Barrier-coated substrate, laminated packaging material and packaging container including the substrate

Abstract

The present invention relates to a method for producing a barrier-coated substrate web (10; 25a) coated with a first layer (12a) of a reducing agent and a water-dispersible polymer and a second layer (13a) of reduced graphene oxide. The present invention further relates to a laminate packaging material (20a) comprising the barrier-coated substrate web (10), in particular intended for liquid carton food packaging, and to a liquid carton packaging container made of this laminate packaging material.

Description

[Technical field]

[0001] The present invention relates to a barrier coated substrate by dispersion coating of a barrier and a method for producing the same. The present invention further relates to a laminated packaging material comprising such a barrier coated substrate, in particular for liquid carton food packaging, and to a liquid carton packaging container comprising such a laminated packaging material. [Background technology]

[0002] Single-use packages for liquid foods are often manufactured from paperboard or carton-based packaging laminates. One such commonly used package is sold under the trademark "Tetra Brik Aseptic" and is primarily employed for the aseptic packaging of liquid foods such as milk, fruit juices, etc., which are sold for long-term ambient storage. The packaging material of this known package is usually a laminate comprising a bulk or core layer of paper, paperboard or other cellulose-based material and an outer liquid-tight layer of thermoplastic. To make the package gas-tight, and in particular oxygen-tight, for the purposes of aseptic packaging or packaging of, for example, milk or fruit juice, these laminates usually comprise at least one additional layer, most commonly aluminum foil.

[0003] On the inside of the laminate, i.e. the side intended to face the filled food contents of the container produced from the laminate, there is an innermost layer applied onto the aluminum foil, which comprises one or more partial layers comprising adhesive polymers and / or heat-sealable thermoplastic polymers such as polyolefins, and, outside the bulk layer, there is an outermost heat-sealable polymer layer.

[0004] Packaging containers are generally produced by modern high speed packaging machines of the type that form, fill and seal packages from webs of packaging material or prefabricated blanks. The packaging containers are produced by joining the longitudinal edges of the web together at overlap joints by welding together the inner and outer heat-sealable thermoplastic polymer layers, and reforming the laminated web of packaging material into a tube. The tube is filled with the desired liquid food product and then divided into individual packages by repeatedly transversely sealing the tube at predetermined distances from each other below the height of the contents in the tube. The packages are separated from the tube by scoring along the transverse seals and formed into the desired geometric shape, usually a cube shape, by creating creases in the packaging material along prefabricated crease lines.

[0005] The main advantage of this continuous tube forming, filling and sealing packaging concept is that the web can be continuously sterilized just before tube formation, thus offering the possibility of an aseptic packaging process, i.e. a process in which the liquid contents to be filled and the packaging material itself are reduced from bacteria and the filled packaging containers are produced under clean conditions such that they can be stored for long periods, even at ambient temperature, without the risk of microbial growth in the filled product. Another important advantage of the Tetra Brik® type packaging process is that it allows continuous high speed packaging, which, as mentioned above, has a great impact on cost efficiency.

[0006] Packaging containers for sensitive liquid foods, such as milk and juice, can also be produced from sheet blanks or prefabricated blanks of the laminate packaging material of the invention. Packages are produced from flat-folded tubular blanks of the packaging laminate by first assembling the blanks to form an open tubular container capsule, one open end of which is closed by folding and heat sealing an integral end panel. The container capsule thus closed is filled from the other open end with a food product, such as juice, and thereafter closed by further folding and heat sealing the corresponding integral end panel. Examples of packaging containers produced from sheet and tubular blanks are the conventional so-called gable top packages. Packages of this type can also be provided with a plastic molded top and / or a screw cap.

[0007] The aluminum foil layer of the packaging laminate provides gas barrier properties that are significantly superior to other gas barrier materials. Conventional aluminum foil-based packaging laminates for aseptic packaging of liquid foods are, at their performance level, the most cost-effective packaging materials available on the market today.

[0008] Other materials competing with foil-based materials must be cost effective in terms of raw materials, have comparable food preservation properties, and require comparable low complexity in converting the material into the finished packaging laminate.

[0009] Among the efforts to develop non-aluminum foil materials for liquid food carton packaging, there is also a general motivation to develop pre-manufactured films or sheets with high barrier properties, or to combine multiple separate barrier materials into multi-layer films or sheets that can replace the aluminum foil barrier materials of conventional laminate packaging materials and are compatible with conventional processes for lamination and manufacture of laminate packaging materials.

[0010] With the increasing demand to use only sustainable materials, polymeric barrier materials derived from fossil resources have received less attention and it remains to work on thin barrier coatings of the type that can be almost negligible in the recycling process, are based on material circulation and renewable (non-fossil) materials and cause few problems for economics, namely aqueous dispersion coatings and deposition coatings. Dispersion-coated polymers have a thickness of about 1-2 μm, while deposition barrier coatings are as thin as 0.5 μm or less, e.g. 10-100 nm, e.g. 15-80 nm, e.g. 20-50 nm. Various types of such coatings have been developed over the years and have been combined in multi-layer packaging material structures in search of improved overall performance. Although some of these coatings show good barrier properties, the beverage carton packaging industry is still looking for the optimal coating or combination of coatings that can replace aluminum foil in all respects.

[0011] Past developments have concerned aqueous polymeric compositions suitable for dispersion and / or solution coating of thin layers of, for example, PVOH, starch, etc. A common drawback of this type of polymeric binder is that it is sensitive to high humidity conditions and loses its inherent oxygen barrier properties as exposure to moisture and water content increases, i.e., a condition in laminate packaging materials for filled liquid carton packaging containers. It has been concluded that such thin dispersion coating polymer layers need to be supplemented with additional materials to improve the gas barrier properties, either in the form of additional compounds in the dispersion composition, such as crosslinkers or inorganic particles, or in the form of additional material layers that act as a barrier to water vapor.

[0012] For vapour deposited (or so called "vacuum coated") barrier coatings, very good crack initiation strain properties can be achieved, making them robust enough for folding and sealing of rigid packaging containers, but of course, 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. Carbon-containing materials such as graphene have the added advantage that they can be used for induction sealing of packages, as disclosed in our WO 21 / 005120.

[0014] However, applying graphene itself as a barrier coating to the entire surface of packaging materials is too costly. In theory, graphene sheets one molecule thick might be sufficient to obtain good gas barrier properties, but in practice such thin layers are very expensive and difficult to manufacture. An alternative would be to disperse monolayer flakes of graphene in organic solvents and coat them by dispersion coating or printing techniques, but such variations of graphene layers are too expensive to include as a full-surface coating on disposable packaging materials. Furthermore, removal of organic solvents from such coatings is an undesirable problem in current sustainable industrial-scale coating operations.

[0015] A cheaper source of material for similar barrier coatings with equivalent or similar properties to graphene includes graphene oxide flakes or particles exfoliated from the very cheap raw material graphite oxide and then chemically reduced. The graphene oxide particles or flakes can then be chemically reduced to produce the corresponding graphene particles or flakes. Graphite is abundant in nature, so graphene obtained by oxidation to graphite oxide / graphene oxide (e.g., by a process called Hummers process) and subsequent reduction to graphene is inexpensive for use in packaging materials.

[0016] However, providing thin, homogenous coatings of reduced graphene oxide by large-scale industrial coating processes starting from reduced graphene oxide, i.e. graphene, is problematic due to the organic solvents required to disperse it and also due to the high cost of the further refined product, i.e. reduced graphene oxide.

[0017] The scientific paper “Impermeable barrier films and protective coating based on reduced graphene oxide” (Y. Su, VG Kravets, SL Wong, J. Waters, AK Geim & R.R. Nair) published in Nature Communications on September 11, 2014, describes a method to reduce a graphene oxide coated substrate by exposing it to hydrogen iodide vapor at 90 °C for 5-30 minutes or by immersing it in a solution of vitamin C as a reducing agent at a temperature of 90 °C for 1 hour to obtain a material with good gas barrier properties. Similar teachings are disclosed in WO 2015 / 145155, which has a common author with this paper. Such methods are not feasible for the production of barrier layers or coatings for single-use packaging materials due to economic reasons and practical impracticality in packaging material processing plants. Treatment with acidic vapors or long treatment of substrates in near-boiling liquids has a high risk of material deterioration and is very impractical for manufacturing processes that usually run wide webs continuously at high speeds.

[0018] Therefore, there is a need for improved methods to apply such reduced graphene oxide based materials in laminated packaging materials at reasonable cost and to meet future requirements for recyclability and sustainable material sourcing and manufacturing. Summary of the Invention [Problem to be solved by the invention]

[0019] It is an object of the present invention to provide an improved method for producing barrier coated substrates from reduced graphene oxide and further for laminating such barrier coated substrates to packaging materials.

