WO2025224633A1

WO2025224633A1 - A method for manufacturing a flexible paper based packaging laminate

Info

Publication number: WO2025224633A1
Application number: PCT/IB2025/054213
Authority: WO
Inventors: Isto Heiskanen; Marko RYYNÄNEN; Niko MELLANEN
Original assignee: Stora Enso Oyj
Current assignee: Stora Enso Oyj
Priority date: 2024-04-24
Filing date: 2025-04-23
Publication date: 2025-10-30
Anticipated expiration: 2026-10-24
Also published as: SE547862C2; SE2430223A1

Abstract

The present invention relates to a method for manufacturing a flexible paper based packaging laminate suitable for use in bags or pouches, said method comprising: a) providing a flexible multiply paper substrate having a grammage in the range of 40-160 g/m², comprising a first outermost ply comprising at least 70 wt% bleached kraft pulp or hardwood pulp based on the dry weight of the ply, and a second outermost ply comprising at least 70 wt% unbleached kraft pulp or high yield pulp, based on the dry weight of the ply, wherein the second outermost ply has an outer surface having a Cobb-Unger oil absorbency of at least 15 g/m² as determined according to the standard SCAN-P 37:77; and b) providing a barrier paper having a grammage in the range of 20-80 g/m²and comprising at least 70 wt% cellulosic material based on the dry weight of the barrier paper, wherein the barrier paper has a Cobb-Unger oil absorbency of less than 10 g/m² as determined according to the standard SCAN-P 37:77; c) laminating the barrier paper to the outer surface of the second outermost ply of the multiply paper substrate using a water-based adhesive to obtain a flexible paper based packaging laminate having a grammage in the range of 80-200 g/m².

Description

A METHOD FOR MANUFACTURING A FLEXIBLE PAPER BASED

PACKAGING LAMINATE

Technical field

The present disclosure relates to flexible paper based packaging laminates for use in bags and pouches, mainly for food packaging, and to methods for manufacturing such laminates.

Background

Bags and pouches for packaging long shelf-life food products, for example pet foods, are commonly made from either plastic based laminates or from flexible paper based laminates. Paper based laminates for use in such bags and pouches are usually made from food packaging paper or board comprising a flexible paper based substrate, an outermost heat-sealable polyolefin (e.g. polyethylene, PE) layer and inner layers of polyolefin and aluminum. The aluminum foil layer, which is included to provide water vapor and oxygen barrier properties, is usually incorporated between tie layers of polyethylene to provide the following structure: PE/flexible paper based substrate/PE/aluminum foil/PE.

Paper generally refers to a material manufactured in thin sheets or webs from the pulp of wood or other fibrous substances comprising cellulose fibers, used for writing, drawing, or printing on, or as packaging material. Paper can either be bleached or unbleached, coated or uncoated, and produced in a variety of thicknesses, depending on the end use requirements. Paper may be a single ply material, formed from a single cellulose based ply, or it may be a multiply material comprised of two or more cellulose based plies. A multiply structure allows for the different plies to be designed differently in order to fulfill specific functional requirements.

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

Also, in many cases the water vapor barrier properties of the polymer coated paper 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 paper is often combined with one or more layers of aluminum foil. The aluminum foil is typically bonded to the laminate using one or more polymeric tie layers. However, the addition of polymer and aluminum foil add significant costs and the combination of polymeric layers and aluminum foils makes repulping and recycling of the materials more difficult. Also, due to its high carbon footprint there is a wish to replace aluminum foils in paper based packaging materials. The paper based packaging materials should also have suitable flexibility or stiffness allowing them to be used in converting lines for manufacturing pouches or bags, such as flat pouches, flat-bottom pouches, standup pouches, and gusseted pouches or bags.

In the prior art, attempts have been made to replace the aluminum foil with more environmentally friendly and/or easier to recycle solutions. For example, microfibri Hated cellulose (MFC) films and coatings have been developed, in which cellulosic fibrils provided by fibrillation of cellulose fibers have been dispersed e.g. in water and thereafter re-organized and rebonded together to form a dense film or coating with excellent gas barrier properties. The MFC films are typically laminated to a paper based substrate in the same manner as aluminum foils. However, challenges still remain in terms of providing sufficient barrier properties, mechanical strength, durability, repulpability and recyclability, at an acceptable cost, in order to effectively replace aluminum foils and plastic films with cellulose based alternatives.

There remains a need for improved solutions to replace the combination of plastic films and aluminum foils in paper based packaging materials, while maintaining acceptable liquid and oxygen barrier properties, as well as acceptable convertability into pouches or bags. 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

It is an object of the present disclosure to provide an alternative to the plastic based laminates and paper based laminates comprising combinations of plastic films and aluminum foils commonly used in bags and pouches for food packaging.

It is a further object of the present disclosure to provide a method for manufacturing a flexible paper based packaging laminate comprising a barrier paper, which is suitable for use in bags and pouches for food packaging.

It is a further object of the present disclosure to provide a simplified method for manufacturing a flexible paper based packaging laminate comprising a barrier paper.

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.

According to a first aspect illustrated herein, there is provided a method for manufacturing a flexible paper based packaging laminate suitable for use in bags or pouches, said method comprising: a) providing a flexible multiply paper substrate having a grammage in the range of 40-160 g/m², comprising a first outermost ply comprising at least 70 wt% bleached kraft pulp or hardwood pulp based on the dry weight of the ply, and a second outermost ply comprising at least 70 wt% unbleached kraft pulp or high yield pulp, based on the dry weight of the ply, wherein the second outermost ply has an outer surface having a Cobb-Unger oil absorbency of at least 15 g/m² as determined according to the standard SCAN-P 37:77; and b) providing a barrier paper having a grammage in the range of 20-80 g/m² and comprising at least 70 wt% cellulosic material based on the dry weight of the barrier paper, wherein the barrier paper has a Cobb-Unger oil absorbency of less than 10 g/m² as determined according to the standard SCAN-P 37:77; c) laminating the flexible barrier paper to the outer surface of the second outermost ply of the multiply paper substrate using a water-based adhesive to obtain a flexible paper based packaging laminate having a grammage in the range of 80-200 g/m².

Paper generally refers to a material manufactured in thin sheets or webs from the pulp of wood or other fibrous substances comprising cellulose fibers, used for writing, drawing, or printing on, or as packaging material. Paper can either be bleached or unbleached, coated or uncoated, and produced in a variety of thicknesses, depending on the end use requirements. Paper may be a single ply material, formed from a single cellulose based ply, or it may be a multiply material comprised of two or more cellulose based plies.

A flexible paper based packaging laminate is a packaging material formed mainly from a flexible multiply paper substrate. In the inventive flexible paper based packaging laminate, both the flexible multiply paper substrate and the barrier paper are formed mainly from cellulose-based materials. In some embodiments, the flexible paper based packaging laminate comprises more than 70 wt%, preferably more than 75 wt%, more preferably more than 80 wt%, and most preferably more than 85 wt%, of cellulose-based material, based on the dry weight of the flexible paper based packaging laminate.

