FR3113859A1 - Stretched multilayer film having high temperature resistance and process for preparing same - Google Patents

Abstract

The present invention relates to a multilayer film 1, comprising: - an outer layer 2 comprising polyvinyl ethylene alcohol (EVOH) - a binder layer 3, - a layer comprising polyethylene (PE) 4 characterized in that said layer of binder 3 is inserted between said outer layer 2 comprising polyvinyl ethylene alcohol (EVOH) and said layer comprising polyethylene (PE) 4. The present invention also relates to a stretched film obtained after stretching the multilayer film according to the invention . The films according to the invention have a higher thermal resistance than those of the prior art. The present invention also relates to a film comprising the stretched film according to the invention, characterized in that it comprises less than 10% by weight of EVOH and even more preferably less than 5% by weight of EVOH. Figure of the abstract: [Fig. 1]

Description

Stretched multilayer film having high temperature resistance and process for preparing same

The present invention belongs to the field of products for packaging and more particularly to that of films intended to form packaging.

The present invention relates to a stretch-oriented multilayer film and its preparation process.

State of the prior art

The packaging field uses many types of flexible films to produce different types of packaging. They can in particular be associated with rigid supports (trays, pots) or constitute all or part of the entire packaging.

The films used can be monolayer, that is to say made up over their entire thickness by a single component or a single mixture of components. Thus, polyethylene films (PE) are well known to those skilled in the art.

Alternatively, the films for packaging can be multilayered, that is to say that their thickness comprises several layers each consisting of a single component or a single component mixture. Mention may thus be made of polyamide (PA)/polyethylene (PE) or PA/polypropylene (PP) films. Each of the layers has different physico-chemical properties which will overlap and/or act in synergy to give the packaging the ideal characteristics for its use.

Between the production stage (for example by lamination or coextrusion) and its final use, the monolayer or multilayer film can be stretched to modify and improve its physical characteristics.

The flexible film stretching process is a recognized process and subject to many developments. There are two main types of stretching, mono-axial stretching and bi-axial stretching. For mono-axial stretching, the film comes into contact with a certain number of heating rolls, then is stretched between two more or less close stretching rolls and is finally relaxed and cooled. This process is widely used in the implementation of polyolefins because after stretching, a polyethylene film sees its rigidity, transparency and its barrier properties improved.

This process has also been carried out on multilayer films comprising layers forming a gas barrier made of ethylene polyvinyl alcohol (EVOH), polyamide or others.

Thus, patent US007794848B2 shows that after stretching a multilayer film sees its barrier and mechanical properties greatly improved and this after a minimum stretching of 5 times in the machine direction.

It has also been shown that the stretching of multilayer films makes it possible to obtain a face on which it is possible to perform quality welds (e.g. EP0673759B1).

The stretched multilayer films can be used in association with other films with which they are associated by methods well known to those skilled in the art, such as hot calendering or rolling. This association can be made after the surface of the stretched multilayer film has served as the printing surface.

The present invention proposes to provide a new stretched multilayer film having a high resistance to temperature both in terms of shrinkage and melting, while being recyclable and easy to laminate. In addition, the film according to the invention has a good barrier to O ₂ and to water vapour.

Thus the present invention relates to a multilayer film, comprising:
- an outer layer comprising ethylene polyvinyl alcohol (EVOH)
- a binder layer,
- a layer comprising polyethylene (PE)
characterized in that said binder layer is inserted between said outer layer comprising ethylene polyvinyl alcohol (EVOH) and said layer comprising polyethylene (PE).

Ethylene vinyl alcohol (EVOH) is a component that makes it possible to obtain layers with oxygen barrier properties. Until now the layers of EVOH were systematically covered by a waterproof layer.

The applicants have been able to show that the presence of an outer layer of EVOH made it possible to obtain films having greatly improved thermal resistance compared to a polyethylene film. Furthermore, the presence of a polar material on the surface of the film improves the resistance of surface treatments (metallization, AlOx, SiOx, etc.), printing processes, or even lamination processes, while giving the film good barrier properties.

In the context of the present invention, the term "external" is intended to mean that, under normal conditions of use, said layer is not permanently covered on both sides but comprises a free face directly accessible from the outside. of said multilayer film.

In the context of the present invention, the term “binder” is intended to designate a product making it possible to permanently associate said outer layer comprising polyvinyl ethylene alcohol (EVOH) and said layer comprising polyethylene (PE).

According to a preferred embodiment of the invention, the multilayer film according to the invention comprises:
a first outer layer comprising ethylene polyvinyl alcohol (EVOH) combined with,
a first layer of binder associated with,
a first layer of polyethylene (PE),
a second layer of polyethylene (PE) combined with,
a second layer of binder associated with,
a second outer layer comprising ethylene polyvinyl alcohol (EVOH).

