Barrier paper for use in a paper or paperboard based packaging laminate

Abstract

The present invention relates to a method of manufacturing a barrier paper for use in a paper or paperboard based packaging laminate, said method comprising at least: a) providing a paper substrate web, wherein said paper substrate web comprises at least 50 wt% refined pressurized groundwood (PGW) pulp fibers having a Canadian Standard Freeness (CSF) value of less than 150 ml, based on the total fiber content of the paper substrate web, and wherein said paper substrate web has a grammage in the range of 30-95 g / m2, and a bulk of at least 1.35 cm3 / g, 10 b) calendering the paper substrate web to a bulk of less than 1.30 cm3 / g to obtain a barrier substrate, wherein the obtained barrier substrate has an opacity of at least 60%.

Description

[0001] BARRIER PAPER FOR USE IN A PAPER OR PAPERBOARD BASED

[0002] PACKAGING LAMINATE

[0003] Technical field

[0004] The present disclosure relates to methods for manufacturing a barrier paper for use as a barrier for light and / or water vapor in paper or paperboard based packaging laminates.

[0005] Background

[0006] In conventional paper or paperboard based packaging laminates aluminum foil is often laminated to the paper or paperboard using one or more polymeric tie layers to form a barrier against for example light and water vapor. However, the addition of aluminum foil and polymers add significant cost to the manufacturing process, and the combination of materials makes recycling of the laminates difficult. Also, due to its high carbon footprint there is a wish to replace aluminum foils in paper or paperboard based packaging materials.

[0007] As an alternative, it has been proposed to replace the aluminum foil with metallized thin high-density paper. The metallized thin high-density paper can be used as a packaging paper by itself or laminated as a barrier layer to a paper or paperboard base layer by an adhesive tie layer.

[0008] The thin high-density paper may for example include greaseproof paper, glassine paper or other high-density papers. Typically, these papers comprise highly refined bleached kraft pulp fibers and / or are supercalendered in order to form a high-density paper. The high-density paper is often treated or coated to enhance its barrier properties.

[0009] Thin high-density paper will typically exhibit low opacity, meaning that it will have a translucent or transparent appearance. This translucent or transparent appearance is advantageous in many applications where visibility is preferred or provides a unique aesthetic characteristic. On the other hand, such paper will not provide a barrier against visible or UV light and is hence not suitable for packaging food products or other goods sensitive to visible or UV light.

[0010] The opacity of the paper can be improved by adding fillers. However, fillers will often impact the mechanical and barrier properties of the thin paper. Use of high scattering pigments such as calcined clay or TiO2 would be a preferred option, but these add costs and have a negative impact on the water vapor barrier properties of the paper.

[0011] Other common solution to increase the opacity of paper is to increase the grammage or to add mechanical fibers to the highly refined bleached kraft pulp fibers. However, higher grammage makes the paper less cost efficient and versatile in e.g. converting and lamination, whereas mechanical fibers increase the permeability and hence reduce the water vapor barrier properties of the paper.

[0012] Another solution proposed in the prior art is to use colorant to increase the opacity. Addition of black or dark colorant improves the opacity of the paper, but simultaneously reduces the brightness. Colorants further add costs to the manufacturing process and require more cleaning. Addition of colorant may also reduce the water vapor barrier properties of the paper.

[0013] Opacity may also be increased by printing the paper, but printing also adds extra converting steps and costs.

[0014] Thus, there remains a need for improved solutions to replace the combination of plastic films and aluminum foils in paper and paperboard based packaging materials, while maintaining acceptable barrier properties to light and / or water vapor. At the same time, there is a need to replace the combination of plastic films and aluminum foils with alternatives that facilitate repulping and recycling of the used packaging materials. Description of the invention

[0015] It is an object of the present disclosure to provide an alternative method of manufacturing a barrier paper for use in a paper or paperboard based packaging laminate, which overcomes at least some of the problems associated with prior art manufacturing methods.

[0016] It is an object of the present disclosure to provide an alternative method of manufacturing a barrier paper with high opacity, such as an opacity of at least 60% determined according to the standard ISO 2471 , for use as a barrier for light in a paper or paperboard based packaging laminate.

[0017] It is an object of some embodiments of the present disclosure to provide an alternative method of manufacturing a barrier paper with high opacity, such as an opacity of at least 60% determined according to the standard ISO 2471 , and acceptable water vapor barrier properties, such as a water vapor transmission rate (WVTR) measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C of less than 10 g / m2 / 24h, for use as a barrier for light and water vapor in a paper or paperboard based packaging laminate.

[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 term “barrier paper” as used herein refers to a paper useful as a barrier for light and / or water vapor. The barrier paper comprises a “barrier substrate” formed from the pulp of wood or other fibrous substances comprising cellulose fibers, and optionally one or more coating layers applied to the barrier substrate. Depending on the required barrier properties, the barrier paper may consist of the barrier substrate alone, or of the barrier substrate with the one or more coating layers applied.

[0020] The present invention is based on the understanding that a barrier substrate for a barrier paper can be obtained by providing a paper substrate web comprising at least 50 wt% refined pressurized groundwood (PGW) pulp fibers based on the total fiber content of the paper substrate web, wherein the paper substrate web has a grammage in the range of 30-95 g / m2, and calendering the paper substrate web to a bulk of less than 1.30 cm3 / g. Thanks to the high content of refined PGW pulp fibers, the obtained barrier substrate has an opacity of at least 60% making it suitable as a light barrier layer. The high opacity also makes the barrier substrate suitable as a printing layer. The barrier substrate may be used as a barrier paper for visible or UV light by itself, but also provides an excellent substrate for further treatment or coating to further enhance its light and water vapor barrier properties. The calendered and optionally surface pigmented barrier substrate may further advantageously be provided with a polymeric coating layer to obtain acceptable water vapor barrier properties. The polymer coated barrier substrate also has a surface suitable for vacuum coating and may further be provided with a vacuum coating layer on the polymeric coating layer to obtain further improved water vapor barrier properties.

