A PACKAGING MATERIAL; AND A SEALING SYSTEM FOR SUCH PACKAGING MATERIAL

Abstract

A packaging material is provided, comprising a core layer and one or more layers of a heat sealable material laminated thereto, and at least one carbon-based layer being configured to form a workpiece of an associated sealing system.

Claims

1. A packaging material, comprising a core layer and one or more layers of a heat sealable material laminated thereto, and at least one carbon-based layer being configured to form a workpiece of an associated sealing system.

2. The packaging material according to claim 1, wherein the at least one carbon-based layer is configured to form a workpiece, of an associated induction heating sealing system.

3. The packaging material according to claim 2, wherein the core layer is a cellulose-based material, such as paper or paperboard.

4. The packaging material according to claim 1, wherein the carbon-based layer is configured to form a workpiece of a transversal sealing system and/or a workpiece of a longitudinal sealing system.

5. The packaging material according to claim 1, wherein the carbon-based layer is laminated into the packaging material.

6. The packaging material according to claim 1, wherein the carbon-based layer is applied locally only at one or more areas corresponding to a location of the workpieces of the associated sealing systems.

7. The packaging material according to claim 1, wherein the carbon-based layer is a graphene-based material.

8. The packaging material according to claim 7, 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 material and multilayer graphene platelets, having up to 20 stacked monolayer flakes of graphene.

9. The packaging material according to claim 7, wherein the graphene-based material comprises at least from 50 weight-% based on dry weight, 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. The packaging material according to claim 7, wherein the graphene-based material layer comprises less than 50 weight-% of conductive and/or magnetic particles, based on dry weight.

11. The packaging material according to claim 7, 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 claim 7, wherein the carbon-based layer is applied to the packaging material in the form of an ink and/or a dispersion coating.

13. The packaging material according to claim 7, wherein the carbon-based layer is applied to the packaging material in the form of a pre-manufactured, 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 claim 1, wherein the thickness of the carbon-based layer is in the range of 0.001-500 μm.

15. The packaging material according to claim 1, wherein the thickness of the carbon-based layer is constant.

16. The packaging material according to claim 1, wherein the heat sealable material comprises a thermoplastic polymer.

17. A method of manufacturing a packaging material, claim 1, comprising laminating one or more layers of a heat sealable material to a core layer, and applying the at least one carbon-based layer to said packaging material, wherein the at least one carbon-based layers forms a workpiece of an associated sealing system.

18. The method according to claim 17, wherein the applying of the carbon-based layer is performed in-line during a packaging material laminating process.

19. The method according to claim 17, wherein the applying of the carbon-based layer is performed as an operation step after or at an end of a packaging material lamination process.

20. A packaging container comprising a main body being formed by a packaging material, as defined in claim 1, and having at least one heat seal arranged at a sealing area, wherein the packaging material comprises a carbon-based layer arranged at said sealing area.

21. A method for manufacturing the packaging container of claim 20, comprising heat sealing a packaging material by activating an electromagnetic device such that heat is generated in a workpiece of said packaging material, wherein said workpiece is formed by the carbon-based layer.

22. The method according to claim 21, wherein the electromagnetic device is operating at a frequency from 100 kHz to above 27 MHz.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

[0035] FIG. 1 is a schematic view of a packaging machine,

[0036] FIG. 2 is a cross-sectional view of a sealing system according to an embodiment, for use with a packaging machine,

[0037] FIG. 3 is a side view of a converting apparatus for manufacturing a packaging material according to various embodiments,

[0038] FIG. 4 is a cross-sectional view of a packaging material according to an embodiment,

[0039] FIG. 5 is a planar view of a packaging material according to an embodiment,

[0040] FIG. 6 is an isometric view of a packaging container according to an embodiment,

[0041] FIG. 7 is a schematic view of a method for manufacturing a package and a packaging material according to an embodiment,

[0042] FIGS. 8a-b are diagrams showing induced power as a function of resistivity for different workpiece materials,

[0043] FIG. 9 is a diagram showing efficiency as a function of workpiece thickness for a first carbon-based layer, and

[0044] FIG. 10 is a diagram showing efficiency as a function of workpiece thickness for a second carbon-based layer.

DETAILED DESCRIPTION

[0045] Starting in FIG. 1, the basic principle of a roll fed carton based packaging machine 10 is shown. The packaging machine 10 is configured for continuous packaging of e.g. liquid food products, and forms the general technical concept used for various different packaging systems, such as the commercially successful Tetra Brik® packaging system. The packaging machine 10 receives a packaging material 100, in the form of a continuous web (as is shown in FIG. 1).

