Multi-layer metallized paper-based packaging material

Abstract

The invention relates to a multilayer metallized paper-based packaging material (1) comprising, from its outer side to its inner side:-a paper layer (2) having a grammage in the range of 30 g / m2 to 120 g / m2; -at least one organic barrier layer (3) of a polymer selected from the list of polyvinyl alcohol (PVOH), ethylene-vinyl alcohol (EVOH), butenediol-vinyl alcohol copolymer (BVOH) or combinations thereof in an amount of from 0.5 g / m2 to 20 g / m2; -at least one inorganic barrier layer (4) selected from the list of: a metal, a metalloid or a combination thereof, the inorganic layer having a thickness of between 1 nm and 100 nm; and-at least one organic heat seal layer (5) made of an acrylic or methacrylic polymer grafted with at least one type of ionomer, the heat seal layer being applied in an amount of between 2 g / m2 and 20 g / m2.

Description

Technical Field

[0001] The present invention relates to a multi-layer paper-based packaging material, which includes a paper layer, an ultra-thin metal or metalloid layer for water vapor barrier, the ultra-thin metal or metalloid layer is sandwiched between ultra-thin coatings, and these ultra-thin coatings provide oxygen barrier and sealing properties for the structure. Background Art

[0002] Plastic packaging is frequently used in the economy and in people's daily lives. It has several advantages, such as its flexibility and its light weight. For example, such weight reduction helps save fuel and reduce CO2 during transportation. 2 Its barrier properties help reduce food waste by having a positive effect on extending shelf life. Barrier properties also help ensure food safety.

[0003] However, with increasing environmental awareness and in order to ensure a reduction in plastic waste, multilayer packaging materials have been developed comprising a paper or paperboard layer and one or several layers of plastic or metal film providing robustness and barrier properties, in particular to oxygen and moisture.

[0004] In recent years, environmental awareness has even further increased, especially with regard to waste materials, such as used packaging, which are not recycled or properly disposed of. The industry takes this challenge very seriously and is spending more and more energy on developing new packaging materials that can be quickly and easily recycled.

[0005] At present, when producing multilayer packaging material structures, the plastic layers are applied by known techniques, in particular extrusion (extrusion-lamination), or similarly by adhesive lamination processes, and the thus obtained high thickness plastic film must be provided on paper.

[0006] Even for relatively low thicknesses of extruded or laminated polymers in multilayer structures as described above, the cohesive strength of the polymer film is very high and the level of adhesion of the polymer to the paper or paperboard (i.e., cellulose) substrate is also high. This will prevent such polymers from detaching from the substrate during recycling and prevent the recycling and repulping of the cellulose fiber fraction in the paper stream recycling process.

[0007] Therefore, multilayer structures comprising a mixture of paper and plastic (polymer) films, which are extruded (by classical techniques such as extrusion lamination or extrusion coating) or adhesive laminated later in the recycling process, have limited recyclability in the paper stream recycling process, because the plastic layer is too thick to be dispersed and at the same time the same layer has cohesive strength and adhesion levels with the adjacent layers of the structure which are too high to be separated from other material layers, in particular from the paper fibers. The extruded plastic film remains intact in the pulp bath, thus making it difficult to recycle the pulp from the repulping process.

[0008] Furthermore, the recycling process of the above-mentioned known laminated materials is expensive and energy-intensive and is characterized by a relatively low yield of recycled paper fibers (less than 80% of the total amount of packaging material in the entire structure) and is therefore not sufficiently environmentally friendly from a disposal and recycling point of view. In the paper recycling stream, there is also room for improving the recyclability of the remaining part of the packaging material, namely the plastic polymers and metal parts, such as aluminum parts.

[0009] Furthermore, for packaging intended for food products, good barrier properties are essential to maintain the safety and quality of the packaged food. Typically, such barrier properties include gas barriers, such as to oxygen and water vapor (moisture), and, if possible, liquid tightness.

