A method for manufacturing a paper or paperboard based packaging laminate

Abstract

The present invention relates to a method for manufacturing a paper or paperboard based packaging laminate, said method comprising: a) providing a paper or paperboard base layer, b) providing a metallized barrier paper layer comprising a barrier paper substrate having a first main surface and a second main surface and a metallization layer having a thickness in the range of 10-500 nm deposited on the first main surface, c) subjecting the metallization layer to a surface treatment process selected from the group consisting of corona treatment and plasma treatment, such that the surface treated metallization layer has a surface energy in the range of 35-75 mN / m, as determined by ISO 19403-2:2017, d) applying a water based adhesive composition to the surface treated metallization layer and / or the paper or paperboard base layer, and e) laminating the paper or paperboard base layer to the surface treated metallization layer using the water based adhesive composition, such that the adhesive composition forms an adhesive tie layer between the paper or paperboard base layer and the metallization layer of the metallized barrier paper layer.

Description

[0001] A METHOD FOR MANUFACTURING A PAPER OR PAPERBOARD BASED PACKAGING LAMINATE

[0002] Technical field

[0003] The present disclosure relates to methods for manufacturing paper and paperboard based packaging materials. More specifically, the present disclosure relates to the manufacture of paper and paperboard based packaging laminates comprising a metallized barrier paper layer.

[0004] Background

[0005] Coating of paper or paperboard with plastics is often employed to combine the mechanical properties of the paper or paperboard with the barrier and sealing properties of a plastic film. Paperboard provided with even a relatively small amount of a suitable plastic material can provide the properties needed to make the paperboard suitable for many demanding applications, for example as liquid or food packaging board. In liquid or food packaging board, polyolefin coatings are frequently used as liquid barrier layers, heat sealing layers and adhesives. However, the recycling of such polymer coated board is difficult since it is difficult to separate the polymers from the fibers.

[0006] Also, in many cases the water vapor barrier properties of the polymer coated paperboard are still insufficient unless the coating layers are thick or combinations of different polymer coating layers are used. Therefore, in order to ensure high water vapor barrier properties, the polymer coated paperboard is often combined with one or more layers of aluminum foil. However, the addition of polymer and aluminum foil add significant costs and the combination of polymer coating layers and aluminum foils makes recycling of the materials more difficult. Also, due to its high carbon footprint there is a wish to replace aluminum foils in paperboard based packaging materials.

[0007] Aseptic packaging for long shelf-life products such as milk and juices are usually made from liquid or food packaging board comprising a multilayer paperboard based substrate, an outermost heat-sealable polyolefin (e.g. polyethylene, PE) layer and innermost layers of polyolefin and aluminum. The aluminum foil layer, needed to provide water vapor and oxygen barrier properties, is usually incorporated between layers of polyethylene to provide the following structure: PE / paperboard / PE / aluminum foil / PE.

[0008] In the prior art, attempts have been made to replace the aluminum foil with more environmentally friendly and / or easier to recycle solutions, but so far with no real success.

[0009] One solution discussed in the prior art is to deposit a thin metallization layer directly onto a paper or paperboard substrate using for example chemical or physical vapor deposition techniques. The thin metallization layer may for example comprise a thin layer of aluminum, AI2O3, AIOx, or SiOx. A problem with applying these metallization layers directly onto a paper or paperboard substrate is that the substrate needs to be degassed. This means that the process adds costs, but the degassing also means that the paper or paperboard substrate is dried to a very low moisture content. This drying and the subsequent remoisturizing to ambient moisture levels changes the mechanical properties of the board. The drying will not only increase the cracking tendency and post-convertability of the board but there is also a significant risk of cracking of the thin and sensitive metallization layer as the board is remoisturized.

[0010] As an alternative, it has been proposed to replace the aluminum foil with metallized polymer or cellulose based films, such as metallized polyethylene or polypropylene films, which are laminated to the paperboard-based substrate by an adhesive tie layer. The adhesive tie layer may for example be applied in melt form by extrusion coating or in the form of a water based solution or dispersion using liquid coating methods.

[0011] A problem with metallized films is that the thin metallization layer is sensitive to movements in the barrier paper substrate on which the metallization layer is applied and movements in the finished laminate, which may cause cracks or pinholes in the metallization. High temperatures applied in the lamination processes when a tie layer or heatsealing layer is extruded might lead to the metallized polymer or cellulose based film being stretched (expanded) and then shrunk when cooled, which can cause pin holes and cracks in the thin and sensitive metallization layer affecting the gas barrier properties of the laminate negatively.

[0012] Dispersion lamination using a water based adhesive composition can be used to laminate barrier paper to board to produce a high performing barrier laminate structure, for instance, in liquid packaging board. The benefit of using dispersion lamination with a water based adhesive instead of conventional extrusion coating with a thermoplastic resin are several, but mainly connected to reduction of fossilbased polymer resins and improved recyclability since the water based adhesive is easy to dissolve / disintegrate in the re-pulping process.

[0013] Dispersion lamination has already been demonstrated to work well for laminating uncoated barrier paper to board, without any special pre-treatment of the barrier paper surface prior adhesive application. However, it has been found problematic to apply the same technique to a metallized paper surface since the metallized surface does not absorb and / or adsorb the water based adhesive, and the surface energy of the metallized paper surface is too low to achieve the required wet and dry adhesion between the adhesive and the metallized paper.

[0014] One solution used in the prior art would be to utilize a primer. However, a primer will add cost and might still impact the barrier performance of the applied adhesive. Another solution would be to utilize a solvent based adhesive or a cosolvent in the adhesive. However, such solvents might lead to problem with VOC's that will be entrapped in the laminate structure or be absorbed by the base board.

[0015] Thus, there is a need to solve the aforementioned problems, and to improve the spreading and adhesion of a water based adhesive on a metallized paper for making a paper or paperboard based packaging laminate. Description of the invention

[0016] It is an object of the present disclosure to provide an alternative method for manufacturing a paper or paperboard based packaging laminate, such as a liquid or food packaging board, which provides good water vapor barrier properties even at higher relative humidity and temperature.

[0017] It is a further object of the present disclosure, to provide an alternative method for manufacturing a paper or paperboard based packaging laminate comprising a metallized barrier paper layer, which overcomes at least some of the problems associated with prior art manufacturing methods.

[0018] The above-mentioned objects, as well as other objects as will be realized by the skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure.

[0019] The present invention is based on the understanding that very thin metal layers, typically having a thickness in the range of 10-500 nm, and more preferably in the range of 50-250 nm, formed by vacuum coating processes, such as physical vapor deposition (PVD) or chemical vapor deposition (CVD), can provide good oxygen and water vapor barrier properties, comparable to the barrier properties of thicker aluminum foils. As the thickness of the metallization layer is typically at least an order of magnitude lower than the thickness of conventional foils, the metal content of the products can be dramatically reduced. However, these thin metallization layers are also very sensitive to damage which can severely impair their oxygen and water vapor barrier properties.