[0021] According to a first aspect illustrated herein, there is provided a method of manufacturing a barrier paper for use in a paper or paperboard based packaging laminate, said method comprising: a) providing a paper substrate web, wherein said paper substrate web comprises at least 50 wt% refined pressurized groundwood (PGW) pulp fibers having a Canadian Standard Freeness (CSF) value of less than 150 ml, based on the total fiber content of the paper substrate web, and wherein said paper substrate web has a grammage in the range of 30-95 g / m2, and a bulk of at least 1.35 cm3 / g, b) calendering the paper substrate web to a bulk of less than 1 .30 cm3 / g to obtain a barrier substrate, wherein the obtained barrier substrate has an opacity of at least 60%, and c) optionally applying a surface pigmentation on the paper substrate web or on the barrier substrate to obtain a surface pigmented barrier substrate. 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.

[0022] 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.

[0023] A barrier paper refers to a cellulose based layer with relatively high density, typically above about 750 kg / m3, and preferably above about 800 kg / m3, designed to provide protection against light and / or water vapor. The barrier paper may be uncoated, or provided with one or more coating layers, such as polymeric coating layers or vacuum coating layers, to further improve the barrier properties of the barrier paper.

[0024] The paper substrate web comprises at least 50 wt% refined pressurized groundwood (PGW) pulp fibers having a Canadian Standard Freeness (CSF) value of less than 150 ml, based on the total fiber content of the paper substrate web. In some embodiments, the paper substrate web comprises at least 60 wt%, and more preferably at least 70 wt%, of the refined PGW pulp fibers based on the total fiber content of the paper substrate web.

[0025] In some embodiments, the paper substrate web comprises 60-75 wt% refined pressurized groundwood (PGW) pulp fibers and 25-40 wt% kraft pulp fibers, based on the total fiber content of the paper substrate web. This fiber blend has been found to offer a favorable balance between opacity, mechanical strength, and processability. The relatively high content of PGW pulp fibers ensures high opacity and good formation, while the inclusion of kraft pulp fibers contributes to improved tear strength and tensile properties. This fiber composition further enhances the runnability of the substrate in high-speed papermaking and coating operations and ensures a good substrate for calendering and subsequent surface treatments.

[0026] Pressurized groundwood (PGW) pulp is a mechanical pulp produced by grinding wood under pressure. This process is distinct from other mechanical pulping methods like thermo-mechanical pulp (TMP). The process for making PGW pulp fibers generally comprises the following steps:

[0027] Wood preparation - The process starts with debarked logs, which are cut into smaller pieces suitable for grinding.

[0028] Pressurized grinding - The wood pieces are fed into a grinder where they are ground against a rotating stone under pressurized conditions. The pressurization helps to soften the lignin in the wood, making it easier to separate the fibers without cutting them too short.

[0029] Screening and cleaning - The pulp obtained from the grinder is screened to remove oversized particles and any remaining wood shives. This helps to ensure a uniform pulp quality.

[0030] Bleaching (optional) - If a brighter pulp is needed, the PGW can undergo a bleaching process. This is often done using peroxide or other chemicals to increase the brightness of the pulp.

[0031] Refining (optional) - In some cases, the pulp is further refined to improve its physical properties, like strength and smoothness.

[0032] The PGW pulp fibers used in the present invention may be bleached or unbleached. Preferably, the PGW pulp fibers are bleached to an ISO brightness of at least 70, preferably at least 73, and more preferably at least 75. Unless specifically stated otherwise, ISO brightness in the present disclosure is determined according to the standard ISO 2470-1. Bleached PGW is preferred, since it is easier to refine, gives high brightness and comprises less extractives and lignin. The bleached PGW is preferably suitable for food contact packaging.

[0033] The preferred raw material for the pressurized groundwood (PGW) pulp fibers used in the present invention is spruce. Spruce is particularly suitable due to its long fiber length and high brightness, which contribute to favorable formation, opacity, and surface properties of the resulting paper substrate web. Additionally, spruce fibers are well-suited for refining and respond favorably to the pressurized grinding process, yielding fibers with good bonding ability and excellent optical characteristics. In some embodiments, the spruce is Norway spruce (Picea abies), due to its favorable fiber morphology and refining characteristics. However, other spruce may also be used, including but not limited to Schrenk's spruce (Picea schrenkiana), or combinations thereof.

[0034] In some embodiments at least 70 wt%, preferably at least 80 wt%, and more preferably at least 90 wt%, of the PGW pulp fibers are obtained from spruce. In some embodiments 100 wt% of the PGW pulp fibers are obtained from spruce. The remaining PGW pulp fibers, if any, may for example be obtained from pine.

[0035] The PGW pulp fibers used in the present invention are refined to a CSF value of less 150 ml. In some embodiments, the refined PGW pulp fibers have a CSF value of less than 115 ml, and preferably less than 80 ml. Unless specifically stated otherwise, Canadian Standard Freeness (CSF) in the present disclosure is determined according to the standard ISO 5267-2:2001. This standard specifies a method for determining the drainability of a pulp suspension. It measures the rate at which a diluted pulp suspension drains, providing an indication of the pulp's fiber quality and its suitability for various paper products. This method is widely used in the pulp and paper industry to assess the refining of pulp fibers.

