Multilayer metallized paper-based packaging material

Abstract

The present invention is related to a multi-layer metallized paper- based packaging material comprising: a paper layer having a grammage in the range of 30 to 120 g / m2; at least one organic barrier layer (3) of a polymer selected within the list of: polyvinylalcohol (PVOH), ethylene vinyl alcohol (EVOH), butenediol vinyl alcohol co-polymer (BVOH), or a combination thereof, in an amount of 0.5 to 20 g / m2; at least one inorganic barrier layer (4) selected within the list of: metals, metalloids, or a combination thereof, said inorganic layer having a thickness comprised between 1 and 100 nm; and at least one organic heat seal layer (5) said heat seal layer (5) being applied in an amount comprised between 2 and 20 g / m2; wherein the at least one organic barrier layer is provided by depositing an aqueous solution of the polymer onto the paper layer, the solution having a concentration of from 1 to 30 wt%, and then drying at a temperature of from 70 to 100 °C for a time of 0.5 to 30 seconds. The present invention also relates to a method for producing said multi-layer metallized paper-based packaging material.

Description

[0001] MULTILAYER METALLIZED PAPER-BASED PACKAGING MATERIAL

[0002] Field of the invention

[0003] The present invention is related to a multi-layer metallized paperbased packaging material with improved barrier properties, methods of producing such multi-layer metallized paper-based packaging materials, and packaging comprising such multi-layer metallized paper-based packaging materials.

[0004] Background of the invention

[0005] 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 CO2reduction 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 and quality. Typically, such barrier properties include gas barrier, for example to oxygen and water vapor (moisture), and if possible, also, liquid tightness.

[0006] One way to provide good moisture barrier in paper-based packaging materials, is the introduction of a metal or metalloid layer in a so-called "metallized" layer. In the present description, the word "metallized" (for instance in the expression "metallized barrier paper layer") is meant to encompass the deposition at the surface of paper or paperboard, of metal or metalloid atoms. One can even consider embodiments comprising the deposition of an alloy of metal and metalloid. Metalloids are close to metals in some of their characteristics. Aluminium oxide and silicon oxide are examples of metalloids. Problematic with the introduction of a metal layer in paper-based packaging material is the sensitivity of the metal layer to mechanical stress as well as poor adhesion of metal to paper surface, poor smoothness and high porosity of paper materials. Mechanical stress can - for example - easily result in a 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 manufacturing of package using for example a form-fill-seal packaging machine, whereby said material is stretched, bent, rolled, compressed and / or heated during forming and sealing of packages by conventional packaging forming methods. Such packaging manufacturing processes cause high mechanical and or chemical stress to the material and in particular to the ultrathin metallized layer of metal or metalloid, and therefore leads to damaging such layers, creating cracks and tears which are in most cases irreversible.

[0007] Organic barrier layers are also used, typically organic polymers, and are deposited by the application and subsequent drying of aqueous solutions and / or aqueous dispersions. These organic barrier layers can have acceptable gas barrier properties, but improvement is desired.

[0008] A further problem encountered with current methodologies for producing the paper-based packaging materials is that the processes for depositing the subsequent layers can dehydrate the paper layer, reducing its pliability and increasing damage to layers deposited thereon (i.e. the barrier layers) during transformation processes. Accordingly, rehydration of the paper layer is required and this is often slowed as a result of the extensive dehydration that occurs during processing.

[0009] Having considered the above, there is a need for a multi-layer metallized paper-based packaging material that exhibits simultaneously:

[0010] - sufficient barrier properties, in particular to oxygen and moisture, - a high resilience to mechanical stress, such that it keeps the same level of barrier even when subjected to transformation processes such as the ones used for manufacturing packages.

