EP4554792A1

EP4554792A1 - Multilayer uniaxially oriented film

Info

Publication number: EP4554792A1
Application number: EP23741719.1A
Authority: EP
Inventors: Raquel LASIERRA MORALES; María Soledad BERMÚDEZ UYARRA; Mariana SANCHEZ CAPUTO; Almudena DOMÍNGUEZ DORADO; Luis Miguel MÉNDEZ LLATAS
Original assignee: Repsol SA
Current assignee: Repsol SA
Priority date: 2022-07-15
Filing date: 2023-07-14
Publication date: 2025-05-21
Also published as: WO2024013378A1

Abstract

It is provided a blocked blown multilayer MDO film comprising a structure comprising (i) a first outer layer (A), (ii) a first core layer (B), (iii)a first inner blocking layer (C), (iv) a second inner blocking layer (C'), (v) a second core layer (B'), and (vi) a second outer layer (A'), wherein the first and second inner blocking layers are fused and form one layer, and wherein the layers (A) and (A') have the same composition and comprise a HDPE, the layers (B) and (B') have the same composition and comprise a mLLDPE, and the layers (C) and (C') have the same composition and comprise a copolymer selected from EVA, EBA, and a mixture thereof. It is also provided a process for its preparation, its use in packaging applications, and an article packaged using the film.

Description

Multilayer uniaxially oriented film

This application claims the benefit of European Patent Application EP22382676.9 filed on July 15, 2022.

Technical Field

This invention relates to a polyethylene multilayer film with some improved mechanical properties that has been uniaxially stretched in the machine direction. In particular, it relates to a multilayer blocked MDO film comprising an inner blocking layer which is an ethylene vinyl acetate (EVA) or an ethylene butyl acrylate (EBA) copolymer. The invention also provides a process for the manufacture of these MDO films and articles packaged using the films.

Background Art

Recyclability is becoming one of the most important requirements for food and non-food packaging. Many current products use non-recyclable multi-material solutions. On the other hand, mono-material PE-based packaging meets recyclability requirements and contributes to global sustainability goals.

Machine Direction Orientation (MDO) is a proven technology based on monoaxial stretching of blown films. This technology allows improving physical and barrier properties, while significantly reducing material costs.

Several processes for the preparation of multilayer machine direction oriented (MDO) films have been disclosed. Of particular interest is the increase of certain mechanical properties such as modulus and stress, the improvement of the shrink behavior, and the increase in gloss and transparency.

In order to manufacture multilayer films, typically several polymer melt streams are coextruded to form a tube which is blown-up. The formed bubble can then be collapsed (blocked) in nip rolls to form a film where the inner layers are contacted inside/inside. Then the multilayer film is subjected to an MDO process.

The first step in the MDO process is preheating, where a film is introduced into the stretching unit and uniformly heated to a temperature slightly below its melting point. This is followed by orientation, where the film is stretched between a series of rollers rotating at different speeds. Then, the film is subjected to an annealing stage, during which the new properties of the film are defined. Finally, it is cooled at or close to room temperature again.

In the blocked MDO structures, it is desirable that the inner layer has some "natural stickiness" so that the tube is well blocked after the film extrusion process. Plastomers and elastomers are currently used for the blocking layer.

Nevertheless, there is a continuous need for alternative films suitable for use in the packaging field, with the required mechanical properties depending on the intended application area.

Summary of Invention

The present inventors have found that a multilayer machine direction oriented blocked blown film which comprises a specific combination of a high density polyethylene (HDPE) outer layer, a metallocene linear low density polyethylene (mLLDPE) core layer, and an EVA or EBA inner blocking layer provides advantageous mechanical properties, such as higher tensile stress and strain at break in transverse direction, than a similar film where a plastomer is used as blocking layer. Additionally, the multilayer MDO film of the invention has also an improved gloss while having a similar or even better haze value compared to prior art films prepared with a plastomer as blocking layer, what means a better aesthetic performance of final package.

Thus, a first aspect of the invention relates to a blocked blown multilayer uniaxially oriented film (multilayer MDO film) comprising a structure comprising:

(i) a first outer layer (A)

(ii) a first core layer (B),

(iii) a first inner blocking layer (C),

(iv) a second inner blocking layer (O’),

(v) a second core layer (B’), and

(vi) a second outer layer (A’), wherein the first and second inner blocking layers are fused and form one layer, and wherein the layers (A) and (A’) have the same composition and comprise a high-density polyethylene (HDPE), the layers (B) and (B’) have the same composition and comprise a metallocene linear low density polyethylene (mLLDPE), and the layers (C) and (O’) have the same composition and comprise a copolymer selected from the group consisting of ethylene vinyl acetate (EVA), ethylene butyl acrylate (EBA), and a mixture thereof.

A second aspect of the invention relates to a process for preparing a blocked blown multilayer MDO film as defined in claim 1, the process comprising a) coextruding at least: a composition comprising a high density polyethylene (HDPE); a composition comprising a metallocene linear low density polyethylene (mLLDPE); and a composition comprising a copolymer selected from the group consisting of ethylene vinyl acetate (EVA), ethylene butyl acrylate (EBA), and a mixture thereof; to form a tubular multilayer film structure comprising: an outer layer (A) comprising HDPE; a core layer (B) comprising mLLDPE; and an inner blocking layer (C) comprising a copolymer selected from the group consisting of EVA, EBA, and a mixture thereof; b) blowing by blown extrusion into the multilayer tubular film to form a bubble; c) collapsing the formed bubble to form a blocked blown multilayer film where layers (C) are contacted; and d) subjecting the blocked blown multilayer film to a subsequent stretching step, wherein the film is oriented in a machine direction.

