MULTI-LAYER PACKAGING MATERIAL, A PACKAGE AND A METHOD FOR MANUFACTURING A MUTI-LAYER PACKAGING MATERIAL

Description

TECHNICAL FIELD

The present disclosure relates to the field of the multi-layer packaging materials. More particularly, the present disclosure relates to a multi-layer packaging material that comprises a cellulose-based material layer, a tie coating layer, an intermediate polymeric coating layer, a metallization layer and an inner polymeric coating layer. The present disclosure further relates to a package, e.g., for containing edible and non-edible products, comprising the multi-layer packaging material and to a method for manufacturing the multi-layer packaging material.

BACKGROUND

Different kinds of plastic packaging materials are commonly used in very diverse fields and for a wide variety of applications. Plastic packaging materials are flexible structures which are generally made from multiple polymeric materials, often comprising layers of different polymeric films, deposited on a layer-by-layer basis, to achieve the required properties. These properties are, among many others, flexibility, lightweight, durability and barrier properties to oxygen, moisture, and aromas. Flexibility allows using these materials for different applications and increases the resistance of the packaged products against shocks, bends, twists or other deformations. The weight reduction decreases costs associated to transport. Durability extends the operational life of the material. The barrier properties increase food safety and extend the life of the products contained within the packages made of said packaging materials, contributing to reduce food waste.

Multiple multi-layer packaging materials that include a cellulose-based material layer, for example, paper or cardboard-based layers, and one or several layers of plastic or metal films have been developed in recent years. These plastic and metallized layers provide robustness and barrier properties, especially to gases, moisture, and aromas. However, these combinations of materials are difficult to recycle. In particular, the mentioned plastic layers, generally made of polymers, are deposited in thick layers by means of processes such as extrusion or lamination, which render the material not recyclable by means of paper recycling processes due to the high amount of polymeric material that it contains. Besides, these packaging materials are weak when subjected to mechanical stress. For example, during the package manufacturing process, these multi-layer packaging materials are twisted and folded to conform the package and it has been found that some of their layers break or separate from each other in the areas that undergo greater mechanical stress.

Document US 2023/0272584 discloses a multi-layer metallized paper-based packaging material comprising a paper layer, a pre-metallization coating layer, a metallized layer, and at least one post metallization coating layer. This document further discloses that the pre-metallization coating layer and the post-metallization coating layer are made of butylvinylalcohol (BVOH). The pre-metallization layer is directly deposited on top of the paper layer. However, the butylvinylalcohol and other polyvinylalcohols due to their hygroscopic nature, tend to absorb humidity from the surroundings, negatively affecting their barrier properties. Water uptake from the paper-based layer or from the external environment causes an almost complete loose of the oxygen barrier properties of these materials. In other words, since the paper layer is in direct contact with the pre-metallization layer, gases, such as oxygen (O2), carbon dioxide (CO2) or nitrogen (N2), vapor, moisture, such as water and oil, and aromas can pass through the paper-based layer and affect directly to the BVOH layers. This causes a significant reduction and degradation of the barrier properties of these BVOH layers which, in turn, may affect to the safety, quality and other properties of the product contained within the package formed with the multi-layer metallized paper-based packing material. This problem is especially important when the multi-layer metallized paper-based packaging material is used for, e.g., packaging food, and/or it has to be stored in environments with a high humidity degree, such as inside a refrigerator.

Document WO 2022/229337 A1 describes a metallized paper where a layer of ethylene acrylic acid (EAA) copolymer is applied on top of the paper layer and then a layer of PVOH is applied on top of the EEA copolymer layer. This PVOH is metallized and then, a layer of extruded HPDE is deposited. However, the adhesion of PVOH on EAA tends to be low, causing failures during the twist folding process. In addition, the heat seal strength is negatively affected due to the low adhesion strength of the PVOH-EAA interface generating delamination of the metallized paper.

Document WO 2022/238280 A1 discloses the use of a polyvinylidene chloride (PVDC)-based top layer. However, it is desirable for multi-layer materials to be devoid of chlorine-containing products for environmental and material recycling reasons.

Document US 2023/0382618 A1 describes a metallized paper with a pre-metallization layer composed of a mixture of polymer and lamellar clay. On top of the aluminum layer there is a topcoat layer that provides flexibility, a tie layer, a PVOH layer and a heat sealable layer.

However, it has been found that the use of mineral pigments in the aluminum receiving layer drastically worsens the barrier properties of the material after metallization. In addition, the presence of laminar pigments negatively affects the barrier preservation after the material undergoes the bending processes and mechanical stresses inherent to the container/package forming process.

Thus, there is a need of a multi-layer packaging material that exhibits an improved adherence of the cellulose-based material layer to the rest of layers deposited thereon, that also ensures adequate barrier properties, even when the muti-layer packaging material is subjected to mechanical stress, and that is easy to recycle in conventional paper recycling processes.

