Substrate coated with barrier, laminated packaging material and packaging container comprising same

Abstract

The invention relates to a substrate material web (10; 25a) coated with a barrier substrate material web 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 invention also relates to a laminated packaging material (20a), in particular for packaging liquid carton food products, comprising a base web (10) coated with a barrier, and to a liquid carton packaging container comprising such a laminated packaging material.

Description

Technical Field

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

[0002] Disposable type packaging containers for liquid foods are usually made of packaging laminates based on paperboard or carton. One such common packaging container is (Tetra Brik ) are sold under the trademark of Aseptic Packaging, mainly for aseptic packaging of liquid foods such as milk, juice, etc., which are intended for long-term storage at room temperature after sale. The packaging material in such known packaging containers is usually a laminate, including a body layer or core layer of paper, paperboard or other cellulose-based materials, and a liquid-tight outer layer of thermoplastic. In order to make the packaging container airtight, in particular oxygen-tight, for example for aseptic packaging and packaging of milk or juice, the laminate in these packaging containers usually includes at least one additional layer, most commonly aluminum foil.

[0003] On the inner side of the laminate, i.e. the side of the container made of the laminate facing the filled food content, there is an innermost layer applied to the aluminum foil, which innermost layer of the inner side may consist of one or more partial layers, comprising a heat-sealable thermoplastic polymer, such as an adhesive polymer and / or a polyolefin. In addition, there is an outermost heat-sealable polymer layer on the outer side of the body layer.

[0004] The packaging containers are usually produced using modern high-speed packaging machines which form, fill and seal packages from a web of packaging material or a preformed blank. Thus, the packaging container is produced by reforming a web of laminated packaging material into a tube by joining together the innermost and outermost heat-sealable thermoplastic polymer layers so that the two longitudinal edges of the web are joined to each other in an overlapping joint. The desired liquid food is filled into the tube, which is then divided into individual packages by repeated transverse sealing of the tube at a predetermined distance from each other below the liquid level of the contents in the tube. The packages are separated from the tube by cuts along the transverse seals and formed into the desired geometric shape, usually a cuboid shape, by folding along prepared crease lines in the packaging material.

[0005] The main advantage of this continuous tube forming, filling and sealing packaging process concept is that the web can be sterilized continuously before the tube is formed, thereby providing the possibility of an aseptic packaging process, i.e. a process in which the liquid contents to be filled as well as the packaging material itself are germ-reduced and the filled packaging containers are produced under clean conditions, so that the filled packages can be stored for a long time even at ambient temperature without the risk of microbial growth in the filled product. (Tetra Another important advantage of the ) type packaging method is that, as mentioned above, continuous high-speed packaging can be achieved, which has a considerable impact on cost efficiency.

[0006] Packaging containers for sensitive liquid foods, such as milk or juice, can also be made from sheet blanks or preformed blanks of the laminated packaging material of the present invention. The packaging is produced from a tubular blank of a folded flat packaging laminate, the blank first being constructed to form an open tubular container capsule, one open end of which is closed by folding and heat-sealing an integral end plate. The container capsule thus closed is filled with the relevant food, such as juice, through its open end, which is then closed by further folding and heat-sealing the corresponding integral end plate. An example of a packaging container produced from sheet and tubular blanks is the conventional so-called gable top package. There are also packages of this type with a molded top and / or a screw cap made of plastic.

[0007] A layer of aluminum foil in packaging laminates provides superior gas barrier properties than most other gas barrier materials. Traditional aluminum foil-based packaging laminates used for aseptic packaging of liquid foods remain the most cost-effective packaging material with the same performance level available in the market today.

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

[0009] In the efforts to develop non-aluminum foil materials for liquid food carton packaging, people generally focus on developing pre-made films or sheets with high barrier properties, or combining several individual barrier materials into multi-layer films or sheets. Such films or sheets will replace aluminum foil barrier materials in traditional laminated packaging materials, and can further adapt to the traditional lamination and manufacturing processes of laminated packaging materials.

[0010] With the increasing demand to use only sustainable materials, polymer barrier materials derived from fossil sources are becoming less popular, so there is still a need to use various thin barrier coatings that are almost negligible in the recycling process and cause almost no problems in an economy based on material and renewable (non-fossil) materials (i.e., aqueous dispersion coatings and vapor deposited coatings). The thickness of the polymer coated dispersion is about 1-2μm, while the vapor deposited barrier coating is as thin as less than 0.5μm, such as 10 to 100nm, such as 15 to 80nm, such as 20 to 50nm. Over the years, various such coatings have been developed and combined in multilayer packaging material structures in search of improved overall performance. Although some of these coatings show excellent barrier properties, the beverage carton packaging industry is still looking for the best coating or coating combination that can replace aluminum foil in all aspects.

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

[0012] Very good crack initiation strain properties have sometimes been achieved for vapor deposited (or so-called "vacuum coated") barrier coatings, making them robust enough for fold forming 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 aluminum foil.

[0013] In recent years, graphene has emerged as a potential barrier material. Carbonaceous materials such as graphene have the further advantage that they can be used for induction sealing of packages, as disclosed by the applicant in WO 21 / 005120.

[0014] However, graphene itself is too expensive for full-surface barrier coatings on packaging materials. In theory, just a layer of graphene sheets with a thickness of one molecule is sufficient to obtain 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 applied by dispersion coating or printing techniques, but this variant of graphene layers is too expensive to be incorporated into disposable packaging materials as full-surface coatings. In addition, the removal of organic solvents from such coatings is an undesirable problem in modern sustainable industrial-scale coating operations.

[0015] A cheaper source of material for similar barrier coatings with the same or similar properties as graphene is graphene oxide flakes or particles which are exfoliated from graphite oxide, a very cheap raw material, and subsequently chemically reduced. Such graphene oxide particles or flakes can thus 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 known as the Hummers process) and subsequent reduction to graphene can be used at a significantly lower cost in packaging materials.

[0016] However, providing a thin and uniform reduced graphene oxide coating via a large-scale industrial coating process starting from reduced graphene oxide, i.e. graphene, is problematic due to the need for an organic solvent to disperse it and the high cost of further refining the product, i.e. reduced graphene oxide.

[0017] In the scientific article "Impermeable barrier films and protective coatings 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, it is described how to reduce the substrate material by exposing the substrate material applied with a graphene oxide coating combined with PVA to hydrogen iodide vapor at 90°C for 5-30 minutes, or immersing it in a vitamin C solution at 90°C as a reducing agent for 1 hour to obtain a material with good gas barrier properties. Similar teachings are provided in WO2015 / 145155, whose authors are the same as those of the article. For economic reasons and the practical impracticability of packaging material conversion plants, this method is not feasible in the production of barrier layers or coatings for disposable packaging materials. Acid vapor treatment or prolonged exposure to near-boiling liquids to treat the substrate will bring considerable risk of deterioration of the material and is also extremely unfeasible in manufacturing processes that are usually characterized by continuous operation of wide webs and high manufacturing speeds.

[0018] Therefore, improved methods are needed to apply such reduced graphene oxide-based materials to laminated packaging materials at a reasonable cost and meet future requirements for recyclability and sustainable materials sourcing and manufacturing. Summary of the invention

[0019] It is an object of the present invention to provide an improved method for manufacturing a substrate material coated with a reduced graphene oxide barrier coating and further laminating such a barrier coated substrate material into a packaging material.

[0020] Another general object of the present invention is to provide a simplified method for manufacturing a barrier coated substrate with reduced graphene oxide providing good barrier properties as well as recyclability capable of meeting the requirements of future sustainable liquid carton laminate packaging materials.

[0021] Yet another general object of the present invention is to provide a method for producing a non-foil laminated packaging material for oxygen sensitive, liquid, semi-solid or wet foods which does not contain aluminum foil but has excellent gas barrier properties suitable for long-term aseptic packaging at a reasonable cost.

[0022] A specific object of the present invention is to provide a cost-effective, non-foil, paper or paperboard based laminated packaging material relative to aluminium foil barrier materials, which has good gas barrier properties as well as recyclability and sustainable environmental characteristics for use in manufacturing packaging for long-term sterile food storage.