Advantageously, the process of the invention allows to reduce neck-in in the MDO stretching and, consequently, trimming after orientation, while requiring lower extruder pressure and motor load than by using a plastomer as blocking layer. All this results in an improved production economy.

Additionally, the use of EVA or EBA as blocking layer provide a better blocking of the primary film, what means a higher security against delamination.

A third aspect of the invention relates to the use of the multilayer MDO film as defined herein above and below in packaging.

Finally, a further aspect relates to an article packaged using a multilayer MDO film as defined herein above and below.

Detailed description of the invention

All terms as used herein in this application, unless otherwise stated, shall be understood in their ordinary meaning as known in the art. Other more specific definitions terms as used in the present application are as set forth below and are intended to apply uniformly throughout the specification and claims unless an otherwise expressly set out definition provides a broader definition.

As used herein, the term "and/or" includes all combinations of one or more of the associated listed items.

As used herein, the indefinite articles “a” and “an” are synonymous with “at least one” or “one or more.” Thus, as used herein, the singular forms ”a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

As mentioned above, a first aspect of the present disclosure relates to a multilayer MDO film as defined above comprising a structure comprising at least six layers, (A), (B), (C), (C’), (B’), and (A’), wherein layers C and C are fused and form one layer. Thus, the inner blocking layer can simply be defined as one layer C, and a ABCB'A' can simply be defined as ABCBA.

In an embodiment, the first outer layer (A) is in direct contact with the first core layer (B) and the second outer layer (A’) is in direct contact with the second core layer (B’). In another embodiment, optionally in combination with one or more features of the embodiments defined above, the first core layer (B) is in direct contact with the first inner first blocking layer (C) and the second core layer (B’) is in direct contact with the second inner second blocking layer (C’). In another embodiment, the first outer layer (A) is in direct contact with the first core layer (B), the first core layer (B) is in direct contact with the first inner first blocking layer (C), the second outer layer (A’) is in direct contact with the second core layer (B’), and the second core layer (B’) is in direct contact with the second inner second blocking layer (C’). Particularly, the structure consists of an ABCBA structure. Also particularly, the blocked blown multilayer MDO film of the invention comprises or consists of an ABCBA structure.

In an embodiment, optionally in combination with one or more features of the embodiments defined above, the outer layers (A) and (A’) comprises from 60 wt.% to 100 wt.% HDPE. In another embodiment, the outer layers (A) and (A’) comprises from 70 wt.% to 100 wt.% HDPE. In another embodiment, the outer layers (A) and (A’) comprises from 80 wt.% to 100 wt.% HDPE. In another embodiment, the outer layers (A) and (A’) comprises from 90 wt.% to 100 wt.% HDPE.

In another embodiment, optionally in combination with one or more features of the embodiments defined above, the core layers (B) and (B’) comprises from 60 wt.% to 100 wt.% mLLDPE. In another embodiment, the core layers (B) and (B’) comprises from 70 wt.% to 100 wt.% mLLDPE. In another embodiment, the core layers (B) and (B’) comprises from 80 wt.% to 100 wt.% mLLDPE. In another embodiment, the core layers (B) and (B’) comprises from 90 wt.% to 100 wt.% mLLDPE.

In an embodiment, optionally in combination with one or more features of the embodiments defined above, the outer layers (A) and (A’) comprises from 60 wt.% to 100 wt.% HDPE and the core layers (B) and (B’) comprises from 60 wt.% to 100 wt.% mLLDPE.

In an embodiment, optionally in combination with one or more features of the embodiments defined above, the outer layers (A) and (A’) consists essentially of a HDPE. In another embodiment, optionally in combination with one or more features of the embodiments defined above, the core layers (B) and (B’) consists essentially of a mLLDPE. In another embodiment, optionally in combination with one or more features of the embodiments defined above, and the inner blocking layers (C) and (C’) consists essentially of a copolymer selected from EVA, EBA, or a mixture thereof.

The term "consisting essentially of', as used herein, is meant to exclude only the presence of other polymer components such as other polyolefin components. Thus said term does not exclude the presence of additives, e.g. conventional film additives, i.e. each layer independently may contain conventional film additives such as antioxidants, UV stabilisers, acid scavengers, nucleating agents, anti-blocking agents, slip agents, etc. as well as polymer processing agent (PPA), and so on. Namely, each one of the layers above comprise the mentioned polyolefin polymers or copolymers in the absence of any other polymer components, particularly of other polyolefins, and, optionally, comprise at least one additive, particularly selected from the ones mentioned above. Additives can be present as part of a masterbatch.

In an embodiment, optionally in combination with one or more features of the embodiments defined above, the outer layers (A) and (A’) consists of a HDPE. In another embodiment, optionally in combination with one or more features of the embodiments defined above, the core layers (B) and (B’) consists of a mLLDPE. In another embodiment, optionally in combination with one or more features of the embodiments defined above, and the inner blocking layers (C) and (C’) consists of a copolymer selected from the group consisting of EVA, EBA, and a mixture thereof.

