Packaging material and sealing system for such packaging material

Abstract

A packaging material is provided that includes a core layer (104), one or more layers (106, 108, 110) of heat-sealable material laminated thereto, and at least one carbon-based layer (112) configured to form a workpiece (60) of an associated sealing system (30).

Description

[Technical field]

[0001] The present invention relates to a packaging material, in particular to a packaging material for forming a free-standing liquid food package. The present invention also relates to a sealing system configured to provide sealing to said packaging material, as well as to a package and a method for manufacturing such a package. [Background technology]

[0002] In recent years, most manufacturers of food packaging containers have focused on meeting recyclability and sustainability standards promoted by various governments and other agencies, such as the European Union. The aim of these efforts is to provide the next generation of carton-based packaging containers that are made from renewable packaging materials to a greater extent and are reusable to a greater extent in order to reduce waste and pollution.

[0003] However, most manufacturers of packaging materials for forming packaging containers still integrate thin foils of aluminum into the packaging materials for food protection. Apart from the shielding properties of aluminum, metal foils are also used as workpieces to provide various heat seals of the packaging materials to form closed and sealed packaging containers. The heat seals can be longitudinal or transverse to the dimensions of the package, depending on the desired shape and appearance of the final packaging container.

[0004] The sealing of the packaging material is based on the principle of induction heating, induced eddy currents in the aluminum foil. When the foil is heated, the thermal energy is transferred by conduction to the plastic laminate layers of the packaging material, which then melt and bond together. When the induction heating is turned off, the plastic layers re-solidify, providing an accurate and durable seal. Good sealing of the packaging container ensures the sterility of the contents throughout the product's life.

[0005] However, aluminum is not a renewable resource, and therefore its widespread use is incompatible with the above-mentioned goal of renewable and recyclable packaging. For this reason, it is becoming increasingly important to develop aluminum-free packaging materials. On the other hand, potential problems may arise for implementing efficient sealing of packaging materials that do not contain aluminum foil. Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above shortcomings of the prior art solutions, there remains a need for a packaging material that allows for robust sealing while not requiring aluminum foil. Still further, it is an object to provide a packaging material that allows for induction heating sealing. [Means for solving the problem]

[0007] According to a first aspect, there is provided a packaging material comprising a core layer and one or more layers of heat-sealable material laminated thereto and at least one carbon-based layer configured to form a workpiece of an associated sealing system.

[0008] The term "workpiece" refers to a part or layer configured to generate heat loss due to a magnetic field created by an electromagnetic device, e.g., an inductor. The carbon-based part or layer may be susceptible to induction heating, thereby heating and partially melting adjacent layers of heat-sealable material. The melted or partially melted layers may melt and be joint-sealed to each other or to adjacent surfaces while resolidifying. At least one carbon-based part or layer may then be configured to form a workpiece of an associated induction heat sealing system, i.e., capable of generating heat due to interaction with an electromagnetic field generated by a device, such as an inductor, in the associated induction heat sealing system.

[0009] The core layer may be a cellulosic material, such as paper or paperboard.

[0010] The heat-sealable material may comprise a thermoplastic polymer, such as a polyolefin or a polyester. Examples of polyolefins are polyethylene and polypropylene, and copolymers and mixtures thereof. Examples of polyesters are polyethylene terephthalate (PET), polyethylene furanoate (PEF), and biodegradable polyesters, such as polylactic acid (PLA) and polyhydroxyalkanoates (PHA).

[0011] The carbon-based layer may be configured to form a workpiece of a transverse sealing system and / or a workpiece of a longitudinal sealing system.

[0012] The carbon-based layer may be laminated into the packaging material, i.e., located between adjacent laminate layers, and / or disposed on the outer surface of the packaging material. The exact positioning of the carbon-based layer may depend on various process parameters and packaging container characteristics.

[0013] The carbon-based layer may be distributed throughout the packaging material such that it forms a continuous layer, and thus may effectively help protect the contents of a packaging container made of the packaging material from the outside environment.

[0014] In another embodiment, the carbon-based layer is applied locally only in one or more areas corresponding to the position of the workpiece of the associated sealing system, i.e. in areas of the packaging material intended to form part of the sealing zone.