[0020] The present invention is based on the realization that at least some of these problems can be overcome by subjecting the metallization layer to a surface treatment process selected from the group consisting of corona treatment and plasma treatment, such that the surface treated metallization layer has a surface energy in the range of 35-75 mN / m, as determined by ISO 19403-2:2017, before applying the water based adhesive composition to the surface treated metallization layer. It has been found that the metallized paper surface after the surface treatment process should have a surface energy of at least 35 mN / m to obtain a sufficient adhesion, but not higher than 75 mN / m, since surface treatment to higher surface energy may typically be associated with damages to the thin and sensitive metallization layer, leading to deterioration of the oxygen and water vapor barrier properties.

[0021] According to a first aspect illustrated herein, there is provided a method for manufacturing a paper or paperboard based packaging laminate, said method comprising: a) providing a paper or paperboard base layer, b) providing a metallized barrier paper layer comprising a barrier paper substrate having a first main surface and a second main surface and a metallization layer having a thickness in the range of 10-500 nm deposited on the first main surface, c) subjecting the metallization layer to a surface treatment process selected from the group consisting of corona treatment and plasma treatment, such that the surface treated metallization layer has a surface energy in the range of 35-75 mN / m, as determined by ISO 19403-2:2017, d) applying a water based adhesive composition to the surface treated metallization layer and / or the paper or paperboard base layer, and e) laminating the paper or paperboard base layer to the surface treated metallization layer using the water based adhesive composition, such that the adhesive composition forms an adhesive tie layer between the paper or paperboard base layer and the metallization layer of the metallized barrier paper layer.

[0022] Paper generally refers to a material manufactured in thin sheets from the pulp of wood or other fibrous substances comprising cellulose fibers, used for writing, drawing, or printing on, or as packaging material.

[0023] Paperboard generally refers to strong, thick paper or cardboard comprising cellulose fibers used for boxes and other types of packaging. Paperboard can either be bleached or unbleached, coated or uncoated, and produced in a variety of thicknesses, depending on the end use requirements. Paperboard may be a single ply material, or a multiply material comprised of two or more plies. A common type of multiply paperboard is comprised of a lower density mid-ply (also sometimes referred to as “bulk ply”) sandwiched between two higher density outer plies. The lower density mid-ply may typically have a density below 750 kg / m3, preferably below 700, below 650, below 600, below 550, below 500, below 450, below 400 or below 350 kg / m3. The higher density outer plies typically have a density at least 100 kg / m3higher than the mid-ply, preferably at least 200 kg / m3higher than the mid-ply.

[0024] A paper or paperboard based packaging laminate is a packaging material formed mainly from a paper or paperboard base layer. The paper or paperboard base layer can be made from pulp, including pulp from virgin fiber, e.g. mechanical, chemical and / or thermomechanical pulps. It can also be made from broke or recycled paper. In addition to the paper or paperboard base layer, the paper or paperboard based packaging laminate may comprise additional layers or coatings designed to improve the performance and / or appearance of the packaging laminate.

[0025] In some embodiments, the paper or paperboard base layer used in the inventive method has a grammage in the range of 20-800 g / m2.

[0026] In some embodiments, the paper or paperboard base layer has a density below 800 kg / m3, preferably below 700 kg / m3, more preferably below 600 kg / m3. Unless otherwise stated, the density is determined according to the standard ISO 534.

[0027] The paper or paperboard base layer may be a single ply paper or paperboard or a multiply paper or paperboard. In some embodiments, the paper or paperboard base layer is a multiply paper or paperboard. In some embodiments the paper or paperboard base layer is a multiply paperboard comprised of two or more plies. In some embodiments the paper or paperboard base layer is a multiply paperboard comprised of three or more plies. In some embodiments the paper or paperboard base layer is a multiply paperboard comprised of a lower density mid-ply sandwiched between two higher density outer plies. The structure of the inventive paperboard based packaging laminate enables the use of recycled fibers in the paper or paperboard base layer since the barrier structure hinders the migration of undesired contaminants, such as mineral oil based compounds from the recycled fibers. Thus, in some embodiments, the paper or paperboard base layer comprises at least 5 wt% recycled fibers, preferably at least 10 wt% recycled fibers. In some embodiments, the recycled fibers are recycled fibers obtained from used food or beverage containers.

[0028] In some embodiments, the paper or paperboard base layer comprises an internal sizing agent in an amount of 50-10 000 g / tn, preferably 100-6000 g / tn, based on the total dry weight of the paper or paperboard base layer. Internal sizing agents are chemicals that are added to the pulp to increase the hydrophobicity of the paper or paperboard base layer and may include acid type sizing chemicals, basic or neutral sizing agents. Examples of internal sizing agents include alkyl ketene dimer (AKD), alkyl succinic anhydride (ASA), rosin size, or combinations thereof.

[0029] In some embodiments, the paper or paperboard base layer further comprises a mineral coating layer on one or both of its main surfaces. In some embodiments, the mineral coating layer comprises 50-95 wt% of a particulate mineral, and 5-50 wt% of a binder, based on the total dry weight of the mineral coating layer. In some embodiments, the mineral coating layer comprises 65-95 wt% of a particulate mineral, and 5-35 wt% of a binder. In some embodiments, the mineral coating layer comprises 80-94 wt% of a particulate mineral, and 6-20 wt% of a binder. In some embodiments, the mineral coating layer comprises 86-94 wt% of a particulate mineral, and 6-14 wt% of a binder. In some embodiments, the particulate mineral is selected from the group consisting of kaolin, calcium carbonate, bentonite, talc, and combinations thereof, preferably kaolin or calcium carbonate, and more preferably kaolin. The binder may comprise a single binder or a combination of binders. The binder may preferably comprise or consist of a water-dispersible or water-soluble binder, or a combination thereof. In some embodiments, the water-dispersible binder comprises a latex binder. In some embodiments, the water-soluble binder comprises a starch or starch derivatives, PVOH or modified versions thereof, a cellulose derivate such as CMC, a protein, or seaweed. An advantage of using a water-soluble binder is that the laminate will be even more easy to recycle. In some embodiments, the binder comprises 10- 100 wt%, preferably 20-100 wt%, and more preferably 30-90 wt% or 30-80 wt%, of a water soluble polymer. In some embodiments, the grammage of the mineral coating layer is in the range of 4-30 g / m2, more preferably in the range of 6-14 g / m2.

[0030] The paperboard base layer, before the lamination, typically has a high water vapor transmission rate (WVTR) value, i.e. poor water vapor transmission resistance. In some embodiments, the paperboard base layer has a water vapor transmission rate (WVTR), measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C, of above 100 g / m2 / 24h, typically above 200 g / m2 / 24h, above 300 g / m2 / 24h, or above 1000 g / m2 / 24h.

