WO2023285496A1

WO2023285496A1 - A metallized paper with improved resistance to hygroexpansive strain

Info

Publication number: WO2023285496A1
Application number: PCT/EP2022/069525
Authority: WO
Inventors: Alexey VISHTAL; Jenni Irina JUKARAINEN; Abhijit Bhattacharya
Original assignee: Société Des Produits Nestlé S.A
Priority date: 2021-07-16
Filing date: 2022-07-13
Publication date: 2023-01-19

Abstract

The present invention is primarily directed to a multilayer paper-based metallized packaging material (1) comprising, from its outer side to its inner side: - a paper layer (2) having a grammage comprised in the range of 40 to 120 g/m2, - a first pre-metallization dispersion coated layer (3) comprising a polymer having a low glass transition temperature (Tg), - a second pre-metallization dispersion coated layer (4) comprising a polymer having a high Tg, - a vacuum deposited metallization layer (5), and - a dispersion coated sealing layer (6).

Description

A METALLIZED PAPER WITH IMPROVED RESISTANCE TO HYGROEXPANSIVE STRAIN

Alexey (NMN) VISHTAL Jenni Irina JUKARAINEN Abhijit (NMN) BHATTACHARYA

Field of the invention

The present invention concerns a paper-based packaging material recyclable in the recycling paper stream, having high barrier properties and being highly resistant to degradation of its barrier properties by moisture caused by moisture uptake in paper.

Background of the invention

Plastic packaging is used frequently in the economy and in people's daily lives. It has multiple advantages, such as its flexibility and its light weight. Such a weight reduction contributes to fuel saving and C0 reduction during transport, for example. Its barrier properties help to reduce food waste due a positive effect on increasing shelf life. The barrier properties also help to secure food safety.

However, according to the European strategy for plastics in a circular economy, recently published by the European Commission, around 25.8 million tons of plastic waste are generated in Europe every year with less than 30% of such waste being collected for recycling and between 150000 to 500000 tons of plastic waste entering the oceans every year.

To ensure that plastic waste is reduced, significant efforts are made in the industry and in commerce, for instance to find packaging solutions based on paper rather than on plastic. However, replacing plastics with paper in food packaging is not an easy task. A change in packaging material must not compromise consumer safety. The packaging must serve to protect the food but must also be robust enough to be handled by machines during the production process, and it must allow that the food product is protected effectively.

Therefore, multilayer packaging materials have been developed which include a paper or cardboard base layer, to which is added at least one layer of a plastic polymer and also possibly at least one layer of metal.

Generally, in the known paper-based multilayer packaging materials, the main role of the polymer layer is to provide barrier properties against oxygen transfer ("OTR") as well as to act as the metal receptive layer in vacuum deposition process, and the main role of the metal layer is to provide robustness as well as barrier properties against moisture ("WVTR").

When manufacturing multilayer paper-based packaging material structures today, known techniques involve applying a layer of plastic by either extrusion (extrusion-lamination or extrusion-coating), or similarly by an adhesive lamination process. However, with such techniques the thickness of the plastic film applied onto the paper is necessarily high.

The second issue with extruded or adhesive-laminated polymers in multilayer structures as described above, is that even for the lowest possible thicknesses of applied polymer, the cohesive strength of the polymer film is very high and the level of adhesion of the polymer to the paper or cardboard (i.e. cellulosic) substrate is also high. This prevents such polymer to detach from the substrate when recycled, and prevents recycling and repulping of the cellulosic fiber portion in a conventional paper-stream recycling process.

Therefore, later during the recycling process, the multilayer structure comprising a mixture of paper and plastic (polymer) films either extruded (by classic techniques as extrusion-lamination or extrusion coating) or adhesive-laminated, cannot be recycled in a paper-stream recycling process because the plastic layer is too thick to be dispersed and at the same time the same layer has cohesion strength and adhesion levels to the adjacent layers of the structure, which are way too high to be separated from the other layers of materials, especially from the paper fibres. The extruded or adhesive- laminated plastic film therefore remains almost intact within the paper pulp bath, hence making it difficult to recycle paper pulp from the repulping process.