[0011] Summary of the invention

[0012] A first aspect of the present invention relates to a multi-layer metallized paper-based packaging material (1) comprising, from its outer side to its inner side:

[0013] - a paper layer (2) having a grammage in the range of 30 to 120 g / m2, at least one organic barrier layer (3) of a polymer selected within the list of: polyvinylalcohol (PVOH), ethylene vinyl alcohol (EVOH), butenediol vinyl alcohol co-polymer (BVOH), or a combination thereof, in an amount of 0.5 to 20 g / m2, at least one inorganic barrier layer (4) selected within the list of: metals, metalloids, oxides thereof, or a combination thereof, said inorganic layer having a thickness comprised between 1 and 100 nm, and

[0014] - at least one organic heat seal layer (5) said heat seal layer (5) being applied in an amount comprised between 2 and 20 g / m2, preferably in an amount comprised between 4 and 9 g / m2, wherein the at least one organic barrier layer is provided by depositing an aqueous solution or dispersion of the polymer onto the paper layer, the solution having a concentration of from 1 to 30 wt%, and then drying at a temperature of 70 to 100 °C for a time of 0.5 to 30 seconds.

[0015] A second aspect of the present invention relates to a multi-layer 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 to 120 g / m2, at least one organic barrier layer (3) of a polymer selected within the list of: polyvinylalcohol (PVOH), ethylene vinyl alcohol (EVOH), butenediol vinyl alcohol co-polymer (BVOH), or a combination thereof, in an amount of 0.5 to 20 g / m2, wherein the degree of crystallinity of the polymer of the at least one organic barrier layer (3) is in the range of 35 to 39; at least one inorganic barrier layer (4) selected within the list of: metals, metalloids, oxides thereof, or a combination thereof, said inorganic layer having a thickness comprised between 1 and 100 nm, and

[0016] - at least one organic heat seal layer (5) said heat seal layer (5) being applied in an amount comprised between 2 and 20 g / m2, preferably in an amount comprised between 4 and 9 g / m2.

[0017] In either the first aspect or the second aspect of the present invention the at least one inorganic layer may comprise metals or metalloids selected within the list of: aluminium, aluminium oxide (AIOx), or silicon oxide (SiOx), optionally wherein said metals and / or metalloids are deposited either by vacuum deposition or transfer metallization.

[0018] In either the first aspect or the second aspect of the present invention the at least one organic heat seal layer may comprise an ionomer. The ionomer may be an acrylic or methacrylic acid polymer, optionally wherein the counterion is sodium, further optionally wherein the ionomer has a molecular weight between 85 and 90 g / mol.

[0019] In either the first aspect or the second aspect of the present invention the at least one organic heat seal layer (5) may be deposited by aqueous dispersion coating. In either the first aspect or the second aspect of the present invention the paper layer (2) may be covered on its outer surface with an ink layer (6), optionally wherein the ink layer is selected within the list of: water-based inks, solvent-less inks, or a combination thereof.

[0020] In either the first aspect or the second aspect of the present invention the paper layer or the ink layer (if present) may be covered on its outer surface by an outermost layer (7) of an overprint varnish (OPV), optionally wherein the overprint varnish outermost layer (7) is a styrene acrylic varnish.

[0021] In either the first aspect or the second aspect of the present invention the packaging material may have a Water VapourTransmission Rate (WVTR) below 0.5 g / m2 / day (measured at 23°C, 85% Relative Humidity) and / or an Oxygen Transmission Rate (OTR) below 0.1 cm3 / m2 / day bar (measured at 23°C, 50% RH).

[0022] In either the first aspect or the second aspect of the present invention the packaging material may have a strain at break under in-plane tensile loading up to 2% in machine direction and up to 8% in the cross-machine direction of the paper.

[0023] A third aspect of the present invention relates to a method of producing a multi-layer metallized paper-based packaging material (1), the method comprising: a) providing a paper layer (2) having a grammage in the range of 30 to 120 g / m2; b) providing at least one organic barrier layer (3) over the paper layer, the at least one organic barrier layer comprising a polymer selected within the list of: polyvinylalcohol (PVOH), ethylene vinyl alcohol (EVOH), butenediol vinyl alcohol co-polymer (BVOH), or a combination thereof, in an amount of 0.5 to 20 g / m2; c) providing at least one inorganic barrier layer (4) over the at least one organic barrier layer, the at least one inorganic barrier layer comprising metals, metalloids, oxides thereof, or a combination thereof, said inorganic layer having a thickness comprised between 1 and 100 nm; and d) providing at least one organic heat seal layer (5) over the at least one inorganic barrier layer, the at least one heat seal layer (5) being applied in an amount comprised between 2 and 20 g / m2, preferably in an amount comprised between 4 and 9 g / m2; wherein providing the at least one organic barrier layer comprises depositing a solution or dispersion of the polymer onto the preceding layer, the solution having a concentration of from 1 to 30 wt%, and then drying at a temperature of 70 to 100 °C for a time of from 0.5 to 30 seconds.

