Multilayer structure for food packaging

Abstract

The present invention relates to a multilayer structure (1) for food packaging comprising: one or more central layers (10) of polymeric material stacked one on the other and defining a central assembly (11) having two free first opposite surfaces (11a, 11b); a barrier layer (20) on each free first surface (11a, 11b) of the central assembly (11) having a relative second barrier surface (20a, 20b), each barrier layer (20) is an ethylene-vinyl-alcohol (EVOH) layer.

Description

[0001] Title: “Multilayer structure for food packaging” DESCRIPTION Technical Field The present invention relates to a multilayer structure for a food package, in accordance with the preamble to claim 1. The object of the present disclosure is used in the field of food packaging. It is further object of the present invention a process for production of the multilayer structure and the food package made with the multilayer structure. State of the art Typically, each wall of the food package, for example a bag, typically has a metallized external layer with the following layering, proceeding from the exterior towards the interior: polyethylene-metallized polyester - polyethylene, and at least one layer of polyethylene, preferably three layers of polyethylene. In some cases, food package also involves a barrier layer on the exterior side. Such a multilayer structure is obtained by coupling separately the layers one on the other using adhesive layer and / or direct coupling such as by pressure. Once the multilayer structure is made, a food package can be produced by coupling separately the layers of each wall and then performing the peripheral heat sealings and, subsequently, transverse cuts to separate one bag from the next, after eventually having inserted beforehand in a wall of the package a mouthpiece for filling the same or having arranged a closure for the package. The known multilayer structures described have, however, disadvantages mainly focused on the recyclability and mutual coupling of the layers. Furthemore, in known multilayer structures, the adhesive layer if not correctly associated to the inner layers could cause the separation of the attached layer. Such behaviour reduces the service life of such multilayer structure and if involved in the filled packages the loss and damages of the food. Object of the invention In this context, the technical task underlying the present invention is to propose a multilayer structure for food packaging which overcomes the drawbacks of the prior art mentioned above In particular, it is an object of the present disclosure to provide a multilayer structure for food packaging flexible and resistant able to provide a correct coupling of layers with a high service life as well as with recyclability properties better than multilayer structures in the state of the art. As noted, a major drawback of known high-barrier multilayer structures is their lack of recyclability, which stems from the lamination of incompatible polymers such as PET and PE. This practice results in packaging waste that cannot be effectively reprocessed in standard recycling systems. It is, therefore, a primary object of the present invention to provide a multilayer structure for food packaging that offers high barrier performance while being fully compatible with existing recycling streams. The invention achieves this object by providing a structure wherein the vast majority of its mass consists of a single polymer type (either polyethylene or polypropylene), and wherein the essential barrier materials, such as EVOH, are incorporated in sufficiently small quantities so as not to interfere with the recyclability of the main polymer matrix as well as providing couplings between the layers and an overall structure which facilitates recyclability. LIST OF DRAWINGS Further features and advantages of the present invention will become more apparent from the description of an exemplary, but not exclusive, and therefore non- limiting preferred embodiment of multilayer structure for food packaging comprising, as illustrated in the appended drawings, in which: - Figure 1 shows schematic section view of the multilayer structure according to a first embodiment of the present disclosure; - Figure 2 shows schematic section view of the multilayer structure according to a second embodiment of the present disclosure; - Figure 3 shows schematic section view of the multilayer structure according to a third embodiment of the present disclosure; - Figure 4 shows schematic section view of the multilayer structure according to a fourth embodiment of the present disclosure; DETAILED DESCRIPTION Even if not explicitly highlighted, the individual features disclosed with reference to the specific embodiments shall be understood as accessory to and / or interchangeable with other features disclosed with reference to other embodiments. With reference to the appended drawings, the present disclosure relates to a multilayer structure for food packaging indicated reference 1. The multilayer structure comprises a plurality of central layers 10 of polymeric material stacked one on the other. Preferably, the plurality of central layers 10 is extruded together. It is to be noted that the layer in the multilayer structure 1 is stacked along a stacking direction X-X perpendicular to the layers. The central layers 10 define a central assembly 11 having two free first opposite surfaces 11a, 11b. Preferably, the central assembly 11 comprises only central layers 10. Such first opposite