In another embodiment, optionally in combination with one or more features of the embodiments defined above, the layer A amounts less than a 60 wt.% of the total weigh of layers A, B and C. This can also be expressed as that layers A and A' amount less than a 60 wt.% of the total weigh of layers A, A', B, B', C, and C. In another embodiment, the layer A amounts less than a 50 wt.% of the total weigh of layers A, B and C. In another embodiment, the layer A amounts less than a 40 wt.% of the total weigh of layers A, B and C. In another embodiment, the layer A amounts less than a 30 wt.% of the total weigh of layers A, B and C. In another embodiment, the layer A amounts less than a 20 wt.% of the total weigh of layers A, B and C. In an example, for an ABCC’B’A’ film structure the thickness of the layers may conform to 7-15%/25-35%/15-25%/25-35%/7-15%, such as of 10%/30%/20%/30%/10%, wherein the total film thickness is 100% and the amount of blocking inner layer is the sum of two layers (C) and (C’).

In another embodiment, optionally in combination with one or more features of the embodiments defined above, the blocked blown multilayer MDO film of the invention does not comprise any barrier layer. As used herein, the phrase "barrier layer" refers to a film layer comprising a barrier polymer such as ethylene vinyl alcohol copolymer (EVOH) or polyamide (PA), known to serve as an oxygen, hydrogen, water vapor, and/or aroma barrier.

HDPE is a thermoplastic polymer produced by the polymerization of ethylene monomers and optionally longer-chain olefins. It provides heat resistance for the laminate during heat seal.

In an embodiment, optionally in combination with one or more features of the embodiments defined above, the HDPE has a density from 940 to 970 kg/m³ such as of 948 kg/m³, 955 kg/m³, or 958 kg/m³.

In another embodiment, optionally in combination with one or more features of the embodiments defined above, the HDPE has an MFI (according to ISO 1133, 190 °C/2.16 kg) from 0.2 to 1.0 g/10 min, such as of 0.25 g/10 min, 0.23 g/10 min, or of 0.55 g/10 min.

In an embodiment, the HDPE has a density of 948 kg/m³ and an MFI of 0.55 g/10 min. In another embodiment, the HDPE has a density of 955 kg/m³ and a MFI of 0.23 g/10 min. In another embodiment, the HDPE has a a density of 958 kg/m³ and a MFI of 0.25 g/10 min.

HDPE polymers are commercially available, for example, from Repsol Quimica. mLLDPE is a polyethylene produced in a low-pressure polymerisation process using a metallocene catalyst to copolymerise ethylene and alpha-olefins such as butene, hexene or octene. The co-polymerization process produces an mLLDPE polymer having a narrow molecular weight distribution, which in combination with the linear structure, provides significant improvements in optical and mechanical film properties. mLLDPEs are commercially available from, for example, Repsol Quimica.

In an embodiment, optionally in combination with one or more features of the embodiments defined above, the mLLDPE is a metallocene ethylene-hexene copolymer.

In another embodiment, optionally in combination with one or more features of the embodiments defined above, the mLLDPE has a density from 914 to 940 kg/m³. In a particular embodiment, the mLLDPE has a density from 916 to 933 kg/m³ (ISO 1183) such as of 918 kg/m³, or of 927 kg/m³.

In another embodiment, optionally in combination with one or more features of the particular embodiments defined above, mLLDPE has a melt flow index (MFI; according to ISO 1133, 190 °C/2.16 kg) of 0.5 to 3 g/10 min. In another embodiment, the mLLDPE has an MFI from 1 to 2 g/10 min. In a particular embodiment, optionally in combination with one or more features of the embodiments defined above, mLLDPE has a density of 918 kg/m³ and an MFI (according to ISO 1133, 190 °C/2.16 kg) of 1.0 g/10min. In another embodiment, the mLLDPE has a density of 918 kg/m³ and an MFI of 2.0 g/10 min. In another embodiment the mLLDPE has a density of 933 kg/m³ and an MFI of 1.0 g/10min. In another embodiment the mLLDPE has a density of 916 kg/m³ and an MFI of 1.4 g/10 min. In another embodiment the mLLDPE has a a density of 927 kg/m³ and an MFI of 1.0 g/10 min. mLLDPE polymers are commercially available, for example, from Repsol Quimica.

Layer (C) - EVA Copolymer

EVA is a copolymer of ethylene and vinyl acetate prepared by high pressure radical polymerization. The weight percent of vinyl acetate ( A) usually varies from 3 to 40%, with the remainder being ethylene. EVA copolymers are commercially available from, for example, Repsol Quimica.

In an embodiment, optionally in combination with one or more features of the embodiments defined above, EVA has a VA content from 7 to 40%. In a particular embodiment, the EVA has a VA content from 13 to 30 wt.%, such as of 7.5 wt.%, 12.5 wt.%, 18 wt.%, 24 wt.%, or 27 wt.%. Particularly, the EVA has a VA content of 24.

