. In order to manufacture such multilayer films according to the invention, normally at least two polymer melt streams are simultaneously extruded (i.e. coextruded) through a multi-channel tubular, annular or circular die to form a tube which is blown-up, inflated and/or cooled with air (or a combination of gases) to form a film. The manufacture of blown film is a well-known process.

The blown coextrusion can be effected 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 to 8 times the diameter of the die.

The blow up ratio (BUR) should generally be in the range 1.2 to 6, preferably 1.5 to 4.

The layered film structure of the invention may also have been subjected to a stretching step, wherein the film after its production is stretched in the machine direction (MDO). Stretching may be carried out by any conventional technique using any conventional stretching devices which are well known to those skilled in the art.

The present invention also relates to a collation shrink film comprising or consisting of a layered film structure according to any one of the embodiments as described herein, and to the use of said collation shrink film for wrapping of articles.

Specifically, the present invention relates to a polyethylene based multilayer collation shrink film comprising recycled LDPE in an amount of 40 wt.-% to 65 wt.-%, preferably 45 wt.-% to 62 wt.-%, more preferably 50 wt.-% to 60 wt.-%, like 53 wt.-% to 58 wt.-% with respect to the total amount of polyethylene in the film having a dart drop impact (DDI) determined according to ASTM D1709 on a 45 pm film of more than 60 g, preferably of more than 70 G, and most preferably of more than 80 g and of less than 290 g, preferably less than 200 g and most preferably less than 150 g.

Preferably such collation shrink film furthermore shows a shrinkage in oil at 140 °C according to DIN 55543-4 in machine direction for a 45 micrometer test film of 75% or higher and of 92% or lower, more preferably of 88% or lower and/or a shrinkage in oil at 140 °C according to DIN 55543-4 in transverse direction for a 45 micrometer test film of 10% or higher and/or of 40% or lower, preferably 25% or lower.

In addition or alternatively to the shrinkage such collation shrink film has a tensile modulus in transverse direction measured on a 45 micrometer test film of 350 MPa or higher, more preferably of 400 MPa or higher and most preferably of 450 MPa or higher and of 890 MPa or lower, more preferably of 700 MPa or lower and most preferably of 600 MPa or lower and/or a tensile modulus in machine direction measured on a 45 micrometer test film of 200 MPa or higher, more preferably of 300 MPa or higher and most preferably of 340 MPa or higher and of 750 MPa or lower, more preferably of 500 MPa or lower and most preferably of 450 MPa or lower.

Such a collation shrink film preferably has a thickness of 100 micrometer or lower, more preferably 60 micrometer or lower, even more preferably 50 micrometer or lower and of 30 micrometer or higher, more preferably 35 micrometer or higher, and most preferably 40 micrometer or higher.

In an embodiment such a collation shrink film consists of a core layer C and external layers E1 and E2.

In a preferred embodiment the polyethylene based multilayer collation shrink film is designed as described above for the layered film structure.

In the following, the invention will further be illustrated by way of examples which refer to the following figures which show:

Fig. 1 : Graphical representation of the values given in Table 4

Measurement and Determination Methods

The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined. a) Measurement of melt flow rate MFR

The melt flow rate (MFR) was determined according to ISO 1133 and is indicated in g/10 min. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR is determined at 190 °C for polyethylene and at a loading of 2.16 kg (MFR₂), 5.00 kg (MFRs) or 21 .6 kg (MFR21).

The quantity FRR (flow rate ratio) is an indication of molecular weight distribution and denotes the ratio of flow rates at different loadings. Thus, FRR21/5 denotes the value of MFR21/MFR5. b) Density

Density of the polymer was measured according to ISO 1183-1 :2019 (method A) on compression moulded specimen prepared according to EN ISO 1872-2 (Feb 2007) and is given in g/cm³. c) Contracting Force/Shrinkage

The shrinkage performance using both the Retratech equipment (according to ISO 14616) and oil bath at 140 °C (according to DIN 55543-4) was tested on the collation shrink films both in machine direction and transverse direction.