surfaces 11a, 11b are configured to receive and coupled with other layers of the multilayer structure 1. Namely, the first surfaces 11a, 11b are defined on the opposite side of the central assembly 11 of one or more central layers 10. The multilayer structure 1 comprises a barrier layer 20 on each free first surface 11a, 11b of the central assembly 11. Namely, the multilayer structure 1 comprises at least two barrier layers 20 on the opposite sides of the central assembly 11. It is to be noted that each barrier layer 20 has a relative free second surface 20a, 20b. The other surface of each barrier layer 20 is coupled with the relative first free surface 11a, 11b. It is to be noted that the free second surfaces 20a, 20b are configured to be coupled to eventually further layers of the multilayer structure. According to the preferred embodiment, each barrier layer 20 is an ethylene- vinyl-alcohol EVOH layer. In this way, the multilayer structure 1 defines a barrier assembly 21 having at the opposite sides the two barrier layers 20 of EVOH. Thanks to two opposite EVOH layers, the second surfaces 20a, 20b can be used as bonding surface for metallisation and / or anchor the metallisation of the multilayer structure in a lamination / coextrusion lamination step. Thanks to the presence of EVOH on the opposite sides gives to the barrier assembly 21 bonding property to the adhesive layers used for bonding with other films and / or layers. Since EVOH is wetting, it is configured to be a good surface to bond with the adhesive enhancing the adhesion in the lamination phase. Preferably, the barrier assembly 21 is produced by an extrusion / coextrusion process. According to a preferred embodiment, the central assembly 11 and the barrier layers 20 are separated by a tie layer 30 configured to couple the barrier layers 20 to the central assembly 11. Alternatively,, the central assembly 11 and the barrier layers 20 are associated directly one to the other for example shown in figure 1. Namely, the tie layers 30 allow the mutual coupling of the barrier layers 20 to the relative free first surfaces 11a, 11b of the central assembly 11. Preferably, each tie layer 30 has a thickness in a range of 1 to 5 µm as a function of the plastic material of the central layers for material compatibility. According to one embodiment, each tie layer 30 is plastic material such as binding resin with functionalised polymers. According to one embodiment, the polymeric material of the central layers 10 is selected from polypropylene, polyethylene or a combination thereof. Preferably both polypropylene and polyethylene layers can include mono- oriented type and / or bio-oriented type. The polyethylene layers can include all grades of polypropylene resins such as homopolymer, copolymer randomic, copolymer heterophasic or a combination thereof. The polyethylene layers can include all grades of polyethylene resins PEAD, LDPE, MDPE, LLDPE or a combination thereof. It is to be noted that both polypropylene and polyethylene can be produced in blown or cast machine. According to the one embodiment, the central layers 10 have a thickness in a range variable between 2 to 4 µm. According to the one embodiment, the barrier layers 20 have a thickness in a range variable between 2 to 4 µm. The thicknesses are measures along the stacking direction X-X. According to one embodiment, for example theine shown in figures 3 and 4, the multilayer structure 1 further comprises a first outer layer 40 configured to define an outer surface 40a of a food package and a second outer layer 50 configured to define an inner surface 50a of the food package. The first outer layer 40 and the second outer layer 50 are associated to a respective barrier layer 20 on opposite sides of the central assembly 11 and then to the barrier assembly 21. Namely, the first outer layer 40 and the second outer layer 50 are respectively associated and coupled to a free surface on the opposite sides of stacked layers. Preferably, each outer layer 40, 50 comprises one or more films selected from polypropylene, polyethylene film or a combination thereof. According to the embodiment for example shown in figures 3 and 4, the multilayer structure 1 further comprises an adhesive layer 60 arranged between the barrier layers 20 and the first and second outer layers 40, 50. Namely, each adhesive layer 60 is applied on each free second surface 20a, 20b of the barrier layers 20. Preferably, each adhesive layer 60 can be solventless or solvent based. More preferably, each adhesive layer 60 can comprise all kinds of adhesive used for bond layers and films. According to the embodiment shown in figures 3 and 4, the multilayer structure 1 further comprises an ink layer 70 arranged between the first outer layer 40 and the relative adhesive layer 20. Preferably, the ink layer 70 can be a flexography, rotogravure or off set. It is to be noted that the ink layer 70 can comprise inks solvent based or without solvent. According to one embodiment as shown in figure 4, at least the barrier layer 20 associated to the first outer layer 40 has a metalized coating 80 which defines the relative free second surface 20a on which is applied the adhesive layer 60. It is to be noted that such combination provides excellent oxygen barrier properties. Namely, the oxygen permeability values obtained are significantly better than any other packaging structure which has encountered using PE + EVOH + METALLIZATION. An indication of such oxygen permeability is reported in the following table related to the OTR tests.

