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

Abstract

The present invention relates to a method for manufacturing a barrier-coated substrate web (10; 25a; 25b) coated with a reduced graphene oxide layer. The present invention further relates to a laminated packaging material (20a; 20b) comprising a barrier-coated substrate web (10), in particular for liquid carton food packaging, and to a liquid carton packaging container comprising the laminated packaging material.

Description

Technical Field

[0001] This invention relates to paper or cellulose-based substrates coated with a barrier layer, and a method for manufacturing the substrate by dispersively coating a barrier pre-coating and subsequently vapor-depositing a barrier deposition coating. The invention further relates to laminated packaging materials comprising such a paper or cellulose-based substrate coated with a barrier layer, particularly for liquid carton food packaging, and to such liquid carton packaging containers comprising the laminated packaging material. Background Technology

[0002] Single-use packaging containers for liquid foods are typically made of cardboard or thick cardboard-based packaging laminates. One common type of such packaging container is the Tetra Brik. These are trademarks sold primarily for the aseptic packaging of liquid foods (such as milk, juice, etc.) intended for long-term environmental storage. The packaging material in such known containers is typically a laminate comprising a main or core layer of paper, cardboard, or other cellulose-based material, and an outer liquid-tight layer of thermoplastic. To ensure the container is airtight, particularly oxygen-tight, for purposes such as aseptic packaging and packaging milk or juice, the laminate in these containers typically includes at least one additional layer, most commonly aluminum foil.

[0003] On the inner side of the laminate, i.e., on the side facing the food contents to be filled into the container produced from the laminate, there is an innermost layer applied to the aluminum foil. This innermost layer may consist of one or more partial layers containing a heat-sealable thermoplastic polymer, such as an adhesive polymer and / or a polyolefin. Similarly, on the outer side of the body layer, there is an outermost heat-sealable polymer layer.

[0004] Packaging containers are typically produced using modern high-speed packaging machines, which form packages from packaging material rolls or preforms, fill them, and seal them. Therefore, packaging containers can be produced by transforming a laminated packaging material roll into a tube by welding the innermost and outermost heat-sealable thermoplastic polymer layers together, such that the two longitudinal edges of the roll are joined together at an overlapping joint. This tube is filled with the desired liquid food, and then the tube is separated into individual packages by repeating transverse seals below the level of the contents and spaced a predetermined distance apart. The packages are separated from the tube by cuts along the transverse seals, and the desired geometry, typically a cuboid shape, is obtained by folding along pre-prepared creases in the packaging material.

[0005] The main advantage of this continuous tube forming, filling, and sealing packaging method is that the roll material can be continuously sterilized before tube formation, thus providing the possibility of aseptic packaging methods. This method involves reducing bacteria in the liquid contents to be filled and the packaging material itself, and the filled packaging containers are produced under clean conditions, allowing the filled packaging to be stored for extended periods even at ambient temperatures without the risk of microbial growth in the filled product. As mentioned above, Tetra... Another important advantage of this type of packaging method is the possibility of continuous high-speed packaging, which has a significant impact on cost efficiency.

[0006] Packaging containers for sensitive liquid foods (such as milk or juice) can also be made from sheet preforms or preforms of the laminated packaging material of the present invention. Packaging is produced using a tubular preform of packaging laminate folded into a flat surface, by first standing the preform upright to form an open tubular container capsule, one open end of which is closed by folding and heat-sealing an integral end panel. The sealed container capsule is then filled with the food in question (e.g., juice) through its open end, which is then closed by further folding and heat-sealing a corresponding integral end panel. Examples of packaging containers made from sheet and tubular preforms are the conventional so-called mountain-top packaging. Packaging of this type, with a molded top and / or screw cap made of plastic, also exists.

[0007] The aluminum foil layer in packaging laminates provides gas barrier performance far superior to most other gas barrier materials. Traditional aluminum foil-based packaging laminates for aseptic packaging of liquid foods remain the most cost-effective packaging materials available on the market at their performance levels.

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

[0009] A common motivation in efforts to develop non-aluminum foil materials for liquid food carton packaging is the development of prefabricated films or sheets with high barrier properties, or the combination of several separate barrier materials in multilayer films or sheets. Such films or sheets would replace aluminum foil barrier materials in traditional laminated packaging materials and could be further adapted to conventional lamination and manufacturing processes for laminated packaging materials.

[0010] As the demand for sustainable materials increases, polymer barrier materials derived from fossil resources are becoming less appealing. Therefore, the use of thin barrier coatings (i.e., aqueous dispersion coatings and vapor deposition coatings) remains necessary, as these are virtually negligible in the recycling process and pose few economic challenges based on the recycling of materials and renewable (non-fossil) resources. Dispersion-coated polymers are typically 1-2 μm thick, while vapor deposition barrier coatings are thinner than 0.5 μm, for example, 10 to 100 nm, 15 to 80 nm, or 20 to 50 nm. Various such coatings have been developed over the years and combined in multilayer packaging material structures to seek improved overall performance. While some of these coatings exhibit excellent barrier properties, the beverage carton packaging industry continues to search for the optimal coating or combination of coatings that can replace aluminum foil in all aspects.

[0011] Past developments have involved aqueous polymer compositions, such as PVOH and starch, suitable for dispersion and / or solution coating thin layers. A common challenge with this type of polymer adhesive is their sensitivity to high moisture conditions and the loss of their inherent oxygen barrier properties with exposure to moisture (i.e., conditions in laminated packaging materials for filled liquid carton containers) and with increasing moisture content. It has been concluded that such thin dispersion-coated polymer layers require additional materials to improve gas barrier properties, either in the form of additional compounds in the dispersion composition, such as crosslinking agents or inorganic particles, or as an additional layer of material acting as a water vapor barrier.

[0012] Vapor-deposited (or so-called “vacuum coating”) barrier coatings sometimes achieve very good crack initiation strain characteristics, making them robust enough for folding and sealing of rigid packaging containers. However, naturally, given that such coatings are very thin, they are relatively sensitive to mechanical stress and damage compared to aluminum foil.

[0013] In the years that followed, graphene emerged as a potential barrier material, although it proved prohibitively expensive for full-surface barrier coatings in packaging materials. Theoretically, a graphene sheet as thin as a single molecule could provide excellent gas barrier properties, but in practice, such a thin layer is extremely expensive and difficult to produce. As an alternative, monolayer graphene sheets can be dispersed in organic solvents and coated using dispersion coating or printing techniques, but these variations of graphene layers are too expensive to be included as full-surface coatings in disposable packaging materials. Furthermore, removing the organic solvents from such coatings poses an undesirable problem in modern sustainable industrial-scale coating operations.

[0014] A cheaper source of material for similar barrier coatings with the same or similar properties as graphene is graphene oxide flakes or particles, which are peeled from graphene oxide, a very inexpensive raw material, and subsequently chemically reduced. Such graphene oxide particles or flakes can therefore be chemically reduced to produce corresponding graphene particles or flakes. Graphite is abundant in nature, so graphene obtained by oxidation to graphene oxide / graphene oxide (e.g., via a process called the Hummers method) and subsequent reduction to graphene is much less expensive for use in packaging materials.

[0015] However, providing thin and uniform reduced graphene oxide coatings through large-scale industrial coating processes that start with reduced graphene oxide (i.e., graphene) is problematic because it requires organic solvents to disperse it, and also because the cost of further refining the product (i.e., reducing the graphene oxide) is higher.

[0016] The scientific paper "Impermeable barrier films and protective coatings based on reduced graphene oxide" (by Y. Su, VG Kravets, SL Wong, J. Waters, AK Geim & R.R. Nair), published in *Nature Communications* on September 11, 2014, describes how substrate materials with applied graphene oxide coatings can be made into materials with good gas barrier properties by exposing them to hydrogen iodide vapor at 90°C for 5–30 minutes, or by immersing them in a vitamin C solution at 90°C as a reducing agent for 1 hour. Such methods are not feasible for producing barrier layers or coatings for disposable packaging materials due to economic reasons and the practical infeasibility of packaging material processing plants. Acid vapor treatment, or prolonged treatment of substrate materials in near-boiling liquids, carries a considerable risk of material alteration and is highly impractical in manufacturing processes typically characterized by continuous wide-width roll operations and high manufacturing speeds.

[0017] Therefore, there is a need to improve methods to apply such reduced graphene oxide-based materials to laminated packaging materials at a reasonable cost and to meet future requirements for the sourcing and manufacturing of recyclable and sustainable materials. Summary of the Invention

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

[0019] A general object of the present invention is also to provide a simplified method for manufacturing a substrate with a reduced graphene oxide-coated barrier layer, thereby providing good barrier properties and recyclability and capability that meet the requirements for sustainable liquid carton laminated packaging materials of the future.