[0015] The carbon-based layer may be a graphene-based material, which may comprise graphene or reduced graphene oxide in one or more layers. Most preferably, the graphene-based material comprises a major amount of graphene or reduced graphene, i.e. graphene obtained by reducing graphene oxide, hereinafter denoted as "reduced graphene oxide". Thus, the graphene-based material comprises at least 50% by weight, such as from 60% by weight, such as from 70% by weight, such as from 80% by weight, such as from 90% by weight, such as from 95% by weight, up to 100% by weight of graphene or reduced graphene oxide material, based on dry weight.

[0016] The definition of "graphene" in the term "graphene-based" includes reduced graphene oxide, monolayers of graphene, exfoliated flakes of graphene, and multilayer graphene flakes, or so-called graphene platelets, i.e. partially exfoliated flake-like stacks of several layers of graphene or reduced graphene oxide up to 20, preferably up to 10 such monolayer flakes.

[0017] According to one embodiment, the graphene-based material comprises one or more materials selected from the group consisting of exfoliated flakes of graphene, reduced graphene oxide, graphene monolayer materials, and multi-layer graphene platelets having up to 20 stacked monolayer flakes of graphene, such as up to 10 stacked monolayer flakes of graphene.

[0018] In one embodiment, the graphene-based material comprises layers resulting from a dispersion of such exfoliated flakes of graphene, reduced graphene oxide or multi-layer graphene platelets having up to 20, preferably not more than 10 stacked monolayer flakes.

[0019] Exfoliated flake graphene can be obtained by exfoliation of graphite particles, for example by microfluidic exfoliation or electrochemical expansion or ultrasonic exfoliation. Depending on the nature and performance of the exfoliation process, the ratio of pure single-layer graphene flakes to such multi-layer graphene flakes may vary.

[0020] Only a relatively small amount, i.e., less than 20 wt. %, such as less than 10 wt. %, for example less than 5 wt. %, based on the dry weight of the graphene-based material, may be graphite flakes that have been exfoliated into more than 20 graphene monolayer flakes but have a smaller lateral particle size than bulk graphite particles, i.e., so-called "graphite nanoplatelets" and thus nano-sized.

[0021] Such relatively small amounts of such laterally nano-sized graphite flakes may be present as long as they do not excessively impair the performance of the graphene-based material. Preferably, the nanographite flakes / platelets are present in the composition in an amount of less than 15 wt%, such as 10 wt%, such as 5 wt% or less based on dry weight. Furthermore, the graphene-based composition may contain conductive and / or magnetic particles in an amount of less than 50 wt%, such as less than 40 wt%, such as less than 30 wt%, such as less than 20 wt%, such as less than 10 wt% dry weight, such as less than 5 wt%. The presence of conductive and / or magnetic metal particles may increase the performance of the part or layer, but the effect will remain secondary, i.e. the majority of the induction heat seal performance of the layer is provided by the graphene-based material. Suitable conductive particles are silver and aluminum particles, among other possible metal particles. The carbon-based layer, preferably the graphene-based layer, may be applied to the packaging material in the form of an ink and / or dispersion coating.

[0022] Suitable application methods are therefore printing methods, such as flexographic printing, gravure printing, screen printing, inkjet printing and various dispersion coating methods, such as slot coating, doctor blade coating, curtain coating and spray coating. By these printing or coating methods, a carbon-based layer may be applied with a suitable thickness of 0.1-25 μm, such as 0.5-20 μm, for example 0.5-10 μm, such as 0.5-8 μm, for example 0.5-7 μm, for example 0.5-6 μm, for example 0.5-5 μm.

[0023] The graphene-based composition may further include solvents and binders, i.e., polymers, to support the film-forming process in coating and drying of the dispersion or ink. The solvent or dispersion medium may include water and / or organic solvents. The composition may further include minor amounts, on a dry matter basis, of additives conventional in the art, such as thickeners, defoamers, waxes, and other viscosity and film-forming modifiers.

[0024] Alternatively, a similar composition of exfoliated graphene flakes may be formed into a wet sheet coating and compressed under high pressure into a graphene sheet, followed by drying, to obtain a compact, flexible sheet of layered graphene flakes. Such graphene flake "paper" or plate may be designed to have relatively high conductivity at thicknesses of a few micrometers, e.g., from 3 μm, e.g., from 5 μm, up to 70 μm, e.g., up to 80 μm.