[0010] One way to provide a good moisture barrier in paper-based packaging materials is to introduce a metal or metalloid layer in a so-called "metallized" layer. In this specification, the term "metallized" (e.g., in the expression "metallized barrier paper layer") refers to a deposition comprising metal or metalloid atoms at the surface of the paper or paperboard. Even embodiments comprising the deposition of alloys of metals and metalloids are contemplated. Metalloids are close to metals in some of their characteristics. Aluminum oxide and silicon oxide are examples of metalloids.

[0011] The problem of introducing metal layers in paper-based packaging materials is the sensitivity of the metal layers to mechanical stresses and the poor adhesion of the metal to the paper surface, the poor smoothness of the paper material and the high porosity. Mechanical stresses can, for example, easily lead to the loss of the required barrier properties that the metallized packaging material should provide. This may be due to the processing of the multilayer material during the manufacture of the package using, for example, a form-fill-seal packaging machine, whereby the material is stretched, bent, rolled, compressed and / or heated during the formation and sealing of the package by conventional packaging forming methods. Such packaging manufacturing methods cause high mechanical and / or chemical stresses to the material, and in particular to the ultra-thin metallized layers of metals or metalloids, and therefore lead to damage to such layers, resulting in cracks and tears, which are irreversible in most cases.

[0012] In view of the above, there is a need for a multi-layer metallized paper-based packaging material that simultaneously exhibits:

[0013] - sufficient barrier properties, especially against oxygen and moisture,

[0014] - a high resilience to mechanical stresses, so that it maintains the same level of barrier even when subjected to conversion processes, such as those used to manufacture packaging,

[0015] - the amount of plastic polymer content is greatly reduced compared to the content of cellulosic material,

[0016] - and preferably also recyclability in the paper stream and / or biodegradability under various environmental conditions, in particular (but not exclusively) in the marine environment. Summary of the invention

[0017] The object of the present invention is achieved by a multi-layer metallized paper-based packaging material, which comprises, from its outer side to its inner side:

[0018] - a paper layer having a thickness comprised between 30 g / m 2 Up to 120g / m 2 Weight within the range,

[0019] - at least one organic barrier layer of a polymer selected from the list of polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), butene glycol-vinyl alcohol copolymer (BVOH) or a combination thereof, in an amount of 0.5 g / m 2 Up to 20g / m 2 , preferably in an amount of 1 g / m 2 Up to 10g / m 2 , more preferably the amount is 2 g / m 2 Up to 8g / m 2 ,

[0020] - at least one inorganic barrier layer selected from the list of metals, metalloids or combinations thereof, the inorganic layer having a thickness between 1 nm and

[0021] 100nm thickness, and

[0022] - at least one organic heat-seal layer, the at least one organic heat-seal layer is made of acrylic acid or methacrylic acid polymer grafted with at least one type of ionomer, the heat-seal layer is between

[0023] 2g / m 2 With 20g / m 2 The amount between, preferably between 4g / m 2 With 9g / m 2The amount between is applied.

[0024] The total thickness of the polymer coating in this structure is greatly reduced compared to the thickness of the paper material, so the inventors have achieved overcoming the technical limitations of the known multilayer barrier structures and achieved a packaging multilayer structure with excellent barrier properties to oxygen and moisture transfer and resistance to liquid contact from its inner or outer surface, while achieving a total content of cellulose fibers of preferably up to 85% or even 95% by weight of the total material.

[0025] Furthermore, the water-soluble pre-coated polymer layer promotes recyclability. The fact that the inventors have succeeded in forming a multilayer structure completely free of polymer layers formed by extrusion lamination and / or adhesive lamination provides a multilayer structure having a ratio of cellulosic fibers to non-cellulosic materials, whose fiber content is extremely high, and in which the polymer layer easily disintegrates during the repulping process, due to the solubility of the pre-coating layer in water, and the relatively high adhesion of the polymer to the metallized layer after metallization (or quasi-metallization) also inhibits the metal layer from fragmenting during repulping, resulting in cleaner fibers from the repulping process. Therefore, the resulting structure exhibits excellent repulpability and high fiber yields of high quality, allowing it to be accepted by standard recycling paper mills in most countries. The content of non-cellulosic polymers and vacuum-deposited metal materials is very low, making the entire material of the present invention easily disintegrated, dissolved and separated in a recycling process designed for cellulosic materials such as paper or paperboard, which is different from existing multilayer barrier structures known in the art.