[0024] A fourth aspect of the present invention relates to a tridimensional closed packaging item made of a multi-layer metallized paper-based packaging material (1) according to the first aspect or the second aspect of the present invention, which is obtained by forming, filling with an edible product for human or animal consumption, and then sealing said packaging material.

[0025] A fifth aspect of the present invention relates to the use of a multilayer metallized paper-based packaging material (1) according to the first aspect or the second aspect of the present invention, for packing an edible product for human or animal consumption.

[0026] A sixth aspect of the present invention relates to a packaged edible product, comprising a multi-layer metallized paper-based packaging material (1) according to the first aspect or the second aspect of the present invention, filled with an edible product for human or animal consumption.

[0027] 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:

[0028] Figure 1 shows a first embodiment of a multilayer structure according to the invention; Figure 2 shows a second embodiment of a multilayer structure according to the invention.

[0029] Detailed description of the invention Definitions

[0030] By "dispersion coating", it is meant a coating technique whereby an aqueous dispersion of fine polymer particles or polymer solution is applied to the surface of paper or board as such, in order to form a solid, non-porous film after drying. Dispersion coating can be performed by gravure, flexo-gravure, rod, blade, slot-die, curtain air knife, roll coating or any other known method of paper coating. Dispersion coating can create a much thinner layer than extrusion lamination and / or adhesive lamination, since the polymer is mixed in an aqueous water solution. This brings advantages in terms of quantity of polymer usage, its barrier performance and recyclability of resulting paper structure. The target of dispersion coating is to achieve a barrier layer against water, water vapour, grease, oil, gas, etc. by environmentally friendly coating. Another target is to prepare surface of paper material for a vacuum deposition process.

[0031] By "fibre", it is meant a cellulosic fibre, which is generally extracted from plants, seeds or trees; such fibres contain not only cellulose molecules, but also hemi-cellulose as well as lignin.

[0032] By "degree of crystallinity", it is meant the percentage of the polymer that is crystalline. The degree of crystallinity is determined using the method described by O.N. Tretinnikov and S.A. Zagorskaya (Journal of Applied Spectroscopy, Vol. 79, No. 4, pages 521 to 526, September 2012), incorporated herein by reference, and is applicable to PVOH, EVOH, and BVOH. The method subjects the polymer film to FTIR in the range of 4000 to 400 cm'1with an air background. The ratio of the absorbance bands An44and Ai094is then determined and inserted into the following equation to determine the degree of crystallinity: , •'4'1 144 cr(%) = — 13.1 + 89.5(—

[0033] •'41094

[0034] Multilayer Structure

[0035] The multilayer structure comprises the following layers, from outer surface to inner surface:

[0036] - a paper layer (2);

[0037] - an organic barrier layer (3);

[0038] - an inorganic barrier layer (4); and

[0039] - a heat seal layer (5).

[0040] In embodiments, the multilayer structure further comprises an ink layer (6) and / or an overprint varnish (7) deposited on the outer surface of the paper layer.

[0041] The multilayer structure may comprise further layers in addition to those described herein. For example, the multilayer structure may include additional layers external to the layers described herein and / or between the layers described herein. In embodiments, the multilayer structure comprises additional organic barrier layers and / or additional inorganic barrier layers.

