SE2350210A1 - Paperboard with improved light barrier properties - Google Patents

Abstract

The invention relates to a paperboard with improved light barrier properties comprising at least three plies; a top ply and a back ply, and a middle ply. The top ply comprises at least 80 wt% of chemical pulp. The middle ply comprises at least 40 wt % CTMP from spruce as calculated on the total fiber weight of respective ply, wherein the CTMP from spruce has a brightness according to ISO 2470-1:2016 of between 40 - 60. The back ply comprises at least 80wt% unbleached hardwood or softwood sulphate pulp as calculated on the total fiber weight of said back ply, whereina) if said unbleached sulphate pulp in the back ply is from hardwood such hardwood unbleached sulphate pulp exhibits a kappa number according to ISO 302:2015 of at least 15,b) if said unbleached sulphate pulp in the back ply is from softwood such softwood sulphate pulp exhibits a kappa number according to ISO 302:2015 of at least 20.The invention further relates to a packaging material, a liquid packaging container made from said packaging material and a method of manufacturing a paperboard.

Description

PAPERBOARD WITH IMPROVED LIGHT BARRIER PROPERTIES Technical field The present disclosure relates to a paperboard, a packaging material comprising said paperboard, a container made from the packaging material and a method of producing a paperboard.

Background Fiber-based packaging materials for product packages, such as beverage or food packaging, are usually applied with polymer coating layers to provide barriers against liquid, moisture and flavors. Beverages are furthermore oftentimes sensitive to light, due to its potential to induce undesired chemical reactions which might create off-flavors or degrade vitamins or nutrients. Visual light or UV light can further change the color of the beverage. Other products, such as pharmaceuticals or cosmetics are also sensitive to light. Polymer coatings conventionally used provide poor gas barrier properties. Therefore, packaging materials for beverages and other light sensitive products are usually provided with one or many layers of aluminum foil to ensure high gas, aroma, and light barrier properties. However, the addition of polymer and aluminum layers adds significant costs and makes recycling of the materials more difficult. Also, due to its high carbon footprint there is a wish to replace aluminum foils in paper and paperboard-based packaging materials.

Aseptic packaging for long shelf-life beverage products such as milk and juices are usually made from liquid packaging board (LPB) comprising a multilayer paperboard based substrate, an outermost heat-sealable polyolefin (e.g. polyethylene, PE) layer and innermost layers of polyolefin and aluminum. The aluminum layer, needed to provide both light and oxygen barrier properties, is usually incorporated between layers of polyethylene (PE) to provide the following structure: PE/paperboard/PE/ aluminum/PE. ln the prior art, attempts have been made to replace the aluminum foil with more environmentally friendly and/or easier to recycle solutions. Barrier cellulose films, such as microfibrillated cellulose (MFC) films, or additional coated oxygen barrier 2 layers, such as PVOH layers, have been proposed as an alternative to aluminum foil to provide oxygen barrier properties. However, such alternative solutions do not provide the light barrier properties needed. lt has further been proposed to include light absorbing or light reflecting pigments or particles in the coating layers. US739460BB discloses a packaging material comprising a heat-sealing layer blended with light-absorbing pigments including carbon black and titanium dioxide. Such solutions are usually costly and cumbersome and may further make the recycling of the paperboard difficult since the plastic is contaminated. ln addition, such pigments might change the mechanical properties of the packaging material and deteriorate the sealability. Other solutions include the use of a barrier layer comprising black polyethylene or polyester. Such a barrier layer is however difficult to recycle.

Thus, there remains a need for more sustainable solutions to replace aluminum foils in paper and paperboard-based packaging materials, while maintaining acceptable light barrier properties. At the same time, there is a need to replace the aluminum foils with alternative solutions that facilitate re-pulping and recycling of the used packaging materials.

Description of the invention lt is an object of the present disclosure to provide an alternative to the aluminum foils commonly used as barrier films for providing light barrier properties in packaging materials for beverage packaging or pharmaceutical packaging. lt is a further object of the present disclosure, to provide a paperboard with inherent light barrier properties, which is suitable to be used in beverage packaging. lt is a further object of the present disclosure to provide a paperboard-based packaging material for the packaging of beverages or pharmaceuticals, which packaging material exhibits high light and gas barrier properties, and which facilitates re-pulping of the board as compared to packaging materials using conventional aluminum foils or other light barrier solutions of the prior art. 3 The above-mentioned objects, as well as other objects as will be realized by the skilled person in the light ofthe present disclosure, are achieved by the various aspects of the present disclosure.