A flexible multiply paper substrate for use in the present disclosure differs from conventional paperboard in that it has relatively low thickness and low bulk. The low thickness and low bulk provide a multiply paper substrate with low stiffness and high flexibility, i.e. a flexible multiply paper substrate. The flexible multiply paper substrate combined with a barrier paper provides a flexible paper based packaging laminate. In addition to the flexible multiply paper substrate, the flexible paper based packaging laminate may also comprise additional layers or coatings designed to improve the performance and/or appearance of the packaging laminate. The flexible paper based packaging laminate obtained by the inventive method has a grammage in the range of 80-200 g/m².

The flexible paper based packaging laminate obtained by the inventive method can provide an alternative to conventional packaging laminates using aluminum foil layers, which can more readily be repulped and recycled.

In some embodiments, the multiply paper substrate is preferably a 2-ply paper substrate. Such a 2-ply paper substrate may also be referred to as a “2-ply kraftliner”. The 2-ply kraftliner has a first outer surface which is preferably configured to be a good printing surface, and an opposite outer surface (backside) which due to its high content of unbleached kraft pulp and/or high yield pulp provides suitable absorption behavior for the water-based adhesive.

The flexible multiply paper substrate has a relatively low grammage in the range of 40-160 g/m². In some embodiments, the flexible multiply paper substrate has a grammage in the range of 40-140 g/m², preferably in the range of 50-120 g/m², and more preferably in the range of 60-100 g/m². Unless otherwise stated, the grammages herein are determined according to the standard ISO 536.

The flexible multiply paper substrate of the present disclosure comprises a first outermost ply comprising at least 70 wt% bleached kraft pulp or hardwood pulp based on the dry weight of the ply. The first outermost ply has an outer surface forming a first outer surface of the flexible multiply paper substrate.

The flexible multiply paper substrate further comprises a second outermost ply comprising at least 70 wt% unbleached kraft pulp and/or high yield pulp based on the dry weight of the ply. The second outermost ply has an outer surface forming a second outer surface of the flexible multiply paper substrate. The outer surface of the second outermost ply has a Cobb-Unger oil absorbency of at least 15 g/m² as determined according to the standard SCAN-P 37:77.

In some embodiments, the flexible multiply paper substrate further comprises a mid ply arranged between the first and second outermost plies, said mid ply comprising at least 70 wt% unbleached kraft pulp and/or high yield pulp, and optionally 1-30 wt% bleached kraft pulp or hardwood pulp, based on the dry weight of the ply. The bleached kraft pulp or hardwood pulp optionally present in the mid ply may for example include bleached kraft pulp or hardwood pulp derived from broke substrate or laminate recycled in the manufacturing method.

In addition to the flexible multiply paper substrate, the flexible paper based packaging laminate comprises a barrier paper which is laminated to the outer surface of the second outermost ply of the flexible multiply paper substrate. The barrier paper has a grammage in the range of 20-80 g/m² and comprises at least 70 wt% cellulosic material based on the dry weight of the barrier paper. The barrier paper has a Cobb-Unger oil absorbency of less than 10 g/m² as determined according to the standard SCAN-P 37:77. The barrier paper preferably has an oxygen transmission rate (OTR) measured according to the standard ASTM F1927-20 at 50% relative humidity and 23 °C of less than 200 cc/m²/24h or less than 50 cc/m²/24h.

The barrier paper is laminated to the outer surface of the second outermost ply of the flexible multiply paper substrate. The outer surface of the second outermost ply of the flexible multiply paper substrate has high roughness and porosity, and the surface has a Cobb-Unger oil absorbency of at least 15 g/m² as determined according to the standard SCAN-P 37:77, making it highly absorbent for the waterbased adhesive. The ply will absorb a large portion of the applied adhesive, causing densification of the second outermost ply and optional mid ply, and increasing the flexibility of the obtained laminate.

The structure and composition of the flexible multiply paper based substrate, in combination with the barrier paper and water-based adhesive produces a paper based packaging laminate with high flexibility, i.e. a flexible paper based packaging laminate. Also, the structure is preferably free from inner layers of extruded polymer which further improves flexibility and allows for high fiber yield in repulping and recycling processes.

The flexible paper based packaging laminate typically has a first outermost surface intended to serve as the outside surface, or print side, and a second outermost surface intended to serve as the inside surface of a packaging container. The first outermost surface intended to serve as the outside surface, or print side, of the laminate may optionally be surface sized or pigment coated to provide high print quality.

The flexible paper based packaging laminate obtained by the inventive method can provide excellent gas and aroma barrier properties, as evidenced by a low oxygen transmission rate (OTR) measured according to the standard ASTM F1927-20 at 50% relative humidity and 23 °C, and excellent water vapor barrier properties, as evidenced by a low water vapor transmission rate (WVTR) measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C.

In some embodiments, the flexible multiply paper substrate provided in step a) of the method has a density in the range of 500-950 kg/m³, preferably in the range of 500-900 kg/m³, and more preferably in the range of 550-850 kg/m³. Unless otherwise stated, the densities herein are determined according to the standard ISO 534.

In some embodiments, the density of the first outermost ply is higher than the density of the second outermost ply and the optional mid ply.

In some embodiments, the flexible multiply paper substrate provided in step a) of the method has a bulk of less than 1.4 m³/kg, preferably less than 1.3 m³/kg. Unless otherwise stated, the bulk herein is determined according to the standard ISO 534. In some embodiments, the flexible multiply paper substrate provided in step a) has a thickness in the range of 50-200 pm, preferably in the range of 75-185 pm, and more preferably in the range of 100-155 pm. The thicknesses herein are determined according to the standard ISO 534.

In some embodiments, the flexible multiply paper substrate provided in step a) has a thickness in the range of 50-200 pm, preferably in the range of 75-185 pm, and more preferably in the range of 100-155 pm, and a bulk of less than 1.4 m³/kg, preferably less than 1.3 m³/kg. This combination of low thickness and low bulk provides a flexible multiply paper substrate.

The flexibility may also be reflected in the relatively low bending stiffness of the flexible multiply paper substrate. In some embodiments, the flexible multiply paper substrate has bending stiffness L&W 15° in the machine direction (MD) of less than 80 mN, preferably less than 65 mN, and more preferably less than 50 mN as measured according to SCAN P 29:95.

The second outermost ply and optional mid ply will typically make up the main portion of the total grammage of the flexible multiply paper substrate. In some embodiments, the first outermost ply has a grammage in the range of 20-80 g/m², and more preferably 20-50 g/m². In some embodiments, the second outermost ply has a grammage in the range of 40-140 g/m², preferably 40-120 g/m², and more preferably 60-100 g/m². In some embodiments, especially where the flexible multiply paper substrate further comprises a mid ply, the grammage of the second outermost ply may be lower. In some embodiments, the second outermost ply has a grammage in the range of 20-80 g/m², and more preferably 20-50 g/m². In some embodiments, the optional mid ply has a grammage in the range of 20-80 g/m², and more preferably 20-50 g/m². In some embodiments, the mid ply has a grammage in the range of 20-80 g/m², and more preferably 20-50 g/m².

In some embodiments, the first outermost ply further comprises 1-15 wt% filler based on the dry weight of the ply. In some embodiments, the bleached kraft pulp or hardwood pulp of the first outermost ply has a Schopper Riegler (SR) value in the range of 15-35 according to standard ISO 5267-1.