The shrinking and contraction forces were determined according to ISO 14616 using a shrinkage film force tester for films (type of testing device Retratech) at an oven temperature of 180°C. The oven lift-up time was about 21 seconds. d) Dart Drop Impact

The dart drop impact (DDI) was determined according to ASTM D1709 “method “A” on films with a thickness as indicated and produced as described below under “Examples”. e) Mechanical Properties

Tensile Modulus

Film TD (transversal direction) and MD (machine direction). Tensile moduli in machine and transverse direction were determined acc. to ISO 527-3 on films with a thickness of 25 micrometer or 40 micrometer at a cross head speed of 1 mm/min for the blown film of the inventive examples.

Relative Tear resistance (determined by Elmendorf tear (N/mm))

The tear strength or tear resistance is measured using the ISO 6383/2 method. The force required to propagate tearing across a film specimen is measured using a pendulum device. The pendulum swings under gravity through an arc, tearing the specimen from a pre-cut slit. The specimen is fixed on one side by the pendulum and on the other side by a stationary clamp. The tear strength or tear resistance is the force required to tear the specimen. The relative tear resistance (N/mm) can be calculated by dividing the tear resistance by the thickness of the film. The films were produced as described below in the film preparation example. The tear strength or tear resistance is measured in machine direction (MD) and/or transverse direction (TD).

Examples

Three layered film structures (one according to the invention and two comparative) were produced on an Alpine Hosokawa film line. All film structures were produced in the same processing conditions (BUR of 3: 1 , thickness 45 micrometres, die-gap of 1 .5 mm, die diameter 200 mm, throughput of 180 kg/h, lower neck-height, internal bubble cooling).

The polymers used for making the layered film structures of the invention and of the comparative examples are given in Table 1 below.

Table 1 :

Furthermore, polymer PE1 was produced as detailed in the following. A loop reactor having a volume of 50 dm³ was operated at a temperature of 70 °C and a pressure of 57 bar. Into the reactor were fed ethylene, propane diluent, 1- butene as a comonomer and hydrogen. Also a solid polymerisation catalyst component produced as described in Example 1 of EP 1378528 was introduced into the reactor together with triethylaluminium cocatalyst so that the molar ratio of Al/Ti was about 15. The estimated production split was about 2 wt.-%.

A stream of slurry was continuously withdrawn and directed to a loop reactor having a volume of 150 dm³ and which was operated at a temperature of 95 °C and a pressure of 56 bar. Into the reactor were further fed additional ethylene, propane diluent and hydrogen so that the ethylene concentration in the fluid mixture was 4.7 mol% and the molar ratio of hydrogen to ethylene was 306 mol/kmol. The estimated production split was 18 wt.-%. The ethylene homopolymer withdrawn from the reactor had MFR2 of 195 g/10 min.

A stream of slurry from the reactor was withdrawn intermittently and directed into a loop reactor having a volume of 350 dm³ and which was operated at 95 °C temperature and 54 bar pressure. Into the reactor was further added a fresh propane, ethylene, and hydrogen so that the ethylene content in the fluid mixture was 5.5 mol% and the molar ratio of hydrogen to ethylene was 563 mol/kmol. The estimated production split was 26 wt.-%. The ethylene homopolymer withdrawn from the reactor had MFR2 of 390 g/10 min.

The slurry was withdrawn from the loop reactor intermittently and directed to a flash vessel operated at a temperature of 50 °C and a pressure of 3 bar. From there the polymer was directed to a fluidized bed gas phase reactor operated at a pressure of 20 bar and a temperature of 82 °C. Additional ethylene, 1 -butene and 1 -hexene comonomer, nitrogen as inert gas and hydrogen were added so that the ethylene content in the reaction mixture was 13.3 mol% and the molar ratio of 1 -butene to ethylene was 92.1 mol/kmol and the molar ratio of 1 -hexene to ethylene was 121.8 mol/kmol. The estimated production split was 54 wt.-%.

The polymer powder was mixed under nitrogen atmosphere with 1200 ppm of Irganox B561 and 400 ppm Ca-stearate. Then it was compounded and extruded under nitrogen atmosphere to pellets by using a JSW CIMP90 twin screw extruder. Final properties of PE1 are reported in Table 2. Table 2: Properties of PE1

The composition and structure of the layered films produced are given in Table 3. All films produced had a total thickness of 45 micrometers, whereby the core layer had a thickness of 32.1 pm and the outer layers each had a thickness of 6.75 pm. In Table 3 “E” means external layer, and “C” means core layer. The external layers of the films produced had each the same composition.