DESCRIPTION

A first aspect of the disclosure is a multi-layer packaging material comprising, from its outermost side to its innermost side: a cellulose-based material layer having a grammage from 40 to 120 g/m2; a tie coating layer, the tie coating layer comprising a polymeric binder material; an intermediate polymeric coating layer, the intermediate polymeric coating layer comprising a polyvinyl alcohol (PVA) polymer; a vacuum deposited metallization layer; and an inner polymeric coating layer, the inner polymeric coating layer comprising a polymer selected from: acrylic copolymers; polyesters; polyurethanes; polyester copolymers; polyurethane copolymers; vinyl acetates copolymers; chloride copolymers; and any combination thereof.

As used herein, the outermost side of the multi-layer packaging material refers to the surface outside the packaging and the innermost side of the multi-layer packaging material refers to the surface in contact with the product to be enclosed in the package made with the multi-layer packaging material.

The cellulose-based material layer may be a paper-based layer, a cardboard-based layer, a regenerated cellulose-based layer, a cellophane-based layer, or any other layer made of a cellulose-based material. Preferably, the cellulose-based material layer may have a grammage from 50 to 120 g/m2, more preferably from 60 to 90 g/m2. Such grammages provide an adequate balance between strength and flexibility to the layer.

This cellulose-based material layer, in particular, its specific material or combination of materials, thickness, roughness, porosity, etc., may be further selected to provide an adequate balance between mechanical resistance (tensile strength, elasticity, flexibility, etc.) and surface properties. This balance will be further selected to optimize the deposition of the subsequent coating layers that will provide the barrier properties to the multi-layer packaging material. Both surfaces of the cellulose-based material layer may be subjected to treatments or coatings to make said surfaces smoother and/or more flexible. For example, the coating (e.g., a latex-based coating) applied to the outer surface of the cellulose-based material layer (the printing surface) may be different from the coating applied to the inner surface of the cellulose-based material layer, the latter having, e.g., a greater amount of latex. The cellulose-based material layer may be further selected to have a tensile strength in a range from 6 to 9 Kg/15 mm.

The tie coating layer contributes to smoothing the surface of the cellulose-based material on which it is deposited layer and to filling out porous thereof. This tie coating layer also prepares said surface for depositing the subsequent intermediate polymeric coating layer.

The tie coating layer protects the intermediate polymeric coating layer deposited on the top surface of the cellulose-based material layer whilst ensuring a good adherence of the intermediate polymeric layer. This prevents the separation of the intermediate polymeric coating layer from the cellulose-based material layer when the multi-layer packaging material is subjected to mechanical stress, in particular, to bending, twisting, folding or any other kind of deformation. The tie coating layer particularly protects the intermediate polymeric coating layer from humidity (water vapour) that could pass through the cellulose-based material layer from the outside (e.g., from the outer surface of the cellulose-based material layer, which may be printed, towards the vacuum deposited metallization layer) affecting and degrading the barrier properties of the intermediate polymeric coating layer. Thus, this tie coating layer extends the operational life of the multi-layer packaging material and ensures the safety and quality of the product contained within the package made with said multi-layer packaging material.

In some embodiments, the tie coating layer comprises a polymeric binder selected from: elastomeric polyurethane, optionally combined with nitrocellulose; a sulfopolyester; a polyethylenimine (PEI), including PEI derivatives; an acrylic polymer, such as low temperature glass transition (Tg) (e.g., Tg<20) acrylic polymers; and combinations thereof. Having a tie coating layer made of elastomeric polyurethane combined with nitrocellulose may advantageously contribute to the processability and to a high elasticity of the muti-layer packaging material. The thickness of the tie coating layer used in the multi-layer packaging material may be adjusted based on the intended purpose of the packaging material. For example, this tie coating layer may be applied in an amount in the range from 0.5 to 4 g/m2.

The amount of coating layers is expressed herein as the amount of solid material, e.g., polymer, per surface over which that amount is present in the multi-layer packaging material. Coating layers are typically applied in liquid form, e.g., in the form of a dispersion. The amount of coating layer being applied is also expressed in terms of the solids content in the liquid form, e.g., the dispersion, and therefore does not include the weight amount of solvent that may be present during the application of the coating layer. Accordingly, the amount in g/m2 of the coating layer present in the multi-layer packaging material is the same as the amount of coating layer applied, e.g. during the process of the manufacture, and may be used interchangeably.

The multi-layer packaging material may typically have a single (one) tie coating layer. It may also have more than one tie coating layer, e.g., two or three tie coating layers, but it has been found that a single layer it is sufficient to protect the intermediate polymeric layer and provides good adhesion to the intermediate polymeric layer without significantly increasing the complexity and weight of multi-layer packaging material.

In some embodiments, the multi-layer packaging material comprises from one to three intermediate polymeric coating layers comprising, e.g., of, a polyvinyl alcohol polymer. Preferably, the multi-layer packaging material comprises three intermediate polymeric coating layers of polyvinyl alcohol polymer, one deposited on top of the other.