In the context of the present invention, the term “associated” is intended to mean that the two associated layers are directly in contact.

According to an even more preferred embodiment of the invention, the multilayer film according to the invention further comprises at least one additional layer between said first layer of polyethylene (PE) and said second layer of polyethylene (PE). Even more preferentially, said additional layer consists of plastomer.

According to another preferred embodiment of the invention, the multilayer film according to the invention consists of five successive layers:
a first outer layer comprising ethylene polyvinyl alcohol (EVOH),
a first layer of binder,
a layer of polyethylene (PE),
a second layer of binder,
a second outer layer comprising ethylene polyvinyl alcohol (EVOH).

Thus, said multilayer film according to the invention has on each of its faces an outer layer comprising ethylene polyvinyl alcohol (EVOH). In the context of the present application, these films will be designated by the term “symmetrical films”.

Symmetrical films have the advantage of being insensitive to the curling phenomenon (the English term "curling" is more commonly used) and are therefore perfectly flat.

According to a preferred embodiment, said outer layer comprising ethylene polyvinyl alcohol (EVOH) comprises between 24% molar and 48% molar ethylene.

According to a preferred embodiment, said outer layer comprising ethylene polyvinyl alcohol (EVOH) comprises between 29% molar and 38% molar ethylene.

According to a preferred embodiment, said outer layer comprising ethylene polyvinyl alcohol (EVOH) consists of a resin chosen from the group consisting of EVAL® L171B, EVAL® XEP 1435B, EVAL® SP521B, EVAL® XEP 1385 , EVAL® XEP 1385B, EVAL® F101B, EVAL® F171B, EVAL® T101B, EVAL® J171B, EVAL® SP482B, EVAL® H171B, EVAL® E105B, EVAL® SP292B and EVAL® E171B.

According to a preferred embodiment, the binder layer preferably comprises a polyethylene/EVOH binder and even more preferably a polyethylene grafted with maleic anhydride.

According to an even more preferred embodiment, the binder layer 3 preferably consists of a polyethylene/EVOH binder and even more preferably of a polyethylene grafted with maleic anhydride.

Polyethylene/EVOH binders and polyethylenes grafted with maleic anhydride are well known to those skilled in the art. These include OREVAC® 18360, OVERAC ® 18300, OVERAC ® 18301, OVERAC ® 18362 and OVERAC® 18363.

According to a preferred embodiment, said layer comprising polyethylene (PE) has a density of between 0.900 and 0.962 g/cm ³ .

According to a preferred embodiment, said layer comprising polyethylene (PE) has a density of between 0.918 and 0.940 g/cm ³ .

According to a preferred embodiment, the multilayer film according to the invention is produced by flat die coextrusion, inflation coextrusion or by lamination.

In the context of the present invention, the inflation coextrusion process is more particularly preferred. This technique is well known to those skilled in the art, it consists of coextruding a sheath of material through an annular die. This sheath is then pinched and inflated with a gas. Under the combined action of stretching and inflation, a bubble-shaped film is formed. This swollen film is cooled and then flattened. A film is therefore obtained in the form of a sheath that can be split, to obtain two equivalent flat films, before carrying out the subsequent stretching steps. Alternatively, it is possible not to split this sheath which will allow obtaining a symmetrical film. If the inner layer of this sheath is made of a material capable of adhering to itself, a symmetrical product will be obtained known as a “bonded sheath”. Among the materials capable of adhering to itself, mention may in particular be made of polymers with a low melting point and preferably PEs with a low melting point. The so-called “glued sheath” process is very particularly preferred for producing the multilayer film according to the invention.

According to a preferred embodiment, the multilayer film according to the invention has a thickness of between 40 and 200 μm

According to an even more preferred embodiment, the multilayer film according to the invention has a thickness of between 50 and 150 μm.

The present invention also relates to a method for preparing a stretched film, characterized in that it comprises:

- a step consisting in providing a multilayer film according to the invention,

- a step consisting in stretching in at least one direction the film provided in the previous step at a temperature of at least 90° C. until the thickness of the stretched film obtained is less than 60 μm and preferentially 50 μm.

The present invention also relates to a stretched film obtained by the process according to the invention.

According to a preferred embodiment of the invention, the degree of stretching practiced in the method according to the invention is between 3 and 10 and even more preferentially between 4 and 6.

According to a preferred embodiment of the invention, said film stretched to a thickness of between 15 and 60 μm and even more preferably between 20 and 50 μm.

According to a preferred embodiment, said stretched film according to the invention has a modulus of rigidity at least equal to 500 MPa. In the context of the present invention, the term “modulus of rigidity” refers to a measurement carried out according to the ISO-527 standard.

According to a preferred embodiment, said stretched film according to the invention has a vapor barrier value of less than 10 g/m2/d. In the context of the present invention, the term “vapour barrier value” refers to a measurement carried out according to standard ASTM E398.