[0042] Preferably the multilayer structure has a Water Vapour Transmission Rate (WVTR) below 0.5 g / m2 / day (measured as described in ISO 2538-20 at 23°C, 85% Relative Humidity) and / or an Oxygen Transmission Rate (OTR) below 0.1 cm3 / m2 / day bar (measured as described in ASTM F3136-22 at 23°C, 50% RH). Paper Layer

[0043] The multilayer structure includes a paper layer (2) as its principle structural component. Paper refers to material comprised of fibres obtained by the pulping of plant sources, such as trees, and is increasingly produced by recycling. Substantially any thickness of paper that possesses the material properties required for the final packaging product may be used in the present invention. The paper should be sufficiently robust that it effectively protects the contents of the final packaged product during transport and storage, but should be sufficiently flexible to permit forming into the final packaged product. In general, paper used for the paper layers of the present invention may have grammage (i.e. weight per unit area) of from about 30 g / m2to about 120 g / m2.

[0044] As mentioned above, a key feature of paper is its flexibility, which is influenced by its water content and, if paper is overly dried, it becomes brittle. In addition, it has been found that excessive dehydration impairs the rate at which the paper may be rehydrated. This often occurs during the deposition of the subsequent layers, meaning that the paper layer of the multilayer structure requires rehydration prior to forming into packaging and / or the application of inks and overprint varnishes. Without rehydration, the brittle paper has an increased propensity to crease, which increases stress and damage to the applied barrier layers, thereby compromising the overall effectiveness of the packaging.

[0045] Organic Barrier Layer

[0046] The multilayer structure includes at least one organic barrier layer (3). The organic barrier layer provides a barrier to the passage of gases (such as oxygen) and moisture through the multilayer packaging. In addition, the at least one organic barrier layer provides a more suitable surface for the deposition and adhesion of the inorganic barrier layer compared to the preceding paper layer.

[0047] The at least one organic barrier layer comprises PVOH, EVOH, BVOH, or mixtures thereof.

[0048] The PVOH may have a degree of hydrolysis of at least 80%, preferably at least 90%, more preferably at least 95%. In embodiments, the degree of hydrolysis is from 95 to 99.9%.

[0049] The EVOH may have a degree of hydrolysis of at least 80%, preferably at least 90%, more preferably at least 95%. In embodiments, the degree of hydrolysis is from 95 to 99.9%.

[0050] The BVOH may have a degree of hydrolysis of at least 80%, preferably at least 90%, more preferably at least 95%. In embodiments, the degree of hydrolysis is from 95 to 99.9%.

[0051] A mixture of the polymers may be used, such as a mixture of PVOH, EVOH, and BVOH, a mixture of PVOH and EVOH, a mixture of EVOH and BVOH, or a mixture of PVH and BVOH. In embodiments, a mixture of PVOH and EVOH is used. The mixture of PVOH and EVOH may comprise 1 to 10 wt% PVOH.

[0052] The at least one organic barrier layer is present in an amount of 0.5 to 20 g / m2, preferably in an amount of 1 to 10 g / m2, more preferably in an amount of 2 to 8 g / m2.

[0053] In embodiments, the at least one organic barrier layer is provided by depositing an aqueous solution or dispersion of the polymer onto the paper layer and then drying at an elevated temperature for a drying period. The elevated temperature may be from 70 to 100 °C, preferably the temperature is from 75 to 95 °C, more preferably from 80 to 90 °C, most preferably about 80 °C. The drying period may be from 0.5 to 30 seconds, preferably from 1 to 15 seconds.

[0054] The time for which the organic barrier layer is dried may be the time taken for a web of coated material to pass through an oven with length of from 10 to 30 m at a line speed of from 100 to 200 m / min, for example, a length of 20 meters at a line speed of 200 m / min.

[0055] The aqueous solution or dispersion may be applied by any suitable technique. For example, by spraying, brushing, roll coating, gravure coating or smooth roll coating.

[0056] In embodiments, the at least one organic barrier layer is deposited through multiple cycles of depositing and drying the aqueous solution or dispersion of the polymer. For example, the at least one organic barrier layer may be deposited in two cycles.

[0057] It has been found that drying the at least one organic barrier layer under these conditions produces an organic barrier layer with superior OTR compared to organic barrier layers of equivalent thickness that are dried under other conditions. In addition, the mild drying conditions employed reduce the extent to which the paper layer is dehydrated and enables the paper to rehydrate at a greater rate. This reduces the rehydration time needed for the paper to regain the required flexibility.