On the other hand, since recyclability of such paper-based multilayer structures in a conventional paper stream recycling process is not possible, specific recycling processes have been developed, but they are complex, expensive, energy consuming and characterized by a relatively low yield of paper fibres that are actually recycled (around 60% from the total amount of packaging materials in the entire structure). Such specific recycling processes are therefore insufficiently environmentally friendly from a disposal and recycling perspective. There is also room for improving the recyclability of the rest of the packaging material (i.e. the plastic polymer and the metal parts (e.g. aluminium parts).

WO 2000/076862 A9 describes in this respect a laminate structure for packaging applications comprising a paper substrate, and at least one polymer/nanoclay composite layer having clay particles with a thickness ranging from 0.7 to 9 nanometers applied to said paper substrate with an extrusion or lamination process.

However, there Similarly, WO 2000/077300 A1 and WO 1996/013380 A1 disclose multilayer packaging materials wherein thick plastic layers are either extruded, co-extruded or laminated to a cellulosic layer.

There is still a need in the art to even further improve the barrier and recyclability properties of such a paper-based packaging materials. Especially, there is a need for a packaging material that can be easily recycled in the recycling stream for paper or cardboard.

Furthermore, packaging materials for human or animal consumption are often not industrially produced at their exact point of sale or consumption.

Very often, the manufacturing and packing facility is distant from the points of sale, which are themselves distant from their point of consumption. Also, such food products can be produced, sold and/or consumed in countries and places where ambient atmosphere contains high levels of humidity.

At the same time, the packaged food, either for human or animal consumption, can be very sensitive to oxidation and/or moisture, hence the need for constant high barrier of the packaging material against oxygen and moisture transfers between the outside and the inside of the package. Ensuring high and constant barrier throughout the shelf life of the product - which can be 18 months, 24 months, or sometimes even more - requires a packaging material which is resistant to mechanical stress applied during forming, filling and closing of the package, during transportation and handling, but also resistant to other types of aggressive conditions which can damage the barrier layers integrity.

It was found by the inventors that, when stored in an environment where the atmosphere contains a high level of humidity, typically when ambient air contains more than 65% Relative Humidity (RH), known multilayer paper-based barrier material start to deteriorate after a few days, and their barrier properties decrease significantly. In such cases, a proper conservation of the food contents cannot be guaranteed anymore. The inventors have found that such deterioration is due to moisture intake within the constitutive materials of the packaging multilayer structure. Said moisture intake triggers so-called "hygroexpansive strain" on the material structure.

More precisely, hygroexpansive strain was found to be induced on the paper component of the multilayer structure, when it is exposed to elevated relative humidity (65-100% RH) by the transversal swelling of cellulosic fibre, caused by adsorption of water vapour from the ambient atmosphere. It was found by the inventors that hygroexpansive strain induced in the cross-direction (CD) of paper, can be as high as 2-3%.

The polymers used in multilayer materials based on paper and a metal layer, have conventionally a low glass transition temperature (low "Tg") and thus exhibit a low resistance to stretching at room temperature (15°C) or above. Therefore, hygroexpansive strain induced on paper by high relative humidity ("RH"), can be easily transferred to a vacuum-deposited aluminium layer and disrupt it, which will lead to inevitable and non-reversible negative changes in water vapour and oxygen barriers. In other words, due to the swelling of fibres in the paper layer, the volume of said paper layer expands, which is not the case for the adjacent layers, in particular, the polymeric layer and the metallic layer if one is present. In principle, polymeric layers, and metallic layers are not subject to swelling caused by the moisture uptake. Due to this difference in volume expansion between the paper layer and polymeric/metal layer, and due to the good adhesion between the paper layer and the polymer layer, a high shear and/or tensile stress is generated into the barrier layers that are adhered to the paper base layer. Therefore cracking or micro-tearing, through-holes and the like can appear throughout the polymer and metallic barrier layers. This is of course extremely detrimental to the barrier properties of the whole packaging structure.