According to a preferred embodiment, said stretched film according to the invention has an oxygen barrier value of less than 2 cm3/m2/d. In the context of the present invention, the term “oxygen barrier value” refers to a measurement carried out according to standard ASTM D3985 .

According to a preferred embodiment, the step consisting in stretching said multilayer film consists in stretching said film in a single direction.

According to another embodiment, the step consisting in stretching said multilayer film consists in stretching said film in two directions and even more preferentially in two directions orthogonal with respect to each other.

According to a preferred embodiment, the method according to the invention further comprises a surface treatment step, subsequent to the step consisting in stretching the film, chosen from the group consisting of corona treatment, vacuum plasma treatment, atmospheric plasma processing, coating, gravure printing, flexogravure printing, rotogravure printing, physical vapor deposition, chemical vapor deposition, plasma assisted chemical vapor deposition.

According to an entirely preferred embodiment, the final film, obtained after any one of these various operations, comprising the stretched film according to the invention comprises less than 10% by weight of EVOH and even more preferably less than 5% mass of EVOH.

Thus, the present invention also relates to a film comprising the stretched film according to the invention, characterized in that it comprises less than 10% by weight of EVOH and even more preferably less than 5% by weight of EVOH.

This type of film has significant recyclability properties.

Brief description of figures

There is a schematic representation of a cross section of a preferred embodiment of a multilayer film according to the invention.

THE And present the results of a heat flux differential scanning calorimetry test carried out on a sample of a multilayer film according to the invention.

A preferred embodiment of the invention is a multilayer film 1 consisting of five successive layers:

- a first outer layer 2 comprising ethylene polyvinyl alcohol (EVOH),

- a binder layer 3,

- a layer of polyethylene (PE) 4

- a binder layer 3,

- a second outer layer 2 comprising ethylene polyvinyl alcohol (EVOH).

In this embodiment and in the other embodiments, said outer layer 2 comprising ethylene polyvinyl alcohol (EVOH) comprises between 10% and 35%, preferentially between 24% and 48% and even more preferentially between 29% and 38 % ethylene.

The outer layer 2 comprising polyvinyl ethylene alcohol (EVOH) preferably consists of EVAL® J171B or EVAL® H171B.

The embodiment presented in preferably has a thickness of between 40 and 200 μm and even more preferably between 50 and 150 μm.

Preferably, each outer layer 2 has a thickness of between 5 and 20% of the total thickness of the film, each binder layer 3 has a thickness of between 5 and 15%, and each polyethylene layer 4 has a thickness of between 20 and 80% of the total film thickness.

Said multilayer film is obtained by inflation extrusion followed by a stretching step. Prior to this last step, the multilayer film is preheated homogeneously to a temperature slightly lower than the melting temperature of the film.

The stretching phase is performed between two cylinders, one rotating at the same speed as the heating cylinders and one at a higher speed (2 to 10 X).

The stretching phase is preferably followed by a relaxation phase carried out between rollers whose temperature is equal to or slightly lower than the preheating temperature.

The relaxation phase is preferentially followed by a cooling phase at room temperature.

The stretched film is then preferably stored in the form of reels.

Examples

A multilayer film according to the invention was prepared using the inflation coextrusion technique. Before stretching, said film has the following characteristics:
7.5%EVOH
10% binder
22.5% PE
20% Plastomer
22.5% PE
10% binder
7.5% EVOH.

The percentages mentioned above refer to the thickness of each layer compared to the total thickness of the multilayer film.

The multilayer film was then stretched 4.8x at a temperature between 115 and 125°C in the machine direction to reach a thickness of 40µm.

Said film was then subjected to a test by heat flow differential scanning calorimetry. This test included the following phases:
- Balancing at 25°C,
- Ramp at 30°C/min up to 300°C,
- Ramp at 30°C/min up to 25°C,
- Ramp at 30°C/min up to 300°C.

The results obtained presented to the And show that the crystallinity of EVOH before stretching is 9% and almost 12% after stretching. Furthermore, the melting temperature after stretching is increased by a few degrees.

The multilayer film was also subjected to welding tests, at temperatures between 130 and 160°C, between two bars with 2bar of pressure and holding the temperature for 0.5 seconds.

The determination of the quality of welding, shrinkage and gluing was done by eye.

The results are presented in the table below.

Temperature Bonding to sealing bars welding on itself Shrink With external EVOH Without external EVOH With external EVOH Without external EVOH With external EVOH Without external EVOH 130 No No No No No No 135 No AVERAGE No AVERAGE No No 140 No AVERAGE No Yes No No 145 No Yes No Yes No No 150 AVERAGE Yes Yes Yes No AVERAGE 155 AVERAGE Degradation Yes Degradation No Degradation 160 AVERAGE Degradation Yes Degradation No Degradation

These results show that the film according to the invention is not very sensitive to shrinkage and sticks to the sealing bars only at high temperature (close to the Vicat softening temperature).