[0031] In the inventive method, the paper or paperboard base layer is combined with a metallized barrier paper layer comprising a barrier paper substrate having a first main surface and a second main surface and a metallization layer having a thickness in the range of 10-500 nm deposited on the first main surface.

[0032] Onto the provided paperboard base layer, the metallized barrier paper layer is laminated using a water based adhesive composition. A surface of the paperboard base layer is laminated to the metallized surface of the metallized barrier paper layer using the water based adhesive composition, for example in a press nip, such that the adhesive composition forms an adhesive tie layer between the paperboard base layer and the metallized barrier paper layer.

[0033] In some embodiments, the barrier paper substrate is a thin high-density paper such as a kraft paper, greaseproof paper, glassine paper, tracing paper, translucent paper, transparent paper, machine glazed paper or parchment paper.

[0034] In some embodiments, the barrier paper substrate is a microfibrillated cellulose (MFC) film. In some embodiments, the MFC film comprises at least 50 wt% of MFC based on the total dry weight of the MFC film. In some embodiments, the barrier paper substrate is coated with 0.5-8 g / m2of a microfibri Hated cellulose (MFC).

[0035] Microfibrillated cellulose (MFC) shall in the context of the patent application mean a cellulose particle, fiber or fibril having a width or diameter of from 20 nm to 1000 nm. Various methods exist to make MFC, such as single or multiple pass refining, pre-hydrolysis followed by refining or high shear disintegration or liberation of fibrils. One or several pre-treatment steps is usually required in order to make MFC manufacturing both energy efficient and sustainable. The cellulose fibers of the pulp used when producing MFC may thus be native or pre-treated enzymatically or chemically, for example to reduce the quantity of hemicellulose or lignin. The cellulose fibers may be chemically modified before fibrillation, wherein the cellulose molecules contain functional groups other (or more) than found in the original cellulose. Such groups include, among others, carboxymethyl (CM), aldehyde and / or carboxyl groups (cellulose obtained by N-oxyl mediated oxidation, for example "TEMPO"), or quaternary ammonium (cationic cellulose). After being modified or oxidized in one of the above-described methods, it is easier to disintegrate the fibers into MFC.

[0036] In some embodiments, the barrier paper substrate comprises an internal sizing agent in an amount of 50-10 000 g / tn, preferably 100-6000 g / tn, based on the total dry weight of the barrier paper substrate. Internal sizing agents are chemicals that are added to the pulp to increase the hydrophobicity of the barrier paper substrate and may include acid type sizing chemicals, basic or neutral sizing agents. Examples of internal sizing agents include alkyl ketene dimer (AKD), alkyl succinic anhydride (ASA), rosin size, or combinations thereof.

[0037] In some embodiments, the barrier paper substrate has a grammage in the range of 20-120 g / m2, preferably in the range of 25-120 g / m2.

[0038] In some embodiments, the barrier paper substrate has a density in the range of 700-1300 kg / m3, preferably in the range of 750-1200 kg / m3. In some embodiments, the barrier paper substrate comprises at least 10 wt% recycled cellulose fiber, such as 15-100 wt%, 20-100 wt%, 30-90 wt%, or 40-85 wt%, based on the total amount of cellulose fiber in the barrier paper substrate.

[0039] The cellulose fiber of the barrier paper substrate preferably has a Schopper Riegler value below 80, such as in the range of 20-65, as determined by standard ISO 5267-1.

[0040] The metallized barrier paper layer typically comprises a metallization layer formed by a metallization process on a barrier paper substrate. In some embodiments, the barrier paper substrate may be surface treated to improve the smoothness and decrease the porosity of the substrate surface and make the surface more suitable for metallization. Possible surface treatments include, but are not limited to providing the surface with a smoothening precoat or mechanical smoothening, e.g. by calandering.

[0041] The surface treatment may for example include applying a precoat or primer layer to the barrier paper substrate. The precoat layer preferably acts to level out unevenness, and fill pores and pinholes present in the fibrous or porous barrier paper substrate. The precoat layer may be surface sizing layer formed using a water soluble polymer selected from cellulose derivatives, starch, alginate, PVOH, hemicellulose, or derivatives thereof. In some embodiments, the precoat layer may also contain microfibri Hated cellulose (MFC) or cellulose nanocrystals (CNC). Further additives such as pigments, lubricants, or softeners are also possible in the precoat layer. The applied amount of the precoat layer is preferably in the range of 0.4-6 gsm per side of the barrier paper substrate.

[0042] Calandering may include hard nip or soft nip calandering in one or several passes or nips. The mechanical smoothening can also be combined with a precoating step, performed before or after the calandering.

[0043] Thus, in some embodiments, the metallized barrier paper layer further comprises a precoat layer disposed between the barrier paper substrate and the metallization layer. In some embodiments, the precoat layer comprises a water-soluble polymer selected from the group consisting of a polyvinyl alcohol, a modified polyvinyl alcohol, a polysaccharide and a modified polysaccharide, or combinations thereof, preferably polyvinyl alcohol.

[0044] The PVOH may be a single type of PVOH, or it can comprise a mixture of two or more types of PVOH, differing e.g. in degree of hydrolysis or viscosity. The PVOH may for example have a degree of hydrolysis in the range of 80-99 mol%, preferably in the range of 85-99 mol%. Examples of useful products are, e.g., Kuraray Poval 4-98, Poval 6-98, Poval 10-98, Poval 15-99, Poval 20-98, Poval 30-98, or Poval 56-98 or mixtures of these. From the less hydrolysed grades, the Poval 4-88, Poval 6-88, Poval 8-88, Poval 18-88, Poval 22-88, or e.g. Poval 49-88 are preferred.

[0045] The modified polysaccharide may for example be a modified cellulose, such as carboxymethylcellulose (CMC) or hydroxypropyl cellulose (HPC), or a modified starch, such as a hydroxyalkylated starch, a cyanoethylated starch, a cationic or anionic starch, or a starch ether or a starch ester. Some preferred modified starches include hydroxypropylated starch, hydroxyethylated starch, dialdehyde starch and carboxymethylated starch.

[0046] In some embodiments, the precoat layer comprises up to 50 wt%, preferably in the range of 1-20 wt%, of micrifibrillated cellulose (MFC) or nanocrystalline celllose (NCC), based on dry weight.

[0047] In some embodiments, the precoat layer comprises up to 20 wt%, preferably in the range of 1-15 wt%, of a flaky phyllosilicate, graphene or a graphene oxide, or a mixture thereof, or a mixture thereof, based on dry weight. In some embodiments, the shape factor of the flaky phyllosilicate, graphene or graphene oxide is at least 15, preferably at least 20, and more preferably at least 30. In some embodiments, the basis weight of the precoat layer is in the range of 0.1- 12 g / m2, preferably in the range of 0.5-8 g / m2, more preferably in the range of 1-6 g / m2.