In some embodiments, the unbleached kraft pulp and/or high yield pulp of the second outermost ply has a Schopper Riegler (SR) value below 28, preferably below 25, and more preferably below 22, according to standard ISO 5267-1.

In some embodiments, the unbleached kraft pulp and/or high yield pulp of the optional mid ply has a Schopper Riegler (SR) value below 28, preferably below 25, and more preferably below 22, according to standard ISO 5267-1.

In some embodiments, the optional bleached kraft pulp or hardwood pulp of the optional mid ply has a Schopper Riegler (SR) value in the range of 15-35 according to standard ISO 5267-1.

As used herein, the term "high yield pulp" refers to a class of pulp derived from lignocellulosic material characterized by a yield that significantly exceeds the yield typically associated with conventional chemical pulping processes. Specifically, "High Yield Pulp" is defined as pulp that is produced with a process yield of at least 65%, preferably at least 75%, and more preferably at least 85%, of the original dry weight of the lignocellulosic material used in its production.

This pulp retains a substantial portion of the lignin and hemicellulose present in the original biomass, distinguishing it from lower-yield pulps where such components are largely removed. The preservation of lignin and hemicellulose contributes to the distinctive properties of high yield pulp, including improved strength, increased bulk, and enhanced sustainability attributes due to reduced chemical usage and waste generation during the pulping process. In some embodiments the high yield pulp has a Klason lignin content >15 wt%. In some embodiments, the high yield pulp has a KAPPA number of at least 50, preferably at least 70, and more preferably at least 80, measured according to ISO 302:2015. High yield pulp is produced through a modified pulping process that may involve mechanical, semi-chemical, or chemi-thermomechanical methods, or combinations thereof, designed to minimize the degradation or removal of cellulose, hemicellulose, and lignin. The high yield pulp may be bleached, delignified or unbleached.

In some embodiments, the unbleached kraft pulp has a KAPPA number of at least 20, such as in the range of 25-100, measured according to ISO 302:2015.

In some embodiments, the unbleached kraft pulp and/or high yield pulp of the second outermost ply is chemi-thermomechanical pulp (CTMP) or high- temperature chemi-thermomechanical pulp (HT-CTMP). In some embodiments, the high yield pulp of the second outermost ply is softwood CTMP or softwood HT- CTMP. In some embodiments, the high yield pulp of the second outermost ply is hardwood CTMP or hardwood HT-CTMP. In some embodiments, the high yield pulp of the second outermost ply comprises a mixture of two or more of softwood CTMP, softwood HT-CTMP, hardwood CTMP and hardwood HT-CTMP.

In some embodiments, the unbleached kraft pulp and/or high yield pulp of the mid ply is chemi-thermomechanical pulp (CTMP) or high-temperature chemi- thermomechanical pulp (HT-CTMP). In some embodiments, the high yield pulp of the mid ply is softwood CTMP or softwood HT-CTMP. In some embodiments, the high yield pulp of the mid ply is hardwood CTMP or hardwood HT-CTMP. In some embodiments, the high yield pulp of the mid ply comprises a mixture of two or more of softwood CTMP, softwood HT-CTMP, hardwood CTMP and hardwood HT-CTMP.

In some embodiments, the unbleached kraft pulp and/or high yield pulp of the second outermost ply and/or the mid ply comprises recycled unbleached kraft pulp fibers and/or recycled high yield pulp fibers. The recycled fibers may be fibers obtained from recycled packaging waste and especially from used beverage cartons. The structure of the inventive flexible paper based packaging laminate enables the use of a larger amount of recycled fibers, such as fibers obtained from used beverage cartons, in the flexible multiply paper substrate since the barrier paper, and in some cases also the tie layer, hinders the migration of mineral oil based contaminants. Thus, in some embodiments, the second outermost ply comprises at least 5 wt% recycled high yield pulp fibers, preferably at least 10 wt% recycled high yield pulp fibers, such as 5-30 wt% or 10-30 wt%, based on dry weight of the ply. In some embodiments, the mid ply comprises at least 5 wt% recycled high yield pulp fibers, preferably at least 10 wt% recycled high yield pulp fibers, such as 5-30 wt%, or 10-30 wt%, based on dry weight of the ply.

Preferably, the extractive content of the unbleached kraft pulp and/or high yield pulp is less than 0.3%, preferably less than 0.25%, and more preferably less than 0.2% as measured by extraction in acetone according to standard SCAN CM- 49:03. This can minimize odor or taste caused by formation of volatile compounds.

In some embodiments, the second outermost ply and/or the mid ply comprises unbleached kraft pulp and/or high yield pulp that has been washed to reduce the content of cellulosic and non-cellulosic fines and other contaminants.

In some embodiments, the second outermost ply comprises 0.1-10 wt%, preferably 0.15-5 wt%, of a strength enhancement agent based on the dry weight of the ply. In some embodiments, the mid ply comprises 0.1-10 wt%, preferably 0.15-5 wt%, of a strength enhancement agent based on the dry weight of the ply. The strength enhancement agent may comprise a polysaccharide or a derivative thereof. In some embodiments the strength enhancement agent is selected from highly refined cellulose, such as microfibrillated cellulose, or starch, or a combination thereof. The strength enhancement agent may be present in the bulk of the plies or at an interface between the two plies, such as in the form of a ply bond layer.

In some embodiments, the second outermost ply comprises 0.05-5 wt%, preferably 0.1-4 wt%, and more preferably 0.2-3 wt%, of a hydrophobizing internal sizing agent based on the dry weight of the ply. In some embodiments, the mid ply comprises 0.05-5 wt%, preferably 0.1-4 wt%, and more preferably 0.2-3 wt%, of a hydrophobizing internal sizing agent based on the dry weight of the ply. The hydrophobizing internal sizing may for example be an alkyl ketene dimer (AKD), an alkenyl succinic anhydride (ASA), a styrene-maleic anhydride (SMA), or a rosin sizing agent. These amounts of a hydrophobizing internal sizing agent, at least in the second outermost ply, have surprisingly been found to facilitate the application of the water-based adhesive by more even and better spreading of the composition.

The outer surface of the first outermost ply is preferably configured to serve as an outer surface, or print surface, of a packaging formed of the finished packaging laminate.

In some embodiments, the flexible multiply paper substrate is surface sized on the outer surface of the first outermost ply. In some embodiments, the outer surface of the first outermost ply is surface sized with a surface sizing composition, preferably comprising starch or a starch derivative, a cellulose derivative, or polyvinyl alcohol (PVOH) or a combination of thereof. The starch derivative may for example be a slightly modified, such as oxidized or cationized starch. The cellulose derivative may for example be a sodium carboxymethyl cellulose with a degree of substitution higher than 0.4 such as in the range of 0.5-1 .5. The PVOH may be fully or partly hydrolyzed. The surface sizing composition may also comprise a hydrophobic sizing agent, such as alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), or a rosin sizing agent. In some embodiments, the grammage of the surface sizing composition is 0.2-10 g/m², preferably 0.4-8 g/m², and more preferably 0.8-5 g/m², based on dry weight. In some embodiments the surface sizing composition is applied by hard nip sizing.