[0020] It is also a general object of the present invention to provide a simple method for producing graphene oxide reduced barrier coated substrates, providing not only good barrier properties but also recyclability and the ability to meet the requirements for future sustainable liquid carton laminate packaging materials.

[0021] It is a further object of the present invention to provide a packaging material for oxygen sensitive products, e.g., a non-foil laminate packaging material for liquid, semi-solid or moist food products, at a reasonable cost, which does not contain aluminum foil but has good gas and other barrier properties suitable for long term aseptic packaging.

[0022] A particular object is to provide a cost-effective, non-foil, paper or paperboard based laminate packaging material, which has good gas barrier properties, is recyclable and has a sustainable environmental profile compared to aluminium foil barrier materials for the manufacture of long term aseptic food storage packages.

[0023] It is a further object of the present invention to provide a cost-effective, non-foil, paper or paperboard based, mechanically robust and heat-sealable packaging laminate with good gas barrier properties for the production of aseptic packaging containers for the long-term storage of liquid foods with maintained nutritional quality under ambient conditions. [Means for solving the problem]

[0024] These objects can therefore be achieved according to the present invention by a barrier coated substrate web, a laminate packaging material and a method for producing a packaging container as defined in the appended claims.

[0025] According to a first aspect of the invention, the invention relates to a method for producing an oxygen barrier material for packaging materials by coating a substrate web with a reduced graphene oxide layer, the method comprising the steps of: a) providing and transporting a substrate web; b) coating a first layer of an aqueous composition comprising a reducing agent and a water-dispersible polymer onto the substrate web while the substrate web is being transported; c) drying the first layer by forced evaporation to form a first dry layer comprising the reducing agent and the water-dispersible polymer; d) providing an aqueous composition comprising graphene oxide, the aqueous composition comprising graphene oxide monolayer flakes and multilayer graphene oxide platelets, the monolayer flakes of graphene oxide being stacked up to 20, e.g., 2-10, e) coating an aqueous composition of graphene oxide onto the substrate web while the substrate web is being transported; f) drying the aqueous graphene oxide wet coating on the substrate web by forced evaporation to obtain a second dry layer of layered graphene oxide particles or flakes; g) reducing the graphene oxide of the second layer with the reducing agent of the first dry layer, preferably at a minimum predetermined temperature and for a minimum predetermined time, to form a barrier coated substrate web having a dry layer of reduced graphene oxide; Equipped with Here, steps c) and d) can be performed before or after steps d), e) and f), and either the first dry layer or the second dry layer can be formed first.

[0026] It has been surprisingly found that, by this method, the reduction reaction continues even after the applied coating has dried, and the conversion of graphene oxide to graphene is sufficient to provide excellent gas barrier properties. This was unexpected, since it was previously believed that the reducing agent solution had to be applied as a liquid bath or spray, or as a vapor treatment, and that the surface of the graphene oxide layer had to be kept wet for a long period of time in order to reduce the dried graphene oxide layer.

[0027] Even more surprisingly, it has been realized that the "dry" reduction reaction can also be promoted and accelerated by heating the coated and dried substrate web to an elevated temperature for a period of time. Thus, by appropriate design of the coating production line, the coated and dried substrate web can be further fully reduced and maintained at elevated temperatures during the extended transport of the dry material web through a heating tunnel or the like. Nevertheless, such continuous production lines must be significantly slower than normal coating or lamination operations, and the elevated temperature treatments must be kept significantly below 90°C so as not to risk causing changes in the properties of the substrate web. Advantageously, however, the production process does not require any wet or liquid treatments along the conversion line, except for the aqueous coating operation itself.

[0028] Preferably, an aqueous composition comprising a reducing agent and a water-dispersible polymer is applied as a pre-coat, followed by application of the aqueous graphene oxide coat (i.e., steps b) and c) are performed before steps d), e) and f).

[0029] The method may further comprise a step i) performed before or after step g) of coating or laminating the barrier-coated substrate web with a further layer of polymer to cover the first and second dry layers. It has surprisingly been found that the reduction reaction between the first and second dry layers continues even after further coating or laminating a polymer layer onto the dry layer, such as an extrusion coating of a thermoplastic polymer. Such high temperature polymer melt lamination operations add further heat acting on the surface of the barrier-coated substrate web. As a result, the reduction reaction is further accelerated while such lamination operations are in progress.

[0030] The method may also include a step h) of winding the coated and dried barrier-coated substrate web onto a reel, performed before or after step g). It has been shown that the reduction reaction of the dried graphene oxide layer does not stop until it is complete, and therefore, even if no further heat treatment is performed after drying, the conversion of graphene oxide to reduced graphene oxide continues at a lower rate until it is complete. Thus, the color of the freshly applied graphene oxide changes to black over time, indicating that the graphene oxide is almost, substantially, completely reduced. This is a great advantage in a coating production line, since no additional heat treatment needs to be incorporated into the coating production line, and the barrier-coated substrate web can be directly wound onto a reel after coating and a short drying operation, for example, within only about 1 minute (e.g., 2 seconds to 1 minute, which corresponds to a speed range of 20 m / min to 600 m / min for a 20 m long oven). Furthermore, the production speed can be as fast as possible, since the reduction reaction is slower and takes place at a slower pace. By planning the logistics around the transportation and distribution of the packaging material reels to customers, sufficient time can be ensured to complete the reduction reaction. Thus, the reels with the barrier-coated substrate webs can be simply stored for a predetermined time after coating and drying to allow the reduction reaction between the reducing agent in the first drying layer and the graphene oxide in the second drying layer to reach a sufficient degree of conversion of graphene oxide to reduced graphene oxide.

[0031] The reduction reaction time is preferably 1 to 14 days at room temperature, with faster results being obtained at 40 to 60° C., which may be possible for 5 minutes to 3 hours.

[0032] As explained above, with time and temperature, the color of the reduced graphene oxide changes from brown (initial color) to black, indicating the reduction of graphene oxide. This color change is expressed in the so-called color space or L * a * b * It can be quantified by measurement. *The value represents the perceived lightness, L * =0 is black, L * =100 is diffuse white. * The lower the value, the darker the surface, and ultimately values ​​below 15 are suitable. The a value represents green / red, and the b value represents blue / yellow. Only when the a and b values ​​are low (close to zero) does the sample have a low color content and shows a black "color". * , a * , b * It is desirable that each of these is as close to zero as possible.

[0033] In one embodiment, before or during step g), the dried barrier coated substrate web resulting from step f) may be irradiated to promote the reduction reaction occurring between the applied first and second drying layers. Such irradiation may comprise UV light, or xenon light, or laser light. It is believed that the combination of the reducing agent of the first drying layer with such auxiliary irradiation promotes a faster, yet still balanced, reduction reaction of the graphene oxide layers. It has been found that reduction of the graphene oxide layers by irradiation alone, in the absence of a reducing agent, is difficult to control and leads to defects in the material.

[0034] The reducing agent may 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, and most preferably, the reducing agent is ascorbic acid. The latter is the most environmentally friendly and sustainable reducing agent, and ascorbic acid is a well-approved and well-functioning reducing agent in the context of food and the food industry, making it ideal for such processes.

[0035] The method of the present invention, which is suitable for industrial production, provides a substrate with an oxygen barrier permeability of less than 1 cc / m 2 , 24 hours, 1 atmosphere, 23°C / 50% RH, and 21% oxygen.

[0036] According to a second aspect of the present invention, there is provided a barrier-coated substrate web obtainable by the method described above for use as an oxygen barrier material in a laminate packaging material for liquid food, the barrier-coated substrate web comprising a substrate web and a dry layer of reduced graphene oxide lamellar particles or flakes applied thereon.

[0037] According to a third aspect of the invention there is provided a laminated packaging material comprising a barrier coated substrate web as described above, the laminate comprising a first outermost protective material layer and a second innermost liquid-tight heat-sealable material layer.

[0038] For purposes of carton packaging of liquid foods, the laminate packaging material may further comprise a bulk layer of paper or paperboard or other cellulose-based material, a first outermost protective material layer, a second innermost liquid-tight heat-sealable material layer, and a barrier-coated substrate disposed inside the bulk layer of paper or paperboard and between the bulk layer and the innermost layer.

[0039] The first, outermost protective material layer may be a protective polymer layer or coating to prevent dirt and moisture from reaching the interior of the laminate material, for example a thermoplastic polymer layer, for example a liquid-tight, heat-sealable polymer layer, for example a liquid-tight, heat-sealable polyolefin layer, for example a polymer layer such as polyethylene, etc. The second, innermost liquid-tight, heat-sealable material layer may be a thermoplastic polymer, for example a polyolefin such as polyethylene.