[0020] Another general object of the invention is to provide a method for manufacturing foil-free laminated packaging materials for oxygen-sensitive, liquid, semi-solid or wet foods, which do not contain aluminum foil but still have excellent gas barrier properties suitable for cost-effective long-term aseptic packaging.

[0021] One specific objective is to provide a non-aluminum foil paper-based or cardboard-based laminated packaging material that is cost-effective compared to aluminum foil barrier materials, while also possessing good gas barrier properties, recyclability, and sustainable environmental characteristics, for use in the manufacture of packaging for long-term aseptic food storage.

[0022] Another object of the present invention is to provide a cost-effective, non-aluminum foil-based or cardboard-based, mechanically robust and heat-sealable packaging laminate with good gas barrier properties for use in the manufacture of aseptic packaging containers for the long-term storage of liquid foods under environmental conditions to maintain their nutritional quality.

[0023] Therefore, according to the present invention, these objectives can be achieved by methods for manufacturing substrate rolls, laminated packaging materials and packaging containers coated with barrier layers as defined in the appended claims.

[0024] Invention Summary

[0025] According to a first aspect of the present invention, a method is provided for producing an oxygen barrier material for packaging materials by coating a substrate material roll with a reduced graphene oxide layer. The method includes the following steps: a) providing and conveying a substrate material roll; b) providing an aqueous composition comprising graphene oxide, the graphene oxide comprising monolayer graphene oxide flakes and multilayer graphene oxide sheets having up to 20, for example, 2-10 stacked monolayer graphene oxide flakes; c) while the substrate material roll is being conveyed, applying the aqueous composition of graphene oxide to the surface of the substrate material roll; d) drying the wet coating of the aqueous graphene oxide on the substrate material roll by forced evaporation to obtain a first dry layer of layered graphene oxide particles or flakes; e) applying an aqueous solution of a reducing agent to the first dry layer of graphene oxide on the substrate material roll; f) after step e) drying the wet aqueous coating of the reducing agent directly by forced evaporation to obtain a second dry layer of the reducing agent; and g) enabling the reducing agent of the second dry layer to reduce the underlying graphene oxide of the first dry layer at a minimum predetermined temperature for a minimum predetermined time to form a substrate material roll coated with a barrier layer having a reduced graphene oxide dry layer.

[0026] Surprisingly, this method allows the reduction reaction to continue even after the applied reducing agent coating has dried, resulting in the complete conversion of graphene oxide into graphene and achieving excellent gas barrier properties. This is unexpected because it was previously thought that the reducing agent solution must be applied as a liquid bath, spray, or vapor treatment, and that it must be allowed to remain moist on the surface of the graphene oxide layer for an extended period to reduce the dried graphene oxide layer.

[0027] Surprisingly, it was also discovered that heating the coated and dried substrate material roll to an elevated temperature for a certain period of time can promote and accelerate the "dry" reduction reaction. Therefore, by properly designing the coating production line, the coated and dried substrate material roll can be further and fully reduced during the extended transport process of the dried material roll through heated tunnels or similar means, where it is maintained at an elevated temperature. Nevertheless, such a continuous production line must still be much slower than normal coating or lamination operations, and the high-temperature treatment must be kept well below 90°C to avoid the risk of altering the properties of the substrate roll. However, it is highly advantageous that, apart from the water-based coating operation itself, the manufacturing method does not require manipulating wet or liquid treatments along the conversion line.

[0028] The method may include further steps performed before or after step g): i) coating or laminating a barrier-coated substrate material roll onto another polymer layer to cover a second dried layer of reducing agent. Surprisingly, the reduction reaction between the first and second dried layers continues even after the polymer layer (e.g., by extrusion coating of a thermoplastic polymer) is further coated or laminated onto the dried layer of reducing agent. This high-temperature, polymer melt lamination operation does indeed add more heat acting on the surface of the barrier-coated substrate material roll. Therefore, the reduction reaction is further accelerated during this lamination operation.

[0029] The method may, or alternatively, further include the step of: h) winding the coated and dried barrier-coated substrate onto a reel, performed before or after step g). It appears that the reduction reaction of the first dried graphene oxide layer does not cease until it is complete, thus it has been shown that even without further heat treatment after drying, the conversion of graphene oxide to reduced graphene oxide will continue at a low rate until it is complete. Therefore, the color of the newly applied graphene oxide will turn black over time, indicating that the graphene oxide is nearly and almost completely reduced. This is a significant advantage in coating production lines because it eliminates the need for additional heat treatment and because the barrier-coated substrate roll can be wound directly onto a reel after coating and a brief drying operation (i.e., within a period of only about one minute). Furthermore, manufacturing speed can be as fast as possible, since the reduction reaction occurs later and at a slower rate anyway. Sufficient time can be provided to complete the reduction reaction by planning the logistics around shipping and distributing the packaging material rolls to customers. Therefore, by simply storing a roll of substrate material coated with a barrier layer for a predetermined time after coating and drying, the reduction reaction between ascorbic acid in the second drying layer and graphene oxide in the first drying layer can reach a level sufficient to convert graphene oxide into reduced graphene oxide.

[0030] In one embodiment, the dried, barrier-coated roll of substrate material from step f) can be irradiated before or during step g) to accelerate the reduction reaction occurring between the applied first and second dried layers. This irradiation can include ultraviolet light, xenon light, or a laser. The combination of the reducing agent in the second dry coating and this auxiliary irradiation appears to promote a faster but still balanced reduction reaction in the graphene oxide layer. It has been found that in the absence of a reducing agent, the reduced graphene oxide layer by irradiation alone is difficult to control and introduces defects in the material.

[0031] The reducing agent can be selected from hydrogen iodide (HI), sodium citrate, ascorbic acid (vitamin C), lemon juice, vinegar, and green tea. Preferably, the reducing agent is selected from sodium citrate, ascorbic acid (vitamin C), lemon juice, vinegar, and green tea, with ascorbic acid being the most preferred reducing agent. Ascorbic acid is the most environmentally friendly and sustainable reducing agent, and because it is well-regarded in the food and food industry and is a functional reducing agent, it is the best choice for this type of process.

[0032] The oxygen barrier permeability of the coated substrate obtained by the method of the present invention, which is applicable and suitable for industrial production, can be as low as 1 cc / m. 2 24h, 1 atm, 23℃ / 50%RH, 21% oxygen.

[0033] According to a second aspect of the invention, a substrate roll (10) coated with a barrier layer obtained by the method of the first aspect is provided, which is used as an oxygen barrier material in the laminated packaging material of liquid food products, comprising a substrate roll (11) and a dried layer formed of layered reduced graphene oxide particles or sheets applied thereon.

[0034] According to a third aspect of the invention, a laminated packaging material is provided, comprising a substrate material coated with a barrier layer as described in the second aspect. The laminated packaging material may further comprise a first outermost protective material layer and a second innermost liquid-tight heat-sealable material layer.

[0035] For the purpose of packaging liquid food in paper boxes, the laminated packaging material may also include a paper or paperboard or other cellulose-based material body layer, a first outermost protective material layer, a second innermost liquid-tight heat-sealable material layer, and a substrate material coated with a barrier layer, wherein the substrate material coated with the barrier layer is disposed inside the paper or paperboard body layer, between the body layer and the innermost layer.

[0036] The first outermost protective material layer can be a protective polymer layer or a protective polymer coating to prevent dust and moisture from reaching the interior of the laminate. Examples include polymer layers such as thermoplastic polymer layers, liquid-tight heat-sealable polymer layers, and liquid-tight heat-sealable polyolefin layers, such as polyethylene. The second innermost liquid-tight heat-sealable material layer can be a thermoplastic polymer, such as a polyolefin, such as polyethylene.

[0037] Reduced graphene oxide thin layers, which can be coated onto substrate rolls in this manner, exhibit the excellent gas barrier properties of graphene as a material and can be laminated into the standard structure of laminated packaging materials as a "direct alternative to aluminum foil" for liquid carton packaging. Compared to earlier attempts to produce such "direct alternative" films or barrier sheets, substrate rolls coated with reduced graphene oxide (e.g., polymer films or paper substrates) are significantly less sensitive in lamination operations and filling machine operations for laminar material folding, filling, and heat-sealing of carton packaging. This is due to the inherent durability and flexibility of graphene as a material, and also because it is a layer obtained by tightly overlapping sheets, so any oxygen molecule penetrating through the barrier coating must follow the so-called tortoise-like path between the sheets. Therefore, this coating is insensitive to strain cracking and can maintain its oxygen barrier properties well during the transition to packaging. Furthermore, the gas barrier properties of reduced graphene oxide are insensitive to moisture and the permeation of water vapor from the liquid contents of the package, thus allowing it to withstand long-term storage in such filled packaging containers.