[0023] Another object of the present invention is to provide a cost effective, non-foil, paper or paperboard based, mechanically strong and heat sealable packaging laminate having good gas barrier properties for use in manufacturing aseptic packaging containers for liquid foods that retain nutritional quality for long term storage under ambient conditions.

[0024] These objects are therefore achieved according to the present invention by a method of manufacturing a barrier coated substrate material web, a laminated packaging material and a packaging container, as defined in the appended claims.

[0025] According to a first aspect, the present invention relates to a method for producing an oxygen barrier material for packaging material by coating a reduced graphene oxide layer on a web of a substrate material, comprising the following steps: a) providing and conveying a web of substrate material, b) coating the web of substrate material with a first layer of an aqueous composition comprising a reducing agent and a water-dispersible polymer while the web of substrate material is being conveyed, c) drying the first layer by forced evaporation to form a first dried layer comprising a reducing agent and a water-dispersible polymer, d) providing an aqueous composition comprising graphene oxide, the graphene oxide comprising single-layer graphene oxide flakes and multi-layer graphene oxide platelets, with up to 20 (e.g., 2-10) stacked single-layer graphene oxide flakes, e) applying an aqueous graphene oxide composition onto a web of substrate material while the web of substrate material is being conveyed, f) drying the aqueous graphene oxide wet coating on the substrate material web by forced evaporation to obtain a second dry layer of layered graphene oxide particles or flakes, g) allowing the reducing agent of the first dry layer to reduce the graphene oxide of the second layer, preferably at a minimum predetermined temperature and for a minimum predetermined time, to form a barrier coated substrate material web having a dry layer of reduced graphene oxide, Steps c) and d) may be performed before or after steps d), e) and f), so that the first drying layer or the second drying layer may be formed first.

[0026] Surprisingly, it has been found that, by this method, the reduction reaction continues even after the applied coating has dried, resulting in a sufficient conversion of the graphene oxide into graphene and excellent gas barrier properties. This is unexpected, since it has been believed until now that the reducing agent solution must be applied in a liquid bath or by spraying or vapor treatment and must remain wet on the surface of the graphene oxide layer for a long time in order to reduce the dried graphene oxide layer.

[0027] Surprisingly, it has also been learned that the "dry" reduction reaction can also be promoted and accelerated by heating the coated and dried web of substrate material to an elevated temperature for a certain period of time. Thus, by appropriately designing the coating line, the coated and dried web of substrate material can be further fully reduced during the extended transport of the dried web of material through a heating tunnel or similar device maintained at an elevated temperature. However, the speed of such a continuous line must be much slower than a normal coating or laminating operation, and the elevated temperature treatment must be kept at a level below 90°C to avoid the risk of changes in the properties of the web of substrate material. Advantageously, however, the manufacturing method does not require wet or liquid treatments along the conversion line, except for the aqueous coating operation itself.

[0028] Preferably, the aqueous composition comprising the reducing agent and the water-dispersible polymer is applied as a pre-coating layer and then the aqueous graphene oxide coating is applied (ie steps b) and c) are performed before steps d), e) and f)).

[0029] The method may include a further step i) of coating or laminating the barrier coated base material web onto another polymer layer to cover the first and second dry layers, which step is performed before or after step g). Surprisingly, it has been found that the reduction reaction between the first and second dry layers continues after a further polymer layer is coated or laminated (e.g. by extrusion coating of a thermoplastic polymer) onto the dry layers. This high temperature, polymer melt lamination operation does add additional heat that acts on the surface of the barrier coated base material web. Therefore, the reduction reaction is further accelerated when this lamination operation is performed.

[0030] The method may additionally or alternatively further comprise the step h) of winding the coated and dried barrier-coated substrate material web onto a reel, which step is performed before or after step g). It appears that the reduction reaction of the dried graphene oxide layer does not stop until it is completed, and it has therefore been shown that even without further heat treatment after drying, the conversion of graphene oxide to reduced graphene oxide continues at a lower rate until it is completed. Thus, the color of the freshly applied graphene oxide changes to black over time, indicating that the graphene oxide has been almost and substantially completely reduced. This has great advantages in coating lines, since no additional heat treatment is required therein, and since the barrier-coated substrate material web can be wound onto a reel directly after coating and a short drying operation, which takes only a minute or so (e.g. 2 seconds to 1 minute: for an oven with a length of 20 meters, this corresponds to a speed range of 20 meters / minute to 600 meters / minute). Furthermore, the manufacturing speed can be as high as possible, since the reduction reaction will anyway take place later and at a slower rate. By planning the transport and distribution logistics of the packaging material reel to the customer, sufficient time can be provided to complete the reduction reaction. Thus, simply by storing the reel with the barrier-coated substrate material web for a predetermined time after coating and drying, the reduction reaction between the reducing agent in the first dry layer and the graphene oxide in the second dry layer can achieve a sufficient degree of conversion of graphene oxide to reduced graphene oxide.

[0031] The reduction reaction time is suitably 1 to 14 days at room temperature; faster results are obtained at 40-60°C and may require a time of 5 minutes to 3 hours.

[0032] As mentioned above, the color of reduced graphene oxide changes from brown (initial color) to black over time and temperature, indicating that graphene oxide is reduced. This color change can be quantified by the so-called color space or L*a*b* measurement. The L* value represents the perceived brightness, where L*=0 is black and L*=100 is diffuse white. The lower the L* value, the darker the surface; a value below 15 is 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 color content of the sample have a low color content, indicating black. It is desirable that L*, a*, and b* are each as close to zero as possible.

[0033] In one embodiment, the dried barrier-coated substrate material web from step f) may be irradiated before or during step g) to accelerate the reduction reaction occurring between the applied first and second dry layers. Such irradiation may include UV light, xenon light or laser light. The combination of the reducing agent of the first dry layer and such supporting irradiation appears to facilitate a faster but still balanced reduction reaction in the graphene oxide layer. It was found that the reduction of the graphene oxide layer by irradiation alone in the absence of a reducing agent was difficult to control and produced 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 the best choice for such a process because it is widely recognized in both food and food industries and is a well-functioning reducing agent.

[0035] By adopting the method of the present invention suitable for industrial production, the oxygen barrier transmission rate of the obtained coating substrate can be as low as 1 cc / m 2 , 24h, 1atm, 23℃ / 50% RH, 21% oxygen.

[0036] According to a second aspect, the present invention provides a base material web obtained by the above method for use as a coated barrier of oxygen barrier material in a laminated packaging material for liquid food, comprising a base material web and a dry layer of layered particles or flakes of reduced graphene oxide applied thereto.

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

[0038] For carton packaging of liquid food, the laminated packaging material may also include a body 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 base material coated with a barrier disposed on the inner side of the body layer of paper or paperboard between the body layer and the innermost layer.

[0039] The first outermost protective material layer can be a protective polymer layer or coating to prevent dust and moisture from reaching the interior of the laminate, 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.

[0040] The thin layer of reduced graphene oxide that can be coated in this way onto an optionally pre-coated web of substrate material exhibits the excellent gas barrier properties that graphene has as a material and can be laminated as a "direct replacement for aluminum foil" to the standard structure of laminated packaging materials for liquid carton packaging. Compared with earlier attempts to produce such "direct replacement" films or barrier sheets, the sensitivity of the web of substrate material (such as a polymer film or paper substrate) coated with reduced graphene oxide in the lamination operation and the filling machine operation of the folding, filling and heat-sealing carton packaging from the laminated material will be significantly reduced. This is because graphene as a material has inherent durability and flexibility, and because it is a layer obtained by closely stacking thin sheets overlapping each other, so that any penetration of oxygen molecules through the barrier coating must follow the so-called tortuous path between the thin sheets. Therefore, this coating is not sensitive to strain cracking and can well maintain its oxygen barrier properties during the process of conversion into packaging. In addition, the gas barrier properties of reduced graphene oxide are insensitive to moisture and water vapor penetration of the liquid contents in the package, and can therefore withstand long-term storage of such filled packaging containers.