The intermediate polymeric coating layer contributes to smoothen the surface on which the vacuum deposited metallization layer is to be deposited and to minimize the presence of the so-called “pin holes”. The presence of these pin holes may cause a reduction in the barrier properties of the vacuum deposited metallization layer. These intermediate polymeric coating layers provide an oxygen barrier (a reduced Oxygen Transmission Rate, OTR). Besides, since the intermediate polymeric coating layers are made of a flexible material, they contribute to increase the mechanical resilience of the metal layer that is deposited thereon.

By depositing two or three intermediate polymeric dispersion coating layers instead one single intermediate polymeric coating layer, the following advantages are achieved: 1) a greater number of “pin holes” are eliminated on the surface of the cellulose-based material layer, so the resulting deposition surface is smoother; 2) A more regular thickness profile of the layer is achieved by applying 2 or 3 layers and a better moisture barrier is obtained through the subsequent drying processes 3) if the intermediate polymeric coating layer is applied in one single layer on top of the cellulose-based material layer, more coating material is required to cover the “pin-holes” of the cellulose-based material layer and to provide the required barrier properties (OTR,WVTR). Thus, a bigger amount of material is required when deposited in one single thick PVA polymer layer than if it is deposited in several thinner PVA polymer layers. Since the PVA polymer is an expensive material, this represents a significant economic saving; and 4) the PVA polymers often comprise a low content of dry solids, which makes them easier to be applied as a thinner layer, on top of another coating, rather than as a thick layer deposited on top of the cellulose-based material layer itself.

In those embodiments in which there are two or three intermediate polymeric coating layers, the layers not in direct contact with the vacuum deposition metallization layer may contain mineral fillings such as exfoliating laminar pigments (preferably in a proportion of less than 10% in weight), that may improve the barrier properties of these layers and reduce their sensitivity to the environmental moisture.

The thickness of the intermediate polymeric coating layer used in the multi-layer packaging material may be adjusted based on the intended purpose of the packaging material. For example, this intermediate polymeric coating layer may be applied in an amount in the range of about from 1 to 3.75 g/m2. This amount applies to the total amount of intermediate coating layer material independently of whether one or more, e.g., two or three, intermediate coating layers are applied. Each layer may be applied as to have a total of amount intermediate polymeric coating layer in such a range. As a mode of example, each intermediate polymeric coating layer may be applied in an amount from about 1 g/m2 up to 3.75 g/m2, preferably from 1 to 2.5 g/m2, when, e.g., there is one intermediate polymeric coating layer; in an amount from 0.5 to 3.25 g/m2 when there are two intermediate polymeric coating layers (e.g., both layers being applied in an amount of 0.5 g/m2 or one layer being applied in an amount of 1 g/m2 and the second layer in an amount from 1 to up to 2.75 g/m2); and, in an amount from 0.5 to 1.25 g/m2, e.g., when there are three intermediate polymeric coating layers (e.g., one layer being applied in an amount of 0.75 and two layers being applied in an amount of 1.5 g/m2 or each layer being applied in an amount from 1 to 1.25 g/m2). Preferably, each one of the intermediate polymeric coating layers may be applied in an amount of 1 g/m2. The intermediate polymeric coating layer comprises a polyvinyl alcohol polymer. The polyvinyl alcohol (PVA) polymer may be unmodified or modified PVA. By unmodified PVA is understood as a polymer with the repeating unit [CH2CH(OH)]n also referred to in the art simply as polyvinyl alcohol (PVA). Commercial examples of unmodified PVA include for instance Selvol™ from Sekisui or Poval™ grades from Kuraray. By “modified” PVA, it is meant PVA polymer which has been chemically modified, including PVA having another monomer (e.g. a polyvinyl alcohol copolymer) or another compound grafted thereto, or PVA resin which has been mixed with other components, e.g., with plasticizers. An example of modified PVA may be, e.g., a PVA copolymer such as ethylene vinyl alcohol (EVOH) copolymer; butanediol vinyl alcohol (BVOH) copolymer. A particular example of modified PVA may be hydrophobically modified PVA, which advantageously may offer high water resistance and strong oil and gas barriers e.g. toward oxygen, carbon dioxide and various aromas even at elevated relative humidity. This modified PVA may be commercially available, e.g., under the name Kuraray Exceval™ or Nichigo G-Polymer™ from Nippon Goshei.

In some embodiments, the polyvinylalcohol (PVA) polymer of the intermediate polymeric coating layer is selected from: unmodified polyvinyl alcohol (PVA), ethylene vinyl alcohol (EVOH) copolymer; butanediol vinyl alcohol (BVOH) copolymer; and combinations thereof.

In some embodiments, the multi-layer packaging material further comprises a primer coating layer between the cellulose-based material layer and the tie coating layer. The primer coating layer may be made of a material selected from a group comprising: acrylic polymers (e.g., obtainable from acrylic emulsions), optionally comprising mineral fillings; polyesters; sulfopolyesters; vinyl acetate copolymers; vinyl chloride; and combinations thereof. The primer coating layer improves the planarization by smoothening the inner surface of the cellulose-based material layer and filling some of its porous. It also provides moisture and oil barrier properties and high flexibility to the multi-layer packaging material. Thanks to this flexibility, layers deposited on top of the primer coating layer are able to maintain their properties after being subjected to bending, twisting or other similar mechanical forces, for example, during the manufacturing of the packages. The thickness of the primer coating layer used in the multi-layer packaging material may be adjusted based on the intended purpose of the packaging material. For example, this primer coating layer may be applied in an amount in the range from 0.5 to 3.5 g/m2. If present, one single primer coating layer may be typically present, although more than one primer layer, e.g., two or three, may also be present.