[0058] The concentration of the polymer in the aqueous solution or dispersion may be from 1 to 30 wt%, preferably from 2 to 20 wt%, more preferably from 5 to 12 wt%. In embodiments, the degree of crystallinity of the polymer of the at least one organic barrier layer is in the range of 35 to 39%. Preferably the degree of crystallinity of the polymer of the at least one organic barrier layer is in the range of 36 to 38.5%, more preferably in the range of 37 to 38%, most preferably the degree of crystallinity is about 38%. The degree of crystallinity of the polymer of the at least one organic barrier layer may be determined by as the method described by O.N. Tretinnikov and S.A. Zagorskaya (Journal of Applied Spectroscopy, Vol. 79, No. 4, pages 521 to 526, September 2012) incorporated herein by reference in its entirety. Without wishing to be bound by theory, it is thought that the degree of crystallinity of the polymer of the at least one organic barrier layer has an influence on the barrier properties of the polymer.

[0059] Inorganic Barrier Layer

[0060] The multilayer structure includes an inorganic barrier layer (4). The inorganic barrier layer provides a barrier to the passage of gases (such as oxygen) and moisture through the multilayer packaging.

[0061] The inorganic barrier layer comprises metals, metalloids, oxides thereof, or a combination thereof. The thickness of the inorganic barrier layer is from about 1 to about 100 nm. Substantially any metal, metalloid, or oxide thereof may be used that provides sufficient barrier properties, robustness, and flexibility in the thickness that it is applied. In addition, the metal, metalloid, or oxide thereof must be food safe.

[0062] In embodiments, the inorganic barrier layer comprises aluminium, aluminium oxide (AIOX), silicon oxide (SiOx), or combinations thereof. Substantially any suitable methodology may be used to deposit the inorganic barrier layer. In embodiments, the inorganic barrier layer is deposited by vacuum deposition or transfer metallization onto the preceding layer, typically the at least one organic barrier layer.

[0063] Heat Sealing Layer

[0064] The multilayer structure includes a heat sealing layer (5). The inclusion of a heat sealing layer permits the multilayer structure to be converted to a packaged product without the application of adhesives by heat sealing, such as by a form, fill, and seal machine. The heat sealing layer also contributes to the overall barrier properties of the multilayer structure.

[0065] The heat sealing layer may be a thermoplastic organic polymer. Substantially any food safe thermoplastic polymer may be used, on condition that it has the requisite material properties of robustness and flexibility in the thickness used. In embodiments, the heat sealing layer comprises an ionomer. The ionomer may be an acrylic or methacrylic acid homopolymer or copolymer with counter ions, such as sodium. In a preferred embodiment, the ionomer is an ethylene acrylic acid copolymer with sodium counter ions.

[0066] The heat sealing layer may be deposited as an aqueous dispersion and subsequently dried onto the surface of the preceding layer, typically the inorganic barrier layer. Ink Layer

[0067] Optional ly, the multilayer structure includes an ink layer (6). The ink layer is used to improve the aesthetic qualities of the packaging and / or present information regarding the contents of the packaging.

[0068] The ink may have a thickness of between about 0.5 and 5 g / m2. Preferably the ink is a water-based ink, a solvent-free ink, or a combination thereof. The ink may be applied using any suitable printer or application technique.

[0069] Overprint Varnish

[0070] Optionally, the multilayer structure includes an overprint varnish (7). The OPV is used to improve the aesthetic qualities of the packaging and also lowers water vapour transmission and protects the paper layer from water external to the packaging.

[0071] The OPV may have a thickness of between about 0.5 and about 10 g / m2. Preferably the OPV is a styrene acrylic varnish. The OPV may be applied using any suitable application technique.