[0026] A particular improvement of the present invention over existing barrier paper materials is the incorporation into the multilayer barrier wrapper of a heat seal layer comprising an acrylic or methacrylic acid polymer grafted with an ionomer.

[0027] The present inventors have surprisingly found that by grafting an acrylic or methacrylic acid polymer to an ionomer, the heat seal innermost coating is improved in at least two different ways.

[0028] Firstly, the heat seal layer made of such acrylic or methacrylic-ionomer materials achieves excellent resistance to mechanical stresses, in particular to bending, tensile and shear forces applied to the material during the manufacture of packaging therefrom. This mechanical resistance protects the entire structure, in particular the adjacent inorganic layers, from damage and more particularly from irreversible cracking.

[0029] Second, it was discovered that grafting acrylic or methacrylic polymers with ionomers changes the molecular set-up of the material: the acrylic or methacrylic-ionomer molecules form a molecular matrix on the surface of the coating made therefrom, causing the heat seal layer to exhibit high hot tack characteristics that lead to excellent seal integrity of the formed and filled packages and ultimately enable barrier maintenance in the final package.

[0030] Advantageously, the organic heat seal material is a methacrylic acid polymer chemically modified (ie grafted) with an ionomer.

[0031] In a highly preferred embodiment of the invention, the inorganic layer comprises a metal or metalloid selected from the list of: aluminum, aluminum oxide (AlOx) or silicon oxide (SiOx), the metal and / or metalloid being deposited by vacuum deposition or transfer metallization. In a particularly preferred embodiment, the inorganic layer is a vacuum deposited aluminum layer.

[0032] Furthermore, in a preferred embodiment of the present invention, the ionomer grafted onto the acrylic or methacrylic acid polymer is a sodium ionomer.

[0033] Preferably, the acrylic or methacrylic acid-ionomer polymer has a molecular weight between 85 and 90 g / mol.

[0034] Each organic layer is preferably deposited onto the adjacent layer from an aqueous dispersion or from aqueous solution deposition.

[0035] Advantageously, the organic barrier layer is deposited by aqueous solution deposition and the organic heat seal layer is deposited by aqueous dispersion coating.

[0036] In one embodiment of the present invention, the paper layer is covered with an ink layer on its outer surface. The thickness of the ink layer is preferably between 0.5 g / m 2 With 5g / m 2 Preferably, the ink layer is selected from the list of: water-based ink, solvent-free ink or a combination thereof.

[0037] More preferably, the paper layer or ink layer is covered on its outer surface by an outermost overprint varnish (OPV) layer. The OPV layer may have a thickness of preferably between 0.5 g / m 2 With 10g / m 2 The weight between.

[0038] The optional OPV layer also contributes to the improved resistance of the barrier paper to hygroexpansive strain, particularly as it provides an improved barrier to moisture (water vapor transmission rate or "WVTR") under high humidity conditions.

[0039] In an advantageous embodiment, the outermost overprint varnish layer is a styrene acrylic varnish.

[0040] The multilayer metallized paper-based packaging material according to the present invention advantageously achieves the following barrier properties to oxygen and moisture: a water vapor transmission rate (WVTR) of less than 0.5 g / m2 / day (measured at 23° C., 85% relative humidity) and / or an oxygen transmission rate (OTR) of less than 0.1 cm3 / m2 / day (measured at 23° C., 50% RH). These values ​​are measured according to the flexibility test standard ASTM F392 or equivalent, after subjecting the sample to an in-plane tensile prestrain of up to 2% and also after subjecting the sample to 3 cycles of the Gelboflex test device.