In some embodiments, the flexible multiply paper substrate comprises a mineral coating layer on the outer surface of the first outermost ply. 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 dry weight of the mineral coating layer. 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 calcium carbonate. The binder may preferably comprise 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 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, based on dry weight. In some embodiments, the outer surface of the first outermost ply, optionally with the mineral coating layer, has an ISO brightness greater than 68%, preferably greater than 70%, and more preferably greater than 72%, as determined according to ISO 2470-1. In some embodiments, the outer surface of the first outermost ply, optionally with the mineral coating layer, has a COBB30 value of less than 35 g/m² as determined according to ISO 535. Due to the high content of bleached kraft pulp, and/or the presence of a mineral coating layer, the first outermost ply may also be referred to as a white top ply.

In some embodiments, the flexible multiply paper substrate is provided by: i) forming a first web layer by applying a first suspension comprising at least 70 wt% bleached kraft pulp or hardwood pulp based on the dry weight of the suspension on a first wire, and partially dewatering the first web layer on the first wire; ii) forming a second web layer by applying a second suspension comprising at least 70 wt% unbleached kraft pulp and/or high yield pulp based on the dry weight of the suspension on a second wire, and partially dewatering the second web layer on the second wire; iii) optionally forming a third web layer by applying a third suspension comprising at least 70 wt% unbleached kraft pulp and/or high yield pulp, and optionally 1-30 wt% bleached kraft pulp or hardwood pulp, based on the dry weight of the suspension on a third wire, and partially dewatering the third web layer on the third wire; iv) couching the partially dewatered first web layer and the partially dewatered second web layer, and optionally the partially dewatered third web layer, to obtain a laminate web, wherein the first web layer forms a first outermost ply and the second web layer forms a second outermost ply, and the optional third web layer forms an optional mid ply; and v) dewatering and drying the formed laminate web to obtain the flexible multiply paper substrate; wherein the obtained flexible multiply paper substrate has a grammage in the range of 40-160 g/m², and the second outermost ply has an outer surface having a Cobb-Unger oil absorbency of at least 15 g/m² as determined according to the standard SCAN-P 37:77.

In some embodiments, the dewatering comprises passing the formed laminate web through at least one shoe press and preferably through at least two shoe presses, preferably wherein at least one shoe press is a double felted shoe press.

Roughness of the outer surface of second outermost ply is preferably high in order to promote absorption of the water-based adhesive. In some embodiments, the outer surface of the second outermost ply has a Bendtsen roughness of at least 300 ml/min, preferably at least 400 ml/min, at least 500 ml/min, at least 600 ml/min, at least 700 ml/min, or at least 800 ml/min, according to standard ISO 8791-2. In some embodiments, the outer surface of the second outermost ply has a PPS surface smoothness at 1.0 MPa in the range of 1-20 pm, preferably in the range of 1.5-10 pm, and more preferably in the range of 2-8 pm, as determined according to ISO 8791-4:2007.

In some embodiments, the outer surface of the second outermost ply has a COBB30 value of more than 25 g/m², preferably more than 30 g/m², and more preferably more than 35 g/m², as determined according to ISO 535.

The flexible multiply paper substrate, before the barrier paper film is laminated to the substrate, typically has high oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) values, i.e. poor oxygen and water vapor transmission resistance. The OTR measured according to the standard ASTM F1927-20 at 50% relative humidity and 23 °C is typically above 1000 cc/m²/24h and the WVTR measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C is typically above 1000 g/m²/24h. The flexible multiply paper substrate, before the barrier paper film is laminated to the substrate, also typically has poor or no grease resistance as measured according to the standard ISO 16532- 1 :2008. The flexible multiply paper substrate used in the present disclosure differs from conventional paperboard in that it has relatively low thickness, low bulk, and low stiffness, but relatively high burst strength. This combination of properties is especially useful for bags and pouches.

The flexible multiply paper substrate, before the barrier paper film is laminated to the substrate, typically has a burst strength of at least 500 kPa, and preferably at least 600kPa, measured according to ISO 2758. In some embodiments, the flexible multiply paper substrate, before the barrier paper film is laminated to the substrate, has a burst strength in the range of 600-900 kPa, measured according to ISO 2758.

A barrier paper is provided as a barrier for oxygen and water vapor in the flexible paper based packaging laminate. The barrier paper has a grammage in the range of 20-80 g/m² and comprises at least comprises at least 70 wt% cellulosic material based on the dry weight of the barrier paper, and the barrier paper has a Cobb- Unger oil absorbency of less than 10 g/m² as determined according to the standard SCAN-P 37:77. Thus, the Cobb-Unger oil absorbency of the barrier paper is significantly lower than the Cobb-Unger oil absorbency of the outer surface of the second outermost ply.

In some embodiments, the grammage of the barrier paper is in the range of 25-80 g/m², and preferably in the range of 30-65 g/m². Unless otherwise stated, the grammage is determined according to the standard ISO 536.

In some embodiments, the barrier paper has a density in the range of 800-1500 kg/m³, preferably in the range of 850-1200 kg/m³, and more preferably in the range of 850-1050 kg/m³. Unless otherwise stated, the density is determined according to the standard ISO 534.

In some embodiments, the density of the barrier paper is higher than the density of the first outermost ply of the flexible multiply paper substrate. Thus, in these embodiments the density of the first outermost ply is higher than the density of the second outermost ply and the optional mid ply, and the density of the barrier paper is higher than the density of the first outermost ply.

In some embodiments, the barrier paper has a bulk of less than 1.3 m³/kg, preferably less than 1.1 m³/kg. Unless otherwise stated, the bulk herein is determined according to the standard ISO 534.

In some embodiments, the bulk of the barrier paper is lower than the bulk of the first outermost ply of the flexible multiply paper substrate. Thus, in these embodiments the bulk of the first outermost ply is lower than the bulk of the second outermost ply and the optional mid ply, and the bulk of the barrier paper is lower than the bulk of the first outermost ply.

In some embodiments, the barrier paper has a thickness in the range of 25-90 pm, preferably in the range of 30-85 pm, and more preferably in the range of 35-70 pm. The thicknesses herein are determined according to the standard ISO 534.

In some embodiments, the barrier paper has a thickness in the range of 25-90 pm, preferably in the range of 30-85 pm, and more preferably in the range of 35-70 pm, and a bulk of less than 1.3 m³/kg, preferably less than 1.1 m³/kg. This combination of low thickness and low bulk provides a flexible barrier paper.

The flexibility may also be reflected in the relatively low bending stiffness of the barrier paper. In some embodiments, the barrier paper has bending stiffness L&W 15° in the machine direction (MD) of less than 80 mN, preferably less than 65 mN, and more preferably less than 50 mN as measured according to SCAN P 29:95.

In some embodiments, the barrier paper comprises at least 50 wt% highly refined cellulose having a Schopper Riegler (SR) value in the range of 70-98, preferably in the range of 80-98, and more preferably in the range of 85-95, according to standard ISO 5267-1 , based on the dry weight of the barrier paper. In some embodiments, the barrier paper comprises at least 70 wt%, preferably at least 75 wt%, and more preferably at least 80 wt%, of highly refined cellulose having a Schopper Riegler (SR) value in the range of 70-98, preferably in the range of 80- 98, and more preferably in the range of 85-95, according to standard ISO 5267-1 , based on the dry weight of the barrier paper.