[0041] In a fourth aspect of the present invention, a packaging container for packaging liquid, semi-solid or wet food is provided, which comprises the laminated packaging material of the third aspect. According to one embodiment, the packaging container is at least partially made of the laminated packaging material of the present invention, and according to another embodiment, the packaging container is entirely made of the laminated packaging material. DETAILED DESCRIPTION

[0042] The term "long-term storage" used in conjunction with the present invention means that the packaging container should be able to maintain the quality (i.e. nutritional value, hygienic safety and taste) of the packaged food under ambient conditions for at least 1 or 2 months, for example at least 3 months, preferably longer, for example 6 months, for example 12 months or more.

[0043] The term "package integrity" generally refers to the sealing of the package, i.e., the leak-proofness or resistance to breakage of the packaging container. The term includes the resistance of the package to the invasion of microorganisms (such as bacteria, dirt and other materials) that may spoil the filled food and shorten the expected shelf life of the package.

[0044] One major contribution of a laminated packaging material to the integrity of the package is good internal adhesion between adjacent layers of the laminate. Another contribution derives from the material's resistance to defects (e.g. pinholes, tears, etc. within each material layer itself), and yet another contribution derives from the strength of the sealing joints by which the materials are sealed together when forming the packaging container. Thus, with respect to the laminated packaging material itself, the integrity focuses primarily on the adhesion of the individual laminate layers to their adjacent layers, as well as on the quality of the individual material layers. With respect to the sealing of the package, the integrity focuses primarily on the quality of the sealing joints, which is ensured by a well-functioning and robust sealing operation in the filling machine, which in turn is ensured by appropriate heat sealing properties of the laminated packaging material.

[0045] The term "liquid or semi-liquid food" generally refers to a food with a flowing content, which may optionally contain food chunks. Dairy and milk, soy, rice, grain and seed beverages, fruit juices, nectar, still drinks, energy drinks, sports drinks, coffee or tea drinks, coconut water, wine, soups, jalapenos, tomatoes, sauces (such as pasta sauce), beans and olive oil are some non-limiting examples of contemplated foods.

[0046] The term "sterile" in relation to packaging materials and packaging containers refers to conditions under which microorganisms are eliminated, inactivated or killed. Examples of microorganisms are bacteria and spores. Typically, when a product is aseptically packaged in a packaging container, an aseptic process is used. In order to maintain sterility during the shelf life of the package, the integrity of the package is of course very important. For a long shelf life of filled foods, it may also be important that the package has barrier properties to gases and vapors (e.g. to oxygen) in order to preserve its original taste and nutritional value, such as its vitamin C content.

[0047] The term "body layer" generally means the thickest layer or the layer containing the most material in a multilayer laminate, i.e., the layer that contributes most to the mechanical properties and dimensional stability of the laminate and the packaging container (such as paperboard or carton) folded from the laminate. It can also mean a layer that provides a greater thickness distance in a sandwich structure, which further interacts with the stabilizing surface layers with higher Young's modulus on both sides of the body layer to achieve sufficient such mechanical properties and dimensional stability.

[0048] Thickness measurements are performed by transmission electron microscopy using a Titan 80-300, FEI Instruments. Samples can be prepared by ultrathin sectioning using an EMUC6 microtome from Leica.

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

[0050] The OTR is determined by determining the amount of oxygen per unit surface area and time that passes through the material at a specified temperature and a specified atmospheric pressure for a specified period of time, for example 21% oxygen at atmospheric pressure in 24 hours.

[0051] Water vapor transmission rate (WVTR) measurements were performed using a Permatran 3 / 33 (Mocon) instrument (standard: ASTM F1249-13, using a modulated infrared sensor for relative humidity detection and WVTR measurement) at 38°C and 90% driving force.

[0052] L*a*b* measurements are performed according to https: / / en.wikipedia.org / wiki / CIELAB_color_space The interpretation in color space was performed using an X-rite eXact instrument.

[0053] The term "graphene oxide" includes single-layer graphene oxide flakes and multi-layer graphene oxide platelets, with up to 20 (e.g. 2-10) stacked single-layer graphene oxide flakes. Only a small amount, i.e. less than 15 wt.%, such as less than 10 wt.%, such as less than 5 wt.%, based on the dry weight of the graphene oxide material, may be graphene oxide flakes that have been exfoliated into a number of more than 20 graphene oxide monolayer flakes, but whose lateral particle size is smaller than that of bulk graphite oxide particles, i.e. so-called "graphene oxide nanoplatelets", and are therefore still nanometer-sized.

[0054] Such smaller amounts of such lateral nano-sized graphite flakes may be present as long as the properties of the graphene-based material are not degraded too much. Preferably, the nano-graphite flakes / platelets are present in the composition only in an amount of less than 15 wt%, such as 10 wt%, such as 5 wt% or less based on dry weight.

[0055] Suitable graphene oxide materials which can be used in the aqueous dispersion of the present invention are, for example, pure qualities (exfoliation degree of at least 95%) from Graphenea, or pasty graphene oxide from Abalonyx.

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

[0057] The polymer film substrate can be made of, for example, polyester or polyolefin. Typical polyester types are polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyhydroxyalkanoate (PHA) and polylactic acid (PLA). Typical polyolefin films can be made mainly of polypropylene or polyethylene, such as biaxially oriented polypropylene (BOPP), or biaxially oriented high-density polyethylene (BOHDPE), or linear low-density polyethylene (LLDPE).

[0058] Cellulose-based substrates may be based on any type of natural cellulose, fibrous or fibrillar cellulose, and they may be further coated with a polymer of the type described above, preferably with a polyolefin (such as polyethylene discussed below), for subsequent application of a barrier coating according to the method of the invention.

[0059] Typically, suitable paper or cellulose based substrate materials for carrying the barrier coating of the present invention should be thin, for example 60 g / m 2 Or below, e.g. 50g / m 2 Or less, preferably 45g / m 2 or less, more preferably 40g / m 2 On the other hand, thinner or weighing less than 30g / m 2 Cellulose-based substrates may have too weak mechanical properties and / or poor dimensional stability when coated with a wet dispersion and subsequently dried, resulting in shrinkage or curling problems. It is therefore more preferred to use a grammage of 30 to 50 g / m 2 The paper is preferably 35 to 45 g / m 2 . High density paper is preferred.

[0060] As described below, the graphene oxide coating is preferably applied to a substrate material on which a first dry layer has been formed as a pre-coating layer. In addition to providing a reducing function, the pre-coating layer also ensures that the surface to be coated is smooth, so that the graphene oxide coating can form neatly arranged flakes uniformly and coherently, thereby preventing oxygen penetration.

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

[0062] The aqueous composition used to form the first dried layer in step b) 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 into the adjacent graphene oxide dispersion before and after drying, where it reduces the graphene oxide to form a barrier layer.

[0063] Preferably, the concentration of the reducing agent is 2 to 10 wt%, such as 2 to 8 wt%, such as 2 to 6 wt%, such as 2 to 5 wt%. 4 wt% is a preferred amount. In order to achieve the desired effect of reducing graphene oxide, a solution containing a minimum amount of reducing agent is required. When the concentration is as high as 10 wt%, the reducing agent will cause the graphene oxide to aggregate, which means that the flakes may not be evenly distributed, but form lumps, resulting in part of the surface being uncovered. This will reduce the oxygen barrier properties.

[0064] Preferably, the concentration of the water dispersible polymer is 1 to 20 wt%, such as 1 to 20 wt%, such as 5 to 15 wt%, such as 7 to 13 wt%, most preferably 9 to 13 wt%, such as 10 wt%.

[0065] The water-dispersible polymer of the first dry layer can be any suitable water-dispersible polymer and / or renewable non-fossil-based polymer. In one embodiment, the polymer of the pre-coating layer can be selected from the group consisting of: polyvinyl alcohol (PVOH, PVAL), polyethylene vinyl alcohol (EVOH, EVAL), water-dispersible "polyolefins", such as copolymers of ethylene and monomers having carboxylic acid functional groups, such as ethylene acrylic acid copolymers (EAA), starch, modified starch, methylcellulose, ethylcellulose, carboxymethylcellulose CMC, hydroxyethylcellulose HEC, hydroxypropylcellulose HPC, hydroxypropylmethylcellulose HPMC, sodium carboxymethylcellulose NaCMC, nano- / microfibrillar cellulose (NFC / MFC / CNF) and nanocrystalline cellulose (NCC / CNC).