In another embodiment, optionally in combination with one or more features of the embodiments defined above, EVA has an MFI (according to ISO 1133, 190 °C/2.16 kg) from 0.3 to 7.0 g/10 min. In a particular embodiment, the EVA has an MFI from 0.5 to 7.0 g/10 min. In another particular embodiment, the EVA has an MFI from 0.3-4 g/10 min, such as of 0.7 g/10 min, 2 g/10 min, 3 g/10 min, or 3.5 g/10 min, 4 g/10 min.

In another embodiment, optionally in combination with one or more features of the embodiments defined above, EVA has a melting point from 70 to 100 °C, such as of 77 °C.

In a particular embodiment, optionally in combination with one or more features of the particular embodiments defined above, the EVA has a VA content of about 24 wt.% and an MFI (ISO 1133) of about 3 g/10 min. In another embodiment, the EVA has a VA content of about 13% by weight and an MFI of 4.0 g/10 min. In another embodiment, the EVA has a VA content of about 18% by weight and an MFI of 0.7 g/10 min. In another embodiment, the EVA has a VA content of about 18% by weight and an MFI of 2.0 g/10 min. In another embodiment, the EVA has a VA content of about 27% by weight and an MFI of 3.5 g/10 min.

It has been found that an EVA copolymer film having a vinyl acetate content of at least 24 wt.% may be film formed to provide a thermoplastic film having a low melting point in the range of about 70-80 °C.

EVA polymers are commercially available, for example, from Repsol Quimica.

In another embodiment, optionally in combination with one or more features of the particular embodiments defined above, the EVA has a density (ISO 1183) from 925 to 955 kg/m³ such as of 926 kg/m³. In another embodiment the EVA has a density of 931 kg/m³. In another embodiment the EVA has a density of 937 kg/m³. In another embodiment the EVA has a density of 941 kg/m³.

In another embodiment, optionally in combination with one or more features of the particular embodiments defined above, the EVA has a Vicat temperature (LINE-EN ISO 306:2015) from 45 to 70 °C. In another embodiment, the EVA has a Vicat temperature from 47 to 62 °C, such as of 49 °C.

Layer (C) - EBA Copolymer

EBA is a copolymer consisting of ethylene and butyl acrylate prepared by high pressure radical polymerization. The weight percent of butyl acrylate (BA) usually varies from 3 to 40%, with the remainder being ethylene. Such copolymers are commercially available, for instance, from Repsol Quimica.

In an embodiment, optionally in combination with one or more features of the embodiments defined above, EBA has a BA content from 3 to 30 wt.%. In a particular embodiment, the EBA has a BA content from 8 to 20 wt.% such as of 3 wt.%, 8 wt.%, 12 wt.%, 13 wt.%, or 17 wt.%. Particularly, the EBA has a BA content of 17 wt.%.

In another embodiment, optionally in combination with one or more features of the embodiments defined above, the EBA has an MFI (according to ISO 1133, 190 °C/2.16 kg) from about 0.3 g/10 min to about 7.0 g/10 min. In a particular embodiment, the EBA has an MFI from 0.3 to 4 g/10 min, particularly of 1.5 g/10 min.

In another embodiment, optionally in combination with one or more features of the embodiments defined above, the EBA has a melting point from 85 to 115 °C, such as of 89 °C, 93 °C, 95 °C, 96 °C, 100 °C, 101 °C, 106 °C, or 110 °C. In a particular embodiment, the EBA has a melting point of 95 °C.

In a particular embodiment, optionally in combination with one or more features of the particular embodiments defined above, the EBA has a BA content of about 17 wt.% and an MFI (ISO 1133) of about 1.5 g/10 min. In another embodiment, the EBA has a BA content of about 13% by weight and an MFI of 0.3 g/10 min. In another embodiment, the EBA has a BA content of about 17% by weight and an MFI of 0.4 g/10 min. In another embodiment, the EBA has a BA content of about 27% by weight and an MFI of 3.5 g/10 min.

It has been found that an EBA copolymer film having a butyl acrylate content of at least 24% by weight may be film formed to provide a thermoplastic film having a low melting point in the range of about 80-90 °C.

EBA polymers are commercially available, for example, from Repsol Quimica.

In another embodiment, optionally in combination with one or more features of the particular embodiments defined above, the EBA has a density (ISO 1183) from 920 to 926 kg/m³. In another embodiment the EBA has a density of 923 kg/m³. In another embodiment the EBA has a density of 925 kg/m³. In another embodiment the EBA has a density of 924 kg/m³.

In another embodiment, optionally in combination with one or more features of the particular embodiments defined above, EBA has a a Vicat temperature from 50 to 90 °C. In a particular embodiment, the EBA has a Vicat temperature from 60 to 80 °C, particularly of 68 °C.

Layer (C) - Plastomer (for comparative examples)

Generally, plastomers that can be utilized in films are very low-density copolymers and terpolymers of ethylene with an alpha olefin, and these plastomers are characterized as having a density of about 0.912 g/cm³ or less and a melting point in the range of about 40- 105 °C. These copolymers typically comprise from 2 to 30 wt.% or from 5 to 25% of the alpha olefin. Examples of alpha olefins include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1 -octene, 1 -decene and 1 -dodecene. Particularly useful alpha olefins include 1-butene and 1-hexene. An example of an ethylene terpolymer is ethylene-1 -hexene-1 -butene.