In some embodiments, the vacuum deposited metallization layer is made of aluminum, aluminum oxide (AIOx) and/or silicon oxide (SiOx). The vacuum deposited metallization also provides barrier properties to oxygen and water vapour (e.g., reduced OTR and WVTR). This metallization layer may be deposited on top of the intermediate polymeric coating layer by physical vapor deposition process, e.g., a vacuum deposition process. Vacuum deposition is an evaporative process in which a metal or metal oxide from a solid phase is transferred to the vapor phase and back to the solid phase, gradually building up film thickness. Coatings produced by vacuum deposition have the advantage of, impact and temperature strength, as well as the capability to be deposited on complex surfaces and very low coating thickness.

In some embodiments, the vacuum deposited metallization layer has a thickness from 20 to 80 nm, and preferably from 30 to 60 nm. However, the thickness of the vacuum deposited metallization layer may be adjusted, being even greater or smaller than in the previous given ranges, for example, depending on the intended shelf life of the multi-layer packaging material, the type of product to be packaged and the overall thickness of the multi-layer packaging material.

In some embodiments, the vacuum deposited metallization layer may have an equivalent optical density (O.D.) in the range from 2 to 4. The equivalent optical density is a measure of total light transmission through the material and may be determined by the following equation:

O . D . = - Log ⁢ ( T τ T total )

Being ‘Tr’ the amount of light transmitted through the material and ‘Ttotal’ the total light before getting to the material.

In some embodiments, the inner polymeric coating layer may be obtainable from a polymeric dispersion. In particular, the polymeric dispersion may be a solvent-based and/or water-based polymeric dispersion. Solvent-based polymeric dispersions may advantageously avoid blocking. As used herein, the term “blocking” may refer to the tendency of some materials to stick to itself when wound in a coil. Thus, preferably, the at least one inner polymeric coating layer may be obtainable from a solvent-based polymeric dispersion.

The inner polymeric coating layer may typically be the layer that faces the packaged product, e.g., it may be the innermost layer, in other words the layer in the innermost side of the multi-layer packaging material.

In some embodiments, the multi-layer packaging material comprises one or more than one, e.g., two, inner polymeric coating layers. Preferably, the multi-layer packaging material comprises two inner polymeric coating layers.

In some embodiments, the inner polymeric coating layer comprises a polymer selected from: acrylic copolymers; polyesters; polyurethanes; polyester copolymers; polyurethane copolymers; vinyl acetate copolymers; chloride copolymers; and combinations thereof. Preferably, when there is one single inner polymeric coating layer, this single layer comprises an acrylic copolymer and when there are two inner polymeric coating layers, a first layer comprises a polymer selected from acrylic copolymers and a second layer comprises a polymer selected from: polyesters; polyurethanes; polyester copolymers; polyurethane copolymers; vinyl acetate copolymers; chloride copolymers; and combinations thereof. All these polymers typically have sealing properties and may preferably be heat-saleable materials.

The inner polymeric coating layer may be applied in an amount from 1 to 4.5 g/m2. Similarly to what is discussed above for the intermediate polymeric coating layer, the total amount of intermediate polymeric layer material may be typically found in this range independently of the number of inner polymeric layers. For instance, the inner polymeric layer may be applied in an amount from 1 to 4.5 g/m2, when there is a single inner polymeric layer (e.g., in an amount of 1 g/m2, or in an amount of 2, 3, or 4 g/m2) or each layer may be applied in an amount, e.g., from 0.5 to 4 g/m2 when there are two inner polymeric layers (e.g., both layers being applied in an amount of 2.25 g/m2, both layers being applied in an amount of 0.5 g/m2, or one layer being applied in an amount of 0.5 and the other layer being applied in an amount of 4 g/m2).

The inner polymeric coating layer also provides oil/grease barrier, water and water-vapour barrier (WVTR). It also provides heat seal functionality and protects the vacuum deposited metallization layer from physical damages.

The intermediate polymeric coating layer and the inner polymeric coating layer are to sandwich the vacuum deposited metallization layer so it is protected from damages due to, e.g., mechanical stress, particularly when the entire packaging material is bent, folded, or subject to other type of deformation, force or pressure such as during heat-sealing (when manufacturing and closing three-dimensional packaging items made of said packaging material).

The tie coating layer and the inner polymeric coating layer are also to sandwich the intermediate polymeric coating layer to prevent that water vapour may negatively impact the barrier properties of the at least one intermediate polymeric coating layer.