[0025] Thus, according to one embodiment, the carbon-based layer is applied to the packaging material in the form of a pre-fabricated, compressed sheet of layered exfoliated flakes of graphene, reduced graphene oxide or graphene monolayer material or multi-layer graphene platelets having up to 20, such as up to 10 stacked monolayer flakes of graphene.

[0026] A particularly good balance of conductivity versus mechanical properties can be obtained with such graphene flake plates having thicknesses of 15 μm up to 40 μm. The compact but flexible sheets of graphene flakes may be applied to packaging materials by pattern lamination, either as fully laminated sheets or, for example, in the form of tapes only in the intended sealing zones.

[0027] In a further possible embodiment, the graphene coating may be applied in the form of a vapor-deposited graphene layer, for example by chemical vapor deposition (CVD), with a thickness of a few nanometers up to 500 nm, for example up to 300 nm.

[0028] The thickness of the carbon-based layer may preferably be constant over the entire extension of the layer, in the range of 0.001-500 μm, such as 0.01-500 μm, such as 0.1-300 μm, such as 1-300 μm, depending on the sealing system properties, e.g. power signal frequency.

[0029] According to a second aspect, there is provided a method for producing a packaging material, the method comprising the steps of laminating one or more heat-sealable layers of thermoplastic material to a core layer and applying at least one carbon-based layer to said packaging material to form a workpiece of a sealing system in which at least one carbon-based, preferably graphene-based, layer is associated.

[0030] The step of applying a carbon-based layer, preferably a graphene-based layer, may be performed in-line during the packaging material lamination process or as a post-step at the end of the packaging material lamination process.

[0031] According to a third aspect, there is provided a sealing system for a packaging material, the sealing system comprising at least one electromagnetic device and a workpiece arranged on said packaging material, said workpiece being formed by a carbon-based layer, preferably a graphene-based layer.

[0032] According to a fourth aspect, there is provided a packaging container comprising a body formed from a packaging material and having at least one sealing disposed in a sealing region, the packaging material comprising a carbon-based layer, preferably a graphene-based layer, disposed in said sealing region.

[0033] According to a fifth aspect, there is provided a method for manufacturing a packaging container, the method comprising the step of sealing a packaging material by activating an induction heating device such that heat is generated in a workpiece of said packaging material, said workpiece being formed by a carbon-based layer, preferably a graphene-based layer.

[0034] Embodiments of the present invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which: [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 is a schematic diagram of a packaging machine. [Diagram 2] FIG. 1 is a cross-sectional view of a sealing system according to one embodiment for use with a packaging machine. [Diagram 3] FIG. 1 is a side view of a converting apparatus for producing packaging material according to various embodiments. [Figure 4] 1 is a cross-sectional view of a packaging material according to one embodiment. [Diagram 5] FIG. 2 is a plan view of a packaging material according to one embodiment. [Figure 6] FIG. 1 illustrates an isometric view of a packaging container according to one embodiment. [Figure 7] 1 is a schematic diagram of a method for producing packaging and packaging material according to one embodiment. [Figure 8a-b] FIG. 13 illustrates induced power as a function of resistivity for different workpiece materials. [Figure 9] FIG. 13 illustrates efficiency as a function of workpiece thickness for a first carbon-based layer. [Figure 10] FIG. 13 illustrates efficiency as a function of workpiece thickness for the second carbon-based layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Starting with Figure 1, there is shown the basic principle of a roll-fed carton-based packaging machine 10. The packaging machine 10 forms the general technical concept used for a variety of different packaging systems, such as the commercially successful Tetra Brik® packaging system, designed for the continuous packaging of liquid food products. The packaging machine 10 receives packaging material 100 in the form of a continuous web (as shown in Figure 1).

[0037] After unrolling the packaging material 100, its longitudinal side edges 101 a-b are brought together to form a longitudinal seal LS, thereby also forming the tube 12 of the packaging material 100. More specifically, the longitudinal side edges 101 a-b are continuously attached to one another in an overlapping manner. The tube 12 is filled with a desired product, preferably a liquid food product, from a filling pipe 13.