These low-density ethylene copolymers are obtained by copolymerization of ethylene with an alpha olefin using single-site metallocene catalysts. Such copolymers are available commercially.

Preparation of the multilayer MDO film

ABCCBA type film structures can be prepared by first coextruding compositions forming the layers (B), (C) and (A) through a multi-channel tubular, annular or circular die; blowing by blown extrusion into a tubular film to form a bubble; and then, collapsing the formed bubble, e.g. in nip rolls to form said film where layers (C) are contacted inside/inside, i.e. ABC/CBA. The two halves, ABC and CBA, are forced together to effectively form a multilayer structure. Thus, an ABCCBA film is formed from two identical ABC films laminated together via their (C) layers. In this way, the film thickness is effectively doubled, and the desired initial film thickness achieved. The manufacture of blocked blown film is a well-known process.

The blown (co)extrusion 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.

The obtained multilayer film is subjected to a subsequent stretching step, wherein the film is stretched in a machine direction. Stretching may be carried out by any conventional technique which are well known to those skilled in the art, for instance, using a conventional MDO line, such as the ones manufactured by Hosokawa Alpine AG in Augsburg/Germany.

The MDO film orientation process is divided into four phases: heating, stretching, annealing, and cooling.

The first step in the MDO process is preheating, where a film obtained from the blown-film line is fed into the stretching unit and evenly warmed to the desired temperature, utilizing multiple heating rollers.

This is followed by orientation, where the film is stretched between a series of rollers that are revolving at different speeds. In a monoaxial stretching line, the film is drawn between two rollers. The rollers rotate at different speeds. During the stretching process, the film thickness is reduced while optical and mechanical properties are improved. Particularly, the temperature range for orientation can be up to 25 °C, such as from 5 °C to 20 °C, below the VICAT A-level of the (outer) film layer material up to the melting temperature of the (outer) film layer material.

The oriented film then enters annealing thermal rollers, which allow stress relaxation by holding the film at an elevated temperature for a period of time and the film’s new properties are locked in and made permanent. The annealing temperature is preferably within the same temperature range as used for stretching or slightly below (e.g. 10 to 20 °C below), with room temperature being the lower limit.

Finally, the film is cooled through cooling rollers to room temperature.

The ratio of the film thickness before and after orientation is called stretch ratio. The stretch ratio varies depending on many factors including the desired film thickness, film properties and multilayer film structures.

Thus, as mentioned above, the second aspect of the invention relates to a process for preparing a multilayer MDO film as defined above, the process comprising a) coextruding a composition comprising a high density polyethylene (HDPE); a composition comprising a metallocene linear low density polyethylene (mLLDPE); and a composition comprising a copolymer selected from the group consisting of ethylene vinyl acetate (EVA), ethylene butyl acrylate (EBA), and a mixture thereof; to form a tubular multilayer film structure comprising an outer layer (A) comprising HDPE, a core layer (B) comprising mLLDPE, and an inner blocking layer (C) comprising EVA, EBA, or a mixture thereof, b) blowing by blown extrusion into the multilayer tubular film to form a bubble; c) collapsing the formed bubble to form a multilayer film where layers (C) are contacted; d) subjecting the multilayer film to a subsequent stretching step, wherein the film is oriented in a machine direction.

In an embodiment, optionally in combination with one or more features of the embodiments defined above, the film is oriented in the machine direction at a stretch ratio greater than 1 :3 and less than 1:10, particularly of 1 :4, 1:5, 1 :6, or 1 :7.

As used herein, a stretch ratio of, for instance, 1 :4, means that the film has been stretched 4 times up its original length in the machine direction, i.e. "1" represents the original length of the film and "4" denotes that it has been stretched to 4 times that original length.

After orientation, the multilayer MDO film of the invention can have a thickness from 15 to 60 pm, particularly from 20 to 55 pm, more particularly of 25 to 50 pm.

The machine direction oriented films according to the invention show advantageous and surprising properties.

As is shown in the experimental part the multilayer MDO films of the invention have a higher gloss, while having similar or even better haze values, and higher tensile stress and strain at break in transverse direction (TD) compared to films comprising a plastomer as an inner blocking layer.

Thus, in an embodiment, optionally in combination with one or more features of the embodiments defined above, the multilayer MDO film of the invention has a gloss (60°) according to ASTM D2457-21 for a film thickness of 50 pm of at least 130, particularly of at least 134, more particularly of at least 135, or even more particularly of at least 137, preferably of at least 140.

In another embodiment, optionally in combination with one or more features of the embodiments defined above, the multilayer MDO film of the invention has a haze according to ASTM D-1003-21 equal to or lower than 4% for a film thickness of 50 pm.

In another embodiment, optionally in combination with one or more features of the embodiments defined above, the multilayer MDO film of the invention has a tensile stress at break TD according to LINE-EN ISO 527-3:2019 of at least 40 MPa, such as of 44 MPa or 45 MPa for a film thickness of 50 pm.

In another embodiment, optionally in combination with one or more features of the embodiments defined above, the multilayer MDO film of the invention has a tensile strain at break TD according to LINE-EN ISO 527-3:2019 of at least 600%, preferably of at least 620%, such as of 622% or 626%, for a film thickness of 50 pm.