In some embodiments, the surface of the cellulose-based material layer on which the tie coating layer is deposited has a Parker Print Surf (PPS) roughness value from 0.9 to 2.3 μm. The PPS roughness is sometimes called printing roughness because it correlates well to the print quality of printing applied to the material in question. The PPS roughness may be measured according to the Dr. John Parker method using a PPS tester as established in, e.g., part 4 of the ISO standard 8791-4:2021 directed to paper and board determination of roughness/smoothness (air leak methods).

In some embodiments, the surface of the cellulose-based material layer opposite to the surface on which the tie coating layer is deposited (the printing surface of the cellulose-based material layer) has a PPS roughness value from 0.9 to 4.5 μm. These PPS roughness values on both surfaces of the cellulose-based material layer advantageously contribute to the smoothness and planarization of the cellulose-based material layer and to a homogeneous and efficient deposition of the subsequent layers on one side and commercial printing on the other. This also contributes to the barrier properties of the layers deposited on top of the cellulose-based material layer have.

In some embodiments, the surface of the cellulose-based material layer on which the tie coating layer is deposited has a COBB index from 2 to 20 g/m2, preferably, from 2 to 6 g/m2. The COBB index is the power of water retention of a material. Preferably, the cellulose-based material layer will have a COBB index as low as possible. The COBB index may be determined by methods known in the art such as, e.g., the ISO standard 535: 2023 directed to paper and board determination of water absorptiveness Cobb method.

In some embodiments, the multi-layer packaging material comprises a coating layer deposited onto the surface of the cellulose-based material layer (the printing surface) opposite to the surface on which the tie coating layer is deposited, the coating layer comprising material selected from a group comprising: kaolinite, calcium carbonate, bentonite, talc, and any combination thereof. This coating layer prepares the printing surface of the cellulose-based material layer for the printing layer and the overprint varnish layer (OPV), if needed.

A second aspect of the disclosure is a package for containing products comprising the multi-layer packaging material as disclosed herein. The package for products material may comprise the multi-layer packaging material as disclosed herein in combination, e.g., with other suitable packaging materials. The package may comprise a shaped multi-layer packaging material as disclosed herein, e.g., shaped to appropriately package products. For instance, the multi-layer packaging material as disclosed herein may be shaped in the form of, e.g., a box or a bottle.

The multi-layer packaging material of the present disclosure may be used to package products so that the metallized layer and the inner polymeric coating layers are located on the side of the cellulosed-based material (e.g., paper) layer that faces the product to be packaged. The product to be packaged may be an edible product such as a food product or a non-edible product such as a mineral powder. The product to be packaged may be also a solid product such as nuts, mineral powders, among many others. The improved barrier properties of the multi-layer packaging material herein disclosed makes it especially suitable for packing products which are sensitive to oxygen and/or moisture and is convenient for containing, e.g., solid or semi-solid products and more in particular food products selected from humid, fatty and/or dry solid or semi-solid food products.

Accordingly, the present disclosure is also directed to a packaged product comprising a product and a multi-layer packaging material as described herein, wherein the product is packaged in the multi-layer packaging material. The product may be as described above, e.g., a solid or semi-solid food product. It may preferably be a solid dry food product.

A third aspect of the disclosure is a method for manufacturing a mufti-layer packaging material, the method comprising the steps of:

• • providing a cellulose-based material layer having a grammage from 40 to 120 g/m2, preferably, from 50 to 110 g/m2, more preferably from 60 to 90 g/m2;
  • depositing, by a dispersion coating technique, a tie coating layer onto the cellulose-based material layer, the tie coating layer comprising a polymeric binder material;
  • depositing, by a dispersion coating technique, an intermediate polymeric coating layer onto the tie coating layer, the intermediate polymeric coating layer comprising a polyvinyl alcohol (PVA) polymer;
  • depositing, by a vacuum deposition technique, a metallization layer onto the intermediate polymeric coating layer; and
  • depositing, by a dispersion coating technique, an inner polymeric coating layer onto the metallization layer, the inner polymeric dispersion coating layer comprising a polymer selected from: acrylic copolymers; polyesters; polyurethanes; polyester copolymers; polyurethane copolymers; vinyl acetate copolymers; chloride copolymers; and combinations thereof.

In some embodiments, the method further comprises depositing, by a dispersion coating technique, a primer coating layer between the cellulose-based material layer and the intermediate polymeric coating layer. This primer coating layer comprise of a polymer, in particular, a polymer selected from: acrylic polymers (e.g., obtainable from acrylic emulsions); acrylic copolymers, optionally comprising mineral fillings; polyesters; sulfopolyesters; vinyl acetate copolymers; vinyl chloride; and combinations thereof.

The tie coating layer, the primer coating layer, the intermediate polymeric coating layer and the inner polymeric coating layer may be typically deposited using dispersion coating techniques such as forward and reverse gravure coating, bar coating and curtain coating, among—others. Accordingly, such layers may also be referred to as dispersion coating layers in the multi-layer packaging material. Thanks to the use of polymer dispersion coating, the overall thickness of polymer material in the whole multi-layer packaging material is low when compared to the thickness of the cellulose-based material layer. Thus, the low thickness obtained by means of the dispersion coating of polymers avoids high cohesion and high adhesion of the polymer to the cellulose, and therefore makes it possible for the multi-layer packaging material to be recycled using, e.g., conventional recycling paper techniques.

