Cellulose-based substrate coated with a barrier layer, laminated packaging material and packaging container comprising a cellulose-based substrate

Abstract

The present invention relates to a method for manufacturing a barrier-coated substrate material (10a; 10b) coated with a reduced graphene oxide layer. The present invention further relates to a laminated packaging material (20a; 20b) comprising a barrier-coated substrate material (10a; 10b), in particular for liquid carton food packaging, and to a liquid carton packaging container comprising the laminated packaging material.

Description

TECHNICAL FIELD

[0001] The present invention relates to a barrier coated paper or cellulose based substrate, and a method of manufacturing the substrate by dispersion coating a barrier pre-coat layer and subsequently vapour deposition coating a barrier deposition coat layer. The invention further relates to a laminated packaging material comprising such a barrier coated paper or cellulose based substrate, in particular for liquid carton food packaging, and to a liquid carton packaging container comprising such a laminated packaging material. BACKGROUND

[0002] Packaging containers of the single-use, disposable type for liquid food products are commonly made from packaging laminates based on paperboard or thick paperboard. One such common packaging container is sold under the trademark Tetra Brik® Aseptic and is primarily used for aseptic packaging of liquid food products, such as milk, fruit juice, etc., which are sold for long-term ambient storage. The packaging material in such known packaging containers is typically a laminate comprising a bulk layer or core layer of paper, paperboard or other cellulose based material and outer liquid-tight layers of thermoplastic plastics. In order to make the packaging containers gas-tight, in particular oxygen gas-tight, for example for the purpose of aseptic packaging and packaging of milk or fruit juice, the laminate in these packaging containers typically comprises at least one additional layer, most typically an aluminium foil.

[0003] On the inner side of the laminate, i.e. on the side for facing the filled food content of the container produced from the laminate, there is an innermost layer applied to the aluminium foil, which innermost inner side layer can consist of one or several partial layers, containing heat-sealable thermoplastic polymers, such as adhesive polymers and / or polyolefins. Also on the outer side of the bulk layer, there is an outermost heat-sealable polymer layer.

[0004] The packaging containers are typically produced by modern high-speed packaging machines of the type that form, fill and seal packages from a web or a preform of packaging material. Thus, the packaging containers can be produced by converting a web of the laminate packaging material into a tube by welding the innermost and outermost heat-sealable thermoplastic polymer layers together so that the two longitudinal edges of the web are joined together at overlapping joints. The tube is filled with the intended liquid food product and the tube is then divided into individual packages by repeated transversal seals of the tube below the level of the content in the tube and at a predetermined distance from each other. The packages are separated from the tube by incisions along the transversal seals and are brought into the desired geometric configuration, typically a cuboid configuration, by folding along prepared crease lines in the packaging material.

[0005] ​The main advantage of this continuous tube forming, filling and sealing packaging method concept is that the web can be sterilized continuously before tube forming, thus providing the possibility of aseptic packaging methods, i.e. methods in which the liquid content to be filled as well as the packaging material itself is reduced in bacteria and the filled packaging containers are produced in clean conditions, so that the filled packages can be stored for a long time even at ambient temperature without the risk of microorganisms growing in the filled product. As mentioned above, Another important advantage of the type of packaging method is the possibility of continuous high-speed packaging, which has considerable impact on cost efficiency.

[0006] Packaging containers for sensitive liquid food products, such as milk or juice, can also be made from sheet blanks or preformed blanks of the laminated packaging material of the present application. With a tubular blank of packaging laminate folded into a plane, the production of the packaging is carried out by first erecting the blank to form an open tubular container capsule, one open end of which is closed by means of folding and heat-sealing the integral end panels. The thus closed container capsule is filled with the food product in question, such as juice, through its open end, which is then closed by means of further folding and heat-sealing the corresponding integral end panels. An example of a packaging container made from sheet and tubular blanks is the conventional so-called gable-top package. There also exist packages of this type with a molded top and / or a screw cap made of plastic.

[0007] The aluminum foil layer in a packaging laminate provides a gas barrier performance that is very superior to most other gas barrier materials. Conventional aluminum foil-based packaging laminates for aseptic packaging of liquid food products are still the most cost-efficient packaging materials available on the market in terms of their performance level.

[0008] Any other material comparable to aluminum foil-based materials must be cost-efficient in terms of raw materials, have comparable food preservation performance and comparable low complexity in converting the material into a finished packaging laminate.

[0009] In the efforts to develop non-aluminum foil materials for carton packaging of liquid food products, there has also been a general motivation to develop preformed films or sheets with high barrier performance or to combine several separate barrier materials in multilayer films or sheets. Such films or sheets would replace the aluminum foil barrier material in conventional laminated packaging materials and could further be adapted to the conventional lamination and manufacturing processes of laminated packaging materials.

[0010] With the increasing demand for the use of only sustainable materials, polymer barrier materials derived from fossil resources are becoming less interesting, so there is still a need for the use of thin barrier coating (i.e. aqueous dispersion coating and vapour deposition coating) types, which are almost negligible in the recycling process and cause few problems in the economy based on material and renewable (non-fossil) material cycles. The thickness of dispersion-coated polymers is about 1-2 pm, while vapour-deposited barrier coatings are thin to below 0.5 pm, for example 10 to 100 nm, for example 15 to 80 nm, for example 20 to 50 nm. Over the years various such coatings have been developed and have been combined in multilayer packaging material structures to seek improved overall performance. Although some of these coatings exhibit excellent barrier properties, the beverage carton packaging industry is still looking for the best coating or combination of coatings that can replace aluminium foil in all respects.

[0011] Past development materials for example involved aqueous polymer compositions suitable for dispersion and / or solution-coated thin layers, for example PVOH, starch, etc. A common difficulty with this type of polymer binder is that they are sensitive to high moisture conditions and lose their inherent oxygen barrier properties with exposure to moisture (i.e. conditions in the laminated packaging material of filled liquid carton packaging containers) and increasing amounts of this moisture. It has been concluded that such thin dispersion-coated polymer layers need to be supplemented with more material to improve the gas barrier properties, either in the form of additional compounds in the dispersion composition, for example cross-linking agents or inorganic particles, or in the form of additional material layers as barrier layers for water vapour.

[0012] With regard to vapour-deposited (or so-called "vacuum-coated") barrier coatings, very good crack initiation strain properties are sometimes obtained, making them sufficiently robust for the folding and sealing of rigid packaging containers, but naturally, given that such coatings are very thin, they are relatively sensitive to mechanical stress and damage compared to aluminium foil.

[0013] In later years, graphene has emerged as a potential barrier material, although it is too expensive for full-surface barrier coating in packaging materials. In theory, only a molecularly thin graphene sheet can achieve excellent gas barrier properties, but in practice, such thin layers are very expensive and difficult to produce. As an alternative, single-layer graphene flakes can be dispersed in organic solvents and coated by dispersion coating or printing techniques, but this variant of graphene layers is too expensive to be included as a full-surface coating in disposable packaging materials. Furthermore, the removal of organic solvents from such coatings constitutes an unwanted problem in modern sustainable industrial scale coating operations.

[0014] A cheaper source of material for similar barrier coatings with the same or similar properties as graphene are graphene oxide flakes or particles, which are exfoliated from graphite oxide, which is a very cheap raw material, and subsequently chemically reduced. Such graphene oxide particles or flakes can thus be chemically reduced to produce corresponding graphene particles or flakes. Graphite is abundant in nature, and thus graphene obtained by oxidation to graphite oxide / graphene oxide and subsequent reduction to graphene is much cheaper to use for packaging materials.

[0015] However, providing a thin and uniform reduced graphene oxide coating by a large-scale industrial coating process starting from reduced graphene oxide, i.e. graphene, is problematic, because an organic solvent is required to disperse it, and also because of the higher cost of further refining the product, i.e. graphene oxide is reduced.

[0016] In the scientific paper "Impermeable barrier films and protective coatings based on reduced graphene oxide" (by Y. Su, V. G. Kravets, S. L. Wong, J. Waters, A. K. Geim & R. R. Nair) published in "Nature Communications" on September 11, 2014, it is described how a substrate material with an applied graphene oxide coating can be obtained with good gas barrier properties by exposing it to hydrogen iodide vapour at 90°C for 5-30 minutes, or by immersing it in a solution of vitamin C as reducing agent at 90°C for 1 hour. For economic reasons as well as practical unfeasibility of a packaging material processing plant, such a method is not feasible for producing barrier layers or coatings for disposable packaging materials. Acid vapour treatment, or long time treatment of the substrate material in almost boiling liquid, carries a considerable risk of material changes, and is also very impractical in manufacturing processes, which are typically characterized by continuous operation in wide web rolls and high manufacturing speeds.