[0038] A series of packages 20 are formed from the tube 12 by making transverse seals TS at the ends of the tube 12 and cutting off the sealed portions, such that as they are formed, each sealed portion represents an independent package 20. Different forming tools may be used during the transverse sealing operation to form the packages 20, or a separate forming process may be performed after the transverse sealing is performed.

[0039] Alternatively, a blank-fed packaging machine is used: a blank, in the form of a pre-cut piece of packaging material, with two ends heat-sealed together to form a folded tubular sleeve, is fed to the filling machine. The blank is erected into the open sleeve and then folded and sealed to form a closed top or bottom. It is then filled with product, sealed and folded to obtain a filled packaging container.

[0040] It should be mentioned that the term "longitudinal" refers to the feed direction of the tube 12, i.e., the machine feed direction. The term "transverse" refers to a direction perpendicular to the longitudinal direction.

[0041] The transverse seal TS is typically formed by a sealing system 30, which is not shown in FIG. 1 but is shown diagrammatically in FIG. 2. Two sets of transverse sealing systems 30 are provided and arranged in a downstream configuration (one sealing system 30 is arranged downstream of another sealing system). Upon actuation of the sealing system, a high-frequency inductor or another electromagnetic device 31 and a counter element 32 positioned in the movable sealing jaw move and press the filled packaging material tube 12 together in the moving direction to form a TS seal zone. When electromagnetic losses, such as eddy currents, occur in the workpiece of the packaging material 100, the packaging material 100 heats up to form a transverse TS seal zone at predetermined intervals by high-frequency induction heating. To generate eddy currents in the workpiece, the inductor 31 is connected to a high-frequency power source, as will be further explained below.

[0042] It should be mentioned that the movement of the sealing jaws also provides a forward movement of the tube 12, so that the seals TS are spaced at predetermined intervals.

[0043] Each transverse TS seal zone is then cut along its centerline by a knife (not shown) and divided to form separate packages 20. The final formation of the packages 20 may be configured in many different ways to obtain various package shapes, such as brick (parallel hexahedron), hexagonal prism, octagonal prism, tetrahedron, Gabeltop containers, etc.

[0044] 3, there is shown a schematic diagram of the lamination process, i.e. the manufacturing process of the packaging material 100. The packaging material manufacturing process is based on the concept of laminating several layers of thermoplastic material onto a core layer.

[0045] The production of the packaging material 100 proceeds as a reel 102 of paper or board core layer web 104 is unwound and passed over nip roller 42 and contacted with chill roller 44. Using an extruder 46, a continuous film 106 of thermoplastic material is extruded between the core layer web 104 on the nip roller 42 and chill roller 44, with the extruded film of thermoplastic material 106, for example polyethylene, adhering to the core layer 104. Compression between the nip roller 42 and chill roller 44 causes the core layer 104 and film 106 to merge and form a composite packaging material laminate. In the same operation, an optional further web of material (not shown) is passed over the chill roller and similarly laminated to the core layer web with an intermediate extruded bonding layer of thermoplastic material 106. In addition to the above conversion process, an outer layer 108 of liquid-tight heat-sealable thermoplastic material and an inner layer 110 of liquid-tight heat-sealable thermoplastic material may also be added to form the packaging material 100. The outer and inner layers 108 and 110 may be laminated to the pre-laminated core layer web by film lamination as shown in Figure 3 following the principles discussed above, such as a heat sealable polyethylene polymer, or as an extrusion coating of a molten thermoplastic material. One or more shielding layers may also be part of the packaging material 100 and may be laminated to the core layer web, preferably on the side of the core layer web that is to form the inside of a packaging container from the resulting laminated packaging material.

[0046] As explained above, induction heating and sealing requires the provision of a workpiece of packaging material 100, where workpiece eddy currents may be generated when the workpiece is subjected to the high frequency magnetic field from inductor 31. This workpiece has traditionally been provided in the form of an aluminum layer over the packaging material 100, but may alternatively be provided by applicator 50. As will be further explained, the workpiece is formed from a carbon-based material and is preferably provided locally on the packaging material 100.