According to a first aspect illustrated herein, there is provided a paperboard comprising at least three p|ies; a top ply and a back ply, and a middle ply arranged between said top ply and said back ply, wherein said top ply comprises at least 80 wt% of chemical pulp, as calculated o the total fiber weight of said top ply, wherein said middle ply comprises at least 40 wt%, preferably at least 50 wt%, CTMP from spruce as calculated on the total fiber weight of said middle ply, wherein said CTMP from spruce has a brightness according to ISO 2470-1:2016 of between 40 - 60, and wherein said back ply comprises at least 80 wt%, preferably of between 80 - 100 wt%, unbleached sulphate pulp from hardwood and/or from softwood as calculated on the total fiber weight of said back ply, wherein a) if said unbleached sulphate pulp in the back ply is from hardwood such hardwood unbleached sulphate pulp exhibits a kappa number according to ISO 302:2015 of at least 15, preferably of between 15 - 40, most preferably at least 20, preferably 20 - 40, and b) if said unbleached sulphate pulp in the back ply is from softwood such softwood sulphate pulp exhibits a kappa number according to ISO 302:2015 of at least 20, preferably 20 - 90, preferably at least 30 - 90,40 - 90. lt has been found that the use of CTMP from spruce with a brightness of between 40 - 60 in at least one middle ply of the paperboard in combination with a back ply comprising unbleached hardwood or softwood pulp with a kappa number within the claimed intervals gives rise to excellent light barrier properties without affecting the printing properties negatively. ln addition, the light barrier properties of the inventive paperboard are less sensitive to creasing and conversion as compared to prior art solutions using Al foils or other light barrier coatings. 4 The invention efficiently limits the UV and light transmission between 200 nm and 800 nm, preferably so that transmission at e.g. 250 nm is below 0.1% and preferably 0% and/or so that the light transmission at 700 nm through the paperboard is below 2%, preferably below 1% and more preferably between 0- 0.2%. The light transmission can be measured for example by using UV-Vis spectrophotometer (Agilent Cary 100 UV-VIS spectrophotometer) and calibrating for no and full transparency.

CTMP with a brightness within the claimed interval can be achieved by adjusting the temperature and pressure in the manufacturing of the CTMP as well as treating the pulp with natrium hydroxide (NaOH) at an optimized pulp concentration and process residence time. The spruce CTMP is preferably unbleached. The spruce CTMP may further be high-temperature CTMP (HT- CTMP) which has been treated or manufactured to exhibit the said brightness. Which pressure and temperature and potential treatment with natrium hydroxide to be used in the manufacturing of the CTMP depends on the wood raw material, specifically on the age and storage of the wood raw material. ln embodiments, the middle ply comprises 40 - 80 wt%, preferably 50 - 80 wt%, CTMP from spruce with the brightness within said interval. The remaining pulp of the middle ply may be e.g. chemical pulp, such as unbleached kraft pulp preferably with a low kappa number or CTMP from e.g. pine, aspen, birch or eucalyptus or mixtures thereof. Preferably, the top ply comprises 80 wt%, most preferably 80 - 100 wt% bleached chemical pulp, preferably from softvvood. ln embodiments, the top ply comprises 100 wt% bleached chemical pulp, preferably bleached kraft pulp. ln embodiments, the back ply comprises said unbleached hardwood or softwood sulphate pulp (with a kappa number within said interval) in an amount of 100 wt% as calculated on the total fiber weight of said back ply. The kappa number of a sulphate pulp can be controlled by adjusting the concentration of cooking chemicals and the cooking temperature, pressure, and time in the manufacturing of the pulp.

Paperboard generally refers to strong, thick paper or cardboard comprising cellulose fibers used for boxes and other types of packaging. Typically, uncoated paperboard has a grammage of between 150 - 400 gsm, preferably 180 - 400 gsm, or 200 - 350 gsm and a density of between 500 - 900 kg/m3, preferably 600 - 850 kg/m3.