As can be seen in the examples, an inherent result of the method of the invention is that it allows obtaining a multilayer MDO film having improved properties compared with the ones of the prior art. Therefore, a multilayer MDO film obtainable by the method defined above is also part of the invention.

Thus, the first aspect of the invention can also be defined as a blocked blown multilayer MDO film comprising a structure comprising:

(i) a first outer layer (A)

(ii) a first core layer (B),

(iii) a first inner blocking layer (C),

(iv) a second inner blocking layer (O’),

(v) a second core layer (B’), and

(vi) a second outer layer (A’), wherein the first and second inner blocking layers are fused and form one layer, and wherein the layers (A) and (A’) have the same composition and comprise a high-density polyethylene (HDPE), the layers (B) and (B’) have the same composition and comprise a metallocene linear low density polyethylene (mLLDPE), and the layers (C) and (C’) have the same composition and comprise a copolymer selected from the group consisting of ethylene vinyl acetate (EVA), ethylene butyl acrylate (EBA), and a mixture thereof; wherein the blocked blown multilayer MDO film is obtainable by a process comprising a) coextruding at least: a composition comprising a high density polyethylene (HDPE); a composition comprising a metallocene linear low density polyethylene (mLLDPE); and a composition comprising a copolymer selected from the group consisting of ethylene vinyl acetate (EVA), ethylene butyl acrylate (EBA), and a mixture thereof; to form a tubular multilayer film structure comprising: an outer layer (A) comprising HDPE; a core layer (B) comprising mLLDPE; and an inner blocking layer (C) comprising a copolymer selected from the group consisting of EVA, EBA, and a mixture thereof; b) blowing by blown extrusion into the multilayer tubular film to form a bubble; c) collapsing the formed bubble to form a blown multilayer film where layers (C) are contacted; and d) subjecting the blown multilayer film to a subsequent stretching step, wherein the film is oriented in a machine direction.

In the process for preparing the multilayer blown film of the present disclosure, coextrusion is carried out with an coextrusion systems comprising a tubular-shaped extruder for each polymer composition. In an example, coextrusion systems usually have from two to nine extruders an produce from three- to seventeen-layer films. As an instance, with a three-extruder system, a symmetrical five-layer [ABCBA] structure film from the three different polymer streams can be produced; with a four-extruder system, a symmetrical seven-layer [ABCDCBA] structure can be produced; and so on.

As mentioned above, another aspect of the invention relates to the use of the multilayer MDO film as defined above in packaging, in particular in a form fill and seal packaging process, that is a process wherein a package is formed, filled with a product, and then seal.

The film is especially suitable for use in grocery sacks, institutional and consumer can liners, merchandise bags, shipping sacks, food packaging films, multi-wall bag liners, produce bags, shrink films, label films, tissue overwrap, deli wraps and shrink wraps.

In the present disclosure, it is noted that when discussing the multilayer MDO film and the process for preparing a multilayer MDO film, each one of the embodiments or features defined for any of the mentioned aspects can be considered applicable to the other aspects, whether or not they are explicitly discussed in the context of that other aspect. Thus, for example, when defining embodiments of the process for preparing a multilayer MDO film perse, such embodiments also refer to the process for preparing a multilayer MDO film, and vice versa.

Throughout the description and claims the word "comprise" and variations of the word, are not intended to exclude other technical features, additives, components, or steps.

Furthermore, the word “comprise” encompasses the case of “consisting of”.

The following examples and drawings are provided by way of illustration, and they are not intended to be limiting of the present invention. Furthermore, the present invention covers all possible combinations of particular and preferred embodiments described herein.

Examples

Methods

Vinyl acetate (VA) and butyl acrylate (BA) contents were measured by Fourier transform infrared (FTIR) spectroscopy using both molded plates and film, applying a thickness correction in the latter case. The measurement of the vinyl acetate content is based on the infrared absorption of the bands 1020 cm^-1 (for contents of 0.5 to 5% VA) and 609 cm^-1 and 3456 cm^-1 (for contents of 5 to 40%. %VA). The infrared absorption of the bands 1465 cm^-1, 2019 cm^-1 or 4632-3731 cm^-1 can be taken as the thickness correction band. The melt flow index (MFI) was measured according to LINE-EN ISO 1133-1 :2012. The density was measured according to LINE-EN ISO 1183-1 :2019. The melting temperature was measured by differential scanning calorimetry (DSC) using a compression molded film or plate and heating the oven at a rate of 10 °C/min to a temperature high enough to eliminate previous thermal history, approximately 30 °C above melting; it is kept in isotherm for 5 minutes and another temperature scan is made at 10 °C/min, recording the heating curve until the transition has taken place. The Vicat softening temperature was measured according to LINE-EN ISO 306:2015.