[0040] Thus, a thin layer of reduced graphene oxide coated on an optionally precoated substrate may be laminated to standard constructions of laminated packaging materials for liquid carton packaging as a "direct replacement for aluminum foil" due to the superior gas barrier properties of graphene as a material. Compared to previous attempts to produce such "direct replacement" films or barrier sheets, substrate webs such as polymer films or paper substrates coated with reduced graphene oxide are significantly less sensitive in lamination operations and in the filling machine operations of folding, filling and heat sealing carton packages from the laminated materials. This is due to the inherent durability and flexibility of graphene as a material, but also because graphene is a layer obtained by closely stacking overlapping flakes, so that the permeation of oxygen molecules through the barrier coating must follow a so-called tortuous path between the flakes. Such coatings are less susceptible to cracking due to strain and can retain their oxygen gas barrier properties during processing into packages. In addition, the gas barrier properties of reduced graphene oxide are less affected by the permeation of moisture or water vapor from the liquid contents of the package, and therefore can withstand long-term storage of such filled packaging containers.

[0041] In a fourth aspect of the present invention, there is provided a packaging container intended for packaging liquid, semi-solid or wet food products, comprising the laminate packaging material of the third aspect. According to one embodiment, the packaging container is at least partially manufactured from the laminate packaging material of the present invention, and according to a further embodiment, all layers of the packaging container consist of the laminate packaging material of the present invention.

[0042] (Detailed Description) The term "long-term storage" as used in the context of the present invention means that the packaging container is capable of preserving the quality, i.e. nutritional value, hygienic safety and taste, of the packaged food at ambient temperature conditions for at least 1 or 2 months, such as at least 3 months, preferably 6 months, such as 12 months or more.

[0043] The term "package integrity" generally refers to the tightness of the package, i.e., the resistance of the packaging container to leakage or breakage. The term encompasses the resistance of the package to the ingress of microorganisms such as bacteria, dirt, and other substances that may deteriorate the food contained therein and shorten the expected shelf life of the package.

[0044] One major contribution to the package integrity of laminate packaging materials is provided by good internal adhesion between adjacent layers of laminate material. Another contribution is the resistance of the material to defects such as pinholes, breaks, etc. in each material layer itself, and yet another contribution is the strength of the seal joints where the material is sealed when the package is formed. Thus, with respect to the integrity of the laminate packaging material itself, the focus is on the adhesion of each laminate layer to its adjacent layers, and the quality of each material layer. With respect to the sealing of the package, the focus is primarily on the quality of the seal joints, which is ensured by a well-functioning and robust sealing operation in the filling machine, which is further ensured by the properly matched heat seal properties of the laminate packaging material.

[0045] The term "liquid or semi-liquid food" generally refers to food that is flowable and optionally contains food particles. Dairy and milk, soy, rice, grain and seed drinks, juices, nectars, soft drinks, energy drinks, sports drinks, coffee or tea drinks, coconut water, wine, soup, jalapeno, tomato, sauces (such as pasta sauce), legumes, and olive oil are some non-limiting examples of foods that are contemplated.

[0046] The term "sterile" in relation to packaging materials and containers refers to a state in which microorganisms have been removed, inactivated, or killed. Examples of microorganisms include bacteria and spores. Generally, when a product is filled aseptically into a packaging container, an aseptic process is used. In order to maintain the sterility during the shelf life of the packaging container, the integrity properties of the package are very important. For the long-term storage of the filled food, and also to preserve the original taste and nutritional value, e.g., vitamin C content, it is important to have a barrier property against gases such as oxygen gas and vapors.

[0047] The term "bulk layer" generally refers to the thickest layer or layer containing the most material in a multi-layer laminate, i.e., the layer that contributes most to the mechanical properties and dimensional stability of the laminate and the package folded from the laminate, e.g., paperboard or carton, etc. It can also refer to the layer that provides the greater thickness distance in a sandwich structure that interacts with stabilizing opposing layers with higher Young's modulus on either side of the bulk layer to obtain sufficient mechanical properties and dimensional stability.

[0048] Thickness measurements were performed by transmission electron microscopy using a Titan 80-300, FEI Instruments. Samples may be prepared by ultramicrotomy on a Leica EM UC6 Microtome.

[0049] The OTR was measured with an Oxtran 2 / 21 (Mocon) instrument based on a coulometric sensor.

[0050] The OTR measurement method specifies the amount of oxygen per surface and time unit that passes through a material at a given temperature, at a given pressure, and for a period of time, e.g., 24 hours, in a 21% oxygen atmosphere.

[0051] Water vapor transmission rate (WVTR) was measured using a Permatran 3 / 33 (Mocon) device (standard: ASTM F1249-13 using a modulated infrared sensor for relative humidity detection and WVTR measurement) at 38°C and 90% operation.

[0052] L * a * b * The measurements were taken using an X-rite eXact device. https: / / en.wikipedia.org / wiki / cielab_color_space The procedure was carried out as described in.

[0053] The term "graphene oxide" includes monolayer flakes of graphene oxide and multilayer graphene oxide platelets, which are stacked with up to 20 monolayer flakes of graphene oxide, e.g., 2-10. Only a smaller amount, i.e., less than 15 wt.%, e.g., less than 10 wt.%, e.g., less than 5 wt.%, based on the dry weight of the graphene oxide material, of the low graphene oxide monolayer flakes may be graphene oxide flakes that have been exfoliated to a number of more than 20 graphene oxide monolayer flakes, but may contain bulky graphene oxide particles with smaller lateral particle size than so-called "graphite oxide nanoplatelets", which are still nano-sized.

[0054] Such laterally nano-sized graphite flakes may be present in small amounts so long as they do not significantly degrade the performance of the graphene-based material. Preferably, the nano graphite flakes / platelets are present in the composition only in minor amounts, such as less than 15 wt. %, e.g., less than 10 wt. %, e.g., less than 5 wt. %, based on dry weight.

[0055] Suitable graphene oxide materials for aqueous dispersions that can be used in the present invention are, for example, pure quality exfoliated to at least 95% from Graphenea or paste-like graphene oxide from Abalonyx.

[0056] Thus, substrates suitable for the barrier coating of the present invention are not limited to a particular type of substrate, but include polymeric films, paper, paperboard or other cellulose-based substrates, or polymer-coated paper or paperboard, or other cellulose-based substrates. The substrate web may be a polymeric film web, a paper or paperboard web, or a polymer-coated paper or paperboard web.

[0057] The polymeric film substrate may be made of, for example, polyester or polyolefin. Representative polyesters are polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyhydroxyalkanoate (PHA) and polylactic acid (PLA). Typical polyolefin films may be made of most polypropylenes or polyethylenes, such as biaxially oriented polypropylene (BOPP), biaxially oriented high density polyethylene (BOHDPE), linear low density polyethylene (LLDPE), etc.

[0058] The cellulose-based substrates may be based on any type of natural cellulose, fibrous cellulose or fibrillar cellulose, which may be further coated with a polymer of the above types, preferably a polyolefin such as polyethylene as described below, before applying a barrier coating according to the present invention.

[0059] Typically, a paper or cellulose-based substrate suitable for carrying the barrier coating of the present invention has a thickness of 60 g / m 2 For example, 50 g / m 2 Less than 45 g / m 2 More preferably, 40 g / m 2 A thickness of 30 g / m or less is required. On the other hand, cellulosic substrates are thin or 30 g / m 2 Below this weight, when coated with a wet dispersion and then dried, it may be mechanically too weak and / or have poor dimensional stability, which may lead to shrinkage and curling problems. Therefore, it is preferable to use a weight of 30 to 50 g / m2 Basis weight of 35 to 45 g / m 2 Preferably, the paper has a basis weight of 1000 g. High density paper is preferred.

[0060] As described below, the graphene oxide coating is preferably applied as a pre-coating onto a substrate on which a first dry layer has already been formed, which provides the reducing function and ensures that the surface to be coated is smooth so that the graphene oxide coating can be formed uniformly and consistently with aligned flakes to block oxygen transmission.

[0061] Prior to forming the first and second dry layers, a further thin pre-coating of polymer (without reducing agent) may be used. This is preferably applied in the form of an aqueous composition in a preceding dispersion coating step. The thickness of the pre-coating may be 0.5-1.5 μm, for example about 1 μm. Such a pre-coating may further improve the smoothness and oxygen barrier properties. This option is particularly suitable if the second dry layer is formed before the first dry layer, in order to avoid applying the graphene oxide flakes directly to a substrate that may have a rough surface.

[0062] In step b), the aqueous composition used to form the first dry layer comprises a reducing agent and a water-dispersible polymer (which may be a water-soluble polymer). Without wishing to be bound by theory, the inventors believe that the reducing agent migrates before or after drying to the adjacent graphene oxide dispersion where it reduces the graphene oxide to form a barrier layer.