Having considered the above, there is a need for a paper-based packaging laminate material that is resistant to mechanical stress (allowing to manufacture packages with the known industrial paper forming techniques), that also features high barrier properties against oxygen ad moisture transfers, which has a greatly reduced amount of plastic polymer contents such that it can be recycled in a conventional recycling paper stream. Furthermore and mainly, there is a need for providing such a packaging material that is highly resistant to hygroexpansive strain, when placed in an atmosphere with high Relative Humidity levels, such as for instance those that often occur in tropical countries.

Summary of the invention

The objectives set out above are met with a multilayer paper-based metallized packaging material according to the independent claim 1, and its dependent claims.

In particular, these objectives are met with a multilayer paper-based metallized packaging material comprising, from its outer side to its inner side:

- a paper layer having a grammage comprised in the range of 40 to 120 g/m², - a first pre-metallization dispersion coated layer comprising a polymer having a lowTg and applied in an amount of 2 to 8 g/m², and said low Tg polymer being selected within the list of: ethylene acrylic and methacrylic acid copolymers, styrene acrylate, styrene-butadiene, propylene acrylic and methacrylic acid copolymers, polyols - such as ethylene vinyl alcohol or polyvinyl alcohol - or polyesters with an elastic modulus less than 2 GPa at the temperature of 20 °C, their blends or copolymers, or a combination thereof,

- a second pre-metallization dispersion coated layer comprising a polymer having a high Tg and applied in an amount of 1 to 5 g/m², said high Tg polymer being selected within the list of: polyurethane, cellulose acetate, cellulose nitrate, polyamide, aromatic polyester with elastic modulus higher than 2 GPa at the temperature of 20 °C, or a combination thereof,

- a transfer metallization or vacuum deposited metallization layer of aluminium, aluminium oxide (AIOx) or silicon oxide (SiOx), having an optical density comprised between 2 and 5 (thickness equivalent to 20-500 nm), and

- a dispersion coated sealing layer.

By "outer side" of the packaging multilayer material it is meant the side facing the ambient atmosphere after the material has been formed as a closed package.

By "inner side" of the packaging multilayer material it is meant the side intended to face the filled food contents of a package produced from said packaging laminate.

By "high Tg", it is meant polymers which have a glass transition temperature above 60°C, preferably above 70°C, more preferably above 75°C. In the scope of the present invention, polymers having a so-called "high Tg" are generally selected within the list of polyurethane (PU), polyvinylalcohol (PVOH), polymethylenacrylates, styrene acrylates, acrylonitrile butadiene styrene, cellulose derivatives (nitrate, acetate, etc.), or a combination thereof.

By "low Tg", it is meant polymers which have a glass transition temperature below 40°C, preferably below 15°C. In the scope of the present invention, polymers having a so-called "low Tg" are generally selected within the list of : ethylene acrylic acid, ethylene methacrylic acid and their copolymers, low density polyethylene (LDPE), polypropylene (PP), high density polyethylene (HDPE), polyvinylidene chloride (PVDC), or a combination thereof.

By "metallization" it is meant that atoms of a metal or a metalloid are deposited onto a support surface.

The invention as claimed and described therein proposes to apply a high Tg polymer layer, on top of low Tg polymer layer, in order to minimize the transfer of tensile stresses which are induced by expanded paper on the low Tg polymer. High Tg polymers have a high elastic modulus and hence, the extent of plastic deformation induced on a vacuum-deposited metal layer, by the expansion of swollen paper is greatly reduced or even completely avoided.