[0048] To minimize the risk of pinholes in the precoat layer, the precoat layer may preferably be applied in at least two different coating steps with drying of the coated film between the steps. The same or different water-soluble polymer (s), for example the same or different polyvinyl alcohol(s) may be used in the at least two different coating steps.

[0049] The precoat layer can be applied by contact or non-contact coating methods. For application on MFC layers, non-contact coating methods are typically preferred to minimize the risk of damage to the substrate during coating. Examples of useful coating methods include, but are not limited to rod coating, curtain coating, film press coating, cast coating, transfer coating, size press coating, flexographic coating, gate roll coating, twin roll HSM coating, blade coating, such as short dwell time blade coating, jet applicator coating, spray coating, gravure coating or reverse gravure coating. In some embodiments, the coating is applied in the form a foam. Foam coating is advantageous as it allows for film forming at higher solids content and lower water content compared to an unfoamed coating. The lower water content of a foam coating also reduces the problems with rewetting of the paperboard base layer.

[0050] The metallization layer is applied to the barrier paper substrate. Metallization refers to a family of processes used to deposit layers of metals and metal oxides, typically atom-by-atom or molecule-by-molecule, on a solid surface. Multiple layers of the same or different materials can be combined. The process can be further specified based on the vapor source; physical vapor deposition (PVD) uses a liquid or solid source and chemical vapor deposition (CVD) uses a chemical vapor.

[0051] The metallization layer may be applied to one or both sides of the barrier paper substrate. Metallization typically results in very thin coatings. In some embodiments, the metallization layer has a thickness in the range of 10-500 nm. In some embodiments, the metallization layer has a thickness in the range of 10-250 nm, preferably in the range of 25-200 nm, and more preferably in the range of 50-150 nm. This should be compared to conventional aluminum foils used in packaging laminates, which foils typically have thickness in the range of about 3-12 pm.

[0052] In some embodiments, the metallization layer comprises a metal or metal oxide selected from the group consisting of aluminum, magnesium, silicon, copper, aluminum oxides, magnesium oxides, silicon oxides, and combinations thereof. In some embodiments, the metallization layer comprises aluminum in the form of aluminum metal or an aluminum oxide, preferably in the form of an aluminum oxide.

[0053] One preferred type of metallization, often used for its barrier properties, in particular water vapour barrier properties, is an aluminum metal physical vapour deposition (PVD) coating. Such a coating, substantially consisting of aluminum metal, may typically have a thickness of from 50 to 250 nm, although a thickness even lower than 50 nm may also be useful, and even preferred in some embodiments. The typical thickness of the metallization layer corresponds to less than 1 % of the aluminum metal material typically present in an aluminum foil of conventional thickness for packaging, i.e. 6.3 pm. Thus, in some embodiments, the metallization layer comprises aluminum.

[0054] The thickness of the metallization layer may also be characterized by the optical density of the layer. In some embodiments the metallization layer has an optical density above 1.8, preferably above 2.0, above 2.5, above 2.7, or above 3.0.

[0055] Aluminum oxide metallization layers also known as AIOx coatings can provide similar barrier properties as aluminum metal coatings, but have the added advantage of thin AIOx coatings being transparent to visible light.

[0056] In some embodiments, the metallization layer is applied to the barrier paper substrate by a transfer coating process. Transfer coating, also commonly referred to as transfer metallization when the coating comprises a metal, generally involves transferring a thin metallization layer from a transfer coating substrate to a barrier paper substrate to be coated, using an adhesive layer applied between the metallization layer and the barrier paper substrate to be coated.

[0057] The transfer coating substrate comprises a metallization layer and a backing layer, and the metallization layer and the backing layer are separated by a release layer having low adhesion to the metallization layer and / or the backing layer, such that the metallization layer can be readily separated from the backing layer.

[0058] For the transfer coating process, an adhesive layer is applied on the barrier paper substrate or on the metallization layer or on both layers. The metallization layer is transferred to the barrier paper substrate using the adhesive layer applied on the barrier paper substrate and / or the metallization layer. The metallization layer is contacted and adhered to the barrier paper substrate using the adhesive layer applied on the barrier paper substrate and / or the metallization layer. Once the metallization layer has adhered to the barrier paper substrate, the backing layer removed from the metallization layer, leaving the adhered metallization layer, and optionally the release layer, on the barrier paper substrate.

[0059] In some embodiments, the metallization layer has less than 20 pinholes / m2, preferably less than 15 pinholes / m2, and more preferably less than 10 pinholes / m2, as determined according to EN 13676:2001.

[0060] In some embodiments, the metallized barrier paper layer has a Gurley hill porosity of 30 000 s / 100ml or higher, preferably 35 000 s / 100ml or higher, or more preferably 40 000 s / 100ml or higher, as measured according to standard ISO 5636 / 5.

[0061] The metallization layer of the metallized barrier paper is subjected to a surface treatment process selected from the group consisting of corona treatment and plasma treatment, such that the surface treated metallization layer has a surface energy in the range of 35-75 mN / m, as determined by ISO 19403-2:2017. Corona treatment, also known as corona discharge treatment, is a surface modification process used to enhance the adhesion properties of various materials. It is commonly applied to plastics, films, foils, and other non-porous materials. The corona treatment process involves passing a high-voltage electrical discharge (corona discharge) over the surface of the material. This discharge generates a plasma, which consists of highly reactive ions and free radicals. Corona treatment increases the surface energy of the material. This enhances its wettability and improves the ability of adhesives to adhere to the surface. The plasma generated during corona treatment can remove contaminants, dust, and oils from the material's surface. The corona discharge creates micro-roughness on the material's surface. This roughening enhances mechanical interlocking between the material and applied adhesives, further improving adhesion. The effects of corona treatment are temporary. The surface energy of the treated material tends to decrease over time, so laminating or bonding processes should preferably be done relatively soon after treatment for the best results.

[0062] Plasma treatment, also known as plasma surface treatment or plasma etching, is a process that modifies the surface properties of materials using plasma, a state of matter composed of ionized gases. Plasma is created by applying an electrical discharge to a gas, usually in a vacuum chamber. This discharge ionizes the gas, creating a mixture of ions, electrons, free radicals, and excited species. The generated plasma is directed towards the material's surface to be treated. Plasma treatment can effectively remove contaminants, organic residues, and other impurities from the material's surface. Plasma treatment increases the surface energy of the material by introducing polar functional groups and enhancing wettability. This improved surface energy allows for better adhesion of coatings and adhesives. The effects of plasma treatment can be temporary, depending on the material and its environment, so laminating or bonding processes should preferably be done relatively soon after treatment for the best results.