[0072] Method of Production

[0073] The method of producing a multi-layer metallized paper-based packaging material comprises: a) providing a paper layer having a grammage in the range of 30 to 120 g / m2; b) providing at least one organic barrier layer (3) over the paper layer, the at least one organic barrier layer comprising a polymer selected within the list of: polyvinylalcohol (PVOH), ethylene vinyl alcohol (EVOH), butenediol vinyl alcohol co-polymer (BVOH), or a combination thereof, in an amount of 0.5 to 20 g / m2, preferably in an amount of 1 to 10 g / m2, more preferably in an amount of 2 to 8 g / m2; c) providing at least one inorganic barrier layer (4) over the at least one organic barrier layer, the at least one inorganic barrier layer comprising metals, metalloids, oxides thereof, or a combination thereof, said inorganic layer having a thickness comprised between 1 and 100 nm; and d) providing at least one organic heat seal layer (5) over the at least one inorganic barrier layer, the at least one heat seal layer (5) being applied in an amount comprised between 2 and 20 g / m2, preferably in an amount comprised between 4 and 9 g / m2; wherein providing the at least one organic barrier layer comprises depositing a solution or dispersion of the polymer onto the preceding layer, the solution or dispersion having a concentration of from 1 to 30 wt%, and then drying at a temperature of from 70 to 100 °C for a time of from 0.5 to 30 seconds.

[0074] Preferably, the temperature is from 75 to 95 °C, more preferably from 80 to 90 °C, most preferably about 80 °C. Preferably, the drying time is from 1 to 15 seconds. Preferably, the solution or dispersion of the polymer has a concentration of from 2 to 20 wt%, more preferably from 5 to 12 wt%.

[0075] The method may further comprise the step of providing an ink layer on the outer surface of the paper layer.

[0076] The method may further comprise the step of providing an overprint varnish on the outer surface of the paper layer or, if present, the ink layer.

[0077] The method may further comprise the step of rehydrating the paper layer, typically prior to the application of an overprint varnish and / or ink layer if used. Rehydration of the paper layer may be achieved by applying moisture as a water film, a spray, or as steam.

[0078] The method may be a batch method or a continuous method. The method may be a rol l-to-rol I process, wherein the paper layer is unspooled from an initial roll and the multilayer packaging material spooled onto a final roll, with processing to convert the paper to the multilayer packaging material, such as the provision of the further layers (e.g. the at least one organic barrier layer, the at least one inorganic barrier layer, and at least one organic heat seal layer) occurring to the length of material that is exposed between the initial and final roll.

[0079] Exemplary Embodiments

[0080] In figure 1 is illustrated a first embodiment of the invention. In this embodiment, the multilayer structure 1 comprises in order, from its outer side (i.e. the side of the material which is turned towards the outside of the package made thereof) towards its inner side (i.e. the inner side in contact with the packaged product in a package made thereof):

[0081] - a highly smooth paper layer 2 of grammage 62 g / m2,

[0082] - an organic barrier layer of polyvinyl alcohol (PVOH) and ethylene vinyl alcohol (EVOH) 3 that provides mainly gas (especially oxygen) barrier properties and is applied as an aqueous solution in weight of 3 g / m2over two deposition cycles, drying at a temperature of 80 to 90 °C and a line speed of 100 to 200 m / min,

[0083] - an inorganic vacuum deposited layer 4 of aluminium having a thickness of between 50 and 100 nm, which provides mainly moisture vapour barrier properties, and

[0084] - a heat sealing layer 5 of methacrylic acid ionomer-based coating which serves as a heat seal layer and is applied as an aqueous dispersion in weight of 5 g / m2. In this embodiment, the deposition techniques for the at least one organic barrier layer, as mentioned above, improves the barrier performance of the resulting packaging, increase the robustness of the resulting packaging, and improve its processability.

[0085] In figure 2, is depicted a structure similar to that described above in relation to figure 1.

[0086] However, in this second exemplary embodiment of the invention, the outer surface of the paper layer 2 is covered with two layers as follows, in order from the outside face to the inside of the packaging material:

[0087] - an outermost acrylic based overprint varnish layer 7, which is applied as an aqueous dispersion in weight of 1 g / m2,

[0088] - a water-based ink 6 applied as an aqueous dispersion in weight of 1 g / m2; this water-based ink layer 6 is located between the outermost overprint varnish layer 7, and the paper layer 2.