[0038] A fourth aspect of the invention provides a packaging container comprising the laminated packaging material of the third aspect, for packaging liquid, semi-solid, or wet food. According to one embodiment, the packaging container is at least partially made of the laminated packaging material of the invention, and according to another embodiment, it is entirely made of the laminated packaging material.

[0039] Detailed description

[0040] The term "long-term storage" as used in conjunction with this invention means that the packaging container should be able to maintain the quality (i.e., nutritional value, hygiene and safety, and taste) of the packaged food under environmental conditions for at least one or two months, for example at least three months, preferably longer, for example six months, for example twelve months, or longer.

[0041] The term "packaging integrity" generally refers to the airtightness of packaging, that is, the leak-proof or breakage-proof nature of the packaging container. This term includes the packaging's resistance to the invasion of microorganisms (such as bacteria, dirt, and other substances) that can spoil the filled food and shorten the package's intended shelf life.

[0042] A major contribution of laminated packaging materials to the integrity of packaging comes from the good internal adhesion between adjacent layers. Another contribution comes from the material's resistance to defects (such as pinholes, cracks, etc. within each layer itself), and yet another contribution comes from the strength of the sealing joints, through which the materials are sealed together during the formation of the packaging container. Therefore, for the laminated packaging material itself, integrity performance primarily focuses on the adhesion between each laminate layer and its adjacent layers, as well as the quality of each individual layer. Regarding the sealing of the packaging, integrity primarily focuses on the quality of the sealing joints, which is ensured by the efficient operation of the filling machine and robust sealing operation, which in turn is guaranteed by the well-suited heat-sealing properties of the laminated packaging material.

[0043] The term "liquid or semi-liquid food" generally refers to a food having a liquid content, which may optionally contain food fragments. Dairy products and milk, soy, rice, grain and seed beverages, fruit juices, nectar, non-carbonated beverages, energy drinks, sports drinks, coffee or tea beverages, coconut water, wine, soup, jalapenos, tomatoes, sauces (such as pasta sauce), beans, and olive oil are some non-limiting examples of the intended food.

[0044] The term "sterile" in relation to packaging materials and containers refers to conditions under which microorganisms are eliminated, inactivated, or killed. Examples of microorganisms are bacteria and spores. Aseptic processes are typically used when products are aseptically packaged in containers. To achieve sustained sterility throughout the shelf life of the packaging, the integrity of the packaging is, of course, crucial. Furthermore, to achieve a long shelf life for filled foods, it may also be important for the packaging to have barrier properties against gases and vapors (such as oxygen) to maintain its original flavor and nutritional value, such as its vitamin C content.

[0045] The term "main layer" generally refers to the thickest layer or the layer containing the most material in a multilayer laminate, i.e., the layer that contributes the most to the mechanical properties and dimensional stability of the laminate (e.g., cardboard or hardboard) and the packaging container folded from the laminate. It can also refer to a layer that provides a greater thickness gap in a sandwich structure, which further interacts with stabilizing facet layers on each side of the main layer to achieve sufficient mechanical properties and dimensional stability.

[0046] Thickness measurements were performed using a Titan 80-300 FEI instrument via transmission electron microscopy. Samples were prepared using ultrathin sectioning on a Leica EM UC6 microtome.

[0047] OTR is measured using the Oxtran 2 / 21 (Mocon) device, which is based on a coulomb sensor.

[0048] The method used to determine OTR determines the amount of oxygen per surface and per unit time when passing through a material at a specific temperature and given atmospheric pressure over a specific time period (e.g., in an atmosphere of 21% oxygen over 24 hours).

[0049] Water vapor transmission rate (WVTR) was measured using a Permatran 3 / 33 (Mocon) instrument (standard: ASTM F 1249-13, using a modulated infrared sensor for relative humidity detection and WVTR measurement) at 38°C and 90% drive force.

[0050] The term "graphene oxide" includes both single-layer graphene oxide sheets and multilayer graphene oxide sheets, having up to 20, for example, 2-10 stacked single-layer graphene oxide sheets. Only a smaller amount, i.e., less than 15% by weight, for example less than 10% by weight, or less than 5% by weight, based on the dry weight of the graphene oxide material, can be a graphene oxide sheet consisting of up to 20 single-layer graphene oxide sheets that have been peeled off, but whose lateral particle size is smaller than that of large-volume graphene oxide particles (i.e., so-called "graphene oxide nanosheets," thus still nanoscale).

[0051] Such small amounts of lateral nanoscale graphite flakes are permissible as long as they do not excessively degrade the performance of the graphene-based material. Preferably, based on dry weight, the nanographite flakes / layers are present in the composition in amounts of less than 15% by weight, such as 10% by weight, such as 5% by weight or less.

[0052] Suitable graphene oxide materials for use in the aqueous dispersions of the present invention are, for example, pure graphene oxide from Graphenea, at least 95% exfoliated, or paste-like graphene oxide from Abalonyx.

[0053] Therefore, the substrates suitable for the barrier coating of the present invention are not limited to a certain type of substrate, but include polymer films and paper, paperboard or other cellulose-based substrates, or polymer-coated paper, paperboard or other polymer-coated cellulose-based substrates. The substrate material roll can be a polymer film roll, a paper or paperboard roll, or a polymer-coated paper or paperboard roll.

[0054] The polymer film substrate can be made of, for example, polyester or polyolefin. Typical polyesters are polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyhydroxyalkanoate (PHA), and polylactic acid (PLA). Typical polyolefin films can be made of mostly polypropylene or polyethylene, such as biaxially oriented polypropylene (BOPP), biaxially oriented high-density polyethylene (BOHDPE), or linear low-density polyethylene (LLDPE).

[0055] Cellulose-based substrates can be based on any type of natural cellulose, fibrous or protocellulose, and they can be further coated with polymers of the aforementioned types, preferably with polyolefins such as polyethylene, for subsequent application of a barrier coating according to the method of the invention.

[0056] Typically, a suitable paper or cellulose-based substrate for carrying the barrier coating of the present invention should be thin, for example, 60 g / m². 2 Or below, for example, 50g / m 2 Or below, preferably 45g / m 2 Or less, and more preferably 40 g / m 2 Or below. On the other hand, when thinner or with a weight below 30g / m³ 2 When a cellulose-based substrate is coated with a wet dispersion and subsequently dried, its mechanical strength may be too weak and / or its dimensional stability poor, leading to shrinkage or curling problems. Therefore, a basis weight of 30 to 50 g / m³ is more preferable. 2 For example, the optimal value is 35 to 45 g / m³. 2 The paper.

[0057] In one embodiment, the concentration of graphene oxide in the aqueous composition is 0.1 to 15 wt%, for example 0.5 to 15 wt%, for example 0.5 to 10 wt%, for example 0.5 to 6 wt%, for example 0.5 to 3 wt%, for example 1 to 2 wt%. If the concentration is below 0.5 wt%, it may be difficult to coat enough graphene oxide onto the substrate material roll, so that the applied coating may not provide sufficient oxygen barrier properties, but if lower barrier properties are required, a thinner coating can be applied, for example as low as 0.1 wt%. On the other hand, if the concentration is above 6 wt%, for example above 10 wt%, for example above 15 wt%, the applied coating may be more difficult to dry because the applied graphene wet oxide material coating is unnecessarily thick and contains a large amount of water between the flakes and layers of the composition. If the concentration of graphene oxide is above 3 wt%, the coating may be difficult to dry, and if it is above 6 wt%, it may be even more difficult to apply. However, aqueous compositions of graphene oxide exhibit shear-thinning behavior, making it possible to apply thicker compositions with reasonable coating thickness and good layer formation, and high coating rates.

[0058] The aqueous composition of graphene oxide essentially comprises only graphene oxide and water. The composition contains virtually no other polymers, i.e., no binders or similar components. Preferably, it contains only up to 5% by weight, such as up to 3% by weight, 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.

[0059] In one embodiment, the aqueous composition of graphene oxide is coated with a wet thickness of 10 to 400 μm. If it is thinner than 10 μm, the coating may not provide sufficient oxygen barrier properties, and if it is thicker than 400 μm, the amount of water that can be dried from the coating or the viscosity of the thicker coating composition may be impractical or unmanageable.

[0060] For coating with a second layer containing a reducing agent, the concentration of the reducing agent, ascorbic acid (vitamin C), is 0.5-15% by weight, for example, 1 to 10% by weight, for example, 2 to 7% by weight, for example, 3 to 6% by weight. A solution having at least 0.5% by weight, for example, 1% by weight, of ascorbic acid is necessary for the desired effect of the reduced graphene oxide, and a better lower limit for a functionally good concentration is about 2% by weight, preferably 3% by weight. When the concentration exceeds 7% by weight, the effect is not significant, and when the concentration exceeds 10% by weight, further increasing the concentration does not seem to have much effect and does not seem to increase the effect.