[0017] Therefore, there is a need for improved methods to apply such reduced graphene oxide based materials to laminated packaging materials at reasonable costs, and also to meet future requirements for recyclability and sustainable material sourcing and manufacturing. SUMMARY

[0018] It is an object of the present invention to provide an improved method for manufacturing a substrate material coated with a barrier coating formed from reduced graphene oxide, and further laminating such a barrier coated substrate material into a packaging material.

[0019] It is also a general object of the present invention to provide a simplified method for manufacturing barrier coated substrates with reduced graphene oxide, thereby providing good barrier properties as well as recyclability and ability to meet the requirements for future sustainable liquid carton laminated packaging materials.

[0020] It is a further general object of the invention to provide a method of manufacturing a foil-free laminated packaging material for oxygen sensitive, liquid, semi-solid or wet food products, which packaging material is free from aluminium foil, but still has excellent gas barrier properties suitable for cost- effective long-term aseptic packaging.

[0021] It is a particular object to provide a non-aluminium foil paper-based or paperboard-based laminated packaging material which is cost-effective relative to aluminium foil barrier materials, which has good gas barrier properties as well as recyclability and sustainable environmental properties for manufacturing packaging for long-term aseptic food storage.

[0022] It is a further object of the invention to provide a cost-effective, non-aluminium foil paper-based or paperboard-based, mechanically robust and heat-sealable packaging laminated material which has good gas barrier properties for manufacturing aseptic packaging containers for long-term storage of liquid food products under ambient conditions to maintain their nutritional quality.

[0023] Thus, according to the invention, these objects are achieved by a method of manufacturing barrier coated substrate web, laminated packaging material and packaging container as defined in the appended claims.

[0024] SUMMARY

[0025] According to a first aspect of the present invention, there is provided a method of preparing a reduced graphene oxide aqueous composition suitable for use as a gas barrier coating composition from graphene oxide in an aqueous dispersion, comprising the steps of: a) providing an aqueous dispersion comprising graphene oxide, said graphene oxide comprising single-layer graphene oxide platelets and multi-layer graphene oxide lamellae, having up to 20, for example 2-10, stacked single-layer graphene oxide platelets, b) providing an aqueous dispersion of a nanocellulose compound, c) providing an aqueous solution of a reducing agent, d) mixing said aqueous dispersions from steps a) and b), e) adding said aqueous solution of said reducing agent to the mixture resulting from step d), and f) allowing said reducing agent to reduce said graphene oxide in the mixed said aqueous composition to form an aqueous gas barrier coating composition comprising well dispersed and reduced graphene oxide, which is sufficiently stable for subsequent use as a gas barrier coating composition. The nanocellulose compound can be selected from the group consisting of microfibrillar cellulose, MFC, and crystalline nanocellulose, CNC.

[0026] Surprisingly it was found that by this method the reduction reaction can be carried out directly in an aqueous dispersion, such that the graphene oxide is essentially completely converted into reduced graphene oxide, i.e. practically graphene, while maintaining the quality of the dispersion. This is surprising, as it is generally expected that the dispersion of graphene platelets requires the presence of an organic solvent. Furthermore, reduction by merely adding a reducing agent to an aqueous dispersion of graphene oxide would immediately lead to the generated reduced graphene oxide to agglomerate. Therefore, so far it was believed that to obtain a coating of reduced graphene oxide either the graphene oxide needs to be dispersed in an organic solvent or solvent mixture or that the graphene oxide needs to be reduced by various difficult and environmentally complex reduction methods such as a wet-impregnation method with a reducing agent solution, a high-temperature heat treatment method, an irradiation treatment method, etc. after the graphene oxide has been coated or applied to the surface of a substrate.

[0027] As a coating with reduced graphene oxide has significantly better oxygen barrier properties than the corresponding graphene oxide coating, it is of great value to be able to produce such a coating from graphene oxide, which is a cost-effective and abundant raw material.

[0028] The concentration of nanocellulose can be 0.1 to 5 wt.%, such as 0.1 to 4 wt.%, such as 0.1 to 3 wt.%, such as 0.5 to 2 wt.%, such as 0.5 to 1.5 wt.%. At higher than 5 wt.% the dispersion starts to exhibit more gel-like properties and it seems not to make sense to use higher concentrations, in fact in some cases such an upper limit can already be perceived at 3 wt.%. As to the lower limit of this range it is believed that the minimum concentration of nanocellulose should be 0.5 wt.%, but lower amounts can also be useful in some cases and types of nanocellulose, such as down to 0.1 wt.% or even down to 0.05 wt.% in the case of nanocrystalline cellulose.

[0029] Thus, the aqueous composition of reduced graphene oxide can be obtained from a mixed composition comprising 0.5 to 15 wt.% graphene oxide, 0.1 to 5 wt.% nanocellulose, 0.5 to 10 wt.% reducing agent and 70 to 99.7 wt.% water.

[0030] According to a second aspect of the present application, there is provided a method for producing a gas barrier coated material by coating a substrate material with a reduced graphene oxide layer, the method comprising the steps of: a) providing a substrate material, b) providing said aqueous gas barrier coating composition comprising reduced graphene oxide as provided above, c) coating said aqueous gas barrier coating composition of reduced graphene oxide onto a surface of said substrate material, d) drying the wet coated substrate material resulting from step c) by forced evaporation to obtain a dry layer of layered reduced graphene oxide particles or flakes on said surface of said substrate material, thereby forming said gas barrier coated material.

[0031] The method for producing a gas barrier coated material can comprise the steps of:

[0032] a) providing a substrate material,

[0033] b1 ) providing a mixed aqueous composition comprising a dispersion of 0.5 to 15 wt% graphene oxide and 0.1 to 5 wt% nanocellulose, said graphene oxide comprising single layer graphene oxide flakes and multi-layer graphene oxide lamellas with up to 20, for example 2-10 stacked single layer graphene oxide flakes,

[0034] b2) adding 0.5 to 10 wt% of a reducing agent to the mixed aqueous composition and enabling the reducing agent to reduce the graphene oxide to form an aqueous gas barrier coating composition comprising well dispersed and reduced graphene oxide,

[0035] c) coating the reduced graphene oxide aqueous gas barrier coating composition resulting from step b2) on a substrate surface,

[0036] d) drying the wet coated substrate material resulting from step c) by forced evaporation to obtain a dry layer of layered reduced graphene oxide particles or flakes on the surface of the substrate material, thereby forming said gas barrier coated material.

[0037] In an industrially feasible method, the substrate material is provided in the form of a continuous web, running at a constant speed. Thus, the substrate material is moved at a constant speed through steps c) and d) of coating and drying the substrate material.

[0038] The method can comprise a further step e) after step d), namely coating or laminating the gas barrier coated substrate material to another polymer or adhesive layer to cover the dry layer of reduced graphene oxide.

[0039] This is a breakthrough finding, as it means that the reduced graphene oxide formed gas barrier coating can be applied to a substrate material just like any other aqueous dispersion of a gas barrier material, and it provides a greatly improved gas barrier material over any known such dispersion-coated barrier coating.

[0040] The reducing agent can be selected from the group consisting of hydrogen iodide (HI), sodium citrate, ascorbic acid (vitamin C), lemon juice, vinegar and green tea. Preferably, the reducing agent is selected from the group consisting of sodium citrate, ascorbic acid (vitamin C), lemon juice, vinegar and green tea, most preferably the reducing agent is ascorbic acid. Ascorbic acid is the most environmentally friendly and sustainable reducing agent, and since ascorbic acid is well recognized in both food and food industry, and is a functional reducing agent, it is the best choice for such a process.

[0041] According to a third aspect of the present invention, there is provided a gas barrier coated substrate material obtained from the method of the second aspect, for use as an oxygen barrier material in a laminated packaging material for liquid food products.

[0042] According to a fourth aspect of the present invention, there is provided a laminated packaging material comprising the gas barrier coated substrate material of the third aspect. The laminated packaging material can further comprise a first outermost protective material layer and a second innermost liquid-tight heat-sealable material layer.

[0043] For the purpose of carton packaging of liquid food, the laminated packaging material can further comprise a paper or paperboard or other cellulose-based material bulk layer, a first outermost protective material layer, a second innermost liquid-tight heat-sealable material layer and said gas barrier coated substrate material arranged on the inner side of the paper or paperboard bulk layer, between said bulk layer and said innermost layer.

[0044] The outermost protective material layer can be a protective polymer layer or a protective polymer coating to prevent dust and moisture from reaching the interior of the laminated material, such as a polymer layer, such as a thermoplastic polymer layer, such as a liquid-tight heat-sealable polymer layer, such as a liquid-tight heat-sealable polyolefin layer, such as polyethylene. The second innermost liquid-tight heat-sealable material layer can be a thermoplastic polymer, such as a polyolefin, such as polyethylene.