[0046] After unwinding the packaging material 100 its longitudinal side edges 101a-b are brought together to form a longitudinal seal LS, thereby also forming a tube 12 of the packaging material 100. More particularly, the longitudinal side edges 101a-b are attached to each other continuously in an overlapping manner. The tube 12 is filled with a desired product, preferably a liquid food product, from a filling pipe 13.

[0047] A series of packages 20 are formed from the tube 12 by making transversal sealings TS at an end of the tube 12, and cutting off the sealed portions, each sealed portion representing an individual package 20, as they are formed. In order to shape the packages 20 different forming tools can be used during the transversal sealing operation, or a separate forming process can be performed after the transversal sealing has been performed.

[0048] Alternatively, a blanks-fed packaging machine is used. The blanks, in the form of pre-cut pieces of packaging material with two ends heat sealed together such that a folded tubular sleeve is formed, are fed to the filling machine. The blanks are erected into an open sleeve, and then folded and sealed such that a closed top or bottom is formed. It is thereafter filled with product and sealed and folded such that a filled package container is obtained.

[0049] It should be mentioned that the term “longitudinal” is referring to the feeding direction of the tube 12, i.e. the machine feeding direction. The term “transversal” is referring to a direction perpendicular to the longitudinal direction.

[0050] The transversal seals TS are typically formed by a sealing system 30, not illustrated in FIG. 1 but shown schematically in FIG. 2. Two sets of transversal sealing systems 30 are provided, arranged in a downstream configuration (one sealing system 30 being arranged downstream another sealing system). By operation of the sealing system, a high-frequency inductor or another electromagnetic device 31 and a counter element 32, positioned on movable sealing jaws, will move and press together the filled packaging material tube 12 in the traversal direction to form TS seal zones. As electromagnetics losses, e.g. eddy currents, are generated in a workpiece of the packaging material 100, the packaging material 100 will be heated to form the transversal TS seal zones at every predetermined interval by high-frequency induction heating. For creating the eddy currents in the workpiece, the inductor 31 is connected to a high frequency power supply, as will be further explained below.

[0051] It should be mentioned that the movement of the sealing jaws will also provide a forward motion of the tube 12, whereby the seals TS will be arranged at predetermined intervals.

[0052] Then, each transversal TS seal zone is cut along a centerline by a cutting knife (not illustrated) and divided to form individual packaging containers 20. Final forming of the package container 20 can be configured in many different ways, in order to obtain various package container shapes such as a brick-shape (parallelepiped), a hexagonal prism, octagonal prism, tetrahedral shape, gable-top containers and the like.

[0053] Now turning to FIG. 3, a schematic overview of a laminating process is shown, i.e. the process of manufacturing the packaging material 100. The packaging material manufacturing process is based on the concept of laminating several layers of thermoplastic material to a core layer.

[0054] Production of the packaging material 100 proceeds such that a reel 102 of a core layer web 104 of paper or board is paid out and led over a nip roller 42 into contact with a cooling roller 44. With the aid of an extruder 46, a continuous film of thermoplastic material 106 is extruded in between the core layer web 104 on the nip roller 42 and the cooling roller 44, in which event the expelled film of thermoplastic material 106, e.g. of polyethylene, will adhere to the core layer 104. By compression between the nip roller 42 and the cooling roller 44, the core layer 104 and the film 106 are united to form a composite packaging material laminate. In that same operation, an optional further web of material (not shown) may be led over the cooling roller to also be laminated to the core layer web, by means of the intermediate extruded bonding layer of thermoplastic material 106. In addition to the above-mentioned converting process, an outside layer 108 of liquid-tight and heat-sealable thermoplastic material and an inside layer 110 of liquid-tight and heat-sealable thermoplastic material may also be added in order to form the packaging material 100. The outside and inside layers 108 and 110 may be laminated to the previously laminated core layer web by means of film lamination as shown in FIG. 3, or as extrusion coating of a molten thermoplastic material, as according to the principle described above, such as of heat-sealable polyethylene polymers. One or more barrier layers may also be part of the packaging material 100, and may be laminated to the core layer web, preferably on that side of the core layer web, which is to form the inside of a packaging container from the resulting laminated packaging material.