[0061] The drying steps d) and f) of the method of the present invention can be carried out by forced evaporation.

[0062] Furthermore, the substrate can be conveyed at a constant speed. This is an important prerequisite for obtaining the optimal and reliable amount of coating to be applied in the coating operation. Moreover, industrially feasible roll-to-roll and coating speeds can range from 100 m / min, for example from 200 m / min, for example from 300 m / min, for example from 400 m / min, depending on the drying capacity within the coating line. Drying is suitable to be carried out by hot air convection, which can be combined with irradiation by an infrared heater. The drying of the wet coating occurs within a few seconds during transit through a drying station, which can be many meters long, for example at least 5 meters, for example at least 10 meters, for example at least 15 meters, for example at least 20 meters, depending on the temperature of the substrate surface and the speed at which the roll-to-roll travels along the coating line.

[0063] Graphene oxide is therefore dispersed in water and can be applied using an aqueous "dispersion coating" process or a so-called "liquid film coating" process. From the perspective of environmental sustainability and occupational safety, an all-aqueous dispersion is preferred.

[0064] The aqueous composition can be applied to a substrate material roll in the form of ink and / or dispersion coating.

[0065] Suitable application methods can therefore include suitable printing methods, such as aniline 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, and spraying, dip coating, and brush coating. Through these printing or coating methods, a suitable dry material thickness of 0.1 to 10 μm can be applied, for example, 0.5 to 8 μm, 0.5 to 6 μm, 0.5 to 4 μm, 0.5 to 3 μm, or 0.5 to 2.5 μm.

[0066] Several consecutive coating steps may be required to form a thick graphene oxide layer to achieve greater thickness. For providing a gas barrier coating, applying 0.1 to 3 μm, such as 0.5 to 2.5 μm, or for example, about 2 μm of dry graphene oxide, will be sufficient. For other purposes, such as conductive coatings or other applications, a thicker coating may be suitable, but it may not be as a full-surface coverage coating, but rather as a coating applied only to selected localized areas of the substrate material roll.

[0067] The experiments of this invention were conducted by gravure coating, but it is believed that any of the above liquid film coating methods are suitable for providing good gas barrier coatings.

[0068] The amount of dispersion stabilizer or similar additive used for dispersion coating may also be included in the aqueous graphene oxide composition, preferably in an amount not exceeding about 1% by weight based on the dry coating.

[0069] The total dry content of the aqueous composition containing graphene oxide should be 0.5 to 15% by weight, for example 0.5 to 10% by weight, for example 0.5 to 8% by weight, for example 0.5 to 6% by weight. At lower dry contents, the quality of the gas barrier layer formation may not be good enough, and therefore the gas barrier performance produced by the dry coating may not be very good.

[0070] 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, the appropriate application amount for each layer is 0.1 to 1.5 g / m². 2 For example, 0.5 to 1 g / m 2This allows for the acquisition of higher quality overall layers with lower amounts of liquid gas barrier compositions. For example, a dry-coated graphene oxide layer with a total thickness of approximately 2 μm will have a total thickness of approximately 0.5 μm (500 nm) after reduction to reduced graphene oxide. It has been evaluated that two consecutively applied and dried graphene oxide coatings will be reduced to graphene oxide as easily as a single, dry graphene oxide coating of the corresponding thickness after coating and drying with an aqueous ascorbic acid solution. Consecutively applied and dried graphene oxide coatings may mask defects that may be present in each coating, as they overlap with defect-free portions of the other coating in most cases. In this way, the entire applied graphene oxide layer can be virtually defect-free.

[0071] Graphene oxide coatings can be applied directly to paper or cardboard substrates, but require a smooth and dense surface to ensure uniform and continuous coating formation.

[0072] For optimal performance of the invention, a thin polymer pre-coating layer may be applied before coating the graphene oxide layer onto the paper or cellulose-based substrate material roll, and suitably in the form of an aqueous composition used in the previous dispersion coating step. The thickness of this pre-coating layer may be 0.5 to 1.5 μm, for example, about 1 μm.

[0073] The pre-coated polymer can be any suitable water-dispersible polymer and / or a renewable, non-fossil-based polymer. In one embodiment, the pre-coated polymer can be selected from the group consisting of: polyvinyl alcohol (PVOH, PVAL), polyvinyl alcohol (EVOH, EVAL), polyolefins such as water-dispersible polyethylene, starch, modified starch, methylcellulose, ethylcellulose, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC), sodium carboxymethyl cellulose (NaCMC), nano / microfiber cellulose (NFC / MFC / CNF), and nanocrystalline cellulose (NCC / CNC).

[0074] In a further embodiment, the pre-coating may comprise a renewable polymer or substance selected from starch, modified starch, methylcellulose, ethylcellulose, carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), hydroxypropyl methylcellulose (HPMC), sodium carboxymethylcellulose (NaCMC), nano / microfiber cellulose (NFC / MFC / CNF), or nanocrystalline cellulose (NCC / CNC).

[0075] This natural, plant-based, non-fossil-based polymer or substance can provide good surface smoothness to deliver a uniform graphene oxide coating.

[0076] Suitable starch materials or starch derivatives may be, for example, oxidized starch, cationic starch, and hydroxypropylated starch.

[0077] In one embodiment, the pre-coated polymer is a very thin polyethylene coating that supports the neat separation of the reduced graphene oxide coating from the paper or paperboard substrate material, so that the recycled fibers can remain essentially free of reduced graphene oxide material.

[0078] Further low-density polyethylene protective polymer coatings can be applied to the reduced graphene oxide layers (including any residual ascorbic acid on their surface) for protection, as the barrier-coated substrate material roll can be further wound onto rollers or further laminated into a multilayer material structure. By encapsulating the reduced graphene oxide between the polyethylene layers, the reduced graphene oxide can remain separated from the fiber portion in subsequent recycling operations.

[0079] Cardboard-based laminated packaging materials for liquid food packaging may include a paper or paperboard body layer, a first outermost protective material layer, a second innermost liquid-tight heat-sealable material layer, and a substrate material roll coated with a barrier layer, wherein the substrate material roll coated with a barrier layer is disposed inside the paper or paperboard body layer, facing the interior of the packaging container made of the packaging material, and between the body layer and the innermost layer.

[0080] The paper or paperboard body layer used in this invention typically has a thickness of about 100 μm to about 600 μm and a g / m² of about 100-500 g / m³. 2 Optimal 200-300g / m 2 The surface weight, and can be regular paper or cardboard with suitable packaging quality.

[0081] For low-cost, aseptic, long-term packaging of liquid foods, thinner packaging laminates with a thinner paper core layer can be used. Packaging containers made from this type of laminate are not folded but rather resemble pillow-shaped pouches. The paper suitable for this type of pouch packaging typically has a strength of approximately 50 to approximately 140 g / m³. 2 Preferably about 70 to about 120 g / m 2 More preferably 70 to about 110 g / m 2 The surface weight. If the substrate material roll coated with the barrier layer in this invention itself brings a certain degree of stability to the laminated material, the paper layer corresponding to the "body" layer may be thinner, and the substrate material roll coated with the barrier layer in the sandwich structure interacts with each other, thereby still producing a laminated packaging material with the full required mechanical properties.

[0082] The substrate material roll can be a polymer film roll, a paper or paperboard roll, or a paper or paperboard roll coated with a polymer.

[0083] Therefore, the substrates suitable for the barrier coating of the present invention are not limited to a certain type of substrate, but include polymer films and paper, paperboard or other cellulose-based substrates, or polymer-coated paper, paperboard or other polymer-coated cellulose-based substrates. The polymer film substrate can be made, for example, of polyester or polyolefin. Typical polyesters are polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyhydroxyalkanoate (PHA), and polylactic acid (PLA). Typical polyolefin films can be made of mostly polypropylene or polyethylene, for example of biaxially oriented polypropylene (BOPP), or biaxially oriented high-density polyethylene (BOHDPE), or linear low-density polyethylene (LLDPE).

[0084] Cellulose-based substrates can be based on any type of natural cellulose, fibrous or protocellulose, and they can be further coated with polymers of the aforementioned types, preferably with polyolefins such as polyethylene, for subsequent application of a barrier coating according to the method of the invention.

[0085] The thickness of the dried layer from the reduced graphene oxide layered particles or sheets can be 50 to 1000 nm, for example 100 to 800 nm, for example 200 to 700 nm, for example 200 to 600 nm, for example 400 to 600 nm, for example 450 to 550 nm.