[0045] In this way the reduced graphene oxide thin layer that can be coated on a substrate material exhibits the excellent gas barrier properties of graphene as a material and can be laminated into the standard structure of a laminated packaging material for liquid carton packaging as a "direct replacement for aluminum foil". In contrast to earlier attempts to produce such "direct replacement" films or barrier sheets, the reduced graphene oxide coated substrate web (e.g. a polymeric film or paper substrate) will be significantly less sensitive to the lamination operation and to the folding forming, filling and heat sealing carton packaging filling machine operation of the laminated material. This is due to the inherent durability and flexibility of graphene as a material and also because it is obtained as a layer of thin sheets that are tightly overlapping each other, so that any penetration of oxygen molecules through the barrier coating must follow the so-called tortuous path between the sheets. Therefore, such a coating is not sensitive to strain cracking and can well maintain its oxygen barrier properties during the transformation into a package. Furthermore, the gas barrier properties of reduced graphene oxide are not sensitive to moisture and to the penetration of water vapor from the liquid content of the package, so that it will withstand the long term storage of such filled packaging containers.

[0046] In a fifth aspect of the present application, a packaging container comprising the laminated packaging material of the fourth aspect is provided for the packaging of liquid, semi-solid or wet food products. According to one embodiment, the packaging container is at least partly made of the laminated packaging material of the present application, and according to another embodiment, it is entirely made of the laminated packaging material.

[0047] DETAILED DESCRIPTION

[0048] The term "long term storage" as used in connection with the present application means that the packaging container should be able to maintain the quality (i.e. nutritional value, hygiene safety and taste) of the packaged food product under ambient conditions for at least 1 or 2 months, such as at least 3 months, preferably longer, such as 6 months, such as 12 months, or longer.

[0049] The term "packaging integrity" generally refers to the sealability of the package, i.e. the leak resistance or breakage resistance of the packaging container. The term includes the resistance of the package to the intrusion of microorganisms (e.g. bacteria, dirt and other substances) that can spoil the filled food product and shorten the expected shelf life of the package.

[0050] A major contribution to the integrity of the package by the laminated packaging material is provided by the good internal adhesion between the adjacent layers of the laminate. Another contribution comes from the resistance of the material to defects, such as pinholes, ruptures etc. within each material layer itself, and yet another contribution comes from the strength of the seal joint, through which the material is sealed together when forming the packaging container. Thus, for the laminated packaging material itself, the integrity properties are mainly focused on the adhesion of each laminated layer to its adjacent layer, and on the quality of each material layer. With regard to the sealing of the package, the integrity is mainly focused on the quality of the seal joint, which is ensured by a good functioning and robust sealing operation in the filling machine, which in turn is guaranteed by the heat-seal properties of the laminated packaging material being sufficiently adapted.

[0051] The term "liquid or semi-liquid food" generally refers to a food having a flowing content, which optionally can comprise food pieces. Dairy and milk, soy, rice, grain and seed beverages, fruit juice, nectar, non-carbonated beverages, energy drinks, sports drinks, coffee or tea beverages, coconut water, wine, soup, salsa, ketchup, beans and olive oil are some non-limiting examples of intended food products.

[0052] The term "sterile" in relation to packaging materials and packaging containers refers to conditions in which microorganisms are eliminated, inactivated or killed. Examples of microorganisms are bacteria and spores. When a product is to be aseptically packaged in a packaging container, an aseptic process is typically used. In order to achieve sustained sterility over the shelf life of the package, the package integrity is of course of great importance. Furthermore, in order to achieve a long shelf life of the filled food product, it can also be of great importance that the package has barrier properties against gases and vapours, such as against oxygen, in order to preserve its original taste and nutritional value, such as its vitamin C content.

[0053] The term "bulk layer" generally refers to the thickest layer or the layer comprising the most material in a multi-layered laminate, i.e. the layer contributing most to the mechanical properties and dimensional stability of the laminate, such as paperboard or cardboard, and the packaging container folded from the laminate. It can also refer to the layer providing the greater thickness distance in a sandwich structure, which layer further interacts with stabilizing face layers having a higher Young's modulus on each side of the bulk layer, in order to achieve sufficient such mechanical properties and dimensional stability.

[0054] Thickness measurements were made by transmission electron microscopy using a Titan 80-300, FEI instrument. The samples can be prepared by ultramicrotomy on a Leica's EM UC6 microtome.

[0055] OTR was measured using an Oxtran 2 / 21 (Mocon) instrument based on coulometric sensors.

[0056] The method for determining OTR determines the amount of oxygen per surface and time unit that passes through the material at a specific temperature, given atmospheric pressure, in a specific time, for example in 24 hours, in an atmosphere of 21 % oxygen.

[0057] The measurement of water vapour transmission rate (WVTR) is performed by Permatran 3 / 33 (Mocon) instrument (standard: ASTM F 1249-13, using modulated infrared sensors for relative humidity detection and WVTR measurement) at 38 °C and 90% driving force.

[0058] The term "graphene oxide" includes single-layer graphene oxide flakes and multi-layer graphene oxide sheets, with up to 20, for example 2-10, stacked single-layer graphene oxide flakes. Only a minor amount, i.e. less than 15 wt%, for example less than 10 wt%, for example less than 5 wt%, based on the dry weight of the graphene oxide material, can be graphene oxide flakes that have been exfoliated to more than 20 but whose lateral particle size is less than that of bulk graphene particles (i.e. so-called "graphene oxide nanosheets", which are thus still nanosized).

[0059] Such a small amount of this laterally nanosized graphene flakes can be present, as long as they do not excessively reduce the properties of the graphene-based material. Preferably, the nanosized graphene flakes are present in the composition in an amount of less than 15 wt%, for example 10 wt%, for example 5 wt% or less, based on the dry weight.

[0060] Suitable graphene oxide materials for use in aqueous dispersions that can be used in the present application are, for example, pure quality from Graphenea, at least 95% exfoliated, or paste-like graphene oxide from Abalonyx.

[0061] The substrate suitable for the barrier coating of the present application is thus not limited to a certain type of substrate, but includes polymeric films as well as paper, paperboard or other cellulose-based substrates, or polymer-coated paper, paperboard or polymer-coated other cellulose-based substrates. The substrate material web can be a polymeric film web, a paper or paperboard web, or a polymer-coated paper or paperboard web.

[0062] The polymeric film substrate can be made, for example, of a polyester or a polyolefin. Typical polyesters are polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyhydroxyalkanoate (PHA) and polylactic acid (PLA) types. Typical polyolefin films can be made of mostly polypropylene or polyethylene, for example of biaxially oriented polypropylene (BOPP), or biaxially oriented high density polyethylene (BOHDPE), or linear low density polyethylene (LLDPE).

[0063] The cellulose-based substrate can be based on any type of natural cellulose, fibrous or fibrillar cellulose, and they can further be coated with a polymer of the above-mentioned type, preferably with a polyolefin such as polyethylene, for the subsequent application of a barrier coating according to the method of the present application.

[0064] Generally, a suitable paper or cellulose-based substrate for carrying the barrier coating of the present application should be thin, for example 60 g / m2 2 or below, for example 50 g / m2 2 or below, preferably 45 g / m2 2 or below, and more preferably 40 g / m2 2 or below. On the other hand, when thinner or cellulose-based substrates having a grammage below 30 g / m2 2 are coated with a wet dispersion and subsequently dried, their mechanical strength can be too weak and / or the dimensional stability is poor, thus shrinkage or curling problems can occur. It is thus more preferred to use paper having a grammage of 30 to 50 g / m2 2 , for example most preferably 35 to 45 g / m2 2 .

[0065] In an embodiment, the concentration of graphene oxide in the aqueous composition is 0.1 to 15 wt%, for example 0.5 to 15 wt%, for example 0.5 to 10 wt%, for example 0.5 to 6 wt%, for example 0.5 to 3 wt%, for example 1 to 2 wt%. If the concentration is below 0.5 wt%, it can be difficult to coat a sufficient amount of graphene oxide onto the substrate material web, such that the applied coating can provide sufficient oxygen barrier properties, but if the required barrier properties are lower, a thinner coating, for example as low as 0.1 wt%, can be applied. On the other hand, if the concentration is above 6 wt%, for example above 10 wt%, for example above 15 wt%, the applied coating can be more difficult to dry, as the applied graphene wet-oxide material coating is unnecessarily thick and contains a large amount of water between the flakes and lamellas of the composition. If the concentration of graphene oxide is above 3 wt%, the coating can be difficult to dry, and if above 6 wt%, it can be more difficult to apply. However, the aqueous composition of graphene oxide exhibits shear thinning behaviour, such that thicker compositions can still be applied with reasonable coating thickness and good layer formation, higher coating speeds.

[0066] Furthermore, the weight ratio of the content of nanocellulose to graphene oxide in the aqueous coating composition should be 0.05:1 to 5:1, depending on the mass of the nanocellulose, preferably 0.05:1 to 2:1, more preferably 0.05:1 to 1 :1

[0067] The aqueous composition of graphene oxide comprises essentially only graphene oxide and water. Preferably, it comprises only up to 5 wt.-%, such as up to 3 wt.-%, of additives, such as dispersants, antifoams, etc. Thus, the aqueous composition of graphene oxide can comprise 0.5 to 15 wt.-% of graphene oxide, 0.1 to 5 wt.-% of additives, and 85 to 99.7 wt.-% of water and, optionally, only further additives.