[0047] In Fig. 3, the applicator 50 is shown only diagrammatically and the applicator 50 may be realized in many different ways. For example, the applicator 50 may be a printing unit, for example an inkjet unit, whereby the workpiece material is provided in the form of a carbon-based, preferably graphene-based, ink. The applicator 50 may in other embodiments be realized as a spray unit, a roll applicator, etc. Importantly, the applicator 50 is configured to apply a layer of carbon-based material to a specific location of the packaging material 100.

[0048] The applicator 50 may not form part of the lamination process, but may instead be used before or after the lamination process. For example, the applicator 50 may be positioned in the packaging machine 10 such that the carbon-based layer is applied before the packaging material 100 is converted into the sealed tube 12.

[0049] When forming part of a lamination process, the applicators 50 may be positioned in various locations, as described with reference to Figure 3. Although several applicators 50 are thus shown in Figure 3, it should be understood that only one applicator 50 may be required at a single location.

[0050] For example, the applicator 50 may be positioned so that the workpiece is printed on the outside of the core layer 104 or on the inside of the core layer 104 prior to lamination. Another possible position for the applicator 50 is shown in FIG.

[0051] In a preferred embodiment, the applicator 50 is positioned so that the carbon-based material is applied to the inside of the packaging material 100, under an innermost heat-sealable layer, or to the inside surface of a shielding film. In an optional embodiment, the applicator 50 is positioned so that the carbon-based material is applied to the outside of a core layer of the packaging material 100, such as paperboard, to enable heat sealing of the longitudinal edges of the packaging material 100 when the tube 12 is formed.

[0052] An example of the resulting packaging material 100 is shown in cross-section in Figure 4, which also shows a workpiece 60 in the form of a carbon-based layer, preferably a graphene-based layer 112. The workpiece 60 may be located either at the interface between the different material layers, on the outer surface of layer 110, between layers 110 and 106, between layers 106 and 104, between layers 104 and 108, or on the outer surface of layer 108, depending on the position of the applicator 50 before or after the lamination process. If a shielding layer is present, the workpiece 60 may be located on both sides of such a shielding layer, but preferably a carbon-based workpiece portion or layer is provided inside the core layer, or the optional shielding layer and the inner layer 110.

[0053] Turning now to Fig. 5, an example of a packaging material 100 is shown. The packaging material 100 is provided in the form of a continuous web, for example to be used by a packaging machine 10 as shown in Fig. 1. The web thereby comprises a series of segments 120, each of which is subsequently used to form an independent package 20. In Fig. 5, three segments 120 are shown. Each segment 120 has a number of folds 122, and each segment 120 is also provided with at least one workpiece 60. In the example shown, a longitudinal workpiece 60a is arranged along one longitudinal edge of the packaging material, and several workpieces 60b are arranged in respective sealing areas 124, each sealing area 124 corresponding to the location of a transverse seal TS to be formed.

[0054] A package 20 resulting from the packaging material 100 of Fig. 5 processed by the packaging machine 10 of Fig. 1 is shown in Fig. 6. The package 20 forms the body 22 of the packaging material 20 and has one longitudinal seal LS and two transverse seals TS. At least one seal, preferably at least two transverse seals TS, are arranged in each sealing area 124. A workpiece 60 formed by a carbon-based layer, preferably a graphene-based layer, is arranged in said sealing area 124.

[0055] The packaging material 100 is formed by a core bulk layer 104, which may be a fiber-based material, for example a cellulosic material. The core layer 104 may be a cellulosic material, for example paper or cardboard or paperboard. The packaging material 100 may also have at least one carbon-based layer, preferably a graphene-based layer 112, configured to form the workpiece 60 of the associated sealing system 30. As mentioned above, the carbon-based layer 112 is configured to form the workpiece 60b of the transverse sealing system 30 and / or the workpiece 60a of the longitudinal sealing system (not explicitly shown but shown in FIG. 1 ).

[0056] A carbon-based layer, preferably a graphene-based layer 112, may be laminated, for example, into the packaging material 100 or disposed on an exterior surface of the packaging material 100.

[0057] Although not discussed above, in some embodiments, the carbon-based layer 112 may be distributed across the width and length of the packaging material 100 such that the carbon-based layer 112 forms a continuous layer.

[0058] However, to enable induction sealing, it is necessary to provide the carbon-based layer 112 only locally in one or more areas 124 , thereby forming the local workpiece 60 of the associated sealing system 30 .