[0086] The dried layer from the reduced graphene oxide sheet or particles can be further coated with a thin protective coating of a thermoplastic polymer (e.g., dispersible coating polyethylene or another water-soluble or water-dispersible polymer). It can be further laminated to adjacent polymer layers, such as polyolefin layers, for example, low-density polyethylene. This further coating and / or lamination can be performed before or after the complete reduction of the graphene oxide in the first dried graphene oxide layer.

[0087] The barrier-coated substrate material roll can be bonded to the main layer using an intermediate adhesive or thermoplastic polymer, thereby bonding the uncoated surface of the barrier-coated substrate material roll to the main layer. According to one embodiment, the adhesive layer is a polyolefin layer primarily comprising ethylene monomer units, such as, in particular, a polyvinyl polyolefin copolymer or blend layer. The adhesive layer bonds the main layer to the barrier-coated substrate material roll by melt-extruding and laminating an adhesive polymer layer between the main layer roll and the substrate material roll, and simultaneously pressing the three layers together as they advance through the gap of laminating rollers, thereby providing a laminated structure through extrusion lamination.

[0088] In another embodiment, a substrate material roll coated with a barrier layer can be bonded to a base layer by wet-applying an aqueous dispersion of an adhesive composition containing a viscous polymer binder to one of the surfaces of the rolls to be laminated, and pressing the two paper rolls together as they advance through the gap of the laminating rolls, thereby providing a laminated structure through wet lamination. During subsequent lamination, the moisture in the aqueous viscous composition is absorbed into the fibrous cellulose network of the base paperboard and partially evaporates over time. Therefore, a forced drying step is not required. The viscous polymer binder is selected from acrylic polymers and copolymers, starch, cellulose and polysaccharide derivatives, and polymers and copolymers of vinyl acetate and vinyl alcohol. For optimal environmental and sustainability properties, viscous binders derived from plant or non-fossil sources are preferred.

[0089] Suitable thermoplastics for both the outermost and innermost heat-sealable liquid-tight layers are polyolefins, such as homopolymers or copolymers of polyethylene and polypropylene, preferably polyethylene, and more preferably low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), mono-site catalyst 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 blend of m-LLDPE and LDPE to obtain optimal lamination and heat-sealing properties.

[0090] The outermost layer is typically applied with a thickness of 5 to 20 μm, for example, 10 to 15 μm. The innermost layer can be applied with a thickness range of 10 to 50 μm, for example, 10 to 40 μm, for example, 10 to 30 μm, for example, 10 to 25 μm.

[0091] The same thermoplastic polyolefin-based materials (particularly polyethylene) listed for the outermost and innermost layers are also suitable for the adhesive layers within the laminate, i.e., the adhesive layer between the host layer or core layer (e.g., 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 can typically be applied in an amount of 10 to 25 μm, for example, 10 to 20 μm, or 10 to 15 μm.

[0092] In another embodiment, the second innermost liquid-tight heat-sealable polyolefin layer is a pre-formed film containing the same or similar polyolefins as described above to improve the robustness of the mechanical properties of the packaging material. Due to the manufacturing processes in blown film and film casting operations, and optional subsequent film orientation steps, the polymer of such films acquires different properties than that of (co)extruded coated polyolefin layers. Such pre-formed polymer films thus contribute to the mechanical robustness of the laminated packaging material and the mechanical strength and packaging integrity of the packaging containers formed and filled by the laminated packaging material.

[0093] According to alternative embodiments, a suitable adhesive or bonding layer within the laminate (such as, for example, between the body layer or core layer and the substrate material roll coated with a barrier layer, or between the outer heat-sealable layer and the substrate material roll coated with a barrier layer) is a so-called viscous thermoplastic polymer (such as a modified polyolefin), primarily based on LDPE or LLDPE copolymers or graft copolymers having monomer units containing functional groups (e.g., carboxyl or glycidyl functional groups) (e.g., (meth)acrylic acid monomers or maleic anhydride (MAH) monomers) (i.e., ethylene-acrylic acid copolymer (EAA) or ethylene-methacrylic acid copolymer (EMAA)), ethylene-(meth)acrylic acid glycidyl ester copolymer (EG(M)A), or MAH-grafted polyethylene (MAH-g-PE). Another example of such a modified polymer or adhesive polymer is a so-called ionomer or ionomer polymer. Preferably, the modified polyolefin is ethylene-acrylic acid copolymer (EAA) or ethylene-methacrylic acid copolymer (EMAA).

[0094] If necessary, the surface of the substrate material roll can be pretreated with oxidation treatments such as corona treatment, plasma treatment, or ozone treatment to improve the adhesion strength to the graphene oxide layer or the reduced graphene oxide layer.

[0095] The laminated packaging material produced according to the above method provides good integrity when transformed into a filled packaging container through good adhesion between adjacent layers within the laminated structure and through the individual and combination of barrier coatings and barrier pre-coatings that provide good quality.

[0096] According to a further embodiment, the packaging container formed of laminated packaging material can be partially sealed, filled with liquid or semi-liquid food, and then sealed by the packaging material itself (optionally combined with the plastic opening or top portion of the packaging).

[0097] In summary, the substrate material rolls coated with barrier layers manufactured by the method of the present invention, and the laminated packaging materials obtained therefrom, provide robust and reliable packaging with excellent oxygen barrier properties for use in packaging liquid foods with long shelf lives and extended storage. The structure of the laminated packaging materials is more suitable for forming foldable packaging, both because of improved adhesion between the substrate and the barrier coating, and because of improved contribution of the barrier coating substrate itself to the gas barrier performance. This may also be due to improved cohesion and adhesion between the pre-coating and the barrier coating in the cellulose-based substrate coated with the barrier layer. Attached Figure Description

[0098] The preferred embodiments of the present invention will now be described with reference to the accompanying drawings, wherein:

[0099] Figure 1a An embodiment of the substrate coated with reduced graphene oxide according to the present invention is shown schematically in cross-section.

[0100] Figure 1b Different embodiments of the substrate coated with reduced graphene oxide according to the present invention are illustrated schematically.

[0101] Figure 2a A schematic cross-sectional view of a laminated packaging material according to the present invention is shown, comprising a coating of... Figure 1a The substrate of reduced graphene oxide,

[0102] Figure 2b A schematic cross-sectional view of a laminated packaging material according to the present invention is shown, comprising a coating of... Figure 1b The substrate of reduced graphene oxide,

[0103] Figure 3 This schematically illustrates a method for dispersing and coating an aqueous composition of graphene oxide onto a substrate.

[0104] Figure 4a The diagram schematically illustrates a method for melt-extruding and laminating two material rolls together via an intermediate thermoplastic polymer.

[0105] Figure 4b A method is schematically shown for melting (co-)extruding one or more thermoplastic polymer coatings onto a roll substrate, for example, to form the innermost and outermost layers of the packaging laminate of the present invention.

[0106] Figure 5a , 5b Figures 5c and 5d illustrate typical examples of liquid carton packaging containers produced from laminated packaging materials according to the present invention, and

[0107] Figure 6 This demonstrates the principle of how such liquid carton packaging containers can be manufactured using packaging laminates through a continuous, roller-feed, forming, filling, and sealing process. Detailed Implementation

[0108] Example

[0109] Example 1

[0110] A 1 wt% aqueous dispersion of graphene oxide monolayer sheets (pure quality, peeled to at least 95%, from Graphenea) was continuously stirred until the moment it was applied to the substrate. The well-dispersed aqueous composition was thus applied to a forward-moving cardboard (bending stiffness of 80 mN, basis weight of 200 g / m²). 2On a liquid paperboard roll, the paperboard was pre-coated with polyethylene to a wet thickness of approximately 400 μm using a Hirano lab-coater. At a roll surface temperature of approximately 60°C, the water in the applied coating composition was evaporated from the surface by air convection in a hot air dryer for approximately 1 minute. The resulting dry coating thickness of graphene oxide applied to the PE-coated paper was measured to be approximately 2.2 μm.

[0111] The resulting substrate coated with a 2.2 μm layered graphene oxide thin dry coating exhibits approximately 25 cc / m². 2 The oxygen permeability was measured using an Ox-Tran 2 / 21Mocon instrument at 24 hours, 1 atmosphere, 23°C / 50% RH, and 21% oxygen. The graphene oxide-coated substrate was light brown.

[0112] The roll coated with graphene oxide was then coated with a 3% by weight ascorbic acid aqueous solution and dried again at a surface temperature of about 60°C for about 1 minute. After cooling to room temperature, it was finally wound onto a spool.