[0066] In another embodiment, the pre-coating layer may include a renewable polymer or substance 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- / microfibrillar cellulose (NFC / MFC / CNF) or nanocrystalline cellulose (NCC / CNC).

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

[0068] The materials listed above are also suitable where a pre-coat layer free of reducing agents is used in addition to the first dry layer; further possibilities for such pre-coat layers free of reducing agents are discussed below.

[0069] Preferably, the first dry layer is applied at a dry thickness of 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 to 15 wt%, such as 0.5 to 15 wt%, such as 0.5 to 10 wt%, such as 0.5 to 6 wt%, such as 0.5 to 3 wt%, such as 1 to 2 wt%, such as 1 wt%. If the concentration is below 0.5 wt%, it may be difficult to apply enough graphene oxide on the optionally pre-coated web of substrate material so that the applied coating may not provide sufficient oxygen barrier properties, but if the barrier properties are less demanding, a thinner coating, such as as low as 0.1 wt%, may be applied. On the other hand, if the concentration is above 6 wt%, such as above 10 wt%, such as above 15 wt%, the applied coating may be more difficult to dry because the applied wet coating of graphene oxide material is unnecessarily thick and contains a lot of water between the flakes and platelets of the composition. If the concentration of graphene oxide is above 3 wt%, the coating may be difficult to dry, and if its concentration is above 6 wt%, it may be more difficult to apply. However, aqueous compositions of graphene oxide exhibit shear-thinning behavior, so thicker compositions are still likely to be applied with reasonable coating thicknesses and good layer formation as well as higher coating speeds.

[0071] The aqueous composition of graphene oxide substantially comprises only graphene oxide and water, and preferably consists of only these two materials. No other polymers are substantially present in the composition, i.e. no binder or similar components. Preferably, it comprises only up to 5% by weight, e.g. up to 3% by weight of additives, such as dispersants, defoamers, etc. Therefore, the aqueous composition of graphene oxide may comprise 0.1 to 15% by weight of graphene oxide, 0 to 5% by weight of additives and 85 to 99.9% by weight of water. Insertion of polymers between reduced graphene oxide flakes (e.g. in induction sealing) may be disadvantageous.

[0072] In one embodiment, the aqueous graphene oxide composition is applied at a wet thickness of 10 to 500 μm, preferably 10 to 400 μm. If the thickness is less than 10 μm, the coating may not provide adequate oxygen barrier properties, while if the thickness is greater than 400 μm, the amount of water dried from the coating or the viscosity of the thicker coating composition may be impractical or impossible to handle. 200 μm is a preferred wet thickness.

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

[0074] In addition, the substrate can also be conveyed at a constant speed. In order to obtain an optimal and reliable coating amount, this is an important prerequisite in the coating operation. In addition, industrially feasible web and coating speeds can be 100 meters / minute, for example 200 meters / minute, for example 300 meters / minute, for example 400 meters / minute, depending on the size of the drying capacity in the coating production line. Drying is suitably carried out by hot air convection, and can also be combined with infrared heater irradiation. In the process of passing through the drying station, the drying of the wet coating takes a few seconds at most, and the drying station can be several meters long, for example at least 5 meters long, for example at least 10 meters long, for example at least 15 meters long, for example at least 20 meters long, depending on the temperature of the substrate surface and the speed at which the web moves forward in the coating production line.

[0075] Graphene oxide is therefore dispersed in water and can be applied by an aqueous "dispersion coating" process or by a so-called "liquid film coating" process. Fully aqueous dispersions are preferred from the perspective of environmental sustainability and work safety.

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

[0077] Therefore, suitable application methods can be suitable printing methods, such as flexographic printing, rotary gravure printing, screen printing, inkjet printing and various dispersion coating methods, such as gravure roller coating, slot coating, doctor blade coating, reverse roller coating, wire rod coating, lip coating, air knife coating, curtain coating, as well as spray coating, dip coating and brush coating. Roll coating method is preferred. By these printing or coating methods, a suitable graphene oxide coating layer dry material thickness of 0.1 to 10 μm, such as 0.5 to 8 μm, such as 0.5 to 6 μm, such as 0.5 to 4 μm, such as 0.5 to 3 μm, such as 0.5 to 2.5 μm can be applied.

[0078] Several consecutive coating steps may be required to form a thick graphene oxide layer to obtain a higher thickness. For the purpose of providing a gas barrier coating, an application of 0.1 to 3 μm, such as 0.5 to 2.5 μm, such as about 2 μm of dry graphene oxide may be sufficient. For other purposes, such as for conductive coatings or other purposes, thicker coatings may be suitable, but perhaps not as a full surface coverage coating, but as a coating applied only to selected local areas of the web of substrate material.

[0079] The experiments of the present invention were conducted by gravure coating, but it is believed that any of the liquid film coating methods described above would be suitable for providing good gas barrier coatings.

[0080] The aqueous graphene oxide composition may also include an added amount of a dispersion stabilizer or a similar added amount of a dispersion coating, preferably in an amount not exceeding about 1 wt % based on the dry coating.

[0081] The total dry content of the aqueous composition containing graphene oxide 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 %. In the case of a lower dry content, the quality of the formed gas barrier layer may not be good enough, and thus the gas barrier properties obtained by the dried coating may not be very good.

[0082] In one embodiment, the graphene oxide coating can be applied as two partial layers in two consecutive steps with drying in between. When applied as two partial layers, each layer is suitably 0.1 to 1.5 g / m 2 (e.g. from 0.5 to 1 g / m 2 ) in an amount less than that of the liquid gas barrier component, and a higher quality total layer is obtained from a lower amount of liquid gas barrier component. For example, the total thickness of the dry applied graphene oxide is about 2 μm, and after reduction to reduced graphene oxide, its total thickness is about 0.5 μm (500 nm). It has been estimated that two consecutively applied and dried graphene oxide coatings will be able to reduce graphene oxide as easily as a single coating of dry graphene oxide of corresponding thickness. The consecutively applied and dried graphene oxide coatings can cover any defects that may exist in each coating because, in most cases, the coating overlaps with a defect-free portion of another coating. In this way, the entire applied graphene oxide layer may actually be free of defects.

[0083] When an additional pre-coating layer without a reducing agent is used, it can be a polyolefin, such as polyethylene, and can be melt extrusion coated (optionally using corona pre-treatment or high temperature to oxidize the surface). In one embodiment, the additional pre-coating layer polymer without a reducing agent is a very thin polyethylene coating, which can support a clean separation of the reduced graphene oxide coating from the paper or paperboard substrate material, so that the recycled fiber can remain substantially free of reduced graphene oxide material.

[0084] For protection purposes, a further protective polymer coating of low density polyethylene may be applied to the first and second dry layers, as the barrier coated substrate material web may be further wound onto a reel, or further laminated into a multilayer material structure. By encapsulating the reduced graphene oxide between the polyethylene layers, the reduced graphene oxide may be kept separate from the fiber components during 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 modified polyethylene (such as the EAA described above) or another water-soluble or water-dispersible polymer that can be dispersed and coated. This can be done in the same dispersion coating line used to apply the first and second dry layers. The web may also be laminated to or melt extrusion coated with an adjacent polymer layer, such as a polyolefin layer, such as a low-density polyethylene. Such further coating and / or lamination may be performed before or after the graphene oxide of the first dry layer of graphene oxide is completely reduced. In one embodiment, the first protective coating is applied by dispersion coating in the same dispersion coating line used to apply the first and second dry layers, the web is then wound onto a reel, and then another laminate layer is added by extrusion coating or lamination.

[0086] A carton-based laminated packaging material for liquid food packaging comprises a body layer of paper or paperboard, a first outermost protective material layer, a second innermost liquid-tight heat-sealable material layer, and a barrier-coated base material web arranged on the inner side of the paper or paperboard body layer, toward the inner side of a packaging container made of the packaging material, and between the body layer and the innermost layer.