[0059] The carbon-based material used to form the workpiece 60 is preferably in the form of an ink, thereby allowing standard equipment to be used (e.g., inkjet technology). The ink may include carbon in the crystalline structure of graphite and graphene. The carbon-based layer preferably includes graphene or reduced graphene oxide in an amount of at least 50% by weight on a dry weight basis in one or more layers. Preferably, the carbon-based layer includes a dispersion of exfoliated flakes of graphene or reduced graphene oxide.

[0060] So far, it has not been possible to produce a pure graphite ink or dispersion with sufficient quality and physical properties to be used within the concept of the present invention, i.e. to heat seal adjacent layers of packaging material. This is due to the inherent properties of the graphite material, which does not provide the required conductivity when in particulate form. An improvement is possible by using graphene or reduced graphene oxide instead. Thus, due to the bulky nature of the graphite material, it has not been possible to exfoliate it so as to be able to provide a coating or layer that has both the required mechanical flexibility properties and the required conductivity. If it is possible to apply graphite as a nano-sized, extremely thin layer, its inherent properties are such that good inductive properties should be possible. However, a homogeneous graphite layer would have to be made too thick and too brittle so that the layer would break, and particulate graphite or graphite in the form of exfoliated flakes cannot reach a concentration in the dispersion to reach sufficient conductivity or susceptibility to magnetic losses. Therefore, for sufficient conductivity, a significant amount of metal particles is required in graphite alone or in graphite-based mixtures.

[0061] On the other hand, a monolayer of graphene, obtained for example by chemical vapor deposition (CVD), can be considered as the thinnest possible layer of graphitic material with desirable mechanical properties: a perfect, continuous monolayer of graphene is highly conductive, but being a monolayer, it is far too thin to produce significant heating effects to perform a proper heat seal with current technology and possible frequencies.

[0062] 7, there is shown generally a method 200 for manufacturing the packaging container 20. The method 200 includes a sub-method 210 of manufacturing a packaging material.

[0063] The sub-method 210 comprises a step 212 of laminating one or more plastic layers 106, 108, 110 to the core layer 104 and a step 214 of applying at least one carbon-based layer, preferably a graphene-based layer 112, to said packaging material 100. The at least one carbon-based layer 112 forms the workpiece 60 of the associated sealing system 30.

[0064] The step 214 of applying the carbon-based layer 112 can be performed in-line during the packaging material converting process or as a post-step at the end of the packaging material converting process.

[0065] The method 200 for manufacturing the packaging container 20 further includes a step 202 of sealing the packaging material 100 by activating the inductor 32 to generate heat in the workpiece 60 of the packaging material 100 .

[0066] The electromagnetic device, e.g. an inductor, may operate at frequencies between 100 kHz and above 27 MHz depending on the design of the heat sealing system. Within the higher MHz range, certain frequency bands have been allocated by national authorities, e.g. 13.65 MHz and 27.12 MHz. In the lower range, the frequency of operation may be chosen more freely. Preferably, the electromagnetic device operates at frequencies between 0.5 MHz and above 27 MHz, e.g. between 1 MHz and above 27 MHz, e.g. between 13 MHz and above 27 MHz.

[0067] As illustrated by the examples below, the exact thickness and resistivity of the carbon-based layer, as well as material type, may vary depending on the desired efficiency, current, quality factor, etc. For the examples described herein, the thickness of the carbon-based layer 112 is preferably constant and in the range of 0.001-500 μm, such as 0.01-500 μm, such as 0.1-300 μm, such as 1-300 μm, depending on sealing system characteristics such as power signal frequency.

[0068] Figure 8a shows the simulation of the induced power in the workpiece as a function of the workpiece material resistivity for a workpiece thickness of 6.35 μm. The power signal has a frequency of 535 kHz, which is the driving frequency for induction sealing systems in the beverage cardboard packaging industry. The inductor model used in the simulation study is an inductor designed for longitudinal sealing. In the model, the minimum workpiece distance from the inductor is set to 1 mm.