[0063] In some embodiments, the surface treatment process is corona treatment. The corona treatment is preferably made with ceramic electrodes. In some embodiments, the total corona treatment dose is in the range of 10-300 W*min / m2, preferably in the range of 10-250 W*min / m2, and more preferably in the range of 10-200 W*min / m2.

[0064] The term "corona treatment dose" refers to the amount or intensity of the corona discharge exposure that a material or surface receives during the treatment process. The treatment dose determines the effectiveness of the corona treatment in modifying the surface properties of the material.

[0065] The optimal corona treatment dose varies depending on the specific material, its surface characteristics, and the desired surface modification outcome. Too low a corona treatment dose might not achieve the desired surface activation, while an excessively high dose could potentially lead to surface damage or over-treatment, resulting in undesirable effects on the material. This has been found to be especially important in the corona treatment of the thin and sensitive metallization layer of the metallized barrier paper layer.

[0066] The corona treatment dose is typically influenced by several key factors:

[0067] Treatment time: The duration for which the material is exposed to the corona discharge. Longer treatment times generally result in a higher dose and more significant surface modification.

[0068] Voltage and frequency: The electrical voltage applied to the corona treater and the frequency of the corona discharge affect the strength and intensity of the treatment. Higher voltage and frequency generally lead to a higher dose.

[0069] Distance from the corona electrode: The distance between the material surface and the corona electrode can influence the dose received. Closer proximity to the electrode typically results in a higher dose.

[0070] Conveyor speed (for continuous treatment): In continuous corona treatment processes, the speed at which the material moves through the corona discharge area affects the dose. Slower conveyor speeds allow for a higher dose, while faster speeds may result in a lower dose.

[0071] In some embodiments, the total corona treatment dose is achieved in two or more treatment steps.

[0072] In the present invention, the metallization layer is subjected to a surface treatment process selected from the group consisting of corona treatment and plasma treatment, such that the surface treated metallization layer has a surface energy in the range of 35-75 mN / m, as determined by ISO 19403-2:2017. The metallization layer will be subjected to corona treatment whether the corona treatment is performed or applied directly on the metallization layer or on the second main surface of the barrier paper substrate.

[0073] In some embodiments, the corona treatment is performed on the metallization layer. In other words, in some embodiments, the corona discharge is applied onto the metallized surface of the metallized barrier paper layer. Performing the corona treatment directly on the metallization layer is the most efficient way of treating the surface.

[0074] In some embodiments, the corona treatment is performed on the second main surface of the barrier paper substrate. In this case, even though the corona disrcharge is applied onto the second main surface of the barrier paper substrate, the metallization layer will still be subjected to the corona treatment. This may for example be due to penetration of the corona discharge through the paper substrate affecting the metallization layer, or induced charges, indirectly subjecting the metallization layer to some level of corona treatment. This could alter the surface energy of the metallized layer, even though the primary treatment is applied on the non-metallized surface. The inventors have found that even when the corona treatment is performed on a non-metallized second main surface of the metallized barrier paper layer, the desired effects in the metallized surface can still be achieved. An advantage of this is that it may be gentler on the sensitive metallization layer. The surface treated metallization layer has a surface energy in the range of 35-75 mN / m, as determined by ISO 19403-2:2017. In some embodiments, the surface treated metallization layer has a surface energy in the range of in the range of 35- 55 mN / m, and more preferably in the range of 37-50 mN / m, as determined according to ISO 19403-2:2017.

[0075] In some embodiments, the surface treated metallization layer has a water contact angle below 50 degrees, preferably below 40 degrees, and more preferably below 30 degrees as determined according to ISO 19403-2:2017.

[0076] In some embodiments, the surface treated metallized barrier paper layer has a Gurley hill porosity of 30 000 s / 100ml or higher, preferably 35 000 s / 100ml or higher, or more preferably 40 000 s / 100ml or higher, as measured according to standard ISO 5636 / 5.

[0077] In some embodiments, the surface treated metallization layer has less than 20 pinholes / m2, preferably less than 15 pinholes / m2, and more preferably less than 10 pinholes / m2, as determined according to EN13676:2001. Preferably, the surface treatment process does not cause formation of additional pinholes in the metallization layer.

[0078] The present inventors also found that the effect of corona treatment can be controlled by monitoring the number of pinholes. Since the effect of corona treatment can vary with conveyor speed, distance from the corona electrode, moisture content, etc., the actual effect on the surface energy of the treated surface may vary. Therefore, the process treatment should be maintained on a suitable level in order to avoid damages on the metallized barrier paper layer, or too low treatment effect. One possible approach to is to continuously monitor that the amount of pinholes remains on a low or constant level before and after the corona treatment. In-line detection of pinholes may for example be performed using optical techniques, such as using a Hawkeye Pinhole Detector (BOBST, Switzerland). The in-line detection of pinholes may be calibrated with the EN13676:2001 method. In some embodiments, the effect of corona treatment is controlled in-line such that the amount of pinholes in the surface treated metallization layer is kept at less than 20 pinholes / m2, preferably less than 15 pinholes / m2, and more preferably less than 10 pinholes / m2, as determined according to EN13676:2001. Optionally, the in-line monitoring of pinholes is connected to an algorithm, such as Al, deep-learning or machine learning, which is pre-trained and contains information about acceptable and non-acceptable treatment conditions for avoiding pinholes.

[0079] Thus, in some embodiments, the method further comprises subjecting the metallization layer to pinhole detection before and after the surface treatment process and adjusting the surface treatment process to keep the amount of pinholes in the surface treated metallization layer at less than 20 pinholes / m2, preferably less than 15 pinholes / m2, and more preferably less than 10 pinholes / m2. In some embodiments, the detection is performed in-line, and the adjustment of the surface treatment process is performed automatically.

[0080] The surface treatment, optional pinhole monitoring, and lamination to a carrier substrate is preferably made in an in-line process at a conveyor speed above 50 m / min, preferably above 100 m / min, such as in the range of 150-1500 m / min. The width of the metallized barrier paper layer is preferably at least 30 cm, and more preferably at least 50 cm.

[0081] A water based adhesive composition is applied to the surface treated metallization layer and / or the paper or paperboard base layer, and the paper or paperboard base layer is laminated to the surface treated metallization layer using the water based adhesive composition, such that the adhesive composition forms an adhesive tie layer between the paper or paperboard base layer and the metallization layer of the metallized barrier paper layer.

[0082] The water based adhesive composition may be applied directly to the metallized barrier paper layer, or it may first be applied to the paperboard base layer surface, and then applied to the metallized barrier paper layer together with the paperboard base layer, or both. An advantage of applying the water based adhesive composition to both surfaces is that the wetting of each of the surfaces can be reduced. In a preferred embodiment, the water based adhesive composition is applied directly to the metallization layer of the metallized barrier paper layer.