[0068] In one embodiment, the aqueous composition of graphene oxide is applied with a wet thickness of 10 to 400 pm. If thinner than 10 pm, the coating can not provide sufficient oxygen barrier properties, and if thicker than 400 pm, the amount of water to be dried from the coating or the viscosity of the thicker coating composition can be impractical or unmanageable.

[0069] The concentration of the reducing agent ascorbic acid (vitamin C) can be 0.5 to 15 wt.-%, such as 1 to 10 wt.-%, such as 2 to 7 wt.-%, such as 3 to 6 wt.-%. A solution with at least 0.5 wt.-%, such as 1 wt.-%, of ascorbic acid is necessary for the intended effect of the reduced graphene oxide, and a good lower range of functional concentrations is about 2 wt.-%, preferably 3 wt.-%. When the concentration exceeds 7 wt.-%, the effect is not significant, and when the concentration exceeds 10 wt.-%, further increasing the concentration seems to have little effect, seemingly without increasing the effect.

[0070] The drying step d) of the coating method of the present application can be performed by forced evaporation, i.e. by heating, so that the water of the dispersion is evaporated and carried away from the substrate surface by air convection, such as from hot air drying.

[0071] Furthermore, the substrate can be conveyed at a constant speed. This is an important prerequisite in the coating operation in order to obtain the best and reliable amount of coating to be applied. Industrially feasible web and coating speeds can be from 100 m / min, such as from 200 m / min, such as from 30 m / min, such as from 400 m / min, depending on the size of the drying capacity in the coating line. Drying is suitably performed by hot air convection, which can be combined with the irradiation of infrared heaters.

[0072] The graphene oxide is thus dispersed in water and can be applied by an aqueous "dispersion coating" process or a so-called "liquid film coating" process. From the perspective of environmental sustainability as well as work safety, an all-aqueous dispersion is preferred.

[0073] The aqueous composition can be applied to a web of substrate material in the form of an ink and / or dispersion coating.

[0074] Suitable application methods can thus be suitable printing methods, such as flexographic printing, rotogravure printing, screen printing, inkjet printing, as well as various dispersion coating methods, such as gravure roll coating, slot coating, blade coating, reverse roll coating, wire bar coating, lip coating, air knife coating, curtain and spray coating, dip coating, brush coating. By these printing or coating methods, a suitable dry material thickness of the graphene oxide coating can be applied, which is 0.1 to 10 pm, such as 0.5 to 8 pm, such as 0.5 to 6 pm, such as 0.5 to 4 pm, such as 0.5 to 3 pm, such as 0.5 to 2.5 pm.

[0075] Several successive coating steps can be needed to form a thick graphene oxide layer for higher thicknesses. For providing a gas barrier coating, applying a dry graphene oxide of 0.1 to 3 pm, such as 0.5 to 2.5 pm, such as about 2 pm, will be sufficient. For other purposes, such as for electrically conductive coatings or other purposes, thicker coatings can be suitable, but can not be as full surface covering coatings, but as coatings applied only to selected local areas of a web of base material.

[0076] The experiments of the present invention were performed by gravure coating, but it is believed that any of the above liquid film coating methods are suitable to provide a good gas barrier coating.

[0077] The amount of dispersion stabilizer or similar additive for dispersion coating can also be included in the aqueous graphene oxide composition, preferably in an amount of not more than about 1 wt.-%, based on the dry coating.

[0078] The total dry content of the aqueous graphene oxide composition should be 0.5 to 15 wt.-%, such as 0.5 to 10 wt.-%, such as 0.5 to 8 wt.-%, such as 0.5 to 6 wt.-%.

[0079] At lower dry contents, the gas barrier layer formation can not be good enough, and thus the gas barrier properties of the dry coating are not very good.

[0080] In an embodiment, the graphene oxide coating can be applied as two partial layers in two successive steps with intermediate drying. When applied as two partial layers, the suitable application amount of each layer is 0.1 to 1.5 g / m 2 , such as 0.5 to 1 g / m 2and enables a higher quality total layer to be obtained from a lower amount of liquid gas barrier composition. For example, a dry coating of graphene oxide of about 2 pm in total thickness will have a total thickness of about 0.5 pm (500 nm) after reduction to reduced graphene oxide. It has been assessed that two consecutively applied and dried graphene oxide coatings will reduce to graphene oxide as easily as a corresponding thick, dry single graphene oxide coating after coating and drying with aqueous ascorbic acid solution. The consecutively applied and dried graphene oxide coatings can mask defects that can be present in each coating, as in most cases it overlaps with a defect-free portion of the other coating. In this way, the entire applied graphene oxide layer can be almost defect-free.

[0081] The graphene oxide coating can be applied directly on a paper or paperboard substrate, but requires the coated surface to be smooth and dense so that the coating can form uniformly and cohesively.

[0082] For best performance of the present invention, a very thin polymer can be applied prior to coating the graphene oxide layer on the paper or cellulose-based substrate material web, also suitably in the form of an aqueous composition in a previous dispersion coating step. The thickness of such a pre-coating can be as low as 0.5 to 1.5 pm, for example about 1 pm.

[0083] The polymer of the pre-coating can be any suitable water-dispersible polymer and / or renewable non-fossil-based polymer. In an embodiment, the polymer of the pre-coating can be selected from the group consisting of polyvinyl alcohol (PVOH, PVAL), polyethylene vinyl alcohol (EVOH, EVAL), polyolefins such as water-dispersible polyethylene, starch, modified starch, methyl cellulose, ethyl cellulose, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC), sodium carboxymethyl cellulose (NaCMC), nano / microfibrillar cellulose (NFC / MFC / CNF), and nanocrystalline cellulose (NCC / CNC).

[0084] In a further embodiment, such a pre-coating can comprise a renewable polymer or substance selected from starch, modified starch, methyl cellulose, ethyl cellulose, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC), sodium carboxymethyl cellulose (NaCMC), nano / microfibrillar cellulose (NFC / MFC / CNF), or nanocrystalline cellulose (NCC / CNC).

[0085] Such a natural, plant-based, non-fossil-based polymer or substance can provide good surface smoothness to provide a uniform graphene oxide coating.

[0086] Suitable starch materials or starch derivatives can for example be oxidized starch, cationic starch and hydroxypropylated starch.

[0087] In one embodiment, the pre-coat polymer is a very thin polyethylene coating that can support the neat separation of the reduced graphene oxide coating from the paper or paperboard substrate material, such that the recycled fibres can remain substantially free of reduced graphene oxide material.

[0088] A further protective polyethylene coating of low density polyethylene can be applied to the reduced graphene oxide layer, including any residual ascorbic acid on its surface, for the purpose of protection, as the barrier coated substrate material web can be further wound onto a roll, or further laminated into a multi-layer material structure. By encapsulating the reduced graphene oxide in this way between polyethylene layers, the reduced graphene oxide can be kept separate from the fibrous fraction in later recycling operations.

[0089] A card based laminated packaging material for liquid food packaging can comprise a paper or paperboard bulk layer, a first outermost protective material layer, a second innermost liquid tight heat sealable material layer and a barrier coated substrate material web arranged on the inner side of the paper or paperboard bulk layer, towards the interior of a packaging container made from the packaging material and between the bulk layer and the innermost layer.

[0090] The paper or paperboard bulk layer for use in the present invention typically has a thickness of about 100 pm to about 600 pm, and a surface weight of about 100-500 g / m 2 , preferably about 200-300 g / m 2 , and can be a conventional paper or paperboard having a suitable packaging quality.

[0091] For low cost aseptic, long term packaging of liquid food, a thinner packaging laminate can be used, with a thinner paper core layer. The packaging containers made from such packaging laminates are not fold formed, but more like pillow shaped pouches. The paper suitable for such pouch packaging typically has a surface weight of about 50 to about 140 g / m 2 , preferably about 70 to about 120 g / m 2 , more preferably 70 to about 110 g / m 2 . If the barrier coated substrate material web in the present invention brings some stability to the laminate itself, the paper layer corresponding to the "bulk" layer can be thinner, and the barrier coated substrate material webs interact in the sandwich structure, still producing a laminate packaging material fully having the required mechanical properties.

[0092] The substrate material web can be a polymeric film web, a paper or paperboard web, or a polymer coated paper or paperboard web.