The solution herein disclosed presents some advantages over other existing solutions. The multi-layer packaging material herein disclosed provides improved barrier properties to packaged semi-solid or solid products, such as dry products, in particular semi-solid or solid dry food products, also under mechanical stress. This multi-layer packaging material can be easily recycled with paper recycling process of the state of the art. For example, the multi-layer packaging material may be recycled with other paper packaging and non-packaging materials such as paper recycling process of the state of the art. It also provides an improved resistance against mechanical stress in such a way that the material is able to withstand bending, twisting, and deformation with the different layers that compose them together and firmly bonded to each other, and, in particular, without losing its barrier properties.

As used herein, the terms “comprise”, “comprising”, and similar terms, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”. However, these terms also encompass specific embodiments that “consist of” the elements they anticipate.

BRIEF DESCRIPTION OF THE DRAWINGS

To complete the description and in order to provide for a better understanding of the disclosure, a set of drawings is provided. Said drawings form an integral part of the description and illustrate an example of the disclosure, which should not be interpreted as restricting the scope of the disclosure, but just as an example of how the disclosure can be carried out.

The drawings comprise the following figures:

FIG. 1 shows a schematic representation of a multi-layer packaging material, according to an embodiment of the disclosure.

FIG. 2 shows a schematic representation of the multi-layer packaging material of FIG. 1 but including three intermediate polymeric coating layers, according to another embodiment of the disclosure.

FIG. 3 shows a schematic representation of the multi-layer packaging material of FIG. 2 but including two inner polymeric coating layers, according to another embodiment of the disclosure.

FIG. 4 shows a schematic representation of the multi-layer packaging material of FIG. 3 but including a primer coating layer, according to another embodiment of the disclosure.

FIG. 5 shows a flow diagram of a method for manufacturing the multi-layer packaging material, according to an embodiment of the disclosure.

DESCRIPTION OF EXAMPLES

FIG. 1 shows a schematic representation of a multi-layer packaging material 100, according to an embodiment of the disclosure. It should be understood that the multi-layer packaging material 100 depicted in FIG. 1 may include additional materials and/or components and that some of the materials and/or components described herein may be removed and/or modified without departing from a scope of the multi-layer packaging material 100.

The multi-layer packaging material 100 comprises a cellulose-based material layer 101, for example, a paper-based layer, having a grammage of, e.g., 40 g/m2. This paper-based layer 101 provides a good balance between strength and flexibility and may comprise a latex-based coating layer (not shown in this figure) on both of its surfaces. The latex-based coating of the inner surface of the paper-based layer (the surface on which the subsequent tie coating layer is to be deposited) has a greater amount of latex than the outer surface (printing surface of the paper-based layer). These latex-based layers improve the smoothness and flexibility of both surfaces. The paper-based layer also may have a tensile strength 7.5 Kg/15 mm.

The inner surface of the paper-based material 101 layer has a PPS roughness value of 1.5 μm and a COBB index of 3.5 g/m2 and the outer surface of the paper-based layer 101 has a PPS roughness value of 2.3 μm.

There may be a printing coating layer (not shown in this figure) on top of the outer surface of the paper-based layer 101. An overprint varnish coating layer (not shown in this figure) may be also deposited on top of the printing coating layer to protect it.

The multi-layer packaging material 100 comprises one tie coating layer 102 made of elastomeric polyurethane combined with nitrocellulose. The elastomeric polyurethane combined with nitrocellulose is a polymeric binder that improves the adherence of the subsequent intermediate polymeric coating layer 103 to the paper-based layer 101 and protects it from vapor and moisture that could pass through the paper-based layer 101 from the outside (i.e., from the printing surface of the paper-based layer 101 towards the vacuum deposited metallization layer 104) affecting and degrading the barrier properties (e.g., increasing the OTR and/or the WVTR) of the intermediate polymeric coating layer 103. The elastomeric polyurethane combined with nitrocellulose also provides a high flexibility and mechanical resistance to the multi-layer packaging material 100.

The one single intermediate polymeric coating layer 103 is made of a polyvinyl alcohol (PVA) polymer. Examples of these PVA polymers are, e.g., PVA copolymers such as Kuraray Exceval™, Kuraray Poval™ or Michem™ Flex B1002 or Nichigo G-Polymer™, among many other possible PVA polymers. This single intermediate polymeric coating layer 103 may have been deposited in a range from 1 to 2.5 g/m2, preferably 1 g/m2, to ensure a regular and homogenous thickness of the layer.

The multi-layer packaging material 100 further comprises a vacuum deposited metallization layer of aluminum with a thickness of 40 nm. In this case, the vacuum deposited aluminum layer may be passivated with a layer of aluminum oxide of about 10-15 nm that is deposited over said aluminum layer and protects it from corrosion. Aluminum, in contact with air, may naturally become passivated, thus generating his aluminum oxide coating.