[0087] The paper or paperboard body layer used in the present invention generally has a thickness of about 100 μm to about 600 μm and a weight of about 100-500 g / m 2 (Preferably about 200-300g / m 2 )'s surface weight and may be conventional paper or paperboard of suitable packaging quality.

[0088] For low-cost aseptic long-term packaging of liquid foods, thinner packaging laminates with thinner paper core layers can be used. Packaging containers made from such packaging laminates are not folded into shape, but more like pillow-shaped flexible bags. Paper suitable for such bag packaging typically has a density 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 web in the present invention itself contributes some stability to the laminate, the paper layer corresponding to the "body" layer can be thinner and interact with the barrier coated substrate web in a sandwich structure to still produce a laminated packaging material with all the desired mechanical properties.

[0089] The thickness of the dried layer formed of reduced graphene oxide layered particles or flakes may be 50 to 1000 nm, such as 100 to 800 nm, such as 200 to 700 nm, such as 200 to 600 nm, such as 400 to 600 nm, such as 450 to 550 nm.

[0090] The barrier coated base material web may be bonded to the bulk layer by an intermediate adhesive or thermoplastic polymer tie layer, thereby bonding the uncoated surface of the barrier coated base material web to the bulk layer. According to one embodiment, the tie layer is a polyolefin layer, such as, in particular, a layer of a polyethylene-based polyolefin copolymer or blend, comprising a majority of ethylene monomer units. The tie layer may be provided by extrusion lamination by laminating the tie polymer layer between the bulk layer web and the base material web by melt extrusion, bonding the bulk layer to the barrier coated base material web, and simultaneously laminating the three layers together while conveying through the lamination nip.

[0091] In another embodiment, the barrier-coated substrate web can be bonded to the bulk layer by wet application of an aqueous dispersion of an adhesive composition comprising an adhesive polymer binder to one of the web surfaces to be laminated and pressing the two paper webs together as they are conveyed through the lamination nip, thereby providing a laminated structure by wet lamination. During the subsequent lamination process, the moisture in the aqueous adhesive composition is absorbed into the fibrous cellulose network of the bulk paperboard and partially evaporates over time. Therefore, a forced drying step is not required. The adhesive polymer binder is selected from the group consisting of acrylic polymers and copolymers thereof, starch, cellulose and polysaccharide derivatives, polymers of vinyl acetate and vinyl alcohol and copolymers thereof. In order to obtain the best environmental and sustainability characteristics, adhesive binders derived from plants or non-fossil sources are preferred.

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

[0093] The outermost layer is typically applied at a thickness of 5 to 20 μm, such as 10 to 15 μm. The innermost layer may be applied at a thickness ranging from 10 to 50 μm, such as 10 to 40 μm, such as 10 to 30 μm, such as 10 to 25 μm.

[0094] The same thermoplastic polyolefin-based materials listed for the outermost and innermost layers, in particular polyethylene, are also suitable for bonding the inner layers of the laminate, i.e. between the bulk or core layer (e.g. paper or paperboard) and the barrier film or sheet. In one embodiment, the thermoplastic bonding layer can be a polyethylene layer, such as a low density polyethylene (LDPE) layer. Its typical application amount is 10 to 25 μm, such as 10 to 20 μm, such as 10 to 15 μm.

[0095] In another embodiment, the second innermost liquid-tight heat-sealable polyolefin layer is a prefabricated film comprising identical or similar polyolefins, as mentioned above, for improving the robustness of the packaging material mechanical properties. Due to the manufacturing process in film blowing and film casting operations, and optional subsequent film orientation operation steps, the polymer of this type of film has a characteristic different from (total) extrusion coating polyolefin layer. Therefore, this prefabricated polymer film contributes to the mechanical robustness of laminated packaging materials, and the mechanical strength and the packaging integrity of the packaging container formed and filled by the laminated packaging materials.

[0096] According to an alternative embodiment, a suitable tie layer or connecting layer inside the laminate, 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, is also referred to as an adhesive thermoplastic polymer, such as a modified polyolefin, which is mainly based on: LDPE or LLDPE copolymers, or graft copolymers with monomer units containing functional groups, such as carboxylic acid or glycidyl functional groups, 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 polymers or adhesive polymers are so-called ionomers or ionomer polymers. Preferably, the modified polyolefin is an ethylene acrylic acid copolymer (EAA) or an ethylene methacrylic acid copolymer (EMAA).

[0097] If necessary, the surface of the base material web may be pre-treated by oxidation treatment (eg, corona plasma or ozone treatment) to improve the adhesion strength to the graphene oxide layer or the reduced graphene oxide layer.

[0098] The laminated packaging material produced according to the above provides good integrity when converted into a filled packaging container by good bonding between adjacent layers within the laminate construction and by providing good quality barrier coating and barrier pre-coat layers (alone or in combination).

[0099] According to another embodiment, a packaging container formed from a laminated packaging material may be partially sealed, filled with a liquid or semi-liquid food, and subsequently sealed by sealing the packaging material to itself, optionally in conjunction with a plastic opening or top of the package.

[0100] In summary, the barrier coated substrate web and the laminated packaging material obtained therefrom manufactured by the method of the present invention can obtain a robust and reliable packaging with excellent oxygen barrier properties for packaging liquid foods for long-term shelf life and storage. The laminated packaging material structure is more suitable for forming folded and formed packages, which is due to the improved adhesion between the substrate and the barrier material coating, and the improved contribution of the barrier coated substrate itself to the gas barrier properties, which may also be due to the improved cohesion and adhesion of the combined pre-coating layer and the barrier coating layer in the barrier coated cellulose-based substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings, in which:

[0102] Figure 1a schematically shows a cross section of an embodiment of a substrate coated with reduced graphene oxide according to the present invention,

[0103] Figure 1b Schematically showing different embodiments of a substrate coated with reduced graphene oxide according to the present invention,

[0104] Figure 2a A schematic cross-sectional view of a laminated packaging material according to the present invention is shown, comprising Figure 1a A substrate coated with reduced graphene oxide,

[0105] Figure 2b A schematic cross-sectional view of a laminated packaging material according to the present invention is shown, comprising Figure 1b A substrate coated with reduced graphene oxide,

[0106] Figure 3 A method for dispersing and coating an aqueous graphene oxide composition onto a substrate is shown.

[0107] Figure 4a Schematic diagram of a method for melt extrusion laminating two material webs together using an intermediate thermoplastic polymer.

[0108] Figure 4b Schematically illustrating a method of forming melt (co)extrusion coating layers of a thermoplastic polymer on a web substrate (e.g., to form the innermost and outermost layers of the packaging laminate of the present invention),

[0109] Figure 5a , 5b5c and 5d show typical examples of liquid carton packaging containers produced from the laminated packaging material according to the present invention, and

[0110] Figure 6 The principle of how such a liquid carton packaging container is manufactured from packaging laminate by a continuous roll-fed form, fill and seal process is shown. DETAILED DESCRIPTION

[0111] Example 1

[0112] Using a Hirano laboratory coating machine, an aqueous solution containing 10 wt% dissolved PVOH and 4 wt% dissolved vitamin C (ascorbic acid) in water was applied to a forward-moving paperboard (bending stiffness of 80 mN and grammage of 200 g / m) pre-coated with polyethylene (wet thickness of about 20 μm). 2 on a web of liquid paperboard).

[0113] The water in the applied coating composition was evaporated from the surface by air convection at a web surface temperature of about 60° C. in a hot air dryer for about 1 minute, providing a smooth surface (first dry layer / pre-coating layer) for the graphene oxide solution in the next step. The calculated dry coating thickness was 2.8 μm. The smooth surface helps to flake the graphene oxide so that it can be more easily oriented on the substrate plane.