[0113] Samples were also collected from coated and dried coated paperboard rolls to be continuously held at a higher surface temperature of 60°C for 2 hours. In these samples, it was concluded that the graphene oxide in at least the surface portion of the coated graphene oxide had been completely reduced by the reduction reaction with the ascorbic acid added in the final coating after a period of elevated temperature. The color of the coated paperboard changed from light brown to dark brown. The OTR of these samples was measured in the same manner as described above, and after two days, it was found to be at 1 cc / m³. 2 The following conditions were observed for 24 hours at 1 atmosphere, 23°C / 50% RH, and 21% oxygen (the time taken to adjust the sample for OTR measurements). By this time, the sample had completely darkened. Measurements showed that the resulting dry coating thickness with the reduced graphene oxide was 530 nm, approximately 0.5 μm. Therefore, through the reduction reaction of the graphene oxide flakes, the distance between the graphene flakes becomes smaller, providing significantly improved barrier properties, and this reduction process therefore occurs within the dry graphene oxide coating and continues over time.

[0114] Therefore, by reducing the applied graphene oxide to graphene, even partially or on the coating surface, the oxygen barrier level is significantly increased to the required and desired level for laminated packaging materials used in aseptic liquid carton packaging, namely below 1 cc / m³. 2 (24 hours, 1 atmosphere, 23℃ / 50%RH, 21% oxygen).

[0115] Two hours before this type of reduction reaction was carried out at high temperature, the graphene oxide on the sample surface was not completely reduced, as evidenced by the fact that the coating was still light brown.

[0116] More samples were taken from the rolls after 1 and 2 weeks of storage at ambient temperature (23°C) and compared with heat-treated samples. After 1 week of ambient storage, the reduction reaction proceeded to a higher level within the dried layer of the paper after being wound onto the roll, but still did not reach a complete reduction level. This yielded a dark brown to almost black color and approximately 10 cc / m² of the sample. 2 The OTR is indicated by 24 hours, 1 atmosphere, 23°C / 50% RH, and 21% oxygen.

[0117] Two weeks later, the sample turned black after being held at high temperature for only 2 hours, indicating that reduction was complete. This conclusion was drawn by measuring the correspondingly low OTR value of the sample from the roll, which was below 1 cc / m. 2 24 hours, 1 atmosphere, 23℃ / 50%RH, 21% oxygen.

[0118] Therefore, the Williams-Landel-Ferry model, or WLF for short, appears to be applicable to the reduction reaction and 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 dried graphene oxide and the ascorbic acid coating until complete conversion is achieved, even after the coated roll has dried and been wound onto a reel for transport and storage.

[0119] This result is advantageous because a 2-hour reaction time is virtually impractical in industrial coating and manufacturing processes, as it means that the reduction to graphene in the applied graphene oxide coating can continue even after the coating operation. Therefore, this can be achieved simply by logically planning the long-term storage of the barrier-coated rolls prior to further use. Alternatively, the barrier-coated substrate rolls can be laminated to form finished packaging materials before the planned storage of the rolls. Further acceleration of the reduction reaction can be advantageously and conveniently achieved in the case of lamination methods involving heating (e.g., polymer melt extrusion coating or polymer melt extrusion lamination). Depending on the specific circumstances, further intermediate storage may be planned to occur partly during transport, partly before transport, and / or partly after transport at the customer's facility.

[0120] In addition, regarding the attached diagram:

[0121] exist Figure 1aThe image shows a cross-section of an embodiment of the substrate material roll 10a coated with a barrier layer according to the present invention. The substrate material 11a is a polyethylene terephthalate (PET) film with a thickness of 36 μm. Its oxygen permeability (OTR) is approximately 30 cc / m². 2 24 hours, 23℃ / 80%RH, 100% oxygen.

[0122] The PET film has a graphene oxide dry coating 12a, which is applied by coating with an aqueous dispersion and then heated and dried to evaporate the water. The dry weight of the graphene oxide coating thus applied is approximately 1.3 μm. Furthermore, the substrate material thus coated has a second ascorbic acid dry coating 13a, which is applied as a 3% by weight aqueous solution of ascorbic acid onto the first graphene oxide dry coating. The second dry coating 13a is also applied as an aqueous coating and then heated and dried to evaporate the water. The dried, thus coated substrate material roll can be further heat-treated for a period of time, or simply stored at ambient temperature for at least two weeks, after which the first dry barrier coating of graphene oxide has been reduced as much as possible to reduced graphene oxide, ideally to graphene. After the reduction reaction is as complete as possible, the thickness of the dry barrier coating 12a has also been significantly reduced. Therefore, in the example above, the dry graphene oxide layer has a thickness of approximately 1.3 μm immediately after drying, while the final thickness of the same reduced graphene oxide is 300 nm, or approximately 0.3 μm. The OTR was measured to be 0.1 cc / m 2 24 hours, 23℃ / 80%RH, 100% oxygen. If the same membrane substrate is coated with half the thickness on each side, i.e., 150nm of dry-reduced graphene oxide is coated on each side of the membrane, then the OTR is changed to 0.02cc / m. 2 24 hours, 23℃ / 80%RH, 100% oxygen.

[0123] Furthermore, the robustness of the reduced graphene oxide coating can be demonstrated (based on a principle similar to the Flex-Gelbo test) by folding and unfolding the coating material once, twice, and up to twenty times. After the first fold, the OTR increased to 0.03 cc / m 2 The reduced graphene oxide was tested at 23°C / 80% RH and 100% oxygen for 24 hours, but did not increase further after 20 folding operations. Furthermore, the reduced graphene oxide is insensitive to moisture and therefore loses its barrier properties at higher humidity levels, such as PVOH. Therefore, the OTR at 80% RH is the same as that of the barrier-coated film in this example.

[0124] exist Figure 1b The image shows different embodiments of the substrate material roll 10b coated with a barrier layer according to the present invention, illustrated in cross-section. The substrate material 11b has a basis weight of 50 g / m². 2The thin paper substrate has a low-density polyethylene thin pre-coating 14, which is applied by dispersion coating and subsequent drying, thus having a final dried thickness of about 1 μm. On the dried surface of the polyethylene pre-coating, a coating is applied... Figure 1a The same type of graphene oxide drying layer 12b and with Figure 1a The application method is the same. Therefore, the dry weight of the graphene oxide coating is approximately 2 μm. Furthermore, the substrate material thus coated has a second ascorbic acid dry coating 13b, which is consistent with... Figure 1a The same method was applied to the first dry coating of graphene oxide, which was then dried and processed in the same manner. Another protective polymer coating 15b of low-density polyethylene, comprising residual ascorbic acid on its surface, can be applied to the reduced graphene oxide layer to provide protection as the substrate material roll coated with the barrier layer is further wound onto a roller. After sufficient time, when the graphene oxide of layer 12b is reduced (i.e., after two weeks of drying and storage in a dark room or on a roller), the thickness of the barrier coating with the resulting reduced graphene oxide eventually reaches approximately 500 nm. After two days (the time required to adjust the sample for OTR measurement), the OTR was measured to be less than 1 cc / m. 2 24 hours, 1 atmosphere, 23℃ / 50%RH, 21% oxygen.

[0125] Protective polymer coating 15a (e.g.) Figure 1b The protective polymer coating in the middle can also optionally be applied to Figure 1a It is on the graphene oxide layer 12a, but not shown.

[0126] exist Figure 2a The image shows a laminated packaging material 20a for liquid carton packaging, wherein the laminated material comprises materials having a flexural strength of 80 mN and a strength of approximately 200 g / m³. 2 The outer layer 21 is a paperboard body layer of paperboard weight, and also includes an outer liquid-tight heat-sealable polyolefin layer 22 applied to the outside of the body layer 21, facing the exterior of the packaging container made of packaging laminate material. Layer 22 is transparent to show outwardly printed decorative patterns 27 applied to the paper or paperboard body layer, thereby informing consumers of the contents of the packaging, the packaging brand, and other information for retail facilities and food stores. The polyolefin of the outer layer 22 is conventional low-density polyethylene (LDPE) of heat-sealable quality, but may also include other similar polymers, including LLDPE. Its application amount is approximately 12 g / m². 2The innermost liquid-tight heat-sealable layer 23 is disposed on the opposite side of the main layer 21, facing the interior of the packaging container made of the packaging laminate material, i.e., layer 23 will be in direct contact with the packaged product. Therefore, this innermost heat-sealable layer 23 forms a strong lateral heat-sealable portion of the liquid packaging container made of the laminated packaging material, comprising a combination of one or more polyethylenes selected from the group consisting of: LDPE, linear low-density polyethylene (LLDPE), and LLDPE (i.e., so-called metallocene-LLDPE (m-LLDPE)) prepared 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 approximately 22 g / m³. 2 .

[0127] The main body layer 21 is laminated to the intermediate low-density polyethylene (LDPE) adhesive layer 26a. Figure 1a The PET film substrate material 25a; 10a is coated with a barrier layer. The intermediate adhesive layer 26a is formed by melt-extruding it into a thin polymer melt curtain between two rolls, thus laminating the main paperboard layer and the barrier-coated PET film substrate together as all three layers pass through the gap of the cooled pressure rolls. The thickness of the intermediate adhesive layer 26a is 12 to 18 μm, more specifically 12-15 μm.