[0055] As described earlier induction heating and sealing requires the provision of a workpiece of the packaging material 100, in which workpiece eddy currents can be generated as the workpiece is subjected to the high frequency magnetic field from the inductor 31. This workpiece, which traditionally has been provided in the form of an Aluminum layer across the entire packaging material 100, may instead be provided by an applicator 50. As will be explained further, the workpiece is formed by a carbon-based material, preferably provided locally at the packaging material 100.

[0056] In FIG. 3 the applicator 50 is shown only schematically, and the applicator 50 could be realized in many different ways. For example, the applicator 50 could be a printing unit, such as an inkjet unit, whereby the workpiece material is provided in the form of a carbon-based, preferably a graphene-based, ink. The applicator 50 could in other embodiments be realized as a spray unit, a roll applicator, etc. Importantly, the applicator 50 is configured to apply a layer of a carbon-based material at specific locations on the packaging material 100.

[0057] The applicator 50 may not even form part of the laminating process but may instead by used before or after the laminating process. For example, the applicator 50 could be arranged in the package machine 10, such that the carbon-based layer is applied before the packaging material 100 is transformed into a sealed tube 12.

[0058] If forming part of the laminating process, the applicator 50, as described with reference to FIG. 3, could be arranged at various locations. Several applicators 50 are therefore indicated in FIG. 3, although it should be understood that it may be necessary with only one applicator 50, at a single location.

[0059] For example, the applicator 50 may be arranged so that the workpiece is printed on the outer side of the core layer 104, or on the inner side of the core layer 104 before lamination. Other possible positions of the applicator 50 are illustrated in FIG. 3.

[0060] In a preferred embodiment, the applicator 50 is arranged such that the carbon-based material is applied at the inside of the packaging material 100, beneath the innermost heat sealable layer, or on the inside surface of a barrier film. In an optional embodiment, the applicator 50 is arranged such that the carbon-based material is applied at the outside of the core layer, such as paperboard, of the packaging material 100, in order to allow for heat sealing of the longitudinal edges of the packaging material 100 when the tube 12 is formed.

[0061] An example of a resulting packaging material 100 is shown in FIG. 4, in cross-section, also indicating the workpiece 60 in the form of a carbon-based, preferably graphene-based, layer 112. The workpiece 60 could, depending on the location of the applicator 50 during, before, or after the lamination process, be arranged at any of the interfaces between the different material layers; on the external side of layer 110, between layers 110 and 106, between layers 106 and 104, between layers 104 and 108, or on the external side of layer 108. If barrier layers are present, the workpiece 60 may be arranged on either side of such barrier layer, but preferably, the carbon-based workpiece portion or layer is provided on the inside of the core layer, or of the optional barrier layer and the inside layer 110.

[0062] Now turning 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, e.g. to be used by a packaging machine 10 as shown in FIG. 1. The web thereby includes a series of segments 120, each segment 120 being later used to form an individual package 20. In FIG. 5, three segments 120 are shown. Each segment 120 has a plurality of crease lines 122, and each segment 120 is also provided with at least one workpiece 60. In the shown example, 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 position of the transversal sealings TS to be formed.

[0063] A package 20 resulting from the packaging material 100 of FIG. 5, processed by a packaging machine 10 of FIG. 1, is shown in FIG. 6. The package 20, forming a main body 22 of the packaging material 20, has one longitudinal sealing LS, and two transversal sealings TS. At least one sealing, preferably at least the two transversal sealings TS, are arranged at respective sealing areas 124. The workpiece 60, formed by means of a carbon-based, preferably graphene-based, layer, is arranged at said sealing areas 124.

[0064] The packaging material 100 is formed by a core bulk layer 104, which may be a fibre based material, such as a cellulose based material. The core layer 104 may be a cellulose-based material, such as a paper or a carton or paperboard. The packaging material 100 also has at least one carbon-based, preferably graphene-based, layer 112 being configured to form a workpiece 60 of an associated sealing system 30. As mentioned earlier, the carbon-based layer 112 is configured to form a workpiece 60b of a transversal sealing system 30 and/or a workpiece 60a of a longitudinal sealing system (not explicitly shown but indicated in FIG. 1).

[0065] The carbon-based, preferably graphene-based, layer 112 can e.g. be laminated into the packaging material 100, or it may be arranged on the exterior surface of the packaging material 100.

[0066] Although not explained earlier, in some embodiments the carbon-based layer 112 could be distributed across the entire width and length of the packaging material 100 such that the carbon-based layer 112 forms a continuous layer.

[0067] However, in order to allow for induction sealing it is necessary to provide the carbon-based layer 112 only locally at one or more areas 124, thereby forming local workpieces 60 of the associated sealing systems 30.