The grammages of the top, back and middle ply may be optimized to provide desired strength- and light barrier properties. For example, the grammage weight split could be: - top ply: 20 - 100 gsm, preferably 20 - 50 gsm - middle ply: 110 - 200 gsm, preferably110 - 150 gsm - back ply: 20 - 100 gsm, preferably 20 - 50 gsm ln embodiments, the CTMP from spruce has a shive content of less than 8 wt%, preferably less than 5 wt%, such as 0 - 5 wt% shives or 0.1 - 5 wt%. Such a low shive content further improves the light barrier properties, since in this way the risk of having spots with low amount of fibers is reduced. To ensure that the CTMP from spruce has a low shive content, the pulp can be fractionized and/or be subjected to refining using e.g. a double disk refiner. ln some embodiments, the CTMP from spruce used in the production of the paperboard comprises a fine fraction, which fine fraction is able to pass through a 200 mesh screen and which fine fraction exhibits a water retention value (WRV) value of less than 280 %, preferably less than 250 % according to ISO 23714:2014 standard. A fine fraction with such low WRV has good scattering properties whereby the opacity of the paperboard is further improved. ln some embodiments, the middle ply further comprises dyes and/or high opacity pigments and/or high reflecting pigments preferably chosen from the group consisting of carbon black, titanium dioxide, calcined clay and ground or precipitated calcium carbonate (PCC). Such dyes and/or high opacity pigments and/or reflecting pigments further decreases the light transmission through the paperboard. The present invention allows the use of less dyes and/or high opacity pigments as compared to prior art solutions solely depending on such dyes 6 and/or high opacity pigments to provide light barrier properties. ln embodiments, the middle ply comprises less than 15 wt% of dyes and high opacity pigments, such as in an amount of 0.1 - 10 wt%, preferably less than 1 wt%, such as in an amount of 0.1 - 0.9 wt%, as calculated on the total weight of said middle ply. The dyes and/or high opacity pigments may be mixed or co-added with microfibrillated cellulose (MFC), carboxymethyl cellulose (CMC) and/or fines. ln this context, fines are meant to define a fine fraction that is able to pass through a 200 mesh screen. MFC, CMC and/or fines provide a high surface area for the dyes/pigments to be spread on and contributes to a higher retention, whereby even less dyes/pigments can be used. ln embodiments, the CTMP from spruce having a brightness of between 40 - 60 is never dried pulp. The use of never dried pulp facilitates the control of the brightness of the CTMP and the amount of fines. ln some embodiments, the inventive paperboard comprises at least a first and a second middle ply wherein said first and said second middle ply comprises: - 40 - 80 wt%, preferably between 50 - 80 wt%, CTMP from spruce having a brightness according to ISO 2470-1:2016 of between 40 - 60, and - 20 - 60 wt%, preferably 20 - 50 wt% chemical pulp all percentages calculated on the total fiber weight of respective ply. These embodiments enable the paperboard maker to use the same pulp mixture in at least two of the middle plies which facilitates the production.

The amount of CTMP from spruce and the amount of chemical pulp as defined herein refer to the total amount of CTMP or chemical pulp respectively originating from dried pulp or never dried pulp including e.g. potential broke. ln embodiments, the paperboard comprises at least a first and a second middle ply, wherein said first middle ply comprises 40 - 80 wt%, preferably 50 - 80 wt%, CTMP with a brightness of higher than 60, such as between 60 - 100, and 60 - 20 wt%, preferably 50 - 20 wt%, chemical pulp, and wherein said second middle ply comprises at least 40 wt%, preferably between 40 - 80 wt%, more preferably between 50 - 80 wt% CTMP from spruce having a brightness according to ISO 7 2470-1:2016 of between 40 - 60, all percentages calculated on the total fiber weight of respective ply. The remaining pulp of said middle plies is preferably chemical pulp, such as bleached or unbleached kraft pulp. ln these embodiments, the first middle ply is preferably arranged adjacent to the top ply and the second middle ply is preferably arranged adjacent to the back ply. These embodiments enable the paperboard maker to optimize both the printing properties of the paperboard and the light barrier properties. By arranging the middle ply comprising the CTMP from spruce with said low brightness adjacent to the back ply and the CTMP with higher brightness adjacent to the top ply, the light barrier properties are optimized while the printing properties of the top ply are not affected negatively. The paperboard may further comprise a third middle ply, arranged in-between said first and said second middle ply, wherein said third middle ply comprises 40 - 80 wt% CTMP from spruce with a brightness according to ISO 2470-1:2016 of between 40 - 60 and 60 - 20 wt% chemical pulp. The paperboard may comprise further middle plies, such as a fourth and a fifth middle ply, arranged between the first and the second middle ply.

Preferably the CTMP from spruce has been fibrillated to a Schopper Riegler value (SR) of between 15 - 35, preferably of between 20 - 30, as determined by standard ISO 5267-1, preferably by low consistency (LC) fibrillation, most preferably at a consistency of at most 10%. ln this way, both the optical properties and the strength properties of the paperboard are optimized. As used herein, optical properties are meant to include transmittance as well as opacity.