[0036] The remaining solids of the paper substrate web can be made up of other types of cellulose pulp fibers, or other fibrous or non-fibrous additives. In some embodiments, the paper substrate web further comprises up to 50 wt% kraft pulp fibers based on the total fiber content of the paper substrate web, preferably wherein the kraft pulp fibers are refined kraft pulp fibers having a Canadian Standard Freeness (CSF) in the range of 100-700 ml, preferably in the range of 100-500 ml, and more preferably in the range of 100-300 ml. The kraft pulp fibers are preferably bleached kraft pulp fibers. The bleached kraft pulp fibers are preferably suitable for food contact packaging.

[0037] The paper substrate web preferably comprises no more than a small amount of mineral fillers since higher amounts of fillers will impact the mechanical and barrier properties of the obtained barrier paper. In some embodiments, the paper substrate web comprises less than 10 wt% of mineral filler based on the total fiber content of the paper substrate web. In some embodiments, the paper substrate web comprises less than 5 wt%, less than 3 wt%, or less than 1 wt%, of mineral filler based on the total fiber content of the paper substrate web, or no mineral filler at all. In some embodiments, the paper substrate web has an ash content of less than 10 wt%, more preferably less than 5 wt%, less than 3 wt%, or less than 1 wt%, as measured according to the standard ISO 1762:2019.

[0038] In some embodiments, the paper substrate web comprises an internal sizing agent in an amount of less than 2 kg / tn, less than 1.5 kg / tn, less than 1.0 kg / tn, less than 0.5 kg / tn, or less than 0.3 kg / tn, such as in the range of 0-0.2 kg / tn, based on the total fiber content of the paper substrate web. Internal sizing agents are chemicals that are added to the pulp to increase the hydrophobicity of the paper substrate web 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. In some embodiments the paper substrate web comprises no internal sizing agent.

[0039] The paper substrate web preferably has a low moisture content when it is subjected to calendering. In some embodiments, the paper substrate web has a moisture content of 10 wt% or less, preferably in the range of 4-10 wt%. Unless specifically stated otherwise, moisture content in the present disclosure is determined according to the standard ISO 287. The paper substrate web may be provided by conventional papermaking methods known to the skilled person. The paper substrate web may for example be produced in a papermaking machine, such as a papermaking machine based on the principles of the Fourdrinier machine. The paper substrate web may for example be provided by: a1) preparing a pulp suspension comprising at least 50 wt% refined pressurized groundwood (PGW) pulp fibers having a Canadian Standard Freeness (CSF) value of less than 150 ml, and optionally other components as set out in the present disclosure, based on the total fiber content of the pulp suspension, a2) forming a wet web having a grammage in the range of 30-95 g / m2from the pulp suspension on a wire, and a3) dewatering and drying the wet web, preferably to a moisture content of 10 wt% or less, preferably to a moisture content in the range of 4-10 wt%, to obtain a paper substrate web having a grammage in the range of 30-95 g / m2, and a bulk of at least 1.35 cm3 / g.

[0040] The paper substrate web prior to calendering has a grammage in the range of SO- 95 g / m2, and a bulk of at least 1 .35 cm3 / g. In some embodiments, the paper substrate web has a grammage in the range of 35-85 g / m2, preferably in the range of 35-75 g / m2, and more preferably in the range of 35-65 g / m2. Unless specifically stated otherwise, grammage in the present disclosure is determined according to the standard ISO 536. In some embodiments, the paper substrate web prior to calendering has a bulk of at least 1 .40 cm3 / g, preferably in the range of 1.40-1.80 cm3 / g. Unless specifically stated otherwise, bulk in the present disclosure is determined according to the standard ISO 534.

[0041] The paper substrate web is subjected to calendering to reduce the bulk and improve the barrier properties. The obtained calendered product is referred to as the barrier substrate. Calendering is a paper finishing process used to improve the surface properties, such as smoothness, gloss, and thickness uniformity of a paper. Calendering may include hard nip or soft nip calendering in one or several passes or nips. In some embodiments, the calendering comprises soft calendering. Soft calendering involves passing the paper through a series of calender rolls, where at least one of the rolls is covered with a soft material, typically a polymer or composite. This soft roll conforms slightly to the paper surface, applying pressure more gently and uniformly compared to hard calendering, which uses hard rolls. Since the pressure applied is more uniform and gentle, the paper retains more of its original bulk and softness compared to hard calendering. Therefore, the paper substrate web of the inventive method is preferably not subjected to hard calendering or supercalendering.

[0042] In some embodiments, the calendering is performed at a nip load of at least 150 kN / m, preferably at least 175 kN / m, and more preferably at least 200 kN / m. In some embodiments, the calendering is performed at a nip load in the range of 150-300 kN / m, preferably in the range of 175-275 kN / m, and more preferably in the range of 200-250 kN / m.

[0043] In some embodiments, the soft calendering comprises passing the paper substrate web through one or more soft calendering nips defined by the interaction of a soft, or resilient, roll and a hard roll, and in some cases by the interaction of two soft rolls. The soft calendering may be carried out as a single-nip or multi-nip process, and may be performed in-line with papermaking or as a separate finishing step.

[0044] Each soft calendering nip comprises a soft roll having a compressible polymeric covering and a hard roll with a substantially non-compliant surface, or two soft rolls. The rolls are pressed together at a nip load (or lineal nip pressure) typically in the range of 150 to 300 kN / m, preferably 175 to 275 kN / m, and more preferably in the range of 200 to 250 kN / m. The compressibility of the soft roll enables more conformal contact with the paper substrate web, thereby promoting uniform densification and improved surface smoothness without excessive degradation of the structural integrity or opacity of the paper substrate web.

[0045] The soft roll typically comprises a steel core covered with a resilient covering.

[0046] Suitable covering materials include polyurethane, thermoset elastomers, synthetic rubber, or polymer-fiber composites. The hardness of the resilient covering is typically in the range of 80 to 90 Shore D, preferably in the range of 84 to 88 Shore D. The soft roll may optionally be heated or cooled and may be crowned or profiled to compensate for deflection and ensure uniform nip load distribution.