[0114] A 1 wt% aqueous dispersion of monolayer graphene oxide flakes (high purity, at least 95% exfoliation, from Graphenea or LayerOne) was stirred continuously until the moment of application to the substrate. The well-dispersed aqueous composition was applied to a web of paperboard pre-coated with polyethylene and dried PVOH / vitamin C solution (as described above, wet thickness of about 200 μm) moving forward using a Hirano laboratory coater. The water in the applied coating composition was evaporated from the surface by air convection at a web surface temperature of about 60°C in a hot air dryer for about 1 minute. The dry coating thickness of the graphene oxide (second dry layer) applied to the paper coated with PE / PVOH / vitamin C was measured to be about 2 μm. The web coated with graphene oxide was cooled to room temperature and finally wound onto a reel.

[0115] The substrate coated with graphene oxide showed a light brown color immediately after coating on the PVOH / vitamin C surface. The measured color content is the so-called L*a*b* value, and the value measured after a few seconds was 20*2*-0.3*. The L* value dropped to 16 after 1 hour and to 14 after 3 days. The corresponding a value was 0.25 and b value was -1.36 after 1 hour, and the measurement results on the 3rd day were a=-0.21 and b=-1.1. Without using a reducing agent such as vitamin C, the L*a*b* value was measured only on a 200μm thick graphene oxide layer, and a value of 40*17*36* was obtained. The change from brown to black in the solution of graphene oxide and reducing agents such as vitamin C indicates that graphene oxide has become reduced graphene oxide.

[0116] The resulting substrate thus coated with a thin dry coating of layered reduced graphene oxide will exhibit a relative humidity of less than 1 cc / m 2 , 24h, 1atm, 23℃ / 50%RH, oxygen permeability of 21% oxygen.

[0117] The thickness of the graphene oxide layer becomes thinner (to about 250 nanometers) as it is reduced.

[0118] The reduction rate can also be increased by increasing the temperature.

[0119] Therefore, the Williams-Landel-Ferry model (or WLF for short) appears to apply to the reduction reaction, and the reduction reaction can be accelerated and controlled by increasing the temperature and / or increasing the reaction time. Most importantly, the reduction reaction appears to continue at the interface between the graphene oxide and the PVOH / ascorbic acid dried coating until complete conversion, even after the coated coil is dried and wound onto a reel for shipping and storage.

[0120] Since a reaction time of 2 hours is hardly feasible in industrial coating and manufacturing processes, this result is advantageous because it means that the reduction of the applied graphene oxide coating to graphene can continue to completion after the coating operation. This can therefore be achieved simply by logistical planning for long-term storage of the barrier.

[0121] The barrier-coated substrate web can also be laminated to other layers to form the finished packaging material before the planned storage of the reels. For lamination processes involving the supply of heat, such as polymer melt extrusion coating or polymer melt extrusion lamination, further acceleration of the reduction reaction may be advantageous and can be conveniently achieved. Depending on the actual situation, further intermediate storage can be planned during transportation, partly before shipment and / or partly after shipment at the customer's facility.

[0122] In addition, regarding the attached drawings:

[0123] exist Figure 1a , an embodiment of a substrate material web 10a of a coated barrier of the present invention is shown in cross section. The substrate material 11a is a polyethylene terephthalate (PET) film having a thickness of 36 μm. Its oxygen transmission rate (OTR) is about 30 cc / m 2 , 24h, 23℃ / 80%RH, 100% oxygen.

[0124] The PET film is provided with a dry pre-coating layer 12a (first dry layer) of ascorbic acid and PVOH, applied by aqueous dispersion coating and then dried by heating to evaporate the water. In addition, the substrate material thus coated has a second dry layer 13a of graphene oxide applied to the pre-coating layer in the form of an aqueous dispersion. The dry weight of the graphene oxide coating thus applied is about 1.3 μm. The second dry layer 13a is then dried by heating to evaporate the water. The dried web of substrate material thus coated can be further heat treated for a period of time, or simply stored at ambient temperature for at least two weeks, after which the dried barrier coating layer of graphene oxide is reduced as much as possible to reduced graphene oxide, i.e., ideally to graphene. When the reduction reaction is as complete as possible, the thickness of the dried barrier coating 13a is also significantly reduced.

[0125] Furthermore, the robustness of the reduced graphene oxide coating can be demonstrated by a test according to which the coated material is folded and unfolded once, twice, up to twenty times (according to a similar principle to the Flex-Gelbo test). Folding has little effect on the fracture of the reduced graphene oxide. Furthermore, the reduced graphene oxide is not sensitive to humidity, so it loses its barrier properties at higher humidity, such as PVOH.

[0126] exist Figure 1b In FIG. 1 , different embodiments of the substrate material web 10b of the barrier coating of the present invention are shown in cross section. The substrate 11b is a web having a grammage of 50 g / m 2 A thin paper substrate is provided with a thin pre-coating layer 14 of low-density polyethylene, applied by dispersion coating and subsequently dried, so that the final dry thickness is about 1 μm. On the dry surface of the polyethylene pre-coating layer, a pre-coating layer / first dry layer 12b of ascorbic acid and PVOH is applied, the type and application method of which are the same as those of Figure 1a Furthermore, the substrate material coated in this way has a second dry layer 13b of graphene oxide applied to the first dry layer in the same manner as Figure 1aThe same is done in the example of the embodiment of the present invention and subsequently dried and processed in the same manner. A further protective polymer coating 15b of low density polyethylene may be applied to the reduced graphene oxide layer to provide protection when the web of barrier coated substrate material is further wound onto a reel. After sufficient time, when the graphene oxide of layer 13b is reduced (i.e. after two weeks of dry storage in a dark room or on a roll), the resulting barrier coating of reduced graphene oxide ultimately has a thickness of about 500 nm. After two days (the time required to condition the sample for OTR measurement), the OTR was measured to be below 1 cc / m 2 , 24h, 1atm, 23℃ / 50%RH, 21% oxygen.

[0127] Although not shown, a protective polymer coating 15a (such as Figure 1b shown in one) is applied to Figure 1a On the graphene oxide layer 13a in.

[0128] exist Figure 2a In the figure, a laminated packaging material 20a for liquid carton packaging is shown, wherein the laminated material comprises a cardboard body layer 21 of cardboard, the bending force of which is 80mN and the gram weight is about 200g / m 2 , and also includes an outer liquid-tight heat-sealable polyolefin layer 22 applied on the outer side of the body layer 21, which side faces the outside of the packaging container made of the packaging laminate. Layer 22 is transparent to show the printed decorative pattern 27 applied to the paper or paperboard body layer to the outside, thereby informing the contents of the package, the packaging brand and other information for consumers in retail facilities and food stores. The outer polyolefin layer 22 is a traditional low-density polyethylene (LDPE) of heat-sealable quality, but may also include other similar polymers, including LLDPE. It is applied in an amount of about 12g / m 2 . The innermost liquid-tight heat-sealable layer 23 is arranged on the opposite side of the body layer 21, which faces the inner side of the packaging container made of the packaging laminate, that is, the layer 23 will be in direct contact with the packaged product. Therefore, the innermost heat-sealable layer 23 is used to form a strong transverse heat seal of the liquid packaging container made of the laminated packaging material, including a combination of one or more polyethylenes selected from the group consisting of: LDPE, linear low-density polyethylene (LLDPE) and so-called metallocene-LLDPE (m-LLDPE), m-LLDPE is LLDPE produced by polymerizing ethylene monomers with C4-C8 (more preferably C6-C8) α-olefin alkylene monomers in the presence of a metallocene catalyst. Its application amount is about 22g / m 2 .

[0129] The bulk layer 21 is laminated to the barrier coated PET film base material 25a, 10a ( Figure 1a). The middle tie layer 26a is formed by melt extruding it as a thin polymer melt curtain between two webs, and thus the body paperboard layer and the barrier-coated PET film substrate are laminated to each other when all three layers pass through the cooled press nip. The thickness of the middle tie layer 26a is 12 to 18 μm, more specifically 12 to 15 μm.

[0130] The innermost heat sealable layer 23 may consist of one layer or alternatively two or more partial layers of the same or different type of LDPE or LLDPE or blends thereof and is well adhered to the barrier layer surface of the barrier coated PET film substrate 10a, 25a via an intermediate coextruded tie layer 24, such as ethylene acrylic acid copolymer (EAA), thereby bonding one (or more) innermost heat sealable layers to the barrier surface of the barrier coated substrate material web 10a when these layers are applied together in a single melt coextrusion coating step.