[0068] The carbon-based material used for forming the workpiece 60 is preferably in the form of an ink, thereby allowing standard equipment to be used (such as ink jet technology). The ink may comprise carbon of the crystalline structure of graphite and graphene. The carbon-based layer preferably comprises graphene or reduced graphene oxide, at an amount of at least 50 weight-% based on dry weight, in one or more layers. Preferably, the carbon-based layer comprises a dispersion of exfoliated flakes of graphene or reduced graphene oxide.

[0069] So far, it has not been successful to manufacture pure graphite inks or dispersions with a sufficient quality and physical properties in order to be used within the concept of the present invention, i.e. to heat seal adjacent layers of a packaging material. This is due to the intrinsic properties of the graphite material when it is in particle form, not providing the required conductivity. By instead using graphene or reduced graphene oxide, improvements are possible. Thus, it has hitherto not been possible to exfoliate graphite such that it has been possible to provide a coating or a layer which has both the required mechanical flexibility properties and the required conductivity, due to the bulky nature of graphite materials. If graphite would be possible to apply as very thin layers, of the nano-dimensions, its inherent properties are such that good induction properties should be possible. However, a homogeneous graphite layer necessarily needs to be too thick and too brittle such that the layer breaks, and particulate graphite or graphite in the form of exfoliated flakes cannot reach the concentration in a dispersion such that sufficient conductivity or susceptibility to magnetic losses is reached. Accordingly, for sufficient conductivity, substantial amounts of metal particles would be needed in a mixture with only graphite or based on graphite.

[0070] On the other hand, a monolayer of graphene e.g. obtained by chemical vapour deposition (CVD) could be considered the thinnest layer possible of a graphite material, having the desired mechanical properties. The conductivity of a perfect, continuous graphene monolayer is high, but since it is a monolayer, it would be way too thin to generate a significant heating effect, to perform a proper heat seal by current technology and allowed frequencies.

[0071] Now turning to FIG. 7, a method 200 for manufacturing a package container 20 is schematically illustrated. The method 200 includes a sub-method 210 of manufacturing a packaging material.

[0072] The sub-method 210 comprises a step 212 of laminating one or more plastic layers 106, 108, 110 to a core layer 104, and a step 214 of applying at least one carbon-based, preferably graphene-based, layer 112 to said packaging material 100. The at least one carbon-based layer 112 forms a workpiece 60 of an associated sealing system 30.

[0073] The step 214 of applying the carbon-based layer 112 can be performed in-line during a packaging material converting process, or as a post-process at the end of a packaging material converting process.

[0074] The method 200 for manufacturing the packaging container 20 further comprises a step 202 of sealing the packaging material 100 by activating an inductor 32 such that heat is generated in the workpiece 60 of the packaging material 100.

[0075] The electro-magnetic device, such as the inductor, may be operated at frequencies from 100 kHz to above 27 MHz, depending on the design of the heat-sealing system. Within the higher MHz range, specific frequency bands are allocated by national authorities, such as 13.65 MHz and 27.12 MHz. At lower ranges, the frequency of operations may be more freely selected. Preferably, the electromagnetic device is operating at a frequency from 0.5 MHz to above 27 MHz, such as from 1 MHz to above 27 MHz such as from 13 MHz to above 27 MHz.

[0076] As will be explained by the following examples, the exact thickness and resistivity, as well as the material type of the carbon-based layer, can 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 from 0.01 to 500 μm, such as from 0.1 to 300 μm, such as from 1 to 300 μm depending on sealing system properties, such as power signal frequency, etc.

[0077] FIG. 8a is a diagram showing simulations of the induced power in the workpiece as a function of workpiece material resistivity for a workpiece thickness of 6.35 μm. The power signal is having a frequency of 535 kHz, which is a drive frequency for induction sealing systems in the beverage carton packaging industry. The inductor model employed in the simulation study is an inductor designed for the longitudinal sealing application. In the model, the workpiece minimum distance from the inductor is set to 1 mm.

[0078] The horizontal bar below the graph indicates relevant resistivity values for the investigated materials. The first material is AA 6063, a commercially available Aluminum alloy, kept at 25° C. The second material is the same AA 6063, but kept at an elevated temperature of 150° C. The two first materials (AA 6063) represent reference values for the traditional Aluminum-based workpieces of prior art. The third material is an ideal, hypothetical graphite layer, which is applied homogeneously but unrealistically thin to still have the mechanical properties desired. The fourth datapoint represents the hypothetical use of a monolayer of graphene (One single graphene monolayer would hypothetically have a good resistivity for the application, but, since it is a monolayer, it would be too thin to generate a significant heating effect). The fifth material is a 4-layer graphene flake ink (GI) as developed by S. Majee et al., Scalable inkjet printing of shear-exfoliated graphene transparent conductive films, Carbon 2016; 102:51-7.