[0047] The hard roll is generally constructed from steel, chilled cast iron, or other high- modulus material, and may include a surface coating such as hard chrome, ceramic oxide, or tungsten carbide to improve wear resistance and dimensional stability. The hard roll may optionally be internally heated to temperatures in the range of 100-250 °C to facilitate thermal softening of surface fibers during calendering. The surface roughness of the hard roll is typically below 0.5 pm Ra, preferably below 0.2 pm Ra.

[0048] In some embodiments, the calendering comprises passing the paper substrate web through a calendering assembly comprising multiple sequential soft calendering nips with alternating roll configurations. The number of nips may typically vary between 2 and 4, depending on the desired final sheet properties, with each nip optionally being independently controllable in terms of pressure and roll temperature.

[0049] For example, the calendering assembly may include a first nip comprising a hard roll above a soft roll (hard-soft), followed by a second nip comprising a soft roll above a hard roll (soft-hard), and so forth. These alternating configurations may be optimized to tailor surface gloss, smoothness, and bulk reduction uniformly or asymmetrically across the paper substrate web. The specific sequence and orientation of the roll pairs may be selected to achieve a desired balance of surface treatment on both sides of the paper substrate web, such as targeting different optical or tactile properties on the wire side and felt side of the substrate.

[0050] A symmetric calendering assembly is preferred in order to achieve a desired balance of surface treatment on both sides of the paper substrate web, but the calendering assembly is not limited to symmetric arrangements. Asymmetrical or interleaved nip arrangements or sequences are also contemplated. Each nip within the calendering assembly may be independently controlled in terms of nip load, roll temperature, and web tension, allowing for precise customization of the surface and structural properties of the resulting barrier substrate.

[0051] In some embodiments, at least one calendering nip is configured as a soft-soft nip, wherein both rolls comprise resilient polymeric or elastomeric coverings. The soft- soft configuration provides a broader and more uniform nip profile compared to conventional soft-hard or hard-soft configurations, resulting in gentle and symmetrical treatment of both surfaces of the paper substrate web. This configuration is particularly advantageous in applications where retention of paper bulk is prioritized, or where low-gloss and two-sided uniformity are desired, such as in high-opacity barrier papers or printing papers requiring minimal surface densification. The soft-soft nip may be employed alone or in combination with other nip configurations within a calendering assembly to achieve targeted balance of optical and mechanical sheet properties.

[0052] In some embodiments, the soft calendering is performed at a nip load of at least 150 kN / m, preferably at least 175 kN / m, and more preferably at least 200 kN / m. In some embodiments, the soft calendering is performed at a nip load in the range of 150-300 kN / m, preferably in the range of 175-275 kN / m, and more preferably in the range of 200-250 kN / m. In some embodiments, the soft calendering is performed at elevated temperature. In some embodiments, the temperature of the coated paper substrate web in a soft nip of the soft calendering is in the range of 60-200 °C. In some embodiments, the temperature of the coated paper substrate web in a soft nip of the soft calendering is in the range of 60-100 °C, such as in the range of 70-90 °C. In some embodiments, the temperature of the coated paper substrate web in a soft nip of the soft calendering is in the range of 100-200 °C.

[0053] The calendering leads to a reduction of the bulk of the paper substrate web from a bulk of at least 1 .35 cm3 / g to a bulk of less than 1 .30 cm3 / g. In some embodiments, the paper substrate web is calendered to a bulk of less than 1.25 cm3 / g, preferably to a bulk of less than 1 .20 cm3 / g, and more preferably to a bulk in the range of 1.10-1.20 cm3 / g. In some embodiments, the calendering leads to a reduction of the bulk of the paper substrate web from a bulk of at least 1 .35 cm3 / g to a bulk of in the range of 1.00-1.30 cm3 / g or in the range of 1.00-1.25 cm3 / g or in the range of 1.00-1.20 cm3 / g. In some embodiments, the calendering leads to a reduction of the bulk of the paper substrate web from a bulk of at least 1 .35 cm3 / g to a bulk of in the range of 1.05-1.30 cm3 / g or in the range of 1.05-1.25 cm3 / g or in the range of 1.05-1.20 cm3 / g. In some embodiments, the calendering leads to a reduction of the bulk of the paper substrate web from a bulk of at least 1 .35 cm3 / g to a bulk of in the range of 1.10-1.30 cm3 / g or in the range of 1.10-1.25 cm3 / g or in the range of 1.10-1.20 cm3 / g.

[0054] Calendering a paper substrate web to low thickness and high density will often lead to a loss of opacity, or increased translucence or transparency, in the calendered product. However, when the paper substrate web comprises at least 50 wt% refined pressurized groundwood (PGW) pulp fibers based on the total fiber content of the paper substrate web, the obtained calendered barrier substrate has been found to still have high opacity, making it useful as a light barrier.

[0055] Specifically, the obtained barrier substrate has an opacity of at least 60%. In some embodiments, the obtained barrier substrate has an opacity of at least 65%, preferably at least 70%, and more preferably at least 75%. Unless specifically stated otherwise, opacity in the present disclosure is determined according to the standard ISO 2471.

[0056] The barrier substrate excluding any surface pigmentation, may have the same composition of solids as the paper substrate web excluding any surface pigmentation. The calendering may lead to a slight reduction in moisture content, but the barrier substrate will preferably still have a moisture content of 10 wt% or less, preferably in the range of 4-10 wt%.

[0057] In some embodiments, the barrier substrate has a specific formation below 0.9 gA0.5 / m, and preferably below 0.8 gA0.5 / m, as measured according to standard SCAN-P 92:09.