[0069] The horizontal bars below the graphs show the relevant resistivity values ​​for the materials investigated. The first material is AA6063, a commercially available aluminum alloy, held at 25°C. The second material is the same AA6063, but held at a higher temperature of 150°C. The first of the two materials (AA6063) represents the reference value for conventional aluminum-based workpieces of the prior art. The third material is an ideal, hypothetical graphite layer that is uniformly applied, but unrealistically thin to still have the desired mechanical properties. The fourth data point represents the hypothetical use of a monolayer of graphene (one single graphene monolayer could hypothetically have good resistivity to apply, but being a monolayer, it is too thin to produce significant heating effects). The fifth material is a four-layer graphene flake ink (GI) developed by S. Majee et al., Scalable Inkjet Printing of Shear Exfoliated Graphene Transparent Conductive Films, Carbon 2016;102:51-7.

[0070] The graph shows that there is an optimum value of resistivity to increase the power coupling between the inductor and the workpiece as a result of the opposition between the induced current and the induced electromotive force according to Lenz's law. -4In the range corresponding to typical graphene inks with resistivity in the Ω-m range and above, the inventors found that the lower the resistivity, the higher the induced power. Therefore, the graphene ink proposed by Majee et al. was further investigated due to its relatively low resistivity compared to other graphene inks. Thus, by increasing the thickness of such applied ink layer, the induced power can be further increased.

[0071] For example, a compact, flexible, compressed sheet of the layered graphene flakes described above is 6.35 μm thick and stretches over 10 -7 It is characterised by an even lower resistivity, on the order of Ωm, thus allowing the system power transfer to be further increased or even maximised.

[0072] Figure 8b is a simulation of the induced power as a function of resistivity for the same hypothetical graphite layer and for graphene ink (both with a layer thickness of 6.35 μm) at different power frequencies. As is evident from the figure, a significant increase in the induced power is obtained for frequencies in the MHz range. For comparison, the reference line (Pow.Ref.) in the graph shows the power value corresponding to a standard workpiece made of aluminum AA6063 at a frequency of 535 kHz and with the same thickness of 6.35 μm.

[0073] 3 * 10 -6The calculated efficiency as a function of the hypothetical layer thickness for a graphite material with a resistivity of Ωm is shown in FIG. 9 for different frequencies. The mark named power reference (Pow.ref) indicates the minimum thickness of graphite required at MHz frequencies to obtain the same induced power as the AA6063 reference of 6.35 μm at 535 kHz. However, at those thicknesses of around 50 nm, the efficiency of the system drops significantly compared to the reference, possibly resulting in the risk of overheating or overvoltage. At 13.65 MHz, a workpiece thickness of at least about 500 nm is necessary to maintain a relatively high efficiency, while at 27.12 MHz a workpiece thickness of only about 200 nm should be sufficient. By further increasing the thickness, it is possible to reach a plateau region where a lower sensitivity to thickness is expected. This plateau region is significantly wider in the investigated thickness range than for the AA6063 foil at 535 kHz.

[0074] In the plot, the "Eff.ref." line corresponds to the efficiency of a standard system featuring a 6.35 μm thick AA6063 foil and operating at 535 kHz.

[0075] 2.5 * 10 -5 For a graphene ink material with a resistivity of Ωm, the efficiency as a function of layer thickness for different power frequencies is shown in FIG. 10. At 13.65 MHz, a workpiece thickness of at least about 4.5 μm is required to maintain a relatively high efficiency. At 27.12 MHz, a workpiece thickness of at least about 1.5 μm is required to keep the efficiency relatively high. By further increasing the thickness, it is possible to reach a plateau region where a lower sensitivity to thickness is expected. This plateau region is also significantly wider at 535 kHz in the investigated thickness range than for the AA6063 foil. The reference values ​​have the same meaning as explained above for FIG. 9.

[0076] A summary of the simulations is further shown in the table below.

[0077] [Table 1]

[0078] Thus, by using frequencies in the MHz range it is possible to use relatively thin layers with good efficiency, thereby allowing carbon-based layers, such as graphene-based layers, to be used as workpieces in packaging materials for induction heating sealing.

Claims

1. A packaging material comprising a core layer (104) and one or more layers (106, 108, 110) of heat-sealable material laminated thereto, and at least one carbon-based portion or layer (112) configured to form a workpiece (60) of an associated sealing system (30); The packaging material, wherein the carbon-based portion or layer (112) is a graphene-based material.

2. The packaging material of claim 1 , wherein the at least one carbon-based portion or layer (112) is configured to form a workpiece (60) of an associated induction heating sealing system (30).