Furthermore, the combination of high Tg and low Tg polymers in separate layers was also surprisingly found to be beneficial in case the material is heat sealed for forming finished packages. When a heat sealable coating (having a low Tg and low melting temperature) is applied directly on the metallized layer, it normally enables low temperature sealing of the material (i.e. between 65°C and 110°C). However, as the polymer melts and flows under heat and pressure, the heat seal process leads to entanglement and shear of the adjacent metallized layer (due to the pressure exerted by the heated sealing jaws), and thus it may impact on final barrier integrity of the seal of the finished package, which is of course undesirable. According to the present invention, the presence of a high Tg polymer layer attached to the metallized layer, and placed between said metallized layer and the innermost low Tg sealing layer, allows to prevent entanglement and shear damage to the metallized layer, because the high Tg polymer layer in contact with the metal layer remains in a non-molten and/or non-softened state, even during the heat sealing operation, while simultaneously, the innermost low Tg polymer sealing layer can be still absorb the heat provided by the sealing jaws, and melt without damaging the metal layer.

Generally, the structure of the multilayer packaging material according to the present invention prevents the detrimental effects of swelling of the paper by having an intermediate set of layers between paper and metal: one intermediate layer that "absorbs" the expansion of the paper, the other intermediate layer in direct contact with the metal layer which is sufficiently rigid to prevent transfer of the paper volume expansion to the metal. Importantly, one single layer of a high Tg polymer could not work because it would not fold easily and would compromise the barrier properties of the finished package. In the present invention, the thickness of the high Tg pre-metallization layer is only 1-2 microns, hence not subject to damage when the whole material is folded (e.g. during operations of forming a packaging). In one optional embodiment of the invention, a second layer of a polymer having a high Tg is applied on the other side of the metallized layer, such that the metallized layer is "sandwiched" between two layers of dispersion coated polymer having a high Tg. In this case, the inventors have found that the resulting packaging material features a very high resistance to tearing.

Generally, in the context of the present invention, all polymers are applied by a dispersion coating process. Due to dispersion coating, the overall thickness of polymer material in the structure is extremely reduced compared to the thickness of paper and paperboard (i.e. cardboard) material, therefore the inventors have achieved to overcome the technical limitations of the known multilayer barrier structures, and achieve a packaging multilayer structure with excellent barrier properties against oxygen and moisture transfer, as well as resistance to liquid contact from their inner or outer surfaces, while achieving a total contents of cellulosic fibres comprised preferably up to 95% of the overall material weight. Furthermore, dispersion coating of polymer avoids high cohesion and high adhesion of the polymer and therefore solves the recyclability problem (solid particles of polymer dispersed in a water carrier medium instead of liquid polymer applied to substrate). The fact that the inventors succeeded in forming a multilayer structure completely deprived of polymer layers formed by extrusion (extrusion-lamination or extrusion coating), provides a multilayer structure with a ratio of cellulosic fibre to non- cellulosic material, which is extremely high in fibre contents, and wherein the polymer layers are easy to disintegrate in repulping process due to the relatively low cohesion strength of the polymer, and also the relatively low adhesion of the same polymer to the rest of the substrate (especially the cellulosic fibres). The resulting structure therefore demonstrates excellent repulping capabilities and high fibre yield which allows it to be accepted in waste paper collection in the most of the countries. The very low content of non-cellulosic polymer and vacuum-deposited metal materials, makes the whole material of the invention easily disintegrated, dissolved and separated during recycling processes designed for cellulosic materials like paper or cardboard, unlike existing multi-layer barrier structures known from the art.

The present invention is further directed to a process for manufacturing a multilayer paper-based metallized packaging material, as claimed in the appended claims. The invention is also directed to a package for containing an edible product for human or animal nutrition, made from a multilayer paper-based metallized packaging material as described and claimed therein.

Brief description of the drawings

Additional features and advantages of the present invention are described in, and will be apparent from, the description of the presently preferred embodiments which are set out below with reference to the drawings in which:

Figure 1 is a schematic profile cut view of a first embodiment of a multilayer packaging material according to the invention;

Figure 2 is a schematic profile cut view of a second embodiment of a multilayer packaging material according to the invention.

Detailed description of the invention

In a first illustrative embodiment of the invention, illustrated in figure 1, is a multilayer paper-based metallized packaging material 1 comprising, from its outer side to its inner side, the following layers.