[0058] In some embodiments, the paper substrate web prior to calendering has a tear strength in the machine direction (MD) above 180 mN, preferably above 200 mN, as determined according to ISO 1974. In some embodiments, the barrier substrate after calendering has a tear strength in the machine direction (MD) above 150 mN, preferably above 170 mN, as determined according to ISO 1974.

[0059] In some embodiments, the barrier substrate after calendering has a tensile index in the machine direction (MD) above 60 Nm / g, preferably above 62 Nm / g, and more preferably above 64 Nm / g.

[0060] The barrier substrate itself, without additional coating layers, will typically have a high permeability for water vapor as well as for gases, such as oxygen, air and carbon dioxide. The barrier substrate itself, without additional coating layers, will typically have a high permeability for water vapor and the water vapor transfer rate (WVTR) as measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C will typically be too high to measure. In some embodiments, the barrier substrate has a Gurley Hill value below 5000 s / 100ml, preferably below 3000 s / 100ml, and more preferably below 2000 s / 100ml, as measured according to standard ISO 5636-5.

[0061] In some embodiments, a surface pigmentation is applied to the paper substrate web or the barrier substrate. A surface pigmentation is a light pigment coating preferably applied at a grammage below 10 g / m2, such as in the range of 2-10 g / m2. The surface pigmentation typically does not close or fill the surface of the paper substrate web or the barrier substrate, but may increase the brightness and printability of the surface. The surface pigmentation may be applied to the paper substrate web before calendering or to the barrier substrate after calendering. Preferably, the surface pigmentation is applied to the barrier substrate after calendering. The surface pigmentation may be applied to one or both sides of the paper substrate web or the barrier substrate. In some embodiments, the surface pigmentation on each side is applied at a grammage in the range of 2-10 g / m2, preferably in the range of 2-8 g / m2, and more preferably in the range of 3-7 g / m2. In some embodiments, the surface pigmentation comprises at least one pigment and at least one binder. Examples of pigments that may be used include, but are not limited to clay, calcium carbonate (GCC or PCC), talc, titanium dioxide, calcium sulfate, colored pigments, and mixtures thereof. In some embodiments, the pigment comprises clay. In some embodiments, the pigment comprises calcium carbonate. In some embodiments, the pigment comprises talc. In some embodiments, the pigment comprises a mixture of clay and calcium carbonate. In some embodiments, the pigment comprises a mixture of clay and talc. In some embodiments, the pigment comprises a mixture of clay, calcium carbonate, and talc. In some embodiments, the pigment comprises at least 50 wt% clay based on the total pigment content. The binder may preferably comprise a water-dispersible or water-soluble binder, or a combination thereof. In some embodiments, the binder is a latex, preferably selected from the group consisting of styrene acrylic (SA) latex, styrene butadiene (SB) latex, or a mixture thereof. The surface pigmentation preferably comprises more than 50 wt% of the pigment(s) and less than 50 wt% of the binder(s). The surface pigmentation is preferably applied at high solids content, such as at a solids content above 50 wt% or above 55 wt%. Typically, the amount of water applied to the barrier substrate with the surface pigmentation is less than 6 g / m2or less than 5 g / m2on each side. The high solids content helps to minimize water transfer and absorption into the barrier substrate when the surface pigmentation is applied, which prevents wrinkling, cockling and curl from occurring in the barrier substrate. In some embodiments the surface pigmentation is combined with a second calendering performed on the barrier substrate with the surface pigmentation. In some embodiments, the second calendering is a soft nip calendering. In some embodiments, the second calendering is performed at a nip load in the range of 150-300 kN / m, preferably in the range of 175-275 kN / m, and more preferably in the range of 200-250 kN / m. The nip load of the second calendering is preferably lower than the nip load of the calendering in step b). The surface pigmentation, optionally combined with the second calendering, also reduces water absorption into the barrier substrate when the polymeric coating layer is applied.

[0062] In some embodiments, the barrier paper consists of the barrier substrate. The barrier substrate is an efficient light barrier due to its high opacity, and may also provide some water vapor and gas barrier properties.

[0063] In some embodiments, the barrier paper consists of the barrier substrate with the surface pigmentation. The barrier substrate with the surface pigmentation is an efficient light barrier due to its high opacity, and may also provide some water vapor and gas barrier properties.

[0064] In some embodiments, the barrier substrate, optionally with the surface pigmentation, may further be provided with a polymeric coating layer to obtain acceptable water vapor barrier properties. The barrier substrate also has a surface suitable for vacuum coating and may further be provided with a vacuum coating layer on the polymeric coating layer to obtain further improved water vapor barrier properties.

[0065] Thus, in some embodiments, the method further comprises the step: d) applying a polymeric coating layer on the, optionally surface pigmented, barrier substrate.

[0066] The polymeric coating layer preferably provides additional barrier properties to the barrier paper. The polymeric coating layer provides improved water vapor barrier properties, and may also provide improved oxygen barrier properties, to the barrier paper.

[0067] Furthermore, the polymeric coating layer also preferably acts to level out unevenness, and fill pores and pinholes present in the fibrous or porous barrier substrate. The polymeric coating layer may be a surface sizing layer or coating formed using a water soluble polymer selected from cellulose derivatives, starch, alginate, PVOH, hemicellulose, or derivatives thereof. In some embodiments, the polymeric coating layer may also contain m icrofi brillated cellulose (MFC) or cellulose nanocrystals (CNC). Further additives such as pigments, lubricants, or softeners are also possible in the polymeric coating layer.