The multilayer film was also subjected to a heat shrinkage test.

A disk 10 cm in diameter was cut from the stretched film and subjected to a temperature of 120° C. for 1 min. At the end of this step, the ribs of the disc are remeasured and the percentages of retraction calculated.

The results obtained show a shrinkage in the weak machine direction (3.5%) and a zero shrinkage in the transverse direction.

The surface tension of the multilayer film was determined by an angle measurement test of a drop on the surface of the film. The polarity is deduced from the use of different liquids.

The results obtained show that the EVOH surface of the multilayer films according to the invention have a significant polar component and that stretching improves said component.

Claims (21)

Multilayer film (1), comprising:
- an outer layer (2) comprising ethylene polyvinyl alcohol (EVOH)
- a binder layer (3),
- a layer comprising polyethylene (PE) (4) characterized in that said binder layer (3) is inserted between said outer layer (2) comprising ethylene polyvinyl alcohol (EVOH) and said layer comprising polyethylene (PE ) (4). Multilayer film (1) according to the preceding claim comprising:
a first outer layer (2) comprising ethylene polyvinyl alcohol (EVOH) combined with,
a first binder layer (3) associated with,
a first layer of polyethylene (PE) (4),
a second layer of polyethylene (PE) (4) combined with,
a second binder layer (3) associated with,
a second outer layer (2) comprising ethylene polyvinyl alcohol (EVOH). Multilayer film (1) according to the preceding claim, characterized in that it further comprises at least one additional layer between said first layer of polyethylene (PE) (4) and said second layer of polyethylene (PE) (4). Multilayer film (1) according to the preceding claim, characterized in that the said additional layer consists of plastomer. Multilayer film (1) according to claim 1 consisting of five successive layers:
a first outer layer (2) comprising ethylene polyvinyl alcohol (EVOH),
a first binder layer (3),
a layer of polyethylene (PE) (4),
a second binder layer (3),
a second outer layer (2) comprising ethylene polyvinyl alcohol (EVOH). Multilayer film (1) according to one of the preceding claims, characterized in that the said outer layer (2) comprising polyvinyl ethylene alcohol (EVOH) comprises between 24% molar and 48% molar ethylene. Multilayer film (1) according to one of the preceding claims, characterized in that the said outer layer (2) comprising polyvinyl ethylene alcohol (EVOH) comprises between 29% molar and 38% molar ethylene. Multilayer film (1) according to one of the preceding claims, characterized in that the said binder layer (3) comprises a polyethylene grafted with maleic anhydride. Multilayer film (1) according to one of the preceding claims, characterized in that the said layer comprising polyethylene (PE) (4) has a density of between 0.900 and 0.962 g/cm ³ . Multilayer film (1) according to the preceding claim, characterized in that the said layer comprising polyethylene (PE) (4) has a density of between 0.918 and 0.940 g/cm ³ . Multilayer film (1) according to one of the preceding claims, characterized in that it is produced by flat die coextrusion, inflation coextrusion or by lamination. Multilayer film (1) according to one of the preceding claims, characterized in that it has a thickness of between 40 and 200 μm. Multilayer film (1) according to one of the preceding claims, characterized in that it has a thickness of between 50 and 150 μm. Process for preparing a stretched film, characterized in that it comprises:
- a step of providing a multilayer film (1) according to claim 13
- a step consisting in stretching in at least one direction the film provided in the preceding step at a temperature of at least 90° C. until the thickness of the stretched film obtained is less than 50 μm. Process for preparing a stretched film according to Claim 14, characterized in that it further comprises a surface treatment step, subsequent to the step consisting in stretching the film, chosen from the group consisting of the corona treatment, the vacuum plasma processing, atmospheric plasma processing, coating, gravure printing, flexogravure printing, rotogravure printing, physical vapor deposition, chemical vapor deposition, assisted chemical vapor deposition by plasma. Process for preparing a stretched film according to one of Claims 14 to 15, characterized in that the step consisting in stretching the film consists in stretching the said film in a single direction. Stretched film characterized in that it is obtained by a process according to one of Claims 14 to 16. Stretched film according to one of Claims 14 to 17, characterized in that it has a modulus of rigidity at least equal to 500 MPa. Stretched film according to one of Claims 14 to 18, characterized in that it has a vapor barrier value of less than 10 g/m ² /d. Stretched film according to one of Claims 14 to 19, characterized in that it has an oxygen barrier value of less than 2 cm ³ /m ² /d. Film comprising the stretched film according to one of Claims 14 to 20, characterized in that it comprises less than 5% by mass of EVOH.