It first comprises a paper layer 2 having a grammage of 60 g/m². The paper is a supercalendered wood-free paper made from bleached chemical pulp.

Next to the paper layer 2, and on its inner side is a first pre-metallization dispersion-coated layer 3. The first pre-metallization layer 3 is applied by a dispersion coating process in an amount of about 3 g/m². The first layer of pre-metallization coating provides planarization of the papersurface and also provides an initial barrier to moisture (low water vapour transmission rate (WVTR)). It also provides flexibility to the metallization layer. It preferably has a thickness comprised between 2 and 8 micrometres, more preferably between 2 and 4 micrometres. The polymer used for this first pre metallization layer is an ethylene acrylic acid copolymer, with clay as a mineral filler in an amount of 20% by total weight of the polymer. The ethylene acrylic acid copolymer is chosen such that its glass transition temperature (Tg) is lower than 10°C. The adhesion strength of the polymer to paper 7N/25mm.

Once applied, this layer is dried until the next layer is applied.

The next layer, applied by a dispersion coating process on the inner side of the first pre-metallization layer 3, is a second pre-metallization dispersion-coated layer 4. It is made of cellulose acetate having a glass transition temperature of 195°C (high Tg) and applied in an amount of about 2 g/m².

Onto the second pre-metallization dispersion-coated layer 4 (after it has dried), a metallization layer 5 of aluminium is vacuum deposited. It has an optical density of about 3 (thickness equivalence to about 35 nm). This layer 4 functions as a rigid layer resisting to hygroexpansive strain, and as an oxygen and water barrier promoter in conjunction with metal layer.

Finally, on the innermost side of the multilayer material 1 is a dispersion-coated sealing layer 6. The sealing layer 6 is a heat seal layer made out of ethylene acrylic acid copolymer, applied in an amount of about 5 g/m².

The multilayer paper-based packaging material in this first embodiment is then folded and formed into a flow-wrap type sachet for packing chocolate bars.

In a second illustrative embodiment of the invention, depicted in figure 2, is a multilayer paper-based metallized packaging material 1 comprising, from its outer side to its inner side, the following layers.

First of all, a printing ink layer 7 and an overprint varnish layer 8 are deposited on the outer surface of a paper layer 2. The ink printing layer is deposited in direct contact with the paper, and covered on the outermost side of the material 1 with the overprint varnish layer 8 which is a protective layer. The overprint varnish layer 8 is deposited in a 1.5 g/m² and is an important contributor to hygroexpansive strain reduction because of its substantial moisture barrier properties, which help reducing the rate of moisture intake of the packaging material 1 from the outside environment.

Next to the paper layer 2, and on its inner side is a first pre-metallization dispersion-coated layer 3. The first pre-metallization layer 3 is applied by a dispersion coating process in an amount of about 5 g/m². The first layer of pre-metallization coating provides planarization of the papersurface and also provides an initial barrier to moisture (low water vapour transmission rate (WVTR)). It also provides flexibility to the metallization layer. It preferably has a thickness comprised between 2 and 5 micrometres. The polymer used for this first pre-metallization layer 3 is a pure ethylene acrylic acid copolymer. The ethylene acrylic acid copolymer is chosen such that its glass transition temperature (Tg) is lower than 10°C. The adhesion strength of the polymer to paper 7N/25mm.

Once applied, this layer is let to dry until the next layer is applied.

The next layer, applied by a dispersion coating process on the inner side of the first pre-metallization layer 3, is a second pre-metallization dispersion-coated layer 4. It is made of polyurethane having a glass transition temperature of 80°C (high Tg) and applied in an amount of about 2 g/m².

Onto the second pre-metallization dispersion-coated layer 4 (after it has dried), a metallization layer 5 of aluminium is vacuum deposited. It has an optical density of about 3 (thickness equivalence to about 35 nm). This layer 4 functions as a rigid layer resisting to hygroexpansive strain, and as an oxygen and moisture barrier promoter.