[0083] In some embodiments, the applied water based adhesive composition is subjected to at least partial drying before laminating the paper or paperboard base layer to the surface treated metallization layer using the water based adhesive composition. The at least partial drying of the applied water based adhesive composition is useful to avoid water-induced defects in the metallization layer and / or the paperboard base layer, and to avoid curl or other dimensional stability related problems caused by wetting of the layers. It is also believed that corona treatment in combination with at least partial drying of the applied water based adhesive composition can improve the performance of the adhesive through better control of delamination when the paper or paperboard based packaging laminate is subsequently disintegrated. The at least partial drying is preferably performed at a surface temperature of at least 75 °C, preferably at least 80 °C, such as in the range of 80-130 °C. In some embodiments, the at least partial drying is performed using a non-contact drying method such as IR drying, hot air drying, microwave drying, or any combination thereof. The at least partial drying is preferably performed on the same side as the water based adhesive composition is applied. In some embodiments, the at least partial drying comprises removing at least 0.3 g / m2, preferably at least 0.5 g / m2, and more preferably at least 0.75 g / m2, of water from the applied water based adhesive composition. In some embodiments, the at least partial drying comprises removing 0.75-6 g / m2of water from the applied water based adhesive composition.

[0084] In a preferred embodiment, the water based adhesive composition is applied directly to the metallization layer of the metallized barrier paper layer and subjected to at least partial drying before laminating the paper or paperboard base layer to the surface treated metallization layer using the at least partially dried water based adhesive composition. The at least partial drying of the applied water based adhesive composition is useful to avoid water-induced defects in the metallization layer and / or the paperboard base layer, and to avoid curl or other dimensional stability related problems caused by wetting of the layers. In some embodiments, the applied water based adhesive composition is subjected to at least partial curing before laminating the paper or paperboard base layer to the surface treated metallization layer using the water based adhesive composition. The at least partial curing of the applied water based adhesive composition is useful for controlling the stickiness of the adhesive and may lead to improved adhesion. In some embodiments, the at least partial curing is performed using a non-contact curing method such as ultraviolet light (UV) curing or electron beam (EB) curing, or any combination thereof. The at least partial curing is preferably performed on the same side as the water based adhesive composition is applied.

[0085] The water based adhesive composition may be any water based adhesive composition providing adhesion between the laminated layers. Typically, the water based adhesive composition comprises an adhesive polymer. The water based adhesive composition may also comprise two or more adhesive polymers. The water based adhesive composition may be comprised entirely of the one or more adhesive polymers, or it may also further comprise other additives for facilitating the coating process or improving the properties of the adhesive tie layer. In some embodiments, the water based adhesive composition comprises at least 50 wt% of an adhesive polymer or mixture of adhesive polymers based on dry weight.

[0086] In some embodiments, the water based adhesive composition comprises an adhesive polymer. The adhesive polymer may preferably be selected from polyvinyl alcohol (PVOH), butenediol vinyl alcohol copolymer (BVOH), styreneacrylate (SA) latex, styrene-butadiene (SB) latex, polyvinyl acetate (PVAc) latex, starch, carboxymethyl cellulose (CMC), ethylene acrylic acid copolymer (EEA), and vinyl acetate ethylene copolymer. In some embodiments, the water based adhesive composition comprises an adhesive polymer selected from polyvinyl alcohol (PVOH), styrene-acrylate (SA) latex, styrene-butadiene (SB) latex, starch, carboxymethyl cellulose (CMC), and vinyl acetate ethylene copolymer. In some embodiments, the water based adhesive composition comprises vinyl acetate ethylene copolymer. The water based adhesive composition may further comprise other additives for facilitating the coating process or improving the properties of the adhesive tie layer. In some embodiments, the water based adhesive composition comprises 0.1 - 15 wt% of a filler based on dry weight. The filler is preferably a clay or a combination of clays, and more preferably a nanoclay or a combination of nanoclays, The filler further contributes to the barrier properties of the laminate.

[0087] In some embodiments, the water based adhesive composition is applied in the form of a dispersion, emulsion or solution of an adhesive polymer in an aqueous carrier.

[0088] In some embodiments, the grammage of the water based adhesive composition applied, and of the adhesive tie layer formed, is a grammage in the range of 1-10 g / m2, preferably in the range of 1 .5-8 g / m2, based on dry weight. In some embodiments, the water based adhesive composition is applied as a single layer at a grammage in the range of 1-10 g / m2, preferably in the range of 1.5-8 g / m2, based on dry weight, in one application step.

[0089] The water based adhesive composition may be applied in at least two different coating steps with drying of the coated adhesive film between the steps. In some embodiments, the water based adhesive composition is applied in two or more consecutive application steps, e.g. 2+2 g / m2or 1+3 g / m2or 2+4 g / m2. Application in two or more consecutive application steps also enables less adhesive penetration into the paperboard base layer since the first adhesive layer acts as a first coating and closes the surface.

[0090] In some embodiments, the water based adhesive composition comprises at least 50 wt% of a water-soluble polymer or mixture of water-soluble polymers based on dry weight. The water-soluble polymer of the water based adhesive composition is soluble in cold water or soluble in hot water, e.g. at a temperature below 100 °C or even above 100 °C, for a given period of time. The water-soluble polymer in addition to acting as an adhesive for the laminate, also facilitates separation of the laminated layers during repulping. In some embodiments, the water based adhesive composition has a solid content in the range of 10-70 wt%, preferably in the range of 15-65 wt%, at the point of application. A solid content of at least 10 wt% and more preferably at least 15 wt% at the point of application enables fast immobilization of the adhesive and good concentration of the water based adhesive composition at the surface. With lower solids too much water is applied which can cause swelling of the substrate and problems with dimensional stability and curing.

[0091] In some embodiments, the water based adhesive composition has a viscosity of in the range of 100-4000 mPas, preferably in the range of 300-2500 mPas, as determined using a Brookfield viscosimeter, such as a Brookfield DVNext rheometer, at rotational speed of 100 rpm. This viscosity ensures good runnability using rod or gravure coating methods.

[0092] In some embodiments, the water based adhesive composition has an AAGWR water retention value (Abo Akademi Water retention value) below 250 g / m2, preferably in the range of 30-150 g / m2, as determined according to TAPPI standard T701 pm-01. This water retention ensures good runnability using rod or gravure coating methods.

[0093] The water based adhesive composition is preferably applied by means of a liquid film coating process, i.e. in the form of an aqueous solution or dispersion which, on application, is spread out to a thin, uniform layer on the substrate and thereafter dried. The water based adhesive composition can be applied by contact or noncontact coating methods. Examples of useful coating methods include, but are not limited to rod coating, curtain coating, film press coating, cast coating, transfer coating, size press coating, flexographic coating, gate roll coating, twin roll HSM coating, blade coating, such as short dwell time blade coating, jet applicator coating, spray coating, gravure coating or reverse gravure coating.