The multi-layer packaging material 100 also comprises one single inner polymeric coating 105 layer made of an acrylic copolymer (e.g., Carbobond™ 3005 or Rhobarrv™ 135) or a combination of more than one acrylic copolymer. Examples of these acrylic copolymers may be ethyl acrylate copolymer, ethylene acrylic acid copolymer or methyl acrylate copolymer, among many others. Acrylic copolymers adhere properly to the vacuum deposited metallization layer 104 and provide flexibility and easy film formation at not very high temperatures. Avoiding these high temperatures during the deposition of the inner polymeric coating layer 105 avoids damaging the vacuum deposited metallization layer 104 that may degrade its barrier properties.

The multi-layer packaging material 100 of FIG. 1 presents the following oxygen and moisture barriers:

OTR	WVTR
25 cm3/m2/day (23° C., 50% RH)	16 g/m2/day (38° C., 90% RH)

The OTR has been measured at a temperature of 23° C. and with a relative humidity of 50%, while the WVTR has been measure at a temperature of 38° C. and with a relative humidity (RH) of 90%. Thus, the multi-layer packaging material herein disclosed presents improved OTR and WVTR values than those provided by other multi-layer packaging materials of the state of the art.

FIG. 2 shows a schematic representation of the multi-layer packaging material 100 of FIG. 1 but including three intermediate polymeric coating layers 103 instead one single intermediate polymeric coating layer 103, according to another embodiment of the disclosure. These three intermediate polymeric coating layers 103 may have the same thickness or a different thickness. For example, each of these layers may have been deposited in an amount of 1 g/m2. By depositing 3 layers of PVA polymer 103 (e.g., PVA copolymers) on top of the tie coating layer 102 the number of pin holes in the paper-based layer 101 is significantly reduced increasing its smoothness. Besides, the surface planarization and barrier properties are improved since the first PVA polymer layer 103a provides surface planarization, the second PVA polymer layer increases planarization and provides oxygen barrier, and the third PVA polymer layer increases surface planarization and oxygen and moisture barriers. Additionally, since it is required less amount of PVA polymer for depositing three thinner PVA polymer layers than to depositing one single thicker PVA polymer layer in order to reach the required surface planarization and the required barrier properties, a significant amount of PVA polymer is saved with the corresponding economic saving. Finally, PVA polymer often comprise a low content of dry solids, which makes them easier to be applied as a thinner layer, on top of another coating, rather than as a thick layer deposited on top of the cellulose-based material layer itself.

The multi-layer packaging material 100 of FIG. 2 presents the following oxygen and moisture barriers:

OTR	WVTR
0.6 cm3/m2/day (23° C., 50% RH)	1.8 g/m2/day (38° C., 90% RH)

The OTR has been measured at a temperature of 23° C. and with a relative humidity of 50%, while the WVTR has been measure at a temperature of 38° C. and with a relative humidity (RH) of 90%. Thus, the multi-layer packaging material herein disclosed presents improved OTR and WVTR values than those provided by other multi-layer packaging materials of the state of the art.

FIG. 3 shows a schematic representation of a multi-layer packaging material 100 of FIG. 2 but including two inner polymeric coating layers 105, according to another embodiment of the disclosure.

In such embodiment, these two inner polymeric coating layers 105 are combined such that each layer is made of at least one material of the following list: acrylic copolymers, polyesters, polyurethanes, polyester copolymers, polyurethane copolymers, vinyl acetates copolymers and chloride copolymers. In this particular embodiment, the first layer 105a is preferably made of an acrylic copolymer, a polyester, a combination of acrylic copolymers or a combination of polyesters that, as previously mentioned, present a good adherence to the vacuum deposited metallization layer 104 but may present some tendency to generate blocking. To minimize the problem of blocking, the second layer 105b may preferably be obtainable from a solvent-based dispersion, such as solvent-based dispersions of an acrylic copolymer, a polyester, a combination of acrylic copolymers or a combination of polyesters, among other materials. In some other examples, the first layer 105a may be of a polyester or a combination of polyesters while the second layer 105b may be of a chloride copolymer or a combination of chloride copolymers. Other combinations from the mentioned list could be possible. For example, the first layer may have been deposited in an amount from 1 to 3.5 g/m2, preferably about 2.5 g/m2, and the second layer may have been deposited in an amount from 0.5 to 2 g/m2, preferably about 1 g/m2.

The multi-layer packaging material 100 of FIG. 3 presents the following oxygen and moisture barriers:

OTR	WVTR
0.6 cm3/m2/day (23° C., 50% RH)	2 g/m2/day (38° C., 90% RH)

The OTR has been measured at a temperature of 23° C. and with a relative humidity of 50%, while the WVTR has been measure at a temperature of 38° C. and with a relative humidity (RH) of 90%. Thus, the multi-layer packaging material herein disclosed presents improved OTR and WVTR values than those provided by other multi-layer packaging materials of the state of the art.