[0063] Preferably, the concentration of the reducing agent is 2-10% by weight, for example 2-8% by weight, for example 2-6% by weight, for example 2-5% by weight. 4% by weight is a preferred amount. A solution containing a minimum amount of reducing agent is required to achieve the desired effect of reducing graphene oxide. If the concentration of the reducing agent exceeds 10% by weight, it will cause aggregation of graphene oxide, resulting in flakes that do not spread uniformly but form clumps, with some of the surface not being exposed. This will result in a decrease in oxygen barrier properties.

[0064] Preferably, the concentration of the water dispersible polymer is from 1 to 20% by weight, for example from 5 to 15% by weight, for example from 7 to 13% by weight, most preferably from 9 to 13% by weight, for example 10% by weight.

[0065] The water-dispersible polymer of the first dry layer may be any suitable water-dispersible polymer and / or renewable non-fossil-based polymer. In one embodiment, the polymer of the pre-coating may be selected from the group consisting of polyvinyl alcohol (PVOH, PVAL), polyethylene vinyl alcohol (EVOH, EVAL), water-dispersible "polyolefins", such as copolymers with ethylene and monomers having carboxylic acid functionality, such as ethylene acrylic acid copolymer (EAA), 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 / microfibril cellulose (NFC / MFC / CNF) and nanocrystalline cellulose (NCC / CNC).

[0066] In a further embodiment, the pre-coating may comprise a renewable polymer or material selected from the group consisting of 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 / microfibril cellulose (NFC / MFC / CNF) or nanocrystalline cellulose (NCC / CNC).

[0067] Suitable starch materials, or derivatives of starch, may be, for example, cold water soluble starch, oxidized starch, cationic starch, hydroxypropylated starch, and the like.

[0068] The above materials are also applicable when a reducing agent-free pre-coating is used in addition to the first dry layer, further possibilities regarding reducing agent-free pre-coatings are described below.

[0069] Preferably, the thickness of the applied and dried first dry layer is 0.5 to 3 μm, more preferably 2 μm.

[0070] In one embodiment, the concentration of graphene oxide in the aqueous composition is 0.1-15 wt%, for example, 0.5-15 wt%, for example, 0.5-10 wt%, for example, 0.5-6 wt%, for example, 0.5-3 wt%, for example, 1-2 wt%. If the concentration is less than 0.5 wt%, it may be difficult to apply a sufficient amount of graphene oxide onto the substrate web, and the applied coating may not exhibit sufficient oxygen barrier properties, but it is possible to apply it as thin as 0.1 wt% if the need for barrier properties is low. On the other hand, if the concentration is higher than 6 wt%, for example, higher than 10 wt%, for example, higher than 15 wt%, the wet coating of the graphene oxide material may be unnecessarily thick and contain a lot of water between the flakes and platelets of the composition, making the applied coating difficult to dry. If the concentration of graphene oxide is higher than 3 wt%, it may be difficult to dry the coating, and if it is higher than 6 wt%, it may be even more difficult to apply. However, because aqueous compositions of graphene oxide exhibit shear thinning behavior, it may be possible to apply thicker compositions at faster coating speeds with reasonable coating thickness and good layer formation.

[0071] Aqueous graphene oxide compositions essentially comprise only graphene oxide and water, preferably consisting of these two materials. The composition is substantially free of other polymers, i.e. binders and similar components. It preferably comprises only additives such as dispersants, antifoamers, etc. up to 5% by weight, e.g. up to 3% by weight. Thus, an aqueous graphene oxide composition may comprise 0.1-15% by weight graphene oxide, 0-5% by weight additives, and 85-99.9% by weight water. The presence of polymers between reduced graphene oxide flakes may be disadvantageous, for example in induction sealing.

[0072] In one embodiment, the aqueous composition of graphene oxide is coated at a wet thickness of 10-500 μm, preferably 10-400 μm. Below 10 μm, the coating may not provide sufficient oxygen barrier properties, and above 400 μm, the amount of water to dry out of the coating or the viscosity of the thick coating composition may be impractical or impossible to handle. 200 μm is the preferred wet thickness.

[0073] The drying steps c) and f) of the process of the invention may be carried out by forced evaporation.

[0074] Furthermore, the substrate may be transported at a constant speed. This is an important prerequisite in the coating operation in order to apply an optimal and reliable amount of coating. Furthermore, industrially feasible web and coating speeds may be 100 m / min, e.g. 200 m / min, e.g. 300 m / min, e.g. 400 m / min, depending on the dimensions of the drying capacity of the coating line. Drying is preferably performed by convection of hot air, which may be combined with irradiation by infrared heaters. Drying of the wet coating takes place in a maximum of a few seconds during the passage through a drying station, which may be several meters long, such as at least 5 meters, at least 10 meters, at least 15 meters, at least 20 meters, etc., depending on the temperature of the substrate surface and the advancement speed of the web in the coating line.

[0075] Graphene oxide may thus be dispersed in water and applied by an aqueous "dispersion coating" process or a so-called "liquid film coating" process, with fully aqueous dispersions being preferred from the standpoint of environmental sustainability and operational safety.

[0076] The aqueous composition may be applied to the substrate web in the form of an ink and / or dispersion coating.

[0077] Thus, suitable application methods may be suitable printing methods such as flexographic printing, gravure printing, screen printing, inkjet printing, and various dispersion coating methods such as gravure roll coating, slot coating, doctor blade coating, reverse roll coating, wire bar coating, lip coating, air knife coating, curtain coating and spray coating, dip coating, and brush coating. By these printing or coating methods, a suitable dry material thickness of the graphene oxide coating layer of 0.1 to 10 μm, for example, 0.5 to 8 μm, for example, 0.5 to 6 μm, for example, 0.5 to 4 μm, for example, 0.5 to 3 μm, for example, 0.5 to 2.5 μm may be applied.

[0078] To obtain a larger thickness, several successive coating processes to form a thick layer of graphene oxide may be necessary. For gas barrier coating purposes, applying 0.1-3 μm, e.g., 0.5-2.5 μm, e.g., about 2 μm, of dried graphene oxide is sufficient. For other purposes, such as conductive coating, thicker coatings are suitable, but perhaps only in selected localized areas of the substrate web, rather than coatings covering the entire surface.

[0079] Although the experiments of the present invention were carried out by gravure coating, it is believed that any of the above liquid film coating methods would be suitable to provide a good gas barrier coating.

[0080] The added amount of a dispersion stabilizer or similar additive for dispersion coatings may also be included in the aqueous graphene oxide composition, preferably in an amount less than about 1 wt % based on the dry coating.

[0081] The total dry content of the aqueous composition comprising graphene oxide is preferably 0.5-15 wt%, such as 0.5-10 wt%, such as 0.5-8 wt%, such as 0.5-6 wt%. At lower dry contents, the quality of the gas barrier layer formation is likely to be insufficient, and as a result the gas barrier properties obtained from the dried coating may be less than satisfactory.

[0082] In one embodiment, the graphene oxide coating may be applied as two partial layers in two successive steps with intermediate drying. When applied as two partial layers, each layer preferably has a thickness of 0.1 to 1.5 g / m 2 , for example, 0.5 to 1 g / m 2 , resulting in a higher quality total layer from a smaller amount of liquid gas barrier composition. As an example, if the total thickness of dried graphene oxide is about 2 μm, the total thickness after reduction to reduced graphene oxide is about 0.5 μm (500 nm). It has been evaluated that graphene oxide is easily reduced when graphene oxide is applied and dried twice in succession, as is the case with a single dried application of graphene oxide. Successively applied and dried coatings of graphene oxide overlap defect-free portions of another coating in most cases, potentially covering defects in each coating. In this way, the entire layer of applied graphene oxide is substantially defect-free.

[0083] If a reducing agent-free additional pre-coating layer is used, it may be a polyolefin such as polyethylene and may be melt extrusion coated (optionally oxidizing the surface using corona pre-treatment or elevated temperature). In one embodiment, the reducing agent-free additional pre-coating polymer is a very thin coating of polyethylene, which allows for clean separation of the reduced graphene oxide coating from the paper or paperboard substrate and allows the recycled fibers to be substantially free of the reduced graphene oxide material.

[0084] An additional protective polymer coating of low density polyethylene may be applied over the first and second dry layers for protection when the barrier-coated substrate web is further wound into a roll or laminated into a multi-layer material structure. This encapsulation of the reduced graphene oxide between layers of polyethylene may keep the reduced graphene oxide separated from the fiber fraction in subsequent recycling operations.

[0085] The first and second dry layers may alternatively or additionally be coated with a thin protective coating of a thermoplastic polymer such as a dispersion coatable modified polyethylene (such as EAA described above) or other water soluble or water dispersible polymer. This may be done on the same dispersion coating line used to apply the first and second dry layers. The web may be further laminated or melt extrusion coated to an adjacent polymer layer, for example a polyolefin layer such as low density polyethylene. Such further coating and / or lamination may be performed before or after fully reducing the graphene oxide of the first dry layer of graphene oxide. In one embodiment, the first protective coating is applied by dispersion coating on the same dispersion coating line used to apply the first and second dry layers, and then further laminate layers are added by extrusion coating or lamination after the web is wound into a roll.