As shown in figure 2, in order to combine both benefits of a reduction of the hygroexpansive strain effects, and a prevention of entanglement and shear cracking of the metal layer by molten polymer during heat sealing, a post-metallization layer 9 of a high Tg polymer can be applied also on the innermost side of the metallized layer 5. One prerequisite is that the level of adhesion between the innermost high Tg polymer and the metallization layer itself shall be higher than 4N/25mm. Generally, the polymer used for such an innermost high Tg post-metallization layer is selected within the same polymers as the ones used for the high Tg pre-metallization layer located at the outer surface of the metal layer. In the embodiment depicted in figure 2, this layer is made of cellulose ester (acetate, nitrate) having a glass transition temperature of 195°C (high Tg) and applied in an amount of about 2 g/m².

Then, a last layer which is a sealing layer 6 is deposited onto the innermost surface of the multilayer packaging material 1. This innermost sealing layer 6 is a heat seal layer comprising a heat sealable polymer applied by a polymer dispersion coating process, in an amount of about 5 g/m². It is made of an ethylene acrylic acid copolymer.

Generally, in the context of the invention, such an optional post metallization layer 6 of a high Tg polymer at the inner surface of the metal layer is of interest in case the sealing layer located at the inner surface of the multilayer material, is a heat seal layer, which is the case in the illustrative embodiment depicted in figure 2. It is not necessary if the sealing layer is a cold seal layer.

It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the appended claims.

Claims

1. A multilayer paper-based metallized packaging material (1) comprising, from its outer side to its inner side: a paper layer (2) having a grammage comprised in the range of 40 to 120 g/m², a first pre-metallization dispersion coated layer (3) comprising a polymer having a low Tg and applied in an amount of 2 to 8 g/m², and said low Tg polymer being selected within the list of: ethylene acrylic and methacrylic acid copolymers, styrene acrylate, styrene-butadiene, propylene acrylic and methacrylic acid copolymers, polyols - such as ethylene vinyl alcohol or polyvinyl alcohol - or polyesters with an elastic modulus less than 2 GPa at the temperature of 20 °C, their blends or copolymers, or a combination thereof, a second pre-metallization dispersion coated layer (4) comprising a polymer having a high Tg and applied in an amount of 1 to 5 g/m², said high Tg polymer being selected within the list of: polyurethane, cellulose acetate, cellulose nitrate, polyamide, aromatic polyester with elastic modulus higher than 2 GPa at the temperature of 20 °C, or a combination thereof, a transfer metallization or vacuum deposited metallization layer (5) of aluminium, aluminium oxide (AIOx) or silicon oxide (SiOx), having an optical density comprised between 2 and 5 (thickness equivalent to 20-500 nm), and a dispersion coated sealing layer (6).

2. A multilayer paper-based metallized packaging material (1) according to claim 1, which further comprises a post-metallization dispersion coating layer (9) located between the inner side of the metallization layer (5) and the outer side of the sealing layer (6), said post-metallization layer (9) being in an amount in the range of 0.5-2 g/m², and comprising a high Tg polymer selected within the list of: polyurethane, cellulose acetate, cellulose nitrate, polyamide, aromatic polyester or polyols - such as ethylene vinyl alcohol or polyvinyl alcohol - with elastic modulus not less than 2 GPa at the temperature of 20 °C, their blends or copolymers, or a combination thereof, applied via polymer dispersion coating technique.

3. A multilayer paper-based metallized packaging material (1) according to any one of the preceding claims, which further comprises a printed layer (7) located on the outer surface of the paper layer, said printed layer (7) being selected within the list of: visible or invisible ink printing, laser printing, embossing or micro-embossing printing, or a combination thereof.

4. A multilayer paper-based metallized packaging material (1) according to the preceding claim 3, which further comprises an overprint varnish protective layer (8) located on the outer surface of said printed layer (7).

5. A multilayer paper-based metallized packaging material (1) according to any one of the preceding claims 1 to 4, wherein said sealing layer (6) comprises a heat sealable polymer applied by a polymer dispersion coating process, in an amount comprised between 3 and 10 g/m², and selected within the list of ethylene acrylic and/or methacrylic acid copolymers, propylene acrylic acid copolymers, polyesters, polyvinylidene chloride (PVDC), polybutylene- succinate, thermoplastic starch, or a combination thereof.