Table 3: Layer structures of examples

Table 4: Performance of layer structures

As can be seen from Table 4 and Figure 1 , using PE1 instead of BorShape FX1002 allows using 10 wt.-% more PCR in the core layer while keeping all performance parameters at the same level. Hence, the present invention allows increasing the total PCR content in the film composition from 50 wt.-% to 56 wt.- % allowing for an extra CO2 footprint saving without sacrificing mechanical properties such as stiffness and toughness.

Claims

1. A layered film structure comprising a core layer C and external layers E1 and E2, wherein core layer C comprises a multimodal ethylene copolymer (I) with at least one alpha-olefin comonomer having an MFRs determined according to ISO 1133 of from 0.1 to 5 g/10 min and a density of 0.930 to 0.950 g/cm³ and a recycled LDPE having a MFR2 determined according to ISO 1 133 of from 0.1 to 10 g/10 min and a density in the range from 910 to 940 kg/m³ and wherein external layer(s) E1 and/or E2 comprise(s) a multimodal ethylene terpolymer (II) having an MFR2 determined according to ISO 1133 of from 0.5 to 10 g/10 min and a density of 0.920 to 0.935 g/cm³.

2. The layered film structure according to claim 1 wherein the multimodal ethylene copolymer (I) is trimodal.

3. The layered film structure according to claim 1 , wherein the multimodal ethylene copolymer (I) is a trimodal copolymer comprising a) 10 to 30 wt% of a first ethylene homopolymer; b) 15 to 35 wt% a second ethylene homopolymer having an MFR2 which is at least 50 g/10 min higher than the MFR2 of component a); and c) 40 to 65 wt% of a third ethylene copolymer with at least one alphaolefin comonomer.

4. The layered film structure according to claim 1 wherein the multimodal ethylene copolymer (I) is a trimodal terpolymer comprising a) 10 to 30 wt% of a first ethylene homopolymer; b) 15 to 35 wt% a second ethylene homopolymer having an MFR2 which is at least 50 g/10 min higher than the MFR2 of component a); and c) 40 to 65 wt% of a third ethylene terpolymer with two alpha-olefin comonomers.

5. The layered film structure according to any preceding claims, wherein the multimodal ethylene terpolymer (II) comprises a multimodal polymer of ethylene with two different comonomers selected from alpha-olefins having from 4 to 10 carbon atoms, which has a ratio MFR21/MFR2 of 13 to 30 and a MWD of 5 or less. The layered film structure according to any one of the preceding claims wherein core layer C comprises 10 wt.-% or more of said multimodal ethylene copolymer (I). The layered film structure according to any one of the preceding claims wherein external layers E1 and/or E2 comprise(s) 60 wt.-% or more of said multimodal ethylene terpolymer (II). The layered film structure according to any one of the preceding claims wherein the film structure has a thickness of 100 pm or lower and/or wherein external layers E1 and E2 have the same composition. The layered film structure according to any one of the preceding claims wherein the film structure has a shrinkage in oil at 140°C in machine direction of 75% or higher determined according to DIN 55543-4 on a 45 pm test film. The layered film structure according to any one of the preceding claims wherein the film structure has a contracting force in machine direction of 2.0 N or higher, preferably of 2.1 N or higher, determined according to ISO 14616 on a 45 pm test film. The layered film structure according to any one of the preceding claims wherein the film structure has a dart drop impact (DDI) determined according to ASTM D1709 on a 45 pm test film of more than 60 g. A process for producing a layered film structure according to any one of the preceding claims wherein the layers of the film structure are coextruded. A collation shrink film comprising or consisting of a layered film structure according to any one of claims 1 to 12. The collation shrink film according to claim 13 comprising recycled LDPE in an amount of 40 wt.-% to 65 wt.-% with respect to the total amount of polyethylene in the film. Use of a collation shrink film according to claims 13 or 14 for wrapping of articles.