[0041] The multilayer metallized paper-based packaging material according to the present invention preferably has a breaking strain of at most 5% in the longitudinal direction of the paper and at most 15% in the transverse direction of the paper under in-plane tensile load. The breaking strain of the total paper structure is 2.5% in the longitudinal direction and 9% in the transverse direction, which leads to high mechanical elasticity.

[0042] The invention also relates to a three-dimensional closed packaging article made of a multilayer metallized paper-based packaging material as described above, obtained by forming, then filling with an edible product for human or animal consumption and then sealing the packaging material.

[0043] The present invention also relates to the use of the aforementioned multi-layer metallized paper-based packaging material for packaging edible products for human or animal consumption.

[0044] The present invention also relates to a packaged edible product comprising a multilayer metallized paper-based packaging material according to the present invention, filled with an edible product for human or animal consumption.

[0045] Preferably, the edible product is a powder, gel or kibble and is selected from the list of: soluble coffee, nutritional compositions for infants, adults or elderly, soups, confectionery or candies, chocolate products, dry animal food, dairy products.

[0046] As used in this specification, the words "include", "comprising" and similar words should not be understood as having an exclusive or exhaustive meaning. In other words, they are intended to mean "including, but not limited to". BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Additional features and advantages of the present invention are described in, and will be apparent from, the following description of presently preferred embodiments given with reference to the accompanying drawings, in which:

[0048] Figure 1 A first embodiment of a multilayer structure according to the present invention is shown;

[0049] Figure 2 A second embodiment of the multilayer structure according to the invention is shown. DETAILED DESCRIPTION

[0050] Generally, in this specification, "extrusion coating" refers to a process for providing a polymer layer by using an extruder that forces a molten thermoplastic resin (e.g., polyethylene) through a horizontal slot die onto a moving web of a substrate (e.g., paper). The resulting product is a permanently coated web structure.

[0051] By "extrusion lamination" is meant a process similar to extrusion coating in which a polymer resin is extruded between two substrates (eg, one layer of paper and another layer of a polymer film) and acts as a bonding agent.

[0052] By "adhesive lamination" is meant a process in which one paper material is coated with an adhesive and laminated to a second paper or paperboard material. In the lamination process, two thick layers of material are joined by extrusion lamination or adhesive lamination, where the thickness of each layer is much greater than that obtained by dispersion coating.

[0053] By "dispersion coating" is meant a coating technique in which an aqueous dispersion of fine polymer particles or a polymer solution is applied to a paper or paperboard surface as such to form a solid non-porous film after drying. Dispersion coating can be carried out by gravure printing, flexographic printing, rods, blades, slot dies, curtain air knives, roller coating or any other known paper coating method. Dispersion coating can produce much thinner layers than extrusion lamination and / or adhesive lamination because the polymers are mixed in an aqueous solution. This brings advantages in terms of polymer dosage, its barrier properties and the recyclability of the resulting paper structure. The goal of dispersion coating is to obtain a barrier layer to water, water vapor, grease, oil, gas, etc. by an environmentally friendly coating. Another goal is to prepare the surface of a paper material for a vacuum deposition process.

[0054] By "fiber" is meant cellulosic fibers typically extracted from plants, seeds or trees; such fibers contain not only cellulose molecules but also hemicellulose and lignin.

[0055] The multi-layer structure according to the present invention is preferably designed to comply with the conditions for being recyclable in a standard recycling paper stream process according to most regional or national paper recycling regulations.

[0056] Recyclability in the paper stream is achieved by the multilayer structure according to the invention, wherein:

[0057] - the fiber content is dominant relative to all the components contained therein (the definition of recyclability in a paper stream depends on national legislation, but on average, it requires that the material contains at least 80% fiber to be accepted in recycling processes dedicated to paper), and

[0058] - the inorganic layer is ultra-thin (i.e. a few nanometers, typically between 1 nm and 100 nm) and its thickness consists of a few atoms,

[0059] - The organic polymer layers are all deposited by deposition coating from aqueous dispersions or solutions, which means that the layers thus obtained are thin enough relative to the paper thickness to achieve a very high paper content of the overall structure, which makes the entire structure compatible with the paper recycling process as explained previously herein

[0060] The organic barrier layer preferably comprises a water-soluble polymer (ie PVOH, EVOH and / or BVOH), which makes it easier to separate the fibres from the rest of the structure, in particular from the cellulosic content.