[0086] A carton-based laminate packaging material for liquid food packaging comprises a bulk layer of paper or paperboard, a first outermost protective material layer, a second innermost liquid-tight heat-sealable material layer, and a barrier-coated substrate web disposed inside the bulk layer of paper or paperboard, toward the inside of a packaging container made from the packaging material, and between the bulk layer and the innermost layer.

[0087] The paper or paperboard bulk layer used in the present invention typically has a thickness of about 100 μm to about 600 μm and a surface weight of about 100 to 500 g / m 2 and preferably about 200 to 300 g / m 2and may be any conventional paper or paperboard of suitable packaging quality.

[0088] For low-cost, long-term, aseptic packaging of liquid foods, thinner packaging laminates with thinner paper core layers may be used. Packages made from such packaging laminates resemble pillow-shaped flexible pouches rather than collapsible. Papers suitable for such pouch packages are typically about 50 to about 140 g / m 2 , preferably about 70 to about 120 g / m 2 , more preferably about 70 to about 110 g / m 2 Since the barrier-coated substrate web in the present invention may itself provide some stability to the laminate material, the paper layer corresponding to the "bulk" layer may be even thinner and interact with the barrier-coated substrate web in a sandwich structure to produce a laminate packaging material with the desired mechanical properties.

[0089] The thickness of the dry layer from the layered particles or flakes of reduced graphene oxide may be from 50 to 1000 nm, such as 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.

[0090] The barrier coated substrate web may be bonded to the bulk layer by an intermediate adhesive or thermoplastic polymeric bonding layer, thereby bonding the uncoated surface of the barrier coated substrate web to the bulk layer. According to one embodiment, the bonding layer is a polyolefin layer, such as a layer of a polyethylene-based polyolefin copolymer or blend, particularly one containing a majority of ethylene monomer units. The bonding layer may be bonded to the barrier coated substrate by melt extrusion laminating the bonding polymer layer between the web of the bulk layer and the substrate web, and simultaneously pressing the three layers together while advancing through a laminating roller nip, providing a laminate structure by extrusion lamination.

[0091] In another embodiment, the barrier coated substrate web may be bonded to the bulk layer by wet applying an aqueous dispersion of an adhesive composition containing an adhesive polymer binder to one of the surfaces of the web to be laminated and pressing the two paper webs together while advancing through a laminating roller nip to provide a wet laminate structure. The water content of the aqueous adhesive composition partially evaporates over time during the subsequent lamination process. Therefore, no forced drying step is necessary. The adhesive polymer binder is selected from the group consisting of acrylic polymers and copolymers, starch, cellulose and polysaccharide derivatives, vinyl acetate and vinyl alcohol polymers and copolymers. To achieve the best environmental and sustainability profile, adhesive binders derived from plant or non-fossil sources are preferred.

[0092] Suitable thermoplastics for the outermost and innermost heat-sealable liquid-tight layers may be polyolefins such as homopolymers or copolymers of polyethylene and polypropylene, preferably polyethylene, more preferably polyethylene selected from the group consisting of low density polyethylene (LDPE), linear LDPE (LLDPE), metallocene catalyzed linear low density polyethylene (m-LLDPE) and blends or copolymers thereof. According to one embodiment, the outermost liquid-tight heat-sealable layer is LDPE and the innermost liquid-tight heat-sealable layer is a blend composition of m-LLDPE and LDPE for optimal lamination and heat-sealing properties.

[0093] The outermost layer is usually applied to a thickness of 5 to 20 μm, for example, 10 to 15 μm. The innermost layer may be applied to a thickness in the range of 10 to 50 μm, for example, 10 to 40 μm, for example, 10 to 30 μm, for example, 10 to 25 μm.

[0094] The same thermoplastic polyolefin-based materials, particularly polyethylene, as listed for the outermost and innermost layers are also suitable for the adhesive layer inside the laminate material, i.e. between the bulk or core layer, such as paper or paperboard, and the barrier film or sheet. In one embodiment, the thermoplastic adhesive layer may be a polyethylene layer, such as a low density polyethylene (LDPE) layer. It may be applied in an amount typically between 10 and 25 μm, such as between 10 and 20 μm, for example between 10 and 15 μm.

[0095] In a further embodiment, the second innermost liquid-tight heat-sealable polyolefin layer is a pre-manufactured film containing 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 film blowing and film casting operations, and optionally the subsequent film orientation operation steps, the polymer of such a film acquires properties different from those obtained from the (co)extrusion coated polyolefin layer. Such pre-manufactured polymer films contribute to the mechanical robustness of the laminate packaging material, and to the mechanical strength and package integrity of the packaging container formed and filled from the laminate packaging material.

[0096] According to an alternative embodiment, suitable bonding or joining layers in the interior of the laminate material, for example between the bulk or core layer and the barrier-coated substrate web, or between the outer heat-sealable layer and the barrier-coated substrate web, are also so-called adhesive thermoplastic polymers, for example modified polyolefins, mainly based on LDPE or LLDPE copolymers or monomer units containing functional groups such as carboxylic acid or glycidyl functional groups, i.e. graft copolymers, such as (meth)acrylic acid monomers or maleic anhydride (MAH) monomers, i.e. ethylene acrylic acid copolymer (EAA) or ethylene methacrylic acid copolymer (EMAA), ethylene-glycidyl (meth)acrylate copolymer (EG(M)A) or MAH-grafted polyethylene (MAH-g-PE). Another example of such modified or adhesive polymers are so-called ionomers or ionomeric polymers. Preferably, the modified polyolefins are ethylene acrylic acid copolymer (EAA) or ethylene methacrylic acid copolymer (EMAA).

[0097] If necessary, the surface of the substrate web may be pretreated by an oxidation treatment such as a corona plasma treatment or an ozone treatment in order to improve the adhesive strength with the graphene oxide layer or reduced graphene oxide layer.

[0098] The laminated packaging material produced in accordance with the above provides good adhesion between adjacent layers in the laminate structure, and good qualities of each and every barrier coating and barrier pre-coating, and in combination, to provide good integrity when transformed into a filled packaging container.

[0099] According to further embodiments, a packaging container formed from the laminated packaging material can be partially sealed, filled with a liquid or semi-liquid food product, and then sealed by sealing the packaging material to itself, optionally in combination with a plastic opening or top of the package.

[0100] In conclusion, the barrier coated substrate web produced by the method of the present invention and the resulting laminate packaging material may provide a robust and reliable package with excellent oxygen gas barrier properties for shelf-stable liquid food packaging. This laminate packaging material structure works well for folding and forming into a formed package due to both the improved adhesion between the substrate and the barrier material coating and the improved contribution to gas barrier properties from the barrier coated substrate itself, which is also believed to be due to the improved bonding cohesion and adhesion between the pre-coating layer and the barrier coating layer in the barrier coated cellulosic substrate.

[0101] ( Examples and Description of the Preferred Embodiments ) Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. [Brief description of the drawings]

[0102] [Figure 1a] FIG. 1 shows a schematic cross-sectional view of one embodiment of a substrate coated with reduced graphene oxide according to the present invention. [Figure 1b] 1A-1D show schematic cross-sectional views of different embodiments of substrates coated with reduced graphene oxide according to the present invention; [Figure 2a] FIG. 1b shows a schematic cross-sectional view of a laminated packaging material according to the present invention comprising a substrate coated with reduced graphene oxide of FIG. [Figure 2b] FIG. 1c shows a schematic cross-sectional view of a laminated packaging material according to the present invention comprising a substrate coated with reduced graphene oxide of FIG. 1b. [Diagram 3] FIG. 1 is a schematic diagram showing a method for dispersion-coating an aqueous composition of graphene oxide onto a substrate. [Figure 4a] FIG. 1 is a schematic diagram illustrating a method of melt extrusion laminating two webs of material with an intermediate thermoplastic polymer. [Figure 4b]FIG. 2 is a schematic diagram illustrating a method of melt (co)extrusion coating layers of thermoplastic polymers onto a web substrate to form, for example, the innermost and outermost layers of the packaging laminate of the present invention. [Figure 5a] FIG. 2 is a diagram showing a typical example of a liquid carton package made from a laminated packaging material according to the present invention. [Figure 5b] FIG. 2 is a diagram showing a typical example of a liquid carton package made from a laminated packaging material according to the present invention. [Figure 5c] FIG. 2 is a diagram showing a typical example of a liquid carton package made from a laminated packaging material according to the present invention. [Figure 5d] FIG. 2 is a diagram showing a typical example of a liquid carton package made from a laminated packaging material according to the present invention. [Figure 6] FIG. 1 illustrates how liquid carton packages are produced from packaging laminate in a continuous roll-fed, form, fill and seal process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0103] ( Example 1 ) A solution of 10% by weight of PVOH and 4% by weight of vitamin C (ascorbic acid) was applied to a polyethylene pre-coated paperboard (flexural stiffness 80 mN, basis weight 200 g / m 2 The solution was applied onto an advancing web of 1000 .mu.m thick using a Hirano lab-coater at a wet thickness of approximately 20 .mu.m.