[0002] In the following, it has been reported oxygen permeability rate (TPO₂) or OTR at 23°C under dry conditions and 1 atm of partial oxygen pressure gradient of a state of art conventional multilayer structure Sample TPO₂ (mL (NTP).m⁻².day⁻¹) M IV CV (%) PE + MET PET + TRANS PET 1.02 0.76- 1.25 20.1 structure (NON-RECYCLABLE) Notes: ^ Values refer to four determinations. ^ M - mean; IV- variation interval; CV- coefficient of variation. ^ Although the oxygen permeability rate is normally expressed in mL (NTP).m⁻².day⁻¹, in the international system of units it is expressed in mol. m⁻².s⁻¹, where 1mL (NTP) is equivalent to 44.62µmol and 1 day is 86.4x10³s. It is to be noted that the state of the art is represented by a packaging material that is explicitly defined as non-recyclable. The table details a structure made of PE + Metallized PET + Transparent PET, described as "NON-RECYCLABLE", which has an average oxygen permeability rate (OTR) of 1.02 mL / m²·day at 23°C under dry conditions. When compared to the present invention, this state-of-the-art material is not better in terms of oxygen permeability. The above reported table reports that the tested multilayer structure has an OTR of just 0.04 cc / (m²·atm·24h) under the same conditions (23°C, 0% RH). Since a lower OTR value indicates a better oxygen barrier, the invention demonstrates significantly superior oxygen permeability compared to the non-recyclable prior art structure. Furthermore, the use of EVOH in the outer layers of the film to ensure good adhesion of the metallization. Preferably, the metalized coating can be ALOX, SIOX types or standard metallization. According to one embodiment, the central assembly 11 comprises a range of from two to eight of central layers 10 of polyethylene, while the first and the second outer layers 40, 50 comprise polyethylene films. Preferably, the central assembly 11 comprises five central layers 10. It is to be noted that the multilayer structure of the present embodiment can comprise or not a metalized coating 80 and it comprises an ink layer 70 and tie layers 30. According to an alternative embodiment, the central assembly 11 comprises a range of from two to eight of central layers 10 of polypropylene, while the first and the second outer layers 40, 50 comprise polypropylene films. Preferably, the central assembly 11 comprises five central layers 10. It is to be noted that the multilayer structure of the present embodiment can comprise or not a metalized coating 80 and it comprises an ink layer 70 and tie layers 30. In the following, the multilayer structure properties have been reported. The multilayer structure tested comprise two EVOH layers, relative tie layers and five central polyethylene layers

[0003] The tested multilayer structure has the following mechanical properties: OTR and WTVR Test method ASTM D3985-10 / ASTM F1249-20 Test condition OTR WVTR T (°C) RH (%) cc / (m².atm.24h) g / (m².24h) 23 0 0,04 37,8 90 0,57 Tensile strength Test method ASTM D882-18

[0004] Puncture resistance Test method ASTM F1306-21

[0005] It is further object of the present invention a production process for the multilayer structure for food packaging previously described. The production process comprises the step a) of providing one or more central layers 10 of polymeric material and the step b) of providing barrier layers 20 of ethylene-vinyl-alcohol (EVOH). Once such layers are provided the production process comprises the step c) of extruding the assembly of such layers. Namely, the step c) extrudes the plurality of central layers 10 to define the central assembly 11 having two free first opposite surfaces 11a, 11b and the barrier layers 20 on the free first opposite surfaces 11a, 11b. in this way the barrier assembly 21 is extruded. In this way, the barrier assembly 21 has at opposite sides the free second surfaces 20a, 20b. Preferably, in the step c) the EVOH layers are extruded on the central assembly 11 by the interposing a tie layer 30 between the central assembly 11 and the relative EVOH layers 20. According to an alternative embodiment, in the step c) the EVOH layers are directly extruded on the central assembly 11. According to one embodiment, the production process further comprises the step d) of printing a first outer layer 40 configured to define an outer surface 40a of a food package and a second outer layer 50 configured to define an inner surface 40a of the food package. Upon printing the layers, the production process comprises the step e) of laminating the first outer layer 40 and the second outer layer 50 on free second surfaces 20a, 20b of the extruded barrier layers 20 applying an adhesive layer 60 therebetween. Afterwards, the production process further comprises the step f) of drying adhesive layers 60 of the laminated layers preferably function of curing time of the adhesive layer 60. Upon drying, the multilayer structure 1 can be used for the package or bag production. According to one embodiment, the step b) comprises the step b1) of coextruding a metalized coating 80 on the barrier layers 20 on which at the step e) the first outer layer 40 will be associated. The step b1) defines with the metalized coating 80 the free second surface 20a on which the adhesive layer will be applied. According to one embodiment, the step e) comprises a step of applying a provided ink layer 70 on the adhesive layer 60 which will be associated to the first outer layer 40 before the relative lamination of the first outer layer 40 on the free second surface 20a. It is further object of the present invention a food package, such as a bag. The food package comprises two opposite facing walls heat sealed one to another along a peripheral line. Such walls comprise the multilayer structure 1 and have an inner surface 50a faced to an inner volume of the food package and an opposite outer surface 40a.