[0094] In some embodiments, the water based adhesive composition is applied in the form of a foam. Foam coating is advantageous as it allows for film forming at higher solids content and lower water content compared to a non-foamed coating. The lower water content of a foam coating also reduces the problems with rewetting of the paperboard base layer. The foam may be formed using a polymeric or non-polymeric foaming agent. Examples of polymeric foaming agents include PVOH, hydrophobically modified starch, and hydrophobically modified ethyl hydroxyethyl cellulose.

[0095] The surface of the paperboard base layer may for example be laminated to a surface of the metallized barrier paper layer using any suitable lamination method. Suitable lamination methods are well known to the person skilled in the art.

[0096] The surface of the paperboard base layer may for example be laminated to a surface of the metallized barrier paper layer using a press nip. The press nip is formed by a press roll configured to apply pressure to the moving laminate. The press roll may typically be made of steel, optionally coated or surface treated steel. The radius of the press roll is preferably at least 10 cm. In some embodiments, the radius of the press roll is at least 20 cm, at least 30 cm, or at least 40 cm. In some embodiments, the press nip is formed between a press roll and a counter roll or belt. The counter roll may also be made of steel, optionally coated or surface treated steel, or it can be made of a polymeric material such as plastic or rubber. The counter belt may be made of steel, optionally coated or surface treated steel, or it can be made of a polymeric material such as plastic or rubber. The paperboard base layer and metallized barrier paper layer and the water based adhesive composition disposed between them are fed into the press nip and subjected to pressure between the press roll and the counter roll or belt. In some embodiments, guide rolls are further provided before and / or after the press nip. The guide rolls can be used for guiding the paperboard base layer, the metallized barrier paper layer, and / or the formed laminate to a desired path.

[0097] The press roll and / or the counter roll or belt may be heated in order to heat the laminate in the nip. Heating of the laminate can improve contact between the paperboard base layer and metallized barrier paper layer and the water based adhesive composition disposed between them and may also accelerate drying and / or curing of the water based adhesive composition. In some embodiments, the press roll and / or the counter roll or belt is heated to a temperature in the range of 40-250 °C, preferably to a temperature in the range of 70-250 °C. The paper or paperboard based packaging laminate may further be provided with a polymeric topcoat layer on one side or on both sides. The polymeric topcoat layers provide improved liquid barrier properties and mechanical protection, and may additionally provide heat sealing capability, to the paper or paperboard based packaging laminate surface. The polymeric topcoat layers may for example be applied by extrusion coating, film lamination or dispersion coating.

[0098] In some embodiments, the method further comprises the step: f) applying at least one polymeric topcoat layer to at least one side of the laminate.

[0099] In some embodiments, the method further comprises the step: f) applying at least one polymeric topcoat layer to both sides of the laminate.

[0100] The polymeric topcoat layers may comprise any of the thermoplastic polymers commonly used in heat-sealable layers in paperboard based packaging laminates in general or polymers used in liquid or food packaging board in particular.

[0101] Examples include polyethylene (PE), polypropylene (PP), polyhydroxyalkanoates (PHA), polylactic acid (PLA), polyglycolic acid (PGA), polybutylene terephthalate (PBT), thermoplastic starch and thermoplastic cellulose. Thermoplastic starch and thermoplastic cellulose refer to starch and cellulose derivatives that have been modified to become thermoplastic. In some embodiments, the polymeric topcoat layer comprises a polyolefin layer, preferably a polyethylene layer. Polyethylenes, especially low density polyethylene (LDPE) and high density polyethylene (HDPE), are the most common and versatile polymers used in liquid or food packaging board. The polymers used are preferably manufactured from renewable materials.

[0102] In some embodiments, the polymeric topcoat layers are formed by extrusion coating of the polymer onto a surface of the paperboard base layer or the obtained laminate. Extrusion coating is a process by which a molten plastic material is applied to a substrate to form a very thin, smooth and uniform layer. The coating can be formed by the extruded plastic itself, or the molten plastic can be used as an adhesive to laminate a solid plastic film onto the substrate. The polymeric topcoat layers may also comprise a dispersion coating. The dispersion coating may for example comprise a latex dispersion, such as an SA latex dispersion or SB latex dispersion, or a polyolefin dispersion, preferably combined with a pigment.

[0103] The basis weight of each of the polymeric topcoat layers is preferably less than 50 g / m2. In order to achieve a continuous and substantially defect free extrusion film, a basis weight of the polymeric topcoat layer of at least 8 g / m2, preferably at least 12 g / m2is typically required. In some embodiments, the basis weight of the polymeric topcoat layer is in the range of 8-50 g / m2, preferably in the range of 12- 50 g / m2. When the polymeric topcoat layers comprise a dispersion coating, the basis weight may in some cases be lower than 8 g / m2.

[0104] The obtained paperboard based packaging laminate has a significantly improved resistance to oxygen transmission. In some embodiments, the obtained paper or paperboard based packaging laminate has an oxygen transmission rate (OTR), measured according to the standard ASTM F1927-20 at 50% relative humidity and 23 °C, of less than 5 cc / m2 / 24h, preferably less than 3 cc / m2 / 24h, and more preferably less than 2 cc / m2 / 24h.

[0105] The obtained paperboard based packaging laminate has a significantly improved resistance to water vapor transmission. In some embodiments, the obtained paper or paperboard based packaging laminate has a water vapor transmission rate (WVTR), measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C, of less than 5 g / m2 / 24h, preferably less than 3 g / m2 / 24h, and more preferably less than 2 g / m2 / 24h. This makes the inventive packaging laminate an interesting and viable alternative to conventional materials using aluminum foil layers.

[0106] Additionally, the inventive paperboard based packaging laminate can provide an alternative to conventional materials using aluminum foil layers, which can more readily be repulped and recycled. The adhesive tie layer of the inventive paperboard based packaging laminate preferably comprises at least 50 wt% of a water-soluble polymer based on dry weight. A water-soluble polymer arranged between and in contact with the paperboard base layer and the metallized barrier paper layer has been found to allow for effective separation of the metallization layer from the paperboard base layer during repulping. In some embodiments, the paper or paperboard based packaging laminate has a reject rate according to PTS RH 021 / 97 of less than 30 %, preferably less than 20 %, more preferably less than 10%.

[0107] Generally, while the products, polymers, materials, layers and processes are described in terms of “comprising” various components or steps, the products, polymers, materials, layers and processes can also “consist essentially of” or “consist of” the various components and steps.