Materials used:

- ULTRACLEAN 210 (formerly called 1810F) is a metallocene linear low density polyethylenes (mLLDPE) having a density of 918 kg/m³ and an MFI of 1.0 g/10 min;

- ULTRACLEAN 230 (formerly called 331 OF) is a metallocene linear low density polyethylenes (mLLDPE) having a density of 933 kg/m³ and an MFI of 1.0 g/10 min;

- ULTRACLEAN 110 (formerly called R4805EP) is a high-density polyethylene (HDPE) of a density of 948 kg/m³ and an MFI of 0.55 g/10 min;

- ULTRACLEAN 410 (formerly called P2430C) is an ethylene vinyl acetate (EVA) copolymer with a VA content of 24%, a melting temperature of 77 °C, MFI of 3, density of 944 kg/m³, and a Vicat temperature of 49 °C;

- ULTRACLEAN 310 (formerly called E1715) is an ethylene butyl acrylate (EBA) copolymer with a 17% BA content, a melting temperature of 95 °C, MFI of 1.5 g/10 min, density of 926 kg/m³, a Vicat temperature of 68 °C; and

- Dow AFFINITY EG 8100G is a mLLDPE type plastomer with C8 comonomer with a melting temperature of 55 °C, an MFI (190 °C/2.16 kg) of 1.0 g/10 min, a density of 870 kg/m³, a Vicat temperature of 46 °C. This grade is considered a reference grade for the processing of collapsed MDO and, therefore, a relevant benchmark, reason why it was used in the comparative examples.

In Table 1 the features of the used materials are shown.

Table 1

Film extrusion

Three co-extruded tube films with a thickness of 150 pm and a film thickness distribution (%) of an ABC layer film of 20%/60%/20% of the total film thickness (100%) were manufactured. The layer distribution consisted of an HDPE outer layer for thermal resistance (A), an mLLDPE core layer for mechanical properties (B), and an inner layer of a blocking material which was a low melt temperature PE grade selected from EVA, EBA, and plastomer (C). Thus, the final film formed from two identical ABC type films had 6 layers, ABCCBA, wherein the two inner C layers had merged to become one.

The three film recipes were extruded on a Windmdller & Hdlscher 3-layer line. The basic specification of the line was the following:

• Three extruders of 50/60/50 mm with barrier screws

• Gravimetric feeders for three materials per extruder

• Die diameter 200 mm

• Chilled air capability

• Output up to 100-150 kg/h

• Back to back 1200 mm dual winder

• Max 1100 mm film width

• Corona treater in-line

• Various slitting options

The recipes are defined in Table 2 below

Table 2

The processing parameters of the W&H line are listed for each recipe in Tables 3 to 7 and discussed with other details of the extrusion trials.

Table 3. Extrusion parameters for Example 1 (with EVA and mLLDPE ULTRACLEAN 210)

Table 4. Extrusion parameters for Example 2 (with EBA and mLLDPE ULTRACLEAN 210) Table 5. Extrusion parameters for Comp. Ex. 1 (with plastomer and mLLDPE

ULTRACLEAN 210)

Table 7. Extrusion parameters for Comp. Ex. 2 (with plastomer and mLLDPE ULTRACLEAN 230)

The pressure and temperature were very stable for A and B layers, with ULTRACLEAN 110 and ULTRACLEAN 210, where the output was the same. Concerning to the C layer:

- For Example 1 , the pressure for ULTRACLEAN 410 was low, and this grade had the highest MFI (3 g/10 min). Furthermore, the rpm was similar for both A and C layer.

- For Example 2, with ULTRACLEAN 310, it was needed to increase the rpm in order to reach the desired output. This grade gave similar low pressure as ULTRACLEAN 410 even with a lower MFR=1 ,5.

- For Comparative Examples 1 and 2, it was needed to increase rpm to reach desired output and due to the high motor load the overall output was reduced. The pressure was also highest of the C-layers, even at the lower output.

MDO process! ng/stretchi ng of film samples

The blocked blown films were processed and stretched on a MDO line manufactured by Hosokawa Alpine AG in Augsburg/Germany.

The MDO line had four main heating rollers (H1-H4) with nip rollers to ensure good contact, followed by two rollers (S5, S6) for one-step stretching with nip rollers to fix the stretch ratio. The film was thereafter annealed and relaxed on three semi-heated rollers (A7-A9) before the two final rollers (C10, C11) for cooling and slitting and winding of the films.

The overview of the processing temperature for each film is presented in Table 8, below: Table 8 -Temperature profiles

The films were able to be processed without break up until a stretch ratio of 1 :7.

MDO process neck-in

During the MDO processing the final film width after stretching for each draw ratio was measured. Since the initial film width was the same (942 mm) for all pre-film rolls, the measured values were a measure of the neck in. The values are reported in Table 9 below in mm as well as in %.

Tabla 9. Film width and neck-in at all stretch ratios

The MDO processing showed that the three samples were able to be processed in a similar way and at similar processing temperatures. All the samples were able to be stretched to a ratio of 7:1 and there was film break at 8:1 , which showed that the stretchability and process behavior was very similar.

The results show that the Example 1 and Example 2, with EVA and EBA copolymer as blocking material, respectively, had less neck-in than Comparative Examples 1 and 2, with a plastomer as blocking material. A reduced neck-in mean that less trimming is required after orientation, what results in an improved production economy.

Film testing

The above films were tested according to the following test methods:

• Tensile properties: modulus, stress and strain at break (LINE-EN ISO 527-3:2019)

• Haze (ASTM D-1003-21) • Gloss (ASTM D2457-21)

• • Coefficient of friction (ISO 8295)

The friction test was made on the films as such, namely without any slip and/or antiblock additives. Thus, a measure of the inherent material friction was obtained. The results are shown in Tables 10 and 11 and below.