In some embodiments, the highly refined cellulose is microfibrillated cellulose (MFC).

In some embodiments, the barrier paper is a microfibrillated cellulose (MFC) barrier paper comprising at least 50 wt% of MFC based on the dry weight of the MFC barrier paper. In some embodiments, the MFC barrier paper comprises at least 70 wt%, preferably at least 75 wt%, and more preferably at least 80 wt%, of MFC based on the dry weight of the MFC barrier paper.

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.

MFC is produced from wood cellulose fibers, both from hardwood and softwood fibers. It can also be made from microbial sources, agricultural fibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fiber sources. It is preferably 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 some embodiments, the MFC has a Schopper Riegler (SR) value in the range of 80-98, preferably in the range of 85-98, more preferably in the range of 90-98, according to standard ISO 5267-1.

In some embodiments, the MFC has a water retention value (WRV) value of at least 230 %, preferably at least 280%, according to standard ISO 23714:2014.

The MFC barrier paper is preferably prepared with controlled MD and CD shrinkage during the drying of the MFC barrier paper web. The MFC barrier paper is preferably prepared with a cross direction (CD) shrinkage of at least 5%, and more preferably at least 6% throughout the drying of the MFC barrier paper web. The drying is preferably performed with at least one double-felted drying section, optionally combined with at least one single-felted drying section.

In some embodiments, the barrier paper further comprises 1-30 wt% of unrefined or slightly refined cellulose based on the dry weight of the barrier paper, wherein the unrefined or slightly refined cellulose has a Schopper Riegler (SR) value in the range of 10-35, preferably in the range of 10-30, according to standard ISO 5267- 1. The unrefined or slightly refined cellulose preferably has an average fiber length of at least 1.8 mm, preferably at least 2.0 mm. A barrier paper comprising a high amount of highly refined cellulose and a lower amount of unrefined or slightly refined cellulose, also sometimes referred to as reinforcement fiber, is useful as it combines the barrier properties of a highly refined cellulose with the mechanical strength properties, such as tear strength, puncture resistance and burst strength, of unrefined or slightly refined cellulose.

In some embodiments, the barrier paper further comprises 0.1-10 wt%, preferably 0.15-5 wt%, of a strength enhancement agent based on the dry weight of the barrier paper. The strength enhancement agent may comprise a polysaccharide or a derivative thereof. In some embodiments the strength enhancement agent is selected from highly refined cellulose, such as microfi brillated cellulose, or starch, or a combination thereof. In some embodiments, the barrier paper comprises 0.1-10 wt%, preferably 0.15-5 wt%, of a cellulose ether or a starch derivative based on the dry weight of the barrier paper. The cellulose ether may for example be carboxymethyl cellulose (CMC) or hydroxypropyl cellulose (HPC). The starch derivative may for example be hydroxypropyl starch, acetylated starch, or octenyl succinic anhydride (OSA) modified starch.

In some embodiments, the barrier paper further comprises 0.1-30 wt% of a polyvinyl alcohol (PVOH) based on the dry weight of the barrier paper. The PVOH may be PVOH or a derivative or analogue thereof. 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 80-99.9 mol%, preferably in the range of 88-99.9 mol%. The PVOH may be present in the bulk of the barrier paper, on one or both surfaces of the barrier paper, or a combination thereof. In some embodiments, the PVOH is present in the form of a coating or an impregnation on one or both surfaces of the barrier paper. In some embodiments, the PVOH is present in the form of a coating or an impregnation on both surfaces of the barrier paper at a coat weight in the range of 0.5-5 g/m² on each surface.

The barrier paper may be a single ply or a multiply barrier paper. In some embodiments, the barrier paper is a multiply barrier paper, wherein at least one of the plies comprises at least 50 wt% MFC based on the dry weight of the ply.

In some embodiments, the barrier paper is polymer coated, mineral coated, and/or vacuum deposition coated. In some embodiments, the barrier paper is polymer coated and/or vacuum deposition coated. In some embodiments, the barrier paper is vacuum deposition coated, preferably metallized. Vacuum deposition 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. Vacuum deposition of a metal or metal oxide may also be referred to as metallization. In some embodiments, the vacuum deposition coating 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, preferably aluminum or an aluminum oxide. 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. Vacuum deposition coating typically results in very thin coatings. In some embodiments, the vacuum deposition coating 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 should be compared to conventional aluminum foils used in packaging laminates, which foils typically have thickness in the range of about 3-12 pm. Vacuum deposition coatings can, especially when combined with a thin polymer layer, such as a polyvinyl alcohol (PVOH) layer, provide good oxygen and water vapor barrier properties, comparable to the barrier properties of thicker aluminum foils. As the thickness of the vacuum deposition coating 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. Thus, in some embodiments, the barrier paper comprises a polymer coating layer, preferably in the form of a polyvinyl alcohol (PVOH) layer, and a vacuum deposition coating layer, preferably in the form of a metallization layer, deposited on the polymer coating layer. When the barrier paper is metallized, metallized surface may be positioned either to be used as the second outermost surface of the laminate, intended to serve as the inside surface of a packaging container, or to be used as the surface of the barrier paper to be laminated to the flexible multiply paper substrate.

The barrier paper preferably has an ash content less than 20 wt%, more preferably less than 15 wt%, measured according to the standard ISO 1762:2019.

In some embodiments, the barrier paper has an oxygen transmission rate (OTR), measured according to the standard ASTM F1927-20 at 50% relative humidity and 23 °C, of less than 200 cc/m²/24h, preferably less than 150 cc/m²/24h, more preferably less than 100 cc/m²/24h. In some embodiments, the barrier paper has an oxygen transmission rate (OTR), measured according to the standard ASTM F1927-20 at 50% relative humidity and 23 °C, of less than 50 cc/m²/24h, preferably less than 15 cc/m²/24h, more preferably less than 5 cc/m²/24h. In some embodiments, the barrier paper 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 30 g/m²/24h, preferably less than 20 g/m²/24h, more preferably less than 10 g/m²/24h, and most preferably less than 5 g/m²/24h.