[0108] While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

CLAIMS1 . A method for manufacturing a paper or paperboard based packaging laminate, said method comprising: a) providing a paper or paperboard base layer, b) providing a metallized barrier paper layer comprising a barrier paper substrate having a first main surface and a second main surface and a metallization layer having a thickness in the range of 10-500 nm deposited on the first main surface, c) subjecting the metallization layer to a surface treatment process selected from the group consisting of corona treatment and plasma treatment, such that the surface treated metallization layer has a surface energy in the range of 35-75 mN / m, as determined by ISO 19403-2:2017, d) applying a water based adhesive composition to the surface treated metallization layer and / or the paper or paperboard base layer, and e) laminating the paper or paperboard base layer to the surface treated metallization layer using the water based adhesive composition, such that the adhesive composition forms an adhesive tie layer between the paper or paperboard base layer and the metallization layer of the metallized barrier paper layer.

2. The method according to any one of the preceding claims, wherein the paper or paperboard base layer has a grammage in the range of 20-800 g / m2.

3. The method according to any one of the preceding claims, wherein the paper or paperboard base layer has a density below 800 kg / m3, preferably below 700 kg / m3, more preferably below 600 kg / m3.

4. The method according to any one of the preceding claims, wherein the paper or paperboard base layer is a multiply paper or paperboard.

5. The method according to any one of the preceding claims, wherein the barrier paper substrate is a thin high-density paper such as a kraft paper, greaseproofpaper, glassine paper, tracing paper, translucent paper, transparent paper, machine glazed paper or parchment paper.

6. The method according to any one of the preceding claims, wherein the barrier paper substrate is a microfibrillated cellulose (MFC) film.

7. The method according to any one of the preceding claims, wherein the barrier paper substrate is coated with 0.5-8 g / m2of a microfibrillated cellulose (MFC).

8. The method according to any one of the preceding claims, wherein the barrier paper substrate comprises an internal sizing agent in an amount of 50-10 000 g / tn, preferably 100-6000 g / tn, based on the total dry weight of the barrier paper substrate.

9. The method according to any one of the preceding claims, wherein the barrier paper substrate has a grammage in the range of 20-120 g / m2, preferably in the range of 25-120 g / m2.

10. The method according to any one of the preceding claims, wherein the barrier paper substrate has a density in the range of 700-1300 kg / m3, preferably in the range of 750-1200 kg / m3.

11. The method according to any one of the preceding claims, wherein the metallization layer comprises aluminum in the form of aluminum metal or an aluminum oxide, preferably in the form of an aluminum oxide.

12. The method according to any one of the preceding claims, wherein the metallization layer has a thickness in the range of 10-250 nm, preferably in the range of 25-200 nm, and more preferably in the range of 50-150 nm.

13. The method according to any one of the preceding claims, wherein the metallization layer has less than 20 pinholes / m2, preferably less than 15 pinholes / m2, and more preferably less than 10 pinholes / m2, as determined according to EN 13676:2001.

14. The method according to any one of the preceding claims, wherein the metallized barrier paper layer has a Gurley hill porosity of 30 000 s / 100ml or higher, preferably 35 000 s / 100ml or higher, or more preferably 40 000 s / 100ml or higher, as measured according to standard ISO 5636 / 5.

15. The method according to any one of the preceding claims, wherein the surface treatment process is corona treatment.

16. The method according to claim 15, wherein the total corona treatment dose is in the range of 10-300 W*min / m2, preferably in the range of 10-250 W*min / m2, and more preferably in the range of 10-200 W*min / m2.

17. The method according to any one of claims 15-16, wherein the total corona treatment dose is achieved in two or more treatment steps.

18. The method according to any one of the preceding claims, wherein the corona treatment is performed on the metallization layer.

19. The method according to any one of the preceding claims, wherein the corona treatment is performed on the second main surface of the barrier paper substrate.

20. The method according to any one of the preceding claims, wherein the surface treated metallization layer has a surface energy in the range of in the range of 35-55 mN / m, and more preferably in the range of 37-50 mN / m, as determined according to ISO 19403-2:2017.

21. The method according to any one of the preceding claims, wherein the surface treated metallization layer has a water contact angle below 50 degrees, preferably below 40 degrees, and more preferably below 30 degrees as determined according to ISO 19403-2:2017.

22. The method according to any one of the preceding claims, wherein the surface treated metallization layer has less than 20 pinholes / m2, preferably less than 15 pinholes / m2, and more preferably less than 10 pinholes / m2, as determined according to EN 13676:2001.

23. The method according to any one of the preceding claims, further comprising subjecting the metallization layer to pinhole detection before and after the surface treatment process and adjusting the surface treatment process to keep the amount of pinholes in the surface treated metallization layer at less than 20 pinholes / m2, preferably less than 15 pinholes / m2, and more preferably less than 10 pinholes / m2.

24. The method according to any one of the preceding claims, wherein the surface treated metallized barrier paper layer has a Gurley hill porosity of 30 000 s / 100ml or higher, preferably 35 000 s / 100ml or higher, or more preferably 40 000 s / 100ml or higher, as measured according to standard ISO 5636 / 5.

25. The method according to any one of the preceding claims, wherein the water based adhesive composition comprises an adhesive polymer, preferably vinyl acetate ethylene copolymer.

26. The method according to any one of the preceding claims, wherein the water based adhesive composition is applied in the form of a dispersion, emulsion or solution of an adhesive polymer in an aqueous carrier.

27. The method according to any one of the preceding claims, wherein the water based adhesive composition has a solid content in the range of 10-70 wt%, preferably in the range of 15-65 wt%, at the point of application.

28. The method according to any one of the preceding claims, wherein the applied water based adhesive composition is subjected to at least partial drying before laminating the paper or paperboard base layer to the surface treated metallization layer using the water based adhesive composition.

29. The method according to claim 28, wherein the at least partial drying comprises removing at least 0.3 g / m2, preferably at least 0.5 g / m2, and more preferably at least 0.75 g / m2, of water from the applied water based adhesive composition.

30. The method according to any one of the preceding claims, wherein the adhesive tie layer has a grammage in the range of 1-10 g / m2, preferably in the range of 1.5-8 g / m2.

31. The method according to any one of the preceding claims, further comprising the step: f) applying at least one polymeric topcoat layer to at least one side of the laminate.

32. The method according to any one of the preceding claims, comprising the step: f) applying at least one polymeric topcoat layer to both sides of the laminate.

33. The method according to any one of claims 31-32, wherein the polymeric topcoat layer comprises a polyolefin layer, preferably a polyethylene layer.

34. The method according to any one of the preceding claims, wherein the obtained paper or paperboard based packaging laminate has an oxygen transmission rate (OTR), measured according to the standard ASTM F1927-20 at 50% relative humidity and 23 °C, of less than 5 cc / m2 / 24h, preferably less than 3 cc / m2 / 24h, and more preferably less than 2 cc / m2 / 24h.

35. The method according to any one of the preceding claims, wherein the obtained paper or paperboard based packaging laminate has a water vapor transmission rate (WVTR), measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C, of less than 5 g / m2 / 24h, preferably less than 3 g / m2 / 24h, and more preferably less than 2 g / m2 / 24h.