[0089] The rest of the layers in the structure 1 remain similar to the structure described in reference to figure 1, that is to say:

[0090] - an organic barrier layer of polyvinyl alcohol (PVOH) and ethylene vinyl alcohol (EVOH) 3 that provides mainly gas (especially oxygen) barrier properties and is applied as an aqueous solution in weight of 3 g / m2over two deposition cycles, drying at a temperature of 80 to 90 °C and a line speed of 100 to 200 m / min,

[0091] - an inorganic vacuum deposited layer 4 of aluminium having a thickness of between 50 and 100 nm, which provides mainly moisture vapour barrier properties, and

[0092] - a heat sealing layer 5 of methacrylic acid ionomer-based coating which serves as a heat seal layer and is applied as an aqueous dispersion in weight of 5 g / m2. The structures corresponding to the above-described embodiments have improved barrier properties, robustness, and processability.

[0093] In all of the embodiments of the invention described above, the multilayer structure can comprise other additional and optional layers not described in full details therein. Such layers can comprise for instance a print layer on the outer surface of the paper layer, as well as optionally a protective layer that is deposited on the external side of the print layer, and therefore constitutes the outermost layer of the whole structure. Print and optional protective layers are not described in more detail because they are known technology to the skilled person.

[0094] Examples

[0095] Paper with a grammage of 62 g / m2was sourced from UPM Communication Papers.

[0096] Exceval 2117 (a PVOH / EVOH polymer mixture) was sourced from Kuraray.

[0097] The PVOH / EVOH polymer mixture was dissolved in water to form an aqueous solution. The aqueous solution was then deposited onto the surface of the paper and dried in two cycles to provide an organic barrier layer with a grammage of 1.5 to 3 g / m2. Multiple samples were prepared, varying the drying temperature and drying time. Drying was achieved by passing the sample through an oven with a length of 20 m at the indicated line speed.

[0098] Samples of each of the papers with the organic barrier layer were subjected to testing to determine:

[0099] - the degree of crystallinity of the polymer of the organic barrier layer, determined using FTIR with an air background in combination with the equation: , 211 144 cr(%) = — 13.1 + 89.5(—

[0100] 211094 as described by O.N. Tretinnikov and S.A. Zagorskaya (Journal of Applied Spectroscopy, Vol. 79, No. 4, pages 521 to 526, September 2012);

[0101] - the water contact angle of the polymer of the organic barrier layer ; - the oxygen transmission rate (OTR) of the flat material, determined as described in ASTM F3136-22, with measurements conducted at 50% RH and 23 °C;

[0102] - the moisture content of the combined paper and organic barrier layer, determined as described in ISO 287:2017.

[0103] The results from the above testing are shown in Table 1.

[0104]

[0105] The results show that drying the deposited organic barrier layers at a temperature of from 70 to 100 °C for a time of 6 to 12 seconds leads to an improvement in OTR. Without wishing to be bound by theory, it is believed that this improvement is attributable to a lowering in the crystallinity of the polymer comprising the organic barrier layer.

Claims

Claims1. A multi-layer 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 to 120 g / m2, at least one organic barrier layer (3) of a polymer selected within the list of: polyvinylalcohol (PVOH), ethylene vinyl alcohol (EVOH), butenediol vinyl alcohol co-polymer (BVOH), or a combination thereof, in an amount of 0.5 to 20 g / m2, at least one inorganic barrier layer (4) selected within the list of: metals, metalloids, oxides thereof, or a combination thereof, said inorganic layer having a thickness comprised between 1 and 100 nm, and at least one organic heat seal layer (5) said heat seal layer (5) being applied in an amount comprised between 2 and 20 g / m2, preferably in an amount comprised between 4 and 9 g / m2, wherein the at least one organic barrier layer is provided by depositing an aqueous solution or dispersion of the polymer onto the paper layer, the solution having a concentration of from 1 to 30 wt%, and then drying at a temperature of 70 to 100 °C for a time of 0.5 to 30 seconds.

2. A multi-layer 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 to 120 g / m2, at least one organic barrier layer (3) of a polymer selected within the list of: polyvinylalcohol (PVOH), ethylene vinyl alcohol (EVOH), butenediol vinyl alcohol co-polymer (BVOH), or a combination thereof, in an amountof 0.5 to 20 g / m2, wherein the degree of crystallinity of the polymer of the at least one organic barrier layer (3) is in the range of 35 to 39%; at least one inorganic barrier layer (4) selected within the list of: metals, metalloids, oxides thereof, or a combination thereof, said inorganic layer having a thickness comprised between 1 and 100 nm, and- at least one organic heat seal layer (5) said heat seal layer (5) being applied in an amount comprised between 2 and 20 g / m2, preferably in an amount comprised between 4 and 9 g / m2.