According to a second aspect illustrated herein, there is provided a packaging material comprising: - the paperboard according to the first aspect, wherein a first side of the back ply is adapted to form the inside of a thereof formed package and a second side of the top ply is adapted to form the printing side of a thereof formed package;and - an oxygen barrier layer applied on the first side of the back ply.

Preferably, the inventive packaging material does not comprise any aluminum foil. 8 lt has been found that when using the paperboard according to the first aspect in a packaging material for beverages, there is no need to add any aluminum foil to provide light barrier. The oxygen barrier layer applied on the first side of the back ply may be a transparent layer, i.e. a layer that per se has a transmission (transparency) of above 20% or at least 30% or between 35 - 100 % or 40 - 95% as measured according to ISO 22891 :2013. The present invention enables the use of a transparent oxygen barrier layer while the paperboard still has high light barrier properties.

The packaging material may further comprise a pigment coating on second side of the top ply, which pigment coating can e.g. be a mineral coating comprising 60 - 95 wt% pigments and 40 - 5 wt% binder. ln preferred embodiments, the oxygen barrier layer comprises a layer applied as an aqueous based solution or dispersion or as a barrier film.

The aqueous based solution or dispersion preferably comprises an oxygen barrier chemical selected from the list consisting of: polyvinylalcohol (PVOH), polyhydroxyalkanoate (PHA), polysaccharide such as microfibrillated cellulose (MFC), carboxymethyl cellulose (CMC) or cellulose nanocrystals, vinyl acetate or mixtures of any of these. ln a preferred embodiment, the oxygen barrier chemical is MFC or cellulose crystals made from unbleached pulp such as a fibrillated fines fraction from the CTMP production. The packaging material comprising such aqueous based solution or dispersion coated oxygen barrier layers can readily be repulped and recycled.

The oxygen barrier layer may alternatively or in addition comprise a cellulose- based barrier film, preferably a film formed from microfibrillated cellulose (MFC), or a translucent paper such as a high-density (HD) paper, a glassine paper, a tracing paper, a parchment paper, a thin kraft paper or a machine-glazed (MG) 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. Such a cellulose-based barrier film or translucent paper has preferably a grammage between 25 - 60 gsm, a density of between 850 - 1300 kg/m3 and an 9 opacity of below 90% or below 85% in accordance with ISO 2471 :2008. The said cellulose-based barrier film may further have a transmittance of above 20%, preferably of above 30 %, most preferably between 35 - 100 % or between 40 - 95 % according to ISO 22891 :2013. lt has been found that when using the paperboard according to the present invention, a cellulose-based barrier film that does not provide any light barrier properties may be used. ln this way, the other barrier properties, e.g. the oxygen barrier properties, of the film may be optimized more efficiently.

The oxygen barrier film may further comprise a polymer-based layer, such as an oriented polyethylene (PE) or a polypropylene (PP) film, ln preferred embodiments, the packaging material comprises a barrier film that has been applied with a vacuum coating layer. The barrier film may be applied with a pre-coating layer before being applied with the vacuum coating layer.

Vacuum coating refers to a family of processes used to deposit layers of material atom-by-atom or molecule-by-molecule on a solid surface including but not limited to metallization. These processes operate at pressures well below atmospheric pressure (i.e. under vacuum). 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. The deposited layers can range from a thickness of one atom up to millimeters, although in the present context, the vacuum coating layer has preferably an average thickness in the range of 10 - 600 nm, preferably in the range of 10 - 250 nm. Due to the use of the inventive paperboard, such deposited layers can be made very thin even though this might lead to that they lose light barrier properties especially at the converting of the paperboard. Most preferably, the vacuum coating layer comprises an inorganic vacuum coating layer, such as a metal, metal oxide, or ceramic vacuum coating layer, preferably an aluminum or aluminum oxide vacuum coating layer. Such an aluminum oxide vacuum coating layer may include Al203 or AlOx. AlOx is particularly preferred due to its good water vapor barrier properties. However, AlOx does not provide any light barrier properties. The present invention enables the use of a vacuum coating layer comprising AlOx in a packaging material, which material still provides good light barrier properties. ln some embodiments, the packaging material comprises a cellulose-based barrier film that is laminated to the first surface of the back ply by means of an adhesive composition applied in the form of a dispersion, latex or solution of an adhesive polymer in an aqueous carrier. Such an adhesive polymer may be applied in one or several layers. The use of such an aqueous based adhesive further facilitates the repulping and recycling of the packaging material. The adhesive composition may preferably comprise polyvinyl alcohol (PVOH) or derivatives thereof such as carboxylated PVOH, styrene-acrylate (SA) latex, styrene-butadiene (SB) latex, starch, starch derivatives, cellulose derivatives such as carboxymethyl cellulose (CMC), or a polyolefin. The PVOH may be fully or partly hydrolyzed.