Claims

CLAIMS 1. Multilayer structure (1) for food packaging comprising: - a plurality of central layers (10) of polymeric material stacked one on the other and defining a central assembly (11) having two free first opposite surfaces (11a, 11b); - a barrier layer (20) on each free first surface (11a, 11b) of the central assembly (11) having a relative free second surface (20a, 20b) - each barrier layer (20) is an ethylene-vinyl-alcohol (EVOH) layer. - the central assembly (11) and the barrier layers (20) are separated by a tie layer (30) configured to couple the barrier layer (20) to the central assembly (11); - a first outer layer (40) configured to define an outer surface (40a) of a food package and a second outer layer (50) configured to define an inner surface (50a) of the food package, the first outer layer (40) and the second outer layer (50) being associated to a respective barrier layer (20) on opposite sides of the central assembly (11), each outer layer (40, 50) comprising a film selected from polypropylene, polyethylene film or a combination thereof; - an adhesive layer (60) arranged between the barrier layers (20) and the first and second outer layers (40, 50), each adhesive layer (60) being applied on each free second surface (20a, 20b) of the barrier layers (20) characterized in that - at least the barrier layers (20) associated to the first outer layer (40) has a metalized coating (80) which define the relative free second surface (20a) on which is applied the adhesive layer (60).

2. The multilayer structure (1) according to claim 1, wherein the polymeric material of the central layers (10) is selected from polypropylene, polyethylene or a combination thereof.

3. The multilayer structure (1) according to claim 1 or 2, wherein: - the central layers (10) have a thickness in a range of 2 to 4 µm; - the barrier layers (20) have a thickness in a range of 2 to 4 µm.

4. The multilayer structure (1) according to any claims 1 to 3, further comprises an ink layer (70) arranged between the first outer layers (40) and the relative adhesive layer (20).

5. The multilayer structure (1) according to any claims 1 to 4, wherein: - the central assembly (11) comprises a range of from two to eight of central layers (10) of polyethylene; - the first and the second outer layers (40, 50) comprises polyethylene film.

6. The multilayer structure (1) according to any claims 1 to 5, wherein - the central assembly (11) comprises a range of from two to eight of central layers (10) of polypropylene; - the first and the second outer layers (40, 50) comprises polypropylene film.

7. Production process for the multilayer structure for food packaging according to claims 1 to 6, comprising the step of a) providing a plurality of central layers (10) of polymeric material; b) providing barrier layers (20) of ethylene-vinyl-alcohol (EVOH); c) extruding: - the plurality of central layers (10) to define the central assembly (11) having two free first opposite surfaces (11a, 11b) and- the barrier layers (20) on the free first opposite surfaces (11a, 11b) by the interposing a tie layer (30) between the central assembly (11) and the relative EVOH layers (20) d) printing a first outer layer (40) configured to define an outer surface (40a) of a food package and a second outer layer (50) configured to define an inner surface (40a) of the food package; e) laminating the first outer layer (40) and the second outer layer (50) on free second surfaces (20a, 20b) of the extruded barrier layers (20) applying an adhesive layer (60) therebetween, f) drying adhesive layers (60) of the laminated layers. wherein the step b) comprises the step b1) of coextruding a metalized coating (80) on the barrier layers (20) on which at the step e) the first outer layer (40) will be associated, the step b1) defining with the metalized coating (80) the free second surface (20a).

8. The production process according to claim 7, wherein the step e) comprises a step of applying a provided ink layer (70) on the adhesive layer (60) which will be associated to the first outer layer (40) before the relative lamination of the first outer layer (40) on the free second surface (20a).

9. A food package comprising: - two opposite facing walls heat sealed one to another along a peripheral line, said walls comprising a multilayer structure according to any claims 1 to 6 and having an inner surface (50a) and outer surface (40a).

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