[0068] The polymeric coating layer is preferably applied in the form of a dispersion or solution of a polymer in water. In some embodiments, the water retention value of the dispersion or solution of the polymer in water is above 100 g / m2, preferably above 150 g / m2, and more preferably above 200 g / m2, as determined according to TAPPI TM-701 PM-01. In some embodiments, the polymeric coating layer comprises a water-soluble polymer selected from the group consisting of a polyvinyl alcohol (PVOH), a modified polyvinyl alcohol, a polysaccharide and a modified polysaccharide, or combinations thereof. In some embodiments, the polymeric coating layer comprises polyvinyl alcohol (PVOH). The polymeric coating layer is preferably applied in the form of a dispersion or solution of a PVOH. In some embodiments, the water retention value of the dispersion or solution of the PVOH in water is above 100 g / m2, preferably above 150 g / m2, and more preferably above 200 g / m2, as determined according to TAPPI TM-701 PM-01.

[0069] 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 SO- 98, or Poval 56-98 or mixtures of these. From the less hydrolyzed 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.

[0070] 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.

[0071] In some embodiments, the polymeric coating layer comprises up to 50 wt%, preferably in the range of 1-20 wt%, of microfibrillated cellulose (MFC) or nanocrystalline cellulose (NCC), based on dry weight.

[0072] In some embodiments, the polymeric coating 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, 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.

[0073] In some embodiments, the grammage of the polymeric coating 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.

[0074] To minimize the risk of pinholes in the polymeric coating layer, the polymeric coating 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.

[0075] The polymeric coating layer can be applied to the, optionally surface pigmented, barrier substrate by contact or non-contact 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. In some embodiments, the coating 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 an unfoamed coating. The lower water content of a foam coating also reduces the problems with rewetting of the barrier substrate.

[0076] In some embodiments, the barrier paper consists of the, optionally surface pigmented, barrier substrate with the polymeric coating layer. The barrier substrate is an efficient light barrier due to its high opacity, and the polymeric coating layer provides water vapor barrier properties.

[0077] The optionally surface pigmented barrier substrate with the polymeric coating layer has a smooth, even and pinhole free surface and provides an excellent substrate for vacuum coating. Thus, in some embodiments, the method further comprises the step: e) applying a vacuum coating layer on the polymeric coating layer.

[0078] Vacuum coating refers to a family of processes used to deposit layers of metals, metal oxides and other inorganic and organic compositions, 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.

[0079] Vacuum coating typically results in very thin coatings. In some embodiments, the vacuum coating layer has a thickness in the range of 10-600 nm, preferably in the range of 10-250 nm, and more preferably in the range of 50-250 nm. This may be compared to conventional aluminum foils used in packaging laminates, which foils typically have thickness in the range of about 3-12 pm.

[0080] In some embodiments, the vacuum coating layer is applied to the polymeric coating layer by physical vapor deposition (PVD) or chemical vapor deposition (CVD).

[0081] In some embodiments, the vacuum coating layer comprises a metal, a metal oxide, or a ceramic.

[0082] In some embodiments, the vacuum coating 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 vacuum coating layer comprises a metal or a metal oxide, preferably aluminum or aluminum oxide.

[0083] One preferred type of vacuum coating, often used for its barrier properties, in particular water vapor barrier properties, is an aluminum metal physical vapor 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 thickness of the vacuum coating 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 vacuum coating layer comprises aluminum.

[0084] The thickness of the vacuum coating layer may also be characterized by the optical density of the layer. In some embodiments the vacuum coating layer has an optical density above 1.8, preferably above 2.0, above 2.5, above 2.7, or above 3.0.

[0085] The coating of the, optionally surface pigmented, barrier substrate with the polymeric coating layer and vacuum coating layer significantly improves the water vapor barrier properties of the coated barrier paper as compared to the uncoated barrier paper.

[0086] In some embodiments, the optionally surface pigmented barrier paper with the polymeric coating layer and vacuum coating layer 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 10 g / m2 / 24h, preferably less than 5 g / m2 / 24h, and more preferably less than 1 g / m2 / 24h.

[0087] In addition to providing good water vapor barrier properties, the inventive vacuum coated barrier paper may also form a good barrier for other gases such as oxygen, as well as aromas and odors.

[0088] When the optionally surface pigmented barrier substrate is coated with the polymeric coating layer, and optionally also the vacuum coating layer, the remaining uncoated side of the obtained barrier paper may still have excellent printability.

[0089] The barrier paper is preferably made entirely from virgin and / or cleaned and / or bleached pulp fibers sources such that the barrier paper is suitable for food contact packaging. According to a second aspect illustrated herein, there is provided a barrier paper for use in a paper or paperboard based packaging laminate, said barrier paper comprising: a barrier substrate, wherein said barrier substrate comprises at least 50 wt% refined pressurized groundwood (PGW) pulp fibers having a Canadian Standard Freeness (CSF) value of less than 150 ml, based on the total fiber content of the barrier substrate, and wherein said barrier substrate has a grammage in the range of 30-95 g / m2, a bulk of less than 1.30 cm3 / g and an opacity above 60%; optionally a surface pigmentation on the barrier substrate; optionally a polymeric coating layer on the, optionally surface pigmented, barrier substrate; and optionally a vacuum coating layer on the polymeric coating layer.

[0090] The barrier paper, the barrier substrate, the polymeric coating layer, and the vacuum coating layer in the second aspect may each be further defined or characterized as set out above with reference to the first aspect. Particularly, the composition of the barrier paper and barrier substrate in the second aspect may each be further defined or characterized as set out above with reference to the barrier paper or barrier substrate in the first aspect. The grammage and bulk of the barrier substrate may each be further defined or characterized as set out above with reference to the barrier paper or barrier substrate in the first aspect. The composition of the polymeric coating layer and the vacuum coating layer in the second aspect may each be further defined or characterized as set out above with reference to the composition of the polymeric coating layer and the vacuum coating layer in the first aspect.