The flexible multiply paper substrate and the barrier paper preferably have similar strain at break in the machine direction (MD). If the differences are too large, the flexible multiply paper substrate and the barrier paper will expand and shrink differently during drying. Different shrinkage behavior may lead to curl as well as a higher risk for delamination and cracking. In some embodiments, both the flexible multiply paper substrate and the barrier paper have a machine direction (MD) strain at break in the range of 1-7 %, more preferably in the range of 1 .5-6 %, as measured according to the standard ISO 1924-3:2005. In some embodiments, both the flexible multiply paper substrate and the barrier paper have a machine direction (MD) strain at break below 4 %, more preferably below 3.5%, as measured according to the standard ISO 1924-3:2005. In some embodiments, the difference in machine direction (MD) strain at break between the flexible multiply paper substrate and the barrier paper is less than 2 percentage units, more preferably less than 1.5 percentage units, as measured according to the standard ISO 1924-3:2005. In some embodiments, the flexible multiply paper substrate and the barrier paper on which the machine direction (MD) strain at break is measured according to the standard ISO 1924-3:2005 both have a moisture content in the range of 1.5-7 wt%, and more preferably in the range of 2.5-6.5 wt%

The barrier paper is laminated to the outer surface of the second outermost ply of the flexible multiply paper substrate using a water-based adhesive, which forms a tie layer between the barrier paper and the outer surface of the second outermost ply. The lamination typically comprises: i) applying the water-based adhesive onto the outer surface of the second outermost ply of the flexible multiply paper substrate, onto the surface of the barrier paper, or onto both, such that a layer of the water-based adhesive is formed, ii) laminating the barrier paper to the outer surface of the second outermost ply of the flexible multiply paper substrate by contacting the barrier paper and the outer surface of the second outermost ply of the flexible multiply paper substrate with the layer of water- based adhesive between them, and allowing the water-based adhesive to dry and/or set to form the tie layer.

The water-based adhesive may be applied in one or several steps.

Using a water-based adhesive in the method of the present disclosure has been found advantageous for several reasons.

The water-based adhesive is particularly useful for laminating a barrier paper to a flexible multiply paper substrate having a relatively high Cobb-Unger oil absorbency of at least 15 g/m² as determined according to the standard SCAN-P 37:77. The high absorbency of the surface promotes absorption of adhesive into the surface of the second outermost ply and optional mid ply, causing densification of the second outermost ply and optional mid ply, and increasing the flexibility of the obtained laminate. The relatively low Cobb-Unger oil absorbency of the barrier paper further boosts this effect as during lamination, the barrier paper will push the water-based adhesive into the outer surface of the second outermost ply.

In some embodiments, the water-based adhesive is only applied onto the surface of the barrier paper since less of the applied water-based adhesive is absorbed into the barrier paper leading to better control over the lamination process. In some embodiments, the water-based adhesive is only applied onto the outer surface of the second outermost ply of the flexible multiply paper substrate, since this surface may be less sensitive to rewetting than the barrier paper. The applied water-based adhesive may optionally be partially dried before the lamination is performed. This may be advantageous in order to reduce the amount of liquid carrier trapped in the formed laminate. Too much trapped liquid carrier may lead to blistering and delamination as the laminate dries.

The water-based adhesive comprises at least one adhesive component, in a water-based carrier. The water-based adhesive may also further comprise other additives for facilitating the coating process or improving the properties of the water-based adhesive. The adhesive component comprises one or more compounds capable of creating an adhesive layer. The adhesive component may preferably comprise or consist of one or more adhesive polymers. In some embodiments, the adhesive component consists of the one or more adhesive polymers.

Examples of adhesive polymers include, but are not limited to, polyvinyl alcohol (PVOH), polyvinyl acetate (PVA), polysaccharides, proteins, synthetic latexes such as styrene acrylic (SA) latex and styrene butadiene (SB) latex, ethyl vinyl alcohol (EVOH), ethylene vinyl acetate (EVA) emulsion, acrylic adhesives, natural rubber latex, and lignin and lignin derivatives. The polysaccharides may be anionic, cationic, non-ionic or amphiphilic or amphoteric. Examples of polysaccharides include, but are not limited to, starch, modified starch, alginate, pectin, agar, bean gum, guar gum, dextrins, cellulose derivatives and hemicellulose.

In some embodiments, the adhesive component of the water-based adhesive comprises one or more adhesive polymers selected from the group consisting of a polyvinyl alcohol (PVOH), a polyvinyl acetate (PVA), a starch, a dextrin, a styrene acrylic (SA) latex, a styrene butadiene (SB) latex, an ethylene vinyl acetate (EVA) emulsion, a natural rubber latex, and a casein.

In some embodiments, the adhesive component of the water-based adhesive is at least partially soluble in cold water or in hot water, e.g. at a temperature below 100 °C or even above 100 °C, for a given period of time. In some embodiments, the adhesive component of the water-based adhesive is fully soluble in cold water or in hot water, e.g. at a temperature below 100 °C or even above 100 °C, for a given period of time. The solubility of the adhesive component of the water-based adhesive allows for the tie layer to dissolve, to fully or partially disintegrate, or to become substantially weakened, when subjected to water such as during repulping.

In some embodiments, the adhesive component of the water-based adhesive comprises a polyvinyl alcohol (PVOH). 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 50-99.9 mol%, preferably in the range of 80-99.9 mol%, and more preferably in the range of 88-99.9 mol%. In some embodiments, the PVOH has an average molecular weight Mw in the range of 15 000-150 000 g/mol.

In some embodiments, the water-based adhesive comprises the adhesive component in an amount of 1-100 wt% based on the total dry weight of the waterbased adhesive. In some embodiments, the water-based adhesive comprises the adhesive component in an amount of 60-100 wt%, 80-100 wt%, or 90-100 wt%, based on the total dry weight of the water-based adhesive. In some embodiments, the water-based adhesive comprises the adhesive component in an amount of 1- 80 wt%, 1-60 wt%, 1-40 wt%, or 1-20 wt%, based on the total dry weight of the water-based adhesive.

In some embodiments, the water-based adhesive further comprises up to a total of 20 wt%, or up to a total of 15 wt%, or up to a total of 10 wt%, of other water soluble or non-soluble additives, based on the dry weight of the water-based adhesive. The other additives in the water-based adhesive may include nanoparticles, cross-linkers, reinforcement agents or texturing agents.

In some embodiments, the water-based adhesive further comprises nanoparticles, such as bentonite, in an amount of 0.1-20 wt%, or in an amount of 0.1-15 wt%, or in an amount of 0.1-10 wt%, based on the total dry weight of the water-based adhesive. The nanoparticles can impart barrier performance to the tie layer.

In some embodiments, the water-based adhesive further comprises a reinforcement agent or texturing agent, preferably selected from the group consisting of carboxymethyl cellulose (CMC), microfibrillated cellulose (MFC), nanocrystalline cellulose (NCC), and starch, in an amount of 0.1-20 wt%, or in an amount of 0.1-15 wt%, or in an amount of 0.1-10 wt%, based on the total dry weight of the water-based adhesive. In some embodiments the water-based adhesive comprises microfibrillated cellulose (MFC) or nanocrystalline cellulose (NCC) in an amount of 0.1-20 wt%, or in an amount of 0.1-15 wt%, or in an amount of 0.1-10 wt%, based on the total dry weight of the water-based adhesive.

The rest of the total dry weight of the water-based adhesive can be made up of other additives including, but not limited to, rheology modifiers, fillers, biocides, defoaming agents, and stabilizers.

The total solid content of the water-based adhesive is preferably above 5 wt%, such as above 7.5 wt%, and more preferably in the range of 10-50 wt%, such as in the range of 30-50 wt% or in the range of 12-35 wt%.

The viscosity of the water-based adhesive during application is preferably in the range of 100-5000 mPas, and more preferably in the range of 100-4000 mPas, determined according to standard SCAN-P 50:84 using a Brookfield viscosimeter at rotational speed of 100 rpm.