[0093] Thus, the substrate suitable for the barrier coating of the present application is not limited to a certain type of substrate, but includes a polymeric film as well as paper, paperboard or other cellulose-based substrate, or a polymer-coated paper, paperboard or polymer-coated other cellulose-based substrate. The polymeric film substrate can for example be made of a polyester or a polyolefin. Typical polyesters are polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyhydroxyalkanoate (PHA) and polylactic acid (PLA) types. Typical polyolefin films can be made of mostly polypropylene or polyethylene, for example from biaxially oriented polypropylene (BOPP), or biaxially oriented high density polyethylene (BOHDPE), or linear low density polyethylene (LLDPE).

[0094] The cellulose-based substrate can be based on any type of natural cellulose, fibrous or fibrillar cellulose, and they can further be coated with a polymer of the above-mentioned type, preferably with a polyolefin such as polyethylene, for subsequent application of the barrier coating according to the method of the present application.

[0095] The thickness of the dry layer from reduced graphene oxide layered particles or flakes can be from 50 to 1000 nm, for example from 100 to 800 nm, for example from 200 to 700 nm, for example from 200 to 600 nm, for example from 400 to 600 nm, for example from 450 to 550 nm.

[0096] The dry layer from reduced graphene oxide layered flakes or particles can be further coated with a thin protective coating of a thermoplastic polymer, for example dispersible coated polyethylene or another water-soluble or water-dispersible polymer. It can be further laminated to an adjacent polymeric layer, for example a polyolefin layer, for example low density polyethylene. This further coating and / or lamination can be performed before or after the complete reduction of the graphene oxide of the first graphene oxide dry layer.

[0097] The barrier-coated substrate material web can be adhered to the bulk layer by an intermediate adhesive or a thermoplastic polymer, thereby adhering the uncoated surface of the barrier-coated substrate material web to the bulk layer. According to one embodiment, the adhesive layer is a polyolefin layer comprising mainly ethylene monomer units, for example in particular a polyethylene-based polyolefin copolymer or blend layer. The adhesive layer adheres the bulk layer to the barrier-coated substrate material web by melt extrusion lamination of the adhesive polymeric layer between the bulk layer web and the substrate material web, and simultaneously pressing the three layers together as the three layers are advanced through a lamination roll nip, whereby the lamination structure is provided by the extrusion lamination.

[0098] In another embodiment, the barrier coated substrate material web can be adhered to the bulk layer by wet application of an aqueous dispersion of a tacky composition comprising a tacky polymeric adhesive to one of the web surfaces to be laminated and pressing the two paper webs together as they are advanced through a lamination roll nip, whereby the laminated structure is provided by wet lamination. In the subsequent lamination process, the water of the aqueous tacky composition is absorbed into the fibrous cellulose network of the bulk paperboard and partially evaporates over time. A forced drying step is thus not required. The tacky polymeric adhesive is selected from the group consisting of acrylic polymers and copolymers, starch, cellulose and polysaccharide derivatives, polymers and copolymers of vinyl acetate and vinyl alcohol. For optimal environmental and sustainability properties, the tacky adhesive is preferably derived from a plant or non-fossil source.

[0099] Suitable thermoplastics for the outermost heat sealable liquid tight layer and the innermost heat sealable liquid tight layer are polyolefins, such as polyethylene and polypropylene homopolymers or copolymers, preferably polyethylene, more preferably selected from the group consisting of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), single-site catalyst metallocene polyethylene (m-LLDPE) and blends or copolymers thereof. According to an embodiment, the outermost heat sealable liquid tight layer is LDPE, while the innermost heat sealable liquid tight layer is a blended composition of m-LLDPE and LDPE to obtain optimal lamination and heat sealing properties.

[0100] The outermost layer is typically applied in a thickness of 5 to 20 pm, such as 10 to 15 pm. The innermost layer can be applied in a thickness range of 10 to 50 pm, such as 10 to 40 pm, such as 10 to 30 pm, such as 10 to 25 pm.

[0101] The same thermoplastic polyolefin based materials, in particular polyethylene, listed for the outermost and innermost layers are also applicable for the adhesive layer inside the laminated material, i.e. between the bulk layer or core layer, such as paper or paperboard, and the barrier layer film or sheet. In an embodiment, the thermoplastic adhesive layer can be a polyethylene layer, such as a low density polyethylene (LDPE) layer. It can typically be applied in an amount of 10 to 25 pm, such as 10 to 20 pm, such as 10 to 15 pm.

[0102] In another embodiment, the second innermost liquid tight heat sealable polyolefin layer is a pre-made film comprising the same or similar polyolefin as described above to improve the robustness of the mechanical properties of the packaging material. Due to the manufacturing process in the blown film and film casting operation, and optionally subsequent film orientation operation steps, the polymer of such a pre-made film obtains different properties than what can be obtained for a (co)extrusion coated polyolefin layer. Such a pre-made polymeric film thus contributes to the mechanical robustness of the laminated packaging material and the mechanical strength and packaging integrity of the packaging containers formed and filled from the laminated packaging material.

[0103] According to alternative embodiments, inside the laminated material, such as for example between the bulk layer or core layer and the barrier-coated substrate material web or between the outer heat-sealable layer and the barrier-coated substrate material web, a suitable adhesive or tie layer, also called tacky thermoplastic polymer, such as a modified polyolefin, such as a LDPE or LLDPE copolymer or a graft copolymer with functional group containing monomer units, such as carboxyl or glycidyl functional groups, such as an ethylene acrylic acid copolymer (EAA) or an ethylene methacrylic acid copolymer (EMAA), an ethylene-glycidyl (meth)acrylate copolymer (EG(M)A) or a MAH-grafted polyethylene (MAH-g-PE). Another example of such a modified polymer or adhesive polymer is a so-called ionomer or ionomer polymer. Preferably, the modified polyolefin is an ethylene acrylic acid copolymer (EAA) or an ethylene methacrylic acid copolymer (EMAA).

[0104] If desired, the surface of the substrate material web can be pre-treated by an oxidative treatment, such as a corona treatment, a plasma treatment or an ozone treatment, to improve the adhesion strength to the graphene oxide layer or the reduced graphene oxide layer.

[0105] The laminated packaging material made according to the above described method provides good integrity by good adhesion between adjacent layers within the laminated structure and by providing a good quality barrier coating and barrier pre-coating each and in combination when transformed into a filled packaging container.

[0106] According to further embodiments, the packaging container formed from the laminated packaging material can be partially sealed, filled with a liquid or semi-liquid food product and subsequently sealed by sealing the packaging material to itself, optionally in combination with a plastic opening or top portion of the package.

[0107] In summary, the barrier-coated substrate material web and the laminated packaging material obtained therefrom, manufactured by the method of the present invention, can obtain a robust and reliable package with outstanding oxygen barrier properties for liquid food packaging with long shelf life and long term storage. The laminated packaging material structure is more suitable for forming a fold-formed package, both because of the improved adhesion between the substrate and the barrier material coating and because of the improved contribution of the barrier coating substrate itself to the gas barrier properties, which can also be due to the improved cohesion and adhesion within the combination of the pre-coating and the barrier coating in the barrier-coated cellulose-based substrate. BRIEF DESCRIPTION OF DRAWINGS

[0108] The preferred embodiments of the present invention will be explained below with reference to the drawings, in which:

[0109] Figure 1a An embodiment of a substrate coated with reduced graphene oxide according to the present application is shown schematically in cross-section,

[0110] Figure 1b Different embodiments of a substrate coated with reduced graphene oxide according to the present application are shown schematically,

[0111] Figure 2a A schematic cross-sectional view of a laminated packaging material according to the present application is shown, comprising a substrate coated with Figure 1a reduced graphene oxide,

[0112] Figure 2b A schematic cross-sectional view of a laminated packaging material according to the present application is shown, comprising a substrate coated with Figure 1b reduced graphene oxide,

[0113] Figure 3 A method for dispersion coating an aqueous composition of graphene oxide onto a substrate is shown schematically,

[0114] Figure 4a A method for melt extrusion lamination of two material webs together via an intermediate thermoplastic polymer is shown schematically,

[0115] Figure 4b A method for melt (co)extrusion of one or more thermoplastic polymer coatings onto a web substrate, for example to form the innermost and outermost layers of a packaging laminate of the present application, is shown schematically,

[0116] Figure 5a , 5b Figures 5c and 5d show typical examples of liquid carton packaging containers produced from laminated packaging materials according to the present application, and

[0117] Figure 6 Figures 6a and 6b show the principle of how such liquid carton packaging containers can be manufactured from packaging laminates in a continuous, roll-fed, form, fill and seal process. DETAILED DESCRIPTION

[0118] EMBODIMENT

[0119] Example 1

[0120] A continuous stirring of an aqueous dispersion of 1 wt% graphene oxide single-layer flakes (pure quality, exfoliated to at least 95%, from Graphenea). Another solution / dispersion of microfibrillar cellulose (MFC) (also called "cellulose nanofibrils" (CNF)) ("Exilva" from Borregaard) was gently mixed with the above graphene oxide composition to a concentration of about 1 wt%, and then the mixture was treated in an ultrasonic bath. The bath was cooled to a temperature between ±0°C and +10°C as the ultrasonic equipment would otherwise heat the mixture and thus affect the quality of the mixture. The graphene oxide was added slowly, little by little, to the mixture over a period of 2-10 minutes to achieve good exfoliation and dispersion.