[0061] exist Figure 1 A first embodiment of the present invention is shown in FIG. In this embodiment, the multilayer structure 1 comprises, in order from its outer side (i.e. the side of the material facing the outside of the package made of it) to its inner side (i.e. the inner side in contact with the packaged product in the package made of it):

[0062] -Weight: 62g / m 2 Highly smooth paper layer 2,

[0063] - A first organic polyvinyl alcohol-based (PVOH) pre-metallized coating 3, which primarily provides gas (especially oxygen) barrier properties and is applied as an aqueous solution at 3 g / m 2 The weight applied,

[0064] - an inorganic vacuum deposited layer 4 of aluminum, 40 nm thick, which primarily provides moisture barrier properties, and

[0065] - A second organic coating 5 of a methacrylic ionomer-based coating, which acts as a heat seal layer and is applied as an aqueous dispersion at 5 g / m 2 of weight applied.

[0066] In this embodiment, the deposition technique for the first organic layer and the second organic layer as described above allows for improved recyclability in paper flow processes.

[0067] The structure 1 of the first embodiment achieves high moisture and gas barrier properties, wherein the oxygen transmission rate (OTR) value measured at 23°C and 50% relative humidity (RH) is less than 0.5 cm 3 / m 2 / day, and the water vapor transmission rate (WVTR) value measured at 23°C and 85% RH is less than 0.5 g / m 2 / sky.

[0068] The strain at break of the overall structure 1 was measured to be 2.5% in the machine direction and 9% in the cross direction. These values ​​provide excellent elastic properties, which allow the aluminum layer to be protected during structural processing in conventional packaging forming processes. When a package is manufactured from this material, no rupture of the aluminum layer is generated during bending, stretching and / or sealing of the material, which results in maintaining the same level of OTR and WVTR barrier properties before and after forming a package from the multilayer structural material.

[0069] exist Figure 2 In the above, the Figure 1 The structure described is similar to the structure.

[0070] However, in this second exemplary embodiment of the invention, the outer surface of the paper layer 2 is covered with the following two layers, in order from the outer side to the inner side of the packaging material:

[0071] - an outermost acrylic-based overprint varnish layer 7, which is applied as an aqueous dispersion at 1 g / m 2 The weight applied,

[0072] -1g / m 2 The water-based ink 6 is applied as an aqueous dispersion by weight; the water-based ink layer 6 is located between the outermost overprint varnish layer 7 and the paper layer 2.

[0073] The remaining layers in Structure 1 remain similar to the reference Figure 1 The structure described is:

[0074] - A first organic polyvinyl alcohol-based (PVOH) pre-metallized coating 3, which primarily provides gas (especially oxygen) barrier properties and is applied as an aqueous solution at 3 g / m 2 The weight applied,

[0075] - an inorganic vacuum deposited layer 4 of aluminum, 40 nm thick, which primarily provides moisture barrier properties, and

[0076] - A second organic coating 5 of a methacrylic ionomer-based coating as an aqueous dispersion at 5 g / m 2 of weight applied.

[0077] The structure corresponding to the above-described embodiment can meet the requirements for the recyclability of the material or the packaging made therefrom under standard recycling mill conditions.

[0078] In all embodiments of the invention described above, the multilayer structure may include other additional and optional layers not described in detail herein. Such layers may include, for example, a printing layer on the outer surface of the paper layer, and a protective layer which is optionally deposited on the outer side of the printing layer and thus constitutes the outermost layer of the entire structure. The printing layer and the optional protective layer are not described in more detail, as they are technologies known to those skilled in the art.