[0079] In the graph, it is shown that there is an optimum value of resistivity to boost power coupling between inductor and workpiece, as a consequence of the counterbalance of induced current and induced electromotive force, according to Lenz's law. In the range corresponding to typical graphene inks, which usually have a resistivity in the range of 10.sup.−4 Ωm or higher, we discovered that the lower the resistivity is, the higher the induced power will be. Therefore, the graphene ink proposed by Majee et al., was further investigated due to its relatively low resistivity, compared to other graphene inks. Accordingly, by increasing the thickness of such an applied ink layer, the induced power may be further increased.

[0080] A compact, flexible, compressed sheet of layered graphene-flakes, such as described above, at a thickness of 6.35 μm, features an even lower resistivity in the order of 10.sup.−7 Ωm, thus enabling further increasing, or even maximizing, system power transfer.

[0081] FIG. 8b is a simulation of the induced power as a function of resistivity for the same hypothetical graphite layer and for the graphene ink (both at a layer thickness of 6.35 μm), at different power frequencies. As is evident from the diagram, a significant increase of induced power is obtained for frequencies in the MHz range. For the sake of comparison, a reference line in the graph (Pow. Ref.) indicates the power value corresponding to the standard workpiece made of aluminium AA 6063 at frequency 535 kHz, and with the same thickness of 6.35 μm.

[0082] For the graphite material, having a resistivity of 3*10.sup.−6 Ωm, the calculated efficiency as a function of hypothetical layer thickness is shown in FIG. 9, for the different frequencies. The marks named power reference (Pow. ref) indicate the minimum thicknesses of graphite which would be needed, at MHz frequencies, to get the same induced power as the 6.35 μm AA 6063 reference at 535 kHz. However, at those thicknesses, around 50 nm, the efficiency of the system would be significantly lower compared to the reference, possibly leading to risks for overheating or overvoltage. At 13.65 MHz, a workpiece thickness of at least about 500 nm is needed to keep 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 the plateau region where less sensitivity to the thickness is expected. This plateau region is significantly wider than for AA 6063 foil at 535 kHz, in the investigated thickness range.

[0083] In the plot, the “Eff. ref.” line corresponds to the efficiency of the standard system featuring a 6.35 μm thick AA 6063 foil and working at 535 kHz.

[0084] For the graphene ink material, having a resistivity of 2.5*10.sup.−6 Ωm, the efficiency as a function of layer thickness is shown in FIG. 10, for the different power frequencies. At 13.65 MHz, a workpiece thickness of at least about 4.5 μm is needed to keep a relatively high efficiency. At 27.12 MHz, a workpiece thickness of at least about 1.5 μm is needed to keep a relatively high efficiency. By further increasing the thickness it is possible to reach the plateau region where less sensitivity to thickness is expected. Also this plateau region is significantly wider than for AA 6063 foil at 535 kHz in the investigated thickness range. The reference values have the same meaning as explained above for FIG. 9

[0085] A summary of the simulations is further shown in the following table.

TABLE-US-00001 Freq t I eff. Q norm Material [kHz] [μm] [A] [0-1] [—] Alu6063 535 6.35 100 0.93 1 Graphite 535 30 100 0.88 1.5 Graphene ink 535 300 100 0.93 N/A Graphite 535 6.35 225 0.93 N/A Graphene ink 535 6.35 too high N/A N/A Graphite 13.65e3 0.050 100 0.57 N/A Graphene ink 13.65e3 0.400 100 0.56 N/A Graphite 13.65e3 0.500 32 0.93 4.3 Graphene ink 13.65e3 4.5 13 0.93 0.3 Graphite 27.12e3 0.030 65 0.69 N/A Graphene ink 27.12e3 0.100 100 0.47 N/A Graphite 27.12e3 0.200 25 0.93 7 Graphene ink 27.12e3 1.5 26 0.93 4

[0086] Hence, by employing frequencies in the MHz range it is possible to have a good efficiency using relatively thin layers, thereby allowing the possibility to use carbon-based layers, such as graphene-based layers, as workpieces in the packaging material for induction heating sealing.