[0104] The water in the applied coating composition was evaporated off the surface by air convection in a hot air dryer at a web surface temperature of about 60°C for about 1 minute to provide a smooth surface (first dry layer / pre-coating layer) for the graphene oxide solution in the next step. The calculated dry coating thickness is 2.8 μm. The smooth surface helps the exfoliated graphene oxide to orient in the plane of the substrate.

[0105] A 1 wt% aqueous dispersion of monolayer flakes of graphene oxide (at least 95% exfoliated pure quality of Graphenea or LayerOne) was continuously stirred until the moment of application on the substrate. The well-dispersed aqueous composition was applied to a wet thickness of about 200 μm on an advancing web of paperboard precoated with polyethylene and the above-mentioned dried PVOH / vitamin C solution using a Hirano Labcoater. The water in the applied coating composition was evaporated from the surface by air convection in a hot air dryer at a web surface temperature of about 60 °C for about 1 min. As a result, the dry coating thickness of the graphene oxide (second dry layer) applied on the PE / PVOH / vitamin C coated paper was measured to be about 2 μm. The web thus coated with graphene oxide was cooled to room temperature and finally wound on a reel.

[0106] The graphene oxide coated substrate showed a light brown color immediately after application to the PVOH / vitamin C surface. The color content, or L * a * b * The value was measured and after a few seconds it was 20 * 2 * -0.3 * The value of L after 1 hour was measured. * The value dropped to 16, and after 3 days it was 14. The a value after 1 hour was 0.25 and the b value was -1.36, and after 3 days the value was a = -0.21 and b = -1.1. * a * b * The value was measured at 40 * 17 * 36 * The color of the solution of graphene oxide and reducing agents such as vitamin C changed from brown to black, indicating the change from graphene oxide to reduced graphene oxide.

[0107] Substrates thus coated with a thin dry coating of layered reduced graphene oxide exhibited a 1cc / m2 dry coating at 1 atm, 23°C / 50% RH, and 21% oxygen for 24 hours, as measured in an Ox-Tran 2 / 21 Mocon instrument. 2 It exhibits an oxygen permeability of less than 1000 .

[0108] The thickness of the graphene oxide layer becomes thinner as it is reduced (to about 250 nm).

[0109] It is also possible to increase the reduction rate by increasing the temperature.

[0110] Therefore, the Williams-Landel-Ferry model (WLF for short) was applied to the reduction reaction, which could be accelerated and controlled by increasing the temperature and / or reaction time. Most importantly, at the interface between the dried graphene oxide coating and the PVOH / ascorbic acid, the reduction reaction continues until it reaches a full degree of conversion, even after the coated web is dried and wound on a reel for transportation and storage.

[0111] Since a reaction time of 2 hours is nearly impossible to achieve in industrial coating or manufacturing processes, this result is advantageous as it means that the reduction of the applied graphene oxide coating to graphene may continue to completion after the coating operation, and therefore may be achieved with simple logistical planning for long-term storage.

[0112] It is also possible to laminate the barrier-coated substrate web to further layers to form the finished packaging material before planned storage of the reels. In the case of lamination methods involving heat supply, such as polymer melt extrusion coating or polymer melt extrusion lamination, a further acceleration of the reduction reaction can be advantageously and conveniently achieved. Depending on the practical situation, further intermediate storage can be planned, partly during transport, partly before shipment and / or partly after shipment at the customer's premises.

[0113] Additionally, regarding the attached diagram: One embodiment of a barrier coated substrate web 10a of the present invention is shown in cross section in Figure 1a. The substrate 11a is a polyethylene terephthalate (PET) film having a thickness of 36 μm. Its oxygen transmission rate (OTR) is approximately 30 cc / m 2 , 24 hours, 23°C / 80% RH, 100% oxygen.

[0114] The PET film is provided with a dry precoat 12a (first dry layer) of ascorbic acid and PVOH, applied by aqueous dispersion coating, and then heated and dried to evaporate the water. Furthermore, the substrate thus coated has a second dry layer 13a of graphene oxide applied on the dry precoat layer as an aqueous dispersion. The dry weight of the graphene oxide thus applied is about 1.3 μm. The second dry layer 13a is then heated and dried to evaporate the water. The substrate web thus dried and coated may be further heat treated for a period of time or may simply be stored at ambient temperature for at least two weeks, after which the dry barrier coating layer of graphene oxide is reduced as far as possible to reduced graphene oxide, i.e. ideally to graphene. After the reduction reaction is as complete as possible, the thickness of the dry barrier coating 13a is significantly reduced.

[0115] Furthermore, the robustness of the reduced graphene oxide coating can be demonstrated by folding and unfolding the coated material once, twice and up to 20 times (using a similar principle to the Flex-Gelbo test). Folding had little effect on the fracture of the reduced graphene oxide. Furthermore, reduced graphene oxide is not sensitive to moisture, so it does not lose its barrier properties at high humidity, as, for example, PVOH does.

[0116] In Figure 1b, a different embodiment of the barrier coated substrate web 10b of the present invention is shown in cross section. The substrate 11b is 50 g / m 2, a thin paper substrate with a thin precoat 14 of low density polyethylene, applied by dispersion coating and then dried, resulting in a final dry thickness of about 1 μm. On the dried surface of the polyethylene precoat is applied a precoat / first dry layer 12b of ascorbic acid and PVOH, applied in the same type and in the same manner as in FIG. 1a. The substrate thus coated is then further coated with a second dry layer 13b of graphene oxide, applied on the first dry layer, in a manner similar to FIG. 1a, and then similarly dried. A further protective polymer coating 15b of low density polyethylene may be applied on the reduced graphene oxide layer for protection when the barrier-coated substrate web is further wound into a roll. After sufficient time, when the graphene oxide of layer 13b has been reduced (i.e. after 2 weeks of dry storage in the dark or on a roll), the thickness of the resulting barrier coating with reduced graphene oxide was finally about 500 nm. The OTR was 1 cc / m after 2 days (the time it takes to prepare the sample for OTR measurement). 2 , 24 hours, 1 atmosphere, 23℃ / 50%RH, oxygen less than 21%.

[0117] Although not shown, a protective polymer coating 15a as in FIG. 1b may also optionally be applied over the graphene oxide layer 13a of FIG. 1a.

[0118] In FIG. 2a, a laminate packaging material 20a for liquid carton packaging is shown, which has a bending force of 80 mN and a compressibility of about 200 g / m 2The packaging laminate comprises a bulk layer 21 of paperboard having a basis weight of about 100 g / m2 and an outermost liquid-tight, heat-sealable layer 22 of polyolefin applied to the outside of the bulk layer 21, said layer 22 being directed towards the outside of the packaging container produced from the packaging laminate. This layer 22 is transparent to allow a printed decorative pattern 27 applied to the bulk layer of paper or paperboard to be visible on the outside, thereby informing the consumer of the package contents, package brand and other information targeted at the consumer in retail establishments and food stores. The polyolefin of the outer layer 22 is a conventional low density polyethylene (LDPE) of heat-sealable quality, but may also include more similar polymers including LLDPE. The coating weight is about 12 g / m2. 2 The innermost liquid-tight heat-sealable layer 23 is located opposite the bulk layer 21, this layer being directed towards the inside of the packaging container produced from the packaging laminate. The innermost heat-sealable layer 23, which forms a strong transverse heat seal of the liquid packaging container produced from the laminate packaging material, thus comprises a combination of one or more polyethylenes selected from the group consisting of LDPE, linear low density polyethylene (LLDPE) and LLDPE produced by polymerizing ethylene monomers with C4-C8, more preferably C6-C8, α-olefin alkylene monomers in the presence of a metallocene catalyst, so-called metallocene-LLDPE (m-LLDPE). It has a density of about 22 g / m 2 is applied in an amount of

[0119] The bulk layer 21 is laminated to the barrier coated PET film substrate 25a; 10a of FIG. 1a by an intermediate tie layer 26a of low density polyethylene (LDPE). The intermediate tie layer 26a is formed by means of melt extrusion as a thin polymer melt curtain between the two webs, and the bulk layer and the barrier coated PET substrate are laminated together when all three layers pass through a chilled press roller nip. The thickness of the intermediate tie layer 26a is 12-18 μm, for example 12-15 μm.

[0120] The innermost heat-sealable layer 23 comprises one or more partial layers of the same or different types of LDPE or LLDPE or blends thereof, and is attached to the surface of the barrier layer of the barrier coated PET film substrate 10a; 25a by an intermediate coextrusion tie layer 24, e.g., ethylene acrylic acid copolymer (EAA), which adheres the innermost heat-sealable layer to the barrier surface of the barrier coated substrate web 10a when the layers are applied together in a single melt coextrusion coating process.