[0131] Alternatively, the barrier coated PET film substrate 10a, 25a may be flipped in the laminate to the opposite orientation, ie, with the barrier coating facing the exterior of the bulk layer and laminate.

[0132] exist Figure 2b In FIG. 1 , another laminated packaging material 20b for liquid carton packaging of the present invention is shown, wherein the laminated material has Figure 2a 25 , except that the barrier-coated substrate 25 b is of a different construction but is located in the same position in the laminate.

[0133] The body layer 21 is laminated to the barrier coated paper substrate 25b, 10b ( Figure 1b On the uncoated side of the intermediate adhesive layer 26b (except for the other protective layer 15b), the intermediate adhesive layer 26b is a thin layer of adhesive polymer, which is 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 gap. This lamination step is completed at industrial speed in an efficient cold or ambient lamination step without any energy-consuming drying operation to accelerate the evaporation of water. The dry weight of the applied intermediate adhesive layer 26b is only 3 to 4 g / m 2 , no drying and evaporation operations are required.

[0134] Therefore, the amount of thermoplastic polymer in the laminate layer can be significantly reduced compared to conventional melt extrusion laminated polyethylene layers. Figure 2a The layer 26a described in .

[0135] The innermost heat sealable layer 23 has a thickness of about 22 g / m 2An amount of the heat sealable layer 23 is applied to the surface of the coated barrier of the paper base material through an intermediate coextrusion tie layer (e.g., ethylene acrylic acid copolymer (EAA)) to bond the innermost heat sealable layer 23 to the paper base 10b of the coated barrier, the layers being applied together in a single melt coextrusion coating step.

[0136] Alternatively, the innermost heat sealable liquid tight layer is a pre-made blown film 23b comprising LDPE or LLDPE polymers in any blend and can be laminated to the barrier coated paper substrate, i.e. laminated to the surface of the barrier coating thereof, via an intermediate melt extrusion lamination tie layer 24b comprising more than Figure 2a The layer 24 used in the blown film 23b is a thicker EAA tie layer, or a simpler LDPE tie layer. The thickness of the blown film 23b is 12 μm, but may be as high as 20 μm.

[0137] In an alternative embodiment, the prefabricated blown film 23b is laminated to the metallized coating by another wet lamination step, wherein the aqueous adhesive of the acrylic (co)polymer adhesive layer 24b' is in an amount of 3 to 4 g / m at ambient (cold) temperature. 2 .

[0138] Other embodiments are also disclosed herein that have Figure 2a All of the features described in the invention and melt extruded body laminate layer 26a, but which instead incorporates the features of a barrier coated paper base material 25b and an innermost heat sealable layer construction 23b', either applied by melt extrusion laminate layer 24b or by wet lamination of a preformed film 24b', such as in combination with Figure 2b described.

[0139] Another embodiment is also disclosed herein, wherein Figure 2b The thin wet aqueous adhesive dispersion laminate layer 26a is combined with conventional melt coextrusion coated inner layers 24a and 23a.

[0140] exist Figure 3 , a process of aqueous dispersion coating 30a is shown, which can be used to apply a pre-coat layer / first dry layer 12a, 12b and another graphene oxide barrier coating / second dry layer 13a, 13b. Figure 1aThe paper 11 in the paper is conveyed to the dispersion coating station 32a, where the aqueous dispersion composition is applied to the top surface of the substrate surface by a roller. Due to the high water content of the dispersion composition, there will be a lot of water on the wet coating substrate, which needs to be dried and evaporated by heating to form a continuous pre-coating layer. Drying is carried out by a hot air dryer 33a, so that the water evaporates and is removed from the surface of the substrate surface by air convection. The temperature of the substrate is kept constant when it passes through the dryer, and the temperature is from 60 to 80°C. Alternatively, the drying can also be partially assisted by combining the irradiation heat of an infrared IR lamp with hot air convection drying.

[0141] Repeat afterwards Figure 3 The process shown is to form a continuous graphene oxide coating that is homogenous and has uniform qualities in terms of barrier and surface properties (i.e., uniformity and wettability).

[0142] The resulting barrier pre-coated paper substrate web 34a is conveyed for cooling and wound onto a reel for intermediate storage and subsequent further lamination operations.

[0143] Figure 4a They are shown respectively Figure 2a and 2b The process of the lamination step in the manufacture of the packaging laminate 20a or 20b, wherein the body layer 21, 43 is laminated to the barrier coated substrate web 34a, 10a, 10b ( Figure 1a or 1b) (i.e. Figure 2a and 2b 25a or 25b).

[0144] As combined Figure 2a and 2b As described, the body layer paperboard 21 can be laminated to the barrier coated base material 10, 25a, 25b by melt extrusion lamination (as shown in the figure) or by wet cold dispersion adhesive lamination (but the latter method is not shown). Thus, a molten polymer (e.g. LDPE) curtain 44 is fed into the nip of a laminating roller 45, and the two webs 34a and 43 are also conveyed into the same laminating nip and connected to each other by the extruded LDPE tie layer 44. Thus, the three layers are pressed together and connected at the nip 45, which is formed between the press roller and the cooling roller, thereby cooling the laminate to properly solidify the extruded LDPE tie layer 44. The resulting laminate is conveyed to be wound onto a reel for intermediate storage, or directly to a subsequent lamination operation.

[0145] exist Figure 4b The resulting pre-laminate 49a of paperboard 31b and barrier web 34a is directly from Figure 4aThe lamination operation 40a or is joined and unwound from an intermediate storage reel and transferred to a further lamination step 40b.

[0146] The non-laminated side of the body layer 21, i.e. the printed side thereof, is joined at a cooling nip 48a to a molten polymer curtain 46a of LDPE, which will form the outermost layer 22 of the laminate, where the LDPE is extruded from an extruder feed block and die 47a. Subsequently, the paper pre-laminated web (now coated with the outermost layer 22 on its printed side, i.e. the outer side) passes through a second extruder feed block and die 47b and a lamination nip 48b, where the molten polymer curtain 46b is joined and coated onto the other side of the pre-laminate, i.e. the uncoated inner 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 inner side of the barrier coated base material web to form a finished laminated packaging material 49b, which is ultimately wound onto a storage reel (not shown).

[0147] Alternatively, the two coextrusion steps at the lamination nips 48a and 48b may be performed as two consecutive steps in reverse order.

[0148] According to another embodiment, one or both of the outermost layers may instead be applied in a pre-lamination station, wherein the coextrusion coating layer is first applied to the outside of the (printed) body paperboard layer or to the inner surface of the paper substrate of the coated barrier, after which the two pre-laminated paper webs may be connected to each other, as described above in connection with Figure 4a As described.

[0149] According to yet another embodiment, the innermost layer of heat-sealable, liquid-tight thermoplastic layers may be applied in the form of a pre-made film which is laminated to the barrier-coated base material 10a, 10b.

[0150] As combined Figure 2a and 2b As explained, the innermost pre-film 23 may be laminated to the barrier coated base material 10a, 10b by wet cold dispersion adhesive lamination or by melt extrusion lamination.

[0151] Figure 5aAn embodiment of a packaging container 50a made of a packaging laminate according to the invention is shown. The packaging container is particularly suitable for beverages, sauces, soups, etc. Typically, the capacity of such a package is about 100 to 1000 ml. It can be of any configuration, but is preferably brick-shaped, with longitudinal and transverse seals 51a and 52a, respectively, and optionally with 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 of the package is folded so that the transverse heat seal at the bottom is hidden under the triangular corner fins, which are folded and sealed to the bottom of the package. The top section transverse seal is not folded. In this way, the packaging container, which is only partially folded, is still easy to handle and dimensionally stable enough to be placed on a shelf in a food store or on any flat surface.

[0152] Figure 5b An alternative example of a packaging container 50b made of an alternative packaging laminate according to the present invention is shown. The alternative packaging laminate is thinner due to having a thinner paper body layer, and therefore its dimensions are not stable enough to form a parallelepiped or wedge-shaped packaging container, and will not fold into shape after the transverse seal 52b. The packaging container is still a pillow-shaped bag-like container and is distributed and sold in this form.