Table 10

MD: machine direction; TD: transverse direction.

Table 11

MD: machine direction; TD: transverse direction.

The film test results show:

- The optical properties are improved in Examples 1 and 2 and 3 compared to Comparative Examples 1 and 2. Particularly, the gloss values are significantly higher in Examples 1 and 2 and 3 than in Comparative Examples 1 and 2, while the haze values are similar or even better when EBA is used as blocking layer (see Example 2).

- Example 1 and 2 had higher tensile modulus in TD and MD than comparative Example

1. Example 3 had higher tensile modulus in TD and MD than comparative Example 2. The higher tensile modulus provides higher stiffness.

- For both Examples 1 and 2, kinetic and static COF are higher than for Comparative Examples 1 and 2, which can be beneficial for some applications such as heavy duty bags, where higher kinetic and static COF values are desired to prevent slippage.

Citation List

1. UNE-EN ISO 1133-1:2012 - Plastics - Determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics - Part 1: Standard method.

2. UNE-EN ISO 1183-1:2019 - Plastics - Methods for determining the density of non- cellular plastics - Part 1: Immersion method, liquid pycnometer method and titration method (ISO 1183-1 :2019).

3. UNE-EN ISO 306:2015 - Plastics - Thermoplastic materials - Determination of Vicat softening temperature (VST).

4. UNE-EN ISO 527-3:2019 - Plastics - Determination of tensile properties - Part 3: Test conditions for films and sheets.

5. ASTM D-1003-21 - Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics.

6. ASTM D2457-21 - Standard Test Method for Specular Gloss of Plastic Films and Solid Plastics.

7. UNE-EN ISO 8295:1995 - Plastics - Film and sheeting - Determination of the coefficients of friction.

Claims

1. A blocked blown multilayer uniaxially oriented film (multilayer MDO film) comprising a structure comprising:

(i) a first outer layer (A)

(ii) a first core layer (B),

(iii) a first inner blocking layer (C),

(iv) a second inner blocking layer (O’),

(v) a second core layer (B’), and

2. The multilayer MDO film of claim 1 , wherein the inner blocking layers (C) and (O’) consists essentially of a copolymer selected from the group consisting of EVA, EBA, and a mixture thereof.

3. The multilayer MDO film of claims 1 or 2, wherein the outer layers (A) and (A’) comprises from 60 wt.% to 100 wt.% HDPE and the core layers (B) and (B’) comprises from 60 wt.% to 100 wt.% mLLDPE.

4. The multilayer MDO film of claims 1 to 3, wherein the structure is ABCC’B’A’.

5. The multilayer MDO film of claims 1 to 4, wherein the layer A amounts less than a 60 wt.% of the total weigh of layers A, B and C.

6. The multilayer MDO film of claims 1 to 5, wherein the EVA has a VA content from 7 to 40%.

7. The multilayer MDO film of claims 1 to 6, wherein the EVA has a melting point from 70 to 100 °C, a melt flow index (MFI) according to ISO 1133 at 190 °C/2.16 kg from 0.3 to 7.0 g/10 min and a density according to ISO 1183 from 925 kg/m³ to 955 kg/m³.

8. The multilayer MDO film of claims 1 to 7, wherein the EBA has a BA content from 3 to 30 wt.%.

9. The multilayer MDO film of claims 1 to 8, wherein the EBA has a melting point from 85 to 115 °C.

10. The multilayer MDO film of claims 1 to 9, wherein the EBA has an MFI according to ISO 1133 at 190 °C/2.16 kg of 0.3 g/10 min to 7.0 g/10 min and the EBA has a density according to ISO 1183 from 920 to 926 kg/m³.

11. The multilayer MDO film of claims 1 to 10 having a gloss (60°) according to ASTM D2457-21 for a film thickness of 50 pm of at least 130, and a haze according to ASTM D- 1003-21 equal to or lower than 4% for a film thickness of 50 pm.

12. Use of a multilayer MDO film as defined in claim 1 to 11 in packaging, in particular in a form fill and seal packaging process.

13. A process for preparing a blocked blown multilayer MDO film as defined in claim 1 , the process comprising a) coextruding a composition comprising a high density polyethylene (HDPE); a composition comprising a metallocene linear low density polyethylene (mLLDPE); and a composition comprising a copolymer selected from the group consisting of ethylene vinyl acetate (EVA), ethylene butyl acrylate (EBA), and a mixture thereof; to form a tubular multilayer film structure comprising: an outer layer (A) comprising HDPE; a core layer (B) comprising mLLDPE; and an inner blocking layer (C) comprising EVA, EBA, or a mixture thereof; b) blowing by blown extrusion into the multilayer tubular film to form a bubble; c) collapsing the formed bubble to form a blocked blown multilayer film where layers (C) are contacted; and d) subjecting the blocked blown multilayer film to a subsequent stretching step, wherein the film is oriented in a machine direction.

14. The process according to claim 13, wherein the film is oriented in the machine direction at a stretch ratio greater than 1 :3 and less than 1:10.

15. An article packaged using a multilayer MDO film as defined in claims 1 to 11.