Claims

1. A multi-layer metallized paper-based packaging material (1), the multi-layer metallized paper-based packaging material comprising, from its outer side to its inner side: - a paper layer (2) having a thickness of 30 g / m 2 Up to 120g / m 2 Weight within the range, - at least one organic barrier layer (3) of a polymer selected from the list of: polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), butene glycol - vinyl alcohol copolymer (BVOH) or a combination thereof, in an amount of 0.5 g / m 2 Up to 20g / m 2 , preferably in an amount of 1 g / m 2 Up to 10g / m 2 , more preferably the amount is 2 g / m 2 Up to 8g / m 2 , - at least one inorganic barrier layer (4) selected from the list of metals, metalloids or combinations thereof, said inorganic layer having a thickness between 1 nm and 100 nm, and - at least one organic heat-seal layer (5), said at least one organic heat-seal layer being made of an acrylic acid or methacrylic acid polymer grafted with at least one type of ionomer, said heat-seal layer (5) having a density of between 2 g / m 2 With 20g / m 2 The amount between, preferably between 4g / m 2 With 9g / m 2 The amount between is applied.

2. The multilayer metallized paper-based packaging material (1) according to claim 1, wherein the inorganic layer comprises a metal or a metalloid selected from the list of: aluminum, aluminum oxide (AlOx) or silicon oxide (SiOx), the metal and / or metalloid being deposited by vacuum deposition or transfer metallization.

3. The multilayer metallized paper-based packaging material (1) according to any one of the preceding claims 1 or 2, wherein the ionomer grafted onto the acrylic or methacrylic acid polymer is a sodium ionomer.

4. The multilayer metallized paper-based packaging material (1) according to any one of the preceding claims 1 to 3, wherein the acrylic or methacrylic acid polymer grafted with an ionomer has a molecular weight between 85 and 90 g / mol.

5. The multilayer metallized paper-based packaging material (1) according to any one of the preceding claims 1 to 4, wherein each of the organic layers is deposited onto the adjacent layer by aqueous dispersion or by deposition from an aqueous solution.

6. The multilayer metallized paper-based packaging material (1) according to the preceding claim 5, wherein the organic barrier layer (3) is deposited by aqueous solution deposition and the organic heat seal layer (5) is deposited by aqueous dispersion coating.

7. The multilayer metallized paper-based packaging material (1) according to any one of the preceding claims, wherein the paper layer (2) is covered with an ink layer (6) on its outer surface.

8. The multilayer metallized paper-based packaging material (1) according to the preceding claim 7, wherein preferably the ink layer is selected from the list of: water-based inks, solvent-free inks or combinations thereof.

9. The multilayer metallized paper-based packaging material (1) according to any one of the preceding claims 7 or 8, wherein the paper layer or the ink layer is covered on its outer surface by an outermost overprint varnish (OPV) layer (7).

10. The multilayer metallized paper-based packaging material (1) according to the preceding claim 9, wherein the outermost overprint varnish layer (7) is a styrene acrylic varnish.

11. The multilayer metallized paper-based packaging material (1) according to any one of the preceding claims, wherein the packaging material has a viscosity of less than 0.5 g / m 2 / day water vapor transmission rate (WVTR) (measured at 23°C, 85% relative humidity) and / or less than 0.1 cm 3 / m 2 Oxygen transmission rate (OTR) of 1.34 g / day (measured at 23°C, 50%RH).

12. A multilayer metallized paper-based packaging material according to any one of the preceding claims, wherein the packaging material has a strain at break under in-plane tensile load of at most 5% in the machine direction of the paper and at most 15% in the cross direction of the paper.

13. A three-dimensional closed packaging article made of the multilayer metallized paper-based packaging material (1) according to any one of the preceding claims 1 to 12, the three-dimensional closed packaging article being obtained by molding, filling with edible products for human or animal consumption, and then sealing the packaging material.

14. Use of a multilayer metallized paper-based packaging material (1) according to any one of the preceding claims 1 to 12 for packaging edible products for human or animal consumption.

15. A packaged edible product comprising the multilayer metallized paper-based packaging material (1) according to any one of the preceding claims 1 to 12, filled with an edible product for human or animal consumption.

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