[0091] In some embodiments, the barrier paper according to the second aspect is obtainable by or obtained by the method according to the first aspect. The use of a high amount of refined pressurized groundwood (PGW) pulp fibers having a Canadian Standard Freeness (CSF) value of less than 150 ml (at least 50 wt% based on the total fiber content of the paper substrate web) has been found to give very good runnability and drainage on the paper machine leading to very good formation. This good formation in turn means that calendering and coating works very well and yields a substrate which is very well suited for vacuum coating.

[0092] According to a third aspect illustrated herein, there is provided a paper or paperboard based packaging laminate, comprising: a paper or paperboard base layer; and a barrier paper according to the second aspect, or obtainable by or obtained by the method according to the first aspect; wherein the barrier paper is laminated to the paper or paperboard base layer by an adhesive tie layer.

[0093] 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. The paper or paperboard based packaging laminate herein comprises at least a paper or paperboard base layer and a barrier paper according to the second aspect, or obtainable by or obtained by the method according to the first aspect.

[0094] 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. 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 specifically stated otherwise, density in the present disclosure is determined according to the standard ISO 534.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] The paper or 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 paper or 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.

[0100] In the method according to the third aspect, the paper or paperboard base layer is combined with a barrier paper. Onto the paper or paperboard base layer, the barrier paper is laminated using an adhesive composition, preferably a water based adhesive composition. A surface of the paper or paperboard base layer is laminated to the barrier paper layer using the adhesive composition, for example in a press nip, such that the adhesive composition forms an adhesive tie layer between the paper or paperboard base layer and the barrier paper. The barrier paper or the paper or paperboard based packaging laminate comprising the barrier paper 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 barrier paper or the paper or paperboard based packaging laminate surface. Particularly, in a barrier paper comprising a vacuum coating layer, the polymeric topcoat layer may protect the sensitive vacuum coating layer. The polymeric topcoat layers may for example be applied by extrusion coating, film lamination or dispersion coating.

[0101] 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. 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 barrier paper or the paper or 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.

[0103] The polymeric topcoat layers may also comprise a dispersion coating, preferably a water based dispersion coating. In some embodiments, the polymeric topcoat comprises a water based acrylate-based copolymer emulsion. In some embodiments, 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.

[0104] The grammage 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 grammage of the polymeric topcoat layer of at least 8 g / m2, preferably at least 12 g / m2is typically required. In some embodiments, the grammage 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 grammage may in some cases be lower than 8 g / m2.

[0105] Additionally, the inventive barrier paper or paper or paperboard based packaging laminate can provide an alternative to conventional materials using aluminum foil layers, which can more readily be repulped and recycled. In some embodiments, the barrier paper has a reject rate according to PTS RH 021 / 97 of less than 30 %, preferably less than 20 %, more preferably less than 10%. 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%.

[0106] 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.

[0107] 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.

[0108] EXAMPLES

[0109] Embodiments of the invention will now be further described by way of the following non-limiting examples.

[0110] Example 1 (comparative) - Barrier substrate with 100% highly refined bleached kraft pulp fibers

[0111] A conventional barrier substrate was prepared using 100% of highly refined bleached kraft (HRBK) pulp fibers (refined to a CSF value below 100 ml), without extensive calendering (as set out in Table I). The obtained barrier paper substrate web exhibited poor runnability and was difficult to coat with an aqueous coating composition by blade or roll coating without web breaks or wrinkling during coating.

[0112] Example 2 and 3 - Barrier substrate with 66 wt% PGW pulp fibers

[0113] In this case, a refined pressurized groundwood (PGW) pulp fibers refined to a CSF value of 50 ml was mixed with refined bleached kraft pulp fibers which had a CSF value of about 200 ml. The fiber mix ratio was 66:34 (PGW pulp fibers: kraft pulp fibers) (as set out in Table I). The pulp mixture contained substantially no broke and no filler. The paper substrate web was run at a speed above 1100 m / min and dried to a moisture content of about 6 wt%.

[0114] The paper substrate web was produced both uncalendered (Example 2) and calendered (Example 3). The calendered paper substrate web was subjected to soft calendering with two soft nips both run at 232 kN / m.

[0115] The obtained barrier substrate had very good specific formation and high opacity, even after the high calendering loads. The water vapor transmission rate (WVTR) of the calendered and uncalendered paper substrate webs were too high to measure and were not determined. Table Example 4, 5, and 6 - Barrier paper with surface pigmentation

[0116] The barrier substrate was then provided with a surface pigmentation on both sides using different surface pigmentation recipes as set out in Table II. In Examples 4, 5 and 6 a small amount of surface pigmentation, 4-5 g / m2, was applied to each side of the barrier substrate of Example 3 as a single coating using a film press coater with a rod applicator. Afterwards, the samples were subjected to soft calendering with two soft nips both run at 220 kN / m and 150 °C. After the surface pigmentation, the surface pigmented barrier substrates still had a Gurley Hill air resistance of 5000-9000 s / 100 ml. The smoothness (PPS 10) was in the range of 3-4 pm.

[0117] Table

[0118] Example 7 and 8 - Barrier paper with polymeric coating and vacuum coating

[0119] The surface pigmented barrier substrates of Example 5 and 6 were first polymer coated with a PVOH (polyvinyl alcohol) coating on one side. The PVOH coating was applied in two layers to a total grammage of 2.4 and 2.2 g / m2, respectively, as set out in Table III. The water vapor transmission rate (VWTR) of the polymer coated barrier substrates measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C was in the range of 3-4 g / m2 / 24h showing that the surface is closed and provides a good moisture barrier. The polymer coated surfaces of the barrier substrates were then subjected to vacuum coating with 100 nm aluminum. After this, the WVTR was clearly improved and was about 0.3-0.5 g / m2 / day when determined at 23 C and 50% RH.

[0120] Table III

[0121] Unless specifically stated otherwise, the parameters used in the present disclosure are determined according to the following methods or standards:

[0122] - Brightness C / 2° +UV was measured at 457 nm according to ISO 2470-1.