3. The multi-layer metallized paper-based packaging material (1) according to any one of claims 1 or 2, wherein the at least one inorganic layer comprises metals or metalloids selected within the list of: aluminium, aluminium oxide (AIOx), or silicon oxide (SiOx), optionally wherein said metals and / or metalloids are deposited either by vacuum deposition or transfer metallization.

4. The multi-layer metallized paper-based packaging material (1) according to any one of the preceding claims 1 to 3, wherein the at least one organic heat seal layer comprises an ionomer.

5. The multi-layer metallized paper-based packaging material (1) according to claim 4, wherein the ionomer is an acrylic or methacrylic acid polymer, optionally wherein the counterion is sodium, further optionally wherein the ionomer has a molecular weight between 85 and 90 g / mol.

6. The multi-layer metallized paper-based packaging material (1) according to any one of the preceding claims 1 to 5, wherein the at least one organic heat seal layer (5) is deposited by aqueous dispersion coating.

7. The multi-layer metallized paper-based packaging material (1) according to any one of the preceding claims, wherein the paper layer (2) is covered on its outer surface with an ink layer (6), optionally wherein the ink layer is selected within the list of: water-based inks, solvent-less inks, or a combination thereof.

8. The multi-layer metallized paper-based packaging material (1) according to any preceding claim, wherein the paper layer or the ink layer, if present, is covered on its outer surface by an outermost layer (7) of an overprint varnish (OPV), optionally wherein the overprint varnish outermost layer (7) is a styrene acrylic varnish.

9. The multi-layer metallized paper-based packaging material (1) according to any one of the preceding claims, wherein the packaging material has a Water Vapour Transmission Rate (WVTR) below 0.5 g / m2 / day (measured at 23°C, 85% Relative Humidity) and / or an Oxygen Transmission Rate (OTR) below 0.1 cm3 / m2 / day bar (measured at 23°C, 50% RH).

10. The multi-layer 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 loading up to 2% in machine direction and up to 8% in the cross-machine direction of the paper.

11. A method of producing a multi-layer metallized paper-based packaging material (1), the method comprising: a) providing a paper layer (2) having a grammage in the range of 30 to 120 g / m2; b) providing at least one organic barrier layer (3) over the paper layer, the at least one organic barrier layer comprising a polymer selectedwithin the list of: polyvinylalcohol (PVOH), ethylene vinyl alcohol (EVOH), butenediol vinyl alcohol co-polymer (BVOH), or a combination thereof, in an amount of 0.5 to 20 g / m2; c) providing at least one inorganic barrier layer (4) over the at least one organic barrier layer, the at least one inorganic barrier layer comprising metals, metalloids, oxides thereof, or a combination thereof, said inorganic layer having a thickness comprised between 1 and 100 nm; and d) providing at least one organic heat seal layer (5) over the at least one inorganic barrier layer, the at least one heat seal layer (5) being applied in an amount comprised between 2 and 20 g / m2, preferably in an amount comprised between 4 and 9 g / m2; wherein providing the at least one organic barrier layer comprises depositing a solution or dispersion of the polymer onto the preceding layer, the solution having a concentration of from 1 to 30 wt%, and then drying at a temperature of 70 to 100 °C for a time of from 0.5 to 30 seconds.

12. A tridimensional closed packaging item made of a multi-layer metallized paper-based packaging material (1) according to any one of the preceding claims 1 to 10, which is obtained by forming, filling with an edible product for human or animal consumption, and then sealing said packaging material.

13. Use of a multi-layer metallized paper-based packaging material (1) accordingto any one of the preceding claims 1 to 10, for packing an edible product for human or animal consumption.

4. A packaged edible product, comprising a multi-layer metallized paperbased packaging material (1) according to any one of the preceding claims 1 to 10, filled with an edible product for human or animal consumption. 1

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