[0128] The innermost heat-sealable layer 23 may consist of a single layer or alternatively two or more partial layers of the same or different types of LDPE or LLDPE or blends thereof, and is well adhered to the surface of the barrier layer of the PET film substrate material 10a; 25a coated with the barrier layer via an intermediate co-extrusion bonding layer 24 (e.g., an ethylene acrylate copolymer (EAA) intermediate co-extrusion bonding layer). Thus, when these layers are applied together in a single melt co-extrusion coating step, the intermediate co-extrusion bonding layer 24 bonds the innermost heat-sealable layer to the surface of the barrier layer of the substrate material roll 10a coated with the barrier layer.

[0129] Alternatively, the PET film substrate 10a; 25a coated with the barrier layer can be turned in the opposite direction in the laminate, i.e., the barrier coating points to the outside of the main layer and the laminate.

[0130] exist Figure 2b The image shows different laminated packaging materials 20b of the present invention for use in liquid carton packaging, wherein the laminated materials have the same properties as... Figure 2a The similar layered structures, except for the substrate material 25b coated with the barrier layer, are located in the same position within the laminated material.

[0131] The main body layer 21b is laminated to the intermediate adhesive layer 26b of the adhesive polymer thin layer by wet lamination. Figure 1bThe paper substrate 25b is coated with a barrier layer; the uncoated side (excluding the additional protective layer 15b) is laminated by applying an aqueous dispersion of polyvinyl acetate adhesive to one of the surfaces that will adhere to each other, followed by pressing them together in the roll gap. This lamination step is performed at industrial speed in an efficient cold lamination or environmental lamination step, without any energy-consuming drying operation to accelerate water evaporation. The dry coating weight of the intermediate adhesive layer 26b is only 3 to 4 g / m². 2 And no drying or evaporation operations are required.

[0132] Therefore, with Figure 2a Compared to the conventional melt-extruded polyethylene adhesive layer described as layer 26a, the amount of thermoplastic polymer in this laminate can be significantly reduced.

[0133] The innermost heat-sealable layer 23 has a density of approximately 22 g / m². 2 The amount is applied to the surface of the coated barrier layer of the paper substrate material through an intermediate co-extrusion bonding layer (e.g., an ethylene acrylate copolymer (EAA) co-extrusion bonding layer), thereby bonding the innermost heat-sealable layer 23 to the paper substrate 10b coated with the barrier layer in a single melt co-extrusion coating step.

[0134] Alternatively, the innermost heat-sealable liquid-tight layer is a pre-formed blown film 23b containing any blend of LDPE or LLDPE polymers, and it can be laminated to the paper substrate coated with a barrier layer via an intermediate melt extrusion laminated adhesive layer 24b, i.e., laminated to the surface of its barrier coating, which includes a higher density than... Figure 2a The layer 24 used is a thicker EAA bonding layer, or a simpler LDPE adhesive layer. The blown film 23b has a thickness of 12 μm, but can reach 20 μm.

[0135] In an alternative embodiment, the pre-formed blown film 23b is heated at ambient (cold) temperature at a concentration of 3 to 4 g / m³. 2 The content of the acrylic (co)polymer adhesive layer 24b' is used as an aqueous adhesive and is laminated onto the metallized coating through another wet lamination step.

[0136] Another implementation scheme, which possesses all the aforementioned features, is also disclosed herein. Figure 2a The melt-extruded main body laminate 26a, but combined with the characteristics of the paper substrate material 25b with the coated barrier layer and the innermost heat-sealable layer structure 23b, the innermost heat-sealable layer structure 23b is applied either by melt extrusion lamination with layer 24b or by wet lamination of pre-formed film 24b', such as in combination Figure 2b As stated above.

[0137] Another implementation plan was also disclosed here, in which... Figure 2bA thin, wet, water-based adhesive dispersion laminate 26a is combined with conventional melt co-extruded inner layers 24a and 23a.

[0138] exist Figure 3 The process of aqueous dispersion coating 30a is shown, which can be used to apply graphene oxide barrier coatings 12a; 12b and further ascorbic acid coatings 13a; 13b. Paper-based roll 31a (e.g.) Figure 1a Paper 11 in 1b is conveyed to dispersion coating station 32a, where the aqueous dispersion composition is applied to the top surface of the substrate by rollers. Since the dispersion composition contains 80 to 99% by weight, a significant amount of moisture remains on the wet-coated substrate, requiring heating and evaporation to form a uniform, continuous coating with consistent quality in barrier properties and surface properties (i.e., uniformity and wettability). Drying is carried out by hot air dryer 33a, which allows moisture to evaporate and be removed from the substrate surface by air convection. The substrate temperature is maintained constant at 60 to 80°C as it passes through the dryer. Alternatively, drying can be partially assisted by radiant heat from infrared (IR) lamps combined with hot air convection.

[0139] Then repeat Figure 3 The process shown involves coating and drying with an aqueous solution of ascorbic acid at a concentration of 3% by weight in the same manner.

[0140] The resulting barrier pre-coated paper substrate roll 34a is conveyed forward to cool and wound onto a reel for intermediate storage and subsequent further lamination operations.

[0141] Figure 4a This shows that as the main body layers 21; 43 are laminated to... Figure 1a Or 1b, the substrate material roll with a barrier layer 34a; 10a; 10b (i.e., respectively) Figure 2a and 2b (25a or 25b) Figure 2a and 2b The process of lamination steps in the manufacture of packaging laminate materials 20a or 20b.

[0142] Such as combination Figure 2a and 2bAs explained, the main layer paperboard 21 can be laminated onto the barrier-coated substrate material 10; 25a; 25b by melt extrusion lamination as shown in the figure or by wet cold dispersion adhesive lamination (but not shown). Therefore, the molten polymer curtain 44 (e.g., LDPE) is fed into the gap of the lamination roller 45, as the two rolls 34a and 43 are also fed into the same lamination roller gap and joined together by the LDPE extruded adhesive layer 44. These three layers are thus pressed together and joined at the gap 45 formed between the pressure roller and the cooling roller, thereby cooling the laminate material to properly cure the LDPE extruded adhesive layer 44. The resulting laminate material is conveyed to be wound on a reel for intermediate storage or used directly for subsequent lamination operations.

[0143] exist Figure 4b In the process, the pre-laminated material 49a of the resulting cardboard 31b and barrier roll 34a is conveyed to a location that allows direct lamination from... Figure 4a The lamination operation 40a can be performed to a further lamination step 40b, or the intermediate storage reel can be engaged and unwound from it to perform a further lamination step 40b.

[0144] The non-laminated surface of the main layer 21, i.e., its printed surface, is bonded at the cooled roll gap 48a to the molten polymer curtain 46a of the outermost layer 22 of LDPE, which will form the laminate material. The LDPE is extruded from the extruder feed block and die 47a. Subsequently, the paper pre-laminated roll now coated on its printed side by the outermost layer 22 passes through the second extruder feed block and die 47b and the lamination roll gap 48b, where the molten polymer curtain 46b is bonded and coated at the lamination roll gap 48b onto the other side of the pre-laminated material, i.e., on the uncoated inner side of the base material rolls 10a; 10b; 25a; 25b coated with the barrier layer. Thus, the innermost heat-sealable layer 23 is co-extruded and coated onto the inner side of the base material rolls coated with the barrier layer to form the final laminated packaging material 49b, which is ultimately wound onto a storage reel (not shown).

[0145] The two co-extrusion steps at the laminating roll gaps 48a and 48b can alternatively be performed as two consecutive steps in reverse order.

[0146] According to another embodiment, one or both of the outermost layers can be applied in a pre-lamination station, wherein the co-extruded coating is first applied to the outer surface of the (printed) main paperboard layer or the inner surface of the paper substrate coated with the barrier layer, and then bonded as described above. Figure 4a The two pre-laminated paper rolls are joined together.

[0147] According to a further embodiment, the innermost layer of the heat-sealable liquid-tight thermoplastic layer can be applied in the form of a pre-formed film, which is laminated onto the substrate material 10a; 10b coated with the barrier layer.

[0148] Such as combination Figure 2a and 2b As explained, the innermost preform 23 can be laminated onto the barrier-coated substrate material 10a; 10b by wet cold dispersion adhesive lamination or melt extrusion lamination.