6. A multilayer paper-based metallized packaging material (1) according to any one of the preceding claims 1 to 4, wherein said sealing layer (6) comprises a cold seal polymer applied in an amount of 3-10 g/m² selected within the list of natural rubber latexes formulated with synthetic adjuvants, or a combination thereof.

7. A multilayer paper-based metallized packaging material (1) according to any one of the preceding claims, which has an oxygen barrier transfer rate (OTR) below 10 cm³/m²/day, preferably below 1 cm³/m²/day measured at 23°C and 50 % Relative Humidity.

8. A multilayer paper-based metallized packaging material (1) according to any one of the preceding claims, which has a moisture barrier transfer rate (WVTR) below 1.5 g/m²/day, preferably below 0.5 g/m²/day, measured at 38°C and 90% Relative Humidity.

9. A process for manufacturing a multilayer paper-based metallized packaging material (1) according to any one of the preceding claims 1 to 8, characterized in that said process comprises the steps of, in order:

(i) providing a paper layer (2) having a grammage comprised in the range of 40 to 120 g/m², then

(ii) applying onto the paper layer, by a polymer dispersion coating technique, a first pre-metallization layer (3) of a low Tg polymer in an amount of 2 to 8 g/m², said polymer being selected within the list of: ethylene acrylic and methacrylic acid copolymers, styrene acrylate, styrene- butadiene, propylene acrylic and methacrylic acid copolymers, polyols - such as ethylene vinyl alcohol or polyvinyl alcohol - or polyesters with an elastic modulus less than 2 GPa at the temperature of 20 °C, their blends or copolymers, or a combination thereof,

(iii) once the first pre-metallization polymer is dry, applying by a dispersion coating technique a second pre-metallization layer (4) of a polymer having a high Tg onto said first pre-metallization layer, in an amount of 1 to 3 g/m², said high Tg polymer being selected within the list of: polyurethane, cellulose acetate, cellulose nitrate, polyamide, aromatic polyester with elastic modulus higher than 2 GPa at the temperature of 20 °C, or a combination thereof,

(iv) once the second pre-metallization polymer is dry, applying onto the second pre-metallization layer, a vacuum-deposited metallization layer (5) of aluminium, aluminium oxide (AIOx) or silicon oxide (SiOx), having an optical density comprised between 2 and 5 (thickness equivalent to 20-80 nm), and

(v) applying a dispersion-coated sealing layer (6) onto said metallization layer.

10. A process for manufacturing a multilayer paper-based metallized packaging material (1) according to claim 9, which further comprises the step of applying by dispersion coating technique a post-metallization dispersion coating layer (9) located between the inner side of the metallization layer (5) and the outer side of the sealing layer (6), said post-metallization layer (9) being in an amount in the range of 0.5-2 g/m², and comprising a high Tg polymer selected within the list of: polyurethane, cellulose acetate, cellulose nitrate, polyamide, aromatic polyester or polyols - such as ethylene vinyl alcohol or polyvinyl alcohol - with elastic modulus not less than 2 GPa at the temperature of 20 °C, their blends or copolymers, or a combination thereof.

11. A process for manufacturing a multilayer paper-based metallized packaging material (1) according to any one of the preceding claims 9 or 10, which further comprises the step of printing a layer (7) on the outer surface of the paper layer (2), by a printing technique selected within the list of: visible or invisible ink printing, laser printing, embossing or micro-embossing printing, or a combination thereof.

12. A process for manufacturing a multilayer paper-based metallized packaging material (1) according to claim 11, which further comprises the step of applying an overprint varnish protective layer (8) on the outer surface of said printed layer (7) by a dispersion coating technique.

13. A package for containing an edible product for human or animal nutrition, made from a multilayer paper-based metallized packaging material (1) according to any one of the preceding claims 1 to 8.