3. The packaging material of claim 2 , wherein the core layer (104) is a cellulosic material.

4. The packaging material according to any one of claims 1 to 3, wherein the carbon-based portion or the carbon-based layer (112) is configured to form a workpiece (60b) of a transverse sealing system (30) and / or a workpiece (60a) of a longitudinal sealing system.

5. The packaging material according to any one of the preceding claims, wherein the carbon-based portion or layer (112) is laminated into the packaging material (100).

6. The packaging material according to any one of claims 1 to 5, wherein the carbon-based portion or layer (112) is applied locally only in one or more areas (124) corresponding to a position of the workpiece (60) of the associated sealing system (30).

7. The packaging material (100) according to any one of the preceding claims, wherein the packaging material (100) does not comprise aluminium foil.

8. 2. The packaging material of claim 1, wherein the graphene-based material comprises one or more materials selected from the group consisting of exfoliated flakes of graphene, reduced graphene oxide, graphene monolayer materials, and multilayer graphene platelets having up to 20 stacked monolayer flakes of graphene.

9. 2. The packaging material of claim 1, wherein the graphene-based material comprises at least 50% and up to 100% by weight, on a dry weight basis, of one or more materials selected from the group consisting of exfoliated flakes of graphene, reduced graphene oxide, graphene monolayer material, and multilayer graphene platelets having up to 20 stacked monolayer flakes of graphene.

10. 10. The packaging material of any one of claims 1 to 9, wherein the graphene based material comprises less than 50% by weight, on a dry weight basis, of conductive and / or magnetic particles.

11. 11. The packaging material of any one of claims 1 to 10, wherein the graphene-based material is obtainable from a composition comprising a dispersion of one or more materials selected from the group consisting of exfoliated flakes of graphene, reduced graphene oxide, graphene monolayer material and multilayer graphene platelets having up to 20 stacked monolayer flakes of graphene.

12. The packaging material according to any one of the preceding claims, wherein the carbon-based portion or layer (112) is applied to the packaging material in the form of an ink and / or a dispersion coating.

13. 12. The packaging material according to any one of claims 1 to 11, wherein the carbon-based portion or the carbon-based layer (112) is applied to the packaging material in the form of a pre-fabricated, compressed sheet of layered exfoliated flakes of graphene, reduced graphene oxide or graphene monolayer material or multilayer graphene platelets having up to 20 stacked monolayer flakes of graphene.

14. The packaging material according to any one of the preceding claims, wherein the carbon-based portion or layer (112) has a thickness in the range of 0.001 to 500 μm.

15. The packaging material according to any one of the preceding claims, wherein the carbon-based portion or layer (112) has a constant thickness.

16. The packaging material according to any one of claims 1 to 15, wherein the heat-sealable material comprises a thermoplastic polymer.

17. A method for manufacturing a packaging material according to any one of claims 1 to 16, comprising the steps of laminating one or more layers (106, 108, 110) of heat-sealable material to a core layer (104) and applying said at least one carbon-based portion or layer (112) to said packaging material, said carbon-based portion or layer (112) being a graphene-based material, said at least one carbon-based portion or layer (112) forming a workpiece (60) of an associated sealing system (30).

18. 20. The method of claim 17, wherein the step of applying the carbon-based portion or the carbon-based layer (112) is performed in-line during a packaging material lamination process.

19. 20. The method of claim 17, wherein the step of applying the carbon-based portion or the carbon-based layer (112) is performed as a post or end operational step in a packaging material lamination process.

20. A packaging container (20) comprising a body (22) formed from the packaging material (100) of any one of claims 1 to 16 and having at least one heat seal (TS) disposed in a sealing area (124), the packaging material (100) comprising a carbon-based portion or the carbon-based layer (112) disposed in the sealing area (124).

21. 21. A method for manufacturing the packaging container (20) of claim 20, comprising heat sealing the packaging material (100) by activating an electromagnetic device (30) such that heat is generated in a workpiece (60) of the packaging material (100), the workpiece (60) being formed by the carbon-based portion or the carbon-based layer (112).

22. The method of claim 21 , wherein the electromagnetic device operates at a frequency between 100 kHz and greater than 27 MHz.

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