[0149] Figure 5a An embodiment of a packaging container 50a produced using the packaging laminate material according to the invention is shown. This packaging container is particularly suitable for beverages, sauces, soups, etc. Typically, such packaging has a volume of about 100 to 1000 ml. It can be of any structure, but is preferably brick-shaped, with longitudinal and transverse seals 51a and 52a respectively, and optionally has an opening device 53. In another embodiment not shown, the packaging container can be formed into a wedge shape. To obtain such a "wedge shape," only the bottom portion of the packaging is folded, such that the transverse heat seal at the bottom is hidden under triangular flaps, which are folded and sealed at the bottom of the packaging. The top transverse seal remains unfolded. In this way, the partially folded packaging container is still easy to handle and dimensionally stable enough to be placed on a food store shelf or any flat surface.

[0150] Figure 5b An alternative example of a packaging container 50b produced using the alternative packaging laminate according to the invention is shown. This alternative packaging laminate is thinner due to its thinner paper body layer, so it is not dimensionally stable enough to form a parallelepiped or wedge-shaped packaging container, and it is not folded into shape after the transverse seal 52b. This packaging container will remain a pillow-shaped bag container and will be dispensed and sold in this form.

[0151] Figure 5c A hilltop-shaped package 50c is shown, which is formed by folding pre-cut stock or blanks into a laminated packaging material comprising a cardboard body layer and a paper substrate coated with a barrier layer according to the present invention. A flat-top package can also be made from similar stock.

[0152] Figure 5d A bottle-shaped package 50d is shown, which is a combination of a sleeve 54 and a top 55 formed from a pre-cut blank of the laminated packaging material of the present invention. The top is formed by injection-molded plastic and an opening device (such as a screw cap). This type of packaging is exemplified by products under the trade name Tetra. and Tetra Sales. These specific packages are formed by attaching a molded top 55 with an opening device in the closed position to a tubular sleeve 54 of laminated packaging material, sterilizing the resulting bottle top capsule, filling it with food, and finally folding it to form the bottom of the package and sealing it.

[0153] Figure 6 The principle described in the introduction of this application is illustrated, wherein a roll of packaging material is formed into a tube 61 by overlapping the longitudinal edges 62, 62' of the roll and heat-sealing them together to form an overlap joint 63. The tube is continuously filled 64 with liquid food to be filled, and the tube is divided into individual filled packages by repeating double transverse seals 65 below the horizontal plane of the contents filled in the tube and spaced a predetermined distance from each other. Packages 66 are separated by cutting between the double transverse seals (top seal and bottom seal) and are ultimately shaped into the desired geometry by folding along pre-prepared crease lines in the material.

[0154] In conclusion, the present invention is not limited to the embodiments shown and described above, but can be varied within the scope of the claims.

Claims

1. A method for producing an oxygen barrier material for packaging materials (20a; 20b) by coating a substrate material roll (10a; 10b) with a reduced graphene oxide layer (12a; 12b), comprising the following steps: a) Providing and delivering substrate material rolls b) Provides an aqueous composition comprising graphene oxide, said graphene oxide comprising monolayer graphene oxide sheets and multilayer graphene oxide sheets having up to 20 stacked monolayer graphene oxide sheets. c) While the substrate material roll is being conveyed, the aqueous composition of the graphene oxide is coated (32a) onto the surface of the substrate material roll. d) By forced evaporation drying (33a) of the wet coating of aqueous graphene oxide on the substrate material roll, a first dry layer of layered graphene oxide particles or sheets is obtained. e) Apply an aqueous solution of the reducing agent to the first dried layer of graphene oxide on the substrate material roll. f) After step e), the wet coating of the reducing agent is directly dried by forced evaporation to obtain a second dry layer of the reducing agent. g) To enable the reducing agent of the second dried layer to reduce the underlying graphene oxide of the first dried layer at a minimum predetermined temperature and within the shortest predetermined time, and Prior to step g), perform further step i): coating or laminating the substrate material roll from step f) onto another polymer layer to cover the second dried layer of the reducing agent; and / or further step h): winding the substrate material roll from step f) onto a reel. A substrate material roll coated with a barrier layer to form a reduced graphene oxide drying layer.

2. The method according to claim 1, wherein the concentration of the aqueous composition of graphene oxide is 0.1 to 15% by weight.

3. The method according to claim 1, wherein the wet coating thickness of the aqueous composition of the graphene oxide is 10 to 400 μm.

4. The method according to any one of claims 1-3, wherein the reducing agent is selected from sodium citrate, ascorbic acid (vitamin C), lemon juice, vinegar and green tea.

5. The method according to any one of claims 1-3, wherein the reducing agent is ascorbic acid.

6. The method according to any one of claims 1-3, wherein the concentration of the reducing agent is 0.5 to 15% by weight.

7. The method according to any one of claims 1-3, wherein the substrate material roll from step f) is irradiated before or during step g) to accelerate the reduction reaction occurring between the applied first dry layer and the second dry layer.

8. The method according to any one of claims 1-3, wherein, The substrate material roll is continuously conveyed at a constant speed.

9. The method according to any one of claims 1-3, comprising providing an aqueous composition comprising graphene oxide, said graphene oxide comprising monolayer graphene oxide sheets and multilayer graphene oxide sheets having up to 2-10 stacked monolayer graphene oxide sheets.

10. The method of claim 2, wherein the concentration of the aqueous composition of said graphene oxide is 0.5 to 10% by weight.

11. The method of claim 2, wherein the concentration of the aqueous composition of said graphene oxide is 0.5 to 6% by weight.

12. The method of claim 2, wherein the concentration of the aqueous composition of said graphene oxide is 0.5 to 3% by weight.

13. The method of claim 2, wherein the concentration of the aqueous composition of the graphene oxide is 1 to 2% by weight.

14. The method of claim 6, wherein the concentration of the reducing agent is 1 to 10% by weight.

15. The method of claim 6, wherein the concentration of the reducing agent is 2 to 7% by weight.

16. The method of claim 6, wherein the concentration of the reducing agent is 3 to 6% by weight.

17. A substrate material roll (10a; 10b) coated with a barrier layer obtained by the method according to any one of claims 1-16, used as an oxygen barrier material in a laminated packaging material (20a; 20b) for liquid food products, comprising a substrate material roll (11a; 11b) and a reduced graphene oxide layer (12a; 12b) applied thereon.

18. The substrate material roll coated with a barrier layer according to claim 17, wherein the thickness of the reduced graphene oxide layer (12a; 12b) is 50 to 1000 nm.

19. The substrate material roll coated with a barrier layer according to claim 18, wherein the thickness of the reduced graphene oxide layer (12a; 12b) is 100 to 800 nm.

20. The substrate material roll coated with a barrier layer according to claim 18, wherein the thickness of the reduced graphene oxide layer (12a; 12b) is 200 to 700 nm.

21. The substrate material roll coated with a barrier layer according to claim 18, wherein the thickness of the reduced graphene oxide layer (12a; 12b) is 200 to 600 nm.

22. The substrate material roll coated with a barrier layer according to claim 18, wherein the thickness of the reduced graphene oxide layer (12a; 12b) is 400 to 600 nm.

23. The substrate material roll coated with a barrier layer according to claim 18, wherein the thickness of the reduced graphene oxide layer (12a; 12b) is 450 to 550 nm.

24. The substrate material roll coated with a barrier layer according to any one of claims 17-23, wherein the substrate material roll (11a; 11b) is a polymer film roll, a paper or other cellulose-based material roll, or a paper or other cellulose-based material roll coated with a polymer.

25. The substrate material roll coated with a barrier layer according to any one of claims 17-23, wherein the reduced graphene oxide layer (12a; 12b) is further coated with an adjacent polymer layer or laminated onto the adjacent polymer layer.

26. A laminated packaging material (20a; 20b) comprising a substrate material roll (10) coated with a barrier layer according to any one of claims 17-25, and further comprising a first outermost protective material layer (22a; 22b) and a second innermost liquid-tight heat-sealable material layer (23a; 23b; 23b').

27. The laminated packaging material (20a; 20b) according to claim 26, further comprising a paper or paperboard or other cellulose-based material body layer (21), a first outermost protective material layer (22a; 22b), a second innermost liquid-tight heat-sealable material layer (23a; 23b; 23b'), and a substrate material roll (10a; 10b) coated with the barrier layer, the substrate material roll (10a; 10b) being disposed inside the paper or paperboard body layer, between the body layer and the second innermost liquid-tight heat-sealable material layer.

28. The laminated packaging material (20a; 20b) according to claim 27, wherein the substrate material roll (10a; 10b) coated with the barrier layer is bonded to the body layer (21) by an intermediate adhesive layer (26a; 26b) comprising a composition comprising an adhesive selected from the group consisting of polymers and copolymers of acrylic polymers and copolymers, starch, cellulose and polysaccharide derivatives, vinyl acetate and / or vinyl alcohol polymers and copolymers.

29. A packaging container (50a; 50b; 50c; 50d) comprising a laminated packaging material (20a; 20b) as defined in any one of claims 26-28.

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