The packaging material may be provided with further barrier and/or heat-sealable layers, such as polymer layers. ln embodiments, the packaging material comprises an innermost layer of a thermoplastic polymer. On the print side, the packaging material may be provided with a thermoplastic polymer layer and/or a dispersion or solution coated barrier layer.

According to a third aspect illustrated herein, there is provided a container, particularly a beverage packaging container, made from the packaging material according to the second aspect, wherein the first side of the back ply, with optional barrier layers, forms an inner side of the container and the second side of the top ply, with optional barrier- or coating layers, forms an outer side of the container. ln this context, the inner side is meant to define the side which is to be in contact with the content of the container while the outer side is meant to define the print side of the container.

According to a fourth aspect illustrated herein, there is provided a method of producing a multiply paperboard comprising a top ply and a back ply and at least one middle ply arranged between said top ply and said back ply, which method comprises the steps of: - forming a top ply from a first pulp mixture comprising at least 80 wt% chemical pulp, 11 - forming a middle ply from a second pulp mixture comprising at least 40wt%, preferably at least 50 wt% CTMP from spruce as calculated on the total fiber weight of said pulp mixture, wherein said CTMP has a brightness according to ISO 2470-1:2016 of between 40 - 60 - forming a back ply from a third pulp mixture comprising at least 80wt% unbleached sulphate pulp from hardwood and/or from softwood, wherein a) if said unbleached sulphate pulp forming the back ply is from hardwood such hardwood pulp exhibits a kappa number according to ISO 302:2015 of at least 15, and b) if said unbleached sulphate pulp forming the back ply is from softwood such softwood sulphate pulp exhibits a kappa number according to ISO 302:2015 of at least 20, - dewatering, pressing and drying the thereby formed multiply web to form the multiply paperboard.

The method of the fourth aspect may be further defined by the features defining the paperboard of the first aspect.

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. ln 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)