[0121] When the composition appeared stable, a saturated aqueous solution of ascorbic acid (pure ascorbic acid from Bulk powders) was added drop by drop under continuous stirring until the composition contained 3 to 7 wt% ascorbic acid, while the colour of the dispersion changed from light brown to black as the reduction reaction proceeded, and the graphene oxide was reduced to "graphene". The reduction reaction was carried out at room temperature 23°C. The reduced dispersion maintained its watery viscosity.

[0122] It was observed that after another 48 hours, the dispersion viscosity increased and changed from watery to more pasty. After 24 hours it was very dark black, but still had a liquid stickiness that could be applied by dispersion coating. Both liquids exhibited shear thinning behaviour, i.e. the viscosity decreased as the shear speed (force) was increased. Thus, the pasty dispersion could also be coated onto a substrate in a suitable equipment and in a suitable environment.

[0123] However, for safety reasons, it was concluded that the coating should be carried out on a substrate at least within 24 hours after the ascorbic acid was mixed into the graphene oxide solution / dispersion.

[0124] The aqueous composition of graphene oxide thus reduced was subsequently dispersion coated onto a forwardly transported paperboard (i.e. pre-coated liquid paperboard with a bending stiffness of 80 mN and a grammage of 200 g / m 2 The coating composition was evaporated from the surface in a hot air drier by air convection at a web surface temperature of about 60°C for about 1 minute. The resulting dry coating thickness of the reduced graphene oxide applied to the PE coated paper was black in colour. The thickness of the coating was measured to be about 500 nm.

[0125] The coated paperboard was black in colour. The oxygen transmission rate was below 0.1 cc / m 2of oxygen, 24 hours, 1 atm, 23°C / 80% RH, 21% oxygen.

[0126] Example 2

[0127] An aqueous composition of graphene oxide was prepared as described above.

[0128] Another solution of crystalline nanocellulose (or cellulose nanocrystals) (CNC) was gently mixed with the composition of graphene oxide (at a concentration of 1 wt%) to reach a CNC concentration of about 1 wt%, and then treated in an ultrasonic bath (US) in the same way as in Example 1 during cooling to a temperature between ±0°C and +10°C.

[0129] As the mixture appeared stable, but while continuously stirring, an aqueous solution of ascorbic acid saturated in water was added dropwise until the composition contained 3 to 7 wt% of ascorbic acid at room temperature 23°C, and the extent of reduction was monitored until the dispersion color completely turned black.

[0130] In this case, it can be seen that the reduced graphene oxide remained stable in the aqueous solution for more than 14 days, without any change / increase in viscosity, without any visible agglomeration of graphene flakes or particles.

[0131] After 14 days of storage of the reduced graphene oxide dispersion, it was coated onto a paperboard substrate in the same way as in Example 1.

[0132] The substrate thus obtained was coated with a dry coating of layered graphene (reduced graphene oxide) flakes of about 500 nm thick, which showed an oxygen transmission rate of less than 0.1 cc / m 2 of oxygen, 24 hours, 1 atm, 23°C / 80% RH, 21% oxygen, as measured by an Ox-Tran 2 / 21 Mocon instrument.

[0133] These results demonstrate that in both examples, the complete reduction of graphene oxide occurred in the aqueous dispersion.

[0134] Thus, it appears possible to significantly reduce graphene oxide to reduced graphene oxide while still in dispersion or solution, even before applying it to a substrate, and to obtain oxygen barrier levels that are at, or even above, the levels that are generally required and desired for laminated packaging materials for aseptic liquid carton packaging.

[0135] As the Williams-Landel-Ferry model, or WLF for short, has been observed to apply to this reduction reaction of graphene oxide, it also appears possible to accelerate and control the reduction reaction by increasing the temperature of the mixed composition of graphene oxide and ascorbic acid.

[0136] Furthermore, the reduction reaction seems to be able to continue to completion in the aqueous composition before the aqueous composition is applied to a substrate and subsequently dried, thus immediately obtaining the desired oxygen barrier properties of the coated material, which also enables immediate further lamination into a laminated packaging material structure. This result is truly groundbreaking, as it enables the use of graphene oxide as a raw material source for the manufacture of high-quality oxygen barrier layers or coatings from reduced graphene oxide in laminated packaging materials in industry.

[0137] Furthermore, with regard to the drawings:

[0138] In Figure 1a an embodiment of a gas barrier coated substrate material 10a of the present invention is shown in cross-section. The substrate material 11a is a polyethylene terephthalate (PET) film with a thickness of 36 μιη. Its oxygen transmission rate (OTR) is about 30 cc / m 2 , 24 hours, 23°C / 80% RH, 100% oxygen.

[0139] The PET film has a graphene oxide dry coating 12a applied by coating a gas barrier coating composition aqueous dispersion of reduced graphene oxide onto the surface of the substrate material, followed by drying the wet coated substrate material by forced evaporation to obtain a layer of dry reduced graphene oxide particles or flakes on the surface of the substrate material, thus forming a gas barrier coating material.

[0140] The dry weight of the reduced graphene oxide coating thus applied is about 400 nm (0.4 μιη). The OTR is measured to be below 0.1 cc / m 2 , 24 hours, 23°C / 80% RH, 100% oxygen. If the same film substrate is coated with half the thickness on each side, the OTR is instead 0.02 cc / m 2 , 24 hours, 23°C / 80% RH, 100% oxygen.

[0141] The robustness of the reduced graphene oxide coating can be illustrated (according to a similar principle as the Flex-Gelbo test) by a test of folding and unfolding the coated material once, twice and up to twenty times. After the first fold, the OTR increases to 0.03 cc / m 2 , 24 hours, 23°C / 80% RH, 100% oxygen, but it does not increase further after 20 folding operations. This indicates that the mechanical properties of this barrier coating are much better than existing gas barrier coatings from vapor deposition processes or existing dispersion coated barrier materials. Furthermore, reduced graphene oxide is not sensitive to humidity, and thus loses its barrier properties at higher humidity, as is the case for PVOH, for example.

[0142] In Figure 1bThe image shows different embodiments of the substrate material roll 10b coated with a barrier layer according to the present invention, illustrated in cross-section. The substrate material 11b has a basis weight of 50 g / m². 2 The thin paper substrate has a low-density polyethylene thin pre-coating 14, which is applied by dispersion coating and subsequent drying, thus having a final dried thickness of about 1 μm. On the dried surface of the polyethylene pre-coating, a coating is applied... Figure 1a The same type of reduced graphene oxide drying layer 12b and with Figure 1a The application method is the same. Therefore, the dry weight of the graphene oxide coating is approximately 400 nm, or 0.4 μm. Another protective polymer coating 15b of low-density polyethylene is applied to the reduced graphene oxide layer to provide protection as the substrate material roll with the barrier layer is further wound onto the roller. The measured OTR is less than 1 cc / m. 2 24 hours, 1 atmosphere, 23℃ / 50% RH, 21% oxygen.

[0143] Protective polymer coating 15a (e.g.) Figure 1b The protective polymer coating in (15b) may also optionally be applied to Figure 1a It is on the reduced graphene oxide layer 12a, but not shown.

[0144] exist Figure 2a The image shows a laminated packaging material 20a for liquid carton packaging, wherein the laminated material comprises materials having a flexural strength of 80 mN and a strength of approximately 200 g / m³. 2 The outer layer 21 is a paperboard body layer of paperboard weight, and also includes an outer liquid-tight heat-sealable polyolefin layer 22 applied to the outside of the body layer 21, facing the exterior of the packaging container made of packaging laminate material. Layer 22 is transparent to show outwardly printed decorative patterns 27 applied to the paper or paperboard body layer, thereby informing consumers of the contents of the packaging, the packaging brand, and other information for retail facilities and food stores. The polyolefin of the outer layer 22 is conventional low-density polyethylene (LDPE) of heat-sealable quality, but may also include other similar polymers, including LLDPE. Its application amount is approximately 12 g / m². 2The innermost liquid-tight heat-sealable layer 23 is arranged on the opposite side of the bulk layer 21 which will be directed towards the interior of the packaging container made of the packaging laminate, i.e. the layer 23 will be in direct contact with the packaged product. Thus, this innermost heat-sealable layer 23 will form the strong transversal heat-seal of the liquid packaging container made of the laminated packaging material, which comprises a combination of one or more polyethylenes selected from the group consisting of LDPE, linear low density polyethylene (LLDPE), and LLDPE prepared by polymerization of ethylene monomer with C4-C8 (more preferably C6-C8) alpha-olefin alkylene monomers in the presence of a metallocene catalyst (i.e. so-called metallocene-LLDPE (m-LLDPE)). Its applied amount is about 22 g / m 2 .