FIG. 4 shows a schematic representation of the multi-layer packaging material 100 of FIG. 3 but including a primer coating layer 106, according to another embodiment of the disclosure. This primer coating layer may be made of an acrylic copolymer with mineral fillings.

The primer coating layer 106 is located between the paper-based layer 101 and the tie coating layer 102 and it is made of an acrylic copolymer such as Carbobond™ 3005F that is a formaldehyde acrylic copolymer, an acrylic emulsion such as Carboset™ GA7424 that is an acrylic copolymer emulsion, among many others. Alternatively, this primer coating layer 106 may be made of other materials such as acrylic copolymers with mineral fillings, acrylic copolymers without mineral fillings, polyesters, sulfopolyesters, vinyl acetate copolymers, vinyl chloride and vinyl acetate copolymers and any combination thereof or any combination of the cited materials with an acrylic emulsions or acrylic copolymers.

The multi-layer packaging material 100 of FIG. 4 presents the following oxygen and moisture barriers:

OTR	WVTR
0.5 cm3/m2/day (23° C., 50% RH)	4 g/m2/day (38° C., 90% RH)

The OTR has been measured at a temperature of 23° C. and with a relative humidity of 50%, while the WVTR has been measure at a temperature of 38° C. and with a relative humidity (RH) of 90%. Thus, the multi-layer packaging material herein disclosed presents improved OTR and WVTR values than those provided by other multi-layer packaging materials of the state of the art.

FIG. 5 shows a flow diagram of a method 200 for manufacturing the multi-layer packaging material, according to an embodiment of the disclosure.

At step 201 of the method 200, a cellulose-based material layer, for example, a paper-based layer, having a grammage comprised in the range from 40 to 120 g/m2, preferably in the range from 50 to 110 g/m2, and more preferably in the range from 60 to 90 g/m2, is provided. This cellulose-based material layer will be selected so as to balance the mechanical resistance (tensile strength, elasticity, flexibility, etc.) and surface properties of the layer.

At step 202 of the method 200, a tie coating layer is deposited, by a dispersion coating technique, onto the cellulose-based material layer. This tie coating layer comprises a polymeric binder. Preferably there will be one single tie coating layer although in some implementations there may be more than one tie coating layer to improve the adherence of the intermediate polymeric coating layers to the cellulose-based material layer.

At step 203 of the method 200, an intermediate polymeric coating layer is deposited by a dispersion coating technique, onto the tie coating layer. The intermediate polymeric coating layer comprises a polyvinyl alcohol (PVA) polymer (e.g., a PVA copolymer). Preferably, three intermediate polymeric coating layers will be deposited onto the tie coating layer.

At step 204 of the method 200, a metallization layer is deposited, by a vacuum deposition technique, onto the intermediate polymeric coating layer. This metallization layer will be preferably made of aluminum, aluminum oxide and/or silicon oxide. For example, the vacuum deposition technique may be a physical vapor deposition process.

At step 205 of the method 200, an inner polymeric coating layer is deposited, by a dispersion coating technique, onto the metallization layer, the inner polymeric coating layer comprising a material selected from a group comprising acrylic copolymers, polyesters, polyurethanes, polyester copolymers, polyurethane copolymers, vinyl acetates copolymers, chloride copolymers and any combination thereof. Preferably, the inner polymeric coating layer will be made of a solvent-based material to avoid blocking.

In some embodiments, a primer coating layer is deposited, by a dispersion coating technique, between the cellulose-based material layer and the tie coating layer. The primer coating layer may be made of a material selected from a group comprising: acrylic polymers (e.g., obtainable from acrylic emulsions), optionally comprising mineral fillings; polyesters; sulfopolyesters; vinyl acetate copolymers; vinyl chloride; and combinations thereof. The primer coating layer improves the planarization by smoothening the inner surface of the cellulose-based material layer and filling some of its porous. It also provides barrier properties to moisture and oils.

The tie coating layer, the primer layer, the intermediate polymeric coating layer and the inner polymeric coating layer are preferably deposited using dispersion coating techniques such as, e.g., forward and reverse gravure coating, bar coating and curtain coating, among—others. In some embodiments, all these layers are deposited using the same dispersion coating technique, while in some other embodiments, they may be deposited using different dispersion coating techniques. Thanks to the use of polymer dispersion coating, the overall thickness of polymer material in the whole multi-layer packaging material is low when compared to the thickness of cellulose-based material layer. Thus, the low thickness of the dispersion coating of polymer avoids high cohesion and high adhesion of the polymer to the cellulose, and therefore makes it possible for the multi-layer packaging material to be recycled using conventional recycling paper techniques.

The overall thickness of the multi-layer packaging material herein may be adjusted by a person skilled in the art based on the intended purpose of the packaging material.

The multi-layer packaging material herein disclosed may have any thickness suitable for packaging materials. A person skilled in the art will be able to determine an appropriate thickness. Typically, however, if the packaging material is intended for use in packaging food products, the packaging material should be as thin as possible, while still ensuring safety and shelf life of the food product. For example, for food packaging it may have an overall thickness in the range of about 35 to 110 μm.