[0153] Figure 5c A gable top package 50c is shown folded from pre-cut stock or blanks, formed from a laminated packaging material comprising a paperboard body layer and a barrier coated base material of the present invention. Flat top packages may also be made from similar material blanks.

[0154] Figure 5d A bottle-like package 50d is shown which is composed of a sleeve 54 formed from a pre-cut blank of the laminated packaging material of the present invention in combination with a top 55 formed by injection moulding plastic in combination with an opening device such as a screw plug or the like. For example, such a package is (Tetra )and (Tetra These particular packages are formed by attaching a molded top 55 with an attached opening device in a closed position to a tubular sleeve 54 of laminated packaging material, sterilizing the bottle-top capsule so formed, filling it with the food product, and finally folding over to form the bottom of the package and sealing it.

[0155] Figure 6The principle described in the introduction of the present application is shown, namely that 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 to each other to form an overlapping joint 63. The tube is continuously filled 64 with the liquid food to be filled and divided into individual filled packages by repeated double transverse seals 65 at a predetermined distance below the level of the filled contents in the tube. The packages are separated 66 by cutting between the double transverse seals (top and bottom seals) and finally formed into the desired geometry by folding along prepared crease lines in the material.

[0156] In a preferred embodiment, the use of a PVOH and ascorbic acid pre-coat layer has several advantages:

[0157] - Applying ascorbic acid in combination with PVOH provides better reduction, as the ascorbic acid is slowly released and migrates into the wet graphene oxide layer. Coating with an aqueous ascorbic acid solution without PVOH, especially at high concentrations and / or when the composition is applied directly to the substrate, can lead to the formation of crystals. Such crystals can cause an immediate and intense reduction, causing the (reduced) graphene oxide to become less dispersible during reduction, resulting in undesirable aggregation. (Graphene oxide is hydrophilic, but reduced graphene oxide is hydrophobic.)

[0158] - The reduction was found to be faster than when using an initially dried graphene oxide layer and then an aqueous ascorbic acid solution, as described in the unpublished co-pending application EP21216620 claiming priority from EP20216735.9.

[0159] - Applying ascorbic acid in combination with PVOH also provides improved interlayer adhesion, since the above-mentioned crystallization affects adhesion even if the reducing agent composition is not applied directly to the substrate. The dried PVOH / ascorbic acid layer has better adhesion to the reduced graphene oxide than the ascorbic acid structure with crystals.

[0160] - Applying PVOH in a pre-coating step allows providing a smooth surface to be coated with graphene oxide, thereby improving the alignment of the graphene oxide flakes and thus improving the oxygen barrier properties.

[0161] - Providing PVOH in a pre-coating step means that the finished packaging laminate has a reduced graphene oxide barrier layer on the liquid content side of the PVOH pre-coating layer. Reduced graphene oxide is a good water vapor barrier. PVOH is a good oxygen barrier material, but is sensitive to humidity as described above. The arrangement of the present invention enables the reduced graphene oxide layer to protect the PVOH from moisture, thereby further enhancing the oxygen barrier properties. Therefore, the amount of graphene oxide can be reduced while maintaining the same oxygen barrier properties.

[0162] Finally, it is to be noted that the invention is not limited to the embodiments shown and described above, but may be varied within the scope of the claims.

Claims

1. A method for producing an oxygen barrier material for packaging material (20a; 20b) by coating a reduced graphene oxide layer (13a; 13b) on a web of substrate material (10a; 10b), the method comprising the following steps: a) providing and conveying a web of substrate material; b) coating (32a) the web of substrate material with a first layer of an aqueous composition comprising a reducing agent and a water-dispersible polymer while conveying the web of substrate material; c) drying (33a) the first layer by forced evaporation to form a first dried layer (12a; 12b) comprising a reducing agent and a water-dispersible polymer; d) providing an aqueous composition comprising graphene oxide, wherein the graphene oxide comprises single-layer graphene oxide flakes and multi-layer graphene oxide platelets having up to 20, e.g., 2-10, stacked single-layer graphene oxide flakes; e) applying the aqueous composition of graphene oxide onto the web of substrate material while conveying the web of substrate material; f) drying the wet coating of aqueous graphene oxide on the substrate material web by forced evaporation to obtain a second dry layer of layered graphene oxide particles or flakes (13a; 13b), g) allowing the reducing agent of the first dry layer to reduce the graphene oxide of the second layer to form a barrier coated substrate material web having a dry layer of reduced graphene oxide, Steps c) and d) may be performed before or after steps d), e) and f), so that the first drying layer (12a; 12b) or the second drying layer (13a; 13b) may be formed first.

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

3. The method according to claim 2, comprising a further step i) to be performed before or after step g): coating or laminating the barrier coated substrate material web to a further polymer layer to cover the first dryness layer and the second dryness layer.

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

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

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

7. A method according to any one of claims 2 to 6, wherein the concentration of the reducing agent in the aqueous composition is 2 to 10 wt%, such as 2 to 6 wt%, such as 2 to 5 wt%.

8. The method according to any one of claims 2 to 7, wherein the water-dispersible polymer is selected from the group consisting of polyvinyl alcohol, polyethylene vinyl alcohol, water-dispersible polyolefins, such as water-dispersible polyethylene modified with carboxyl groups, such as water-dispersible ethylene acrylic acid copolymers, starch, modified starch, methylcellulose, ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, sodium carboxymethylcellulose, nano / microfibrillar cellulose and nanocrystalline cellulose.

9. A method according to any one of claims 2 to 8, wherein the concentration of the water-dispersible polymer in the aqueous composition is 1 to 20 wt%, such as 5 to 15 wt%, such as 7 to 13 wt%, most preferably 9 to 13 wt%.

10. The method according to any one of claims 2 to 9, wherein the concentration of graphene oxide in the aqueous composition is 0.1 to 15 wt%, such as 0.5 to 10 wt%, such as 0.5 to 6 wt%, such as 0.5 to 3 wt%, such as 1 to 2 wt%.

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 10 to 500 μm.

12. The method according to any one of the preceding claims, wherein the aqueous composition of graphene oxide consists essentially of graphene oxide and water and is free of polymer.

13. A method according to any one of claims 2 to 12, wherein before or during step g), the dried barrier-coated substrate material web from step f) is irradiated to accelerate the reduction reaction occurring between the applied first and second dry layers.

14. A method according to any one of claims 2 to 13, wherein the web of substrate material is conveyed continuously at a constant speed.

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

16. The barrier-coated substrate material web according to claim 15, wherein the dry layer (13a; 13b) of layered particles or flakes of reduced graphene oxide has a thickness of 50 to 1000 nm, such as 100 to 800 nm, such as 200 to 700 nm, such as 200 to 600 nm, such as 400 to 600 nm, such as 450 to 550 nm.

17. The barrier coated substrate material web according to any of claims 15-16, wherein the substrate material web (11a; 11b) is a polymer film web, a paper or other cellulose based material web, or a polymer coated paper or other cellulose based material web.

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

19. The laminated packaging material (20a; 20b) according to claim 18, further comprising a body layer (21) of paper or paperboard or other cellulose-based material, a first outermost protective material layer (22a; 22b), a second innermost liquid-tight heat-sealable material layer (23a; 23b; 23b'), and a substrate web (10a; 10b) of the barrier coating arranged on the inner side of the body layer of paper or paperboard, between the body layer and the innermost layer.

20. A laminated packaging material (20a; 20b) according to claim 19, wherein the barrier-coated substrate web (10a; 10b) is bonded to the body layer (21) by an intermediate bonding layer (26a; 26b) comprising a composition comprising a binder selected from the group consisting of: acrylic acid polymers and copolymers, starch, cellulose and polysaccharide derivatives, polymers and copolymers of vinyl acetate and / or vinyl alcohol.

21. A packaging container (50a; 50b; 50c; 50d) comprising a laminated packaging material (20a; 20b) as defined in any one of claims 18 to 20.

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