[0145] The bulk layer 21 is laminated to the Figure 1a gas-barrier-coated PET film substrate material 25a; 10a by an intermediate low density polyethylene (LDPE) adhesive layer 26a. The intermediate adhesive layer 26a is formed by melt extrusion into a thin polymer melt curtain between two reels and thus laminates the bulk paperboard layer and the barrier-coated PET film substrate to each other when all three layers pass through a cooled press roll nip. The thickness of the intermediate adhesive layer 26a is 12 to 18 pm, more specifically 12-15 pm.

[0146] The innermost heat-sealable layer 23 can consist of one or alternatively of two or more partial layers of the same or different kind of LDPE or LLDPE or blends thereof and is well adhered to the surface of the barrier layer of the gas-barrier-coated PET film substrate material 10a; 25a by an intermediate co-extruded tie layer 24, such as an ethylene acrylic acid copolymer (EAA) intermediate co-extruded tie layer, thus, when applying these layers in a single melt co-extrusion coating step, the intermediate co-extruded tie layer 24 bonds the innermost heat-sealable layer to the barrier layer surface of the barrier-coated substrate material web 10a.

[0147] Alternatively, the barrier-coated PET film substrate 10a; 25a can be turned in the opposite direction in the laminate, i.e. the barrier coating points towards the bulk layer and the outside of the laminate.

[0148] In Figure 2b the different laminate 20b of the present invention for liquid carton packaging is shown, which has a similar layer structure as in Figure 2a , except that the barrier-coated substrate material 25b differs in its structure but is located in the same position in the laminate.

[0149] The bulk layer 21b is laminated to the Figure 1bthe barrier-coated paper substrate 25b; 10b uncoated side, by applying a water dispersion of polyvinyl acetate adhesive to one of the surfaces to be adhered to each other, followed by pressing together in a nip. This lamination step is performed at industrial speeds in a high-efficiency cold lamination or ambient lamination step, without any energy-consuming drying operation to accelerate the evaporation of water. The dry coating weight of the intermediate adhesive layer 26b is only 3 to 4 g / m 2 and does not require drying and evaporation operations.

[0150] Thus, in contrast to the conventional melt extrusion laminated polyethylene adhesive layer described in Figure 2a as layer 26a, the amount of thermoplastic polymer in this laminated layer can be significantly reduced.

[0151] The innermost heat-sealable layer 23 is applied to the barrier-coated surface of the paper substrate material in an amount of about 22 g / m 2 by an intermediate co-extruded tie layer, for example an ethylene acrylic acid copolymer (EAA) co-extruded tie layer, thereby bonding the innermost heat-sealable layer 23 to the barrier-coated paper substrate 10b in a single melt co-extrusion coating step.

[0152] Alternatively, the innermost heat-sealable liquid-tight layer is a pre-made blown film 23b comprising any blend of LDPE or LLDPE polymers and which can be laminated to the barrier-coated paper substrate, i.e. to its barrier-coated surface, by an intermediate melt extrusion adhesive layer 24b which comprises a thicker EAA tie layer than the layer 24 used in Figure 2a or a simpler LDPE adhesive layer. The blown film 23b has a thickness of 12 pm, but can reach 20 pm.

[0153] In an alternative embodiment, the pre-made blown film 23b is laminated to the metallized coating at ambient (cold) temperature, using an aqueous adhesive of an acrylic (co)polymer adhesive layer 24b' at a content of 3 to 4 g / m 2 by another wet lamination step.

[0154] Further embodiments are also disclosed herein which have all the features described above and Figure 2a the melt extrusion bulk layer lamination layer 26a described above, but which are combined with the features of the barrier-coated paper substrate material 25b and the innermost heat-sealable layer structure 23b which is either applied by melt extrusion lamination with the layer 24b or by wet lamination of a pre-made film 24b' as described in connection with Figure 2b .

[0155] Yet further embodiments are also disclosed herein in which Figure 2b the thin, wet, aqueous adhesive lamination layer 26a described above is combined with conventional melt co-extrusion coated inner layers 24 and 23.

[0156] In Figure 3 , the process of aqueous dispersion coating 30a is shown, which can be used to apply the reduced graphene oxide barrier coating 12a; 12b. A web of substrate material 31a (e.g. substrate material 1 la; 1 lb in Figure 1a , 1b) is conveyed to a dispersion coating station 32a, where an aqueous dispersion composition is applied to the top surface of the substrate by means of a roll. Due to the water content of the dispersion composition being 70 or 80 to 99 wt%, there will be a significant amount of water on the wet coated substrate, which needs to be dried and evaporated off to form a uniform continuous coating and have a uniform quality in terms of gas barrier properties and surface properties (i.e. uniformity and wettability). Drying is carried out by a hot air dryer 33a, which allows the water to evaporate and be removed from the substrate surface by air convection. The substrate temperature is kept constant at a temperature of 60 to 80 °C as it passes through the dryer. Alternatively, the drying can be partially assisted by radiant heat from infrared IR lamps in combination with hot air convection drying.

[0157] The process as shown in Figure 3 , can then be repeated once or twice to provide a thicker dried reduced graphene oxide layer.

[0158] The resulting barrier pre-coated paper substrate web 34a is conveyed forward to cool and can be wound onto a reel for intermediate storage and subsequent further lamination operations, or directly to such further lamination stations.

[0159] Figure 4a The process of the lamination step in the manufacture of the packaging laminate 20a or 20b as Figure 1a or 1b is shown, as the bulk layer 21 ; 43 is laminated to the barrier coated substrate material web 34a; 10a; 10b of Figure 2a and 2b , respectively 25a or 25b, Figure 2a and 2b .

[0160] As combined with Figure 2a and 2bAs explained, the bulk layer paperboard 21 can be laminated to the barrier coated base material 10; 25a; 25b by melt extrusion lamination as shown or by wet cold dispersion adhesive lamination (but this wet cold dispersion adhesive lamination is not shown). Thus, a molten polymer curtain 44, for example being LDPE, is fed into the nip of the lamination roll 45 as both web 34a and 43 are also conveyed to the same lamination nip and are connected to each other by the LDPE extrusion adhesive layer 44. The three layers are thus pressed together and connected at the nip 45 formed between the press roll and the cooling roll, cooling the laminated material to properly solidify the LDPE extrusion adhesive layer 44. The resulting laminated material is conveyed to be wound on a spool for intermediate storage or directly used for subsequent lamination operations. The gas barrier coating of reduced graphene oxide can advantageously be directed to the inside of the laminated packaging material, i.e. to the side intended to be directed directly towards the inside of the packaging container formed from the laminated material. Alternatively, it can be directed to the outside. In a further embodiment, both sides of the base material can be coated with a reduced graphene oxide barrier coating.

[0161] In Figure 4b , the resulting pre-laminated material 49a of paperboard 31b and barrier web 34a is conveyed to be directly from Figure 4a the lamination operation 40a to a further lamination step 40b, or to be spooled and unwound from the spool for the further lamination step 40b.

[0162] The non-laminated side of the bulk layer 21, i.e. its printed side, is engaged at the cooled nip 48a with a molten polymer curtain 46a of LDPE that will form the outermost layer 22 of the laminated material, the LDPE being extruded from an extruder block and die 47a. Subsequently, the paper pre-laminated web now coated with the outermost layer 22 on its printed side is passed through a second extruder block and die 47b and lamination nip 48b, where a molten polymer curtain 46b is engaged and coated on the other side of the pre-laminated material, i.e. on the uncoated inside side of the barrier coated base material web 10a; 10b; 25a; 25b. Thus, the innermost heat sealable layer 23 is co-extrusion coated onto the inside side of the barrier coated base material web to form the final laminated packaging material 49b, which is finally wound onto a storage spool (not shown).

[0163] The two co-extrusion steps at the lamination roll nips 48a and 48b can alternatively be performed as two consecutive steps in reverse order.

[0164] According to another embodiment, one or both of the outermost layers can be applied in a pre-lamination station, where a co-extrusion coating is first applied to the outside of the bulk paperboard layer (printed) or to the inside surface of the barrier coated paper base material, and then the two pre-laminated paper webs are engaged with each other as explained above in connection with Figure 4a the lamination operation 40a.

[0165] According to a further embodiment, the innermost liquid-tight thermoplastic layer can be applied in the form of a pre-made film, which is laminated onto the barrier-coated substrate material 10a; 10b.

[0166] As explained in connection with Figure 2a and 2b the innermost layer pre-made film 23 can be laminated onto the barrier-coated substrate material 10a; 10b by wet cold dispersion adhesive lamination or by melt extrusion lamination.