[0121] Alternatively, the barrier coated PET film substrate 10a; 25a may be rotated in the opposite direction within the laminate, i.e., the barrier coating layer may face the bulk layers and the outside of the laminate.

[0122] FIG. 2b shows a different laminate packaging material 20b of the present invention for liquid carton packaging, which has a similar layer structure as FIG. 2a, except for the barrier coating substrate 25b, which is configured differently but is located in the same place in the laminate material.

[0123] The bulk layer 21 is laminated to the uncoated side of the barrier-coated paper substrate 25b; 10b of FIG. 1b by wet lamination with an intermediate adhesive layer 26b of a thin layer of adhesive polymer, obtained by applying an aqueous dispersion of polyvinyl acetate adhesive to one of the surfaces to be bonded to each other and then pressing them together in a roller nip. This lamination step does not require an energy-consuming drying operation required to promote the evaporation of water, but is carried out in an efficient cooling or cold lamination step at industrial speeds. The dry coating weight of the intermediate adhesive layer 26b is 3-4 g / m 2 This requires no drying or evaporation operations.

[0124] Thus, the amount of thermoplastic polymer in this laminate layer can be significantly reduced as compared to the conventional polyethylene melt extrusion laminate adhesive layer illustrated in Figure 2a as layer 26a.

[0125] The innermost heat sealable layer 23 is formed by an intermediate coextrusion tie layer, e.g., ethylene acrylic acid copolymer (EAA), at about 22 g / m2 on the barrier coated surface of the paper substrate. 2 which adheres the innermost heat-sealable layer 23 to the barrier-coated paper substrate 10b when the layers are applied together in a single melt co-extrusion coating step.

[0126] Alternatively, the innermost heat sealable liquid tight layer may be a prefabricated blown film 23b comprising LDPE or LLDPE polymers in any blend, which is laminated to the barrier coated paper substrate, i.e., to its surface. The barrier coating may be laminated to the barrier coated paper substrate, i.e., to its surface, by an intermediate melt extruded laminate tie layer 24b, which may comprise a tie layer of EAA, or a simpler tie layer of LDPE, that is thicker than layer 24 used in Figure 2a. The thickness of the blown film 23b is 12 μm, but may be up to 20 μm.

[0127] In an alternative embodiment, the pre-fabricated blown film 23b is laminated by a separate wet lamination step with a water-based adhesive of acrylic (co)polymer adhesive layer 24b' at ambient (low) temperature with a thickness of 3-4 g / m 2 is laminated to the metallized coating.

[0128] Further embodiments are also disclosed herein that have all the features described and combine them with the features of a barrier coated paper substrate 25b and a heat sealable innermost layer configuration 23b' having the melt extruded bulk layer laminate layer 26a of FIG. 2a, but instead applied by means of either melt extrusion lamination with layer 24b, as described in connection with FIG. 2b, or by means of wet lamination of a prefabricated film 24b' as described in connection with FIG. 2b.

[0129] A further embodiment is also disclosed herein that combines a thin wet water-based adhesive dispersion laminate layer 26a of FIG. 2b with conventional melt coextrusion coated inner layers 24 and 23.

[0130] In FIG. 3, the process of aqueous dispersion coating 30a is shown, which may be used to apply a pre-coating / first drying layer 12a; 12b and a further graphene oxide barrier coating / second drying layer 13a; 13b. A paper substrate web 31a (e.g. paper 11 in FIG. 1a) is fed to a dispersion coating station 32a, where an aqueous dispersion composition is applied by a roller to the top surface of the substrate surface. Because the dispersion composition has a high aqueous content, there is a lot of water on the wet-coated substrate that needs to be dried and evaporated away by heat to form a continuous pre-coating. Drying is performed by a hot air dryer 33a, which evaporates and removes moisture from the substrate surface by air convection. The substrate temperature passing through the dryer is kept constant at 60-80°C. Alternatively, the drying may be partially assisted by radiation heat from infrared IR lamps in combination with hot air convection drying.

[0131] The process shown in Figure 3 can then be repeated to form a continuous graphene oxide coating with homogeneous and uniform quality in terms of barrier and surface properties, i.e. uniformity and wettability.

[0132] The resulting barrier precoated paper substrate web 34a is cooled and wound onto a reel for intermediate storage and subsequent lamination operations.

[0133] FIG. 4a shows the process of the lamination step in the manufacture of the packaging laminate 20a or 20b of FIG. 2a and FIG. 2b, respectively, in which a bulk layer 21; 43 is laminated to the barrier coated substrate web 34a; 10a; 10b of FIG. 1a or FIG. 1b (i.e. 25a or 25b of FIG. 2a and FIG. 2b, respectively).

[0134] As explained in relation to Figures 2a and 2b, the bulk layer paperboard 21 may be laminated to the barrier coating substrate 10; 25a; 25b by melt extrusion lamination as shown in this figure, or by wet cold dispersion adhesive lamination, although the latter method is not shown. For example, a molten polymer curtain 44 of LDPE is fed into the nip of the lamination rollers 45, and the two webs 34a and 43 are also fed into the same lamination nip and bonded to each other by the extruded bond layer 44 of LDPE. In this way, the three layers are pressed together and bonded in the nip 45 formed between the press roller and the cooling roller, and the laminate material is cooled to properly solidify the extruded bond layer 44 of LDPE. The resulting laminate material is wound on a reel for intermediate storage or sent directly to a subsequent lamination operation.

[0135] In Figure 4b, a pre-laminate 49a of paperboard 31b and barrier web 34a is fed to a further lamination station 40b either directly from the lamination station 40a of Figure 4a or from engagement and unwinding with an intermediate storage reel.

[0136] The non-laminate or printed side of the bulk layer 21 is bonded at a chill roller nip 48a to a molten polymer curtain 46a of LDPE forming the outermost layer 22 of the laminate material, which is extruded from an extruder feedblock and die 47a. The coated paper pre-laminate web, with the outermost layer 22 printed or outward, then passes through a second extruder feedblock, die 47b and lamination nip 48b, where the molten polymer curtain 46b is bonded to and coated on the other side of the pre-laminate, i.e., the uncoated inner side of the barrier-coated substrate webs 10a; 10b; 25a; 25b. In this manner, the heat-sealable innermost layer 23 is coextrusion coated onto the inside of the barrier-coated substrate web to form the finished laminate package 49b, which is ultimately wound up on a storage reel, not shown.

[0137] These two coextrusion steps in laminating roller nips 48a and 48b may alternatively be performed as two successive steps in reverse order.

[0138] According to another embodiment, one or both of the outermost layers may instead be applied at a pre-lamination station, in which case a co-extrusion coating layer may first be applied to the outside of the (printed) bulk paperboard layer or to the inside of the barrier coated paper substrate, and then the two pre-lamination paper webs may be bonded together as described above in relation to FIG. 4a.

[0139] According to a further embodiment, the innermost layer of the liquid-tight, heat-sealable thermoplastic resin layer may be applied in the form of a prefabricated film, which is laminated to the barrier-coated substrate 10a; 10b.

[0140] As described in connection with Figures 2a and 2b, the innermost prefabricated film 23 may be laminated to the barrier coating substrate 10a; 10b by wet, cold dispersion adhesive lamination, or melt extrusion lamination.

[0141] FIG. 5a shows an embodiment of a packaging container 50a made from a packaging laminate according to the invention. This packaging container is particularly suitable for beverages, sauces, soups, etc. Typically, such packages have a volume of about 100-1000 ml. It may be of any shape, but is preferably brick-shaped, with longitudinal seals 51a and transverse seals 52a, respectively, and optionally an opening device 53. In another embodiment, not shown, the packaging container may be wedge-shaped. To obtain such a "wedge shape", only the bottom of the package is folded and formed such that the transverse heat seal at the bottom is hidden under a triangular corner flap that is folded and sealed against the bottom of the package. The transverse seal at the top is left unfolded. Thus, even a packaging container that is only partially folded is easy to handle and dimensionally stable enough to be placed on a grocery store shelf or on a flat surface.

[0142] Figure 5b shows an alternative packaging container 50b made from an alternative packaging laminate according to the invention. The alternative packaging laminate is thinner by having a thinner paper bulk layer and therefore is not dimensionally stable enough to form a parallelepiped or wedge shaped package and is not folded and formed after the transverse seal 52b. The package is in the form of a pillow-shaped pouch and is sold and distributed in this form.

[0143] 5c shows a gable-top package 50c folded and formed from a pre-cut sheet or blank of a laminated packaging material including a bulk layer of paperboard and a barrier-coated substrate of the present invention. Flat-top packages may also be formed from similar blanks of material.