[0123] - Opacity, 0 / 2° +UV was measured according to ISO 2471.

[0124] - Gurley Hill air Permeance was measured according to ISO 5636-5.

[0125] - Surface smoothness, PPS 10 at 1.0 MPa was measured according to ISO 8791-4.

[0126] - Oil and grease resistance, KIT, was measured according to ISO 16532-2

[0127] - Specific formation of the sheet was determined according to SCAN-P 92:09.

[0128] - Grammage was determined according to ISO 536.

[0129] - Density was determined according to ISO 534.

[0130] - Thickness was determined according to ISO 534.

[0131] - Bulk was determined according to ISO 535.

[0132] - Tear Strength was determined according to ISO 1974, MD (machine direction).

[0133] - Tensile index, MD and CD, was determined according to ISO 1924-3.

[0134] - L* C / 2° +UV, (Cielab) determined according to ISO 5631-1 - a* +UV, (Cielab) determined according to ISO 5631-1

[0135] - c* +UV, (Cielab) determined according to ISO 5631-1

[0136] - COBB30 TS(top side) / BS(back side) was determined according to ISO 535.

[0137] - Water vapor transmission rate (WVTR) was measured according to ASTM F1249-20 at 50% relative humidity and 23 °C.

Claims

CLAIMS1 . A method of manufacturing a barrier paper for use in a paper or paperboard based packaging laminate, said method comprising: a) providing a paper substrate web, wherein said paper substrate web comprises at least 50 wt% refined pressurized groundwood (PGW) pulp fibers having a Canadian Standard Freeness (CSF) value of less than 150 ml, based on the total fiber content of the paper substrate web, and wherein said paper substrate web has a grammage in the range of 30-95 g / m2, and a bulk of at least 1.35 cm3 / g, b) calendering the paper substrate web to a bulk of less than 1 .30 cm3 / g to obtain a barrier substrate, wherein the obtained barrier substrate has an opacity of at least 60%, and c) optionally applying a surface pigmentation on the paper substrate web or on the barrier substrate to obtain a surface pigmented barrier substrate.

2. The method according to claim 1 , wherein the paper substrate web comprises at least 60 wt%, and more preferably at least 70 wt%, of the refined PGW pulp fibers based on the total fiber content of the paper substrate web.

3. The method according to any one of the preceding claims, wherein the refined PGW pulp fibers have a CSF value of less than 115 ml, and preferably less than 80 ml.

4. The method according to any one of the preceding claims, wherein the paper substrate web further comprises up to 50 wt% kraft pulp fibers based on the total fiber content of the paper substrate web, preferably wherein the kraft pulp fibers are refined kraft pulp fibers having a Canadian Standard Freeness (CSF) in the range of 100-700 ml.

5. The method according to any one of the preceding claims, wherein the paper substrate web comprises less than 10 wt% of mineral filler based on the total fiber content of the paper substrate web.

6. The method according to any one of the preceding claims, wherein the paper substrate web has a moisture content of 10 wt% or less, preferably in the range of 4-10 wt%.

7. The method according to any one of the preceding claims, wherein said paper substrate web has a grammage in the range of 35-85 g / m2, preferably in the range of 35-75 g / m2, and more preferably in the range of 35-65 g / m2.

8. The method according to any one of the preceding claims, wherein the paper substrate web has a bulk of at least 1.40 cm3 / g, preferably in the range of 1 .40- 1.80 cm3 / g.

9. The method according to any one of the preceding claims, wherein the calendering comprises soft calendering.

10. The method according to any one of the preceding claims, wherein the calendering is performed at a nip load of at least 150 kN / m, preferably at least 175 kN / m, and more preferably at least 200 kN / m.

11. The method according to any one of the preceding claims, wherein the paper substrate web is calendered to a bulk of less than 1 .25 cm3 / g, preferably to a bulk of less than 1.20 cm3 / g, and more preferably to a bulk in the range of 1.10-1.20 cm3 / g.

12. The method according to any one of the preceding claims, wherein the obtained barrier substrate has an opacity of at least 65%, preferably at least 70%, and more preferably at least 75%.

13. The method according to any one of the preceding claims, wherein the surface pigmentation is applied at a grammage in the range of 2-10 g / m2, preferably in the range of 2-8 g / m2, and more preferably in the range of 3-7 g / m2.

14. The method according to any one of the preceding claims, further comprising: d) applying a polymeric coating layer on the, optionally surface pigmented, barrier substrate.

15. The method according to claim 14, wherein the polymeric coating layer comprises polyvinyl alcohol (PVOH).

16. The method according to claim 14 or 15, further comprising: e) applying a vacuum coating layer on the polymeric coating layer.

17. The method according to claim 16, wherein the vacuum coating layer comprises a metal or a metal oxide, preferably aluminum or aluminum oxide.

18. A barrier paper for use in a paper or paperboard based packaging laminate, said barrier paper comprising: a barrier substrate, wherein said barrier substrate comprises at least 50 wt% refined pressurized groundwood (PGW) pulp fibers having a Canadian Standard Freeness (CSF) value of less than 150 ml, based on the total fiber content of the barrier substrate, and wherein said barrier substrate has a grammage in the range of 30-95 g / m2, a bulk of less than 1.30 cm3 / g and an opacity above 60%; optionally a surface pigmentation on the barrier substrate; optionally a polymeric coating layer on the, optionally surface pigmented, barrier substrate; and optionally a vacuum coating layer on the polymeric coating layer.

19. A paper or paperboard based packaging laminate, comprising: a paper or paperboard base layer; and a barrier paper according to claim 18 or obtained by the method according to any one of claims 1-17; wherein the barrier paper is laminated to the paper or paperboard base layer by an adhesive tie layer.

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