[0167] Figure 5a An embodiment of a packaging container 50a produced with a packaging laminate according to the present application is shown. This packaging container is particularly suitable for beverages, sauces, soups, etc. Typically, such a packaging has a volume of about 100 to 1000 ml. It can be of any construction, but is preferably brick-shaped, having longitudinal and transversal seal portions 51a and 52a, respectively, and optionally an opening device 53. In another embodiment, not shown, the packaging container can be shaped as a wedge. In order to obtain such a "wedge", only the bottom portion of the packaging is folded into shape, so that the transversal heat seal of the bottom is hidden under a triangular flap, which is folded and sealed at the bottom of the packaging. The top transversal seal remains unfolded. In this way, the only partially folded packaging container is still easy to handle and dimensionally stable enough to be placed on a shelf in a grocery store or on any flat surface,

[0168] Figure 5b An alternative example of a packaging container 50b produced with an alternative packaging laminate according to the present application is shown. This alternative packaging laminate is thinner due to the thinner paper body layer, so it is not dimensionally stable enough to form a parallelepiped or wedge-shaped packaging container and is not folded into shape after the transversal seal 52b. This packaging container will remain a pillow-shaped pouch container and is distributed and sold in this form.

[0169] Figure 5c A peak-top packaging 50c is shown, which is formed from a pre-cut sheet or blank, folded from a laminated packaging material comprising a paperboard body layer and a barrier-coated paper substrate of the present application. A flat-top packaging can also be made from a similar blank.

[0170] Figure 5d A bottle-shaped packaging 50d is shown, which is a combination of a sleeve 54 and a top 55 formed from a pre-cut blank of the laminated packaging material of the present application, said top being formed in combination with an injection-moulded plastic and an opening device, such as a screw cap or the like. This type of packaging is for example known under the trade name and Sales. These particular packages are formed by attaching a molded top 55, with the opening device attached in the closed position, to a tubular sleeve 54 of laminated packaging material, sterilizing the bottle top capsule thus formed, filling it with food product, and finally folding-forming the bottom of the package and sealing it.

[0171] Figure 6 The principles described in the introduction of the present application are shown, i.e. that a web of packaging material is formed into a tube 61 by overlapping and heat-sealing together the longitudinal edges 62, 62' of the web to form an overlap joint 63 therebetween. The tube is continuously filled 64 with liquid food product to be filled, and is divided into individual filled packages by repeated double transverse seals 65 in the tube at a predetermined distance from each other and below the level of the contents filled in the tube. The packages 66 are separated by cutting between the double transverse seals (top and bottom seals), and are finally shaped into the desired geometric configuration by folding over the prepared crease lines in the material.

[0172] As a final comment, the present application is not limited to the embodiments shown and described above, but can vary within the scope of the claims.

Claims

1. A method for producing a material (10a; 10b) coated with a gas barrier layer by coating a substrate material (11a; 11b) with a reduced graphene oxide layer (12a; 12b), comprising the following steps: a) Provide base material. b1) Provides an aqueous composition comprising a dispersion of 0.5 to 15 wt% graphene oxide and 0.1 to 5 wt% nanocellulose compound, wherein the graphene oxide comprises monolayer graphene oxide sheets and multilayer graphene oxide sheets having up to 20 stacked monolayer graphene oxide sheets. b2) Add 0.5 to 10% by weight of a reducing agent to the mixed aqueous composition and enable the reducing agent to reduce the graphene oxide to form an aqueous gas barrier coating composition containing well dispersed and reduced graphene oxide. c) The aqueous gas barrier coating composition containing reduced graphene oxide obtained in step b2) is applied (32a) to the surface of the substrate material. d) The wet-coated substrate material obtained in step c) is dried by forced evaporation (33a) to obtain a layered reduced graphene oxide particles or flakes on the surface of the substrate material, thereby forming the material coated with the gas barrier layer.

2. The method according to claim 1, wherein the nanocellulose compound is selected from the group consisting of microfibrillated cellulose (MFC) and crystalline nanocellulose (CNC).

3. The method according to any one of claims 1 or 2, wherein the concentration of graphene oxide in the aqueous composition is 0.5 to 10% by weight.

4. The method according to any one of claims 1 or 2, wherein the concentration of graphene oxide in the aqueous composition is 0.5 to 6% by weight.

5. The method according to any one of claims 1 or 2, wherein the concentration of graphene oxide in the aqueous composition is 0.5 to 3% by weight.

6. The method according to any one of claims 1 or 2, wherein the concentration of graphene oxide in the aqueous composition is 1 to 2% by weight.

7. The method according to any one of claims 1-2, wherein the reducing agent is selected from the group consisting of sodium citrate, ascorbic acid, lemon juice, vinegar and green tea.

8. The method according to any one of claims 1-2, wherein the reducing agent is ascorbic acid.

9. The method according to any one of claims 1-2, wherein the concentration of the reducing agent is 1 to 10% by weight.

10. The method according to any one of claims 1-2, wherein the concentration of the reducing agent is 2 to 7% by weight.

11. The method according to any one of claims 1-2, wherein the concentration of the reducing agent is 3 to 6% by weight.

12. The method according to any one of claims 1-2, wherein the concentration of the nanocellulose is 0.5 to 5% by weight.

13. The method according to any one of claims 1-2, wherein the concentration of the nanocellulose is 0.5 to 4% by weight.

14. The method according to any one of claims 1-2, wherein the concentration of the nanocellulose is 0.5 to 3% by weight.

15. The method according to any one of claims 1-2, wherein the concentration of the nanocellulose is 0.5 to 2% by weight.

16. The method according to any one of claims 1-2, wherein the concentration of the nanocellulose is 0.5 to 1.5% by weight.

17. The method according to any one of claims 1-2, further comprising a step e) following step d): coating or laminating the substrate material coated with the gas barrier layer onto another polymer or adhesive layer to cover the reduced graphene oxide dried layer.

18. The method according to any one of claims 1-2, wherein the wet coating thickness of the aqueous gas barrier coating composition of the reduced graphene oxide is 10 to 400 μm.

19. The method according to any one of claims 1-2, wherein, The substrate material is a roll material, which is continuously conveyed at a constant speed.

20. The substrate material (10a; 10b) coated with a gas barrier layer obtained by the method according to any one of claims 1-19, which is used as an oxygen barrier material in laminated packaging materials (20a; 20b).

21. The substrate material coated with a gas barrier layer according to claim 20, wherein the thickness of the reduced graphene oxide drying layer (12a; 12b) is 50 to 1000 nm.

22. The substrate material coated with a gas barrier layer according to claim 20, wherein the thickness of the reduced graphene oxide drying layer (12a; 12b) is 100 to 800 nm.

23. The substrate material coated with a gas barrier layer according to claim 20, wherein the thickness of the reduced graphene oxide drying layer (12a; 12b) is 200 to 700 nm.

24. The substrate material coated with a gas barrier layer according to claim 20, wherein the thickness of the reduced graphene oxide drying layer (12a; 12b) is 200 to 600 nm.

25. The substrate material coated with a gas barrier layer according to claim 20, wherein the thickness of the reduced graphene oxide drying layer (12a; 12b) is 400 to 600 nm.

26. The substrate material coated with a gas barrier layer according to claim 20, wherein the thickness of the reduced graphene oxide drying layer (12a; 12b) is 450 to 550 nm.

27. The substrate material coated with a gas barrier layer according to any one of claims 20-26, wherein the substrate material (11a; 11b) is a polymer film, paper or other cellulose-based material, or polymer-coated paper or other polymer-coated cellulose-based material.

28. The substrate material coated with a gas barrier layer according to any one of claims 20-26, wherein the dried layer of layered reduced graphene oxide particles or sheets (12a; 12b) is further coated with an adjacent polymer or adhesive layer (15b) or laminated onto the adjacent polymer or adhesive layer (15b).

29. A laminated packaging material (20a; 20b) comprising a substrate material (10a; 10b) coated with a gas barrier layer according to any one of claims 20-28, and further comprising a first outermost protective material layer (22) and a second innermost liquid-tight heat-sealable material layer (23; 23b).

30. The laminated packaging material (20a; 20b) according to claim 29, further comprising a paper or paperboard or other cellulose-based material body layer (21), a first outermost protective material layer (22), a second innermost liquid-tight heat-sealable material layer (23; 23b), and a substrate material (10a; 10b) coated with a gas barrier layer, the substrate material (10a; 10b) being disposed inside the paper or paperboard body layer, between the body layer and the second innermost material layer.

31. The laminated packaging material (20a; 20b) according to claim 30, wherein the substrate material (10a; 10b) coated with the gas barrier layer is bonded to the body layer (21) by an intermediate adhesive layer (26a; 26b) comprising a composition comprising an adhesive selected from the group consisting of polymers and copolymers of acrylic polymers and copolymers, starch, cellulose and polysaccharide derivatives, vinyl acetate and / or vinyl alcohol polymers and copolymers.

32. A packaging container (50a; 50b; 50c; 50d) comprising a laminated packaging material as defined in any one of claims 29-31.

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