[0144] Figure 5d shows a bottle-like package 50d which is a combination of a sleeve 54 formed from a pre-cut blank of the laminated packaging material of the present invention, and a top 55 formed by injection molding of plastic in combination with an opening device such as a screw cork. Packages of this kind are sold, for example, under the trade names Tetra Top® and Tetra Evero®. These particular packages are formed by attaching a top 55 with an opening device attached in a closed position to a tubular sleeve 54 of laminated packaging material, sterilizing the bottle-top capsule thus formed, filling it with a food product, and finally folding and sealing the bottom of the package.

[0145] 6 illustrates the principle described in the introduction of this application, i.e. a web of packaging material is formed into a tube 61 by overlapping the longitudinal edges 62, 62' of the web and heat sealing them together to form an overlap joint 63. The tube is continuously filled (64) with the liquid food product to be filled and divided into individual filled packages by repeated double transverse seals 65 of the tube at predetermined distances from each other below the level of the filled contents in the tube. The packages 66 are separated by cutting between the double transverse seals (top seal and bottom seal) and finally formed into the desired geometric shape by forming folds along crease lines prepared in the material.

[0146] In a preferred embodiment, the use of a pre-coating of PVOH and ascorbic acid provides several advantages. - Application of ascorbic acid in combination with PVOH improves reducibility due to the slow release of ascorbic acid which migrates to the wet graphene oxide layer. Coating with aqueous ascorbic acid solutions without PVOH can result in the formation of crystals, especially at higher concentrations and / or if the composition is applied directly to the substrate. Such crystals can immediately cause strong reduction and, as a result, undesirable aggregation of the (reduced) graphene oxide, since it becomes less dispersible upon reduction (graphene oxide is hydrophilic, whereas reduced graphene oxide is hydrophobic). - It was found that the reduction was faster than when an initial dried layer of graphene oxide was followed by an aqueous ascorbic acid solution, as described in the unpublished continuing European application 21216620, which has priority to EP20216735.9. - When ascorbic acid is applied in combination with PVOH, the adhesion between the layers is also improved, even if the reducing agent composition is not applied directly to the substrate, due to the crystallization mentioned above affecting adhesion. The dried PVOH / ascorbic acid layer shows improved adhesion to the reduced graphene oxide compared to the ascorbic acid structure with crystals. - Applying PVOH in a pre-coating step can provide a smooth surface for coating the graphene oxide, improving the alignment of the graphene oxide flakes and therefore the oxygen barrier properties. - Providing PVOH in a pre-coating step means that the final packaging laminate has a reduced graphene oxide barrier layer on the liquid content side of the PVOH pre-coat layer. Reduced graphene oxide is an excellent water vapor barrier layer. PVOH is a good oxygen barrier material, but is sensitive to moisture as explained above. With the inventive arrangement, the PVOH is protected from moisture by the reduced graphene oxide layer, further contributing to the oxygen barrier properties. As a result, the amount of graphene oxide can be reduced while maintaining the same oxygen barrier properties.

[0147] Finally, it should be noted that the invention is not limited to the embodiments shown and described above, but that various modifications may be made within the scope of the appended claims.

Claims

1. A method for producing an oxygen barrier material for a packaging material (20a; 20b) by coating a substrate web (10a; 10b) with a reduced graphene oxide layer (13a; 13b), comprising the steps of: a) providing and transporting said substrate web; b) coating the substrate web with a first layer of an aqueous composition comprising a reducing agent and a water-dispersible polymer while conveying the substrate web (32a); c) drying (33a) said first layer by forced evaporation to form a first dry layer (12a; 12b) comprising said reducing agent and said water-dispersible polymer; d) providing an aqueous composition comprising graphene oxide, the composition comprising graphene oxide monolayer flakes and multilayer graphene oxide platelets, the graphene oxide monolayer flakes being stacked up to 20 pieces, e.g., 2-10 pieces, e) coating the aqueous graphene oxide composition onto the substrate web while the substrate web is being transported; f) drying the aqueous graphene oxide wet coating on said substrate web by forced evaporation to obtain a second dry layer of layered graphene oxide particles or flakes (13a; 13b); g) reducing the graphene oxide of the second layer with the reducing agent of the first dry layer to form a barrier coated substrate web having a dry layer of reduced graphene oxide; Equipped with said steps c) and d) are carried out before or after said steps d), e) and f), and said first drying layer (12a; 12b) or said second drying layer (13a; 13b) is formed first; method.

2. the steps b) and c) are performed before the steps d), e) and f), the first dry layer is a pre-coating layer, and the second dry layer is formed on the pre-coating layer; The method of claim 1.

3. the method further comprising a step i) performed before or after step g) of coating or laminating the barrier coated substrate web to a further layer of polymer to coat the first drying layer and the second drying layer; The method of claim 2.

4. and further comprising a step h) performed before or after step g) of winding the coated and dried barrier coated substrate web onto a reel. The method according to claim 2 or claim 3.

5. the reducing agent is selected from the group consisting of sodium citrate, ascorbic acid (vitamin C), lemon juice, vinegar and green tea; The method according to any one of claims 2 to 4.

6. The reducing agent is ascorbic acid. The method according to any one of claims 2 to 5.

7. the concentration of the reducing agent in the aqueous composition is 2 to 10% by weight, for example 2 to 6% by weight, for example 2 to 5% by weight; The method according to any one of claims 2 to 6.

8. the water-dispersible polymer is selected from the group consisting of polyvinyl alcohol, polyethylene vinyl alcohol, water-dispersible polyolefins such as copolymers with ethylene and monomers having carboxylic acid functionality such as ethylene acrylic acid copolymers, starch, modified starch, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, sodium carboxymethyl cellulose, nano / microfibril cellulose and nanocrystalline cellulose (NCC / CNC); The method according to any one of claims 2 to 7.

9. The concentration of the water-dispersible polymer in the aqueous composition is from 1 to 20% by weight, for example from 5 to 15% by weight, for example from 7 to 13% by weight, most preferably from 9 to 13% by weight; The method according to any one of claims 2 to 8.

10. The concentration of the graphene oxide in the aqueous composition is 0.1 to 15% by weight, for example 0.5 to 10% by weight, for example 0.5 to 6% by weight, for example 0.5 to 3% by weight, for example 1 to 2% by weight; The method according to any one of claims 2 to 9.

11. 11. The method according to any one of claims 2 to 10, wherein the wet coating thickness of the aqueous composition of graphene oxide is from 10 to 500 μm.

12. the aqueous graphene oxide composition consists essentially of graphene oxide and water and is polymer-free; The method according to any one of claims 1 to 11.

13. irradiating the dried, barrier-coated substrate web resulting from step f) prior to or during step g) to promote a reduction reaction between the first and second drying layers. The method according to any one of claims 2 to 12.

14. advancing the substrate web continuously at a constant speed; The method according to any one of claims 2 to 13.

15. A barrier-coated substrate web (10a; 10b) obtainable by the method according to any one of claims 1 to 14, comprising a substrate web (11a; 11b) and a dry layer of layered particles or flakes of reduced graphene oxide (13a; 13b) applied onto said substrate web, for use as an oxygen barrier material in a laminate packaging material (20a; 20b) for liquid food. A barrier coated substrate web (10a; 10b).

16. the thickness of the dry layer of reduced graphene oxide lamellar particles or flakes (13a; 13b) is from 50 to 1000 nm, such as 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; 16. The barrier coated substrate web of claim 15.

17. The substrate web (11a; 11b) is a polymeric film web, a paper or other cellulosic material web, or a polymer-coated paper or other cellulosic material web, 17. A barrier coated substrate web according to claim 15 or 16.

18. A barrier-coated substrate web (10) according to any one of claims 13 to 17, further comprising a first outermost protective material layer (22a; 22b) and a second innermost liquid-tight heat-sealable material layer (23a; 23b; 23b'). A laminated packaging material (20a; 20b).

19. a bulk layer of paper or paperboard or other cellulosic material (21), said first outermost protective material layer (22a; 22b), said second innermost liquid-tight heat-sealable material layer (23a; 23b; 23b'), and said barrier coated substrate web (10a; 10b) disposed inside said bulk layer of paper or paperboard and between said bulk layer and said innermost layer.

19. A laminate packaging material (20a; 20b) according to claim 18.

20. The barrier coated substrate web (10a; 10b) is bonded to the bulk layer (21) by an intermediate bonding layer (26a; 26b) comprising a composition comprising a binder selected from the group consisting of acrylic polymers and copolymers, starch, cellulose and polysaccharide derivatives, polymers and copolymers of vinyl acetate and / or vinyl alcohol.

20. A laminate packaging material (20a; 20b) according to claim 19.

21. A packaging container (50a; 50b; 50c; 50d) comprising a laminate packaging material (20a: 20b) according to any one of claims 18 to 20.

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