1. Claims A paperboard comprising at least three plies; a top p|y and a back ply, and a middle p|y arranged between said top p|y and said back ply, wherein said top p|y comprises at least 80 wt% of chemical pulp, as calculated on the total fiber weight of said top ply, wherein said middle p|y comprises at least 40 wt% CTMP from spruce as calculated on the total fiber weight of said middle ply, wherein said CTMP from spruce has a brightness according to ISO 2470-1:2016 of between 40 - 60, and wherein said back p|y comprises at least 80 wt% unbleached sulphate pulp from hardwood and/or from softwood as calculated on the total fiber weight of said back ply, wherein a) if said unbleached sulphate pulp in the back p|y is from hardwood such hardwood unbleached sulphate pulp exhibits a kappa number according to ISO 302:2015 of at least 15, b) if said unbleached sulphate pulp in the back p|y is from softwood such softwood sulphate pulp exhibits a kappa number according to ISO 302:2015 of at least A paperboard according to claim 1, wherein the CTMP from spruce has a shive content of less than 8 wt%, preferably less than 5 wt%. A paperboard according to anyone of claims 1 and 2, wherein the CTMP from spruce used in the production of the paperboard comprises a fine fraction, which fine fraction is able to pass through a 200 mesh screen and which fine fraction exhibits a water retention value (WRV) value of less than 280 %, preferably less than 250 % according to ISO 23714:A paperboard according to anyone of the preceding claims, wherein the CTMP from spruce having a brightness according to ISO 2470-1:2016 of between 40 - 60 is never dried pulp.A paperboard according to anyone of the preceding claims, wherein the paperboard comprises at least a first and a second middle ply and wherein said first and said second middle ply comprises: - between 40 - 80 wt% CTMP from spruce having a brightness according to ISO 2470-12016 of between 40 - 60, - 20 - 60 wt% chemical pulp, all percentages calculated on the total fiber weight of respective ply. A paperboard according to any one of the claims 1 - 4, wherein the paperboard comprises at least a first and a second middle ply, wherein said first middle ply comprises 40 - 80 wt% CTMP with a brightness according to ISO 2470-12016 of higher than 60 and 60 - 20 wt% chemical pulp, and wherein said second middle ply comprises at least 40 wt%, preferably between 40 - 80 wt%, CTMP from spruce having a brightness according to ISO 2470-12016 of between 40 - 60, all percentages calculated on the total fiber weight of respective ply. A paperboard according to claim 6, wherein the first middle ply is arranged adjacent to the top ply and the second middle ply is arranged adjacent to the back ply. A paperboard according to any one of the claims 6 or 7, wherein the paperboard comprises a third middle ply arranged in-between said first and second middle ply, wherein said third middle ply comprises 40 - 80 wt% CTMP from spruce with a brightness according to ISO 2470-12016 of between 40 - 60 and 60 - 20 wt% chemical pulp, all percentages calculated on the total fiber weight of respective ply. A paperboard according to any one of the preceding claims, wherein the CTMP from spruce has a Schopper Riegler (SR) value of between 20 - A packaging material comprising:-the paperboard according to any one of the claims 1 - 9, wherein a first side of the back ply is adapted to form the inside of a thereof formed package and a second side of the top ply is adapted to form the printing side of a thereof formed package; and - an oxygen barrier layer applied on the first side of the back ply. A packaging material according to claim 10, wherein the packaging material does not comprise any aluminum foil. A packaging material according to anyone of the claims 10 or 11, wherein the oxygen barrier layer is applied as an aqueous based solution or an aqueous based dispersion or as a barrier film. A packaging material according to claim 12, wherein the oxygen barrier layer is applied as an aqueous based solution or dispersion comprising an oxygen barrier chemical selected from the list consisting of: polyvinylalcohol (PVOH), polyhydroxyalkanoates (PHA), polysaccharide, vinyl acetate, or mixtures of any of these. A packaging material according to claim 13, wherein the oxygen barrier layer is a cellulose-based barrier film, preferably a film formed from microfibrillated cellulose (MFC), or a translucent barrier paper such as a glassine paper, a machine-glazed paper (MG) or a grease proof paper. A packaging material according to claim 15, wherein the cellulose-based barrier film has a transmittance of above 20 % as measured according to ISO 22891 : A packaging material according to any one of the claims 14 or 15, wherein at least one surface of the barrier film has been applied with a vacuum coating layer. A packaging material according to claim 16, wherein the vacuum coating layer comprises an inorganic vacuum coating layer, such as a metal, metal oxide, or ceramic vacuum coating layer, preferably an aluminum or aluminum oxide vacuum coating layer. A packaging material according to any one of the claims 16 or 17, wherein the vacuum coating layer has a thickness in the range of 10 - 600 nm, preferably in the range of 10 - 250 nm. A packaging material according to any one of claims 14 - 18, wherein the cellulose-based barrier film is laminated to the first surface of the back ply by means of an adhesive composition applied in the form of a dispersion, latex emulsion or solution of an adhesive polymer in an aqueous carrier. A packaging material according to claim 19, wherein the adhesive composition comprises polyvinyl alcohol (PVOH), styrene-acrylate (SA) latex, styrene-butadiene (SB) latex, starch, starch derivatives, carboxymethyl cellulose (CMC), or a polyolefin. A packaging material according to any one of claims 10 - 18, further comprising an innermost layer of a thermoplastic polymer. A container made from the packaging material according to any one of claims 10 - 19, wherein the first side of the back ply forms an inner side of the container and the second side of the top ply forms an outer side of the container. A method of producing a multiply paperboard comprising a top ply and a back ply and at least one middle ply arranged between said top ply and said back ply, which method comprises the steps of: - forming a top ply from a first pulp mixture comprising at least 80 wt% chemical pulp, - forming a middle ply from a second pulp mixture comprising at least 40wt% CTMP from spruce as calculated on the total fiber weight of said pulp mixture, wherein said CTMP has a brightness according to ISO 2470-1:2016 of between 40 -forming a back ply from a third pulp mixture comprising at least 80wt% unbleached sulphate pulp from hardwood and/or from softwood, wherein a) if said unbleached sulphate pulp forming the back ply is from hardwood such hardwood pulp exhibits a kappa number according to ISO 302:2015 of at least 15, preferably of between 15 - 40, most preferably at least 20, preferably 20 - 40, and b) if said unbleached sulphate pulp forming the back ply is from softwood such softwood sulphate pulp exhibits a kappa number according to ISO 302:2015 of at least 20, preferably of between 20 - 90, preferably at least 30 - 90 or 40 - 90, dewatering, pressing and drying the thereby formed multiply web to form the multiply paperboard.