The water-based adhesive is preferably applied by means of a liquid film coating process. In some embodiments, the water-based adhesive is applied by a noncontact application method. In some embodiments, the water-based adhesive is applied by an application method selected from the group consisting of roller coating, spray coating, curtain, blade coating, slot coating, immersion coating, gravure roll coating, reverse direct gravure coating, rod coating, soft-tip blade coating, short dwell, and soft-tip rod coating, and combinations thereof. The waterbased adhesive may be applied directly or indirectly, for example via a transfer roll or belt.

The temperature of the applied water-based adhesive is preferably in the range of 25-75 °C, and more preferably in the range of 35-65 °C. This allows for faster drying and/or setting of the water-based adhesive before or during the lamination step.

In some embodiments, the lamination comprises passing the barrier paper and the flexible multiply paper substrate with the applied water-based adhesive between them through at least one lamination nip in order to press the barrier paper and the flexible multiply paper substrate together. The lamination nip pressure should be high enough to obtain good adhesion, but not so high that the bulk of the flexible multiply paper substrate is destroyed. In some embodiments the lamination nip pressure is in the range of 0.5-100 kg/cm, preferably in the range of 1-50 kg/cm. Pressure and heating may for example be provided in a heated nip or an extended nip.

The water-based adhesive is dried to obtain the tie layer. In some embodiments, the drying comprises subjecting the water-based adhesive to heating. In some embodiments, the drying comprises subjecting the water-based adhesive to at least one non-contact drying step, such as infrared radiation, electron beam radiation, ultraviolet radiation, microwave radiation, steam, hot air or a combination thereof. Optionally, the water-based adhesive is then subjected to at least one additional drying step, which can be a hot air drying step or a contact drying step, e.g. using a heated belt or heated cylinders.

In some embodiments, the water-based adhesive is applied in at least two different coating steps with drying of the coated layer between the steps.

In some embodiments, the water-based adhesive is applied at a grammage in the range of 0.5-15 g/m², preferably in the range of 0.5-12 g/m², and more preferably in the range of 1-8 g/m², based on dry weight.

In some embodiments, the obtained flexible paper based packaging laminate has a total grammage in the range of 100-180 g/m², and more preferably in the range of 100-160 g/m².

In some embodiments, the obtained flexible paper based packaging laminate has a bulk of less than 1.4 m³/kg, preferably less than 1.3 m³/kg, and more preferably less than 1.2 m³/kg. Unless otherwise stated, the bulk herein is determined according to the standard ISO 534.

In some embodiments, the obtained flexible paper based packaging laminate has a thickness in the range of 100-300 pm, preferably in the range of 125-275 pm, and more preferably in the range of 150-250 pm. The thicknesses herein are determined according to the standard ISO 534.

In some embodiments, the obtained flexible paper based packaging laminate has a thickness in the range of 100-300 pm, preferably in the range of 125-275 pm, and more preferably in the range of 150-250 pm, and a bulk of less than 1.4 m³/kg, preferably less than 1.3 m³/kg, and more preferably less than 1.2 m³/kg. This combination of low thickness and low bulk provides flexible paper based packaging laminate.

The flexibility may also be reflected in the relatively low bending stiffness of the obtained flexible paper based packaging laminate. In some embodiments, the obtained flexible paper based packaging laminate has bending stiffness L&W 15° in the machine direction (MD) of less than 180 mN, preferably less than 175 mN, and more preferably less than 150 mN as measured according to SCAN P 29:95.

The obtained flexible paper based packaging laminate has a low permeability for oxygen. This makes the inventive packaging laminate an interesting and viable alternative to conventional materials using aluminum foil layers.

In some embodiments, the obtained flexible paper 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 200 cc/m²/24h, preferably less than 150 cc/m²/24h, more preferably less than 100 cc/m²/24h. In some embodiments, the obtained flexible paper 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 50 cc/m²/24h, preferably less than 15 cc/m²/24h, more preferably less than 5 cc/m²/24h.

In some embodiments, the obtained flexible paper based packaging laminate has a grease resistance of more than 24 hours, measured according to the standard ISO 16532-1 :2008. In some embodiments, the obtained flexible paper based packaging laminate has a KIT grease resistance of at least 10, and more preferably of at least 12, measured according to the standard TAPPI T 559.

Thanks to the relatively low grammage and type of fibers in the flexible multiply paper substrate, the low grammage of the barrier paper, and the use of a waterbased adhesive which causes densification of the second outermost ply and optional mid ply, the obtained paper based packaging laminate will exhibit high flexibility.

In some embodiments, the obtained flexible paper based packaging laminate has a Scott Bond of at least 80 J/m² according to standard TAPPI um-403.

In some embodiments, the obtained flexible paper based packaging laminate has a Z-strength of at least 200 kPa according to standard SCAN-P 80:98.

In some embodiments, the obtained flexible paper based packaging laminate comprises more than 70 wt%, preferably more than 75 wt%, more preferably more than 80 wt%, and most preferably more than 85 wt%, of cellulose-based material, based on the dry weight of the flexible paper based packaging laminate.

The inventive packaging laminate is an interesting and viable alternative to conventional materials using metal foil layers, such as aluminum foil layers. Thus, in some embodiments the obtained flexible paper based packaging laminate comprises no metal foil layer. Vacuum deposition coatings comprising metals are not considered as metal foils in this context, since they are not free-standing foils.

In some embodiments the obtained flexible paper based packaging laminate comprises no extrusion coated plastic layer.

In some embodiments, the obtained flexible paper based packaging laminate has a total reject according to PTS-RH 021 :2012 of less than 20 %, preferably less than 10 %, and more preferably less than 5 %. The flexible paper based packaging laminate may further be provided with polymeric sealing layer(s) on one side or on both sides thereof. The polymeric sealing layer(s) preferably serve as the outermost layers of the packaging laminate. The polymeric sealing layer(s) preferably provide liquid barrier properties and mechanical protection for the flexible paper based packaging laminate surface. At least one of the polymeric sealing layer(s) is preferably also heat- sealable.

Thus, in some embodiments, the method further comprises the step: d) applying a first polymeric sealing layer to the barrier paper side of the laminate.

In some embodiments, the method further comprises the step: e) applying a second polymeric sealing layer to the flexible multiply paper substrate side of the laminate.

The polymeric sealing layer(s) may of course interfere with repulpability but may still be required or desired in some applications. The polymeric sealing layer(s) may for example be applied by extrusion coating, film lamination or dispersion coating.

The polymeric sealing layer(s) may comprise any of the thermoplastic polymers commonly used in protective and/or heat-sealable layers in flexible paper based packaging laminates in general or polymers used in liquid or food packaging board in particular. Examples include polyethylene (PE), polyethylene terephthalate (PET), polyethylene furanoate (PEF), polypropylene (PP), polyhydroxyalkanoates (PHA), polylactic acid (PLA), polyglycolic acid (PGA), starch and cellulose.

In some embodiments, the first and/or second polymeric sealing layer comprises a polyolefin, preferably a polyethylene (PE). 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. Modified PE such as ethylene and acrylic acid (EAA) and ethylene methacrylic acid (EMAA) copolymers may also be used. The polymers used are preferably manufactured from renewable materials.

Thermoplastic polymers are useful since they can be conveniently processed by extrusion coating techniques to form very thin and homogenous films with good liquid barrier properties. In some embodiments, the additional polymer layer(s) comprise polypropylene or polyethylene. In preferred embodiments, the polymeric sealing layer(s) comprise polyethylene, more preferably LDPE or HDPE.

In some embodiments, the polymeric sealing layer(s) are formed by extrusion coating of the polymer onto a surface of the flexible multiply paper substrate or 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. Common plastic resins used in extrusion coating include polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET).

The basis weight of each of the polymeric sealing layer(s) is preferably less than 50 g/m², based on dry weight. In order to achieve a continuous and substantially defect free film, a basis weight of the polymeric sealing layer of at least 8 g/m², preferably at least 12 g/m² is typically required. In some embodiments, the basis weight of the polymeric sealing layer is in the range of 8-50 g/m², preferably in the range of 12-50 g/m², based on dry weight.

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.

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

1. A method for manufacturing a flexible paper based packaging laminate suitable for use in bags or pouches, said method comprising: a) providing a flexible multiply paper substrate having a grammage in the range of 40-160 g/m², comprising a first outermost ply comprising at least 70 wt% bleached kraft pulp or hardwood pulp based on the dry weight of the ply, and a second outermost ply comprising at least 70 wt% unbleached kraft pulp and/or high yield pulp, based on the dry weight of the ply, wherein the second outermost ply has an outer surface having a Cobb-Unger oil absorbency of at least 15 g/m² as determined according to the standard SCAN-P 37:77; and b) providing a barrier paper having a grammage in the range of 20-80 g/m² and comprising at least 70 wt% cellulosic material based on the dry weight of the barrier paper, wherein the barrier paper has a Cobb-Unger oil absorbency of less than 10 g/m² as determined according to the standard SCAN-P 37:77; c) laminating the barrier paper to the outer surface of the second outermost ply of the flexible multiply paper substrate using a water-based adhesive to obtain a flexible paper based packaging laminate having a grammage in the range of 80- 200 g/m².

2. The method according to claim 1 , wherein the multiply paper substrate has a grammage in the range of 50-120 g/m², and more preferably in the range of 60- 100 g/m².

3. The method according to any one of the preceding claims, wherein the flexible multiply paper substrate has a density in the range of 500-950 kg/m³, preferably in the range of 500-900 kg/m³, and more preferably in the range of 550-850 kg/m³.

4. The method according to any one of the preceding claims, wherein the first outermost ply has a grammage in the range of 20-80 g/m², and preferably in the range of 20-50 g/m².

5. The method according to any one of the preceding claims, wherein the first outermost ply further comprises 1-15 wt% filler based on the dry weight of the ply.

6. The method according to any one of the preceding claims, wherein the unbleached kraft pulp and/or high yield pulp of the second outermost ply is chemi- thermomechanical pulp (CTMP) or high-temperature chemi-thermomechanical pulp (HT-CTMP), preferably softwood CTMP or softwood HT-CTMP.

7. The method according to any one of the preceding claims, wherein the second outermost ply comprises 0.1-10 wt%, preferably 0.15-5 wt%, of a strength enhancement agent based on the dry weight of the ply.

8. The method according to any one of the preceding claims, wherein the outer surface of the second outermost ply has a Bendtsen roughness of at least 300 ml/min, preferably at least 400 ml/min, at least 500 ml/min, at least 600 ml/min, at least 700 ml/min, or at least 800 ml/min, according to standard ISO 8791-2.

9. The method according to any one of the preceding claims, wherein the grammage of the barrier paper is in the range of 25-80 g/m², and more preferably in the range of 30-65 g/m².

10. The method according to any one of the preceding claims, wherein the barrier paper has a density in the range of 800-1500 kg/m³, preferably in the range of 850-1200 kg/m³, and more preferably in the range of 850-1050 kg/m³.

11. The method according to any one of the preceding claims, wherein the barrier paper is a microfibrillated cellulose (MFC) barrier paper comprising at least 50 wt% of MFC based on the dry weight of the MFC barrier paper.

12. The method according to any one of the preceding claims, wherein the barrier paper further comprises 0.1-10 wt%, preferably 0.15-5 wt%, of a strength enhancement agent based on the dry weight of the barrier paper.

13. The method according to any one of the preceding claims, wherein the barrier paper is polymer coated and/or vacuum deposition coated.

14. The method according to any one of the preceding claims, wherein the barrier paper has an oxygen transmission rate (OTR), measured according to the standard ASTM F1927-20 at 50% relative humidity and 23 °C, of less than 50 cc/m²/24h, preferably less than 15 cc/m²/24h, more preferably less than 5 cc/m²/24h.

15. The method according to any one of the preceding claims, wherein both the flexible multiply paper substrate and the barrier paper have a machine direction (MD) strain at break in the range of 1-7 %, more preferably in the range of 1 .5-6 %, as measured according to the standard ISO 1924-3:2005.

16. The method according to any one of the preceding claims, wherein the difference in machine direction (MD) strain at break between the flexible multiply paper substrate and the barrier paper is less than 2 percentage units, more preferably less than 1.5 percentage units, as measured according to the standard ISO 1924-3:2005.

17. The method according to any one of the preceding claims, wherein the water-based adhesive is applied at a grammage in the range of 0.5-15 g/m², preferably in the range of 0.5-12 g/m², and more preferably in the range of 1-8 g/m², based on dry weight.

18. The method according to any one of the preceding claims, wherein the water-based adhesive comprises one or more adhesive polymers selected from the group consisting of a polyvinyl alcohol (PVOH), a polyvinyl acetate (PVA), a starch-based adhesive, a dextrin, a styrene acrylic (SA) latex, a styrene butadiene (SB) latex, an ethylene vinyl acetate (EVA) emulsion, a natural rubber latex, and a casein.

19. The method according to any one of the preceding claims, wherein the water-based adhesive comprises a polyvinyl alcohol (PVOH).

20. The method according to any one of the preceding claims, wherein the obtained flexible paper based packaging laminate has a total grammage in the range of 100-180 g/m², and more preferably in the range of 100-160 g/m².

21. The method according to any one of the preceding claims, wherein the obtained flexible paper 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 50 cc/m²/24h, preferably less than 15 cc/m²/24h, more preferably less than 5 cc/m²/24h.

22. The method according to any one of the preceding claims, wherein the obtained flexible paper based packaging laminate has a grease resistance of more than 24 hours, measured according to the standard ISO 16532-1 :2008.

23. The method according to any one of the preceding claims, wherein the obtained flexible paper based packaging laminate has a KIT grease resistance of at least 10, and more preferably of at least 12, measured according to the standard TAPPI T 559.

24. The method according to any one of the preceding claims, wherein the obtained flexible paper based packaging laminate comprises more than 70 wt%, preferably more than 75 wt%, more preferably more than 80 wt%, and most preferably more than 85 wt%, of cellulose-based material, based on the dry weight of the flexible paper based packaging laminate.

25. The method according to any one of the preceding claims, wherein the obtained flexible paper based packaging laminate has a total reject according to PTS-RH 021:2012 of less than 20 %, preferably less than 10 %, and more preferably less than 5 %.